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Preferential reduction of quadriceps over respiratory muscle strength and bulk after lung transplantation for cystic fibrosis

¹ Department of Chest Medicine, Erasme University Hospital, Brussels, Belgium
² Department of Radiology, Erasme University Hospital, Brussels, Belgium
³ Department of Physiotherapy, Erasme University Hospital, Brussels, Belgium
⁴ Department of Intensive Care Medicine, Erasme University Hospital, Brussels, Belgium

Correspondence to:
Correspondence to:
Dr M Estenne
Chest Service, Erasme University Hospital, 808 Route de Lennik, B-1070 Brussels, Belgium; mestenne{at}ulb.ac.be

Background: In the absence of complications, recipients of lung transplants for cystic fibrosis have normal pulmonary function but the impact of the procedure on the strength and bulk of respiratory and limb muscles has not been studied.

Methods: Twelve stable patients who had undergone lung transplantation for cystic fibrosis 48 months earlier (range 8–95) and 12 normal subjects matched for age, height, and sex were studied. The following parameters were measured: standard lung function, peak oxygen uptake by cycle ergometry, diaphragm surface area by computed tomographic (CT) scanning, diaphragm and abdominal muscle thickness by ultrasonography, twitch transdiaphragmatic and gastric pressures, quadriceps isokinetic strength, and quadriceps cross section by CT scanning, and lean body mass. Diaphragm mass was computed from diaphragm surface area and thickness.

Results: Twitch transdiaphragmatic and gastric pressures, diaphragm mass, and abdominal muscle thickness were similar in the two groups but quadriceps strength and cross section were decreased by nearly 30% in the patients. Patients had preserved quadriceps strength per unit cross section but reduced quadriceps cross section per unit lean body mass. The cumulative dose of corticosteroids was an independent predictor of quadriceps atrophy. Peak oxygen uptake showed positive correlations with quadriceps strength and cross section in the two groups, but peak oxygen uptake per unit quadriceps strength or cross section was reduced in the patient group.

Conclusions: The diaphragm and abdominal muscles have preserved strength and bulk in patients transplanted for cystic fibrosis but the quadriceps is weak due to muscle atrophy. This atrophy is caused in part by corticosteroid therapy and correlates with the reduction in exercise capacity.

Abbreviations: BMI, body mass index; CF, cystic fibrosis; FBM, fat body mass; FRC, functional residual capacity; FEV₁, forced expiratory volume in 1 second; LBM, lean body mass; Mdi, diaphragm mass; Pdi, trandiaphragmatic pressure elicited by twitch stimulation of the phrenic nerves; Pga, change in gastric pressure elicited by abdominal stimulation; PT, peak torque of quadriceps muscle; TLC, total lung capacity; VC, vital capacity

Keywords: cystic fibrosis; respiratory muscles; corticosteroids; quadriceps; transplantation

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