Calculating Hydrostatic Blood Pressure in Different Body Positions

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Homework Help Overview

The discussion revolves around calculating hydrostatic blood pressure in different body positions, specifically for a person transitioning from standing upright to being upside down. The problem involves understanding how the height of the heart relative to the feet and head affects blood pressure readings.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the calculations for hydrostatic pressure based on the height of the heart and the distances involved when the person is upright versus upside down. Questions arise about the relevance of the heart's position and how to determine the correct distances for calculations in different orientations.

Discussion Status

There is an ongoing exploration of how to apply hydrostatic principles to the scenario of being upside down. Some participants have provided calculations for the upright position and are questioning how to adapt these for the headstand. The discussion includes varying interpretations of pressure reference points and the implications of negative pressure values.

Contextual Notes

Participants note that the calculations are based on specific assumptions about the reference point for pressure and the height of the individual. There is uncertainty about how to handle the transition from upright to inverted positions in terms of hydrostatic pressure calculations.

robertsa
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Homework Statement




a person is 1.8 m tall, standing upright. His heart is 1.4m above his feet. He is doing a head stand. Calculate the hydrostatic blood pressure in (a) his feet and (b) his head.

Homework Equations


P-Po= density x g x d


The Attempt at a Solution



When standing upright:

Brain
Pheart-Pbraind=1059.5 x 9.81 x 0.4
13500-Gauge P in brain= 9.3 KPa

Feet
Pfeet-Pheart=1059.5 x 9.81 x 1.4
feet-13500=1059.5 x 9.81 x1.4
P feet= 28 KPa

How do I know what distance to use when he is upside down? You would think these numbers would just be opposite?
 
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Interesting question! I'm wondering why the position of the heart matters? "Hydrostatic" suggests to me that it is the pressure ignoring the pumping, as if you have a column of blood 1.8 m tall.
 
We did the solution for the same height, when standing upright in class. We always to the distance to be from the heart..im just not sure how to approach when he's upside down.
 
He is 1.8 m high and the heart is 1.4 m high, so it is 0.4 m from head to heart. The heart is 0.4 m above the head when he is "standing" on his head. Your calc is correct, if the calculation is to be done with reference to the heart.

Will the feet pressure then be negative because the feet are above the heart?
 
The calculation i did above was for when he was standing upright.. when he is upside down the pressure in the brain should be greater than that of the presure in the feet.
 
Yes, that is why I suggested that the 28 kPa for the feet should be negative, since you are taking the pressure with respect to the heart level.

To my mind, it would make more sense to make the pressure zero at height 1.8 m, but of course you or your prof can take the reference pressure anywhere you like.
 

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