I98 THE CHANGES OF THE CIRCULATION DURING ASPHYXIA. 



If the blood-pressure be measured in a systemic artery, e.g., the carotid, it is 

 found that the blood-pressure rises very rapidly, and to a great extent during the 

 first and second stages ; the pulse-beats at first are quicker, but soon become slower 

 and more vigorous. During the third stage it falls rapidly to zero. The great 

 rise of the blood-pressure, during the first and second stages, is chiefly due to the 

 action of the venous blood on the general vaso-motor centre, causing constriction of 

 the small systemic arteries. The peripheral resistance is thus greatly increased, 

 and it tends to cause the heart to contract more vigorously, but the slower and 

 more vigorous beats of the heart are also partly due to the action of the venous 

 blood on the cardio-inhibitory centre in the medulla. 



If the second method be adopted, viz., to open the chest, keep up artificial 

 respiration, and measure the blood-pressure in a branch of the pulmonary artery, 

 as well as in a systemic artery, e.g., the carotid, we find that when the artificial 

 respiration is stopped, in addition to the rise of the blood -pressure indicated in the 

 carotid manometer, the cavities of the heart and the large veins near it are engorged 

 with venous blood. There is, however, but a slight comparative rise in the blood- 

 pressure in the pulmonary artery. This may be accounted for, either by the pul- 

 monary artery not being influenced to the same extent as other arteries by the 

 vaso-motor centre, or by its greater distensibility ( 88). But, as the heart itself is 

 supplied through the coronary arteries with venous blood, its action soon becomes 

 weakened, each beat becomes feebler, so that soon the left ventricle ceases to con- 

 tract, and is unable to overcome the great peripheral resistance in the systemic 

 arteries, although the right ventricle may still be contracting. As the blood 

 becomes more venous, the vaso-motor centre becomes paralysed, the small systemic 

 arteries relax, and the blood flows from them into the veins, while the blood-pressure 

 in the carotid manometer rapidly falls. The left ventricle, now relieved from the 

 great internal pressure, may execute a few feeble beats, but they can only be feeble, 

 as its tissues have been subjected to the action of the very impure blood. More 

 and more blood accumulates in the right side from the causes already mentioned. 

 The violent inspiratory efforts in the early stages aspirate blood from the veins 

 towards the right side of the heart, but of course this factor is absent when the 

 chest is opened.] 



[Convulsions during asphyxia occur only in warm-blooded animals, and not in 

 frogs. If a drug when injected into a mammal excites convulsions, but does not 

 do so in the frog, then it is usually concluded that the convulsions are due to its 

 action on the circulation and respiration, and not to any direct stimulating effect 

 upon the motor centres. But if the drug excites convulsions both in the mammal 

 and frog, then it probably acts directly on the motor centres {Brunton).~\ 



[Recovery from the condition of Asphyxia. If the trachea of a dog be closed suddenly and 

 completely, the average duration of the respiratory movements is 4 minutes 5 seconds, while 

 the heart continues to beat for about 7 minutes. Recovery may be obtained if proper means be 

 adopted before the heart ceases to beat ; but after this, never. If a dog be drowned, the result 

 is different. After complete submersion for 1 minute, recovery did not take place. In 

 drowning, air passes out of the chest, and water is inspired into and fills the air-vesicles. It 

 is rare for recovery to take place in a person deprived of air for more than five minutes. If the 

 statements of sponge-divers are to be trusted, a person may become accustomed to the deprival 

 of air for a longer time than usual. In cases where recovery takes place after a much longer 

 period of submersion, it has been suggested that, in these cases, syncope occurs, the heart beats 

 but feebly or not at all, so that the oxygen in the blood is not used up with the same rapidit}'. 

 It is a well-known fact that newly-born and young puppies can be submerged for a long time 

 before they are suffocated.] 



Artificial Respiration in Asphyxia. In cases of suspended animation, artificial respiration 

 must be performed. The first thing to be done is to remove any foreign substance from the 

 respiratory passages (mucus or cedematous fluids) in the newly-born or asphyxiated. In doubt- 

 ful cases, open the trachea and suck out any fluid by means of an elastic catheter (v. Hitter). 

 Recourse must in all cases be had to artificial respiration. There are several methods of dilating 

 and compressing the chest so as to cause an exchange of gases. One method is to compress the 

 chest rhythmically with the hands. 



