CVS

Question 1

MAP (mean arterial pressure)

Answer 1

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).

Question 2

MAP in relation to 3 types of circulatory shock

Answer 2

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

Question 3

Central Venous Pressure

Answer 3

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).

Question 4

Pulmonary Artery Wedge Pressure (PAWP)

Answer 4

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.

Question 5

Cardiac Index

Answer 5

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).

Question 6

stroke volume

Answer 6

-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)

Question 7

Stroke Index

Answer 7

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).

Question 8

Systemic Vascular Resistance index

Answer 8

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).

Question 9

Pulmonary Vascular Resistance Index

Answer 9

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).

Question 10

Oxygen Delivery

Answer 10

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.

Question 11

Oxygen Uptake (aka Oxygen Consumption)

Answer 11

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.

Question 12

Oxygen Extraction Ratio

Answer 12

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.

Question 13

Preload

Answer 13

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.

Question 14

Frank-Starling relationship of the heart

Answer 14

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

Question 15

Ventricular compliance

Answer 15

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.

Question 16

Diastolic HF

Answer 16

Diastolic Failure: High EDP / Low EDV / Normal EF

Question 17

Systolic HF

Answer 17

Systolic Failure: High EDP / High EDV / Low EF

Question 18

Afterload

Answer 18

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.

Question 19

Forces on afterload

Answer 19

Question 20

Impedance

Answer 20

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

Question 21

Resistance

Answer 21

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

Question 22

SVR and PVR

Answer 22

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

Question 23

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

Answer 23

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.

Question 24

Define viscosity. What determines viscosity of blood

Answer 24

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)

Question 25

Normal measures of oxygen in arterial and venous blood

Answer 25

Question 26

oxygen saturation

Answer 26

SO2 = oxygenated Hb/ total Hb

Question 27

Oxyhemoglobin dissociation curve

Answer 27

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.