Sir,—Staniforth et al correctly pointed out that arterial desaturation is common in patients with congestive heart failure, especially while sleeping.1The desaturation is commonly associated with apnoeic pauses, presumably as a result of depression of the respiratory centres (Cheyne-Stokes episodes). However, the seriousness of this depression requires emphasis.

Nocturnal desaturation in obstructive sleep apnoea has been associated with increased severity of hypertension, congestive heart failure, angina pectoris, atrial fibrillation, complete heart block, and possibly precipitation of myocardial infarction. Cerebral blood flow is reduced with the anoxia of obstructive sleep apnoea.2 Platelet aggregation and activation are increased two- and threefold.3 These changes are normalised with improved oxygenation. Vgontazs and colleagues4 and Entzian and colleagues5 identified severely increased inflammatory cytokines, and tumour necrosis factor α and interleukin 6 with anoxia.

Staniforth et al stated that “only 4% of their subjects were obstructive and no subject fulfilled the diagnostic criteria for obstructive sleep apnoea.” However only 41 (of 104) patients had polysomnography. One wonders about the other patients. Mechanical obstruction should be …