Diving Response in Humans

[pufferfish]

I am new to the board but have been a back room reader for about a year and have always been very impressed with the quality of discussion on this board. After reading Dr. Paul Thomas's post about his recent accident and incredible recovery one really does take a step back and say that could easily have been me. No obvious "pilot error" seems to have been a factor as Dr. T stated, and depending on one's belief a hefty dose of divine intervention may have played a part in his recovery.

After having a look at the 'index' dive profile posted what strikes the observer is that after the spike where the attempted rescue occured is an incredibly long interval of fifteen minutes where Dr. Thomas remained apneic (not breathing) at sixty feet in 12 degree water. Anyone who has done a CPR course knows the time limits for hypoxia above water are well below eight minutes. This period of apnea underwater and subsequent full recovery is not only phenomenal but further evidence for the existence of a diving reflex in humans, much like a seal or beaver might have with submersion.

Please have a look at this link from a Swedish research group who continues to do studies in this most fascinating area. It appears the reflex to slow down the heart, contract the spleen, and divert blood from the peripheral organs to the brain and heart so as to preserve the brain under hypoxic conditions is mediated by receptors on the forehead. Wearing a full face mask then would have not allowed or reduced the full effect of the reflex which exists to protect the brain from oxygen deprivation. Secondly the degree of reflex is set by the difference between the ambient skin air temperature and the water temperature with 10 centigrade water temperature having the greatest drop in heartrate. The profile shows a temp of 12 degrees. Previous exposure of the face to diving in cool water seems to also augment the human diving reflex. Longterm diver training also enhances the response.

I hope I am not being disrespectful by considering some of the diving physiology which may have allowed Dr. T such a wonderful full recovery. In the end I decided to post as Dr.Thomas's posts over the last year have been some of the best in allowing me to understand more about the many facets of diving physiology. In this regard I posted in Dr. Thomas's tradition of always remaining curious and asking the question, why?

So glad to see you back on the board Dr. Thomas and hope to see lots more of your insightful posts in the future.


Human diving response research group

 

[The Iceni]

pufferfish once bubbled...
After having a look at the 'index' dive profile posted what strikes the observer is that after the spike where the attempted rescue occured is an incredibly long interval of fifteen minutes where Dr. Thomas remained apneic (not breathing) at sixty feet in 12 degree water.

The spike was the start of my, rather rapid, practice CBL, which came to an abrupt halt when we reached 12m and I lost consciousness.

Anyone who has done a CPR course knows the time limits for hypoxia above water are well below eight minutes. This period of apnea underwater and subsequent full recovery is not only phenomenal but further evidence for the existence of a diving reflex in humans, much like a seal or beaver might have with submersion.

Hi pufferfish,

I am sure the diving reflex exists but I suspect the real reason for my miraculous and relatively intact survival was hypothermia. In fact I must have inhaled vast quantities of cold, (not-so) fresh water simply because I was not using a full-face mask.

On the one hand this was the cause of the gross, disfiguring oedema and massive haemolysis but on the other it was COLD WATER and caused rapid-onset hypothermia. I have seen the summary of my hospital stay. I was anaemic and hypothermic on admission with a Glasgow score of 3 and a pulse rate of 20 bpm. Apart from divine intervention, which I am sure played a major part, I have no doubts whatsover that it was this hypothermia that protected my brain. I still question the temperature of 12 degrees C recorded by my dive computer. It was very cold.

It may be a controversial opinion, but I am certain unconscious diver casulaties must not be re-warmed until they are in hospital on ventilatory and circulatory support in order to protect the brain.

My story reinforces the current recommendation not to stop CPR in any hypothermic casualty even if it appears hopeless, as it clearly did in my case.

Thanks for your flattering comments pufferfish! Sorry it has taken me so long to reply to your post. I only came across it today.:mean:

Interesting link!

I find it odd that researchers place so much emphasis on splenic contraction yet appear to ignore the gross haemodymanic changes that affect the pulmonary bed during free diving. After all this is where most of the displaced circulation moves as the gas volume in the pleural cavity is reduced by compression.

 

[SARmedic]

Dr Paul Thomas once bubbled...
My story reinforces the current recommendation not to stop CPR in any hypothermic casualty even if it appears hopeless, as it clearly did in my case.

Very true, the saying goes "they are ***** *****, ***** *******". These are the rare situations when hypothermia is a good thing.

Edited by request, I am sorry if I offended anybody by my statement. I am a career paramedic and I am a bit numb to terms like that I guess. I make a special apology to Dr Thomas if that upset him in the least, I do appreciate what he went through.

Once again, If I offended anybody, I am sorry.

 

[pufferfish]

Hi Paul,

Your story continues to amaze me both the probable physiology involved and whatever other unknown 'forces' were involved. I emailed Dr. Andersson from the research group in Sweden and asked him if he had any ideas as to mechanisms and he provided this abstract which suggests the diving response may be more important than we think. Here it is:

Gooden, B. A. (1992). "Why some people do not drown. Hypothermia versus the diving response." Med J Aust 157:
629-32.
OBJECTIVE: To examine our present state of knowledge regarding the remarkable survival of some victims from prolonged
submersion for an hour or more. Debate continues on the relative importance of the two explanatory theories--diving
response and hypothermia. DATA SOURCES: A wide range of physiological, pathophysiological and clinical papers
relating to the diving response, hypothermia and near-drowning, with emphasis on the period 1981-1991. DATA
SYNTHESIS: The normothermic human brain suffers irreversible damage if subjected to acute asphyxia for longer than 10
minutes. Significant resistance of brain tissue to hypoxia occurs only after its temperature has fallen from 37 degrees C to 30
degrees C or less. Body surface cooling depresses core temperature by only one-third of this drop in 10 minutes. Hence an
additional factor, other than hypothermia, is required to explain survival from near-drowning. The idea that ingestion and
aspiration of large amounts of cold water produce such a temperature drop lacks quantitative evidence. The diving response
seen in marine mammals also occurs in humans but to a lesser extent; however, about 15% of volunteers tested exhibit a
profound response. This response which starts immediately upon submersion prevents aspiration of water, redistributes
oxygen stores to heart and brain, slows cardiac oxygen use and initiates a hypometabolic state. The possible influence of
alcohol on these processes is considered. CONCLUSIONS: Survival from prolonged near-drowning appears to depend
upon a specific temporal interplay between the diving response and hypothermia, resulting in a protective state of
hypometabolism.


It is interesting that the human reflex bradycardia from cold face immersion is from the opthalmic branch of the trigeminal nerve just above the eyes. Most of the medical texts still say the bradycardia reflex is from water on the nostrils which is incorrect. Maybe it is the seal or beaver where the nose is the sensor, but not homo sapiens.

As for splenic contraction I am surprised it is so pronounced as well, but I assume someone has quantified the response as it would be fairly simple to do pre and post facial immersion.

Good to see your posts again. Puffer

 

[The Iceni]

pufferfish once bubbled...
. . the diving response may be more important than we think. Here it is:

The normothermic human brain suffers irreversible damage if subjected to acute asphyxia for longer than 10
minutes. Significant resistance of brain tissue to hypoxia occurs only after its temperature has fallen from 37 degrees C to 30
degrees C or less. . . The idea that ingestion and
aspiration of large amounts of cold water produce such a temperature drop lacks quantitative evidence.

Single-point statistics are not very convincing. I doubt I aspirated as much as 20 litres of fresh water (I suppose I was weighed on admission so I could find out exactly how much) and even 20 Kg at ~273 degrees K would not, by itself, have reduced my 100 Kgs core temperature to 303 degrees.

The diving response may indeed have prevented aspiration of water, redistributed oxygen stores to heart and brain, slowed cardiac oxygen use and initiated a hypometabolic state.

CONCLUSIONS:

Survival from prolonged near-drowning appears to depend upon a specific temporal interplay between the diving response and hypothermia, resulting in a protective state of hypometabolism. .

Makes a great deal of sense to me!

 

[The Iceni]

SARmedic once bubbled...
Once again, If I offended anybody, I am sorry.

No offence taken by me at least!

Doctors and paramedics do indeed deal with life and death situations routinely and become hardened to the very real facts of life and death. Personally I feel it is a shame you felt obliged to edit out your statement. After all it gets the message across and that is what is important; - Most diver casualties will be hypothermic and this protects the brain from hypoxic damage.

In a nutshell, diver rescuers must not stop CPR and must use 100% oxygen in all circumstances.

(This does not apply, of course, when death is quite obvious - gross trauma or delayed rescue i.e. days or hours.)

 

[pufferfish]

Same message which is don't stop CPR until the victim's core temperature using a low reading thermometer has risen to at least 32 degrees centigrade.

From Sclerlis, L. Poetical Version of the Rules of Humane Society for Recovering Drowned Persons, Crit. Care Medicine 1981;9:430-432

When in the stream, by accident is found
A pallid body of the recent drown’d,
Tho’ ev’ry sign of life is wholly fled,
And all are ready to pronounce it dead,
More patient thou, with ardour persevere
Four hours at least’ the gen’rous heart will fear,
To quit its charge, too soon, in dark despair;
Will ply each mean, and watch th’effect with care
For should the smallest spark of life remain,
Life’s genial head may kindle bright again.

I know when I last read about CPR in the hypothermic patient there was some controversy as to whether one should start CPR if the core temperature was less than 28 degrees C due to cardiovascular instabilty.

This piece is lifted from Clinical Pediatric Emergency Medicine
Sept 2001 V2 n3 Corneli, H; Hot Topics in Cold Medicine :Controversies in Accidental Hypothermia

CPR and Life Support

Less clear is the role of CPR, although anecdotal evidence suggests that CPR performed for bradycardia or apparent pulseless electrical activity may precipitate VF. Even a bradycardic, hypotensive circulation may satisfy the reduced metabolism in hypothermia, and CPR is less effective during hypothermia.[98] Almost all experts[99] [100] [101] [102] [103] agree that CPR should be withheld in the severely hypothermic patient with a pulse, regardless of heart rate or blood pressure. Extra time and effort may be required to detect the slow, weak pulse in severe hypothermia. Some investigators would also withhold CPR if a narrow complex appeared on the EKG at body temperatures below 28°C, [101] or even if EKG monitoring were unavailable. [99]

All of these recommendations are more of a guideline than a rule. We have already remarked on successful recovery after prolonged CPR in cases of severe hypothermia. Evidence that CPR provokes VF is circumstantial. Accurate temperature measurement is often difficult at the time of rescue, which is when such decisions are made. Furthermore, CPR at standard rates is clearly indicated when circulatory arrest has occurred. Although rendering CPR less effective initially, hypothermia may limit its usual loss of effectiveness over time.[98]


So I guess the message for a first responder with a hypothermic pulseless victim is to check carefully for a pulse and if none is found start CPR with O2 if available until the medics arrive. It would be interesting to hear from medics on this board what the current protocol is in this situation? Do you measure core temperature with a low reading thermometer and if it is less than say 28c do you continue CPR and intubate?

I think if it was me I would forego the above controversies and say please put that tube in my trachea :yawn: and start compressions. I have read of recoveries from 14c and several hours CPR. And remember,

"Life's genial head may kindle bright again"

 

[pufferfish]

That first statement about stopping CPR when a warm core temperature is reached of course is made by the casualty officer or ER physician in a hospital ER not in the field.

Therefore all dive rescuers would follow Dr. Paul's sound advice in red to start and continue CPR with oxygen until relieved by the arriving medics.