How does diving affect blood pressure?

[darushin]

According to an Emedicine Article on Hyperbaric Oxygen Therapy (404 Not Found, 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.

You forgot one thing, temp. Water temp is usually way colder then the chamber air temp. Cold water will cause constriction of vessel to preserve heat


Daru

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[EFX]

I remember reading somewhere about the body's reaction to water pressure that reduced the blood volume. I don't have that reference with me so I am guessing. The blood and/or fluids pool in the body's core when diving. The kidney's reaction is to remove water from the blood. This explains the strong tendency for some divers the need to urinate during the dive or very soon after. Removing water reduces the blood volume. Some tissues may not be getting enough blood therefore the blood vessels dilate. This causes the blood pressure to drop slightly which may cause the heart to beat faster to bring the blood pressure back to what it was. Or, it could be that shunting occurs to reduce volume in one area to maintain pressure in the system. Another factor that reduces blood volume is the loss of water through respiration. Freewillie (or anyone else) is this correct?

 

[freewillie]

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 the blood is mostly water. Water will not compress at 100 ft. as per the original question. Gases will be affected at 3 ATM but not fluid. Take an egg to 100 ft., crack open, and the egg will stay in place due to the pressure exerted at that depth but the volume of the egg does not decrease.

Short answer to the original question is that if all factors are equal at the surface and at 100 ft. the diver's blood pressure should be the same. But since the activity of diving and the influence of temperature and fitness also come in to play the diver may have the same, higher, or even lower, but not because of the depth.

 

[AfterDark]

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

It does absorb gas which is subject to Boyle's law. I'll bet a good case of the bends will increase the blood pressure.

 

[EFX]

I found the following in one of the threads in the Accidents and Incidences forum:

//begin quote
Diving exposes divers' bodies to various stressors that independently affect cardiovascular function. The major stressors are immersion, exposure to cold, increased partial pressure of oxygen and increased work of breathing. The combined effect of these factors is that the volume of blood in the vessels of the chest and heart increases significantly, stretching the walls of heart and large vessels. Pressure in the right atrium and blood pressure slightly increase — more so in cold water. The heart has to work harder to maintain circulation. These conditions contribute to various arrhythmias, from bradycardia (slow heart rate) caused by cold to tachyarrhythmia (racing heart rate) caused by cardiac and neuroendocrine responses to stress. Older people, especially those with structural cardiovascular changes and weaker function, are at greater risk of adverse reactions to these stresses.
//end quote

To revisit fisherdvm's questions In light of the above:

If you took a blood pressure cuff down to 100 ft, and used a doppler to check for pulse - will the blood pressure taken on a diver at 100 ft be the same as blood pressure on the surface, or will it be increased by his blood pressure plus 3 ATM?

Blood pressure will not increase according to the water pressure at depth.

If there were an increase in blood pressure, will this increase the load on the heart?

It appears that diving increases the load on the herat which results in a slight increase of pressure.

My gut feeling is that the blood pressure will be the same, and there is no increase work demand on the heart.

There will be an increased demand on the heart simply for the fact that there is breathing resistance at depth.

 

[Got2Go]

I found the following in one of the threads in the Accidents and Incidences forum:

//begin quote
Diving exposes divers' bodies to various stressors that independently affect cardiovascular function. The major stressors are immersion, exposure to cold, increased partial pressure of oxygen and increased work of breathing. The combined effect of these factors is that the volume of blood in the vessels of the chest and heart increases significantly, stretching the walls of heart and large vessels. Pressure in the right atrium and blood pressure slightly increase — more so in cold water. The heart has to work harder to maintain circulation. These conditions contribute to various arrhythmias, from bradycardia (slow heart rate) caused by cold to tachyarrhythmia (racing heart rate) caused by cardiac and neuroendocrine responses to stress. Older people, especially those with structural cardiovascular changes and weaker function, are at greater risk of adverse reactions to these stresses.
//end quote

For those interested in further reading (and the source of this quote):

Alert Diver | Matters of the Heart