Blood pressure is the force that the blood exerts against a blood vessel wall. When measuring BP, both the systolic and the diastolic blood pressure are recorded. The systolic blood pressure records the peak arterial blood pressure reached in the arteries during ventricular contraction, while the diastolic blood pressure records the minimum arterial blood pressure reached in the arteries during ventricular relaxation…
Normal Blood Pressure = 120/80 mmHg
PULSE PRESSURE is the difference between systolic and diastolic blood pressure…
Normal Pulse Pressure = 40 mmHg
MEAN ARTERIAL PRESSURE (MAP) is the average pressure in the arteries within a cardiac cycle…
MAP = (Diastolic X2) + Systolic = Answer / 3
or
MAP = CO X TPR
A stroke volume increase or a heart rate increase result in an increase in cardiac output. Total Blood Volume affects MAP as well.
Blood Pressure is determined by 3 main principles:
- Cardiac Output (CO)
- Blood Volume (BV)
- Total Peripheral Resistance (TPR)
Venous Return, which is the volume of blood flowing towards the heart through systemic veins, affects BV resulting in a change in CO and stroke volume. Venous return is affected by the pressure difference between the pressure in the venules and the pressure within the right ventricle.
The Skeletal Muscle Pump and the Respiratory Pump are responsible for pumping blood from the lower body back to the heart through the inferior vena cava thanks to the valves present within the veins.
At rest, the proximal and distal valves within the calf are open, allowing blood flow to move upwards towards the heart. In leg muscle contraction, veins are compressed, pushing blood through the proximal valve, leading to the distal valve to close due to blood pushing against it.
Within the respiratory pump, the diaphragm moves downwards during inhalation, leading to a decrease in the intrathoracic pressure and an increase in the intrabdominal pressure. This creates compression within the abdominal veins.
Total Peripheral Resistance (TPR) refers to the resistance to flow due to friction of blood against the vessel walls. TPR depends on:
- Blood Viscosity
- Vessel Length
- Vessel Radius
Blood Pressure control can be applied by:
- Neural Regulation (Baroreceptors and Chemoreceptors)
- Hormonal Regulation (RAAS, Epinephrine and Norepinephrine, AntiDiuretic Hormone ADH and Atrial Natriuretic Peptide ANP)
- Auto Regulation (regulation of tissues on their own blood flow eg. in kidneys, mesentery, skeletal muscle, brain, liver and the myocardium)
Below you can find a collection of videos that can help provide a more visual approach to Blood Pressure Physiology.
Cardiac Output, Stroke volume, EDV, ESV and Ejection Fraction
Calculating The Mean Arterial Pressure
Regulation of the Mean Arterial Pressure MAP
Venous Return, Skeletal Muscle Pump and the Respiratory Pump – Animation
Systemic Vascular Resistance (Total Peripheral Resistance)
Regulating Peripheral Resistance (TPR)
Autoregulation of Blood Flow – Animation
Special thanks to the creator of the featured video on this post, specifically Youtube Channel Alila Medical Media, Janux, Registered Nurse RN, Dr Matt & Dr Mike and Interactive Biology.
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