Distortion of chest movement by increased airways resistance.

The movement of the chest during breathing has been recorded in normal and asthmatic subjects by means of electronic transducers which measured changes in anteroposterior and lateral diameters. Preliminary studies showed that exercise-induced bronchoconstriction caused distortion of the movement of the diameters in relation to each other and to volume change recorded at the mouth. Because of the thoracic gas compression which occurs during breathing, volume change at the mouth does not represent the change in chest volume and further studies were therefore undertaken in a whole-body plethysmograph. These studies showed that the addition of a resistance to the airway of a normal subject distorted the movement of one diameter (usually the anteroposterior) in relation to the other and to volume. With exercise-induced asthma, the movement of both diameters was affected with the anteroposterior lagging behind the volume change. There was an approximate linear relationship between the degree of distortion and airways resistance in the asthmatic subjects and in one normal subject. The physical sign of costal margin paradox could be related to the severity of the obstruction. Paradoxical movement of the costal margin, with a decrease in transverse diameter relative to anteroposterior diameter, is a common physical sign in patients with obstructive lung disease (Campbell, 1969) but the observer variation in reporting its presence is considerable (Godfrey et al., 1969a). It was noted in 8 out of 16 patients with chronic obstructive lung disease, but the correlation with the severity of airways obstruction was poor (Godfrey, Edwards, Campbell, and Newton-Howes, 1970). On the other hand, Agostoni and Mognoni (1966) found that distortion of chest movement occurred in normal adults when breathing through a resistance, and the degree of distortion could be related to transpul-monary pressure changes. Connolly and Godfrey (1969) reported the results of preliminary studies of asthmatic children in whom reversible distortion of chest movement could be related to peak expiratory flow rate. In all the previous studies, chest movement was assessed from the tidal volume change recorded at the mouth. Now it is well known that this does not record correctly the changes of chest volume owing to the compression of gas during breathing, especially in the presence of airways obstruction (Ingram and Schilder, 1966). The only reliable way to record changes of chest volume in such circumstances is with a whole-body plethysmograph. Simple displacement transducers can be used to record changes in chest diameter (Godfrey, Kagle, …