Laryngeal and diaphragmatic muscle activities and airflow patterns after birth in premature lambs.

The nature and control of early neonatal respiratory patterns were determined in 10 premature, asphyxiated lambs. Severe retardation of early expiratory airflow (braking) characterized an initial pattern (A), but was absent in a final one (B). During a transition pattern (pattern T), pattern A and B airflow types occurred. Close temporal relationships between the airflow patterns and posterior cricoarytenoid (PCA), thyroarytenoid (TA), and diaphragm (D) integrated muscle activities were demonstrated quantitatively. Specifically, in pattern A, the duration of braked expiratory airflow was related to the durations of TA burst activity and the absence of PCA burst activity (r2 = 0.99). In pattern A, pH, but not arterial PCO2 or arterial PO2, differed from that in patterns T and B [7.01 +/- 0.14 (A), 7.11 +/- 0.12 (T), 7.19 +/- 0.08 (B) (P < 0.03)]. Within-breath airflow and respiratory muscle activity relationships and differences in neural and mechanical respiratory timing intervals between patterns suggested that neural feedback was important in the control of central pattern generation. Thus activities of PCA, TA, and D shape the early neonatal airflow patterns and are influenced mainly by neuromechanical, and not chemical, feedback.