Cardiac Output, Blood Flow, and Blood Pressure Study Guide.

Cardiac Output (CO) − The volume of blood ejected by the ventricles per 1 minute o mL/min o ~5L at rest o Increases with:  Sympathetic stimulation and exercise − CO= HR X SV o HR and SV are directly proportional to CO  ↑CR  ↑CO  ↑SV  ↑CO o HR = beats/min o Stroke volume = mL/beat  Strength of muscle contraction o Factors that increase heart rate  Sympathetic nervous system  Increases contraction strength  increases SV o Factors that decrease heart rate  Parasympathetic nervous system o Factors that affect stroke volume  Stretch  contraction strength  End-diastolic volume (EDV)  Amount of blood it receives  Heart stretches by being filled with blood Stroke Volume (SV) − The volume of blood pumped by the ventricles per beat (or per systole) o SV= EDV-ESVà ~70 ml at rest/beat − SV can be increased during periods of ↑metabolic demand − Disease: ↑ESV  ↓SV − Factors that affect stroke volume o Inotropy = contractibility o Preload o Afterload Contractility − Strength of contraction − The ability of the heart muscle to generate force during myocardial ventricular contraction − Positive inotropic agents: o ↑contractility o Include: 1  Hypercalcemia  Calcium contracts muscle  More calcium  more contraction  Catecholamines and sympathetic stimulation  Increase force on contraction − Negative inotropic agents: o ↓contractility o Include:  Hypocalcemia  Hyperkalemia  No gradient  No repolarization  can’t have new action potential  Parasympathetic stimulation  Not a direct effect Preload − Pressure within ventricles by blood contained after diastole before it contracts − EDV generates pressure − Pressure generated in ventricles by blood if contains − The more stretch  the more force of contraction − Amount of tension in the L ventricle immediately before it contracts o ↑ preloadà ↑force of contraction o Closely related to venous return (VR)à  Volume of blood that comes back to the heart  closely related to EDV  ↑VRà ↑preload − Frank-Starling law of heart - SV EDV o Ventricles eject as much blood as they receive o The more they are stretched, the harder they contract Factors that affect end-diastolic volume − EDV: increases force of contraction o Blood volume and venous pressure are the two major determinants − Venous return