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

Abstract

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.

Endotracheal Measurement of Thyroarytenoid Activity in Newborn Lambs

“…The nature and relationships between TA and PCA activities during eupnea and grunting have been quantitatively analyzed in lambs and demonstrated to be important determinants of airflow pattern [4,5]. In this study, TA activity was present in every lamb with an open-ended endotracheal tube in situ and was absent when not intubated.…”

“…Computer analysis of the TA and ET-TA EMG timings of onset, peak and burst duration, and peak amplitude, were performed on a mean of 20 breaths (SD B 9) from each of the 7 lambs. To facilitate these computations, a 50-ms rectangular window was used to compute moving time averages for each EMG tracing [5,7]. Statistical analyses of the TA and ET-TA EMG timings were performed using Student's paired t test with p !…”

“…Analysis of PCA activity was limited to qualitative analysis after intubation as previous work by the authors had detailed quantitatively the reciprocal nature of PCA and TA activities [5].…”

“…Volume loss in expiration is limited by: shortening the duration of expiratory time; retarding (braking) expiratory flow with laryngeal adduction and post-inspiratory inspiratory diaphragmatic activity, and at end-expiration, inverting the normal relationship of the onsets of diaphragm and laryngeal abductor muscles such that diaphragmatic activity precedes that of laryngeal opening [4]. In neonatal respiratory distress with atelectasis laryngeal closure is pronounced [5] and produces audible grunting with generation of a positive airway pressure and improved oxygenation [5,6]. After endotracheal (ET) intubation, grunting is absent [5] and in artificial ventilation a positive end-expiratory pressure is applied [6].…”

“…In neonatal respiratory distress with atelectasis laryngeal closure is pronounced [5] and produces audible grunting with generation of a positive airway pressure and improved oxygenation [5,6]. After endotracheal (ET) intubation, grunting is absent [5] and in artificial ventilation a positive end-expiratory pressure is applied [6]. Electrode wires were placed inside an endotracheal tube.…”