For a long time, sleep researchers have asked why we sleep and what are the physiological and mental needs which 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 this?
During the past few decades the research field on sleep 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 publication of the latest classification and coding manual in 2014, the third edition of the International Classification of Sleep Disorders (ICSD-3) by the American Academy of Sleep Medicine (AASM), defined and provided severity criteria for 66 distinct sleep disorders . Assessment starts with complaints about not sleeping, insomnia, or 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, this is not an appropriate dimension. This is because somebody may report good sleep quality but still have many apnea or other troubling events that result in sleepiness with no perceivable effects on subjective sleep quality. Therapy is needed in this 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 too short, with having awakenings which we remember (if awakenings are very brief, we do not remember them normally), with perceived disturbance from light, noise, motion, and other external or internal sensations. All this is not necessarily related to sleep disorders or sleep medicine. Still it might impair subjective sleep quality and well-being during daytime. How can we quantify this? Sleep physicians do 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 (PSQI). An alternative is the sleep quality scale (SQS). Simpler tools are just visual analogue scales where the patient marks a value between zero (lowest sleep quality ever) and 10 (highest sleep quality ever). Then the sleep physician performs tests to see whether patient complaints correspond to objective sleep recordings – which sometimes they do and sometimes they do not.
In view of this, what is the main road block to quantifying sleep quality? It is that we do not have a psychological and physiological 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 the questionnaires and scales given so far.
Where can we go with quantifying sleep quality? Can technology help us? Today, with the ‘quantifying yourself’ movement everywhere, assessment of sleep quality raises new and wide interest. Sleep researchers and sleep physicians should not ignore this interest and awareness. Instead our discipline should realize this opportunity and should try to explain subjective components of sleep quality and objective impairments. This is accessible by simple tools such as assessment of sleep duration, sleep disturbance, misbehavior prior to sleep such as strong exercise or excessive meals or drinking. As a discipline we can give advice about appropriate sleep duration (at least 7 hours) and appropriate behavior regarding sleep, as recently published . Comping back to physiology, this is urgently required because sleep is not an autonomous function like the heartbeat, but is half autonomous and half behavior. We do need good quality sleep and we have to prepare ourselves (and the sleep environment) to get good quality sleep.
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- American Academy of Sleep Medicine. International classification of sleep disorders, 3rd ed. Darien, IL: American Academy of Sleep Medicine, 2014.
- 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, 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 11(6): 591–592, 2015.