Sleep apnea is when you stop breathing while sleeping. After a while, due to lack of oxygen, you wake up. The most common form of sleep apnea is obstructive sleep apnea, OSA, in which the airway in the back of the neck collapses during sleep. As the airway starts to collapse in OSA, snoring may occur.
A less common apnea is central sleep apnea, in which the airway remains open, but the patient stops breathing, anyway. (Perhaps it is called “central” because it is caused by the central nervous system.)
After not sleeping well for over a year, my doctor scheduled a sleep study, which is a night in the hospital with wires to monitor the brain’s electrical activity, oxygen sensor on the finger, microphone near the nose (to pick up snoring), and an infrared camera watching me sleep. As I recall, the system found I had 12 apneas per hour. (Over about 5 an hour indicates sleep apnea, as I understand.) Perhaps this condition was brought on by gaining weight. A long-term approach, then, is to lose weight. In the mean time, the sleep doctor prescribed a CPAP machine (continuous positive airway pressure), which forces air through a mask into your lungs to keep the airway from collapsing.
In my case, my main complaint is that I wake up after three or four hours of sleep. Hopefully, using the CPAP will let me sleep longer.
These machines are pretty sophisticated. The patient is not told how to change the settings, which is reasonable for most patients. For myself, I wanted to know everything about the machine, so I went to the web, and learned how to access the software controls, plus I read the clinician’s manual, which explained what the controls do.
The primary variable with these machines is the pressure, measured in centimeters of water, cm H2O. The range of pressures is 4 to 20. I used my CPAP in auto-CPAP mode for a while, with a starting pressure of 8 and a maximum of 20. For a while the pressure went up to 13 during the night, but one night it went up to 17. I changed the auto-CPAP range to 9 to 20, and it went up to 17 consistently. I tried getting used to these higher pressures by gradually increasing the minimum pressure up to 17.0. The pressure would increase to about 17.9. On about 5 nights I’ve seen the pressure at 18 or higher. The number of apneas per hour is called the AHI, apnea hypopnea index, where hypopneas are less severe apneas. The AHI at these pressures was often less then 0.5; that is, on average, half an event per hour. (It isn’t clear if those are all apneas, or apneas that the CPAP did not successfully prevent.)
Those high pressures are hard to stand. My mask, called a full facial mask, covers the mouth and nose. When the mouth drops open during sleep, air enters through the mouth, drying the tongue out. I purchased a chin strap to hold my mouth closed. However, I finally realized that these high pressures are just plain uncomfortable, and that is why I was not sleeping soundly. One feature of this CPAP is EPR: expiratory pressure relief. The machine senses when I exhale, and reduces the pressure by 3 cm H2O, which is kinda cool. Nonetheless, these high pressures take several days if not longer to get used to. There is some discomfort in the chest until the body is used to the pressure.
So, instead of focusing on reducing the number of events per hour (the AHI), I have been focusing on increasing the length of time that I can sleep without waking up. I’ve switched from auto-CPAP mode to CPAP mode, which provides a constant pressure throughout the night, except for the very start of a session, when the pressure ramps up over five minutes. (The machine also has an auto-ramp, which doesn’t start to ramp the pressure up until it detects from your breathing that you are asleep.)
I’ve gradually reduced the pressure, looking to find the point at which I sleep best. I suspect a pressure around 15.5 may be best, but I need to go back and check that.
Jan. 20, 2018 Last night I was down to a pressure of 11.0. The AHI was 1.8. I woke up several times during the night, and finally got up after 3 hours on the machine. I conclude that 11.0 is too low to help me sleep well. I am about to go back to bed with the pressure at 12, and hope that I sleep better. I’ll record nightly results below.
Jan. 26, 2018 Still at a pressure of 12. Took some getting used to the pressure (didn’t expect that). I’ve forced myself not to get up and stay up in the middle of the night (that may have gotten to be a habit). However, I wake up many times during the night. The last two days the AHI rose to 5, then 3 events per hour. I suspect that, now that I’m used to the pressure, I’m sleeping more deeply, resulting in more apneas per hour. I’m able to stay in bed for around 8 hours, but the quality of sleep is not good.
Jan. 27, 2018 Increased the pressure to 13. Slept much better for the first part of the night, but then the pressure increase caught up with me, and the discomfort in the chest made it hard to sleep. Couldn’t get back to sleep with the machine on, so I got up.
Jan. 28, 2018 Another night at 13. Slept a little longer, but the pressure still wakes me up. Since the quality of sleep is noticeably better, I’ll tough it out, and get used to 13, rather than lowering the pressure, and gradually getting used to 13.