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How changes in the serial distribution of bronchoconstriction affect lung mechanics
F M Robatto1, S Simard, M S Ludwig
1Meakins-Christie Laboratories, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 1, 1993
Summary
Histamine and methacholine cause similar changes in lung mechanics, including airway and tissue resistance, and lung heterogeneity. These findings suggest comparable direct effects on lung parenchyma, challenging traditional views of their distinct actions.
Area of Science:
- Pulmonary Physiology
- Respiratory Medicine
- Pharmacology
Background:
- Methacholine (MCh) is traditionally thought to primarily affect central airways, while histamine (H) is believed to act on the lung periphery.
- Understanding the distinct and overlapping effects of these bronchoconstrictors is crucial for interpreting lung function tests and developing targeted therapies.
Purpose of the Study:
- To investigate and compare the effects of methacholine and histamine aerosols on lung mechanics and heterogeneity.
- To test the hypothesis that MCh and H aerosols would differentially affect lung mechanics based on their presumed sites of action.
Main Methods:
- Concentration-response curves for MCh and H were generated in 12 anesthetized, paralyzed mongrel dogs.
- The alveolar capsule technique was employed to partition total lung resistance (RL) into airway resistance (Raw) and tissue resistance (Rti).
- Lung mechanical heterogeneity was assessed by calculating the coefficient of variation for alveolar pressures.
Main Results:
- Both MCh and H significantly increased RL, Rti, Raw, and elastance, with comparable percentage increases across all measured parameters.
- The degree and pattern of lung mechanical heterogeneity, assessed by the coefficient of variation, were similar for both MCh and H.
- No significant differences were observed in the concentration-response patterns between MCh and H.
Conclusions:
- Histamine and methacholine exert comparable effects on overall lung mechanics and induce similar patterns of heterogeneity.
- The data suggest that both agents may have direct effects on lung parenchyma, not solely confined to their traditionally accepted sites of action.
- The observed similarities challenge the notion of distinct peripheral versus central actions for H and MCh in terms of their impact on lung mechanics.