286 RESPIRATION 



arterial blood ; but some relief may come from compensatory in- 

 crease in the percentage of haemoglobin in the blood. In a bad 

 heart case the heart has usually broken down owing to either some 

 more or less acute infection or to too much muscular exertion; 

 and usually the main question is whether, and to what extent, the 

 heart will recover with rest and the passing off of the infection. 



In many heart affections the defect is in the nervous regulation 

 of the heart, either without or with a valvular defect. The ac- 

 celerator, inhibitory, depressor, or pressor reflexes may be acting 

 excessively. Cases with evident defects of nervous control have 

 been very common during the war, under such names as "soldier's 

 heart," "disordered action of the heart," "neurasthenia," etc. In 

 the commonest form of this defect there is very abnormal increase 

 in pulse rate on slight exertion or emotional and other stimuli; 

 and accompanying the increase there is pain and hyperalgesia in 

 the areas where pain is usually felt in heart affections. The exag- 

 gerated cardiac reflexes seem to be similar to the exaggerated 

 Hering-Breuer respiratory reflex in the same cases, and to be due 

 to the same causes (see Chapter III). Reflexes and nervous or 

 emotional responses of all kinds are exaggerated in these cases of 

 neurasthenia; and the exaggeration of cardiac reflexes is fre- 

 quently only one symptom of a condition of general neurasthenia. 

 The pain is probably only an expression of fatigue produced by 

 the over-frequent heartbeats. 



A similar condition is very commonly present as an accompani- 

 ment of valvular defect; and the associated shallow breathing 

 may cause very serious secondary anoxaemia in the manner al- 

 ready described in Chapter VII. This seems to be the explanation 

 of the orthopnoea and Cheyne-Stokes breathing so often seen in 

 bad heart cases, and also explains the marked effects of oxygen 

 inhalation in relieving the symptoms. Continuous inhalation of 

 air enriched with oxygen is likely to prove a very valuable remedy 

 in promoting recovery where failure of the respiratory center is 

 complicating defects of circulation. 



A very interesting investigation demonstrating a relation be- 

 tween vasular disturbances in the lungs and the Hering-Breuer 

 reflex has recently been published by J. S. Dunn,^^^ who wa> 

 working at the time in conjunction with Barcroft. He produced 

 multiple embolism of pulmonary arterioles by intra- venous injec- 

 tion of starch granules. When only a moderate degree of embolismj 

 was produced (so as not to cause immediate death) he observed 



"^ Dunn, Quart. Journ. of Med,, XIII, p. 129, 1920. 



