Sleep apnoea is a condition that is characterised by repeated breathing interruptions during sleep. It is a serious condition that affects an estimated one billion people worldwide,¹ many of whom are unaware of it and are, thus, undiagnosed. 

Sleep apnoea disrupts sleep and affects the uptake and distribution of oxygen within the body. It is also linked to an increased risk of developing other conditions like diabetes and heart diseases, like hypertension.

This article explores how the two conditions, sleep apnoea and hypertension, are related with the aim of understanding and addressing both conditions and mitigating their impact on overall health, offering a way to improve the well-being of those affected.

What is sleep apnoea?

Sleep apnoea is a highly prevalent yet underdiagnosed condition. It is characterised by a minimum of 10-second intervals of irregular breathing during sleep. The breathing stops and starts intermittently, which causes reduced oxygen distribution throughout the body and results in arousal from sleep.² Sleep apnoea can only be identified with the help of a sleep study.

Symptoms of sleep apnoea

A patient with sleep apnoea can exhibit some, or all, of the following symptoms :

• Altered breathing when sleeping
• Gasping for air while asleep
• Snoring
• Dry mouth upon waking
• Morning headaches
• Insomnia
• Increased tiredness and lethargy during the day
• Irritability and other behavioural changes
• Reduced brain function, like memory, concentration, etc
• Higher incidence of anxiety and depression

Types of sleep apnoea

Sleep apnoea is categorised into two different primary types;

1. Obstructive sleep apnoea

It is caused by the relaxation of the soft tissues in the throat muscles, leading to the blocking of the airways to the lungs, obstructing breathing. This is the more common of the two.

2. Central sleep apnoea

It is caused when the brain sends improper signals to the muscles that control breathing, adversely affecting regulated breathing.

A commonly seen subtype of sleep apnoea is Treatment-Emergent Central Sleep Apnoea (Complex Sleep Apnoea), which occurs when the treatment/ therapy for Obstructive Sleep Apnoea results in the development of Central Sleep Apnoea in the patient. 

What is hypertension?

Hypertension, commonly known as high blood pressure, is a condition marked by the increased pressure exerted on the walls of the blood vessels by the blood flowing in them. This condition is highly underdiagnosed and is often identified during routine medical check-ups.

Symptoms of hypertension

In most cases, patients are unable to identify any symptoms of hypertension, making it a dreaded “silent killer”.

However, there are a few symptoms that indicate elevated blood pressure. These are:

• Heaviness in the head or headaches
• Dizziness
• Nausea
• Blurred vision
• Shortness of breath
• Nosebleed
• Heart palpitations and anxiety

Relationship between sleep apnoea and hypertension

Sleep apnoea has been found to be closely linked to hypertension. Approximately 40% of high blood pressure patients also struggle with sleep apnoea. And nearly half of the cases of sleep apnoea have been found to be hypertensive.

Sympathetic response

Sleep apnoea repeatedly results in obstructed breathing, affecting the amount of oxygen that reaches the lungs and organs. This hypoxia leads to stress, triggering the brain’s “fight or flight” response. The body responds by releasing stress hormones. 

Physiologically, when the airflow into the lungs is interrupted due to airway collapse, there is a drop in air pressure in the lung with contraction of the diaphragm. This results in a pressure difference between inside and outside of the blood vessels. This causes blood vessels to widen in an attempt to balance the pressure, lowering the blood pressure and the amount of blood reaching the heart with each contraction. This results in a signal to the brain to increase sympathetic nervous system activity, thereby releasing the stress hormones. The stress hormones increase the heart rate, resulting in elevated blood pressure.³

Hypoxic stress results in another phenomenon called reverse dipping. This happens when people have the same or even higher blood pressure levels at night compared to the day, as opposed to a fall in blood pressure that is normally observed in healthy individuals. This happens because repeated airway collapse and the constant struggle to breathe as a result of sleep apnoea puts the body under constant stress at night, resulting in elevated blood pressure.⁴ This can lead to consistently high blood pressure over time throughout the day.

Renin angiotensin aldosterone pathway activation

The RAAS pathway is a hormonal system whose function is to regulate blood pressure and the fluid and electrolyte balance in the body. Renin, an enzyme produced in the kidneys, is overactivated by low oxygen levels in the body. Renin further activates angiotensin, which causes the constriction of blood vessels, resulting in higher blood pressure.⁵

RAAS activation also causes the body to hold onto more salt and water, raising blood pressure even more.

Hypoxemia and systemic inflammation

People with sleep apnoea often have higher levels of inflammatory markers like cytokines in their blood. This indicates that their bodies are experiencing increased inflammation. During sleep apnoea, periods of not breathing lead to drops in oxygen levels. When breathing resumes, the sudden return of oxygen can cause damage, similar to the harm seen when blood flow resumes after a blockage. This releases harmful molecules that further inflame tissues. The ongoing stress and inflammation from these repeated events can raise the risk of developing high blood pressure over time.

Nighttime fluid shift

During the day, fluid builds up in your legs due to gravity, especially if you sit for long periods. At night, when you lie down, this fluid moves upwards towards the upper body and head. Fluid may accumulate in the neck, narrowing the upper airway and leading to sleep apnoea. This fluid shift can worsen sleep apnoea by making it harder to breathe.⁶

Management of sleep apnoea-associated hypertension

While the primary mode of management of hypertension is anti-hypertensive drugs, there are several other effective strategies that can be applied. These include;

Lifestyle alterations

There are some conditions that not just affect sleep apnoea but also directly influence hypertension. These include obesity, smoking, alcoholism, etc. Managing these conditions can have a significant effect on both conditions.

Surgical interventions

In conditions where anatomical abnormalities have been identified as the reason for sleep apnoea development, nasal surgery can be considered as a highly effective management method.

Bariatric surgery is another weight management method that has seen significant results in reducing the severity of sleep apnoea in patients.

Continuous positive airway pressure (CPAP)

The CPAP is the most effective means of managing sleep apnoea. The machine functions by pumping air into the airways of the patient through a mask, preventing a collapse during sleep.

CPAP has seen success in not only reducing nighttime blood pressure but also during the day. It also has documented success in reducing the release of stress hormones in the body.

One of the challenges with this method is patient compliance. This is a result of poor tolerance coupled with the challenge of understanding and operating its complex machinery. 

Oral appliance therapy

This is an effective management technique for people suffering from mild to moderate sleep apnea, although it is not as effective as CPAP. ⁷

The types of oral appliances in the management of sleep apnoea-related hypertension are;

1. Soft palate lifters - They lift both the soft palate and the uvula
2. Tongue retaining devices (TRD) - They hold the tongue forward and prevent its collapse into the airway by holding it forward with suction
3. Mandibular advancement devices (MAD) - They move the mandible and the attached tongue forward, increasing the cross-sectional passage for the airway to pass through

Positional therapy

Positional therapy causes the patient to avoid sleeping on their back in cases where positional sleep apnoea is seen. By placing something behind the patient’s back, preventing them from rolling over in their sleep, their sleep apnoea is often reduced or eliminated.

Pharmacological treatment

Drug therapy has been suggested by research to be a good alternative to CPAP in mild to moderate cases of apnoea. The mechanisms for this method include a reduction in REM sleep when apnoeas are found to be most frequent, increasing the muscle tone for the upper airway or increasing the respiratory tone. 

By combining these various treatment strategies, individuals with sleep apnoea-associated hypertension can achieve better management of both conditions, leading to improved overall health.

Summary

Sleep apnoea is a medical condition affecting millions of people globally, marked by the repeated stopping and starting of breathing during sleep. This interrupted breathing reduces oxygen levels, triggering a stress response and inflammation in the body, leading to elevated blood pressure, especially at night. If left untreated, sleep apnoea can result in long-term hypertension and other serious health problems like heart disease and diabetes.

While anti-hypertensive medications help manage high blood pressure, it is important to treat the sleep apnoea for overall health improvement. Sleep apnoea-associated hypertension can be managed by a combination of lifestyle changes, surgical interventions, medication and medical treatments. Of the different methods, CPAP therapy has shown the highest success in studies, though patient compliance has been identified to be a challenge due to the need for overnight mask usage. By integrating various strategies, individuals can achieve better control over their sleep apnoea and hypertension, leading to improved health outcomes.