Sleep apnea and cardiovascular effects

Obstructive sleep apnea (OSA) is associated with high blood pressure and cardiac arrhythmias. When someone has a sleep apnea event, their heart rate typically slows down. Heart rate then speeds up during the subsequent recovery breaths. It's this repetitive slow-fast cycle during the night that is thought to contribute to arrhythmia. And research has shown that the more oxygen levels decrease during sleep apnea, the greater the risk to the heart and blood vessels. This study was done in a rat model of OSA. The results showed that the low oxygen levels from OSA damaged vital neurons in the rats' brains that regulate blood pressure and heart rate. This could explain why OSA increases risk of high blood pressure and cardiac rhythm problems. More research will be needed to determine if treating OSA can reverse the damage to those neurons.

Yawning may cool the brain

I sometimes get asked why we yawn and I am not sure. I was taught that it was to increase oxygen supply to the blood, but research has not demonstrated that definitively. This study showed that yawning may be a way that the brain gets cooled. Specifically researchers studied contagious yawning - that type of yawning which occurs when you see another person yawn. This is in contrast to spontaneous yawning. The results showed that contagious yawning was more common at warm temperatures. However, it was not more common at very hot temperatures, such as in Arizona in the summer.

Obstructive sleep apnea and cardiovascular disease

Research has shown that obstructive sleep apnea (OSA) increases risk of cardiovascular disease - possibly by multiple pathways - repeated oxygen level drop offs, broken up sleep, chronic hyperactivity of central nervous system, and systemic inflammation. However, the studies have looked only at the apnea-hypopnea index (AHI) as a marker for OSA severity. AHI is good for this, as it tells me how many times per hour your airway collapsed, but it does not tell me about oxygen levels or sleep quality. So researchers did this study to address this issue. Specifically, they studied >10,000 people with a wide variety of OSA severity. They examined the relationship between OSA related variables and cardiovascular outcomes as well as all-cause mortality. They even controlled for traditional cardiovascular risk factors like gender, age, body mass index, etc. The results were surprising - the AHI did not correlate with cardiovascular outcomes when controlling for the potential confounders. However, other related variables did correlate - things such as amount of time asleep with oxygen saturations < 90%, the number of awakenings, mean heart rate, total sleep time, and presence of excessive daytime sleepiness. Specifically, the time spent asleep with oxygen saturations less than 90% increased risk of cardiovascular event or death by 50%.