Optimal heart rate for N2 reduction

[glbirch]

In another thread discussing multi-day diving( http://www.scubaboard.com/t58234.html ) there was a recommendation made that one should avoid moderate to heavy excercise before and after diving. There has been research done that supports this. It was also suggested that sleeping between dives should be avoided as it will slow respiration, and thus offgassing, potentially throwing your computer off with regards to the amount of calculated N2 remaining in your system for the next dive.

This has me curious about a number of things.

Is there experimental research or documentation that supports the theory that sleeping should be avoided? IIRC, many people have poor conscious breathing habits. When we sleep, respiration and heart rate slow, but our breathing tends to deepen. Would the one factor balance the other? Also, if this is the case, then am I being credited with too much when I sleep at night? If a two hour nap is bad, but eight hours is ok, where's the break-even point? I ask because I have (rarely) been up for my morning dive and noticed my computer was still counting down from the last night dive.

If an increase is bad, and a decrease is bad, is there an optimal heart/respiration rate for N2 removal? The two views seem on the surface to contradict somewhat. At-rest heart rates can vary between less than 40bpm to something like 80 or 90, depending on factors like age, genetics and fitness level. My own at-rest rate was mid-fifties a few years ago, but is likely mid-sixties now. (Dang desk job.) Obviously my computer doesn't know my personal statistics. Do the various decompression models have an assumed rate built in?

I'm guessing that the blood stream flushes N2 fairly rapidly and that it's the slower compartments in the various models that come into play during the later parts of a surface interval. If this is the case, then does heart-rate/respiration really matter that much? Or is it more of an overall 'slowed metabolism' issue?

 

[Dr Deco]

Hello glbirch:

“Is there experimental research or documentation that supports the theory that sleeping should be avoided?”

This is purely my idea, however, some time ago, the US Navy halted ascents during saturation decompressions during the sleep interval, because they were experiencing DCS during ascents when the divers awoke.

My reason for it is that the tissue perfusion is at its lowest during sleep. Sleep during the interdive surface interval will reduce the rate of off gassing of dissolved nitrogen.

“When we sleep, respiration and heart rate slow, but our breathing tends to deepen.”

The effect of sleeping is purely one of tissue perfusion, not gas exchange in the lung. Perfusion is based on two factors. One is the heart rate that controls the arterial blood pressure. The other is muscle physical activity that operates the “muscle pump” and also local mediators (such as carbon dioxide) that control capillary blood flow (the primary effect).

“If a two hour nap is bad, but eight hours is ok, where's the break-even point?”

The problem is not the length of rest; the problem is when it occurs. If it is at the end of the dive day, it is irrelevant. If it is between dives, rest will reduce the tissue off gassing.

“If an increase is bad, and a decrease is bad, is there an optimal heart/respiration rate for N2 removal?”

There is not an optimal resting heart rate, and breathing is of little consequence – providing you are, of course, breathing. What is of more concern is that you move around some to open capillaries and activate the “muscle pump.” There is also a “pump” from breathing (decreasing the pressure in the thorax, the “respiratory pump”) but this is of less importance.

“Obviously my computer doesn't know my personal statistics. Do the various decompression models have an assumed rate built in? “

Decompression algorithms are based on gas exchange (and sometimes surface tension of bubbles) and parameters derived from actual dives. There are no true physiological models currently existing. They all incorporate “fitting constants” (”allowable supersaturation” is one such example) such that the tables will accord with actual diving experience. :280:

Because actual heart rates are not adjustable within the model, it is necessary that one use the tables in the manner they were derived. This means, no excessive activity below water, and no excessive activity topside.


“I'm guessing that the blood stream flushes N2 fairly rapidly and that it's the slower compartments in the various models that come into play during the later parts of a surface interval. If this is the case, then does heart-rate/respiration really matter that much? Or is it more of an overall 'slowed metabolism' issue?”

In actuality, the slow compartments represent free nitrogen that is sequestered in tissue bubbles. It is not a perfusion-limited exchange of nitrogen. This is one reason that one does not want to generate or enlarge tissue nuclei.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[pipedope]

Remember that any DCI symptoms will not be noticed by a sleeping diver.

 

[ArcticDiver]

Oh...what about pain like joint pain and the like?



Oh I agree that a sleeper will not notice small pains. But I couldn't help point out that even sleepers will be aroused by sharp or crushing pain. One of the classic cardiac related pain questions that applies to other fields as well.

As for me, unless drug induced for a medical procedure I want to be fully awake when anyone does anything that could adversely affect me. Come to think of it, there are several really, really nice things whose sensations I want to be Fully Awake for!

 

[Santa]

Hello glbirch:

“Is there experimental research or documentation that supports the theory that sleeping should be avoided?”

This is purely my idea, however, some time ago, the US Navy halted ascents during saturation decompressions during the sleep interval, because they were experiencing DCS during ascents when the divers awoke.

My reason for it is that the tissue perfusion is at its lowest during sleep. Sleep during the interdive surface interval will reduce the rate of off gassing of dissolved nitrogen.

“When we sleep, respiration and heart rate slow, but our breathing tends to deepen.”

The effect of sleeping is purely one of tissue perfusion, not gas exchange in the lung. Perfusion is based on two factors. One is the heart rate that controls the arterial blood pressure. The other is muscle physical activity that operates the “muscle pump” and also local mediators (such as carbon dioxide) that control capillary blood flow (the primary effect).

“If a two hour nap is bad, but eight hours is ok, where's the break-even point?”

The problem is not the length of rest; the problem is when it occurs. If it is at the end of the dive day, it is irrelevant. If it is between dives, rest will reduce the tissue off gassing.

“If an increase is bad, and a decrease is bad, is there an optimal heart/respiration rate for N2 removal?”

There is not an optimal resting heart rate, and breathing is of little consequence – providing you are, of course, breathing. What is of more concern is that you move around some to open capillaries and activate the “muscle pump.” There is also a “pump” from breathing (decreasing the pressure in the thorax, the “respiratory pump”) but this is of less importance.

“Obviously my computer doesn't know my personal statistics. Do the various decompression models have an assumed rate built in? “

Decompression algorithms are based on gas exchange (and sometimes surface tension of bubbles) and parameters derived from actual dives. There are no true physiological models currently existing. They all incorporate “fitting constants” (”allowable supersaturation” is one such example) such that the tables will accord with actual diving experience. :280:

Because actual heart rates are not adjustable within the model, it is necessary that one use the tables in the manner they were derived. This means, no excessive activity below water, and no excessive activity topside.


“I'm guessing that the blood stream flushes N2 fairly rapidly and that it's the slower compartments in the various models that come into play during the later parts of a surface interval. If this is the case, then does heart-rate/respiration really matter that much? Or is it more of an overall 'slowed metabolism' issue?”

In actuality, the slow compartments represent free nitrogen that is sequestered in tissue bubbles. It is not a perfusion-limited exchange of nitrogen. This is one reason that one does not want to generate or enlarge tissue nuclei.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

I keep seeing the name Dr deco popping up - or referred to in threads. Who is it/are you - what is this elusive creatures' background. I like what he says, don't get me wrong - I just feel compelled to know my sources when it comes to dive theory.

Sincerely Santa

 

[Dr Deco]

Hello santa:

Michael Powell, aka "Dr Deco"

Some information is included in the profile provide by SCUBA SOURCE. Below is a narrative resume that I use for speaking engagements.

While I have a secret identity and a name, as of yet, I do not have a mask or cape (or a sidekick).

BRIEF NARRATIVE RÉSUMÉ

Dr. Michael Powell received his bachelor’s degree in chemistry and then went on to receive a doctorate in molecular biophysics in 1969 from Michigan State University.

He then started work in the laboratories of the Ocean System Division of Union Carbide studying problems concerning decompression sickness. In 1975, Dr. Powell went to Seattle, Washington, to work with Merrill Spencer, MD, at the Institute of Applied Physiology and Medicine.

In 1977, he took a leave to work in Germany for three years at the Institute for Aerospace Medicine in Bonn. He returned and remained at I.A.P.M.

In 1989, he joined NASA at the Johnson Space Center in Houston. He is currently in the Human Adaptation and Countermeasures Office of the Space Life Sciences Directorate. His research there involves decompression problems associated with Extravehicular Activity.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[fishoutawater]

Oh Good! Finally the right guy to ask!
I've always wondered about the effects on various bodily tissues in the event of a rapid decompression in an astronaut suit. Would an astronaut experience DCS like divers do? Or something more radical like in the movies, where they show a guys head exploding inside his helmet? I know that fluids aren't compressible, so I don't think eyeballs would explode. OTOH, the human body does have dissolved gases in it everywhere, mostly in muscle and blood tissues. Would these dissolved gases expand?
And what kind of gas mix do the astronauts use up there?

 

[Dr Deco]

Hello fish:

DCS in Space

Indeed astronauts can get DCS in space. Avoidance of this problem is what I work on at NASA. The pressure in the suit is much lower than in the spacecraft. Low pressures are necessary to avoid a stiff suit and attendant fatigue.

No, your eyeballs will not pop out as seen in “Total Recall” – but it looks cool! Low pressure would cause the body fluids to “boil” and you would have DCS in every organ of your body. Ugh.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Santa]

Hello santa:

Michael Powell, aka "Dr Deco"

Some information is included in the profile provide by SCUBA SOURCE. Below is a narrative resume that I use for speaking engagements.

While I have a secret identity and a name, as of yet, I do not have a mask or cape (or a sidekick).

BRIEF NARRATIVE RÉSUMÉ

Dr. Michael Powell received his bachelor’s degree in chemistry and then went on to receive a doctorate in molecular biophysics in 1969 from Michigan State University.

He then started work in the laboratories of the Ocean System Division of Union Carbide studying problems concerning decompression sickness. In 1975, Dr. Powell went to Seattle, Washington, to work with Merrill Spencer, MD, at the Institute of Applied Physiology and Medicine.

In 1977, he took a leave to work in Germany for three years at the Institute for Aerospace Medicine in Bonn. He returned and remained at I.A.P.M.

In 1989, he joined NASA at the Johnson Space Center in Houston. He is currently in the Human Adaptation and Countermeasures Office of the Space Life Sciences Directorate. His research there involves decompression problems associated with Extravehicular Activity.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

"Cool" is the word that leaps to mind. Thank you dr.

Being a struggling scriptwriter myself I'd recommend erring to the conservative side concerning masks and capes (remember Ben Affleck as the red demon? - no wait. Don't.)

A word in favor of the comic sidekick, though:

They are low-maintenance, heavy-duty, useful creatures that make you look good, and tend to outlive everyone else unless the great author in the sky is to cheap to kill off major characters (which is really so much more satisfying to everyone) and needs to feed the sharks something else.

Anyway I' shall pay close attention from now on.

Ride the swells
Santa