CARDIOVASCULAR FUN'CTIONS— D'AMATO 153 



TABLE III 



C.\KU1.\C UU'irUT IN THE I Ivi'UTlIKKMU: \J()i, 



No. 



of .\it. O. Veil. O2 



'l\ni|). dogs Vol. '/(! Vol. % 



Norm 9 20.1 14.1 



17° C 8 22.0 17.1 



Expt. No. 12, 17° C 1 23.0 3.9 



temperature of 17° C, cardiac output was reduced to 18 per cent of control. The 

 ninth dog, when cooled, presented a unique case. At 20° C. the pulse rate and blood 

 pressure were 29 per minute and 68 mm. Hg., respectively. Then the heart suddenly 

 stopped and the blood pressure fell to zero. Both heart rate and blood pressure re- 

 covered periodically until the rectal temperature reached 17° C, at which tempera- 

 ture these measurements were made. Undoubtedly, during these bouts of relative 

 asystole a substantial oxygen debt was incurred. In the face of this oxygen debt a 

 greater volume of oxygen was extracted from a unit of blood, hence the low venous 

 oxygen content and the high A-V oxygen difference. During rewarming the A-V 

 oxygen difference returned to normal (4.2 vol. per cent), indicating that the oxygen 

 debt had been paid off. This demonstrates that in the presence of tissue hypoxia 

 the required oxygen can be extracted from the blood in spite of the increased affinity 

 of hemoglobin for oxygen at low temperatures. The failure of such increased extrac- 

 tion in the remaining eight hypothermic dogs indicates that the ordinary demands 

 at the cold temperatures are met by other means. 



In the same experiments cardiac work was computed at normal body temperature 

 and at the cold temperature. The results are summarized in table IV. If we apply 

 the simple formula W = QR, in which Q is the stroke volume and R is the mean 

 arterial pressure, at normal temperature the work performed by the heart is 

 15.4 gram meters per stroke, or 2618 gram meters per minute. At the cold tempera- 

 ture these values become 7.6 gram meters per stroke, or 198 gram meters per minute. 

 Thus the work performed by the heart per minute is reduced to seven to eight per 

 cent of normal. The work performed by the heart per stroke is reduced only by 

 50 per cent. 



Blood flow. The observations of coronary blood flow in hypothermia by Berne 

 have been described in a previous section. Reductions in cerebral blood flow of simi- 

 lar magnitude (approximately 75 per cent of control) have been reported by Roso- 

 moff and Holaday.^° In their experiments the diminution of cerebral blood flow was 

 linear and directly proportional to an observed decrease in cerebral oxygen consump- 

 tion. Cerebral arterio-venous oxygen difference remained unchanged, indicating an 

 adequate supply of oxygen to the brain in hypothermia. Splanchnic blood flow has 



TABLE IV 

 Cardiac Work ix the Hypothermic Dog 



Work Work 



Blood .Stroke Pulse per per 



pressure vol. rate stroke min. 



Temp. mm. Hg. ml. per min. gm. meters gm. meters 



Norm 126 9.0 170 15.4 2618 



17° C. (16-18) 54 10.4 26 7.6 198 



