Acute respiratory distress syndrome: the prognostic value of ventilatory ratio--a simple bedside tool to monitor ventilatory efficiency.

investigate the direct impact of IH on working memory in healthy young adults. This study demonstrated that shortterm exposure to IH per se (i.e., without the confounding influence of sleep fragmentation and medical comorbidities) can negatively impact performance on spatial working memory tasks, even in healthy young adults. Previous studies did not observe this effect possibly due to the lack of a control group (i.e., participants not exposed to IH) (12, 13). These studies did not control for a possible learning effect on n-back task performance. It is also important to note that only verbal n-back tasks were used in these previous studies and no significant effects of IH on verbal tasks were observed in the present study. Finally, Thomas and colleagues (12) exposed participants to continuous hypoxia, which has been shown to have different physiological effects than IH, a closer approximation of OSA (14). These results provide the basis for future studies. The results are limited by the small sample size due to the intensive data collection required for these studies. Future studies should attempt to replicate these results with a larger number of participants. The replication of these findings in an older population would also be important as OSA occurs more frequently in older adults. In fact, it is hypothesized that a larger detrimental effect of IH on working memory function would be observed in older participants due to the age-related decline in brain resilience. Although these findings are preliminary, the significant shortterm effects of acute IH exposure on spatial working memory raise the possibility of more significant effects of chronic IH exposure on working memory function in patients with OSA. Early treatment of sleep apneamay be important tominimize potential long-term effects on working memory and other cognitive functions. Recent studies also suggest that some interventions such as exercise training could be proven useful in minimizing cognitive dysfunctions and improving selected aspects of daytime functioning in patients with OSA (15, 16).