This gas is one of the major waste products of cellular respiration. The burning of carbohydrate foods (bread, potato, pasta, rice, muesli, porridge, breakfast cereal, beer, Scotch) for energy, produces carbon dioxide (C02). Because cellular respiration never stops, carbon dioxide is continually building up and can make blood dangerously acid if not removed.
Breathing out is the major vehicle for carbon dioxide removal. Like oxygen, this gas also diffuses down a pressure gradient. The same blood that picks up oxygen from the lungs brings carbon dioxide back to the lungs. Because the concentration (pressure) of carbon dioxide in the blood is so high it readily diffuses into the lung to be blown off in the next ‘out’ breath. Because most of the blood vessels that serve the lung are found around its lower lobes, carbon dioxide tends to build up and sit there for extended periods when shallow (upper lobe) breathing is habitual.
Deep breathing reaches down to the lower lobes and draws the stale carbon dioxide out, leaving us feeling fresh and bright. At the end of each exhalation a holding period of three seconds is observed before inhaling again. The three second negative pressure of the empty lungs allows for maximum diffusion, or drawing off, of carbon dioxide from the blood. The lower lobes begin to fill once more. The positive pressure created by the next deep inhalation of air does not force the carbon dioxide back into the blood as so much of it is produced by cellular respiration that the blood concentrations of it are always higher than the lung concentrations.
One interesting side effect of excessive carbon dioxide build-up in the blood is its effect on thyroid gland function. The thyroid hormone, thyroxine, is responsible for the rate at which the cells burn carbohydrate food (which has now been digested down to glucose) for energy. The more thyroxine, the faster they burn carbohydrate and the more heat and energy they produce.
One of the body’s compensatory mechanisms for normalising carbon dioxide levels in the presence of shallow breathing is to slow down its production. By reducing the production of thyroxine it slows the rate at which carbohydrate is burned to produce energy and although less carbon dioxide is produced, body weight tends to increase if food intake (particularly carbohydrate) is not decreased. Food that is not burned for energy is stored as energy reserve in the form of fat.
Just as carbon dioxide slows the metabolic rate, oxygen increases it and it’s not uncommon to raise a sweat while doing the deep breathing exercises described in the chapter on stress.
The advantage of the deep breathing exercises over vigorous physical exercise is that vigorous exercise stimulates the burning of carbohydrate for energy with the attendant build-up of carbon dioxide in the tissues. The deep breathing associated with vigorous exercises manages only to contain carbon dioxide build-up.
Carbohydrate metabolism is not as vigorously stimulated by deep breathing. This enables these exercises to draw out excess carbon dioxide from the blood. The slow rythmic movements of yoga and Tai Chi don’t stimulate carbohydrate metabolism to the degree that football, tennis, jogging, aerobics, weight training and swimming do. As a result, they too have the net effect of normalising blood carbon dioxide levels when combined with their appropriate deep breathing exercises.
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