Effects of technique and analytic conditions on tidal breathing flow volume loops in term neonates

The tidal breathing flow volume loop (TBFVL) may provide objective assessments of infant airway function. We examined whether infant biologic variability and technical limitations of commercial equipment might affect tidal breathing indices. TBFVLs were obtained in 79 sleeping, healthy, 1-5-day-old infants, divided into two groups: 1) TBFVLs were obtained immediately after face mask placement, i.e., within 5-20 sec (Group A), or 2) after a delay of 2-3 min following face mask placement (Group B). Both tidal volume (VT) and respiratory rates (RR) were significantly lower (25% and 20%, respectively) in Group A than in Group B. VT mean (SD) was 4.45 (0.93) ml/kg for Group A and 6.09 (1.11) ml/kg for Group B (P < 0.0001); RR was 48.4 (12.2) min-1 and 60.0 (15.60) min-1 for Groups A and B, respectively (P < 0.0003). The time to peak expiratory flow as a ratio of total expiratory time (tPTEF:tE), purported to be a useful index of airway obstruction, was also significantly (P < 0.0001) attenuated in TBFVLs obtained immediately after face mask placement; tPTEF:tE was 0.26 (0.09) and 0.37 (0.05) in Groups A and B, respectively. Reproducibility of tPTEF:tE was affected by the timing of recordings. Intraindividual coefficients of variation were greater in Group A (36.53%) than Group B (18.82%). Similarly, significant differences were observed in mean value and variability of other indices of airway function between Groups A and B. Although they are easy to perform, we conclude that tidal breathing analyses may be significantly complicated by simple differences in measurement conditions.