Explain the physiological determinants of mean arterial pressure (MAP). Discuss how each individual variable affects the blood pressure change.
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Explain the relationship among mean arterial pressure, cardiac output, and peripheral resistance.
Adi S.
Explain the underlying cause of the Korotkoff sounds. Why can these sounds only be detected when the pressure in the cuff is between systolic and diastolic pressure? [4 marks] The sphygmomanometer increases pressure in the cuff surrounding the arm, hence the pressure in the cuff becomes greater than the systolic pressure. This pressure compresses the artery, which prevents blood flow. The pressure decreases when air is released from the cuff and artery compression also decreases. When the pressure is slightly lower than systolic pressure, the artery opens slightly, allowing blood flow. Blood flows through the artery with high velocity as there is a large pressure difference and a small space between openings. High velocity is what causes these audible Korotkoff sounds. When the pressure is further decreased, diastolic pressure is reached and Korotkoff sounds are not heard anymore. The sound can only be heard between systolic and diastolic pressure because compression of the artery by the cuff causes blood to flow in a turbulent and interrupted manner. 2. Which method, auscultation with the cardio-microphone or the oscillometric method using the finger pulse transducer, gives the most accurate measure of systolic arterial pressure? Briefly justify your answer. The auscultation method using the cardio microphone is more accurate at representing systolic arterial pressure. The auscultation method allows to detect systolic pressure accurately at the beginning of Korotkoff sounds, as this is when blood starts to pass through the artery after being compressed. The oscillometric method is not accurate because the pulse of blood flowing through the artery is felt by the transducer. The pulse requires more blood to flow through the artery for oscillations. The oscillation method measures oscillations in the artery wall. It often underrepresents the systolic blood pressure because only 1/3 of blood is ejected. 3. Based on what you have learned from the lectures, what is the immediate effect of a sudden change in posture from lying down to standing up on your stroke volume and why does this happen? How do you expect this change in stroke volume to affect arterial pressure? [4 marks] When there is a sudden change in posture from lying down to standing, gravity tends to pull blood downwards towards the feet. Hence, blood pools in the veins of the feet and lower legs and increases pressure in the feet. As blood pools in the lower limbs, there is less blood circulating back to the heart. The change in volume causes a decline in central pressure, which decreases pressure in the ventricles being filled. There is a decrease in venous return, therefore low stroke volume and cardiac output. When all of that happens, arterial pressure decreases. The change in posture acts as a hemorrhage in the body due to less venous return and thus relies on baroreceptors to bring arterial pressure back to normal. 4. What are the compensatory responses that restore relatively normal arterial pressure when we stand up? [4 marks] Baroreceptors restore arterial pressure to normal when we stand up. These receptors are located in the aortic arch and carotid sinus of the heart and are capable of detecting pressure by the stretch of arterial walls of the heart. The firing rate of these baroreceptors is directly proportional to the arterial pressure, hence a decrease in pressure means decreased firing of baroreceptors. Less firing means more sympathetic activity and less parasympathetic activity. This causes an increase in heart rate, which increases cardiac output. Along with an increase in cardiac output, arterial pressure goes back to the normal range. 5. How did systolic arterial pressure measured using the finger pulse differ with the arm in different positions? Why do you think it differed? Systolic arterial pressure is different in different arm positions because of pressure changes and the force of gravity on the blood flow. Hydrostatic pressure is equal to the pressure produced by cardiac contraction when the arm is level with the heart. Blood pools at the lower part of the body when the arm is lowered. When the arm is above the head, pressure is lower as there is increased resistance in the artery due to gravity. Hence, it can be said that the level of the finger to the heart does affect blood pressure value at fingers, thus fingers must be kept at the level of the heart for accurate results.
Suman K.
Madhur L.
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