More Biology Answers
Question Library
Ask a question about Biology
Volunteer
Experts of the Month
Expert Login
Awards
About Us
Tell friends
Link to Us
Disclaimer
|
| |
|
|
| |
| | | |
About John Locke
Expertise
I will answer all biology-related questions through the undergraduate level. I will explain unclear concepts and suggest approaches to solving problems, but would prefer not to completely solve homework problems for you. If you are completely stumped on homework, tell me what you already know and I will help you as much as possible. Please do not ask me for ideas on school research projects; part of research is determining a suitable area of investigation, and that's not a task that should be completed by someone else.
Experience
I have a BS in Bioengineering with a concentration in Chemical Engineering (which included a heavy focus on biology), and have taught biology, biochemistry, and related subjects for some time now.
Education/Credentials
BS Bioengineering, Penn State University
MCAT/DAT/OAT Instructor
| | |
| |
You are here: Experts > Science > Biology > Biology > Biology
Expert: John Locke - 10/21/2009
Question
I chose a science fair question, which is How does body position affect the autonomic regulation of the cardiovascular function? I had a few questions:
1) does height and weight have an affect on your blood pressure and heart rate?
2) if so how much will it affect the various body positions which are standing, sitting, laying, or bending
thanks in advanced and i would appreciate it if you were to reply back by Wednesday night.
Answer
Thanks for using AllExperts.
1. I'm afraid the question is a little complex, so I'll have to answer it at length.
First, height seems to have a negligible effect on blood pressure in adults. Children do have a relationship between height and blood pressure, as you can see here:
http://www.nhlbi.nih.gov/guidelines/hypertension/child_tbl.pdf
Once we reach adulthood, however, the variability in blood pressure between individuals becomes very large, so the effect of height on blood pressure becomes basically negligible. As such, you can assume safely that height doesn't affect BP for adults.
Weight does have an influence on blood pressure; the effect is indirect but predicatble. It is well established that being overweight increases the likelihood of having high blood pressure. You can read a study on this subject here:
http://aje.oxfordjournals.org/cgi/content/abstract/131/4/589
There appears to be a predictable change in both systolic and diastolic blood pressures with increasing weight.
However, I don't think that you should necessarily be concerned with the effect of weight. As seen from the study at the link, the effect is modest (3 mm Hg for each 10 kg difference in weight). Normal variations in BP between standing and laying down can easily exceed 20 mm Hg; similar increases can also occur when excited or agitated. Because of this variability, it is generally accepted that 120/80 represents a reasonable estimate of blood pressure for the population. In other words, if you assume that height and weight have no effect on blood pressure, your results will not be significantly affected.
2. People automatically regulate their blood pressure around a physiological set point. They use mechanisms including the renin-angiotensin-aldosterone system and the baroreceptor reflex to control it within a physiologically acceptable range. Some of these mechanisms are short-acting while others act over the long term.
Blood pressure variation with posture occurs in a predictable but not exact fashion. BP decreases temporarily when moving from laying down to sitting to standing, but it quickly increases to the set point. Heart rate will increase in that same sequence to compensate for the decrease. Once it stabilizes, blood pressure will tend to be higher in the standing and sitting positions relative to laying down. This reflects the extra pressure that must be added to overcome the effect of gravity when sitting or standing. However, I am not aware of any way to predict the magnitude of this variation.
This brief discussion is taken from the British Medical Journal:
"Posture affects blood pressure, with a general tendency for it to increase from the lying to the sitting or standing position. However, in most people posture is unlikely to lead to significant error in blood pressure measurement provided the arm is supported at heart level. None the less, it is advisable to standardise posture for individual patients and in practice blood pressure is usually measured in the sitting position. Patients should be comfortable whatever their position. No information is available on the optimal time that a subject should remain in a particular position before a measurement, but three minutes is suggested for the lying and sitting positions and one minute standing. Some antihypertensive drugs cause postural hypotension, and when this is expected blood pressure should be measured both lying and standing."
Let me know if you have further questions.
Add to this Answer Ask a Question
|
|
