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

Abstract

Experimentally modified breathing pattern in human subjects, by varying the inspired gas mixture or administering different neuromodulators, has been studied extensively in the past, yet unmodified breathing has not. Moreover, most data refer to infants during sleep and adults during wakefulness. We studied the baseline breathing pattern of preterm infants [n= 10; GA 30 (27–34) wk (median, range)]; term infants [n= 10; GA 40 (39–41) wk)], and adult subjects [n= 10; age 31 (17–48) y)] during quiet sleep. A flow‐through system was used to measure ventilation. We found: (i) instantaneous ventilation was 0.273 ± 0.006, 0.200 ± 0.003, and 0.135 ± 0.002 Lmin‐1.kg‐1 in preterm, term infants, and adult subjects; the coefficients of variation were 39%, 25%, and 14% (p <0.01). The greater coefficient of variation in neonates compared to adults related to increased variability in Vt (39% and 25% in preterm and term infants vs 14% in adults; p < 0.01) and f (39% and 22% vs 9%; p < 0.01). The major determinant of frequency in preterm infants was Te (81% variability), Ti varying less (25% variability); (ii) VT/Ti decreased and Ti/Ttot increased with age; (iii) the higher breath‐to‐breath variability in preterm infants was associated with larger changes in alveolar PCO2 and a larger variability in O2 saturation than later in life. We conclude: (i) the high breath‐to‐breath variability in frequency in preterm infants closely relates to variation in Te; (ii) decreased effective inspiratory timing (Ti/Ttot) in preterm infants compared with adults likely reflects their high pulmonary impedance; and (iii) greater breath‐to‐breath variability in ventilation in neonates with large variations in alveolar PCO2 and O2 saturation remains when compared with values in the sleeping adult. We speculate that high variability in Te early in life represents an effort to maintain lung volume through increased post‐inspiratory diaphragmatic activity and increased upper airway resistance in an attempt to avoid collapse due to poor chest wall recoil.

Variability of End-Expiratory Lung Volume in Premature Infants

“…In animals, a positive long-term correlation of EELV was found in anesthetized rats, suggesting that EELV had fractal properties [19] . In infants, variability of EELV has not been reported previously, whereas variability of respiratory timing and amplitude has been shown to be greater in premature infants in comparison to older infants or adults [15] . Breathing variability is not purely random; a long-range correlation that follows a power-law distribution has been demonstrated for VT and respiratory timing in infants [6,16] .…”

“…The active control of EELV implies the flow-breaking action of the larynx [23] and of the diaphragm by its tonic activity [22] , and the respiratory timing pattern with relatively short TE [24] . Both tonic diaphragmatic activity and TE have high intrinsic variability [15,22] . In the present study, important variations of TE and VT were also observed, which may have favored EELV fluctuations.…”

“…Autocorrelation is higher when a respiratory load is added [3] or in certain respiratory diseases [4,5] . During infancy, VT, inspiratory time (TI), and expiratory time (TE) are also highly variable [14,15] , and presence of autocorrelation has been observed [6,16] .…”

“…Tonic diaphragmatic activity has a high intrinsic variability [22] , which can be modified by an external load [25] . Variability of TE is a major determinant for timing variability in infants [15] . The variations of these two key parameters suggest that resultant EELV likely presents fluctuations.…”

Obstructive Sleep Apnea in Infants

“…During NREM sleep, the coefficient of variation of minute ventilation is highest in preterm infants (39%), compared with term infants (25%) and adults (14%) (49). Further, peripheral chemoreceptor function, as measured by a 100% oxygen challenge, demonstrates a much larger reduction in minute ventilation in infants (38%) compared with adults (6%), thus contributing to infant ventilatory instability (50).…”