Thursday, June 3, 2010

Journal of Physiology - The effect of mental stimulation on the apneaist's' heart rate

I have had a spot of spare time lately and took to reading some literature on apnea heart rate and factors affecting it. One article I found from 30 years back was of great interest to me. Here follows a description of what the study involved and their findings. I also include some personal observations.

The article appeared in the Journal of Physiology - here is the reference if you choose to read the whole study.


From the Department of Psychology, St George's Hospital Medical School,
London, SW17 ORE
J. Physiol. (1980), 302, pp. 387-393

Their Objective:

To study the effect of mental stimulation on heart rate reduction (bradycardia) of breatholders. Ten males were recruited from the student population at St George's Hospital Medical School.The average age was 19 years. No more is said of the subjects - presumably they were not freedivers or spearos.
Electrocardiogram (ECG) was used to measure heart rates.
The following activities were studied - where breathholds are mentioned they are 60 second holds:

(1) Breath holding in air.

(2) Breath holding in air with subject doing arithmetic or listening to another person reading.

(3) Breath holding in water*.

(4) Breath holding in water* with arithmetic or reading (as in 2 above).

* A transparent Perspex tank filled with water to within 6-8 cm of the rim, was used for face immersion. The water was cooled to 15 deg C

In the mental arithmetic test, individuals were presented with 1 or 2-digit numbers, every 5 sec throughout breath holding, the successive numbers were to be added or subtracted from the cumulative total, and at the end of the trial, the subject had to announce the result. Not difficult but enough to fire up the brain. In the reading test, volunteers listened to prose read by the experimenter throughout the trial. They did not say what the prose was but I imagine some non-scary stuff.

Over the entire breath hold, heart rate decreased on average of 15.5 % during face immersion, compared with 4.6 % in air. Facial immersion played quite a large role there - it was in 15 deg C water. Apparently if the temp is close to body temp it has a reduced effect - depending on how the study is conducted.

The average reduction in heart rate from base line (subject heart rate before the breathold) to the last 10 secs of the breathold was 19 beats/min in the absence of arithmetic, compared with 15 beats/min during the task. So if you are counting the fish you see or shot on dives, expect a shorter hold.

Heart rate reductions or bradycardias were unaffected by the presence of the sound of reading. I would guess if the subjects were made to read it would probably interfere.

The study shows that cortical activity (mathematics)can produce substantial attenuation of the cardiac reflex elicited by breath holding and face immersion.

I have often been shocked at the variation in my breathholds on land or in a pool when I am disturbed or distracted from my task. Even if I am working during breathold - say running, doing weights, or training on my very efficient G3 system I can up my work tremendously by being fully focused. Certain concentration exercises boost breathholds into a new range. The research by Ross and Steptoe proved that this is the case - mental activity should be excluded from breathholds and replaced with a laserlike focus.
Should the focus be on the activity?
Should it be on the taste of CO2 in your mouth,
or the burn in your legs, or that srceaming desire to breathe,
or should it be on stabilizing yourself so as to prevent injury if you pass out and fall.

What do you think?
(if you have done my advanced spearfishing course, or my online mentorship you will know the answer).

I'll give my opinion and some more literature review in my next post.


Michel Adjes said...
This comment has been removed by the author.
Michel Adjes said...

Michel Adjes said...
What do suggest is the best thing to do? It is often said that you need to let you mind wonder away from the fact that you need to breath. Question: Is that safe,and what would be an effective distraction if this finding mentioned is correct? Love to know, because when I think about breathing ,my hold is shorter. Am I dangerous?!!


Gletwyn Rubidge said...

Michel - I think that focuss on the breath and need to breathe will make it worse for most people - it include me.
My focus is redirected. THere will definately be variation from person to person.
The effects of redirection cannot be generalized - especially in terms of safety. Doing redirective focus alone in the water is obviously dangerous. I used to do it (SOLO!!!) and had many flustered staff in the gym who were sure I was dead as I lay super still on the pool floor. I quit that solo risky stuff. Do not do it.
I will write some more in my next post on focus - but realise that it is my experience - I have some yoga experience that helps me.
I think using distractions can be safe if you make it safe with incremental advances and be sure to have qualified safety - i.e. someone who can pull you out in event of a blackout and administer CPR. I have dived with two guys who are now dead from pool training blackouts.
My suggestion is study you distractive technique out of the water.