Cardiovascular System Design

Question 1

What is the interstitial compartment and how much volume does it hold?

Answer 1

Space between capillaries and cells, holds 12L

Question 2

Flow in the systemic circulation is divided between different tissues in series or in parallel?

Answer 2

Parallel

Question 3

How much fluid is in the circulating plasma compartment?

Answer 3

3L (blood plasma and lymph fluid)

Question 4

What is Starling’s Law? What determines the rate of Cardiac output?

Answer 4

The stroke volume of the heart increases in response to an increase in the volume of blood filling the heart (the end diastolic volume) when all other factors remain constant.
Venous return determines CO almost entirely

Question 5

What effect does venous vasoconstriction have on CO and venous volume?

Answer 5

A reduced venous volume and an increase in cardiac output via Starling’s law.

Question 6

Effective cardiac function means efficient ventricular pumping. What are the requirements for this?

Answer 6

Synchronized and regular intervals of cardiac cell contraction. 
Valves must fully open. 
Valves must not leak.
Forceful contraction.
Adequate ventricular filling.

Question 7

How much fluid is in the intracellular compartment?

Answer 7

30L

Question 8

Where is flow velocity the greatest? Where is resistance the greatest? Where is volume the greatest?

Answer 8

Arteries. Arterioles. Venules and veins.

Question 9

What is mean arterial pressure? What is the formula to solve for it?

Answer 9

It is the average pressure over the entire cardiac cycle. It is estimated from diastolic pressure and pulse pressure. MAP=DP+1/3 (SP-DP).
Normal is about 93mmHG

Question 10

What is cardiac output? What is it equal to?

Answer 10

Defined as the quantity of blood per unit time pumped into the aorta by the heart. It equals the quantity of blood per unit time that flows through the circulation.

Question 11

How is arterial pressure measured directly?

Answer 11

For pressures in the arteries, aorta and left ventricle a catheter is passed in a retrograde fashion (against blood flow)

Question 12

How is venous pressure directly measured?

Answer 12

For pressure in veins, right atrium, and right ventricle - a catheter is passed antegrade (with flow).

Question 13

In what two organs does flow most differ from oxygen consumption?

Answer 13

The Brain and the Kidney. More O2 use than flow in the brain. More Flow than O2 use in the kidney

Question 14

Is it possible to measure pulmonary venous and left atrial pressures directly?

Answer 14

NOT possible. Use pulmonary capillary wedge pressure.

Question 15

What determines MAP?

Answer 15

Cardiac output and total peripheral resistance

MAP=CO x TPR

Question 16

How is short-term MAP primarily controlled?

Answer 16

Altering CO and peripheral resistance (neuronal and hormonal control).
Altering peripheral resistance counteracts most moment-to-moment fluctuations of MAP

Question 17

What happens to peripheral resistance with arteriole vasoconstriction?

Answer 17

An increase in peripheral resistance

Question 18

The pulmonary and cardiovascular systems are in series or in parallel?

Answer 18

Series

Question 19

What percent of the blood is in the heart, lungs, and systemic circulation?

Answer 19

7% in the heart. 9% in the pulmonary system. 84% in the systemic system with more than 50% in the veins (~60%)

Question 20

How are most short-term alterations in MAP countered?

Answer 20

Via the baroreceptor reflex

Question 21

What is pulse pressure?

Answer 21

The difference between systolic and diastolic presures. PP=SP-DP.
PP=Stroke volume/ Compliance.
SV=80mL
Compliance=2mL/mmHg

Question 22

How is long-term control of MAP achieved?

Answer 22

Primarily by altering blood volume via the kidneys.

Question 23

What is the dichrotic notch (or incisura)?

Answer 23

It is a small dip caused by the backfilling of the aortic valve as it closes.

Question 24

Does the heart act as a generator of constant pressure or constant flow?

Answer 24

Constant pressure

Question 25

How do you calculate cardiac output?

Answer 25

CO mL/min = SV (mL) x HR beats/min.

Typically it is 5L/min at rest