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