62-years old astronaut who has spent eight months at the International Space Sta
ID: 3524733 • Letter: 6
Question
62-years old astronaut who has spent eight months at the International Space Station collapse in the middle of his speech and was submitted to the local ER. Here what was recorded into his chart: heart rate 85 b/min; BP = 116/66 mm Hg; while laying down his vital signs changed – 112b/min; BP = 94/52 mm Hg when standing, reflexes normal, and there is NO sign of head trauma, occasional dizziness and blackouts when standing.
Questions:
1. Calculate his pulse pressure and MAP when laying down and is standing
2. His heart rate increase when patient stood up. Explain what most likely happen, and what cause that?
3. While standing up patient complains of dizziness and he turn pale. What cause that and why does it happen?
4. His drop in BP when standing up? This is most likely due to what reason? Explain!
Explanation / Answer
1. Pulse pressure simple calculated as ( Systolic pressure[SP] - diastolic pressure[DP] )
Pulse pressure at Standing = 94 - 52 = 42 mmHg
Pulse pressure at laying down = 116 - 66 = 50 mmHg
MAP at standing = DP + 1/3(SP-DP) = 52 + 1/3(42) = 52 + 14 = 76 mmHg
MAP at laying down = DP +1/3(SP-DP)= 66 + 1/3(50) = 66+17 = 83 mmHg
2. During standing position his BP falls due to gravitational pooling of blood ( as he was in the ISS, he did not have that effect as there is no gravitational force) This pooling of blood cause low blood supply to brain which is sensed by baroreceptors and as a counter mechanism sympathetic activity is increased ( by brain, medulla ) --> that leads to increase heart rate.
3. As already mentioned that he did not experience gravity for a long time in the space, that causes his baroreceptors to respond late to the pressure changes in the arteries of brain( it means that his baroreceptors were adapted to constant pressure of space, as in the space there were no such differences in blood pressure due to gravitational force) . This leads to late activation of his baroreceptors and thereby till his baroreceptors are activated and sympathetic nervous system increases heart rate and thereby stabilize the BP by increased cardiac output, he feels dizziness and also turns pale due to peripheral pooling of blood due to gravity ( which occurs due to standing up).
4. As already mentioned, due to peripheral pooling of blood lower limbs, the heart receives less blood and his baroreceptors response late, there is low cardiac output from the heart his blood pressure falls.
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