Lung resistance and elastance in spontaneously breathing preterm infants: effects of breathing pattern and demographics

Reported values of lung resistance(RL) and elastance (EL) in spontaneouslybreathing preterm neonates vary widely. We hypothesized that thisvariability in lung properties can be largely explained by both inter-and intrasubject variability in breathing pattern and demographics.Thirty-three neonates receiving nasal continuous positive airwaypressure [weight 606-1,792 g, gestational age (GA) of25-33 wk, 2-49 days old] were studied. Transpulmonary pressure was measured by esophageal manometry and airway flow by facemask pneumotachography. Breath-to-breath changes in RL andEL in each infant were estimated by Fourier analysis ofimpedance (Z) and by multiple linear regression (MLR).RL_MLR (RL_MLR = 0.85 × RL_Z 0.43; r² = 0.95) and EL_MLR(EL_MLR = 0.97 × EL_Z + 8.4; r² = 0.98) werehighly correlated to RL_Z andEL_Z, respectively. Both RL(mean ± SD; RL_Z = 70 ± 38, RL_MLR = 59 ± 36 cmH₂O · s · l¹)and EL (EL_Z = 434 ± 212, EL_MLR = 436 ± 210 cmH₂O/l)exhibited wide intra- and intersubject variability.Regardless of computation method, RL was found to decreaseas a function of weight, age, respiratory rate (RR), and tidal volume(VT) whereas it increased as a function ofRR · VT and inspiratory-to-expiratorytime ratio (TI/TE). EL decreasedwith increasing weight, age, VT and female gender andincreased as RR and TI/TE increased. Weconclude that accounting for the effects of breathing patternvariability and demographic parameters on estimates of RLand EL is essential if they are to be of clinical value.Multivariate statistical models of RL and ELmay facilitate the interpretation of lung mechanics measurements inspontaneously breathing infants.