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Dear Dr. Roach: I read your recent column on people with obstructive sleep apnea (OSA) needing to urinate more than others. What about those who have central sleep apnea (CSA)? I'm a 74-year-old male who's taking medications for an enlarged prostate, high cholesterol, and high blood pressure, which are all under control. I urinate maybe twice a night during my sleep, sometimes not at all.
I had a sleep study done in 2017, which showed CSA that wasn't controlled by the end of the study. A CPAP device didn't help, and I'm now using a BiPAP machine. Does the frequent urination ever diminish? Or can this be a result of taking finasteride and tamsulosin for my prostate? -- C.M.
Answer: Most people know that OSA is a condition where people are unable to breathe properly, because their throat relaxes in such a way that the airway gets closed by soft tissue in the back of the throat. Although OSA is much more common in people who are heavier, it may occur in people of any size.
CSA isn't caused by airway obstruction; the process instead happens at the level of the brain. One condition that can predispose people to CSA is a stroke, but in most people, CSA is self-limited after a stroke. Heart failure is a more common underlying condition in people with CSA.
The faster, deeper breathing that's common in people with heart failure causes the carbon dioxide level to go so low in the blood that the brain "forgets" to breathe. This leads to the CO2 level getting so high that the brain triggers increased breathing. The person then cycles between too little breathing and excess breathing many times throughout the night.
CSA itself isn't a common cause for excess urination at night. However, if you had heart failure, this could explain the urination at nighttime, since it's a common feature.
To put it very simply, the heart output during the day is concentrated on keeping the muscles going. At night, there's enough heart output that the system can direct more blood flow to the kidneys. So, the kidneys remove the excess salt and water at night, which causes a person to get up frequently.
Twice a night is more in the range of what I'd expect in a 74-year-old man with a treated enlarged prostate, than what I'd expect in a man with heart failure or OSA.