the cardiac cycle, pump function & blood pressure
TRANSCRIPT
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 vesselsR = resistance
Vessel diameter/radius is the most critical factor
determining blood flowD = 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 πΔPr4
8vl
Blood Pressure Level (mmHg)
Category Systolic Diastolic
Normal < 120 and < 80
Prehypertension 120-139 or 80-89
High Blood Pressure
Stage 1 Hypertension
140-159 or 90-99
Stage 2 Hypertension
>159 or >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.
