Normal Range of Methacholine Responsiveness in Relation to Prechallenge Pulmonary Function: Results

Between April 1984 and June 1990, 1,410 men reported for at least one examination. Two hundred fifteen subjects were lifetime nonsmokers and denied any history of respiratory illness or symptoms. Regression analysis restricted to these 215 subjects yielded the following equations:
Predicted FVC (L) = -4.46 + 0.155 height (in) – 0.0324 age (yrs)
Predicted FEV, (L) = – 1.34 + 0.0976 height (in) – 0.0326 age (yrs)
Predicted FEV,/FVC ratio (%) = 137 – 0.655 height (in) – 0.184 age (yrs)
The distribution of FEVl (percent predicted) and FEVj/FVC ratio (percent predicted) among these 215 men revealed that only 5 percent had values less than 77 percent predicted and 86 percent predicted, respectively. These values were chosen as the lower limits of normal FEVX and FEVj/FVC ratio for this analysis.
Of the 1,410 subjects who were examined during this time period, 105 men were ineligible for methacholine challenge testing because of cardiovascular disease or prechallenge FEVj less than 60 percent of predicted. Of the 1,305 eligible subjects, 1,024 (78 percent) performed at least one acceptable methacholine challenge. Acceptable challenge data were not obtained from the remaining 281 subjects because of unacceptable subject performance of aerosol inhalations or forced expiratory maneuvers (n = 40), refusal to undergo or to complete challenge (n = 224), physician decision to stop test because of minor side effects or discomfort (n = 7), or technician error and miscellaneous other reasons (n = 10). www.mycanadianpharmacy.com

Of the 1,024 subjects with acceptable methacholine challenge data, 841 had a FEV, greater than or equal to 77 percent predicted and a FEV,/FVC ratio greater than or equal to 86 percent predicted, ie, in the normal range as defined above. Three subjects experienced a 20 percent or greater drop in FEV, after inhaling diluent (phenol-buffered saline solution) and are excluded from further analyses. Characteristics of the 838 subjects included in further analyses, as well as those excluded, are given in Table 1. As expected on the basis of the exclusion criteria employed, the excluded subjects have lower pulmonary function and higher prevalences of smoking and respiratory symptoms than the included subjects. Among the 838 subjects with normal FEV, and FEV,/FVC ratio, 547 (65 percent) denied any history of respiratory illness or chronic respiratory symptoms. The PD20FEV, was significantly correlated with prechallenge FEV, (percent predicted) among these 547 subjects (Spearman correlation coefficient = 0.35, p < 0.0001). Among these 547 subjects, the fifth percentile of PD20FEV, (ie, the value of PD20FEV, which has 5 percent of the measurements below it) was 8.3 (Xmol).

Table 1—Characteristics of 1,410 Male Normative Aging Study Subjects

Characteristic Included in Analysis (n = 838) Excluded from Analysist (n = 572)
Age, vr 60.5 (7.7) 61.3 (8.1)
Height, cm 172.0 (6.6) 172.0 (6.4)
FVC’, percent predicted\ 99.4 (12.4) 83.4 (17.7)
FEV,, percent predicted| 98.9 (11.9) 89.1 (16.3)
FEV/FVC 0.80 (.05) 0.75 (.09)
Smoking status
Current 9.4 22.7
Former 53.0 53.7
Never 37.6 23.6
Asthma
Yes, still 1.1 1.9
Yes, in past 2.3 3.5
Never 96.7 93.5
Missing 1.0
Persistent wheeze
Yes 5.1 12.8
No 94.7 85.8
Missing 0.1 1.4
Ever had attack of
wheeze and dyspnea
Yes * 3.6 7.9
No 94.7 89.3
Missing 1.7 2.8

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