Breath hold diving

I had a conversation with a friend today who was telling me about the Buteko breathing technique as a support therapy for those with asthma. She told me her husband’s ability to breath hold was quite substantial after he trained himself to breathe better. Buteko breathing involves training ourselves to breathe in through our nose and out through your mouth. The treatment is based on the concept that hyperventilation is the underlying cause of medical conditions such as asthma. It is known that hyperventilation can lead to low carbon dioxide levels in the blood (hypocapnea), which can subsequently lead to disturbances of the acid-base balance in the blood and lower tissue oxygen levels.

Although the research is sceptical of this treatment for asthma it could be beneficial to asthmatics as the function of the respiratory conduction system is to warm and humidify the air in order for the lungs to efficiently diffuse the gasses through the alveolar membranes. Asthmatics constantly complain that cold air can set off attacks.

We compared my friends husbands breath-hold performance to a free diver who can hold his breath for over 8 minutes – a little less but interesting nevertheless. I related the article I read about the “100m Man” William Trubridge (Scott, 2007) to her. I explained that his capacity for breath holding was related to his body’s ability to hold more air, his body’s efficiency for supplying O2 to his muscles and his ability to increase his ability to maintain his acid balance within his body and fight the urge to breathe. It’s also interesting that Trubridge warns to not use hyperventilation techniques before a breath hold dive as this can cause blackouts underwater and at the surface.

So how is Oxygen transported to the tissues?

Oxygen is carried in the blood. The Oxygen carrying component within blood is called haemoglobin. Haemoglobin carries four heme (iron) molecules, like pockets to carry O2, which oxygen binds to when they diffuse across the lungs alveolar membrane into the blood (McArdle, Katch and Katch, 2010).

So how does oxygen get off the haemoglobin train?

When the CO2 concentration gets to a certain level within the blood, this signals the heme to release the oxygen molecule. This is then diffused through the cells membrane and is consumed by the cell (Marieb and Hoehn, 2010). If the CO2 levels in the blood get higher the heme releases its second molecule and so forth. The article recalls Trubridges comments that this build-up of CO2 causes this overwhelming desire to breath which he has to resist.

So how did he do it?

The article states there are many things a free diver must overcome to hold their breath for large extended periods. There are things that both hinder and help a free diver. First of all he has to psychologically overcome the body’s desire to maintain homeostasis – this is the urge to breathe so it can lower the acidity of the blood by expelling CO2 via diffusion through the lungs to the atmosphere. Secondly the partial pressures of inert gasses at the surface , such as nitrogen, are now at depth, which increases nitrogen’s partial pressure within the air space in his lungs.. At depth this high partial pressure of N within the airspace within his lungs diffuses from the air in the lungs into the blood stream. At 30M (which is four times the pressure than at the surface) excessive nitrogen causes a narcotic effect which can impair cognitive function such as dizziness, delayed responses, and effects psychomotor function. What a performance hurdle!

However, the mammalian dive reflex is a response to water being splashed on the face and this signals the parasympathetic nervous system to slow down the heart rate so that the consumption of O2 is conserved.

So why does the parasympathetic nervous system do this?

I know from the hot cold test we did in the lab that when the arm was immersed in the hot water the blood vessels experienced vasodilation. This vasodilation caused a decrease in blood volume and subsequently lowered the blood pressure within the body. The sympathetic nervous system detected this and caused an effector to speed up the heart rate up in order to increase blood pressure to keep the circulation of blood within the body steady in order to transport O2 to the tissues.



(comprehensivephysiology.com)

In exercise muscle contraction creates heat. In order to maintain a stable internal temperature the body redirects blood flow to the outer extremities to be cooled. The arteries expand therefore increasing blood flow and thus decreasing blood pressure.

In contrast, West reports at a 30M depth the lung starts to collapse. The blood vessels supplying the lungs swell (dilate) as the external pressure pushes the blood from the extremities blood to the core to feed the heart and brain. These physiological experiences of pressure creates tension, constricting the blood vessels (a type of environmentally forced vasoconstriction). This in turn raises his blood pressure and in order to compensate for this, a baroreceptor detects this increased pressure and signals the parasympathetic nervous system to slow the heart rate.

So how does one adapt to this tough environment I ask? Trubridges main strategy is to be able to inhale as much air as he can and move very slowly underwater to limit the consumption of O2 by the muscles therefore limiting the production of CO2. He trains by doing lung stretching exercises to stretch the intercostal muscles and his diaphragm so it can create more volume in his thorax (where the lungs reside) so that there is an increased lower pressure in this cavity to cause an increased volume of air to be inhaled. This is where air will always move from a high pressure to a low pressure. The higher the difference the more air he can move into his lungs.

This is where increased pulmonary capacity affects performance. Trubridge trains his intercostal muscles to increase the pressure gradient between the atmosphere and the cavity inside his lungs in order to increase his total lung capacity. This training has enabled Trubridge to improve the area variable in Ficks law of diffusion to enhance his total lung capacity for better performance.

So what do I not understand? Well the article didn’t go in to depth with other possibilities of adaptation Trubridge had also developed. It can’t be all muscular adaptation within the mechanics of breathing. When comparing the adaptations of altitude training where this can increase haemoglobin capacity, it is not likely that a Trubridge would utilise this method to increase O2 carrying capacity as he lives in long island in the Bahamas and this type of training would be impractical.