CIRCULATOKY CHANGES DURING MUSCULAR EXERCISE 1055 



This production of acid products in the muscles aids also dissociation of 

 the oxyhsemoglobin passing through the capillaries and therefore sets free 

 oxygen for the use of the muscles. On this account we find almost invariably 

 that the utilisation of the oxygen taken in from the lungs is more complete 

 during exercise. The oxygen utilisation per litre of blood as it flows round 

 the circulation is known as the ' co-efficient of utilisation.' Thus if 328 c.c. 

 of oxygen were used per minute and the blood flow were 4-5 litres per minute, 



= 73 c.c. oxygen would be utilised per litre of blood. If the oxygen 



capacity of the blood were 193 c.c. per litre, the co-efficient of utilisation 

 73 



would be = 38 per cent. 



13.40 



In Fig. 483 the co-efficient of the oxygen 



utilisation is given by the curve C. 

 It has been shown by Cannon 

 that every state of excitement, and 

 especially fear and anger, is attended 

 with increased secretion of adrena- 

 line into the blood stream. During 

 the violent exercise associated or 

 caused by emotional stress, there 

 will be an excess of adrenaline 

 circulating in the blood, which will 

 reinforce the activity of the circu- 

 lation. Thus it will increase the 

 constriction of the splanchnic area 

 already excited by the central 

 effects of the increased C0 2 or 

 lactic acid in the blood. In the 

 heart the adrenaline will increase 

 the contractile power and also the 

 rate of beat, while by its dilator 

 action on the coronary vessels it 

 will aid the supply of oxygen to 

 the heart muscle. At the same 



5.6d 



3.00 



Kg.Mterj 105 210 



315 420 525 

 Work per Minute 



630 735 



FIG. 484. Chart showing the effects of mus- 

 cular work on the blood flow and oxygen 

 consumption in a subject with aortic 

 disease, as compared with a normal indi- 

 vidual (shown in lighter lines). (From 

 MEANS and NEWBURGH.) 



(For oxygen consumption omit the decimal 

 point and read in c.c.s.) 



time, as we have seen (p. 844), 

 adrenaline will cause a rapid con- 

 version of the glycogen of the liver into sugar, so that the contracting 

 muscles may be rapidly supplied with the food which they can utilise with the 

 greatest ease and readiness. It is doubtful whether these adjuvant effects 

 of adrenaline are to be reckoned with except in cases of severe emotional 

 stress. 



Training. The muscular efficiency of a man is measured by the extent 

 to which he can call upon his body for increased efforts, i. e. by his margin 

 of response. This margin in normal individuals may be 600 per cent., 

 i. e. over a moderate period of time the individual may increase his muscular 

 work, his respiratory exchanges, and the rate of his circulation six times 



