The MW/FEV, Ratio in Normal and Asthmatic Subjects: Asthmatic airways

11 Oct

In our study, there were also significant correlations between MW/FEV! and the effects of lung volume history as well as between MW/FEVi and response to methacholine.
Previous studies have shown that MW/FEV! values are often reduced in subjects with poor muscle strength or endurance, extrathoracic upper airway obstruction, and/or in the presence of suboptimal effort during pulmonary function testing. The FEV! value has been multiplied by a constant factor (eg, FEVX x 37.5) to predict maximal ventilation during exercise. Cold and/or dry air bronchoprovocation challenges often are performed using a sustained period of hyperventilation, the magnitude of which may be estimated as FEVi X a constant factor. Our study demonstrates that asthma is another cause of reduced ratios of MW/FEV!. This has clinical implications since the finding of a low MW/FEVj ratio might otherwise be attributed to other causes, such as suboptimal effort. In addition, maximal ventilatory capacity cannot be well predicted by multiplying the FEVi by a constant (in asthmatic subjects or normal individuals). Harber and colleagues have also concluded that MW is not well predicted by multiplying FEVi by a constant value.

In our asthmatic subjects, a single DI often resulted in reduced airway caliber, as indicated by SGaw/ SGawDI ratios >1.0. In normal individuals, the reverse was true. Both results are consistent with previous data. However, in this study, we also found that repetitive DI (during MW maneuvers) caused reduction in airway caliber (compared with a single DI) in asthmatic subjects but not in normal individuals (Table 2). The magnitude of reduction in SGawMW correlated with the MW/FEVi ratio (Fig 2), suggesting that an altered response to DI was associated with low ratios of MW/FEV,.