To determine 1) the effect of arterial CO2 change on the neonatal cerebral circulation and 2) whether 100% O2 would produce significant decrease in cerebral blood flow (CBF), we studied 24 preterm infants to explain the late (5 min) hyperventilation observed in them during hyperoxia. Of these, 12 were studied before and during inhalation of 2-3% CO2 and 12 before and during the inhalation of 100% O2. We measured CBF by a modification of the venous occlusion plethysmography technique and found that CBF increased 7.8% per Torr alveolar carbon dioxide pressure change and that it decreased 15% with 100% O2. These findings suggest that 1) CO2 is an important regulator of CBF in the perterm infant, 2) CBF-CO2 sensitivity in these infants may be greater than in adult subjects, 3) 100% O2 reduced CBF significantly, and 4) a decrease in CBF during administration of 100% O2 may be at least partially responsible for the increase in ventilation with hyperoxia.

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SummaryThe authors studied 10 preterm infants (birth weight, 1840 + 270 g; gestational age, 31 k 3 wk) and 10 term infants (birth weight, 3700 + 320 g; gestational age, 40 f 1 wk) to evaluate the effect of sleep state on chest distortion and on the ventilatory response to CO2. Sleep state was defined on the basis of body movements, eye movements, and electroencephalogram. Chest distortion was assessed using micromagnetometers applied to the rib cage and abdomen. After a control period breathing 21% O2 in each sleep state, infants were given 3% COZ to breathe. Respiratory minute volume and frequency, tidal volume, alveolar P C 0 2 and PO2, CO2 response curves, and chest distortion were measured. It was found that: l) respiratory minute volume increased and PaCOz decreased during REM as compared to non-REM sleep in preterm and term infants ( P < 0.05); 2) chest distortion was not affected by sleep state, but was more frequent in preterm than in term infants ( P < 0.02); 3) the ventilatory response to C 0 2 was not affected by sleep state ( P > 0.4); and 4) COz did not affect chest distortion ( P > 0.1). These findings indicate: 1) contrary to previous observations, chest distortion is independent of sleep state; and 2) the ventilatory response to CO2 was not affected by sleep state. The authors suggest that the higher prevalence of chest distortion in preterm infants is related to their highly compliant chest wall rather than to differences in sleep state. SpeculationTeleologically, almost anything increases with gestational age. Chest stability, non-REM sleep, ventilatory response to C02, and prevalence of regular breathing, all increase with maturation. The authors would like to speculate, therefore, that the differences in chest distortion are immaturity rather than sleep state dependent. The authors believe that distortion is present not only because the rib cage muscles are weak or chest wall reflexes inefficient, but also because the bone structure of the rib cage is highly cartilagenous and cannot afford stability.It has long been known that the respirator pattern is more regular during non-REM than during REM sleep. Only recently, however, the physiologic differences between these two sleep states have been more thoroughly investigated (2,4,5,7,8,14,16,19,20). In this regard, two provocative observations were made. First, it was suggested that the clinical "see-saw" breathing of preterm and, less frequently, term infants, with indrawing of the rib cage and outward displacement of the abdomen, is characteristic of REM sleep (17). This paradoxical movement of rib cage and abdomen has also been named "chest distortion," because the rib cage moves inwards instead of outwards during inspiration. Second, the ventilatory response to COa was decreased during REM as compared to non-REM sleep in adult dogs (19). The issue became controversial, however, when one study in newborn primates showed similar (13) and another in newborn infants showed a decreased (6) response to Con during REM sleep. Because chest distortio...

Summawflowmeter was used to record flow. tidal volume. end-tidal CO?To examine the influence of feeding on the chemical control of breathing in neonates, we studied the ventilatory response to 3% CO2 in air in nine bottle fed (BOT) and eight breast fed (BR) term infants during feeding while the infants were alert: Control responses were obtained either before or after feeding. VE, respiratory frequency, tidal volume, inspiratory time, expiratory time, and sum of inspiratory and expiratory time, VT/Ti, Ti/TtOt, PACOz and slope (S) of CO2 response (liter/min/kg/mmHg) were determined. During 3% C02 while resting BR had a lower VE, VT, VT/ Ti than BOT and S in BR was 40% of BOT (P < 0.05). During feeding and CO2 when compared to resting and COz there was no difference in either BR or BOT in VT/T~ but Ti/Tbt decreased in both groups. During feeding, S in BOT was reduced from 0.049 * 0.012 (mean f S.E.) to 0.013 f 0.002 (74% reduction) and in BR from 0.020 f 0.002 to 0.009 f 0.002 (55%). Thus, behavioral activity (either BR or BOT) markedly depresses the ventilatory response to chemical stimuli (Cod. This modification is primarily related to changes in "effective" respiratory timing (Ti/TtOt) rather than mean inspiratory flow (VT/Ti). SpeculationThis is the first demonstration in the newborn infant that behavioral activity (feeding) can override the usual ventilatory control mechanisms. Tbe precise mechanism is unknown and requires further study.Breathing is controlled by two functionally integrated elements: the behavioral (voluntary) control system, which originates in the forebrain, is involved in activities such as phonation; and the metabolic (automatic) respiratory control system, centered in the brain stem (2, 12). Studies in healthy adult subjects have shown that during normal speech there is a marked disruption of the ventilatory response to C 0 2 (3, 15), suggesting that during phonation there is a relaxation or overriding of metabolic respiratory control. The influence of behavioral activity on the chemical control of breathing in neonates has not been studied. We designed this study, therefore, to examine the interaction of the metabolic and behavioral respiratory control systems, by comparing the ventilatory response to COz in bottle fed and breast fed infants while resting and during feeding. MATERIALS AND METHODSWe studied nine bottle fed healthy term infants (BOT): birth weight (mean * S.E.) 3.15 f 0.15 kg; gestational age 39.2 f 1.0 wk; postnatal age 6.4 * 2.4 days; and 8 breast fed healthy term infants (BR); birth weight 3.35 f 0.14 kg; gestational age 39.8 * 0.3 wk; postnatal age 4.2 * 0.7 days. There were five males and four females in the BOT group, and five males and three females in the BR group. The study was explained to the parents of each subject and informed consent obtained.A nosepiece with a constant background flow and a screen and 0 2 concentrations, according tb methods described in detaii previously (18,19), and recording was done with a Gould Brush 480 Recorder. The ventilatory re...

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