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Kawada, Tomoyuki MD, PhD
Department of Hygiene and Public Health, Nippon Medical School, Bukyo-Ku, Tokyo, Japan
The author has no funding or conflicts of interest to disclose.
To the Editors:
Gamaldo et al1 conducted a cross-sectional study to examine the relationship between sleep parameters and cognitive performance in 36 HIV-positive individuals using sleep polysomnography, actigraphy, and some questionnaires. They concluded that sleep quality and duration had an impact on cognitive performance in HIV-positive individuals.
I have some concerns on their study outcome. First, they did not set controls to evaluate sleep and cognition in HIV. Although they calculated correlation coefficients between sleep parameters and several cognitive performances, the absolute values of correlation coefficient were 0.4 or lower, and causality of the association could not be determined by cross-sectional analysis. About setting the controls, the same authors presented basic information on the difference of several sleep parameters between 25 HIV-positive individuals and 19 controls.2 I recommend the authors preparing controls to know the effect of HIV infection on the association between sleep and cognition.
Second, the authors quoted a reference on their research design and sleep methods.2 Unfortunately, they quoted only 1 reference on the validity of this apparatus, named Actiwatch.3 I have a query on the information of validation for wrist actigraphy. Actigraphy is an accelerometer, and it does not always reflect sleep status in cases of insomniacs. The cut-off value of sensitivity for making sleep/wake judgment by Actiwatch was initially set at 40 counts per minute. As there was no description of the cut-off value in the article, I suppose that initial setting was used for their analysis. The cut-off value should be determined by using sleep polysomnography as a gold standard in each test situation. For example, there is a discrepancy in significance of sleep onset latency by actigraphy and polysomnography between HIV-positive individuals and controls.2 Validation of actigraphy should be carefully conducted in their HIV-positive individuals to determine the association between sleep and cognition.
The authors mentioned that the number of samples was limited in their study, and further study is needed to make a conclusion with statistical power. In addition, causality on the association should be determined by follow-up study. I also recommend the authors considering clinical status of HIV infection to know the effect of HIV infection on the association between sleep and cognition and to know the mutual interaction on HIV infection and insomnia.4
© 2014 by Lippincott Williams & Wilkins
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