Cardiopulmonary Interactions - Scharf

Question 1

Formula for venous return

Answer 1

venous return = Mean systemic pressure - right atrial pressure / venous return resistance

Vr curve: slope between RAP and VR is 1/Rvr

Flow limitationis y-intercept when right atrial pressure is theoretically zero (maximum venous return)

Question 2

Cardiac function curve and effect of interthoracic pressure

Answer 2

CF curve intersects with VR curve, and moves down it (to the right) with increased ITP, to the left (up) with decreased ITP

Question 3

What is the effect of max pressure in mechanical ventilation on the vessels in the chest?

Answer 3

Compresses the vessels causing decreased aortic filling, decreased venous return and decreased stroke volume. One cause of pulsus paradoxus (hear heart beat but can’t feel radial pulse. Blood pressure increases in exhalation and decreases in inhalation.

Question 4

Ventricular interdependence

Answer 4

Increased volume of one ventricle means increased pressure in the other.

 Similarly, if you increase volume of one ventricle,
you tend to decrease the volume of the other.
– What happens to cardiac volume between systole and
diastole?-doesn’t change (ventricles and atria counteract)
– Whole heart hypothesis
 What are the effects of large increases in RV
volume transiently with increased venous return?-decreased LV filling

Question 5

Mueller vs. Valsalva maneuvers

Answer 5

Both in closed glottis: In Mueller try to expand volume of chest and in Valsalva try to compress chest.

Volume inside lung stays the same. ITP decreases in Mueller and increases in Valsalva. Same end systolic pressure. Transmural pressure increases in Mueller (apparent increase in afterload) and decreases in Valsalva.

After MI free wall can’t counter pressure and bulges in Mueller.

Question 6

What is the effect of hyperinflated lung on the heart?

Answer 6

Decreased filling because of increased pericardial pressure (as in emphysema or asthma).