The Cardiac Cycle, Pump Function & Blood Pressure

Hemodynamics P R = Q P1 P2 Q = blood flow rate (mL/sec) P= pressure difference between ends of vessels R = resistance

Vessel diameter/radius is the most critical factor determining blood flow D = 1, Q = 1 mL/sec D = 2, Q = 16 mL/sec D = 4, Q = 256 mL/sec

Figure 23.9 The physics of flow through tubes

Poiseuille’s Equation R =radius, v = blood viscosity, l = length increase radius, increase blood flow Q  πΔPr 4 8vl

Blood Pressure Level (mmHg) CategorySystolicDiastolic Normal< 120and< 80 Prehypertension or80-89 High Blood Pressure Stage 1 Hypertension or90-99 Stage 2 Hypertension >159or>99 Categories for Blood Pressure Levels in Adults

Determinants of Systolic Pressure Stroke Volume Heart Rate Distensibility of walls of aorta Ejection velocity peripheral “run off” Blood volume remaining in aorta before next ejection

Determinants of Diastolic Pressure Systolic Pressure Aortic Distensibility Rate of peripheral “run off” Heart Rate (duration of diastole)

Effects of Posture on BP Supine mean arterial BP=100 mmHg Upright pressure varies with level above or below the heart –For every 1 cm above heart, pressure decreases by.77 mmHg. –For every 1 cm below heart, pressure increases by.77 mmHg.