resistance. The technique has been validated by comparison with cadavers and computerized tomography (Hilberg et al., 1989), but much more extensive clinical trials are needed to evaluate this technique for clinical use.
Nasal lavage can be readily performed following nasal inhalation challenge. Analysis of cells, mediators, and proteins can then be conducted to study the pathogenesis of allergic and nonallergic rhinitis (Bascom et al., 1986). However, normal values have not been determined for most measures.
There are simple, reliable measures of lung function that may be used for studying diseases caused by indoor allergens. Indeed, objective measures of respiratory function should be a part of protocols to determine the efficacy of therapeutic strategies for these diseases. Predicted values for pulmonary function fall along a normal distribution curve with 95 percent confidence intervals for FEV1 and FVC of approximately 80–120 percent. The lower limit of variation in population studies for the midlevel expiratory flow rate (FEF25–75) is approximately 60 percent.
Spirometry is limited in its ability to detect impairment of ventilatory function in asymptomatic individuals (Morris et al., 1971) because of the wide range of normal values, even with predicted levels that control for age, sex, and height. Significant inaccuracy can result from errors in spirometry performance, almost all of which lead to underestimation of the true respiratory function. These tests can, however, help to evaluate the effects on an individual of sensitization to specific allergens (J. M. Smith, 1988). They can also help to diagnose respiratory diseases that may be caused or worsened by indoor allergens (Lopez and Salvaggio, 1988; NHLBI, 1991; Woolcock, 1988) and to assess disease severity, which is often critically important in clinical decisionmaking (NHLBI, 1991). Serial pulmonary function testing in the home or workplace can demonstrate causal relationships between the indoor environment and respiratory illness. Serial pulmonary function testing coupled with bronchoprovocation can demonstrate the causal relationship between specific allergens and respiratory responses (Chan-Yeung and Lam, 1986).
In epidemiological studies, measures of environmental factors and of pulmonary function can be evaluated for associations that suggest causal relationships (S. Weiss et al., 1983). Pulmonary function tests may also be used to assess the efficacy of therapy, determine response to treatment, or determine the effect of environmental modification (Ehnert et al., 1991; Platts-Mills et al., 1982). Such tests are required when physicians are asked to determine impairment resulting from a respiratory disease for insurance or benefit systems such as workers' compensation and social security disability