POSTNATAL MATURATION OF THE RESPIRATORY RHYTHM GENER ATOP (RRG) IN NEONATAL SWINE

Abstract

Efferent phrenic nerve (PHR) activity (monitor of RRG) was recorded in piglets <1 day-39 days old, anesthetized with Althesin, immobilized with C-10 and artificially ventilated. Recordings were made on magnetic tape of left and/or right PHR activity (bandpass 10 or 30 Hz to 10,000 Hz), integrated (INT) PHR activity (time constant 0.1 sec), intratracheal pressure (ITP), blood pressure and EKG. Computer analyses (PDP 11/45) included correlation and averaging techniques as well as power spectral analysis. During inspiration (I), peaks of power at higher frequencies (ca.150 Hz) were observed in older piglets when compared to younger animals (<1 wk)(ca.100 Hz). Maturational differences in responses of the RRG to hyperoxia, hypoxia and hypercapnia were observed. PHR activity always increased during hypercapnia. Hyperoxia elicited biphasic changes in PHR discharge: initially decreased peak power, followed by an increase. During hypoxia, peak power increased in magnitude during I in piglets >3 wk of age. During maintained hypoxia, in piglets <1 wk old, peak power was not significantly greater than during control. During Maintained Lung Inflation (LI) Tests: expiratory time (T_E) lengthened at all ages without apparent change in I bursts of PHR activity. During No LI Tests: T_E decreased; PHR activity tended to decrease in piglets <1 wk old, with increased PHR activity in piglets >2 wk of age. The results, to date, indicate that changes in INT PHR activity and power spectral analysis can be used to demonstrate postnatal maturation of RRG. (Supported by NIH Grant #HL-20864).

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