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Effect of Severe Isolated Unilateral and Bilateral Diaphragm Weakness on Exercise Performance

Respiratory Muscle Laboratory and Lung Function Unit, Royal Brompton Hospital, London, United Kingdom; Department of Clinical Physiology, Raymond Poincaré Hospital, Garches, France; Department of Respiratory Medicine and Allergy, Guy's, King's and St. Thomas' School of Medicine, King's College Hospital, London, United Kingdom

Correspondence and requests for reprints should be addressed to Nicholas Hart, M.D., Respiratory Muscle Laboratory, Royal Brompton Hospital, Fulham Road, London SW3 6NP, UK. E-mail: drnhart{at}aol.com

Patients with isolated diaphragm paralysis depend on recruitment of extradiaphragmatic respiratory muscles to increase ventilation, but little is known about exercise performance or the response of the inspiratory muscles to loaded breathing. By convention, unilateral diaphragm paralysis is regarded as a trivial condition whereas bilateral paralysis is considered to be potentially life-threatening. In fact, no data exist concerning exercise performance under these conditions. We studied incremental treadmill exercise performed by eight patients with bilateral diaphragm paralysis, eight patients with unilateral diaphragm paralysis, and eight age-matched control subjects. Respiratory muscle endurance (RME) was also measured by an inspiratory threshold loading method. Exercise time, compared with control subjects (671 seconds), was moderately reduced in unilateral diaphragm paralysis (512 seconds, p = 0.07) and further reduced in bilateral diaphragm paralysis (456 seconds, p = 0.02). Similarly, peak minute ventilation was lower in patients with unilateral diaphragm paralysis (84 L · min^-1, p = 0.01) and in patients with bilateral diaphragm paralysis (69 L · min^-1, p = 0.001) compared with control subjects (114 L · min^-1). However, patients with unilateral diaphragm paralysis and patients with bilateral diaphragm paralysis had increased ratios of peak oxygen consumption to peak minute ventilation compared with control subjects (p = 0.0007 and p < 0.0001, respectively). Nine patients had normal RME; exercise time was moderately increased in these patients (502 seconds) compared with seven patients with reduced RME (461 seconds). In conclusion, although exercise performance is impaired in bilateral diaphragm paralysis, these patients can sustain a reasonable exercise load, particularly if RME is preserved and compensatory mechanisms have developed. In addition, exercise tolerance is diminished in patients with unilateral diaphragm paralysis.

Key Words: diaphragm weakness • exercise • respiratory muscle endurance

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