How does diving affect blood pressure?

[FireDiver443]

According to an Emedicine Article on Hyperbaric Oxygen Therapy (http://www.emedicine.com/plastic/topic526.htm), cardiovascular effects of hyperbaric therapy are as follows:

Heart rate - Decreased
Contractility - No effect
Stoke volume - No effect
Cardiac output - Decreased
Blood pressure - Possible minimal increase
Systemic vascular resistance - After load increases, arterial vasoconstriction

Remember, obviously, a blood pressure cuff won't work underwater because you have to inflate it with air (but wouldn't it be neat if...nevermind) so the only data available is obtained from a chamber. But pressure is pressure. Any folks with chamber experience (working in it, preferrably, but sitting in it after a barometric misadventure will do too) are invited to jump in and clarify this with certainty.

I'm with MichaelBaranows though: Although this is strictly anecdotal, I think my blood pressure decreases at depth because I'm at peace.

 

[halschmidt]

I have high blood pressure and I am on medications to lower it, but it is still high. I have the best doc in Tulsa working on it. My blood pressure before a recent dive was 150 over 69 several hours after a dive to 22 feet ii was 104 over 56. A similar thing happened on a previous dive and have only measure it twice, so that is every dive measured. I am new to diving so it looks like it is good for me. Maybe if I could find a medicine that would do the same thing as diving, I could get my BP to normal. Any suggestions? :blinking:

 

[NateS]

Imagine you have a pump and a loop of hose filled with water coming out of the pump and going back in the pump. Now you submerge this contraption. The increased pressure from the water outside the hose presses on the hose from all directions. The water inside the hose doesn't compress (close enough science for these purposes). Has the water in the hose changed pressure? Does the pump need to work harder to move the water through the hose?

 

[dmaziuk]

Imagine you have a pump and a loop of hose filled with water coming out of the pump and going back in the pump. Now you submerge this contraption. The increased pressure from the water outside the hose presses on the hose from all directions. The water inside the hose doesn't compress (close enough science for these purposes). Has the water in the hose changed pressure? Does the pump need to work harder to move the water through the hose?

Well, if you really want to pick nits, capillary constriction due to cold and tight wetsuits is believed to be a contributing factor for SIPE. I.e. sometimes (very rarely) around the patches where the hose is worn really thin you might see a bit of "sweating" that wasn't there before. Edit: external water pressure isn't listed, but that may be due to the fact that SIPE studies are mostly done on people who swim up top (triathletes, long-distance swimmers) where there isn't one.

 

[EFX]

Good illustration NateS. The key in thinking about pressure is that any pressure reading at one point is relative to some other pressure reading at another point. In your submerged pump example the output pressure of the pump is measured (is relative) to the input (or suction, or tank) pressure. The water pressure is transmitted through solid and liquids of the pump system so that if you were to measure a pressure at any one point in the pump system relative to the water it would be zero because those two points will be at the same pressure.

A similar example is a car's coolant system. Let a car's engine reach its rated operating temperature. Eventually, the thermostat opens to allow the circulation of coolant to cool the engine. As the coolant heats up the pressure of the fluid relative to the atmosphere increases. It increases so much that if you open the radiator cap you will get a guyser of scalding hot water, yet the pressure of the water pump output relative to its input is only about 15 lbs.

 

[freewillie]

Haven't had a chance to respond earlier, something weird is going on with work computer and doesn't allow me to respond. I don't know how to say this without sounding at least a little arrogant or condescending but I really don't mean it to be so please try not to take it as an insult. But it usually amuses me as a doctor when lay people try to answer medical questions.There are actually three principles that factor into the original question. The first is that depth itself has no actual bearing on fluids within the body. Discussions regarding atmospheric pressures relate to gases not liquids. Blood itself is not affected by the pressures at depth. The nitrogen and oxygen gases yes, water and blood, no.But the blood pressure is affected by activity. The other factor involved is heart rate and exertion. How physically fit you are and how your heart and cardiovascular system reacts to exercise also determines your current blood pressure. Typically your body will open many small arterioles and capillaries to increase flow to muscles with exercise. This increase area of now open blood vessels may actually decrease the person's pressure. But older patients and less physically fit patients may actually have a rise in blood pressure with activity. You may actually see a hypertensive response in those patients with increasing levels of exertion.The last would be temperature. Your body tries to shunt blood for your extremeties to your core in cold water. This may actually result in a decrease area for blood vessels which may increase the pressure. But if you have warm water the vessels may open in an attempt to give off heat and the blood pressure may drop. This is the basis for dizziness warnings on jacuzzis.But all of these factors are independent of depth. It should have no bearing itself on your blood pressure.

 

[NAM001]

Body is non compressable. you are only pumping against a differential pressure. that differential is the blood flow resistance. for the heart to work harder the water pressure would have to increase and the artery pressure stay the same for the arteries to collapse to make the heart work harder to keep them expanded to allow blood flow..

 

[kevindsingleton]

Haven't had a chance to respond earlier, something weird is going on with work computer and doesn't allow me to respond. I don't know how to say this without sounding at least a little arrogant or condescending but I really don't mean it to be so please try not to take it as an insult. But it usually amuses me as a doctor when lay people try to answer medical questions.There are actually three principles that factor into the original question. The first is that depth itself has no actual bearing on fluids within the body. Discussions regarding atmospheric pressures relate to gases not liquids. Blood itself is not affected by the pressures at depth. The nitrogen and oxygen gases yes, water and blood, no.But the blood pressure is affected by activity. The other factor involved is heart rate and exertion. How physically fit you are and how your heart and cardiovascular system reacts to exercise also determines your current blood pressure. Typically your body will open many small arterioles and capillaries to increase flow to muscles with exercise. This increase area of now open blood vessels may actually decrease the person's pressure. But older patients and less physically fit patients may actually have a rise in blood pressure with activity. You may actually see a hypertensive response in those patients with increasing levels of exertion.The last would be temperature. Your body tries to shunt blood for your extremeties to your core in cold water. This may actually result in a decrease area for blood vessels which may increase the pressure. But if you have warm water the vessels may open in an attempt to give off heat and the blood pressure may drop. This is the basis for dizziness warnings on jacuzzis.But all of these factors are independent of depth. It should have no bearing itself on your blood pressure.

I didn't find that response to be arrogant, at all, freewillie. Nicely articulated.

 

[NateS]

But all of these factors are independent of depth. It should have no bearing itself on your blood pressure.

You described how blood pressure works whether at depth or otherwise, but we're talking about blood pressure at depth. Your post only says "it doesn't change". Ok, why?

 

[MikeT73]

You described how blood pressure works whether at depth or otherwise, but we're talking about blood pressure at depth. Your post only says "it doesn't change". Ok, why?

Because blood is a liquid and therefore not subject to Boyle's law.