Henrique Rigatto

Airway closure during mixed apneas in preterm infants: is respiratory effort necessary?

Airway closure during mixed apneas in preterm infants may be due to lack of tone in the upper airway followed by collapse and obstruction or diaphragmatic action inducing obstruction. We examine whether respiratory efforts are necessary for airway closure using a new method of detecting airway obstruction, based on the disappearance of an amplified cardiac pulse observed on the respiratory flow tracing. We analyzed 198 episodes of mixed apnea of various lengths (> or = 3 seconds) observed in 33 preterm infants (birth weight, 1.4 +/- 0.1 kg [mean +/- SEM]; study weight, 1.7 +/- 0.1 kg; gestational age, 29 +/- 1 weeks; post-natal age, 33 +/- 4 days). The great majority of these episodes (88%) had a central, followed by an obstructive, component. Infants were studied by using a nosepiece and a flow-through system. Respiratory efforts (abdominal and chest movements) were recorded. Of the apneas, 20 were or = 20 seconds. Of the 198 mixed apneas, 151 (76%) occurred in the absence of any respiratory effort; 43 (22%) showed a simultaneous cessation of the cardiac oscillation and respiratory effort; and 4 (2%) showed diaphragmatic activity appearing after cessation of the cardiac oscillation (airway occlusion). Respiratory efforts never preceded the cessation of the cardiac oscillation. The findings suggest that diaphragmatic action is not needed to occlude the airway in mixed apneas. The simultaneous cessation of cardiac oscillations (airway occlusion) and onset of respiratory efforts may indicate that such effort contributes to closure or is induced by the same stimulus that closes the airway. We speculate that the mechanism for airway closure in mixed apneas is most likely a lack of upper airway tone, which normally occurs with the cessation of a central drive to breathe.

Diaphragmatic flutter with an electromyographic study

Summary A case of diaphragmatic flutter was demonstrated in an 8-year-old boy by fluoroscopy and by electromyographic study of the diaphragm and abdominal muscles, both of which showed an entirely abnormal electrical pattern. The observation that the abdominal movements are active suggests that abnormal excitability of the phrenic nerve cannot entirely explain the pathologic mechanism of this disease.

Control of Breathing in Newborns

There are at least three important considerations regarding the study of the control of breathing during the neonatal period. First, the neonates are noncooperative subjects. This means that we must study their respiratory control without their being aware and try to compare the measurements with those of the adult under similar conditions. This is difficult to do. Second, measurements in the neonate are usually made, by necessity, in the decubitus position, whereas those in the adult subject are usually made in the sitting or standing position [1, 2]. Third, babies are usually studied with a nosepiece because they are nose breathers; adults are usually studied using a mouthpiece. These methodological differences have made comparison of breathing in newborns with that in adult subjects difficult to interpret. There is currently a major need for studies to be done using similar methodology. Unless there is some consistency in the methodology, it is hard to define what is actually distinct or unique about the control of breathing in the neonate. In recent years, we have experienced tremendous advances in the field of respiratory control, and we are now witnessing the initial discovery of several of the genes that control the development and maturation of multiple neurally controlled respiratory functions

In Search of the Respiratory Center: Medullary Pacemaker Cells and Their Response to Neurotransmitters

In Search of the Respiratory Center: Medullary Pacemaker Cells and Their Response to Neurotransmitters

Inhalation of Low (0.5-1.5%) CO2 As a Potential Treatment for Apnea of Prematurity

Apnea of prematurity is common and none of the treatments being used are fully effective and free of significant adverse side effects. We hypothesized that low concentrations of CO2 (< or = 1.5%) may reduce apnea without causing discomfort from an increase in ventilation. We studied 10 preterm infants at a gestational age of 32+/-1 wk (mean +/- SEM) and birthweight 1.8+/-0.2 kg. After a control period of 1 hour, concentrations of CO2 were given (0.5%, 1%, and 1.5%) for 1 hour each, followed by a recovery period of 1 hour. Apnea number significantly decreased from 2.0+/-0.3 apneas/min during control to 1.0+/-0.1 apneas/min (0.5% CO2; P < .05), 1.1+/-0.2 (1% CO2; P < .05), and to 0.7+/-0.2 (1.5% CO2; P < .01). The apnea time significantly decreased from 14.2+/-2.5 s/min during control to 5.2+/-0.8 (0.5% CO2; P < .01), 5.8+/-0.7 (1% CO2; P < .01), and to 3.7+/-0.9 (1.5% CO2; P < .01). Minute ventilation significantly increased with CO2 without evidence of respiratory discomfort. TcPCO2 did not change and TcPO2 increased slightly. These findings suggest that inhalation of low concentrations of CO2 in preterm infants with apnea 1) decreases the number and time of apneas, 2) improves oxygenation, 3) increases ventilation, and 4) is effective even in such low concentrations as 0.5%. We speculate that inhalation of CO2 (< 1%) is more effective and safer than methylxanthines for the treatment of apnea of prematurity.