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1653A EFFECT OF ABDOMINAL LOADING ON DIAPHRAGMATIC ACTIVITY IN POSTNATAL RHESUS MONKEYS

Tonic diaphragmatic activity (electrical activity at end-expiration) measured transcutaneously has been reported to occur in infants and adults during quiet sleep and to increase during abdominal loading (J Appl Physiol 47:279,1979). However, Harding et al., showed that tonic activity in the peripheral diaphragm of lambs was independent of phrenic innervation and concluded that it resulted from contamination with respiratory and postural activities of adjacent muscles (J Physiol 292:57P,1979). We sought to determine if abdominal loading altered diaphragmatic activity in five monkeys (14 to 34 days of age) during quiet sleep or during sedation with Sernylan. Respiratory events were timed from the esophageal pressure tracing. Squeezing the abdomen (10 to 40 mmHg pressure) increased phasic diaphragmatic activity which resulted from: 1) greater activity during Ti, 2) lengthening of Ti (increased by 140±60 msec at 40 mmHg compared to 0 mmHg) and 3) increased post-inspiratory activity (increased by 93±13 msec at 40 mmHg compared to 0 mmHg). Although abdominal loading increased post-inspiratory activity, tonic activity did not occur at any time. As in lambs (J Physiol 292:22P,1979), phasic activity recorded from different parts of the diaphragm was asynchronous.We conclude that abdominal loading increases phasic diaphragmatic activity but does not elicit tonic diaphragmatic activity in monkeys. (Supported by HL 0.7159 and Wellcome Trust 9594-1.5)