Dependence of maximal flow-volume curves on time course of preceding inspiration in patients with chronic obstruction pulmonary disease.

Abstract

Thirteen patients with chronic obstructive pulmonary disease (COPD) performed forced vital capacity (FVC) maneuvers either immediately after a rapid inspiration (maneuver 1) or after a slow inspiration with a 4- to 6-s end-inspiratory pause (maneuver 2). Seated in a body plethysmograph, they breathed through a pneumotachograph. Inspirations were initiated from resting end-expiratory lung volume. Abdominal muscle activity was recorded by means of surface electrodes. With maneuver 1: (1) expiratory flows were 20 to 40% larger in the volume range 10 to 95% FVC; (2) peak expiratory flow was on average 30% higher; and (3) FEV1, expressed as percent of FVC, increased by about 8%. No substantial differences in the pattern of abdominal muscle activity occurred between maneuvers. The dependence of maximal flow-volume curves on the time course of the preceding inspiration is probably related in part to the viscoelastic elements present within the respiratory system, which, stretched during rapid inspirations, increase the effective elastic recoil during the FVC maneuver 1. This cannot occur with maneuver 2, because of stress relaxation of the viscoelastic elements during the 4- to 6-s breathhold preceding the FVC maneuver. Other factors (e.g., time constant inequality) might also be involved. In any case, the results imply that the inspiratory maneuver prior to FVC must be standardized.

Bronchodilation test in COPD: effect of inspiratory manoeuvre preceding forced expiration

“…2. Indeed, it has been shown that even substantial differences in apparently maximal voluntary expiratory efforts play little or no role in COPD patients [5] and time dependency of FVC manoeuvres is also observed when lung volume changes are assessed plethysmographically [4,5]. The present results, in line with previous findings [4,6], suggest that loss of elastic recoil during breath-holding at full inspiration, i.e.…”

“…2 under baseline conditions 76% of patients could be classified as responders, whereas with the opposite combination the number would drop to 2%. These observations, which are in line with those performed on a small number of COPD and asthmatic patients in the laboratory [5,6], indicate that FVC manoeuvres before and after bronchodilator administration for the assessment of bronchodilator responsiveness must be made under standardised conditions even in the clinical setting under routine conditions. From a practical point of view, it is important to note that standardisation does not imply the choice of the type of manoeuvre.…”

“…2 and these differences persisted after administration of an inhalatory b 2 -agonist (table 2). These results, when compared to those obtained in the laboratory on normal subjects and COPD patients [4,5], indicate that the dependence of maximal flow volume curves on the volume-time course preceding the FVC manoeuvre manifests itself in a similar manner in the clinical setting under routine conditions. Several mechanisms could be responsible for the higher maximal expiratory flows during manoeuvre no.…”

“…1 than manoeuvre no. 2, both in normal subjects and COPD patients [5]. The fact that the relative change in FEV1, as well as in FEFs and MMEF, between manoeuvres no.…”

“…The procedure of FVC measurement and its reproducibility have been described in detail previously [1][2][3]. In the early 1990s, D9ANGELO and coworkers [4,5] showed that FEV1, peak expiratory flow (PEF) and the forced expiratory flow at 25, 50 and 75% of FVC both in healthy subjects and in chronic obstructive pulmonary disease (COPD) patients, are affected by the speed of the inspiration and duration of the end-inspiratory pause before the forced expiration. In particular, FEV1 was found to be, on average, 5 and 8% higher in healthy subjects and COPD patients, respectively, when FVC was performed immediately after a rapid inspiration rather than a slow inspiration with an end-inspiratory pause of 4-6 s. Therefore, the suggestion was made that a more precise standardisation of the FVC manoeuvre was required.…”