Updated: 1/24/2021

Cardiac / Vascular Function Curves

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Overview
  • Cardiac output (CO) curve 
    • describes a state of cardiac function
    • a plot of the relationship between CO and right atrial pressure 
      • ↑ venous return → ↑ right atrial pressure → ↑ end-diastolic volume (EDV), end-diastolic fiber length → ↑ CO
      • ↓ venous return → ↓ right atrial pressure → ↓ EDV, end-diastolic fiber length → ↓ CO
  • Vascular return curve
    • describes a state of vascular function
    • a plot of the inverse relationship between venous return and right atrial pressure
      • ↓ right atrial pressure → ↑ ΔP (systemic arteries, right atrium) → ↑ venous return
      • ↑ right atrial pressure → ↓ ΔP (systemic arteries, right atrium) → ↓ venous return
  • Mean systemic pressure
    • also known as mean circulatory pressure
    • the x-intercept of the vascular function curve
    • shows pressure that would be measured throughout cardiovascular system if the heart were stopped
      • stopping the heart guarantees that pressure is equal throughout the vasculature
Inotropic Effects
 
  • Inotropy describes the state of cardiac contractility
  • Positive inotropy (↑ contractility)
    • positive inotropic agent → ↑ cardiac contractility, ↑ stroke volume, and ↑ CO
      • e.g., sympathetic nervous system activity, and digitalis
    • CO curve shifts upward
    • new steady state or equilibrium → ↓ right atrial pressure (EDV)
      • ↓ right atrial pressure → more blood is ejected from the heart on each beat as a consequence of increased contractility and increased stroke volume
  • Negative Inotropy (↓ contractility
    • negative inotropic agent → ↓ cardiac contractility, ↓ stroke volume, ↓ CO
      • e.g., congestive heart failure and narcotic overdose
    • CO curve shifts downward  
    • new steady state, or equilibrium → ↓ CO, ↑ right atrial pressure (EDV)
      • ↑ right atrial pressure → less blood is ejected from the heart on each beat as a consequence of decreased contractility and decreased stroke volume
  • Effects of changes in blood volume 
    • increases in blood volume
      • ↑ blood volume (e.g., transfusion) → ↓ venous compliance → ↑ mean systemic pressure
        • ↓ venous compliance → blood is shifted from veins to arteries
      • venous return curve shifts to the right
      • new steady state or equilibrium → ↑ CO and ↑ right atrial pressure (EDV)
    • decreases in blood volume
      • ↓ blood volume (e.g., hemorrhage) → ↑ venous compliance → ↓ mean systemic pressure
        • ↑ venous compliance → blood is shifted from arteries to veins 
      • venous return curve shifts to left
      • new steady state or equilibrium → ↓ CO, ↓ right atrial pressure (EDV)
  • Effects of changes in total peripheral resistance (TPR) 
    • increase in TPR
      • vasoconstriction of arterioles → ↑ TPR
        • e.g., hemorrhage
      • ↑ TPR → ↑ mean arterial pressure (MAP) → ↑ afterload → ↓ CO
        • cardiac function curve shifts downward
      • ↑ TPR → ↓ venous return
        • venous return curve rotates counterclockwise
    • decrease in TPR
      • vasodilation of arterioles → ↓ TPR
        • e.g., exercise
      • ↓ TPR → ↓ MAP → ↓ afterload → ↑ CO
        • cardiac function curve shifts upward
      • ↓ TPR → ↑ venous return
        • venous return curve rotates clockwise

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(M1.CV.13.143) A 60-year-old African American gentleman presents to the emergency department with sudden onset "vice-like" chest pain, diaphoresis, and pain radiating to his left shoulder. He has ST elevations on his EKG and elevated cardiac enzymes. Concerning his current pathophysiology, which of the following changes would you expect to see in this patient? Tested Concept

QID: 100659
1

No change in cardiac output; increased systemic vascular resistance

6%

(3/50)

2

No change in cardiac output; decreased venous return

0%

(0/50)

3

Decreased cardiac output; increased systemic vascular resistance

70%

(35/50)

4

Decreased cardiac output; decreased venous return

22%

(11/50)

5

Increased cardiac output; increased systemic vascular resistance

2%

(1/50)

M 1 E

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