Author: Patricia Nicholson

When someone is diagnosed with sleep apnea, it’s often because their partner complained about snoring. They seek help not for the condition, but for the symptom. But the real dangers of sleep apnea are its links to high blood pressure and possibly cardiovascular disease.

That’s why Dr. Anu Tandon, a respirologist at Women’s College Hospital in Toronto, calls sleep apnea the not-so-silent killer.

‘Snoring can actually be a little more sinister than people think, and it’s not just cosmetics,’ she says.

An apnea is a stoppage of breathing for at least 10 seconds, during which there is no air flow. In obstructive sleep apnea, this is the result of a collapse of the upper airway, which blocks breathing.

People with obstructive sleep apnea have recurrent episodes of upper airway obstruction during the night, and repeated awakenings. Causes include obesity and very large tonsils, although it is also seen in women who are very petite and who have very small airways.

One of the big dangers of sleep apnea is its association with one of the most significant cardiovascular risk factors: hypertension.

The severity of sleep apnea is measured using an apnea-hypopnea index. Hypopnea is a drop in respiration, such as breathing that is very shallow or very slow, but not stopped like apnea. The index is based on the number of apnea and hypopnea incidents that occur on one hour.

‘It’s actually normal to stop breathing up to five times an hour,’ Dr. Tandon says. ‘Five to 15 times an hour is consistent with a mild degree of sleep apnea, 15 to 30 is consistent with a moderate degree of sleep apnea and greater than 30 times an hour is consistent with a severe degree.’

Linking sleep apnea and blood pressure

There are several studies that show a relationship between sleep apnea and high blood pressure. Physiologically, it is thought that when a person stops breathing at night, it alerts the sympathetic nervous system (the one responsible for ‘fight or flight’ responses in stressful situations), which then releases compounds called catecholamines that act like stress hormones. Prolonged high levels of catecholamines have been linked to high blood pressure.

‘There’s a constant surge in sympathetics, or catecholamines, overnight that can essentially be flogging the heart, increasing the heart rate, increasing the blood pressure,’ Dr. Tandon says.

Studies have shown that the risk of high blood pressure increases with the severity of sleep apnea. Clinical studies have also shown that severe sleep apnea is an independent risk factor for high blood pressure.

‘Even after adjusting for body mass index, neck circumference, waist to hip ratio, all of the things that could be confounding factors, you still have increased odds of developing hypertension with the obstructive apnea being untreated,’ Dr. Tandon says.

‘So we have the doom and gloom: that obstructive apnea can cause high blood pressure.’

However, it appears that treating the sleep apnea may help to reverse this effect.

The treatment for sleep apnea is CPAP (continuous positive airway pressure). While sleeping, the patient wears a mask over her nose, which is connected to a small machine which takes in air, pressurizes it and delivers airway pressure through the mask.

‘That opens up the airways,’ Dr. Tandon explains. ‘Your oxygen levels stay up and you’re able to breathe freely throughout the night.’

Studies have found that one month of effective CPAP treatment was associated with a 10 mmHg drop in blood pressure.

Heart health

While there is conclusive evidence linking sleep apnea to high blood pressure, a possible relationship between sleep apnea and cardiovascular disease is still being explored.

‘It’s a difficult area to tease out because there’s such an overlap between cardiovascular risk factors and risk factors for obstructive sleep apnea,’ Dr. Tandon says. For example, excess weight, age and smoking are all risk factors for sleep apnea. However, she adds that there are mechanisms that are unique to obstructive sleep apnea that would make it a possible risk factor for coronary disease:

• Repeated bouts of hypoxemia (lack of oxygen in the arterial blood, which results from the oxygen desaturation associated with sleep apnea) can put extra stress on the lining of the blood vessels, which can lead to changes in the blood vessels that can aggravate blood pressure and contribute to heart disease.
• When nightly airway blockages and awakenings frequently kick the sympathetic nervous system into gear (and prompt it to release catecholamines), it can raise the heart rate as well as blood pressure.
• Patients with obstructive sleep apnea have been shown to have elevated levels of fibrinogen and homocysteine, both of which can contribute to coronary heart disease. Fibrinogen is a protein involved in blood clotting, and homocysteine is an amino acid that can damage the walls of blood vessels and also increase risk of blood clots that can cause a heart attack or stroke.
• People with sleep apnea may also have an increased risk of plaque rupture – a crack in the unstable plaque on the inside of a blood vessel. The crack itself is not necessarily harmful (it does not go through the wall of blood vessel), but it causes clotting activity as the vessel tries to seal over the crack.

‘From a physiology standpoint, we know that patients with obstructive sleep apnea have reduced oxygen levels,’ Dr. Tandon says. ‘They frequently wake up at night, which seems to increase sympathetic activity at night as well. The thought is that all of these factors have set the stage for increased cardiovascular disease in this population.’

Snoring: safe or sinister?

It’s important to note that not all snoring is caused by sleep apnea. Also, some people with sleep apnea do not snore. Dr. Tandon also notes that snoring is very subjective.

‘Unless you hear your own snoring and are woken up by your own snoring, you’re relying on your partner to report snoring,’ she says. ‘It’s well determined that men report it less than women, simply because men are likely snoring more.'

There are also apnea patients who progress from mild obstructive sleep apnea to moderate or severe apnea. Weight gain is the most predominant risk factor for progression of apnea, but age is also an issue, because airways lose their structural integrity and become floppier with age. Age is a risk factor for women in particular: risk of sleep apnea triples after menopause when estrogen and progesterone levels go down, because those hormones help to protect and maintain airways.

Sleep apnea may put more at risk than a good night’s sleep, but it may be possible to avoid its more dangerous effects.

‘Obstructive sleep apnea affects about four per cent of the population, and it has been identified as an independent risk factor for hypertension. Possibly for ischemic heart disease, possibly for heart failure and possibly for stroke,’ Dr. Tandon says, noting that strong evidence from clinical trials was only available for high blood pressure.

‘Treating severe sleep apnea can possibly reduce the risk of these conditions, and the mortality associated with them.’