Immediate Effects of Thixotropy Conditioning of Inspiratory Muscles on Chest-Wall Volume in Chronic Obstructive Pulmonary Disease

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Abstract:

INTRODUCTION:Thixotropy is a passive property of the skeletal muscle that depends on the muscle's immediate history of contraction and length change. Inspiratory-muscle thixotropy affects the end-expiratory position of the rib cage in normal subjects. OBJECTIVE: To determine whether a reduction in end-expiratory chest-wall volume occurs after thixotropy conditioning of inspiratory muscles in patients with chronic obstructive pulmonary disease. METHODS: Ten male subjects with chronic obstructive pulmonary disease (mean ± SD forced expiratory volume in the first second 70 ± 20% of predicted) showed an increased ratio of residual volume to total lung capacity (49 4.7%). The subjects conducted inspiratory muscle thixotropy conditioning maneuvers at 3 different chest-wall volumes (end-expiratory volume of baseline breathing, residual volume plus 40% of expiratory reserve volume, and residual volume) and with 3 levels of inspiratory effort (0%, 30%, and 100% of maximal inspiratory mouth pressure at each volume), with airway-closure, in the sitting position. Using respiratory induction plethysmography, we measured the effect of effortintensity and volume at the time of the conditioning maneuver on the end-expiratory chest-wall volume of the 5 respiratory cycles immediately following the conditioning maneuver. RESULTS: There was a reduction in end-expiratory chest-wall volume after the conditioning maneuver, except when conditioning was performed at end-expiratory baseline with 0% effort. The reduction increased as effort intensity increased (p = 0.011) and as volume decreased (p < 0.001), and the reduction was attained by rib-cage movement rather than abdominal movement. CONCLUSIONS: Thixotropy conditioning of inspiratory muscles, at a reduced chest-wall volume, decreased end-expiratory chest-wall volume in the 5 subsequent breaths in patients with chronic obstructive pulmonary disease.

Keywords: CHRONIC OBSTRUCTIVE PULMONARY DISEASE; END-EXPIRATORY LUNG VOLUME; HYPERINFLATION; INSPIRATORY MUSCLES; THIXOTROPY

Document Type: Research Article

Affiliations: 1: Department of Physiology, Showa University School of Medicine, Tokyo, Japan, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan;, Email: masahiko@med.showau.ac.jp 2: Department of Physical Therapy 3: Department of Internal Medicine, Toyosu Hospital, Showa University, Tokyo, Japan 4: Department of Physiology, Showa University School of Medicine, Tokyo, Japan

Publication date: July 1, 2006

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