For a long time, sleep researchers have asked why we sleep and what physiological and mental needs require sleep . Today, we understand that sleep is important for productivity, health, cognition, and well-being. As a consequence, physical recreation, hormone secretion, immune systems, memory functions, and mood are all related to sufficient and restorative sleep. Thus, a good sleep quality is essential. As biomedical engineers, we would like to quantify this ultimate “sleep quality,” but how can we assess it?
Over the past few decades, research on sleep has expanded rapidly, following the exploding development of sleep medicine. Sleep medicine began with research on drugs that help put us to sleep and help make us wide awake. With the recognition of distinct and highly prevalent disorders such as sleep apnea, the field developed much further. The latest classification and coding manual, the 2014 third edition of The International Classification of Sleep Disorders by the American Academy of Sleep Medicine, defined and provided severity criteria for 66 distinct sleep disorders . Assessment starts with complaints about not sleeping, insomnia, excessive sleepiness, hypersomnolence, or adverse or odd events during sleep.
But what about sleep quality? This is not an entity assessed or quantified by sleep medicine. In fact, in terms of sleep medicine, sleep quality is not an appropriate dimension. This is because someone may report good sleep quality but still have many apneic or other troubling events that result in sleepiness with no perceivable effects on subjective sleep quality. Therapy is needed in such a case. Another person may have low sleep quality a few days before taking an exam or due to other stress. This does not require immediate treatment.
We do know that reported sleep quality correlates strongly with sleeping for intervals that are too short, with having awakenings that we remember (if awakenings are very brief, we normally do not remember them), and with perceived disturbance from light, noise, motion, and other external or internal sensations. These are not necessarily related to sleep disorders or sleep medicine. Still, they might impair subjective sleep quality and well-being during the daytime.
How can we quantify sleep quality? Sleep physicians have many questionnaires and scales available to quantify subjective sleep quality because it is part of the overall assessment of subjects suffering from sleep disorders. The best established tool is the Pittsburgh Sleep Quality Index. An alternative is the sleep quality scale. Simpler tools are just visual analogue scales where the patient marks a value between zero (lowest sleep quality ever) and ten (highest sleep quality ever). Then, the sleep physician performs tests to see whether patient complaints correspond to objective sleep recordings; sometimes they do, and sometimes they do not.
In view of this, what is the main roadblock to quantifying sleep quality? It is that we do not have a psychologically and physiologically justified scientific definition for sleep quality. And because sleep quality is not well related to sleep disorders—or, in other words, it only reflects one aspect of sleep disorders—sleep medicine has not taken efforts to define sleep quality more than can be provided by the questionnaires and scales presented so far.
Where can we go with quantifying sleep quality? Can technology help us? Today, with the “quantifying yourself” movement everywhere, sleep quality assessment raises new and wide interest. Sleep researchers and sleep physicians should not ignore this interest and awareness. Instead, our discipline should recognize this opportunity and try to explain subjective components of sleep quality and objective impairments, which may be addressed using simple tools such as assessment of sleep duration, sleep disturbance, and negative behavior prior to sleep, including strong exercise, large meals, or alcohol consumption. As a discipline, we can give advice about appropriate sleep duration (at least 7 h) and appropriate behavior regarding sleep, as recently published .
Coming back to physiology, finding a way to quantify sleep quality is urgently required because sleep is not an autonomous function like heartbeat; rather is half autonomous and half behavior. We need good-quality sleep and we have to prepare ourselves (and the sleep environment) to get it.
- J. M. Siegel, “Clues to the functions of mammalian sleep,” Nature, vol. 437, no. 27, pp. 1264–1271, Oct. 2005.
- American Academy of Sleep Medicine. The International Classification of Sleep Disorders, 3rd ed. Darien, IL: American Academy of Sleep Medicine, 2014.
- N. F. Watson, M. S. Badr, G. Belenky, D. L. Bliwise, O. M. Buxton, D. Buysse, D. F. Dinges, J. Gangwisch, M. A. Grandner, C. Kushida, R. K. Malhotra, J. L. Martin, S. R. Patel, S. F. Quan, and E. Tasali, “Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society,” J. Clin. Sleep Med., vol. 11, no. 6, pp. 591–592, 2015.