Introduction Primary function of the cardiovascular system is to maintain perfusion The heart serves as a pump the heart contracts and generates pressure to drive blood through the body Cardiac Output Cardiac output (CO) = stroke volume (SV) x heart rate (HR) Fick principle for cardiac output there is a conservation of mass the oxygen consumption must equal the amount of oxygen leaving the lungs in the pulmonary vein minus the amount of oxygen returning to the lungs in the pulmonary artery O2 consumption = CO x [O2]pulmonary vein - CO x [O2]pulmonary artery SV is determined by contractility intrinsic ability of myocardial cells to develop force contractility ∝ end-diastolic volume (preload) Frank-Starling relationship may reduce cardiac output in heart failure with reduced ejection fraction when preload increased preload afterload SV = end diastolic volume (EVD) - end systolic volume (ESV) SV increases with anxiety, exercise, and pregnancy Pulse pressure ∝ SV pulse pressure = systolic pressure - diastolic pressure Distribution of CO liver > kidney > muscles > brain Myocyte Action Potentials Initiated in the sinoatrial (SA) node, the pacemaker of the heart Slowed by the atrioventricular (AV) node, which allows for ventricular filling Action potential causes influx of Ca2+ ions, which triggers the release of Ca2+ from the sarcoplasmic reticulum this allows for the cell to contract Relative conduction velocities bundle of His = Purkinje fibers > atria > ventricles > AV node Myocardial O2 Demand Increased with ↑ contractility ↑ afterload ↑ heart rate ↑ diameter of the ventricle (or wall tension) Maintenance of Mean Arterial Pressure Mean arterial pressure (MAP) is maintained by baroreceptors chemoreceptors renin-angiotensin-aldosterone system anti-diuretic hormone atrial natriuretic peptide MAP = CO x total peripheral resistance (TPR) MAP = 2/3 diastolic pressure + 1/3 systolic pressure