Individual canine Airway Response Variability to a Deep Inspiration

Author:

Brown Robert H.123,Kaczka David W.4,Fallano Katherine2,Shapiro Steve2,Mitzner Wayne12

Affiliation:

1. Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland.

2. Department of Environmental Health Sciences, Johns Hopkins University, Baltimore, Maryland.

3. Department of Radiology, Johns Hopkins University, Baltimore, Maryland.

4. Department of Anesthesia, Critical Care, and Pain Medicine, Beth Israel Deaconess Medical Center, Boston, MA.

Abstract

In healthy individuals, a DI can reverse (bronchodilation) or prevent (bronchoprotection) induced airway constriction. For individuals with asthma or COPD, these effects may be attenuated or absent. Previous work showed that the size and duration of a DI affected the subsequent response of the airways. Also, increased airway tone lead to increased airway size variability. The present study examined how a DI affected the temporal variability in individual airway baseline size and after methacholine challenge in dogs using High-Resolution Computed Tomography. Dogs were anesthetized and ventilated, and on 4 separate days, HRCT scans were acquired before and after a DI at baseline and during a continuous intravenous infusion of methacholine (Mch) at 3 dose rates (17, 67, and 200 μg/mm). The Coefficient of Variation was used as an index of temporal variability in airway size. We found that at baseline and the lowest dose of Mch, variability decreased immediately and 5 minutes after the DI ( P < 0.0001). In contrast, with higher doses of Mch, the DI caused a variable response. At a rate of 67 μg/min of Mch, the temporal variability increased after 5 minutes, while at a rate of 200 μg/min of Mch, the temporal variability increased immediately after the DI. Increased airway temporal variability has been shown to be associated with asthma. Although the mechanisms underlying this temporal variability are poorly understood, the beneficial effects of a DI to decrease airway temporal variability was eliminated when airway tone was increased. If this effect is absent in asthmatics, this may suggest a possible mechanism for the loss of bronchoprotective and bronchodilatory effects after a DI in asthma.

Publisher

SAGE Publications

Subject

Cardiology and Cardiovascular Medicine,Pulmonary and Respiratory Medicine

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