The Large Vessels
Damping – reduction in pulsatility – accomplished by placing resistance and capacitance in system.
Capacitance is larger in arteries compared to arterioles.
Capacitance is ability to distend. Change in volume/Change in pressure
Capacitance is less at high pressure than at low pressure and decreases with aging and disease.
Veins have large capacitance.
Venous blood volume is variable. Passive postural change. When you stand, transmural pressure increases in abdomen and legs. Almost 1L of blood can be displaced into legs.
Intrathoracic pressure increases during exhalation.
Skin, liver, lungs and spleen are important blood reservoirs because they undergo substantial venoconstriction.
Mean Pressure – 100mmHg = Pd + (Ps-Pd)/3
Pressure = Flow x Resistance
Flow = Cardiac Output
So systemic pressure = CO x R = SV x HR x R
Pulsatile pressure – Stroke volume and arterial capacitance are key determinants
When mean pressure rises with nonlinear capacitance, elevation of systolic pressure is greater than diastolic pressure.
Pressure pulse of radial artery. Velocity varies inversely with capacitance. High frequency components tend to be damped out. Systolic portions are more pronounced.
