DECOMPRESSION 



357 



blood volume is also 3-5 litres, we may substitute minutes for 

 rounds of the circulation, and state that it requires 23 miiuitcs to 

 render the tissues half-saturated to a new pressure of nitrogen. 



The process of desaturation, provided physiological conditions 

 are kept constant, follows the same curve. If the tissues are 

 exposed to blood-carrying nitrogen in excess of the normal amount, 

 for sufficiently long to be in gaseous equilibrium with that blood — 

 i.e. to be saturated — then in order to prevent the formation of 

 bubbles, the process of desaturation would need to be carried out 



MINUTES 

 (l20) (iSO) 



O 1 Z 3 '^ 5 



MULTIPLES OF THE. TIME REQUIRfO TC PRODUCE HfiiLfSfiiTURfiiTiOH 



Fig. 84. — Curve showin<; the progress of saturation of any part of the body with nitrogen 

 after any given sudden rise of air pressure (after Haldane). 



at the same rate as the saturation. If the desaturation rate were 

 too rapid, then gas would be released from the tissues more 

 rapidly than it was being passed from blood to alveolar air. This 

 would entail a very slow and uniform rate of decompression. 

 A diver's ascent from the sea bed might have to be spread over 

 hours. Paul Bert, from his experiments on animals, concluded 

 that the decompression period should be 30 minutes for under 

 3 atmospheres, and 60 minutes for 3 to 4 atmospheres. This 

 ruling of the famous French scientist has never been carried out 

 in industrial practice, the usual period for " leaking out " being 

 about 15 minutes altogether. As a result of this haste to get into 



