Lung mechanics in subjects showing increased residual volume without bronchial obstruction.

Abstract

Fourteen subjects showing an increase of residual volume (RV) Residual volume is determined by the point at which the pressure produced by the muscles of expiration is dissipated entirely on the elastic recoil of the respiratory system. Increase in residual volume may result from loss of elastic recoil, any form of airways obstruction, or both. The purpose of this work was to study some aspects of lung mechanics in subjects with an increased residual volume in the absence of any evidence of bronchial obstruction. MethodsWe examined 14 patients, 13 men and one woman, with a mean age of 45-5-+8-92 years (range 29-56 yr). These subjects complained of minor respiratory disability, mainly slight exertional dyspnoea. All save one were smokers-three smoked less than 10 cigarettes per day, the remainder 15-20.Clinical examination showed no signs of cardiac disease or bronchial obstruction and all chest radiographs were considered to be normal. Study of respiratory function showed only an increase, in comparison with normal values,' of residual volume measured by plethysmography, the average increase being 5814%-+-26-33 (range: +32-104%).Address for reprint requests: Dr S Vulterini, Divisione di Medicina Generale, Ospedale Fatebenefratelli, Isola Tiberina, Rome, Italy.Vital capacity (VC), forced expiratory volume in one second (FEV1), forced expiratory volume in one second/vital capacity ratio X100 (FEV,/ VC), and airways resistance (Raw) were close to predicted values in every patient (table 1).Vital capacity and FEV1 were measured with a pneumotachograph (Jaeger) coupled to a pressure transducer (Jaeger) and were obtained by integration of the flow measured at the mouth and recorded on an X-Y recorder.

Pathophysiology of changes in absolute lung volumes

“…Similarly, patients have been reported to have significant elevations of RV without abnormalities of FEV1, presentations that were attributed to early emphysema [104,105]. In asthma, "isolated" elevations of RV may also occur in the absence of recognizable decrements in maximal flow rates [106].…”

Respiratory mechanics and lung structure in rodent models of emphysema

“…Several studies using animal models of emphysema have pointed out that the tissue destruction manifested in elevations in TGV and decreases in elastance are not associated with increased airway or pulmonary resistance (2,4,5,9,33), and some observations on human emphysema also indicate that airspace enlargement and airflow limitation do not necessarily combine (10,38,47). In this context, the changes following elastase treatment observed in the present study may characterize an initial or mild degree of emphysema where the loss of alveolar attachments, which must have accompanied the marked increase in both alveolar size and lung volumes, is compensated by new elastic equilibria within the lung parenchyma itself as well as between the lung and chest wall so that the patency of the airways is retained.…”

“…Specifically, the physiological characterization of emphysema requires the measurement of pulmonary or respiratory mechanics (18,39). In clinical studies, absolute lung volumes such as residual volume (RV), functional residual capacity, or total lung capacity (TLC), as well as their ratios are used to characterize the emphysematous changes (14,47,49). To gain insight into the pathogenesis and progression of the human disease, various small animal models of emphysema have been developed (11,25,32,41,45).…”

“…The low-frequency respiratory impedance (2-19 Hz) was measured at 3 cmH 2 O PEEP with optimal ventilation waveforms 47 by measuring the piston volume displacement and cylinder pressure while delivering 2-s oscillatory volume perturbations to the airway opening. Respiratory compliance (C=1/H), R N and G were calculated by fitting the constant-phase model to input impedance 9 .…”

Crackle sounds and lung recruitment

“…In clinical studies, absolute V L s [such as the residual volume (RV), FRC and total lung capacity (TLC)] and their ratios are used to characterize emphysematous changes [47][48][49]. To gain an insight into the pathogenesis and progression of the human disease, various small animal models of emphysema have been developed [45,[50][51][52][53].…”