Cardio - Physio (Resistance, pressure, flow, & Cardiac/vascular function curves)

Question 1

What is the equation that relates resistance, pressure, and flow in the cardiovascular system? On what is this equation based?

Answer 1

Pressure gradient or driving pressure (deltaP) = Flow (Q) x Resistance (R); Ohm’s law (V = I*R or I = V/R)

Question 2

What is/are the equation(s) that defines/characterizes resistance? To what factors does resistance relate, and how so?

Answer 2

Resistance = driving pressure (deltaP) / flow (Q) =( (8(eta)(viscosity) x length) / (pi)(radius)^4 ; See FA p. 255 for equation ; Based on equation, resistance is directly proportional to viscosity and vessel length & inversely proportional to radius to the 4th power

Question 3

How do you calculate the total resistance of vessels in series? What about in parallel?

Answer 3

TOTAL RESISTANCE OF VESSELS IN SERIES = R1 + R2 + R3…; 1/TOTAL RESISTANCE OF VESSELS IN PARALLEL = 1/R1 + 1/R2 + 1/R3…

Question 4

On what does viscosity mostly depend? What are 3 conditions in which viscosity is increased?

Answer 4

Hematocrit; (1) Polycythemia (2) Hyperproteinemic states (3) Hereditary spherocytosis

Question 5

Again, on what does viscosity mostly depend? What is a condition in which viscosity is decreased?

Answer 5

Hematocrit; Anemia

Question 6

Again, what is the Ohm’s law based equation that applies to the cardiovascular system? What role does pressure gradient play?

Answer 6

Q = deltaP / R; delta P = Pressure gradient, which drives flow from high pressure to low pressure

Question 7

What accounts for most of the total peripheral resistance? In turn, what does/do this/these regulate?

Answer 7

Arterioles; Capillary flow

Question 8

What effect does inotropy have on cardiac/vascular function curves?

Answer 8

Changes in contractibility –> altered CO for a given RA pressure (preload)

Question 9

What are 2 examples of positive inotropy?

Answer 9

(1) Catecholamines (2) Digoxin

Question 10

What are 2 examples of negative inotropy?

Answer 10

(1) Uncompensated heart failure (2) Narcotic overdose

Question 11

What effect does venous return have on cardiac/vascular function curves?

Answer 11

Changes in circulating volume or venous tone –> altered RA pressure for a given CO. Mean systemic pressure (x-intercept) changes with volume/venous tone

Question 12

What are 2 examples of increased venous return?

Answer 12

(1) Fluid infusion (2) Sympathetic activity

Question 13

What are 2 example of decreased venous return?

Answer 13

(1) Acute hemorrhage (2) Spinal anesthesia

Question 14

What effect does total peripheral resistance have on cardiac/vascular function curves?

Answer 14

Changes in TPR –> altered CO at a given RA pressure; however, mean systemic pressure (x-intercept) is unchanged

Question 15

What is an example of increased TPR?

Answer 15

Vasopressers

Question 16

What are 2 examples of decreased TPR?

Answer 16

(1) Exercise (2) AV shunt

Question 17

What represents mean systemic pressure on cardiac/vascular function curves? How does venous return versus TPR affect mean systemic pressure?

Answer 17

Mean systemic pressure (x-intercept) changes with volume/venous tone; Mean systemic pressure (x-intercept) is unchanged with TPR

Question 18

What does the intersection of cardiac and vascular function curves represent?

Answer 18

Intersection of curves = operating point of heart (i.e., venous return and CO are equal)

Question 19

What are the axes for cardiac and vascular function curves?

Answer 19

x-axis: RA pressure or EDV; y-axis: Cardiac output/Venous return

Question 20

Draw cardiac and vascular function curves in the following contexts: (1) operating point of heart (2) positive inotropy (3) negative inotropy.

Answer 20

See p. 269 in First Aid 2014 for graph on left

Question 21

Draw cardiac and vascular function curves in the following contexts: (1) operating point of heart (2) increased volume/venous tone (3) decreased volume/venous tone.

Answer 21

See p. 269 in First Aid 2014 for graph in middle

Question 22

Draw cardiac and vascular function curves in the following contexts: (1) operating point of heart (2) increased TPR (3) decreased TPR.

Answer 22

See p. 269 in First Aid 2014 for graph on right

Question 23

In general, how do changes affecting cardiac and vascular function often occur? What are 2 ways in which this may happen? Give an example of each way.

Answer 23

Changes often occur in tandem, and may be (1) reinforcing (exercise increases inotropy & decreases TPR to maximize CO) or (2) compensatory (heart failure decreases inotropy –> fluid retention to increase preload to maintain CO)