On Sleep

This morning, I awoke sleepy and dim-witted. For the fifth consecutive day, I had underslept due to mismanagement of my time (it is tempting to claim that I am so busy with work that I was forced to forego sleep, but alas, no first-year is that deep in it). I had a discussion over the net with some of my contacts as I sat in a stupor on the floor of  my bathroom, coddling a caffeine-rich tea. One person insisted that 6 hours per night was completely adequate: That my fatigue was "just an illusion" and that anyone can adapt to that amount of sleep with full, normal function and presumably no detriment to health. I'd like to postpone my post on parasites (I have one lecture left to attend anyway) and discuss instead about a topic which should be more immediately relatable: Sleep.

Any four-year old can tell you what sleep is. What he or she can't tell you is why we do it--and in this respect, experts aren't much more aware. There are many theories competing to explain: It is needed for restoration and recovery and to replenish energy stores, it is an evolutionary measure to conserve energy, it is needed for memory consolidation and reinforcement of learning, it is required for brain development. These are all probably true, but each theory faces evidence to the contrary.

Most people are aware that there are different stages to sleep, and we define them primarily on hypnogram readings (electroencephalography during sleep). Stage 1 and stage 2 sleep feature "brain waves" of high frequency and low amplitude. Stages 3 and 4 are "deep" sleep, and are characterized by long, high amplitude readings. But REM sleep, the next progression of the sleep cycle, looks strikingly like awake brain activity. REM ("Rapid Eye Movement") is so named because of the transient phasic events that occur during it. In addition, glucose usage and blood flow in the brain are both elevated during REM sleep! So, we characterize it as a period of high activity and discharge--not exactly what we would expect of sleep in general, yet it is known that REM sleep is the one which we seem to need the most--less REM sleep (without change in stages 1-4) is correlated with higher feelings of fatigue and sleepiness, and the sleep-deprived are quicker to enter REM sleep when they do go to bed. This fact has even generated a curious practice--the "Uberman" sleep cycle--which seeks to maximize the amount of awake hours in one's day, basically by becoming so sleep deprived that you hit enter REM sleep right away, and then only take ~4 half-hour naps per day, since REM sleep only constitutes about a quarter of normal sleep time. I do not particularly recommend this fad, as we are not quite sure what the long-term effects of shorting your stages 1-4 sleep are.

What happens to the body when you sleep? A lot. I don't want to bore you with lists of effects, but a few key points are worth mentioning. As sleep sets in, the body adapts what I will describe as a state of decreased metabolism: body temperature drops slightly (1-2 degrees celsius), blood pressure and heart rate fall, muscles become atonic (with the important exception of the lung diaphragm) and GI motility decreases. Secretion of various hormones also fluctuates and spikes throughout the duration of the night, another argument against polyphasic sleep. Note, however, that most of these metabolic changes flip on their head during REM sleep, a condition of elevated activity above an awake, resting baseline.

You have probably heard of the phrase "circadian rhythm". Basically, all mammals (and presumably many other animals) maintain a sort of biological rhythm. It is maintained by a structure pretty close behind the eyes, the Suprachiasmatic nucleus. Interestingly, the rhythm is not perfect, and relies on environmental input from the eyes, particularly short-wavelength (blue) light. In the absence of any such light, the rhythm appears to drift towards a 26 hour cycle in humans, and this is different for other animals. This has an important implication--our circadian rhythms, which evolved during a time in which the only light was from the daily rise and fall of the sun, are presumably subject to disruption from our lives of artificial light at any and all times. Here are a couple of useful takeaways: red lights do not appear to disrupt the rhythm--the 24hr darkness animal facilities at my undergrad school used red lights so that researchers could navigate the room, without disturbing the animals' rhythms. Later in this electronic discussion thread, another member mentioned the software f.lux, which dims the blue levels on your computer display when the sun has set (based on your latitude). This may be worth a try, if your curiosity is piqued.

So, how does this circadian rhythm affect our sleep drives? We can generally describe our sleep drives under a "two-process model", in which process C (for "circadian") oscillates on a roughly 24hr cycle. You may find around 9pm that you are very, very sleepy, but when you get in bed two hours later, suddenly the drive isn't as strong. That is the waning of process C, which occurs at night and continues until mid-morning. This leaves process H ("homeostatic"), which can be described as sleep debt or sleep load. This is what increases the longer we go without sleep, and it's why I have been feeling progressively junkier as this week has progressed. It appears that adenosine (produced in normal catabolism) is central to this phenomenon, but there are boatloads of hormones and brain chemicals that affect your wakefulness.

So what happens as we become sleep deprived? Nothing unexpected--cognitive function declines, physical health and overall affect suffer, the immune response becomes slower and less competent, and other sensitive processes like weight gain/loss and depression are implicated as well. The scariest thing that the typical person will be exposed to is a tendency to dose off--very problematic when operating a motor vehicle. I had a college friend get into 1-2 collisions because he fell asleep at the wheel, and I myself have been guilty of driving sleepy at least once. Being terrified of dying in a high speed crash helps a bit, but it's better to be well-rested before making any such trips. Oh, and go long enough without sleep (~10 days) and you'll die, though I can't currently find a source that explains exactly how.

So how much sleep is healthy? Well, there is no good single answer for everyone. 8 hours is a typical recommendation, and my clinical preceptor (a pulmonary/CCM/sleep doctor who regularly sees patients suffering from OSA, or obstructive sleep apnea) concurs with that amount. Does this mean you've been sleep deprived for the past 10 years? Well, not necessarily. The amount that we need seems to differ from person to person. According to the doctor, about 5% of people only need about 6 hours per night to function, and another 5% need around 10--it's a bell-curve. So, my friend's comments that 6 hours is enough may be true for him, but it is certainly not true for everyone. Still, you don't want to be on the ends of that bell-curve--morbidity is generally higher for both groups of outliers. Sucks to be the 10+hr people. To answer the question: You know how much sleep you need--your body tells you, so listen to it. Furthermore, the amount of sleep you need changes with age, with infants needing as much as 16-18 hours per day. The changes are greatest during childhood, and are pretty subtle in adulthood. Now, while it is true that an 80yr old needs less sleep than a 20yr old to function, studies have found that the elderly have much higher incidence of sleep disturbance--they get less sleep, but they still need more than they're getting. So give Grandpa a break when he says he's tired.

So, are you sleep deprived? Clinicians in sleep medicine use the Epworth scale to gauge tiredness and as a screening for potential sleep disorders. I will probably write in depth later about obstructive sleep apnea, as I learn some more about it. For now, follow this link to see the survey: Epworth Sleepiness Scale. Report how likely you would fall asleep (on a scale from 0-3) in each of the given situations, then tally your score. A normal score would probably be around 2-7. Above a 10, and your sleep patterns are probably harming your overall health. I scored about an 8.

The sources of information from which this topic was based include a lecture given by Hubert Forster, PhD on December 9th, 2013 at the Medical College of Wisconsin in Milwaukee, WI, as well as verbal discussion with a clinician preceptor.