The Clinical Relevance of very Severe Pure Diaphragm Weakness

Abstract

Previous studies suggest that patients with bilateral diaphragm paralysis are at high risk of developing chronic respiratory failure due to alveolar hypoventilation. However such studies mostly describe patients with generalised neuromuscular disorders in which other respiratory muscles are also weak. We therefore studied three patients with diaphragm paralysis (two due to neuralgic amyotrophy, one following traumatic diaphragm rupture) but no weakness of the other respiratory muscles. All were breathless on exertion (MRC Grade 4) with orthopnoea and abdominal paradox but with no symptoms of nocturnal hypoventilation. Maximum expiratory mouth pressure was >100% pred. consistent with normal intercostal and abdominal muscle strength. Vital capacity was 45–65% pred., falling by 36–55% when supine. Transdiaphragmatic pressure (Pdi) was zero during (a) tidal breathing, (b) inspiration to TLC, and (c) supermaximal stimulation of both phrenic nerves. It was also very low during a maximum sniff (10, 7.5 and 12.5 cm H₂O respectively, normal >100 cm H₂O). Maximum inspiratory mouth pressure was 35–70% pred. Arterial blood samples sitting at rest showed a pO₂ of 10.6–12.3 kPa and normal pCO₂ of 4.7–5.5 kPa. Continuous overnight monitoring on two consecutive nights, in normal sleeping positions (one on his side, two propped up), using an ear oximeter (Biox 3) and a Hewlett Packard capnometer, showed no significant pO₂ desaturation nor any increase in pCO₂. These patients have now remained stable for one to four years without developing any signs of nocturnal hypoventilation or respiratory failure, nor have daytime blood gases deteriorated. We conclude that in the absence of generalised respiratory muscle weakness, severe diaphragm weakness does not lead to respiratory failure.