Regional and temporal variation in canine peripheral lung responses to dry air

Variation in dry airflow-induced broncho-constriction (AIB) in the canine lung periphery was examined using a wedged bronchoscope technique. Collateral system resistance (Rcs) was measured before and after dry-air challenge. Base-line Rcs was similar throughout the lung periphery, between dogs, and over time. Increasing base-line Rcs was correlated with increasing maximum Rcs 5 min postchallenge (Rcs5), increasing change in Rcs (dRcs5), and decreasing percent change in Rcs above base line (%Rcs5). In contrast to repeated challenge in which base-line Rcs was similar, the magnitude of AIB associated with consecutive challenges with unequal base lines depended on the parameter used to evaluate the response (i.e., Rcs5, dRcs5, or %Rcs5). Peripheral lung resistance then increased to a stimulus specific maximum regardless of base-line Rcs, although data expressed as %Rcs5 or dRcs5 may obscure this observation. Although a change in peripheral lung resistance does not necessarily imply airway narrowing, it is consistent with the idea that changes in Rcs are independent of the collateral system's resting tone.