Speed and Profile of the Arterial Peripheral Chemoreceptors as Measured by Ventilatory Changes in Preterm Infants

Abstract

MATERIALS AND METH ODSchemo receptor response could be determined in "healthy" preterm infants by measuring the changes in ventilation indu ced by inha lation of 100% O 2 • Subjects. We studied 13 healthy preterm infants with a birth weight of 1602 ± 230 g (mean ± SEM), a study weight of 1652 ± 260 g, a gestational age of 31 ± 1 wk, and a postnatal age of 15 ± 1 d. The study was approved by the faculty committee on the use of human subjects in research, University of Manitoba, and written parental consent was obtained from one of the parents.M ethods. We have previously described the system to measure ventilation (6, 7). Briefly, we used a nosepiece and a screen flowmeter to measure respiratory minu te volume and alveolar gases. We used a constant background flow (3 L'min) to eliminate valves and to reduce dead space. T he infant breathed through the nostril adapters and added to (expiration) or subtracted (inspiration) flow from the background flow. This background flow was electrically balan ced to an artificial zero.We monitored breath-to-breath alveolar P0 2 and Pco, using Beckman analyzers. The 95% rise times of the analyzers were 0. 16 and 0.18 s for CO2 and O2, respectively. T he EEG was monitored using a single channel with an electrode placed in the right frontal position and referenced to the left mastoid. Th e electrooculogram was recorded from eye electrodes referenced to the right ear. Oxygen saturations and ECG were used to monitor the infant' s well-being but not as an end point of this study. Sleep state was monitored according to previous criteria (4). All variables were recorded on a polygraph (model 4221, Nihon Kohden , Tokyo, Japan ).Procedure . Infants were studied on the Ohio Neonatal Intensive Care Unit (Ohio Medical Products, Madison , WI) in a neut ral thermal environment with skin abdominal temperature at 36.5 ± 0.03°C. After appropriate placement of the various electrodes and the nosepiece, infant s were allowed to sleep. Once they had been in quiet sleep breathi ng 21% O 2 for 2 min, 100% O 2 was given for I min. Minute ventilation, tidal volume, frequency, alveolar Po 2 , alveolar Pco-, inspiratory drive, and the "duty cycle" were measured breath by breath during 2 1% O2 (I S ± 5 s) and during 100% O 2 ( I min ).Data collection and analysis. We analyzed the records by hand and transferred the data to a com puter for appropriate treatment. Control values were taken from the last eight breaths preceding the adm inistration of O 2 • The speed of the response was measured from the initiation of inspiration imm ediately after the increase in fraction of inspired O2• We used a paired t test to assess the significance of the differences between control values and those obtained in response to 100% O 2 • To find the 1st breath after 100% O 2 showing hypoventilation, we used a variation of the 226 ABSTRACf. To measure the response time of the peripheral chemoreceptors, we studied 13 preterm infants [birth weight 1602 ± 230 g (mean ± SEM); gestational age 31 ± 1 wk; postnatal age 15 ± 1 d) dur...

A study of breathing pattern and ventilation in newborn infants and adult subjects

“…The decreased Ti/ Ttot in infants related primarily to a disproportionately long expiratory time. The values for inspiratory ow and Ti/Ttot are comparable to those we and others observed previously in term infants and adult subjects (10,13,(24)(25)(26). The lower values for alveolar PCO 2 in infants compared with adults during sleep probably relate to a lower bicarbonate in small infants (4,27).…”

“…Alveolar ventilation is also greater, with lower alveolar PCO 2 . This is true for preterm and term infants, and also adult subjects (8,9,10,13,(24)(25)(26). Because breathing becomes somewhat irregular during REM sleep in adults, it is likely that the clear differences between the three groups might have been less distinct in this sleep state (26).…”

“…Because breathing becomes somewhat irregular during REM sleep in adults, it is likely that the clear differences between the three groups might have been less distinct in this sleep state (26). However, from selective studies in infants and adults during REM sleep, it seems that the differences observed in quiet sleep would still be easily detectable in REM sleep (9,10,13,15,25). These are hypothetical considerations and a nal answer to the question of whether REM sleep will show unique changes between groups will have to be determined in future studies.…”

Delayed chemoreceptor responses in infants with apnoea

“…[4][5][6] Very preterm infants with apnoea and periodic breathing exhibit diminished chemoreceptor responsiveness, [7][8][9] while full term infants with OSA can exhibit either subtle changes, 10 11 or normal responses to hypercapnia. 12 It can be difficult to make a clear and unequivocal distinction between different types of apnoeas.…”