PHYSIOLOGICAL EFFECTS OF LABOUR 



201 



fatigue, the force exerted must not impede the expiration 

 (dyspnoea) and the clothing must allow free play to the thoracic 

 walls. This problem of respiration is of prime importance. Its 

 irregularity gives the first indication of fatigue. 



143. Effects of Work on the Circulation. The graphic method 

 is also used to register the movements of the heart. The tracing 

 obtained by the cardiograph (Technics, 195) gives the phases 

 of the complete cycle of movement of the heart : the systole, 

 which is the contraction necessary to pump the blood into the 

 arteries, and the diastole, which is the phase of repose. 



The cardiac pulsation corresponds to the systole of the ventricles 

 (the lower extremity of the heart). 



This systole is shown by an elevation in the trace and some 



undulations, generally three 

 in number which indicate a 

 sustained contraction, of 

 tetanic form. Its duration 

 represents the quarter of 

 the total period, the diastole 

 covering the other three 

 , quarters (fig. 140). 



The cardiac pulsation can 

 be felt, and even seen, at 

 It is occurs 72 to 75 times 



Fie 140. 

 Cardiographic Record. 



'Dicrotism 



about the level of the left nipple. 

 per minute in an adult in repose. 



The beats of the heart cause the beats of the arteries to take 

 place at the same rhythm. On 



the radiial the pulsation is + 



found to be J second later than 

 the movement of the heart. 

 The record of the pulse is taken 

 by means of the sphygmograph 

 (Technics, 195). After the 

 systolic phase there is a little 

 jump due to the arterial elas- 

 ticity, this being called the dicrotism (fig. 141). The ascending 

 portion of the curve corresponds to the cardiac impulse and the 

 descending portion marks the passage of the blood into the capil- 

 lary vessels. As to the dicrotism, it is sometimes duplicated or 

 triplicated, and is then called the polyciotism. It is more 

 noticeable under the effect of a high temperature, or when wearing 

 very thick clothes, as also after taking alcoholic drinks. 



Another very important element in the pulse is the arterial 

 pressure. If an artery (the brachial artery, for instance) be 

 attached to a manometer a pressure of 120 millimetres of mercury 



Fis. 141, 

 Sphygmographic Record. 



