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Respiratory Sensation and Ventilatory Mechanics during Induced Bronchoconstriction in Spontaneously Breathing Low Cervical Quadriplegia

Respiratory Investigation Unit, Department of Medicine, Queen's University, Kingston, Ontario, Canada

Correspondence and requests for reprints should be addressed to Dr. M. Diane Lougheed, 102 Stuart Street, Kingston, ON, K7L 2V6 Canada. E-mail: mdl{at}post.queensu.ca

Intensity of dyspnea during induced bronchoconstriction in asthma is strongly related to the reduction in inspiratory capacity (IC) as a result of dynamic hyperinflation. To determine the role of rib cage and intercostal muscle afferents in symptom perception during bronchoconstriction, we measured the relationship between dyspnea intensity and IC during induced bronchoconstriction in six subjects with complete C4-C7 quadriplegia who did not require assisted ventilation. Spirometry, lung volumes, breathing pattern, esophageal pressure (Pes), and dyspnea intensity (Borg Scale) were measured during high-dose methacholine bronchoprovocation up to 256 mg/ml or a maximum change () in FEV₁ of 50%. Contemporaneous control data from subjects with asthma (n = 12) who had completed the same protocol were used for comparison. At maximum response in quadriplegia, FEV₁ decreased by 1.42 ± 0.18 L (62 ± 4%predicted) (mean ± SEM), and IC decreased by 0.89 ± 0.12 L (30 ± 4%predicted). Dyspnea at maximum response was rated "moderate" to "severe": Borg 3.6 ± 0.3. The predominant qualitative respiratory sensations were inspiratory difficulty and unsatisfied inspiration. The best correlate of dyspnea (Borg) was IC(%predicted) (p < 0.0005), whereas changes in FEV₁, Pes-derived measurements and breathing pattern did not contribute further to the strength of this relationship. Dyspnea intensity, quality, and changes in spirometry and lung volumes at maximum response were similar to those reported previously in asthma. The relationship between dyspnea intensity and IC(%predicted) was linear and consistent across groups. We conclude that the quality and intensity of dyspnea during methacholine-induced bronchoconstriction and dynamic hyperinflation was not altered by extensive chest wall deafferentation.

Key Words: quadriplegia • asthma • bronchoconstriction • lung hyperinflation • dyspnea • methacholine challenge

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