During recent years there has been increasing interest in the measurement of tidal breathing parameters, such as the time to reach peak tidal expiratory flow as a proportion of total expiratory time (TPTEF:TE), and their application to population-based studies of the determinants of early respiratory morbidity. However, little is known about factors influencing the within and between-subject variability of these parameters. This study examines the influence of sedation on TPTEF:TE, estimates the optimal number of breaths and breath epochs required to measure TPTEF:TE, and assesses short-term repeatability of this parameter during the first year of life, taking account of age-related differences. Measurements were made in 266 healthy infants and young children (1 d to 19 mo old). Mean (SD) TPTEF:TE fell from 0.49 (0.11) in the first 2 wk of life to 0.34 (0.09) by 5 to 8 wk, remaining similar thereafter. Sedation with triclofos sodium (75 mg/kg) had no significant effect on TPTEF:TE, which was 0.33 (0.10) in 23 unsedated 6-wk-old infants and 0.32 (0.08) in 49 sedated infants of similar age and weight (95% CI for the difference: -0.05, 0.04). At least 10 breaths in each of two separate epochs from each infant were required to provide a representative estimate of TPTEF:TE. The mean (SD) difference between repeat measurements made 5 to 108 min apart was 0.02 (0.08) in 34 infants younger than 6 wk of age (95% limits of agreement: -0.15, 0.18) and -0.01 (0.04) (95% limits of agreement -0.09, 0.08) in 30 infants 6 wk and older.(ABSTRACT TRUNCATED AT 250 WORDS)

During recent years there has been renewed interest in noninvasive methods of assessing respiratory function in infants, since the use of face masks and pneumotachographs (PNT) have both been shown to affect breathing pattern [1]. Respiratory inductive plethysmography (RIP) is a means of measuring breathing movements without any connections at the airway opening, and therefore has numerous potential applications in infants, including prolonged respiratory monitoring in the intensive care unit or postoperatively. RIP uses inductance coils within elasticated bands to measure the respiratory excursion of the ribcage (rc) and abdomen (abd). The respiratory system is assumed to move with two "degrees of freedom", so that changes in inductance are proportional to changes in ribcage and abdominal volume. The weighted sum of the rc and abd is therefore proportional to the tidal volume (VT). Studies using RIP have increased our understanding of respiratory control and mechanics [2,3], including the fact that infancy is characterized by abdominal breathing [4], and that halothane anaesthesia is associated with a loss of ribcage recruitment [5].Whereas uncalibrated RIP is a valuable means of assessing both respiratory timing and various qualitative aspects of rc and abd asynchrony [6][7][8], calibration is essential if quantitative changes in ventilation are to be assessed. Such calibration, which involves a two-stage process of determining the relative contributions of rc and abd to each breath and then ascertaining a proportionality coefficient in order to scale the weighted sum to actual tidal volume, has, however, proved to be a major challenge when using RIP in infants. Three main methods of calibration have been proposed, as outlined below.1) The rc and abd signals are compared with simultaneous recordings of VT from a PNT, according to the equation:where Vrc is the inductance (voltage) of the rc signal and Vabd is that of the abd signal. Providing VT is measured over a large enough number of breaths, a proportionality coefficient K can then be derived using a least squares or graphical solution to the equation. However, since this always requires the simultaneous use of a PNT, the advantages of RIP are at least partially lost.2) In 1987, KONNO and MEAD [9] described the isovolume manoeuvre, as a means of determining the relative contribution of rc and abd without a PNT. This requires the subject to shift gas gently between the rc and abd during a breath hold or airway occlusion, thereby producing paradoxical movements of the two compartments. Since VT does not change, equation (1) Measurements were made during spontaneous (SV) and intermittent positive pressure (IPPV) ventilation, sighs and airway occlusions. The VT,DIF was the difference between VT,QDC and VT,PNT (%VT). The contribution of the ribcage (rc) to VT,QDC (%rc) and the thoracoabdominal phase lag were also derived. Twenty-eight infants, mean (SD) age 14.0 (6.2) months were studied.VT,QDC represented VT,PNT most closely when Š20 breaths were analysed. The...

This study examines the association between the time taken to achieve peak tidal expiratory flow as a proportion of total expiratory time (tPTEF:tE) and specific airways conductance (SGaw) in healthy infants and those with prior physician diagnosed, associated, lower respiratory illness with wheezing (prior LRI) during the first year of life. We compared tPTEF:tE and SGaw, the latter estimated during both initial inspiration (ll) and end-expiration (EE), in 168 infants (94 males), measured on 220 occasions. Mean (range) tPTEF:tE was 0.321 (0.150-0.522) in 73 healthy infants aged less than 3 months (mean, 7.8 weeks), in whom mean (range) EE SGaw and plethysmographic thoracic gas volume at functional residual capacity (FRCpleth) were 2.47 s-1 kPa-1 (0.6-5.8) and 141 mL (87-204), respectively. Both tPTEF:tE and EE SGaw were significantly lower in older infants with prior LRI (n = 79; mean age, 50.0 weeks) compared to a similarly aged group of healthy infants (n = 68; mean age, 48.5 weeks), the mean difference [95% confidence intervals (CI)] being -0.039 (-0.013, -0.064) and -0.48 s-1 kPa-1 (-0.24, -0.72), respectively. A significant but weak association between tPTEF:tE and EE SGaw was found among infants above 3 months of age, irrespective of prior wheezing status. However, this relationship was not significant in healthy younger infants, in whom a significant but weak association with FRCpleth was found. Further work is needed to elucidate the factors influencing tidal expiratory flow patterns in infancy.

Single-breath technique (SBT) measurements of total respiratory resistance (Rrs) were compared with plethysmographic measurements of airway resistance (Raw) in healthy infants < or = 13 wk of age (Group 1; n = 49) and > 13 wk of age (Group 2; n = 37) and in infants > 13 wk of age with prior wheeze (Group 3; n = 49). A significantly higher percentage of Rrs (19%) than of Raw (2%) measurements were technically unsatisfactory, alinearity of the flow-volume curve accounting for 54% of Rrs failures. Although both Rrs and Raw were significantly higher in Group 3 infants, between-subject variability was wide in all groups. Rrs was significantly higher than initial expiratory (IE) Raw in all groups. Mean difference Rrs-IE Raw (95% CI) values were 1.98 (1.51, 2.48), 1.29 (0.96, 1.62), and 1.97 (1.56, 2.38) kPa.L-1.s for Groups 1, 2, and 3, respectively. Significant but smaller differences were seen for end-expiratory (EE) Raw in Groups 1 and 2 but not in Group 3. Mean difference Rrs-EE Raw (95% CI) values were 0.68 (0.11, 1.26), 0.55 (0.19, 0.92), and 0.31 (-0.06, 0.69) kPa.L-1.s for Groups 1, 2, and 3, respectively. Despite wide between-subject variability in Rrs and a relatively high failure rate, the SBT is simple to use, and it may be applicable to epidemiologic studies. However, clinical applications in individual infants may be limited by failure to detect the dynamic changes in resistance throughout the breath evident from plethysmographic studies.

Chloral hydrate is frequently used to sedate infants for lung function testing. While no effect on respiratory function has been demonstrated, a recent study has reported a fall in oxygen saturation (Sa O 2) following sedation in wheezy infants. This study was designed to assess the effects of the closely related but less gastrically irritant drug triclofos sodium on respiratory rate (RR), heart rate (HR), and Sa O 2 in infants without cardiopulmonary disease. Paired measurements using respiratory inductance plethysmography and pulse oximetry were obtained in 10 infants (4–19 months of age) during natural and sedated sleep. Following sedation with triclofos, mean RR rose by 1.9 breaths min−1 (95% confidence intervals [Cl] of the mean difference: 0.13–3.7 min−1). Mean heart rate rose by 5.5 beats min−1 (95% Cl: −0.9–11.9 min−1). Mean Sa O 2 fell by 0.68% (95% Cl – 1.8–0.45%). None of these changes are considered to be of clinical importance, and only the change in RR reached statistical significance at the 5% level. Pediatr Pulmonol 1991; 10:40–45.