4. [Total: 23 pts] Cardiac output and venous return

The figure below displays the cardiac output (Qc) and venous return (Q₂) curves that represent the

steady state characteristics of the heart and the rest of the circulation of a subject who is bleeding

badly from a knife wound in the abdomen. Point N shows the steady state operating point of the

system under normal circumstances prior to the stabbing and subsequent bleeding.

Venous return and cardiac output (mL/min)

2800

2400

2000

1600

1200

800F

400

E

0

G

-8

B

D

-4

0

4

8

Right atrial pressure (mmHg)

a) [3 pts] Bleeding reduces blood volume and increases circulatory resistance. Which curve (A, B, C,

D, E, F or G) best represents these changes from the normal case? Briefly explain the reason for

your selection.

12/nb) [5 pts] From the information displayed in the figure, provide a rough estimate of the total volume

of blood lost, assuming that the sum of arterial and venous compliances is 0.53 L-mmHg¹. Briefly

explain how you arrived at your answer.

c) [4 pts] In the compensated stage of shock from the bleeding, the heart becomes hypereffective

(i.e., it generates a higher cardiac output for the same Pra). Label on the figure "c", the new steady

state equilibrium values of Pr. and cardiac output in the compensated stage of shock following

blood loss. Briefly explain your answer.

d) [3 pts] If this subject remains in this state without medical care, the irreversible stage of shock

sets in. The heart is no longer able to sustain its hypereffective performance and deteriorates

progressively. Which curve (A, B, C, D, E, F or G) best represents this situation? Briefly explain

your selection. Label on the figure "d", the new steady state equilibrium values of Pra and cardiac

output in the irreversible stage of shock./ne) [4 pts) Assuming arterial pressure (PA) to be 40 mmHg and pleural pressure (Pi) to be -4 mmHg,

provide your best estimate of what the ratio of systolic to diastolic compliance (Cs/Co) of the

heart would be in the irreversible stage of shock from the bleeding, based the information

displayed in the figure.

f) [4 pts] if the subject were to receive blood transfusion at the irreversible stage of shock, can the

blood transfusion restore the cardiac output to the normal level? Assume that the body has not

yet adjusted to the replenished blood volume. Explain your answer.