Thyroarytenoid Muscle Electrical Activity During Spontaneous Apneas in Preterm Lambs

Abstract

Laryngeal dynamics plays a major role during perinatal life, a period of respiratory control immaturity. Continuous electromyographic (EMG) activity of a laryngeal adductor muscle (thyroarytenoid [TA] muscle), was recently observed throughout provoked central apneas, either isolated or during induced periodic breathing, in full-term lambs. The aim of the present study was to test if continuous TA EMG activity was also present during spontaneous apneas in nonsedated preterm lambs. We studied 7 premature lambs (term 131 +/- 1 d of postconceptional age). Premature birth was induced after acceleration of fetal lung maturation. Electrodes for diaphragm, inferior pharyngeal constrictor (IPC), and TA electromyograms, electrocardiogram, electroencephalogram, eye movement, and airflow recordings were implanted. Radiotelemetry recordings were repeated from 135 to 149 +/- 8 d of postconceptional age. A total of 2,088 apneas (2,020 central and 68 mixed) >/= 3 s were recorded in the lambs, including 57 epochs of periodic breathing. Continuous TA EMG activity was present throughout 88.4% of all apneas and 98.4% of apneas during periodic breathing, regardless of the sleep stage. These results suggest that active glottic closure is frequent during spontaneous central apneas in this model of prematurity. This unique model will allow us to study controlling mechanisms and consequences of glottic closure during neonatal apneas.

Origins of the inhibiting effects of nasal CPAP on nonnutritive swallowing in newborn lambs

“…Since the inhibiting effect of CPAP is specific to QS (19), only the data recorded during QS were considered. Standard electrophysiological and behavioral criteria were used to define sleep states (17).…”

Laryngeal chemoreflexes induced by acid, water, and saline in nonsedated newborn lambs during quiet sleep

“…One lamb received one intramuscular injection of dexamethasone (0.5 mg/kg) 1 day after surgery to decrease laryngeal inflammation manifested by weak bleating. Bipolar enameled chrome wire electrodes were inserted into the thyroarytenoid (TA, a glottal adductor) and diaphragm muscles for recording of electrical activity (EMG) (14), together with custom-designed electrodes for EEG (EEG) recordings (30). A cup electrode was also inserted under the scalp as a ground.…”

“…The percentage of decrease in heart rate [%dec HR ϭ (HRBL Ϫ HRmin) ϫ 100/HRBL] was calculated, with HRBL representing the baseline heart rate (HR) value averaged over a 10-s period, within 30 s before challenge and HR min the minimal HR value observed within 30 s after the challenge. Moreover, any presence of bradycardia was noted, as defined by a %dec HR greater than 30% (30). Similarly, the percentage of increase in mean arterial pressure [%inc MAP ϭ (MAP max Ϫ MAPBL) ϫ 100/MAPBL] was calculated, with MAPBL representing the baseline mean arterial pressure (MAP) value averaged over the same 10-s period within 30 s before challenge and MAP max the maximal MAP value observed within 30 s after challenge.…”

Effects of postnatal environmental tobacco smoke on non-nutritive swallowing-breathing coordination in newborn lambs

“…Standard electrophysiological and behavioral criteria were used to define wakefulness (W), quiet sleep (QS), active sleep (AS) and arousals (Renolleau et al, 1999).…”