Factors affecting airways conductance: a study of 752 working men.

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Abstract
Measurements of airways conductance (Gaw) and lung volume (Vtg) made in 752 men with a body plethysmograph were expressed as volume standardized airways conductance, SGaw (Gaw/Vtg), after studies of the Gaw/Vtg relationship in 671 of the subjects; this index was expressed as its logarithm for statistical reasons. Log SGaw fell as height increased in normal subjects, but there was little change in men with simple chronic bronchitis or airways obstruction. This may be due to differences in factors controlling upper and lower airway conductance which are obscured in patients by variability of the measurements. There was no advantage in considering body surface area, which combines height and body weight, as well as height alone. Log SGaw was correlated with FEV1 [forced expiratory volume in 1 sec.] only in patients with severe airways obstruction. Log SGaw fell with age, particularly in men with chronic bronchitis. The rate of fall was similar in current and ex-smokers, but nonsmokers showed no change with age. FEV1 measurements also showed a fall with age but are probably less discriminative of slight degrees of airways obstruction.