In today's fast-paced society, sleep deprivation has become increasingly pervasive in our demanding daily routines. Whether we lose out on sleep because we don't make it a priority or due to unwelcome stress, insomnia or sleep disordered breathing, we put ourselves at a growing risk for a number of cardiovascular issues – including high blood pressure, stroke, atrial fibrillation, and heart disease.
Although it may be hard to believe that people spend around one-third of their lives sleeping, emerging research has begun to elucidate the complex inter-relationship and importance between sleep disordered breathing and cardiovascular disease. "Sleep is no longer considered a passive and homogenous state; instead it is understood to consist of cyclic periods of complex and changing brain activity, behavior and physiology," says Shailendra Singh, MD, FACC interventional cardiologist at Steward Medical Group. Sleep cycles can be divided into rapid eye movement (REM) and non-rapid eye movement (NREM), which individually carry out various functions that impact cardiovascular physiology and biomechanics, as well as activation of the sympathetic nervous system.
"Most people wonder how the cardiovascular system can be negatively affected during the seemingly benign activity of sleep. What transpires during sleep, which is designed to be restful and reparative for the body's processes, that can adversely affect the heart?" says Dr. Singh. "Pathological sleep begins as respiratory-related issue, most commonly termed sleep apnea or sleep disordered breathing. There are two main types of sleep apnea: obstructive and central."
Obstructive sleep apnea (OSA) is the more common form associated with snoring and occurs due to intermittent collapse of the upper airway, which translates to cessation or significant decrease in airflow.
"Collapse of the upper airway may happen during the deep stages of REM sleep, since we lose postural muscle tone thus allowing the airway to become transiently flaccid. Therefore, when we breathe in, the airway collapses on itself, and stays obstructed until we overcome the physical obstruction or when the brain actually wakes up momentarily," says Dr. Singh.
These episodes may occur hundreds of times nightly – up to one to two times per minute – in patients with severe OSA. It is often accompanied by wide swings in heart rate, a precipitous decrease in oxygen saturation, and brief electroencephalographic (EEG) arousals concomitant with loud breathing sounds as a bolus of air is exhaled when the airway reopens.
When we continuously have hypoxemia (decreased oxygen levels in the bloodstream) and carbon dioxide retention accompanied by many brain awakenings throughout the night, our body's reflex response is to increase the production of hormones, which also lead to sympathetic nerve activation. This in turn leads to increased blood pressure and heart rate, which over time can cause repetitive damage to blood vessels, structural damage to the heart, and cardiac arrhythmias thus leading to the possible sequelae of hypertension, atrial fibrillation, heart attack, stroke, and heart failure.
Dr. Singh explains, "we may think we have had a good night's sleep and unknowingly brush off symptoms – including disruptive snoring, daytime sleepiness, fatigue, morning headache and confusion – which could be signs of sleep apnea."
One of the larger problems with diagnosing sleep apnea is that many adults may not be aware of the abrupt awakenings they experience throughout the night, which are usually accompanied by gasping or choking for air before they drift back to sleep again. It is estimated that one in every five adults has mild OSA, one in 15 adults has moderate to severe OSA, and at least 75 percent of those who could benefit from treatment remain undiagnosed.
A polysomnography (overnight sleep study) is necessary to accurately diagnose OSA and to assess treatment benefit. Data is collected in the laboratory in the presence of a qualified technician. This protocol provides the opportunity to directly observe a variety of sleep-associated disturbances (such as, apneas, periodic leg movements, seizures, or REM behavior disorder).
The treatment of OSA usually entails reduction of weight and a continuous positive airway pressure (CPAP) machine, which provides a constant stream of forced air through a face mask and prevents the back of the throat from collapsing and obstructing airflow. "The delivery of oxygen at that high pressure opens up the airway for the patient, which decreases the effort required to breathe and thus reduces snoring with gaining continuous sleep without interruption. Although it may take time to adjust to having oxygen therapy while sleeping, many innovative devices have improved options for patient comfort and my patients dramatically feel better," Dr. Singh says of CPAP treatment.
"The question we are investigating now is, essentially, whether effective CPAP treatment causally decreases cardiovascular mortality. We have recently developed randomized trials that are currently being administered, but we don't have a definitive answer yet. Often there is an improvement in high blood pressure. But the most encouraging result is that thousands of patients have said it improves their quality of life."
As with any medical condition, one of the more difficult things to fully comprehend is the comprehensive scope of potential health risks associated with lack of sleep, poor sleep quality or sleep apnea. Dr. Singh has found that when discussing these risks, breaking it down into non-complex terminology leads to patient satisfaction, more effective communication with patients, and increased adherence overall.