Cardiology measurement Flashcards

Question

Draw the bipolar limb leads including their direction of current and + vs -

Answer 1

* A ground electrode - the activity of the lead of interest is compared to the ground electrode and anything in common is discarded as noise - “common mode rejection”

Answer 2

* A ground electrode - the activity of the lead of interest is compared to the ground electrode and anything in common is discarded as noise - “common mode rejection”

Answer 3

ECG frequency is 0.5 - 100Hz and frequency outside this range can be ignored using high or low pass electrical filters ◦ Monitor mode - amplifier only responds to frequencies 0.5 - 40Hz ‣ Loses resolution but reduced interference due to narrow bandwidth ◦ DIagnostic mode - 0.5 -100Hz ◦ More accurate ◦ Increased interference

Answer 4

* A ground electrode - the activity of the lead of interest is compared to the ground electrode and anything in common is discarded as noise - “common mode rejection” * Amplifiers - ECG frequency is 0.5 - 100Hz and frequency outside this range can be ignored using high or low pass electrical filters ◦ Monitor mode - amplifier only responds to frequencies 0.5 - 40Hz ‣ Loses resolution but reduced interference due to narrow bandwidth ◦ DIagnostic mode - 0.5 -100Hz ◦ More accurate ◦ Increased interference * ECG cables are shielded with an insulator to reduce induction currents from external sources * Conductive paste connecting the electrodes to the skin * Patient factors ◦ Remaining still - relax without movement to avoid EMG interference; avoiding shivering ◦ Skin preparation -dry and no hair ◦ Removing electronic devices from patient near the leads if possible ‣ Diathermy plate * DIsplay - accurate with printer at correct speed and appropriate amplification (vertical calibration)

Answer 5

* Oscillometric - measures MAP, estimates SBP and DBP * Auscultatory - measures SBP and DBP, estimates MAP * Pulse palpation measures/estimates SBP only * Flush measures SBP only - exsanguinating a tourniquetted limb by tight pressure bandage then gradually deflating the cuff until the pale bloodless limb flushes pink again * Ultrasound - measures SBP and DBP, estimates MAP

Answer 6

* Oscillometric - measures MAP, estimates SBP and DBP * Auscultatory - measures SBP and DBP, estimates MAP * Pulse palpation measures/estimates SBP only * Flush measures SBP only - exsanguinating a tourniquetted limb by tight pressure bandage then gradually deflating the cuff until the pale bloodless limb flushes pink again * Ultrasound - measures SBP and DBP, estimates MAP

Answer 7

* Oscillometric - measures MAP, estimates SBP and DBP

Answer 8

* Auscultatory - measures SBP and DBP, estimates MAP

Answer 9

‣ Cuff - width 20% greater than diameter of the arm ‣ Manometer - either Bourdon gauge, or a fluid manometer column ‣ Inflating bulb to elevate cuff pressure ‣ Deflating valve

Answer 10

‣ Cuff - width 20% greater than diameter of the arm ‣

Answer 11

Phlebostatic axis

Answer 12

* As the cuff is deflated blood released into the distal limb makes characteristic sounds which can be related to pulse pressure range - as turbulent flow is present as flow only occurs in brief spurts when pressur exceeds occlusion pressure ◦ Phase 1 - loud clear snapping tone with repeated tapping - short bursts of blood flow aat systolic pressure ◦ Phase 2 - Murmurs/soft swishing - low flow blood; occasionally an auscultatory gap after phase 1 before phase 2 ◦ 3 - Disappearance of murmurs and appearance of tone resembling the first phase but less marked - increased blood flow ◦ 4 - less clear quality or dull tones thumping/blowing occuring 10mmHg above diastolic ◦ 5 - disappearance - steady laminar flow resumes at diastolic pressure

Answer 13

* NIBP ausculatory Underestimates BP in hypotension, may be unable to detect BP in low cardiac output states ◦ Whereas the oscillometric overestimates it in shock

Answer 14

* Inaccuracy from ◦ Interference with measurement ‣ User auditory sensitivity ‣ Stephoscope quality ‣ Ambient noise ◦ User related ‣ Cuff size ‣ stethoscope bell misplaced ‣ Deflation of cuff too fast ‣ Arm positioned too far above or below phlebostatic axis ‣ Arm not relaxaed ◦ Unavoidable errors ‣ Stress/white coat syndrome ‣ Underestimation fo systolic - as the cuff needs to be deflated BELOW the systolic to measure it ‣ Underestimates diastolic

Answer 15

Oscillometer - an instrument for measuring the changes in pulsations in the arteries

Answer 16

* Components ◦ Cuff ◦ Microprocesser to inflate with an air pump ◦ Bleed valve to slowly deflate ◦ Pressure sensor monitor

Answer 17

◦ Cuff applied to a measuring site over an artery typically the brachial and inflated above systolic pressure where there is no flow - the pressure in the cuff is monitored as the arterial pulse will convey changes in the volume of the limb and therefore air filled tubing causing a change in presssure ◦ The cuff pressure is then gradually decreases 2-3mmHg per secnod and the pressure is held for a brief period and this continues - during each holding period the machine detects where the pressur eis constant or if there are small regular oscillations and the size of the fluctuations from baseline is measured ◦ The maximum size of oscillations above the baseline rpessure is the MAP ◦ The cuff inflates above the systolic (i.e. when the oscillometer no longer sees any oscillations) ‣ This was thought to originally be the point at which systolic blood pressure should be measured however there is no distinct transition above the systolic or below the diastolic as some oscillations are still measured ‣ The cuff is gradually deflated until oscillations are 25-50% of their maximal amplitude: this is the systolic. Each brand will have a slightly different proprietary way of calculating the systolic * % of maximum amplitude * When the small oscillations rise significantly ' * When they are first heard ◦ The cuff is gradually deflated until maximal amplitude is reached: this is the MAP ◦ The cuff is deflated until the amplitude decreases again by 80% or more; this is the diastolic. This is the least accurate measurement

Answer 18

◦ The cuff is deflated until the amplitude decreases again by 80% or more; this is the diastolic. This is the least accurate measurement ‣ Other measures will utilise equations e.g. MAP = diastolic + (systolic - diastolic)/3 ‣ MAP = 2 x DBP/3 + SBP/3

Answer 19

◦ MAP = diastolic + (systolic - diastolic)/3 ‣ MAP = PP/3 ‣ MAP = 2 x DBP/3 + SBP/3

Answer 20

* Sources of innaccuracy ◦ Technique ‣ Cuff size is a major influence of measurement ‣ Deflation too rapid ◦ Interference with measurement ‣ Oscillometer is confused by arrhythmia, movement e.g. shivering, or tremor. ◦ Unavoidable ‣ Wildly inaccurate: 95% CI for NIBP within the normal range is 15mmHg * Due to use of coefficients and constats ‣ Even more inaccurate in the extremes of blood pressure; over-estimates low blood pressure and under-estimates high blood pressure ‣ Impossible to calibrate

Answer 21

* No invasive procedure * Cheap * Reusable * Minimal training * No monitoring equipment or electronics * Durable, robust * Does not require regular recalibration

Answer 22

* Less reliable at extremes * Continuous monitoring not possible * Painful if repeated freqeuntly * Pressure areas * Maximum accuracy requires manual operation

Answer 23

◦ Arterial catheter 20g (radial) 18g (femoral)- short, parallel walled, rigid, patent. Balance of thin enough to reduce clot risk but thick enough to reduce damping ◦ Incompressible tubing - rigid, non compiant, wide bore and fluid filled with tap for zeroing and sampling ◦ Pressure transducer - fluid filled tubing and a counterpressure bag ‣ 300mmHg with flow of 3-5ml/hr ◦ Electrical transducer - wheatstone bridge strain gauge. Electrical connection to the silicon chip is isolated from the saline by a compliant silicone elastomer gel allowing pressure to be transmitted from liquid to chip but prevents electric shock from sensor to patient or alternatively circuit destruction from defribrillation of the aptient ◦ Monitoring -

Answer 24

◦ Arterial catheter 20g (radial) 18g (femoral)- short, parallel walled, rigid, patent. Balance of thin enough to reduce clot risk but thick enough to reduce damping

Answer 25

◦ Incompressible tubing - rigid, non compiant, wide bore and fluid filled with tap for zeroing and sampling ◦ Pressure transducer - fluid filled tubing and a counterpressure bag ‣

Answer 26

Fourier analysis from sine wave harmonics

Answer 27

* Indications ◦ Rapidly or dangerously fluctuating BP ◦ Prolonged course of BP moniotring - neuropraxias, tissue injury ◦ Titration of vasoactive agents ◦ Frequent blood sampling ◦ Inaccuracy of non invasive - massive obesity, burns

Answer 28

◦ Continuous - bea ot beat variation, close monitoring of those who rapidly change ◦ Sampling ◦ Waveform itself a source of information ◦ Gold standard

Answer 29

◦ Arterial puncture ◦ Non reusable ◦ Moniotring requirepemtn required and expensive ◦ Re-zeroing and re-levelling ◦ Transducers can drift and fail

Answer 30

◦ Device ‣ Cannula or tubing kinked ‣ Air bubbles or clots ‣ Inadequate freqency response of the transducer ‣ Inappropriately zero'd or levelled ‣ Faulty calibration ◦ Patient ‣ Damaged artery or spasm

Answer 31

transducer sets the atmospheric pressure to 0

Answer 32

The transducer is set at a particular height along a fluid column with the transducer at the reference point to avoid additional hydrostatic pressure leading to inaccuracy - phlebostatic axis

Answer 33

‣ Easily accessable ‣ Generous collateral circlation ‣ No collateral damage with surroudning structures ‣ does not restrict movement ‣ Disadvantages * Pulse amplification making systolic and diastolic less accurate * Highly mobile site - easy to dislodge * Small * Anatomical variation

Answer 34

‣ Large and proximal - more accurate ‣ Much larger than radial therefore easier to access ‣ Easily compressible ‣ Disadvantages * Difficult to access during CPR * End artery - limb ischaemia risk * Next to median nerve * Kink and occludes with aptient movement

Answer 35

‣ Largest and most proximal ‣ Most accurate reading - least affected by PVD and pulse amplification ‣ Easily palpable ‣ Accessable in crisis ‣ Disadvantaes * Retroperitoneal haematoma which si not compressible * AV fistula if through and through puncture * Higher risk of infection * Mobilistion issue

Answer 36

* Device factors ◦ Non-invasive measurement error ‣ The cuff is the wrong size ‣ The oscillometric measurement is confused by an arrhythmia ‣ The patient is moving around too much ◦ Invasive measurement error ‣ The transducer is zeroed incorrectly ‣ The zero level is incorrectly selected ‣ The transducer system is incorrectly set up * Patient factors ◦ The artery being measured is in spasm ◦ There is peripheral vascular disease, which is unequally distributed ◦ The patient has subclavian artery stenosis ◦ There is aortic pathology which influences flow into the limbs (eg. aneurysm) * Relative reliability ◦ Invasive measurement is the "gold standard" of BP measument overall ◦ Mercury sphygmomanometer is the gold standard of non-invasive measurement ◦ Peripheral and central invasive measurements of arterial pressure tend to show good agreement, but in context of severe shock the peripheral lines tend to overestimate the blood pressure.

Answer 37

nIBP - more proximal artery

Answer 38

◦ Common piezoelectrical pressure transducers convert kinetic energy (pressure) into a change in electrical resistance

Answer 39

Usually a thin semiconductive silicone membrane 0.02mm in diametre ‣ This membrane increases its resistance whenever it undergoes deformation - high sensitivity - property changes with temperature but accurate between 15-40 degrees ◦ It is usually built into an integrated circuit which contains the Wheatstone bridge circuit and other electronic components

Answer 40

* Wheatstone bridge ◦ an electrical circuit used to measure an unknown electrical resistance where the resistance of the unknown resistor is determined by pressure thus becoming a pressure gauge ◦ This is a circuit with four resistors: ‣ Three have a known resistance and the fourth (Rx) is the semiconducting membrane. ‣ If the ratio of resistance in the R1/R2 limb is the same as the resistance of the R3/Rx limb, there should be no current flowing through the galvanometer VG. ‣ The variable resistor R2 is adjusted until the current drops to zero (which is when the resistance of R2 is the same as the resistance of Rx) ‣ Alternatively, you can calculate what the Rx resistance is using Kirchhoff's circuit laws, which is what ends up happening in the common hospital-grade blood pressure monitor. ‣ Thus, the resistance of Rx, and therefore pressure, is determined. ◦ component of the pressure transducer that allows the transducer to calculate the change in resistance resulting from the change in pressure ◦ Alternatively ‣ Classically, these were arranged with three resistors of known resistance and one of variable resistance (the strain gauge). When the ratio of the resistors on the known side of the circuit (R2/R1) equals the ratio on the other side of the circuit (R3/Rx) the bridge is balanced, no current will flow and no potential difference will be measured by the galvanometer (VG). When the resistance of the strain gauge (Rx) changes due to pressure applied to the attached diaphragm, the two sides of the bridge become unbalanced and a current flows. The resulting potential difference is measured by the galvanometer and is proportional to the magnitude of the pressure applied

Answer 41

◦ This is a circuit with four resistors: ‣ Three have a known resistance and the fourth (Rx) is the semiconducting membrane. ‣ If the ratio of resistance in the R1/R2 limb is the same as the resistance of the R3/Rx limb, there should be no current flowing through the galvanometer VG. ‣ The variable resistor R2 is adjusted until the current drops to zero (which is when the resistance of R2 is the same as the resistance of Rx) ‣ Alternatively, you can calculate what the Rx resistance is using Kirchhoff's circuit laws, which is what ends up happening in the common hospital-grade blood pressure monitor. ‣ Thus, the resistance of Rx, and therefore pressure, is determined.

Answer 42

◦ an electrical circuit used to measure an unknown electrical resistance where the resistance of the unknown resistor is determined by pressure thus becoming a pressure gauge

Answer 43

* The further you get from the aorta ◦ The taller the systolic peak - higher systolic pressure ◦ Further the dicrotic notch is from the peak ◦ Lower the end diastolic pressure - wider pulse pressure ◦ Later the arrival of the pulse - 60msec delayed in radial ◦ MAP pretty much the same

Answer 44

phlebostatic axis corresponding to RA. Axis intersection of midazillary line and 4th IC space. Minimised hydrostatic pressure ensuring accuracy. for every 2.5cm change the pressure is 1.87 mmHg

Answer 45

phlebostatic axis corresponding to RA. Axis intersection of midazillary line and 4th IC space. Minimised hydrostatic pressure ensuring accuracy. for every 2.5cm change the pressure is 1.87 mmHg

Answer 46

No conducted pressure - pressure wave travels much faster than the blood ejected

Answer 47

◦ Systolic - rapid increase to peak, followed by rapid decline. LV ejection. The peak represents the systolic ◦ Dicrotic notch ◦ Diastolic phase - run off of blood into peripheral circulation - and the trough is the diastolic BP ◦ MAP - area under the curve

Answer 48

* Heart rate * Systolic pressure * Diastolic pressure (coronary filling) * Mean arterial pressure (systemic perfusion) * Pulse pressure (high in AR, low in cardiac tamponade or cardiogenic shock) * Changes in amplitude associated with respiration (pulse pressure variation) - >10mmHg thought to be significance * Slope of anacrotic limb associated with aortic stenosis, contractility * Area under the curve - stroke volume index

Answer 49

160-180msec at the aortic root Isovolumetric contraction

Answer 50

Because the transmitted pressure wave is 160-180msec after the QRS and contraction begins and if this is based on peripheral arterial line it is even more delayed not even accounting for circuit related delays in conduction back to the aortic balloon

Answer 51

systolic upstroke

Answer 52

◦ Ventricular ejection - initial fast moving 10,/sec wave correpsonding to peak aortic blood flow accelaration. The slope of this segment has some relationship with rate of LV pressure change and aortic valve --> if slurred = AS (poor LV contraction however has not shown relationship)

Answer 53

◦ ventricle struggles to squeeze blood out so systolic upstroke less steep ◦ Systolic peak may be loewr as generating high aortic pressures higher ◦ Pulse pressure can be narrowed especially if no aortic regurgitation concurrently ◦ Incisura lost and dicrotic notch may disappear

Answer 54

◦ Maximal pressure in central arteries - this is what you bleed with, shear force maximal, maximal wall stress on aneurysm or clot ◦ Major factors influencing this will be ‣ LV contraction ‣ Central arterial compliance - high compliance = low peak systolic pressure ‣ Reflected pressure wave - the shape is influenced from the reflected waves coming back from the vascular tree in particular the transition to the arterioles ◦ Distal systolic pulse amplification ‣ Action of reflected waves as the more distal you proceed the greater the accumulation of reflected waves on top of the systolic peak

Answer 55

◦ Sharp systolic upstroke as instead of contracting isovolumetrically pressure from early contraction is transmitted to the aorta and steep systolic decline, low end diastolic pressure and a widened pulse pressure ◦ The more incompetent the valve the closer diastolic pressure gets to LV end disastolic presssure - 5mmHg ◦ No dicrotic notch, small incisura

Answer 56

Systolic decline - downslope ◦ Rapid decline in arterial presure as contraction comes to an end - efflux of blood from the central arterial compartment is faster than the influx of blood emptying left ventricle - flow from the ventricle is minimal ◦ Decline more rapid if outflow tract obstruction as systole comes to an abrupt halt prior to the LV being finished

Answer 57

◦ Widely believed to be the effect of the aortic valve closing - when measured in the aorta it is called the insisura however further doen the arterial tree it is replaced by the dicrotic notch a combination fo reflected waves - requires high frequency waves to be detected ◦ This reflected wave is lost in severe aortic stenosis as well as AR ◦ As you move further into the peripheral circulation the incisura ends up being slurred and softened and the peripheral dicrotic notch owes more of its shape to vascular resistance of peripheral vessels than aortic valve ◦ The dicrotic notch becomes further and further separated from the systolic area the further you go from the aorta

Answer 58

◦ Drop in pressure after AV closes - no flow from LV and pressure gradually decreases due to arrterial cushioning as the arterial reservoir elastically recoils contributing up to 40% of stroke volume ◦ The older you are the less compliant your arteries are, the higher pressure the reservoir is under and the diastolic run off curve will be more elevated --> contributes more to pressure, but is also earlier adding to afterload and myocardial workload whereas in the young it is a reflection wave in diastole contributing to coronary perfusion

Answer 59

◦ Exerted back on the aortic valve by the vascular tree - hardened non compliant vessels will vause this pressure to be raised ◦ AR will cause this pressure to be much lower

Answer 60

* Inadequate right heart filling, for example: ◦ Hypovolemia (thus, it can imply a degree of fluid responsiveness) ◦ Vasodilated shock state (central venous venodilation) * Excessive right heart afterload, for example: ◦ Acute severe asthma with gas trapping and hyperinflation ◦ Tension pneumothorax ◦ Massive pulmonary embolism * Decreased right ventricular compliance, for example: ◦ Cardiac tamponade or large pericardial effusion ◦ RV failure due to infarction ◦ Post-radiotherapy changes or infiltrative disease, eg. amyloid ◦ LV failure with LV dilatation (causing RV diastolic failure)

Answer 61

* The natural frequency of the system is the frequency at which it will oscillate freely (in the absence of sustained stimulus)

Answer 62

* Resonance is the amplification of signal when is its frequency is close to the natural frequency of a system - as it oscillates with greater amplitude at this frequency than any other

Answer 63

* Equation denoting the natural frequency of a fluid filled pressure transducer system --> ◦ Lengthening tube = increased elasticity --> decreased natural frequency ◦ Increasing the diameter of the tubing - increased natural frequency ◦ Stretchy tubing increases elasticity, decreasing the natural frequency ◦ Air bubbles increase elasticity and decrease natural frequency

Answer 64

tendnacy of a volume t return to its initial shape after being distorted

Answer 65

◦ An arterial waveform is a composite of many waveforms of increasing frequencies (harmonics), the amplitude of which decreases as their frequency increases. ‣ These can be separated into a series of simple component sine waves fo different amplitudes and frequencies by Fourier analysis and the frequencies are whole numbe rmultiples or harmonics of the fundamental frequency ◦ At least five harmonics must be analysed to accurately represent the pulse pressure ◦ At least eight harmonics must be analysed to represent the arterial pressure waveform with sufficient resolution to see the dicrotic notch ◦ The transducer system must therefore have a natural frequency well above the 8th harmonic frequency of a rapid pulse, i.e. higher than 24Hz

Answer 66

◦ Damping is the process of the system absorbing the energy (amplitude) of oscillations - natural tendancy of fluid or air bubbles ot extinguish motion

Answer 67

◦ One can make the general statement that the diameter of the tubing has the greatest effect on damping; damping increases by the third power of any decrease in the diameter of the tubing. In other words, narrower tubing increases damping

Answer 68

◦ An index of the tendency of the system to resist oscillations - how quickly the vibrations comes to rest ◦ Given by the equation, ◦ γ = c / 2m ◦ where ‣ - γ is the damping coefficient, ‣ - c is the friction coefficient, and ‣ - m is the mass of the oscillating thing.

Answer 69

‣ A damping coefficient around 0.7 is optimal, >1.0 is overdamped, and <0.7 is underdamped, * >1 will lead ot an excessive delay in return to baseline missing fine detail, and reduction in amplotide e.g. bubbles or blood clots * Too low and the frictional force of the system is not enough to stop it overshooting the zero point following the change in dsignal - exaggerating signals * Optimal damping: A damping coefficient of around 0.64-0.7 ◦ Maximises frequency response ◦ Minimises overshoot of oscillations ◦ Minimises phase and amplitude distortion ◦ Corresponds to 2-3 oscillations following an arterial line flush test

Answer 70

* Critical damping: a damping coefficient of 1.0 ◦ The oscillator returns to the equilibrium position as quickly as possible, without oscillating, and passes it only once. ◦ Occurs when the damping coefficient is equal to the resonant frequency of the oscillator ◦ As the damping coefficent increases the higher frequencies are lost as they already have low amplitude

Answer 71

* The effects of damping: ◦ The transducer system must be adequately damped so that amplitude change due to resonance should not occur even when it is close to the system's natural frequency ◦ The frequency response of a system (the flat range) is the range of frequencies over which there is minimal amplitude change from resonance, and this range should encompass the clinically relevant range of frequencies ◦ The natural frequency (and thus the frequency response) of an arterial line transducer can be interrogated using the fast flush test.

Answer 72

From this, the beneficial effects of damping become clear. The damped system has a larger range over which there is little amplitude increase with increasing frequency, and even at its natural frequency the amplitude change is smaller. As a result, the measured pressure waves will not be overestimated as much.

Answer 73

ynamic response test * Fast flush test/square wave test - assesses the natural freuqency of the system and the damping coefficient * When the fast flush is performed the transducer is exposed to a pressure straight from the counter pressure bag (300mmHg) and the transducer system oscillates at its natural freuqency * Measure the time interval between oscillations with digital calipres and convert to a frequency in Hz (oscillations per second) and this is the natural freuqency * f the natural frequency is over 30-40 Hz, you'd be able to confidently say that the clinically relevant range of frequencies (0-24 Hz) is well within the flat range of this system, and the pressure values you are recording are accurate. Generally speaking, at the bedside you will find most arterial line systems have a natural frequency somewhere between 10 and 25 Hz

Answer 74

Presence of a dicrotic notch

Answer 75

High frequency waveforms, low amplitude and more susceptable to damping

Answer 76

* Multiple artefacts in the waveform, systolic blood pressure is overestimated, MAP accurate and diastolic BP is underestimated. Multiple oscillations take place after the fast flush * Use shorter wider, stiffer tubing * Causes ◦ Excessive tubing length ◦ Multiple 3 way taps ◦ tachycardia and high output cardiac states

Answer 77

higher frequency components are lost - system is also slow to respond due to frictional drag in system * Underestimated systolic and overestimated diastolic * Dicrotic notch is lost * MAP accurate * e.g. ◦ Clot in the catheter tip ◦ Air bubble - pressure is absorbed by airbubble ◦ Catheter too long - resistance and inertia of saline is proportional to catheter length ◦ Catheter too thin, or line too thin ◦ Tubing too compliant ◦ Cathter against vessel wall or vasospasm ◦ Kinks

Answer 78

* The incisura - the notch measured in the aortic waveform cuts into the waveform related to the aortic valve closing, further down the arteria tree it disappears and is replaced by the dicrotic notch which is a reflection of several waves no longer as related to the aortic valve as it is slurred and softened. The position and prominence of the dicrotic notch depends on multiple factors - it is high frequency and therefore easily dampened out; and is more of a reaction of vascular resistance of peripheral vessels than the aortic valve. The dicrotic notch is the trough, and the subsequent peak moves further and further away from the initial waveform the further you get from the aorta

Answer 79

Lengtening delay in the onset due to distance travelled, BP wave also becomes narrower

Answer 80

* High frequency components of the pulse - incisura (notch at the end of ventricular ejection) are damped out and disappear —> due to the viscoelastic characteristics of the arterial tree

Answer 81

* Systolic portions of the pressure wave become narrow and elevated - reflection, tapering of the arteries (change in diameter), resonance and pulse wave velocity (on average 5mmHg higher at the radial artery, even higher at dorsalis pedis); and the diastolic pressure is about 8mmHg lower ◦ The reflected wave in the upper aorta is more prominent however they merge as you progress down the vascular tree, amplification increases as the vascular tree becomes less compliant and more and more reflection waves accumulate —> windkessel effect as the stored energy waves become reflected and accumulate into 1

Answer 82

These findings are more prominent in young individuals and diminish with age; as the arterial tree ages and becomes stiffer the wave remains similar to the aorta

Answer 83

◦ The reflected wave in the upper aorta is more prominent however they merge as you progress down the vascular tree, amplification increases as the vascular tree becomes less compliant and more and more reflection waves accumulate —> windkessel effect as the stored energy

Answer 84

a graph of concentration of substance against time if the substance is removed or washed away by liquid flow - the most basic is exponential decay

Answer 85

thermodilution, indicator dilution and doppler

Answer 86

rate of dye removal = liquid flow x dye concentration

Answer 87

amount of dye added / area under the graph

Answer 88

* The diagram of actual circulatory flow is seen below ◦ Dye injected at T0 ◦ Dye detected later as it takes time to travel from injection to sensor ◦ Rapid rise in oncentration leading to a rounded peak due to the fact laminar flow is occuring so dye travels at a range of velocities from injection to sensor; and also reflects the eddies occuring in circulation ◦ Exponential decay of concentration then occurs - second peak due to recirculation of fast moving dye ◦ Cardiac output calculated by: amount of dye injected / atrea under the graph ‣ the recirculation must be removed

Answer 89

Amount of dye injected / area under graph

Answer 90

indocyanine green 50% metabolised by the liver in 10 minutes allowing repeated measurement

Answer 91

Relies on temperature change in blood flowing past the catheter - COld saline injected - Measuring the thermal washout curve with temperature change measured by a pair of temperature sensors one upstream and one downstream from the point of injection- downstream is just behind the balloon; injection port 20-30cm before Advantages - No reciruclation peak, measurement can be repeated easily, no blood sampling

Answer 92

It works by heating the blood using a heating filament incorporated between two thermisters and the heating filament is turned on and off by a random signal producing miniwashout curves

Answer 93

Lithium, chloride dilution

Answer 94

Comparible in accuracy Electrochemical lithium ion detector used in place of optical dye detector. IJ venous access required and radial arterial line for sampling. This produces an arterial lithium concentration time curve. No known pharmacological effects

Answer 95

Doppler velocity measurements leading to estimation of flow This utilises the doppler shift of sound waves reflected from moving RBC and continuous wave ultrasound Doppler is used to insonate large arteries ad veins

Answer 96

f is sound wave freuqency in hertz V is blood cell velocity C is velocity of sound in tissue (1500m/s) As C is so much greater than V the denominator can be simplified Note if velocities do not all act along the same line we add an angle factor (cos angle) to the numerator - the angle is the angle between the probe and the direction of flow

Answer 97

Continuous wave gives an average velocity in the vessel - but cannot record flow because the diamtre must be known. Pulsed wave doppler operates in a radar like mode - having a brief burst of signal and then reflections are received at a later time. Delay gives an indication of distance,. 8MHz pulse of 1 microsecond duration producing a travelling sound wave 1.5mm long is standard. Pulsed systems have increased accuracy

Answer 98

Cardiac output Detects visible light scattered from moving blood cells - Helium-Neon light source or diode laser transmits laser light to and from the tissue and a fractional shift in light frequency occurs. V = c x change in frequency / frequency Since light is detected from all angles; the mean cosine of all angles is used as 0.5 which means the factor of 2 disappears Laser doppler measures flux - which is the product of blood cell velocity and the concentration of moving blood cells. Flux is different to flow, as flux is the amount of red cells passing through a volume of tissue in a given time, but does not apply to pure solvent with particles as the flux in this case would be 0 regardless of flow rate

Answer 99

leads 1, 2 and 3 which constitute measurement of right arm, left arm and left foot combination vectors

Answer 100

wilsons central terminal

Answer 101

lets through low frequencies and blocks high frequencies reducing distortions form muscle movement, mains electricity (50-60Hz) and other equipment

Answer 102

Reduces signals from body movement including breathing

Answer 103

Low pass filter - lets through low frequencies and blocks high frequencies reducing distortions form muscle movement, mains electricity (50-60Hz) and other equipment High pass filter - Reduces signals from body movement including breathing

Answer 104

Monitoring - hevaily filtered Diagnostic - less filtered, susceptabel to interference and artfacts

Answer 105

* Total uptake of oxygen by the body is equal to the product of the cardiac output and the arterial-venous oygen content difference

Answer 106

* CO = VO2/ Ca - Cv ◦ Blood flow to an organ = rate of uptake or excretion of a substance / arterio-venous concentration difference

Answer 107

* VO2 measurement ◦ patients breaths through a spirometer containing a known volume of 100% oxygen and a CO2 absorbed, after a minute the volume of O2 remaining in the spirometer allows the calculation of O2 uptake

Answer 108

0.2mL O2 per mL of blood

Answer 109

0.15mL of O2 per mL of venous blood

Answer 110

◦ Gold standard ◦ Good accuracy ◦ Necessary invasive devices

Answer 111

◦ Stable CO required ◦ Highly invasive - PAC and arterial line ◦ Requires cumbersome VO2 measuring equipment - as the actual total inhaled and exhaled oxygen using a mask or collection bag is required as well as simultaneous arterial and mixed venous blood measurements. ‣ Notably direct measurements do not account for pulmonary oxygen consumption e.g. in ARDS or pneumonia (can be as much as a 13-15% difference) ◦ Even being the gold standard there is +/- 8% variability ‣ There is increasing inaccuracy the closer the arteriovenous oxygen content difference is ◦ The time taken to measured VO2 over which time the cardiac output must be stable ◦ Intracardiac shunt completely destroys CVO2 accuracy

Answer 112

* Measured of cardiac outptu using the Fick equation but substituting estimated values for the some of the measured variables * Estimations ◦ Uses age/weight and sex based nomogram to estimate VO2 - especially inaccurate if morbidly obese, paralysed, thyrotoxicosis, burns, sepsis, hypothermia where metabolically not normal patients. Additionally pulmonary O2 consumption can be dramatically increased in pnumonia overestimating cardiac output ◦ Mixed venous blood assumed on the basis of normal vlues or estimated from CVC samplws; or from end tidal ◦ Arterial oxygen content can be estimated from pulse oximetry

Answer 113

Stewart Hamilton equation underlies Methods * Thermodilution by PAC or PICCO * Lithium dilution * Conductivity dilution using saline * Indicator dye dilution

Answer 114

* Giving a known dose of a substance IV can be used to measured cardiac output by measuring the rate of transit of the substance at a downstream detector fr ◦ The area under the concnetration time curve which is = mean concentration x time interval * Washout curve - a graph of the concentration of a subtance against time if the substance is removed or washed away by a flow of liquid. The most simple being an exponential decay * If a simple bucket with inflow and outflow rates that are steady has a dye added then the following graph applies -> * Rate of dye removal from an insertion site can be measured as a reflection of flow x dye concentration * The concentration will decrease more quickly at higher flow rates such that ◦ Flow rate = amount of dye added / area under the graph * These principles can be applied using indocyanine green dye via a large vein and then measurement in peripheral arterial tree using optical based sensor

Answer 115

* The diagram of actual circulatory flow is seen below ◦ Dye injected at T0 - 10mL ◦ Dye detected later as it takes time to travel from injection to sensor ◦ Rapid rise in oncentration leading to a rounded peak due to the fact laminar flow is occuring so dye travels at a range of velocities from injection to sensor; and also reflects the eddies occuring in circulation ◦ Exponential decay of concentration then occurs - second peak due to recirculation of fast moving dye - logarithmic transformation of concentration is used and this makes area under the first curve easier to measure ◦ Cardiac output calculated by: amount of dye injected / atrea under the graph ‣ the recirculation must be removed

Answer 116

Used in the indicator dilution technique for calculating cardiac output Indocyanine blue is used because 50% is metabolised by the liver in 10 minutes allowing repeated meaurement * 150second hepatic clearance * Protein bound

Answer 117

* Does not require mixed venous blood * Numerous indicator options e.g. thermodilution * Good accuracy - correlation with gold standard * Can be automated and continuous

Answer 118

* Accuracy is highly technique dependent ◦ Injectate delivery technique including temperature, rate of injection, volume of injectate and timing with respiratory cycle play a major role * Rendered inaccurate by intracardiac shunts and valve disease - disperse or dilute injected indicator ◦ Uniform mixing and unidirectional flow required * Amount of injectate needs to be calibrated to body size ◦ Large injectate volumes overestimate cardiac output in small children * Accuracy reduced by estimated coefficients in the equation ◦ Especially in the thermodilution version * Sampling rate of detector or dye - if recirculation as in indicator dye * Manual integration of area under the curve is laborious

Answer 119

Relies on temperature change in blood flowing past the catheter * Cold saline injected - 5-10mls of cold 5% dextrose into the RA during EXPIRATION ◦ Rate of blood flow is inversely proportional to the change in temperature over time ◦ Mean decrease in temperature is inversely proportional to the cardiac output ◦ Repeat measurement 3 times - mean has to be 15% different to the previous mean otherwise within the range of error * Measuring the thermal washout curve with temperature change measured by a pair of temperature sensors one upstream and one downstream from the point of injection ◦ - downstream is just behind the balloon; injection port 20-30cm before

Answer 120

* No reciruclation peak - avoiding errors seen in dye dilution models * Measurement can be repeated easily * No blood sampling * It can be used accurately even with intra aortic balloon pumps and arrhythmias

Answer 121

* Technique ◦ AMount of injectate ‣ Too much cold injection will underestimate cardiac output ‣ Too little overestimates it ‣ Small volume also increases signal to noise ratio ◦ Temperature of injectate ‣ Room temperature injections produce less accurate readings but are safer ‣ Very cold injectate 0-4 degreess is more accurate but can cause bradycardia and reduce cardiac output ‣ Needs to be consistent ◦ Concurrent infusion of IV fluids leading to underestimation of CO ◦ Timing with respiration can be difficult and erratic - needs to be end expiration ◦ Equipment ‣ Catheter in wrong position ‣ Thermister against the vessel wall * Technical ◦ Estimated rather than measured coefficient in Stewart Hamilton equation ◦ Sensitivty of thermister ◦ Sampling rate of thermister * Aberrant flow ◦ Intracradiac shunt - underestimates CO ◦ TR - underestimates CO ◦ Cardiac arrhtyhmia ◦ Extremely low CO - overestimates * Extracardiac abnormalities ◦ Haematocrit changes - interferes with Stewart Hamilton equaiton ◦ Small body mass - adjust injectate volume ◦ Hypothermia ◦ Pulmonary oedema

Answer 122

* Technique ◦ AMount of injectate ‣ Too much cold injection will underestimate cardiac output ‣ Too little overestimates it ‣ Small volume also increases signal to noise ratio ◦ Temperature of injectate ‣ Room temperature injections produce less accurate readings but are safer ‣ Very cold injectate 0-4 degreess is more accurate but can cause bradycardia and reduce cardiac output ‣ Needs to be consistent ◦ Concurrent infusion of IV fluids leading to underestimation of CO ◦ Timing with respiration can be difficult and erratic - needs to be end expiration ◦ Equipment ‣ Catheter in wrong position

Answer 123

* Aberrant flow ◦ Intracradiac shunt - underestimates CO ◦ TR - underestimates CO ◦ Cardiac arrhtyhmia ◦ Extremely low CO - overestimates * Extracardiac abnormalities ◦ Haematocrit changes - interferes with Stewart Hamilton equaiton ◦ Small body mass - adjust injectate volume ◦ Hypothermia ◦ Pulmonary oedema

Answer 124

* Arrhythmias * Infection * TR and pulmonary valve damage * Pulmonary artery rupture

Answer 125

Detects visible light scattered from moving blood cells - Helium-Neon light source or diode laser transmits laser light to and from the tissue and a fractional shift in light frequency occurs. V = c x change in frequency / frequency Since light is detected from all angles; the mean cosine of all angles is used as 0.5 which means the factor of 2 disappears Laser doppler measures flux - which is the product of blood cell velocity and the concentration of moving blood cells. Flux is different to flow, as flux is the amount of red cells passing through a volume of tissue in a given time, but does not apply to pure solvent with particles as the flux in this case would be 0 regardless of flow rate Doppler velocity measurements leading to estimation of flow This utilises the doppler shift of sound waves reflected from moving RBC and continuous wave ultrasound Doppler is used to insonate large arteries ad veins

Answer 126

* Uses cross sectional area of the LV outflow tract and from integrating the area under the velocity time curve measured by doppler the cardiac output can be calculated ◦ Assumes the volume of blood moves as a cylindrical column ◦ The flat dimension of the column is assumed to be circular * The velocity is measured on a velocity over time curve - the area under this curve is the VTI ◦ Pulsed wave doppler used ◦ Apical 5 chamber view with the sample volume placed below the aortic valve * CO = HR x (VTI x CSA)

Answer 127

* Advantages ◦ Non invasive ◦ Easily available * Limitations ◦ High interobserve variability ◦ Limited by ultrasound window availability ◦ Accuracy dependent on beam angle - anything within 20 degrees likely sufficiently accurate but any angle alters VTI ◦ Stroke volume variability within the respiratory cycle so serial measurements over 3-4 beats required - more beats needed in AF ◦ Assumes laminar flow (which it isnt)

Answer 128

a small ultrasound transducer mounted on the tip of a flexible probe inserted through the nose or mouth into the oesophagus --> tip adjusted to lie immediately alongside descending thoracic aorta with the ultrasuond beam orientated at an angle 45 degrees to the aortic blood flow where it reflects off the passing red blood cells

Answer 129

◦ V = F (d)c / 2 F(O) cos (theta) ‣ V = velocity of blood in descending aorta ‣ F(d)c = change in frequency of the reflected ultrasound x speed of ultrasound in tissue ‣ F(O) = transmitted ultrasound freqeuncy ◦ Blood flow is then determined by velocity x cross sectional area of the descending aorta (thoracic) estimated from patients height and weight

Answer 130

70% of SV passes into descending thoracic aorta so calculated flow has to be adjusted

Answer 131

area undet the velocity time curve, distance in centimetres the blood moves along the aorta with each heart beat

Answer 132

indicator of LV contractility * 90-120cm/s for 20 eyar old * 50-80cm/s for a 70 year old

Answer 133

‣ Flow time corrected (FTc) * Duration of blood flow when corrected for HR and reflects LV preload ◦ Normal 330-360 ◦ Low values suggest low preload or increased afterload, high FTc suggests vasodilation

Answer 134

* Advantages ◦ Arterial and central lines not required ◦ Oeosphageal tone holds the probe in place - repositioning occasionally required ◦ No calibration ◦ Continuous readings * Disadvantages ◦ Poorly tolerated if awake ◦ Movement leads to a poor tyrace ◦ Surgical diathermy interferes with trace ◦ Estimates of aorta cross section and division of SV may be inaccurate ◦ Contraindicated in pharyngooesophgeal pathology e.g. varices

Answer 135

* Stroke volume can be calculated from under the area under flow/time curve derived from arterial pressure waveform using a calibration factor ◦ The arterial waveform is a pressure measurement - the calibration factor converts it to a volume measurements ‣ This is done by first converting to a flow time waveform and then integrating the area under the curve for volume ‣ The morphology of the arterial pressure waveform is related to SV and SVR ◦ This is derived from information about he pressure volume relationship in the aorta and incorporates arterial impedance, compliance and SVR ◦ These variables are either measured using indicator dilution measurements or estimated from nomograms based on patient demographic data

Answer 136

◦ Standard central line and a thermistor tipped arterial line in the femoral, brachial or axillary ◦ Calibrated using transpulmonary thermodilution using cold saline and resultant temperature changes ◦ Heat is dissipated as the cold injectate passes through the lungs introducing error

Answer 137

◦ Requires only a standard arterial line ◦ Arterial pressure waveform is analysed ina similar way to PiCCO ◦ LiDCO is calibrated with lithium dilution where it is injected peripherally or centrally and the lithium electrode sampling arterial line is used ◦ Recalibration 8hrly ◦ Lithium avoids the error introduced by heat dissipationhowever it cannot be used when ‣ Lithium is used therapeutically ‣ Frequent calibration is required ‣ Muscle relaxants can cross react with the lithium electrode

Answer 138

◦ Less invasive - arterial line and CVC (mixed venous blood not required) ◦ Continuous ◦ Reasonably accurate ◦ Additional derived measurements e.g. SVV --> if >15% suggestive of fluid responsiveness; and someone with a SVV <10% is unlikely to respond to fluid

Answer 139

◦ Calibration factor needs to be measured ‣ If measured by thermodilution then error from this style of measuremen ‣ If calibration factor estimated then significant assumptions ‣ If the patients condition changes markedly then the calibration needs to be recompleted ‣ Drifts from calibration between measurements ◦ Dependent on good arterial waveforms ◦ Confused by AF and balloon pump - pulse contour change ◦ Ineffective where flow is non pulsatile e.g. ECMO

Answer 140

* FLoTrac/Vigileo ◦ Specialised pressure sensor attached to a standard arterial line ◦ Pressure transducer connected to Vigileo monitor ◦ Arterial pressure waveform analysed ‣ Uses an estimate of aortic vascular complianc ebased on population demographics and patient age, height, weight, gender * LiDCO rapid ◦ Based on same pulse power calculation as LiDCO system however uncalibrated using nomograms

Answer 141

In general correlates well with PAC thermodilution except where * Arterial trace overdamped or underdamped * Cardaic arrhtyhmias * Aortic regurgitation * Intra aortic balloon pump

Answer 142

These are indexed to BSA- The normal average adult BSA is 1.9 m2 for males and 1.6 m2 for females. Thus, a normal adult male with a cardiac output of 5.0 L/min would score a cardiac index (CI) of 2.6 L/min/m2.

Answer 143

* Morbidly obese - BSA higher than actual required output, so required index may be below expected * Children - BSA and metabolic rate do not correlate as well, so even with normal index can be insufficent

Answer 144

Cardiac output / BSA COmparison between cardiac output of patients of a different size Normal 2.5 - 4 L/min/metre squared

Answer 145

the volume of blood pumped out fo the L of the heart during each systolic contraction

Answer 146

cardiac output / HR --> i.e. average SV over 1 minute

Answer 147

60 -100mL/beat

Answer 148

CI / HR x 1000 Indexed for body size 33 - 47 mL/metre squared / beat

Answer 149

80 x (MAP - CVP) / cardiac output Normal 800 - 1200 dynes-sec/cm ^ -5

Answer 150

SVR indxed to body size 80 x (MAP - CVP) / CI Normal vlue 1970 - 2390 dynes-sec/cm^-5 x metres squared

Answer 151

80 x (MPAP - PAWP) / cardiac output Normal value <250 dynes - sec / cm^ -5

Answer 152

Global end diastolic volume - it is the combination of all of the diastolic volumes of each of the chambers of the heart GEDV = CO x (MTt - DSt)

Answer 153

mean transit time -0 time taken for the cold indiactor to pass before recirculation

Answer 154

the down slope time or the time it takes for the extrapolated downslope to reach 0 the starting point is taken at 85% of the temperature response adn the end point is 45% of the temperature response

Answer 155

PICCO derived variables for resuscitation * Cardinal variables ◦ CI ◦ Intrathoracic blood volume index (ITBVI) ◦ Extravascular lung water index (EVLWI) * If the CI is low --> what is the ITBVI ◦ If there is not enoguh intrathoracic blood volume more filling is required --> if there is enough ITBVI then a fluid bolus will not help and inotropes are needed * If the CI is normal or high ◦ If ITBVI is low --> fluids ◦ If ITBVI is high --> vasopressors ◦ If ITBVI is low and EVLWI is high then there is too much fluid on board

Answer 156

SV max - SV min/SV mean Under 10% normal and predicts lack fo fluid response

Answer 157

1. Balloon - red 2. Thermister connectors x2 - round for thermodilution, flat is the powerplug for the heating filament 3. PA distal lumen yellow 4. PA proximal lumen blue - CVP and cold injectate flush 5. Continuous oximetry cable

Answer 158

Pulmonary artery pressure monitoring Pulmonary artery wedge pressure Cardiac output monitoring O2 sats Access and sampling Temperature monitoring Pacing swan Aspiration of an air embolism

Answer 159

0-6cm CVP 30-35cm RV 40-45cm PA Wedge at 50cm usually

Answer 160

Sensor - column of fluid, sensor a bonded strain gauge in a wheatstone bridge Processor - Fourier analysis and breakdown into component sine waves. Fundamental wave an series of harmonics. Broken down into components then reconstrictured from fundamental frequency +9 harmons Display - pressure trace on a onitoring screen

Cardiology measurement Flashcards

(218 cards)