Physiology Flashcards
Cardiac Output =
Stroke Volume * Heart Rate
Fick Principle
Cardiac Output = rate of O2 consumption/(arterial O2 content - venous O2 content)
Mean arterial pressure (MAP)
Cardiac Output * Total Peripheral Resistance
OR
2/3 diastolic pressure + 1/3 systolic pressure
Pulse pressure
systolic pressure - diastolic pressure
Pulse pressure is proportionate to stroke volume
Stroke volume
CO/HR
or
EDV - ESV
In exercise how is CO maintained
Early
Late
What if HR gets too high?
Early: Increased HR and increase SV
Late: Increased HR only (SV plateaus)
If HR is too high, diastolic filling is incomplete and CO decreased (VT)
What effects stroke volume?
Increased stroke volume when…
Contractility, Afterload, Preload (SV CAP)
Increased stroke volume when increased preload, decreased afterload, or increased contractility
Contractility increased with
- Catecholamines (Increased activity of Ca2+ pump in sarcoplasmic reticulum)
- Increased intracellular Ca2+
- Decreased extracellular Na+ (decreased Na+/Ca+ exchanger)
- Digitalis (blocks Na+/K+ pump -> increased intracellular Na+ -> decreased Na+/Ca+)
Contractility decreased with
- Beta-blockade (decreased cAMP)
- Heart failure (systolic dysfunction)
- Acidosis
- Hypoxia/hypercapnea (decrease PO2/increased PCO2)
- Non-dihydropyridine Ca2+ channel blockers
Stroke volume increased in these conditions
anxiety, exercise, pregnancy
Stroke volume decreases in this condition
Heart failure
Myocardial O2 demand is increased by
Increase afterload
Increase contractility
Increase HR
Increased heart size (increase wall tension)
Preload =
ventricular EDV
Afterload =
mean arterial pressure (proportional to peripheral resistance)
Venodilators do what to preload
Decrease preload (nitroglycerin)
Vasodilators do what to afterload
Decreased afterload (hydralazine)
Preload increases with
Exercise (slightly)
Increased blood volume (overtransfusion)
Excitement (increased SNS)
Force of contraction is proportional to what
End diastolic length of cardiac muscle fiber (preload)
Starling curve axis
Slope of curve decreases with
X axis = ventricular EDV (preload)
Y axis = CO or Stroke Volume
Slope decreases with CHF + digoxin, CHF
Slope increases with exercise (sympathetic nerve impulses)
Ejection fraction =
What is it an index for?
Normal percent?
Stroke Volume/End Diastolic Volume or EDV - ESV/EDV Index for ventricular contractility Normally greater/equal to 55% (decreases in systolic HF)
Driving pressure =
Flow * Resistance (Q*R) (similar to Ohm’s of change in V = IR)
Resistance =
driving pressure/flow (deltaP/Q)
or
8n (viscosity) * length/ pi*r^4
Total resistance in vessels in series =
R1 + R2 + R3….
Total resistance in vessels in parallel =
1/R1 + 1/R2 + 1/R3…