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.
Freed
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Department of Environmental Health Sciences, Johns Hopkins University, Baltimore, Maryland 21205.
D000388:Air; D000403:Airway Resistance; D000704:Analysis of Variance; D000818:Animals; D001980:Bronchi / Q000502:physiology; D001999:Bronchoscopy; D004285:Dogs; D008168:Lung / Q000502:physiology*; D008297:Male; D012016:Reference Values