Wednesday, March 5, 2014
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%.