Density-dependence of maximal expiratory flow and its correlation with small airway disease in smokers.

Density-dependence of maximal expiratory flow was measured in 110 patients prior to resection for peripheral coin lesions. The resected lung or lobe was examined morphologically and graded for emphysema, membranous bronchiolitis, and respiratory bronchiolitis. Density dependence did not decrease with increasing airway obstruction, and there was no relationship between density-dependence and peripheral airway abnormality or emphysema in the group as a whole. When patients were arbitrarily divided into those with forced expiratory volume in one second (FEV1) greater than 80% predicted (n = 80) and FEV1 less than 80% predicted (n = 30), density-dependence correlated significantly and negatively with membranous bronchiolitis in those with FEV1 greater than 80% predicted and significantly but positively in those with more advanced airway obstruction. We conclude that density-dependence of maximal expiratory flow is not an accurate predictor of peripheral airway abnormality in patients with mild to moderate air-flow obstruction.

Errors in the measurement of total lung capacity in chronic obstructive lung disease.

The standard plethysmographic method of measuring total lung capacity (TLC) has been reported to result in spuriously high estimates in patients with severe airway obstruction. The helium-dilution method is known to underestimate TLC in the same patients. To determine the magnitude of these possible errors we measured TLC by four methods in 20 patients with varying degrees of chronic obstructive lung disease and in 11 normal subjects. TLC was measured by (1) helium dilution (TLCHe); (2) a volume-displacement body plethysmograph, box volume being plotted against mouth pressure (TLCm); (3) the same body plethysmograph with volume plotted against pressure measured with an oesophageal balloon (TLCes); and (4) a radiological technique (TLCxr). In normal subjects there was no difference between TCLm (6.57 +/- 1.20) and TLCes (6.51 +/- 1.24). In the patients with chronic obstructive lung disease TLCm gave results significantly higher than those of any other method. If TLCes is taken as the closest estimate of true TLC, TLCm consistently overestimates and TLCHe underestimates TLC. There was no relationship between the degree of airway obstruction and (TLCm - TLCes) but there was between (TLCes - TLCHe) and severity of airway obstruction. We conclude that using mouth pressure in the plethysmographic measurement of TLC in patients with chronic obstructive lung disease results in consistent but slight overestimation of TLC.

Carbon monoxide in alveolar air as an index of exposure to cigarette smoke.

1. A rapid method for the analysis of CO in expired air has been developed, which is suitable for use in studies of smoking. 2. The Bohr equation has been used to calculate the mean alveolar CO partial pressure (PA,CO). 3. The values of PA,CO obtained are highly correlated with direct measurements of venous carboxyhaemoglobin (r = 0-96). 4. The method will distinguish between populations of smokers and non-smokers, and can allow the changes of CO in a smoker throughout a 12 h period to be followed. It provides a measure of the dose of cigarette smoke (vapour phase) that results from smoking a single cigarette.