In my last week of summer immersion, I was able to participate in a nighttime polysomnograph study; that is, I had a sleep study performed on myself. This wasn't done simply on a lark: I had a legitimate medical reason for having the study performed. I had complained some time before to my family physician of being tired during the day (excessive daytime somnolence) and he, suspecting sleep apnea, suggested I have a sleep study performed. People with an elevated body mass index (BMI) often suffer from obstructive sleep apnea in which the upper airway passage collapses. In this condition, the chest continues to rise and fall (effort is seen), but no air is admitted.
The "hook-up" was only mildly uncomfortable: the scalp has to be scoured with alcohol to ensure firm electrode connection. Despite the multitude of connections and wires, it wasn't too cumbersome. However, I experienced a good deal of difficulty falling asleep. This phenomenon is so frequently encountered that it has its own name: the "first night effect." Participants in sleep studies often experience difficulty falling asleep. If the study is conducted for more than a single night, the subjects often acclimate to their new surroundings and sleep soundly. I recall repeatedly being on the verge of sleep only to awaken abruptly with a spastic twitch, much like when trying to stay awake when tired in a lecture. It was as a result of one of these spastic, involuntary twitches that I jerked the finger pulse oximeter loose, prompting one of the technicians to enter to reconnect it. After a fitful night's sleep, I was awakened by one of the technicians. Feeling not at all refreshed, I dressed, walked back to my dormitory, and sunk into a deep sleep.
Later in the day, I was able to sit through the scoring of my sleep quality with one of the technicians. It was definitely a unique ̶ and somewhat unnerving ̶ experience viewing myself on the video. Initially, I had been concerned that I had "failed" the sleep test. Upon waking in the morning, I was firmly convinced that I hadn't slept at all, or at most, only dozed off. I had, in fact, slept for 3 hours and 45 minutes, enough for an assessment to be made.
Much to my surprise and relief, it turns out that I don't have sleep apnea. The index for number of breathing events was well within the normal range. Specifically, my Apnea/Hypopnea (A/H) index was 1.1. Sleep apnea is considered mild if 5-15 such events occur per hour. Moderate in the range of 15-30 events per hour. Severe is above 30 events per hour. While it seems that I am clear of sleep apnea, I was cautioned that sleep apnea tends to be more severe during REM sleep and due to the disturbed nature of my sleep, I experienced only a modest about of REM sleep (about 15 min). However, during this period of REM sleep, no episodes manifested. Also, I stayed on my back (the supine position) for most of the night. As sleep apnea is most severe in the supine position, I don't have to fear the assessment was skewed by my body position.
There was one unnerving breathing episode in which I appeared to stop breathing for an entire minute. The distinction between obstructive and central sleep apnea is an easy one to make. In central apnea, the chest fails to expand (a nervous system condition). In obstructive apnea, the chest continues to rise and fall, but air is unable to be drawn into the lungs. In this one minute cessation of breathing, my chest was seen to rise and fall, so this was an example ̶ and a disconcertingly long one at that ̶ of obstructive sleep apnea. When breathing resumed, I was seen to stir, being momentarily awakened. While it may sound alarming, my saturated blood oxygen level (SaO2) barely dipped in the aftermath of this breathing cessation. The technician explained that in some people, such as those with chronic obstructive pulmonary disease (COPD), such a breathing episode would be followed by a precipitous drop in SaO2. Throughout the course of the night, my SaO2 levels remained in the high 90s. Also, much to my surprise, it turns out that I do not snore.
While sleep apnea was ruled out, I was still left wondering what may account for my daytime drowsiness. Another technician looked at my sleep study and identified it as a textbook case of "delayed sleep phase syndrome." DSPS is a "circadian rhythm sleep disorder, a chronic disorder of the timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily rhythms relative to societal requirements." People with this condition report being unable to fall asleep until early morning and find it difficult to wake early for their obligations and commitments. There are a number of ways to remedy this condition, mostly through lifestyle modifications. These changes include abstaining from caffeine after noon, not engaging in strenuous physical exercise in the evening, and adherence to a strict sleep regimen. My lifestyle was definitely not following these simple rules as I would routinely consume caffeine throughout the day, lift weights late at night (thinking it might serve to tire me out), and had little regularity in my sleep cycle due to the changes in my workload.
I enjoyed my summer immersion experience at Weill Cornell and have a newfound respect for physicians and support staff who must interact with the sick on a routine basis. I now appreciate just how hectic their lives are and the pressing need that exists for engineers to provide superior devices to shorten wait times when every second matters and to lengthen patients' lives when every extra day is cherished.