Continuous positive airway pressure improves vascular function in obstructive sleep apnoea/hypopnoea syndrome: a randomised controlled trial.

BACKGROUND: The obstructive sleep apnoea/hypopnoea syndrome (OSAHS) is associated with hypertension and increased cardiovascular risk, particularly when accompanied by marked nocturnal hypoxaemia. The mechanisms of these associations are unclear. We hypothesised that OSAHS combined with severe nocturnal hypoxaemia causes impaired vascular function that can be reversed by continuous positive airways pressure (CPAP) therapy. METHODS: We compared vascular function in two groups of patients with OSAHS: 27 with more than 20 4% desaturations/h (desaturator group) and 19 with no 4% and less than five 3% desaturations/h (non-desaturator group). In a randomised, double blind, placebo controlled, crossover trial, the effect of 6 weeks of CPAP therapy on vascular function was determined in the desaturator group. In all studies, vascular function was assessed invasively by forearm venous occlusion plethysmography during intra-arterial infusion of endothelium dependent (acetylcholine 5-20 microg/min and substance P 2-8 pmol/min) and independent (sodium nitroprusside 2-8 microg/min) vasodilators. RESULTS: Compared with the non-desaturator group, patients with OSAHS and desaturations had reduced vasodilatation to all agonists (p = 0.007 for all). The apnoea/hypopnoea index and desaturation frequency were inversely related to peak vasodilatation with acetylcholine (r = -0.44, p = 0.002 and r = -0.43, p = 0.003) and sodium nitroprusside (r = -0.42, p = 0.009 and r = -0.37, p = 0.02). In comparison with placebo, CPAP therapy improved forearm blood flow to all vasodilators (p = 0.01). CONCLUSIONS: Patients with OSAHS and frequent nocturnal desaturations have impaired endothelial dependent and endothelial independent vasodilatation that is proportional to hypoxaemia and is improved by CPAP therapy. Impaired vascular function establishes an underlying mechanism for the adverse cardiovascular consequences of OSAHS.

Inhibition, contextual segregation, and subject strategies in list method directed forgetting.

This experiment tested alternative explanations of list method directed forgetting effects. Two word lists were studied by 135 subjects. Between lists, subjects were instructed to remember both lists (remember group), remember both lists as well as in which list words were studied (segregate group), or to forget the first list and remember the second (forget group). All subjects took both recall and recognition tests with test order varied between subjects. Among subjects who took the recall test first, the forget group showed a directed forgetting effect (poorer performance on List 1 than List 2) with both recall accuracy, recall typing time, and recognition reaction time measures. Contextual segregation of List 1 words by forget subjects was ruled out as a sufficient cause of the effect. Limited support was obtained for a differential rehearsal explanation of the effect. Within-group comparisons and findings of release from directed forgetting support inhibitory processes as the major cause of the directed forgetting effect.