Exploring the relationship between forced maximal flow at functional residual capacity and parameters of forced expiration from raised lung volume in healthy infants

Abstract

The raised volume rapid thoraco-abdominal compression technique (RVRTC) is being increasingly used to assess airway function in infants, but as yet no consensus exists regarding the equipment, methods, or analysis of recorded data. The aim of this study was to explore the relationship between maximal flow at functional residual capacity (V'(maxFRC)) and parameters derived from raised lung volumes, and to address analytical aspects of the latter technique in an attempt to assist with future standardization initiatives. Forced vital capacity (FVC) from lung volume raised to 3 kPa, timed forced expiratory volumes (FEV(t)), and forced expiratory flow parameters at different percentages of expired FVC (FEF(%)) were measured in 98 healthy infants (1-69 weeks of age). V'(maxFRC) using the tidal rapid thoraco-abdominal compression (RTC) technique was also measured. The within-subject relationships and within-subject variability of the various parameters were assessed. Duration of forced expiration was < 0.5 sec in 5 infants, meaning that FEV(0.3) and FEV(0.4) were the only timed volume parameters that could be calculated in all infants during the first months of life, and even when it could be calculated, FEV(0.5) approached FVC in many of these infants. It is recommended that FEV(0.4) be routinely reported in infants less than 3 months of age. Contrary to previous reports, within subject variability of V'(maxFRC) was less than that of FEF(75) (mean CV = 6.3% and 8.9%, respectively).A more standardized protocol when analyzing data from the RVRTC would facilitate comparisons of results between centers in the future.

Bronchodilation in infants with malacia or recurrent wheeze

“…Assessing airway patency by means of the RVRTC technique is promising but has not yet proved to be beneficial over the RTC technique. 19 Furthermore, RVRTC technique is not standardised since it lacks consensus. 16 20 Although the RTC technique is well accepted and standardised, several disadvantages have become apparent.…”

Assessment of tidal breathing parameters in infants with cystic fibrosis

“…Tidal breathing parameters, including respiratory rate (RR), tidal volume (VT), minute ventilation (MV), and time to TPTEF as TPTEF:TE were calculated during tidal breathing. FEV0.4 was reported from the "best" flow/volume curve (defined as the technically acceptable manoeuvre with the highest sum of forced vital capacity and FEV0.4) [16,22,24]. Results were expressed both in absolute terms and as SD scores, based on measurements obtained in the healthy infants.…”

“…Manoeuvres were repeated until at least two acceptable and repeatable flow/volume curves were obtained [16,22].…”

“…Measurements of FEV0.4 were performed as described in detail previously using the raised volume technique at a lung inflation pressure of 3 kPa [16,22]. Manoeuvres were repeated until at least two acceptable and repeatable flow/volume curves were obtained [16,22].…”

Early intervention studies in infants and preschool children with cystic fibrosis: are we ready?

“…Success in obtaining technically acceptable data depends on experience [54]. Mean within-test, withinsubject coefficients of variation range from 3.4% to 4.1% for forced expired volumes (FEV) and from 7.8% to 8.9% for forced expiratory flows (FEF) [55,56]. Measurements made 1 month apart in 41 infants with CF provide evidence for good reproducibility, with a mean intraclass correlation of 0.85 and o0.9 for FEF and FEV, respectively [54].…”