Comparison of the constant flow and occlusion methods for assessment of bronchoconstriction in guinea-pigs

Assessments of total respiratory compliance (C) and conductance (G) with the constant inspiratory flow and the occlusion methods were compared in the basal state and during histamine or serotonin induced bronchoconstriction in 22 normal, anaesthetized, paralysed, mechanically ventilated guinea-pigs. In the basal state, no significant difference was found between the C and G values measured by both methods. During drug-induced bronchoconstriction, small but significant differences were observed between the respiratory parameters measured by the two methods, and expressed as the percentage ratio (R) to the corresponding basal values (respectively RCCF and RCOC, and RGCF and RGOC). This discrepancy, which was independent of the drug and of the dose, was probably attributable to a modification of the visco elastic properties of the lung due to either the mechanical ventilation or the infused drug. Nevertheless, this study demonstrates that both methods can be considered as equivalent for bronchoconstriction assessment because very strong correlations were found between RCCF and RCOC (r = 0.96, p less than 0.001) and between RGCF and RGOC (r = 0.97, p less than 0.001), and because the slopes of the linear relationships were not significantly different from unity in both cases.