A simple method to monitor performance of forced vital capacity

Abstract

The forced vital capacity (FVC) maneuver is the most common lung function test. One of its major prerequisites is that it be performed with sufficient effort to achieve the maximal flows that are due to expiratory flow limitation. To verify this, in nine normal subjects, short (0.25-s) pulses of negative pressure (-5 to -20 cmH2O) were applied at the mouth at different times (0.25-1 s) after the onset of 1) FVC maneuvers and 2) vital capacity expirations with submaximal expiratory efforts (SVC). All subjects were experienced in FVC maneuvers. With FVC, the expiratory flow did not change with application and removal of negative-pressure pulses, apart from brief flow transients, mainly reflecting displacement of air from the compliant oral and neck structures. With SVC, flow increased throughout the application of the negative-pressure pulses. Thus application of pulses of negative pressure provides a simple method for on-line recognition of whether an FVC maneuver is performed with sufficient effort to achieve flow limitation.

Performance of forced expiratory manoeuvre in children

“…HYATT et al [5] originally estimated that in normal adults effort dependence encompassed 30±50% of FVC. This estimate was subsequently decreased to 20±30% FVC [6,19], which is close to the values obtained in the older children in the present study, and to~13% FVC in well trained adults [7].…”

“…The poorer coordination of specialized motor acts in young children is consistent with the observations that tPEF (table 1) was markedly longer than that observed in normal, experienced adults (11625 ms) [7], and that application of NEP significantly decreased tPEF in those children who exhibited longer tPEF under control conditions. It should also be noted that the children had no previous experience in FVC manoeuvres, and that lack of experience can affect the performance of the FVC manoeuvres in adults [7].…”

“…for online recognition of whether the FVC manoeuvre is performed with sufficient effort to achieve FL over most of the expired volume [7]. In younger children the volume range over which FL occurs is considerably smaller ( fig.…”

“…In the past, there was no online method available to assess whether expiratory FL was reached during the forced expiratory manoeuvre. Recently, however, the negative expiratory pressure (NEP) technique has been successfully applied in normal adults to assess FL during forced vital capacity (FVC) manoeuvres by VOLTA et al [7]. They showed that adults with considerable previous experience in lung function testing performed FVC manoeuvres with sufficient effort to achieve FL over most of the vital capacity.…”

“…They showed that adults with considerable previous experience in lung function testing performed FVC manoeuvres with sufficient effort to achieve FL over most of the vital capacity. In contrast, in subjects without previous experience multiple efforts may be required to obtain acceptable FVC manoeuvres [7].…”