Blood Vessels Pressure
Peripheral blood vessels are important mediators of systemic blood pressure. Explain the physiological mechanisms of the vasculature that affect systemic blood pressure at rest and during exercise.
The blood pressure is determined by the rate of blood flow produced by the heart (cardiac output), and the resistance of the blood vessels to blood flow. This resistance is produced mainly in the arterioles and is known as the systemic vascular resistance (SVR) or the peripheral vascular resistance (PVR)(4).
Blood pressure is measured in two reading
Systolic pressure: this is the maximum pressure during systole when blood is being ejected through the valves
Diastolic pressure: this is the minimum that is reached at the end of diastole and immediately before the valves open again.
It is necessary to know that the systolic pressure in the aorta and pulmonary artery is equal to which occurs simultaneously with the systolic pressure in the left and right ventricle. This is because there is a link with each ventricle and artery and the valves are open. However with the diastolic pressure when this gets to aorta and pulmonary artery it is much higher than the diastolic in the ventricles this is due to the valves close part way through the diastolic until the next systole there no linkage between the ventricle and artery and pressure deviate.
Another thing to know is vascular resistance
TPR(total peripheral resistance) this when all of the blood vessels are downstream the aorta This is the same for pulmonary vascular resistance (PVR). It is necessary to know that total peripheral resistance is seven times bigger than pulmonary vascular resistance.
Mean blood pressure depends on the flow of blood from the heart (cardiac output) and the resistance to flow in the small arteries and microscopic resistance vessels (arterioles).
These relationship between pressure flow and resistance and can be express mathematically( 1-3)
Systemic MABP = CO X TPR
Pulmonary artery = CO X PVR
It is necessary to know these formulas because it can tell you the mean pressure or voltage and tell how much energy is needed to push blood or electrons through the blood vessels or wires.
However systemic MABP can either increase or decrease the activity of the individual from rest state. This can be due to a change in cardiac output or total peripheral resistance or both. Even though MABP can change dramatically either from rest value to exercise there another thing which control system is known as baroreceptor reflex (1-3)
When blood passage through the vessels energy is lost which means pressure falls. However due to energy lost this is by the resistance to flow of blood by the vessels walls therefore energy is lost by friction and flowing of blood. The amount of energy lost is important it shown by the difference in pressure between blood in the arteries and in large veins where they drain into the right and left atria .
The central venous pressure is also very important because it indicates when the heart is congested or over filled due to ventricular muscle is not contracting properly(1-3).
Physical exercise causes very major effects on the circulation. Due to the enormously increased blood flow through the exercising muscle, the amount of blood pumped by the heart may increase by four times. The increased volume of blood ejected at each heart beat causes systolic blood pressure to increase, perhaps to 180 mm Hg. However, because blood flows very rapidly out of the arteries, particularly to the working muscle where the resistance vessels are widely dilated, diastolic pressure remains relatively unchanged or may even decrease. Isometric exercise has quite a different effect. Here there is a much smaller effect on the total amount of blood pumped by the heart, but reflexes, particularly those arising from the contracting muscle itself, cause blood vessels elsewhere to constrict, and consequently both systolic and diastolic blood pressure rise sharply. This response may also be augmented by a straining effect (4)
References
- Davies A, Blackeley Ash G.H, Kidd C (2001) Human Physiology
- Levick J.R (1995) An Introduction to Cardiovascular Physiology (2nd edition)
- Powers S.K, Howley E.T(1990 Exercise Physiology theory and application to fitness and performance (3rd edition)
- www.answers.com
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