What is the link between sleep apnoea and high blood pressure?
When someone has sleep apnoea, their airways partially or completely close during apnoeic episodes. This reduces airflow, so the person’s oxygen levels drop. The body detects this as a problem and sends messages to the brain to correct this by making the blood vessels squeeze a bit tighter to provide more blood, and hence more fuel and oxygen, to the brain. If this occurs frequently and repeatedly, high blood pressure can develop.
Eventually, the body adapts. The blood vessels modify to the increased force from the blood, by becoming thicker and stronger. However, this can lead to a further reduction of oxygen delivery to important organs like the kidneys. This can then cause an increase of the enzyme renin in the body, which further drives up blood pressure.
The brain also works to wake you up so that you breathe again. It is this combination of low oxygen and arousal from sleep that is thought to be the main driver of high blood pressure. It is well accepted that sleep apnoea is the leading cause of secondary high blood pressure (also known as secondary hypertension), which is high blood pressure with a known cause, and this is what my research is focusing on.
What symptoms should I look for?
High blood pressure (hypertension) is what we call a ‘silent disease’. The problems occurring are all inside the body, so outwardly you just don’t look sick as you can do with other illnesses, and you may not feel any differently either. People often find out they have hypertension after they’ve presented to a doctor or hospital for something else. That’s why it’s so important to have annual blood pressure checks with your medical professional, keep an eye on your blood pressure numbers and know your family medical history. If, for example, you have a family history of high blood pressure, then you should be checked more diligently.
Sleep apnoea is a tricky one. As it occurs during sleep, usually the sufferer is the last one to know they have symptoms. They are normally alerted by their bed-sharing partner. Snoring isn’t always indicative of sleep apnoea, but it is common. As sleep apnoea progresses and becomes more severe, the sufferer is likely to wake more often throughout the night with a gasping, coughing or choking sensation, as their body wakes to improve oxygen levels. They will have a dry mouth and feel very tired in the morning despite having (seemingly) a full night’s sleep. Daytime fatigue can set in, which can cause a mental fog.
How does it differ between men and women?
Traditionally sleep apnoea was thought to more frequently affect men who are larger in size, sleep on their back and snore loudly. However, women experience sleep apnoea as well. More research needs to be done in this area, but from what we are seeing, women present differently to men with their symptoms.
Women snore less and do not necessarily have the obvious waking with choking and gasping. Their symptoms are more generalised, with symptoms of tiredness, fatigue and feeling run down. This can be during the perimenopausal time, when women are either working or raising children or doing both, so the symptoms may be put down to it simply being an exhausting time of life.
How does this affect diagnosis?
Women tend to be diagnosed with other things, such as depression or thyroid conditions, but these tag along with sleep apnoea, so the actual cause is not being treated. Presently, one woman is diagnosed with sleep apnoea for every nine men, even though the limited research available suggests that sleep apnoea is present in one woman for every three men.
What positive steps can I take?
Sleep studies have evolved quickly. Instead of spending a night of observation in a clinic, as was traditional, there are now take-home packs that will give you a diagnosis after one night’s sleep. These sleep study packs are available from your local sleep clinic.
Results are surprising, as 20 per cent of sufferers are not overweight and follow a reasonably healthy lifestyle, so it is worth getting yourself checked.
If you are experiencing sleep apnoea, you have a number of treatment options, including the gold-standard continuous positive airway pressure (CPAP) machine, which blows air into your airways as you sleep, continuously preventing them from collapsing. This can help your quality of sleep return, along with your energy levels.
Other positive steps to take are to modify your lifestyle by decreasing alcohol consumption, stop smoking, lose some weight if you are carrying extra and eat a balanced nutritional diet. Always consult your health practitioner or sleep clinician on the best and safest steps for you.
What is the goal of your research?
Ultimately, if I can figure out the mechanisms behind sleep apnoea and how it affects the body longer-term, then we can develop more targeted treatments to prevent high blood pressure and other cardiovascular diseases from developing further down the line. This will reduce the risk of heart attack or stroke later in life, thus allowing everyone the best chance for a better quality of life.
What else are you researching?
I’m also looking into what is happening in the brain that causes excessive sympathetic activation, which also leads to long-term problems. The sympathetic nervous system controls the fight or flight response, which affects blood pressure, blood glucose control, breathing and so on. When activated, it prepares your body to either run or fight, so it shuts down your digestive functions and funnels everything to your muscles and your heart. This is why you experience an increased heart rate and dry mouth.
The other side of the coin is the parasympathetic system, which is your rest and digest system. This takes over after you’ve eaten and funnels the blood away from your muscles to your gut to aid digestion. Much of this happens while you sleep.
The relationship between the sympathetic and the parasympathetic nervous system features in the production of glucose. My other research project is looking at sympathetic function in diabetes, as this is another key feature of people with sleep apnoea.
What motivated you to study this field?
Everybody knows somebody with sleep apnoea, myself included. But even more importantly, sleep apnoea appears to be central to a number of diseases – 80 per cent of people with hypertension have sleep apnoea, 80 per cent of people who have heart failure have sleep apnoea, and 70–80 per cent of people with diabetes have sleep apnoea. It just boggled my mind that the underlying processes which are occurring in the brain to cause these long-lasting effects were not being adequately studied. It is a hugely relevant area for many people, and there is just so much more to discover.
Look out for Dr Melissa Farnham in the February 2021 edition of Australian Women’s Weekly, as she discusses ‘How to keep your arteries healthy’.