The present investigation of 500 women is an extension of a study of 298 women reported in 1971. The study as a whole had been designed to investigate 500 women as it was considered likely that this number would be required for definitive conclusions to be made. The impression was reinforced by preliminary analysis of data from the first 100 women examined where no statistical differences were shown between the smokers and nonsmokers in clinical findings, sputum examinations and pulmonary function tests. After 200 women had been examined, differences became apparent and, in the published report of 298 women, many differences between the smokers and nonsmokers were found. It was shown that, with increase in cigarette smoking, the prevalence of cough, sputum production, wheezing and shortness of breath increased progressively. Abnormalities on physical examination of the chest were found more frequently in smokers than in nonsmokers. Cytologic abnormalities were found in the sputum but differences between smokers and nonsmokers were not statistically significant. The results of tests of ventilatory function and of gas transfer (during exercise ) were lower in smokers than in nonsmokers.
The present report of examinations on 500 women confirms most of the findings described in the previous paper dealing with 298 women but some differences are shown. There are now statistical differences in the prevalence of various cell types in the sputum where these differences were shown only as trends in the previous report.
Volunteers for the study came mainly from large commercial firms and women only between the ages of 25 and 54 years were accepted. Women with asthma, heart disease, obesity or chest wall deformities were excluded.
The women were divided into five groups according to smoking habit. Nonsmokers were those who had never smoked cigarettes. Ex-smokers were those who had not smoked for at least one year (13 had not smoked for 1 year, 8 for 2 years, 10 for 3 years and 31 for more than 3 years). Smokers were divided into three groups: light smokers were those who smoked 70 or fewer cigarettes per week, moderate smokers smoked 71 to 140 cigarettes per week, and heavy smokers more than 140 cigarettes per week. The women were divided into smoking categories according to the present (and probably the most reliable) smoking situation. The mean number of cigarettes smoked was 40 for the light smokers, 117 for the moderate smokers, and 189 for the heavy smokers. The mean number of years of smoking was 13.2 years for the ex-smokers, 14.2 years for light smokers, 16.0 years for the moderate smokers, and 17.7 years for the heavy smokers. There were 183 nonsmokers, 62 exsmokers, 40 light smokers, 92 moderate smokers, and 123 heavy smokers. There was a fairly even age distribution in all groups (Table 1). Married to single women were in the proportion of approximately 2:1 in all groups. More than 80 percent of the volunteers had lived most of their lives in the central parts of towns with populations greater than 100,000.
The order of investigation was an extensive history and physical examination, sputum specimen collection, fluoroscopy, pulmonary function tests, induced sputum specimen collection, and chest roentgenograms (posteroanterior and lateral films).
The details of the investigation have been previously reported. The clinical examinations were performed, in most cases, by a research associate (Dr. J. T. Suero). Sputum induction was done by breathing a 45°C mist of 20 percent propylene glycol in 15 percent saline solution for as long as 30 minutes.
The pulmonary function tests were selected to give information about the abnormalities most likely to result from smoking, but the tests were selected also on the basis of causing the least discomfort in order to maintain the flow of volunteers. Blood gases were measured on arterialized blood from a finger. Blood oxygen tensions were measured with the use of an oxygen micro-electrode and, for the first 300 women, pH and carbon dioxide tension were estimated in the Astrup Micro Equipment but, for the last 200 volunteers, a Coming model 16 gas analyzer was used. Forced vital capacity, FEVi, and maximal mid-expiratory flow rate were calculated from the best of at least three single breath tracings recorded by use of a Stead Wells spirometer. A treadmill exercise test was performed by the volunteer walking at 1.5 mph up a 4 percent grade. Measurements were made during the fifth minute of exercise. Ventilation, oxygen consumption, steady-state pulmonary diffusing capacity for carbon monoxide, end-tidal carbon dioxide tension, arterial oxygen saturation (using a ear oximeter), and pulse rate were recorded. Airway resistance was measured in a body plethysmograph and the results were expressed also as specific conductance. The airway resistance measurements were repeated after the volunteer inhaled dust containing carbon particles (8m to 12p in size, 1.6 X particles) and repeated again following a further inhalation of 8.0 xlO particles.
To examine differences among the groups, an analysis of covariance was performed on the data for each of the pulmonary function tests; allowance was made for the effects of variation between subjects in age, height and weight. Further comparisons were made between the mean values of the test results in different groups by t tests. In analyzing the clinical data, the exact test of Fisher was used to show differences in the different groups. The prevalence of various cells in the sputum was analyzed by analysis of co-variance and further comparisons were made between the test results in different groups by t test.
Table 1—Smoking Habit and Age Distribution of 500 Women
|Age (yrs)||Nonsmokers||Ex-smokera||Light Smokers <71 cig/wk||Moderate Smokers 71-140 cig/wk||Heavy Smokers > 140 cig/wk