Flashcards in Caitlin-Physio Deck (18)
What is the main measure of cardiac function?
Cardiac output (L/min): volume of blood that is pumped into the aorta per unit time
What is the normal resting value for cardiac output?
Can increase 6x during exercise
What is cardiac index, and what is the normal value range?
Cardiac output adjusted for differences in body surface area (L/min/m^2)
Normal: 2.5-4.0 L/min/m^2
What is the normal range for ejection fraction? What is the significance of an abnormally high or abormally low measure?
40-55%: indicates damage (e.g., previous heart attack)
Under 40%: may be evidence of current heart failure or cardiomyopathy; at risk for complications
Over 75%: may indicate hypertrophy cardiomyopathy
Generally, reduced --> systolic heart failure; preserved: diastolic heart failure
What are the 3 factors that affect contractility?
1. number of acting/myosin crossbriges
2. speed of forming crossbridges
3. availability/sensitivity to Ca^2+
What is the index of contractility
dP/dt (change in pressure over change in time)
Define stroke work. What are its components (3)?
Amt of energy that the heart converts to to work during one contraction cycle.
Components: almost all external work (incl 1. pressure work and 2. volume work) and 3. increase blood velocity
What is the most important determinant of myocardial consumption?
Wall tension (impt because it can be affected by disease states)
What is the normal efficiency of cardiac contraction?
Describe the phases of the pressure/volume relationship of the left ventricle during the contraction cycle.
- Phase I: gradual increase in pressure as heart fills with blood (Pre-load)
- Phase II: pressure rises rapidly with no change in volume just before the valve opens (isovolumic contraction)
- Phase III: pressure drops slightly as volume drops sharply while ventricle contracts (Afterload)
- Phase IV: pressure drops as volume stays constant (maximally contracted), before valve closes (isovolumic relaxation)
Name the 2 methods of intrinsic regulation of cardiac function.
1. Frank-Starling Mechanism: greater force of contraction with increased stretch during filling (lengthen heart fibers to optimal, increased sensitivity to Ca^2+)
2. Right Atrial Stretch (SA node): affects discharge frequency
Generally, what affects end diastolic volume? (3)
- effective filling pressure (pre-load)
- filling time
- wall distensibilty or compliance
What are the major factors affecting pre-load (effective filling pressure)? (7)
ALL STRETCH MYOCARDIUM:
- total blood volume (e.g., hemorrhage)
- intrathoracic pressure (respiration)
- peripheral venous tone (e.g., vasodilation)
- pumping action of skeletal muscle (e.g., exercise)
- impaired inflow (e.g., mitral and tricuspid valve stenosis)
- atrial contribution to ventricular filling (e.g., atrial arrhythmias)
- body position (e.g., gravity)
How does increased heart rate affect filling time?
It reduces both diastolic period and filling time
What is the main mechanism of extrinsic regulation of the heart?
innervation (sympathetic and parasympathetic)
What's the simple way to calculate maximal heart rate?
What can increase intracellular Ca^2+ in the heart?
sympathetic stimulation (phosphorylation of L-type channels and phopholamban)