Cardiovascular Hemodynamics and Shock

Question 1

How are right sided intracardiac, pulmonary artery and pulmonary capillary wedge pressure tracing obtained?

Answer 1

with a balloon-tipped Swan-Ganz catheter

Question 2

1. Normal right atrial pressure is in what range and characterized by which waves? Describe these waves.

Answer 2

normal 2-6 mmHg
> a wave
> c wave
> v wave and 
> x, x' and y descents

Question 3

1. Describe the physiologic basis of the a wave and associated pathology.

Answer 3

a wave is generated by contraction of the atrium, following the p wave

pathology: pulmonary hypertension and RV hypertrophy, atrial contraction can be heard as S4; a wave is absent in atrial fibrillation

Question 4

1. Describe the physiologic basis of the c wave and associated pathology.

Answer 4

C wave is produced by the contraction of the ventricles causing pressure on tricuspid valve and therefore the atrium, it follows the QRS complex: c wave follows the a wave in time equal to the PR interval

pathology: AV block results in more obvious c wave

Question 5

1. Describe the physiologic basis of the x’ descent.

Answer 5

x’ descent occurs as a consequence of the sudden downward motion of the atrioventricular junction during early ventricular systole

Question 6

1. Describe the physiologic basis of the v wave.

Answer 6

v wave is produced due to pressure generated during venous filling of atria during atrial diastole, the peak of the right atrial v wave corresponds with the end of the T wave when the atrium is maximally filled

Question 7

1. Describe the physiologic basis of the y descent and associated pathology.

Answer 7

y descent reflects the decay in atrial pressure with the opening of the tricuspid valve

note inspiration causes a more prominent y descent

Question 8

Which is bigger in normal atrial waveforms, a wave or v wave

Answer 8

in the right atrium, a wave is larger, in the left atria the v wave is larger

Question 9

1. What is the normal right ventricular systolic pressure and end-diastolic pressure. Describe the waves of ventricular waveform.

Answer 9

normal systolic 20-30mmHg
ED pressure 2-8mmHg (should be very near to atrial pressure unless tricuspid valve stenosis

there are no named waves, tracings are characterized by rapid pressure rise during ventricular contraction and rapid pressure decay (possible to see an a wave due to atrial contraction at the end of diastole)

Question 10

1. What are the normal pulmonary artery systolic and diastolic pressures?

Answer 10

systolic 20-30 mmHg and diastolic 5-15mmHg

pulmonary artery end diastolic pressure is sometimes used as an estimate of the left atrial pressure (can be inaccurate if abnormal resistance)

(if pulmonary valve- right ventricular systolic pressure will exceed pulmonary artery systolic pressure)

Question 11

1. Although pulmonary artery wave form is very similar to atrial waveform, highlight some of its unique characteristics.

Answer 11

well defined dicrotic notch from pulmonary valve closure

peak systolic pressure occurs within the T wave

Question 12

What is pulmonary capillary wedge pressure and what will its waveform resemble?

Answer 12

a measurement via the Swan-Ganz catheter from a branch of the pulmonary arterial system, reflection of left atrial pressure and will resemble typical atrial tracing with a and v waves and x and y descents, c wave is often dampened

timing of waveform is delayed with a wave following the QRS complex and the v wave occurring after the T wave
normal PCWP is 5-15 mmHg

Question 13

What conditions may lead to a larger difference between left ventricular end-diastolic pressure, left atrial pressure and PCWP?

Answer 13

mitral stnosis, mitral regurgitation, aortic regurgitation and pulmonary venous obstruction

Question 14

1. Describe the normal LV pressures and when ED pressure is measured.

Answer 14

systolic pressure is 100-140mmHg and LV end-diastolic pressure is 5-15mmHG (measured right after the a wave and before the abrupt rise in systolic pressure or peak QRS)

note a wave may be inscribed in the left ventricular tracing at end diastole, especially if the ventricle is non-compliant

Question 15

What are the normal aortic systolic pressures? What is an anacrotic notch?

Answer 15

100-140/60-90
anachrotic notch may be present due to turbulent flow during ejection

note reflected waves that are apparent on aortic waveform can be characteristic of the state of peripheral vessels

Question 16

2. What are the basic mechanical events of the cardiac cycle and their corresponding heart sounds.

Answer 16

S1 sound of aortic and pulmonic valves closing
1. LV isovolumetric contraction and ejection
2. LV relaxation
S2 sound of mitral and tricuspid valves closing
3. LV filling, rapid then slowly (diastasis)

Question 17

3. How are cardiac output and oxygen consumption related to each other through Fick’s equation?

Answer 17

blood flow can be determined based on oxygen extraction from a tissue, so if we understand the rate at which oxygen enters the blood from the lungs, we can figure out the CO
CO= O2 consumption/ (A-V) O2 content difference (O2 consumption at rest set. 125mLO2/min/m2)

(faster speeds make it harder to exchange with the blood so increased O2 saturation can correlate to low CO)

Question 18

4. Explain the formula linking pressure, flow and resistance

Answer 18

the flow of blood (Q) through vascular resistance is driven by a pressure gradient (delta P) so therefore deltaP= QR

generalized out to the body
CO = (MAP-RAP)/SVR

Question 19

5. Contrast the pulmonary and systemic vascular resistance. What would you expect oxygen saturation to be for the cardiac chambers?

Answer 19

PVR 1.325-2.5 wood units
SVR 11-17 wood units

right side of the heart 70-80%
left side of the heart 90-100% O2 sat.

Question 20

6. What is the normal cardiac output (CO)?

Answer 20

4-7 L/min

Question 21

Is shock defined by a drop in blood pressure?

Answer 21

no, although changes in pressure can occur with shock, shock is defined by the adequacy of the tissue perfusion and oxygenation

Question 22

What three characteristics are used to separate the different types of shock?

Answer 22

pulmonary capillary wedge pressure (represents left ventricular filling pressure/preload)
cardiac output (represents blood flow)
systemic vascular resistance

Question 23

7. Which variable is most effected by hypovolumeic shock?

Answer 23

PCWP declines due to loss of intravascular volume which precipitates changes in CO and SVP

Question 24

7. Which variable is most effected by cardiogenic shock?

Answer 24

CO declines due to loss heart contractility or arrhythmia which precipitates changes in SVP and PCWP (both increase, except in right sided heart failure)

Question 25

7. Which variable is most effected by distributive shock?

Answer 25

loss of vascular tone causes a decrease in SVR, CO increases in response, with PCWP generally low with higher flow

Question 26

8. Describe the pressure, flow and resistance changes that accompany PE.

Answer 26

PCWP and CO will be decreased due to the obstruction and compensatory increase in PVR will occur