Cold Water Immersion - Extreme Physiology

Cold water immersion takes us significantly outside of normal temperature profile

400-1000 accidental deaths by drowning in UK per annum

372000 worldwide

67% occur in strong swimmers

55% occur within 3m of safe refuge

Water is so dangerous because:

Water density is 827 x the density of air

Thermal conductivity is 27x greater than air

Human body cools 4-5x quicker 

There is rapid initial cooling

1. Initial response - skin cooling

2. Short term responses - superficial nerve and muscle cooling

3. Long term responses - cooling of deep tissues

4. Post immersion - collapse of arterial pressure, post rescue respiratory disturbance

Respiratory:

Gasp response - decreased breath hold time

Inspiratory shift - difficulty in breathing

Hyperventilation - muscle spasm (tetany)

Cardiovascular:

Peripheral vasoconstriction - hypertension

Tachycardia - increased cardiac workload

Noradrenaline - arrythmias

Treading water:

Facilitates bouyancy and also restores brain blood flow to pre immersion levels

Arms are major site of heat loss

Reduced contractile force

More fast twitch fibres recruited

Causes of decreased contractile force:

Reduced enzyme activity

Decreased ACH and calcium release

Slower rates of diffusion

Exercise implications:

Disturbances of aerobic metabolism, effector response disruption, reduced oxygen delivery, increase in relative work rate, rapid onset of fatigue

Deep body cooling:

Confusion, disorientation

Cardiac arrythmias

Shivering replaced by persistant muscle rigidity

Unconciousness

Ventricular fibriliation

Hydrostatic squeeze facilitates venous return

Blood volume has often been adjusted because of cold, also hydrostatic squeeze, cold induced duiresis

Blood volume redistributed to central spaces

Removal from water removes peripheral squeeze, which lowers blood pressure and increases CV demand

Helicopter rescure in vertical position can exaggerate changes and induce a collapse in arterial pressure

Death due to hypoxia, hypercapnia and acidosis

Fresh water - surfactant washed out leading to alveolar collapse, poor ventilation/perfusion and pulmonary shunt

Sea water - hyperosmotic fluid causes transduction of fluid into the alveoli, aspiration of debris causes reactive exudate

Sea water is more lethal - it has a greater irritant and greater retention, accumulation of fluid in lung raises pulmonary pressure and hastens right heart failure