What is the unit of measuring blood pressure?
mmHg- millimetres of mercury
Why is mercury used in measuring blood pressure?
Mercury is a stable fluid with a high density, that expands less as pressure changes
Normal blood pressure
120mmHg systolic
80mmHg diastolic
MAP definition
Mean Arterial Pressure is an average blood pressure in an individual during a single cardiac cycle
How can MAP be determined?
(Cardiac output x systemic vascular resistance) = central venous pressure
normal range of MAP
65-110 mmHg
Pulse pressure definition
the difference between systolic and diastolic blood pressure.
Represents the force that the heart generates each time it contracts
normal pulse pressure
40mmHg
What is the systemic pulse pressure similar to?
stroke volume- the amount of blood ejected from the left ventricle during systole
How is pulmonary pulse pressure measured?
Measured by right heart catheterisation or may be estimated by transthoracic echocardiography
process of sphygmomanometry
Blood pressure meter is composed of an inflatable cuff and a manometer.
The cuff is placed around the patients arm and inflated- causing the brachial artery to collapse.
The artery beneath the cuff is then released in a controlled manner.
The mercury or mechanical manometer meaures the pressure.
Korotkov sounds definition
Sounds that medical personnel listen for when they are taking blood pressure using a non-invasive procedure
Are the sounds the same as the vibrations of the ventricles? explain
No, as there should be no audible sound in a normal person with no arterial disease.
If the cuff of the sphygomanometer is placed around the patient’s upper arm and inflated to a pressure above systolic, there should be no audible sound. This is due to the pressure in the cuff being high enough such that it completely occludes the blood flow
When is the first Korotkoff sound heard?
When the pressure is dropped to a level equal to that of the patient’s systolic blood pressure
Why is the sound heard?
Some blood will be able to pass through the upper arm when the pressure in the artery rises during systole. The blood flows in spurts as the pressure in the artery rises above the pressure i the cuff, then drips down in the uncuffed region- resulting in turbulence that produces an audible sound.
5 phases of Korotkov sounds
- faint, repetitive, clear tapping sounds which gradually increase in intensity- systolic pressure
- brief period may follow during which the sounds soften and acquire a swishing quality
- return of sharper sounds, crisp and regain intensity
- distinct abrupt muffling sounds
- point at which all sounds finally disappear- diastolic pressure
central venous pressure definition
blood pressure in the venae cavae, near the right atrium of the heart
normal pressure range
3-8 mmHg
How is CVP measured?
connecting the patients central venous catheter to a special infusion set which is connected to a small diameter water column.
How is the patient lying during CVP measuring?
semi supine- tilted 45 degree
Define jugular venous pressure
The indirectly observed pressure over the venous system via visualisation of the internal jugular vein.
How is the jugular venous pressure visualised?
at the semi supine angle, the height from the atria can be visualised- if it is greater than 10cmH2O then it could suggest heart failure and other conditions
What is the normal central venous pressure?
5mmHg or 7cmH2O
Cardiac Output definition
The amount of blood ejected from the left ventricle in one minute
Average CO
5 litres/minute
What is the relationship between atrial and venous pressures, cardiac output and systemic vascular resistance
MAP-CVP = CO x SVR
What determines the systemic vascular resistance?
vascular compliance determined by the muscle tone in the tunica media and the elasticity of fibres
viscosity of blood, length of vessel, radius of blood vessel
compliance definition
relationship between volume and pressure
The ability of a vessel to distend and increase volume with increasing pressure and to resist recoil
What vessels have high compliance + what does this mean?
veins- higher compliance means they deform more easily than others would under the same pressure and resistance
flow definition
volume moved over time
Explain conservation of flow
right and left flows are equal- at a steady state
two different types of flows explained
laminar- most efficient delivery of blood in one direction
turbulent- suboptimal, favoured by wide diameter, fast velocity . Occurs mainly in ventricles and increases the risk of blood clotting
how does lymph flow return to circulation?
Via the thoracic duct
