I recently asked a patient about his compliance with therapy for obstructive sleep apnea (OSA) and got an odd response. "What does it matter to you if I use my CPAP?" The CPAP to which he referred is the mask that OSA sufferers wear at night to improve their oxygen levels during sleep.
On one level I can understand his question. This is a sleeping problem, after all—not exactly the realm of cardiology. Why should I care if he starts his day refreshed or drags himself out of bed feeling hung over? Other patients have similarly expressed confusion (albeit less bluntly) about the relationship between OSA and heart function. Before I clarify this connection, let me walk you through the normal physiology of sleep.
A night's slumber is composed of many periods where the brain drifts between various levels of consciousness. The deepest—and most restorative—stage is REM sleep, the period during which your brain is at its most active. Since your dreams can become pretty vivid (like showing up to school for final exams that you haven't studied for, and wearing no pants—I guess I'm revealing too much personal information) your body compensates by disconnecting your brain from your muscles. That way when you dream about trying to fly you don't end up smacking your spouse as you flap your wings.
The problem with this sleep-induced paralysis is that the muscles in your neck—normally in a constant state of mild contraction during breathing—relax and allow the weight of your double chin to press down on your airway and effectively choke you. A person suffering OSA will be seen to fight violently against a closed airway while trying to get a breath in—sucking but pulling in no air, like a vacuum cleaner that accidentally engulfed the family gerbil. This can go on for up to a minute before he succumbs to the stress of suffocation and exits REM sleep—not rousing enough to remember the episode, but with sufficient sleep disruption that he spends the next day exhausted. This pattern can repeat itself dozens of times during the night.
Obese men are at highest risk, but I've seen OSA in all types. In my opinion, if a patient or spouse suspects OSA then it's highly likely to be present. A sleep study will confirm the diagnosis. The treatment is to wear a contraption known as CPAP (continuous positive airway pressure) that forces air into the lungs during inhalation so that the airway doesn't collapse.
So how does it affect the heart? Here's a step-by-step lesson in OSA pathology:
- Nighttime breath-holding episodes lead to low oxygen levels, triggering constriction in the blood vessels that pass through the lungs.
- Night after night of vascular constriction leads to scarring of the small vessels.
- The pressure required to push blood through the lungs gradually rises, causing the right ventricle to enlarge and weaken.
- Without an effective right ventricle, fluid builds up in the abdomen and legs.
- Your doctor tries to treat swelling with diuretics (water pills), which cause the kidneys to eliminate water in the urine. For the kidneys to get rid of fluid the blood must be effectively circulated to the kidneys, which doesn't happen because of the weak right ventricle; the kidneys begin to fail.
- The patient is left with swelling that is refractory to medication; kidneys that are heading for dialysis; and, of course, feeling tired and exhausted.
Leg swelling and fatigue aren't the only byproducts of untreated OSA. For reasons too complicated to describe here OSA can lead to high blood pressure that is often refractory to standard doses of medications. Furthermore, the persistent strain on the right chambers of the heart frequently leads to heart rhythm disturbances such as atrial fibrillation.
So, while I'd rather spend my office time discussing problems I can fix with catheters and pacemakers I find that I'm frequently talking about sleep habits. Early use of CPAP can mitigate nearly all the adverse cardiac effects of OSA as well as return the patient to restorative sleep (this works even better when coupled with weight loss). The first step to get someone to try CPAP is teaching him why he needs it.
I wish I could report that my patient listened carefully to my reasoning and vowed to renew his efforts at CPAP and lifestyle compliance. In reality I think he blew off both me and his OSA therapy. I'm sure I'll see him again in the future but by then the damage might be permanent.
On an unrelated note I'd like to provide a plug for the Lifesaving Award, a new recognition at the AHA Heart Walk this May. The purpose of this honor is to recognize people who have been placed in the challenging situation of having to perform CPR on a victim of cardiac or respiratory arrest. The hope is that we can elevate the public's recognition of the importance of learning basic life support skills. If you know of someone who fits this description you can nominate her or him at this website. The deadline is April 20th.