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Involuntary actions operated by the autonomic nervous system involve lateral flapping or paddling with the arms to press them down into the water in the effort to raise the mouth long enough to breathe, and tilting the head back. As an instinctive reaction, this is not consciously mediated nor under conscious control.
The diving reflex is a set of physiological responses that occur in response to cold water immersion, particularly when the face or body is exposed to cold water. It is an evolutionary adaptation that helps mammals , including humans, manage the challenges of being submerged in cold water.
Human physiology of underwater diving is the physiological influences of the underwater environment on the human diver, and adaptations to operating underwater, both during breath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply.
The oxygen affinity of the blood is related to lung volume. Where the lungs do not represent an oxygen store, the oxygen affinity is low to maximise the unloading of oxygen and to maintain a high tissue oxygen tension. Where the lungs are utilised as an oxygen store, the affinity is high and maximises uptake of oxygen from the alveolar volume. [13]
Drowning is a leading cause of unintentional injury and death worldwide, and the highest rates are among children. Overall, drowning is the most common fatal injury among children aged 1–4 years in the USA, [8] and is the second highest cause of death altogether in that age range, after congenital defects.
Slowing the heart rate reduces the cardiac oxygen consumption, and compensates for the hypertension due to vasoconstriction. However, breath-hold time is reduced when the whole body is exposed to cold water as the metabolic rate increases to compensate for accelerated heat loss even when the heart rate is significantly slowed. [2]
Hypothermia does not easily occur in a diver with reasonable passive thermal insulation over a moderate exposure period, even in very cold water. [1] Body heat is lost by respiratory heat loss, by heating and humidifying (latent heat) inspired gas, and by body surface heat loss, by radiation, conduction, and convection, to the atmosphere, water ...
This is about 4% oxygen in the lungs and 45% oxygen saturation of the arterial blood. At 30 msw (4 bar), 2% by volume oxygen in the lung gas gives a P O 2 of 60 millimetres of mercury (80 mbar). At 10 msw (2 bar), for the same 2% oxygen, the P O 2 would be 30 millimetres of mercury (40 mbar), i.e. marginal. At the surface the same 2% oxygen ...