The link between sleep and high blood pressure
The effects of high blood pressure are well documented – greater risk of heart attack or stroke being top of the list. But did you know that there’s also a link between high blood pressure and a lack of good-quality sleep?
At the Sleep Laboratory, located at the New Zealand Respiratory & Sleep Institute (NZRSI), where clients with possible sleep apnoea are tested overnight, blood pressure is carefully monitored. That’s because about 10% of individuals with high blood pressure have an underlying cause. One of the important and common secondary causes is obstructive sleep apnoea (OSA).
In untreated OSA, disturbed sleep often means that blood pressure goes up overnight rather than falling as it is meant to. This ‘nocturnal rise’ is an important risk for heart disease and stroke, and one of the important benefits of OSA treatment is to restore a healthy overnight drop in blood pressure, even if overall blood pressure is still a little high.
High blood pressure: did you know?
The medical term for high blood pressure is hypertension.
It is the most common chronic disease in adults. At any one time, 26% of all adults with suffer from hypertension.
Each year 20,000 more people in the greater Auckland area will develop hypertension.
Hypertension is the most important treatable cause of premature disability and death.
Although hypertension is more common in those aged 40 years and above, it can and does occur at any age, even in otherwise slim, healthy, active people.
The reason it has become known as ‘the silent killer’ is because it is mostly asymptomatic. Most people with high blood pressure have no symptoms at all, until they present with a complication.
High blood pressure tends to go undiagnosed for long periods, especially in younger men who tend not to visit the doctor frequently.
The only way to detect hypertension is to have your blood pressure checked at least once a year.
Being overweight, and high dietary sodium (salt) intake, are the two most important environmental risk factors for developing high blood pressure.
Untreated high blood pressure is a risk factor for stroke, heart failure, heart attack, kidney disease, and visual loss.
In general a blood pressure of 140/90 (when measured at a clinic or doctor’s surgery) is the threshold for treatment.
High blood pressure and sleep
At night, the normal physiological response is for an individual’s blood pressure to drop to under 120/70. This natural process, which is part of our circadian rhythms, is known as ‘dipping’ and is beneficial to the body and the brain.
People with OSA do not experience deep sleep, and so this dipping may not occur. A typical sufferer will endure a nightly cycle of loud snoring and a temporary cessation of breathing (which results in a drop in oxygen levels). After this, they will wake up and gulp for air – and their body is flooded with adrenalin.
In poor sleepers with OSA, the sympathetic nervous system (which controls involuntary activities such as bowel movements and blood pressure) can be in a constant state of over-stimulation. This is effectively a ‘fight or flight’ physiological state and your blood pressure will naturally rise.
People who work shifts or are chronically sleep deprived have a higher risk of hypertension.
There is evidence that chemically induced sleep (as in sleep that results from pharmaceutical or is alcohol-induced) does not cause the same beneficial ‘dipping’ of blood pressure levels.
Patients with untreated sleep apnoea (OSA) usually feel too tired during the day to exercise and so lack motivation. Once they start to use the CPAP (continuous positive airway pressure) machine at night, their sleep improves and their ability and willingness to exercise does too.
Image / FreeDigitalPhotos.net – marin