Diaphragmatic Activity and Ventilation in Preterm Infants

Abstract

To determine the effects of inhaled CO2 and abdominal loading on diaphragmatic electromyography (EMGdi) and ventilation during sleep, we studied 10 preterm infants (birth weight 1,840 +/- 50 g; gestational age 32 +/- 0.6 weeks and postnatal age 10.4 +/- 1.4 days). We measured surface and esophageal diaphragmatic activity. Ventilation was measured using a nasal flowmeter and a flow-through system. Diaphragmatic activity was analyzed for the duration of total phasic and expiratory activities, the expiratory to total phasic activity ratio and the presence of tonic activity (defined by the presence of electrical activity of the diaphragm at the end of expiration). With 3% CO2 in quiet and REM sleep, the intensity of EMGdi increased, but the duration of total phasic activity, the expiratory to total phasic activity ratio and tonic activity did not change. During quiet sleep with 3% CO2, ventilation increased (0.392 +/- 0.028 to 0.616 +/- 0.058 l/min; p = 0.001) due to an increase in tidal volume and frequency. Similar changes occurred in REM sleep. Abdominal loading with sandbags increased the duration of total phasic activity (0.68-0.78 s; p = 0.03), expiratory phasic activity (0.21-0.32 s; p = 0.01), the expiratory to total phasic activity ratio (0.28-0.39; p = 0.03) and diaphragmatic tonic activity (20-60%; p = 0.04) as measured with surface electrodes in REM sleep. It also increased the expiratory to total phasic activity ratio and tonic activity, as measured with surface electrodes in quiet sleep. Abdominal loading did not alter ventilation or the structure of the average breath in either sleep state.(ABSTRACT TRUNCATED AT 250 WORDS)