Flashcards in 3.2.3. Regulation of cardiac function Deck (22):
Define heart rate:
-determined by time required for one complete period of diastolic filling and systolic ejection
-completion of one full loop
Define: stroke volume
volume of blood pumped into the aorta during one cardiac cycle (normal is 60-100 mL/beat)
-power developed by the muscle for any given sarcomere length independent of preload and afterload
-determines rate and magnitude of force generation
-determines end systolic volume
Define ejection fraction:
-the clinical index of contractility
-fraction of EDV that is ejected during systole, expressed as percentage
Ejection fraction=(EDV-ESV)/EDV = SV/EDV
-normal is 50-70%
Define cardiac output (CO):
-volume of blood that is pumped into aorta per unit time (L/min) (normal is 5 L/min)
-CO=heart rate x stroke volume
Define cardiac index:
-cardiac output (CO) adjusted for differences n body surface area (BSA)
-cardiac index=CO/BSA (m^2)
-normal values are 2.5-4.0 L/min/m^2
Define stroke work:
amount of energy that the heart converts to work during a single cardiac cycle (normal values are 45-75 mg-m/m^2/Beat)
-degree of tension on the muscle when it begins to contract
-equal to end diastolic pressure at end diastolic volume
-tension or force acting on the myocardium during ventricular ejection
-equals systolic pressure in artery outside ventricle (generally)
What is intrinsic regulation of cardiac function?
-adjustment of cardiac function through properties inherent to the muscle itself (Frank-Starling mechanism and Right Atrial stretch)
What is the Frank-Starling Mechanism?
-greater force of contraction with increased stretch during filling (intrinsic)
What are the factors effecting end diastolic volume?
-effective filling pressure (preload)
-wall distensibility or compliance
What is extrinsic regulation of cardiac function?
-adjustment of cardiac function through neural or hormonal signaling, which increases cardiac function beyond that available through intrinsic regulation (sympathetic and parasympathetic nerves)
What are the major effects of sympathetic stimulation?
1. increased heart rate
2. increased force and magnitude of atrial and ventricular contractions
3. end systolic volume is decreased
What are the major effects of parasympathetic stimulation?
1. decreased heart rate
2. decreased force of contraction
How is stroke volume affected by preload?
-increased preload causes larger EDV and larger stroke volume through the Frank-Starling mechanism
How is stroke volume affected by afterload?
-increase in afterload causes a larger ESV and smaller stroke volume
How is stroke volume affected by contractility?
-increased contractility results in decreased ESV and a larger stroke volume
How is stroke volume affected by afterload when preload is NOT constant?
-increase in afterload causes larger ESV and smaller stroke volume on FIRST beat
-when venous return is added to this larger ESV, a larger EDV results for the next beat (increased preload) and stroke volume increases
What are the 4 main determinants of cardiac function?
4. heart rate
What is the function of the cardiovascular system?
-to maintain arterial pressure in order to meet the demands over a wide variety of condition, while maintaining regulatory flexibility and minimizing cardiac work.