Variations in Blood Pressure
Describe the physiological factors that may contribute to pulse variations in blood pressure
Blood pressure is not uniform throughout the circulation. Ventricular ejection generates two waves:
- A blood flow wave
Travels at ~20cm.s-1.
- An arterial pressure wave
Distends the elastic walls of the large arteries during systole, which then recoil during diastole to facilitate continual blood flow. This is the Windkessel effect.
- This wave travels at 4m.s-1
- This is what is felt when pulses are palpated
Changes by Site of Measurement
Measured pressure changes predictably at more distal sites:
- All gradients are increased
Arterial upstroke and falloff are both steeper.
- The SBP increases
- DBP decreases
- MAP is constant
- The dicrotic notch occurs later and becomes less sharp
This occurs due to reflections in arterial pressure waves.
Changes in circulatory function:
The rate of systolic upstroke is related to , and therefore contractility.
The gradient between the peak systolic pressure and the dicrotic notch gives an indiciation of SVR. E.g., a steep downstroke suggests a low SVR, as the pressure in the circulation rapidly falls when ejection ceases.
A beat-to-beat variation is seen with the respiratory cycle, due to the change in preload occurring with changes in intrathoracic pressure.
Some pathological causes include:
- Aortic Stenosis
Causes a reduction in:
- Pulse pressure
Due to reduced stroke volume.
- Gradient of upstroke
Due to reduced stroke volume and reduced velocity of ejection.
- Pulse pressure
- Aortic Regurgitation
- Chambers D, Huang C, Matthews G. Basic Physiology for Anaesthetists. Cambridge University Press. 2015.