Dose considerations in the SO2-exposed exercising asthmatic.

In this study we have demonstrated that by combining data from several recent controlled human exposure studies it is possible systematically to relate increases in airways resistance to the rate of SO2 exposure (Dmin) in the exercising asthmatic. It was determined that the mode of SO2 exposure (oral vs. oronasal) greatly influences the degree of response in the asthmatic. Forced oral breathing consistently produces larger percentage increases in SRaw per unit increase in SO2 exposure rate. We have demonstrated further that while the dose/effect relationship which describes the increases in specific airways resistance (SRaw) versus exposure rate (Dmin) of SO2 is most consistently exponential in character, a linear (more conservative) model also can be used to fit the data. Using both the linear and exponential model, we have constructed a matrix which allows direct estimation of the combined minute ventilation (VE) and SO2 concentration (as ppm or microgram/L) required to achieve various levels of specific airways resistance increase. In this report this matrix is constructed only on subjects breathing in an unencumbered (oronasal) manner. Future reports will explore these relationships in the asthmatic breathing in an encumbered (oral) manner.