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Published ahead of print on August 18, 2005, doi:10.1164/rccm.200412-1695OC

Am. J. Respir. Crit. Care Med., Volume 172, Number 10, November 2005, 1259-1266

A more recent version of this article appeared on November 15, 2005
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Submitted on December 17, 2004
Accepted on August 18, 2005

Diaphragm Length and Neural Drive after Lung Volume Reduction Surgery

Robert B Gorman1, David K McKenzie1, Jane E Butler1, Jane F Tolman1, and Simon C Gandevia1*

1 Prince of Wales Medical Research Institute and University of New South Wales, Sydney, Australia

* To whom correspondence should be addressed. E-mail: s.gandevia{at}unsw.edu.au.

Rationale: Patients with chronic obstructive pulmonary disease (COPD) have shorter inspiratory muscles and higher motor unit firing rates during quiet breathing than age-matched healthy subjects. Lung volume reduction surgery (LVRS) in COPD patients improves lung function, exercise capacity, and quality of life. Objectives: We studied the effect of LVRS on diaphragm length and motor unit firing rates in diaphragm and scalene muscles. Methods: Diaphragm length was estimated using ultrasound and magnetometers, and firing rates recorded with needle electrodes in patients (5 female, 7 male) with severe COPD, before and after surgery. Measurements and Main Results: Pre-LVRS total lung capacity (TLC) was 135 ± 10 %predicted (mean ± SD), and forced expiratory volume in 1-s (FEV1) was 30 ± 12 %predicted. After surgery, median firing frequency of diaphragmatic motor units reduced from 17.3 ± 4.2 Hz to 14.5 ± 3.4 Hz (P < 0.001), and scalenes motor units reduced from 15.3 ± 6.9 Hz to 13.4 ± 3.8 Hz (P < 0.001). Tidal volume and diaphragm length change during quiet breathing did not change, but at end-expiration the zone of apposition length of diaphragm against the rib cage (LZapp) increased (30 ± 28 %, P = 0.004). Improvements in quality of life measures and exercise performance after surgery were related to increased forced vital capacity (FVC) and LZapp. Conclusions: Increased diaphragm length resulted in lower motor unit firing rates and reduced breathing effort, and this is likely to contribute to improved quality of life and exercise performance after LVRS.
Key words: COPD, LVRS, pneumonectomy, emphysema, ultrasound, electromyography




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