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Article #80

SUMMARY     The authors conducted a pre-CPAP evaluation of mood, sleepiness, vigilance, and reaction time, and repeated the assessment 1 year later on CPAP. They studied 80 patients attending their sleep clinic between November 1995 and April 1997. They required a minimum Apnea Hypopnea Index of 20 respiratory-related arousals per hour of sleep. They excluded patients with drug abuse, psychiatric disorders, shift work, epilepsy, narcolepsy, or periodic leg movements of sleep. These exclusion criteria resulted in screening out 9 of an original sample of 89 study candidates.     Their 80 subjects were overwhelmingly male (78/80), averaged 49 years of age, and had moderately severe average AHIs averaging 60/hour.     They compared these patients with control subjects matched with the patients on age and sex. These were nonmedical workers or visitors to the hospital, not including any relatives of apnea patients. In these subjects, sleep apnea was ruled out on the basis of clinical history, and only three controls received actual sleep studies (leading to a diagnosis of sleep apnea in two of them).     Patients, but not controls, underwent the assessment procedure after 3 months on CPAP as well as after 1 year. Controls were assessed only at intake and 1 year later. The assessment included a questionnaire asking about occupation, prior medical conditions, use of drugs, alcohol, and coffee, and number of hours of sleep per day. The Epworth scale was used to measure sleepiness and the Beck questionnaires were used to measure anxiety and depression. Reaction time was measured by having the subjects press a button as soon as they saw a red light which flashed at random intervals 80-85 times during the course of 10 minutes. Vigilance was assessed with the Steer-Clear Test, simulating a driving experience on screen for 30 minutes. Compliance with CPAP was assessed with a time counter built into each machine.     Despite the matching procedure, patients turned out to be a little older than controls (49 vs. 46 years). Patients were significantly more obese, with Body Mass Indices averagin 33 versus 26 for controls. Patients' average systolic and diastolic blood pressure were significantly higher (132/84 vs. 124/76). Patients had average lowest nocturnal oxygen saturations of 64%, like the AHIs, supporting the severity of their illness. Patients, more often than controls, were taking either antianxiety or antidepressant medications (13 vs. 5).     Before CPAP, patients were more depresssed and anxious than controls, though the authors note that their scores on the Beck scales were only moderately elevated. Patients appeared much sleepier than controls on the Epworth Scale (12 vs. 3). Patients performed somewhat more poorly on the reaction time test and the Steer-Clear test of vigilance than controls.     The patients' sleepiness improved considerably after 3 months on CPAP, and a little more after 1 year, by which time their scores on the Epworth Scale approximated those of controls. Results of vigilance and reaction time tests showed a similar pattern over time. On the other hand, the scales measuring depression and anxiety did not improve significantly. The magnitude of these improvements indicated a large effect (effect size over 0.8). Compliance with CPAP indicated a more favorable effect on sleepiness. Results for controls subjects showed no change with time.     The authors considered that the main impact of their findings was to substantiate, with an unusually large sample of subjects and length of follow-up, the usefulness of CPAP over the first year of treatment. The only exception was their failure to find significant improvement in anxiety and depression. Their results indicated that the beneficial effects on sleepiness, vigilance, and reaction time were strong and lasting--in contrast to the opinion of some that the effects are weak and transient.

This is a fairly straightforward follow-up study of people with sleep apnea before treatment and 1 year later. The results are simple and believable. The important point, to my view, concerns the magnitude of CPAP effect and its lasting nature. On the other hand, they also suggest that improvement after 1 year is little better than after 3 months, an important consideration in deciding when to assess its effectiveness.     I am skeptical about the validity of their control group, but this is a common problem. Most researchers compare patients and controls on just a few variables, perhaps to minimize the risk of turning up unexpected differences. The imperfect matching indicates a need for caution when comparing the patients with the controls. I was not entirely happy with the use of a simple clinical evaluation to rule out various problems in controls.     I was not terribly surprised at the authors' failure to find significant improvement in their measures of depression and anxiety, which are rather minimal self-report scales. Moreover, the patients did not appear conspicuously depressed or anxious at the outset, reducing the chances of finding significant change on the basis of a small subgroup who probably were.     Studies like this, which are more like clinical evaluations than experimental procedures, are open to many criticisms. However, it is usual to find this kind of study taking place early in research, helping more experimental researchers to establish the hypotheses they will want to put an inordinate amount of effort into testing rigorously.     Incidentally, such findings may prove useful when the patient with sleep apnea wants to persuade employers he is well enough to return to work, or to persuade his doctor that he should be able to drive safely once again!

"A life of leisure and a life of laziness are two things. There will be sleeping enough in the grave." Benjamin Franklin

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