Diaphragm length and neural drive after lung volume reduction surgery.
BACKGROUND
Patients with chronic obstructive pulmonary disease have shorter inspiratory muscles and higher motor unit firing rates during quiet breathing than do age-matched healthy subjects. Lung volume reduction surgery (LVRS) in patients with chronic obstructive pulmonary disease improves lung function, exercise capacity, and quality of life.


OBJECTIVE
We studied the effect of LVRS on length and motor unit firing rates of diaphragm and scalene muscles.


METHODS
Diaphragm length was estimated by ultrasound and magnetometers, and firing rates were recorded with needle electrodes in patients (five females and seven males) with severe chronic obstructive pulmonary disease, before and after surgery.


RESULTS
Pre-LVRS total lung capacity was 135 +/- 10% predicted (mean +/- SD), and FEV1 was 30 +/- 12% predicted. After surgery, median firing frequency of diaphragmatic motor units fell from 17.3 +/- 4.2 to 14.5 +/- 3.4 Hz (p < 0.001), and scalene motor unit firing rates were reduced from 15.3 +/- 6.9 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 (L(Zapp)) increased (30 +/- 28%, p = 0.004). Improvements in quality-of-life measures and exercise performance after surgery were related to increased forced vital capacity and L(Zapp).


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.
Gorman
Robert B
RB
Prince of Wales Medical Research Institute, Barker Street, Sydney, Randwick NSW 2031, Australia.
McKenzie
David K
DK
Butler
Jane E
JE
Tolman
Jane F
JF
Gandevia
Simon C
SC
D000368:Aged; D003964:Diaphragm / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000294:innervation*; D004576:Electromyography; D015444:Exercise / Q000502:physiology; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008280:Magnetics; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D011013:Pneumonectomy; D029424:Pulmonary Disease, Chronic Obstructive / Q000601:surgery*; D011788:Quality of Life; D014463:Ultrasonography