STUDIES ON DIFFUSION RESPIRATION. VIII. CHANGES IN THE HEART RATE, BLOOD PRESSURE AND ELECTROCARDIOGRAM IN DOGS DURING DIFFUSION RESPIRATION

Abstract

The trachea was cannulated under light pentothal anesthesia in 15 medium-sized dogs. The animals were partially denitrogenated by breathing pure O2 for 45 min. Blood from the abdominal aorta was withdrawn through a catheter introduced via the femoral artery for pH detn. In 12 expts, femoral arterial pressure was recorded. Atropine, 1/150 g., was given subcut. before the start of the expt. and heparin was given intraven. at irregular intervals. After denitrogenation apnea was produced by an overdose of pentothal Na in 11 expts., and by the combination of intocostrin and pentothal in 4 expts. In 6 expts, the dogs were resuscitated after 45 min. and were killed subsequently; in the other 9 diffusion respiration was continued until death. No marked change was observed in heart rate during the expts. The systolic blood pressure fell markedly in the first 5 min. of diffusion respiration, then returned to normal and was well maintained as the respiratory arrest continued. The blood pressure rose markedly when respiration was re-established. Premature ventricular extrasystoles were observed in the first half of the diffusion respiration, but in every case disappeared by the 30th min. A progressive rise in the amplitude of the T wave was also noted. The initial drop in blood pressure was more marked when intocostrin with pentothal was used to produce apnea.