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Flashcards in CVS Deck (27)
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1
Q

MAP (mean arterial pressure)

A

MAP = (CO x SVR) + RAP Right atrial pressure is negligible in most patients, and is often eliminated from the equation (when there is no RHF).

2
Q

MAP in relation to 3 types of circulatory shock

A

MAP = (CO x SVR) + RAP a. Low RAP = hypovolemic shock. b. Low CO = cardiogenic shock c. Low SVR = vasogenic shock (e.g., septic shock

3
Q

Central Venous Pressure

A

CVP = RAP = RVEDP -measure of right ventricular filling pressure -normal range 0-5 mmHg The pressure in the right atrium is the same as the pressure in the superior vena cava, and these pressures are collectively called the central venous pressure (CVP). In the absence of tricuspid valve dysfunction, the CVP should be equivalent to the right-ventricular end-diastolic pressure (RVEDP).

4
Q

Pulmonary Artery Wedge Pressure (PAWP)

A

PAWP = LAP = LVEDP -measure of left ventricular filling pressure (slightly higher than CVP) -normal range 6-12mmHg The PAWP is a measure of left-atrial pressure (LAP), which is equivalent to the left-ventricular end-diastolic pressure (LVEDP) when mitral valve function is normal.

5
Q

Cardiac Index

A

CI = CO/BSA In the average-sized adult, the cardiac index is about 60% of the cardiac output -normal range is 2.4–4 L/min/m2. The thermodilution cardiac output (CO) is the average stroke output of the heart in one minute periods. It is typically adjusted to body surface area (BSA), and is called the cardiac index (CI).

6
Q

stroke volume

A

-normal range 20-40 mL/m^2 stroke volume is the volume of blood ejected in one pumping cycle. The stroke volume is equivalent to the average stroke output of the heart per minute (the measured cardiac output) divided by the heart rate (HR)

7
Q

Stroke Index

A

SI = CI/HR -normal range 20-40 mL/m^2 - measure or systolic performance of the heart during one cardiac cycle The heart is a stroke pump, and the stroke volume is the volume of blood ejected in one pumping cycle. The stroke volume is equivalent to the average stroke output of the heart per minute (the measured cardiac output) divided by the heart rate (HR). When cardiac index (CI) is used, the stroke volume is called the stroke index (SI).

8
Q

Systemic Vascular Resistance index

A

SVRI= (MAP -CVP)/CI - expressed in Wood units The hydraulic resistance in the systemic circulation is not a measurable quantity for a variety of reasons (e.g., resistance is flow-dependent and varies in different regions). Instead, the systemic vascular resistance (SVR) is a global measure of the relationship between systemic pressure and flow. The SVR is directly related to the pressure drop from the aorta to the right atrium (MAP – CVP), and inversely related to the cardiac output (CI).

9
Q

Pulmonary Vascular Resistance Index

A

PVRI = (PAP-PAWP)/CI The pulmonary vascular resistance (PVR) has the same limitations as mentioned for the systemic vascular resistance. The PVR is a global measure of the relationship between pressure and flow in the lungs, and is derived as the pressure drop from the pulmonary artery to the left atrium, divided by the cardiac output. Because the pulmonary artery wedge pressure (PAWP) is equivalent to the left atrial pressure, the pressure gradient across the lungs can be expressed as the difference between the mean pulmonary artery pressure and the wedge pressure (PAP – PAWP).

10
Q

Oxygen Delivery

A

DO2 = CI x CaO2 or DO2 = CI x ( 1.3 × Hb × SaO2) rate of oxygen transport in arterial blood is called the oxygen delivery (DO2) The rate of oxygen transport in arterial blood is called the oxygen delivery (DO2), and is the product of the cardiac output (or CI) and the oxygen concentration in arterial blood (CaO2). The O2 concentration in arterial blood (CaO2) is a function of the hemoglobin concentration (Hb) and the percent saturation of hemoglobin with oxygen (SaO2): CaO2 =1.3 × Hb × SaO2.

11
Q

Oxygen Uptake (aka Oxygen Consumption)

A

VO2 = CI x (CaO2 - CvO2) or VO2 = CI x 1.3 x Hb x (SaO2 -SvO2) Oxygen uptake (VO2), also called oxygen consumption, is the rate at which oxygen is taken up from the systemic capillaries into the tissues. The VO2 is calculated as the product of the cardiac output (or CI) and the difference in oxygen concentration between arterial and venous blood (CaO2 – CvO2). The venous blood in this instance is “mixed” venous blood in the pulmonary artery.

12
Q

Oxygen Extraction Ratio

A

O2ER = VO2/DO2 (X 100) The oxygen extraction ratio (O2ER) is the fractional uptake of oxygen from the systemic microcirculation, and is equivalent to the ratio of O2 uptake to O2 delivery. Multiplying the ratio by 100 expresses it as a percent. The O2ER is a measure of the balance between O2 delivery and O2 uptake. It is normally about 25%, which means that 25% of the oxygen delivered to the systemic capillaries is taken up into the tissues.

13
Q

Preload

A

Preload is defined as the force imposed on resting muscle that stretches the muscle to a new length. The preload force acts to augment the strength of muscle contraction. The volume in the ventricles at the end of diastole is the force that stretches the resting muscle to a new length. Therefore, the end-diastolic volume of the ventricles is the preload force of the intact heart.

14
Q

Frank-Starling relationship of the heart

A

In the normal heart, diastolic volume is the principal force that governs the strength of ventricular contraction. At any given end-diastolic volume, the increment from end-diastolic pressure to peak systolic pressure is a reflection of the strength of ventricular contraction during systole

15
Q

Ventricular compliance

A

Delta EDV/Delta EDP A decrease in ventricular compliance will result in a greater change in EDP for a given change in EDV, or a smaller change in EDV for a given change in EDP. Therefore, at angiven end-diastolic volume, the end-diastolic pressure is higher in the noncompliant ventricle. Therefore, when ventricular compliance is reduced, the end-diastolic pressure will overestimate the end-diastolic volume.

16
Q

Diastolic HF

A

Diastolic Failure: High EDP / Low EDV / Normal EF

17
Q

Systolic HF

A

Systolic Failure: High EDP / High EDV / Low EF

18
Q

Afterload

A

The weight in this situation represents a force called the afterload, which is the load imposed on a muscle after the onset of muscle contraction. Unlike the preload force, which facilitates muscle contraction, the afterload force opposes muscle contraction. In the intact heart, the afterload force is equivalent to the peak tension developed across the wall of the ventricles during systole (3). Afterload is thus the wall stress associated with ejection of the stroke volume.

19
Q

Forces on afterload

A
20
Q

Impedance

A

The force that opposes pulsatile flow is known as impedance.

: Vascular impedance is the force that opposes the rate of change in pressure and flow, and it is expressed primarily in the large, proximal arteries, where pulsatile flow is predominant. Impedance in the ascending aorta is considered the principal afterload force for the left ventricle, and impedance in the main pulmonary arteries is considered the principal afterload force for the right ventricle

21
Q

Resistance

A

the force that opposes steady flow is resistance

Vascular resistance is the force that opposes non-pulsatile or steady flow, and is expressed primarily in small, terminal blood vessels, where non-pulsatile flow is predominant. About 75% of the vascular resistance is in arterioles and capillaries

22
Q

SVR and PVR

A

SVR = (MAP-RAP)/CO

PVR = (PAP-LAP)/CO

MAP = mean arterial pressure, RAP = right atrial pressure, PAP = mean pulmonary artery pressure, LAP = left atrial pressure, and CO = cardiac output

23
Q

Most important factor in determing resistance to steady flow in peripheral circulation

A

Based on Hagen-Poiseuille equation

The radius of blood vessels as the single most important factor in determining the resistance to steady flow in the peripheral circulation; i.e., a two fold increase in vessel radius will result in a 16-fold increase in flow rate (r4 × r4 = r16). This highlights the importance of vasodilator therapy for promoting cardiac output in patients with heart failure.

24
Q

Define viscosity. What determines viscosity of blood

A

Viscosity is defined as the resistance of a fluid to changes in flow rate , and has also been called the “gooiness” of a fluid. The viscosity of whole blood is the result of cross-linking of erythrocytes by plasma fibrinogen, and the principal determinant of whole blood viscosity is the concentration of erythrocytes (the hematocrit)

25
Q

Normal measures of oxygen in arterial and venous blood

A
26
Q

oxygen saturation

A

SO2 = oxygenated Hb/ total Hb

27
Q

Oxyhemoglobin dissociation curve

A

describes relationship b/n SO2 and PO2

A shift of the curve to the right facilitates oxygen release. Shift to the left facilitates oxygen uptake.