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The biphasic ventilatory response to hypoxia in preterm infants is not due to a decrease in metabolism
Author(s) -
Rehan Virender,
Haider A. Zia,
Alvaro Ruben E.,
Nowaczyk Bogdan,
Cates Donald B.,
Kwiatkowski Kim,
Rigatto Henrique
Publication year - 1996
Publication title -
pediatric pulmonology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.866
H-Index - 106
eISSN - 1099-0496
pISSN - 8755-6863
DOI - 10.1002/(sici)1099-0496(199611)22:5<287::aid-ppul1>3.0.co;2-i
Subject(s) - hyperventilation , hypoxia (environmental) , medicine , pco2 , gestational age , respiration , oxygen , hypoventilation , respiratory minute volume , hypoxic ventilatory response , tidal volume , anesthesia , ventilation (architecture) , metabolism , endocrinology , respiratory system , biology , chemistry , pregnancy , anatomy , mechanical engineering , organic chemistry , engineering , genetics
The mechanism underlying the biphasic ventilatory response to hypoxia in neonates is poorly understood. Because alveolar P CO2 (P ACO2 ) decreases and remains low during hypoxia, it has been argued that a decrease in metabolism may occur. We hypothesized that if the late decrease in ventilation during hypoxia is due to a decrease in CO 2 production, an increase in P ACO2 should abolish it. We studied 27 preterm infants [birth weight, 1,700 ± 41 g (mean ± SEM); study weight, 1,760 ± 36 g; gestational age 32 ± 0.2 weeks; postnatal age, 17 ± 1 days]. A flow‐through system and Beckman analyzers were used to measure ventilation and alveolar gases. Metabolism was expressed as changes in oxygen consumption. Infants were studied randomly during hypoxia alone (15% O 2 + N 2 , n = 55) and during hypoxia plus CO 2 , (0.5% CO 2 , n = 30; 2% CO 2 , n = 10). Each experiment consisted of 2 minutes of control measurements (21% O 2 ), 5 minutes of measurements during hypoxia alone or hypoxia plus CO 2 , followed by 2 minutes of recovery (21% O 2 ). We found a biphasic response to hypoxia with or without CO 2 supplementation, the percent change in ventilation from initial peak hyperventilation to late hypoventilation at 5 minutes being ‐16 ± 2 on 15% O 2 ; ‐9 ± 3 on 15% O 2 ; + 0.5% CO 2 and ‐15 ± 9 on 15% O 2 ; + 2% CO 2 ; (P < 0.05).The decrease in ventilation was primarily due to a significant decrease in frequency; tidal volume increased. Oxygen consumption decreased similarly with the various inspired gas mixtures during hypoxia. These findings indicate that the decrease in ventilation during hypoxia is unlikely to be solely due to a decrease in metabolism since the late decrease in ventilation following initial hyperventilation still occurred despite the elimination of a fall in P ACO2 . We speculate that the mechanism underlying the late decrease in ventilation is likely of central origin, probably mediated through the release of inhibitory neurotransmitters. Pediatr Pulmonol. 1996; 22:287–294. © 1996 Wiley‐Liss, Inc.