Although Vtg values were significantly higher in the asthmatic subjects, Vtg clearly did not vary with volume history in either group. Accordingly, changes in SGaw with different volume histories reflected changes in airway resistance (and presumably, therefore, bronchomotor tone). In the stable asthmatic subjects (but not the normal individuals), a significant negative correlation was found between SGawDI/SGawMVV and MW/FEVi (r=-0.39, p<0.02; Fig 2). In the asthmatic subjects, SGawDI/ SGawMW was slightly but significantly higher than in the normal group (Table 2).
All 12 asthmatic subjects had positive methacholine tests. Although age and baseline pulmonary function were similar, asthmatic subjects with M W/FEVX ratios <34.8 were more responsive to methacholine (Table 3). Consistent with the results in the overall stable asthmatic subject group, SGawDI/SGawMW ratios were also significantly higher in the individuals with lower MW/FEVi ratios (and greater methacholine responsiveness). Significant correlations were present between MW/FEV, and reactivity of the airways (rs = 0.75, p<0.05) as well as between MW/FEV! and slopes of the methacholine dose-response curves for FEVi (rs = 0.64, p<0.05) and SGaw (rs = 0.63, p<0.05). There was no significant correlation between sensitivity of the airways (PC^FEV!, PC^SGaw) and MW/ FEVi nor between sensitivity and reactivity of the airways (p>0.9). review
Our results indicate that ratios of MW/FEVj were, on average, lower in stable, nonhospitalized asthmatic subjects than in normal subjects. Depending on the criterion used to define the normal lower 95 percent confidence limit, 22.5 to 32.5 percent of our asthmatic subjects had abnormally low MW/FEVj ratios. We also found that the MW/FEVj ratio increased with age in normal individuals as well as in asthmatic subjects, a result which differs from the observations of Harber et al; the reason for this discrepancy is unclear but might be related to different subject populations in the two studies.
Figure 2. Correlation between specific conductance after a deep breath/specific conductance after maximal voluntary ventilation (SGawDI/SGawMW) and MW/FEVj in stable asthmatic subjects. The correlation is inverse (r= -0.39) and statistically significant (p<0.02); this indicates that MW/FEV, ratios were lower in asthmatic subjects whose airways narrowed after maximal voluntary ventilation.
Table 3 — Methacholine Results (Mean ± SD)
|MW/FEV, <34.8||MW/FEV, >34.8|
|Age, years||31 ±9||31 ±11|
|FEV, (% predicted)!||78 ±16||74 ±15|
|MW/FEVjt||31.1 ±2.7||40.0 ±3.8$|
|SGawDI/SGawWt||1.05 ±0.03||1.00 ±0.03*|
|PCaoFEV, (mg/ml)||0.084 ±0.069||0.275 ±0.222|
|PCMSGaw (mg/ml)||0.041 ±0.027||0.138 ±0.077$|
|FEV, dose-response (A% FEV/GMD)||-1452 ±1287||-349± 114$|
|SGaw dose-response (A% SGaw/GMD)||-2542 ± 2647||-549 ± 200$|
|Reactivity (A% SGaw/mg/ml)||-781 ±431||-180 ±149$|