Overview 

Hypoxia is a condition relating to low oxygen levels in the organs and has a significant influence on the cardiovascular system. Whether it is caused by existing heart conditions, induced by environmental factors or triggers the onset of other health conditions, hypoxia can have devastating effects. This article gives an overview of hypoxia, its relation to the cardiovascular system and how it can be treated. 

What is hypoxia?

Hypoxia is a state in which there is a lack of oxygen in the tissues of the body. Low levels of oxygen cause cells to adapt to the changes in the environment, which revert back when oxygen levels return to normal in healthy individuals.¹ However, if low oxygen levels persist, cells can become stressed and damaged. 

Hypoxic states are normally linked to underlying health conditions that are related to problems in the cardiovascular or respiratory system. Hypoxia is an umbrella term for its four main types, these being:²

Symptoms

As there are so many different tissue types in the human body that require oxygen to function, low levels of oxygen can cause a large array of symptoms. Many of these symptoms are nonspecific to hypoxia, but it is important to seek medical attention if they are experienced:²

• Blue colouring on the skin/nails (Cyanosis)
• Increased heart rate
• Shortness of breath
• Restlessness
• Headache
• Depression

The cardiovascular system 

The cardiovascular system consists of the heart, blood vessels and the blood. As the main transportation system of the body, its main role is to deliver oxygen and nutrients to tissues, as well as take away waste products and carbon dioxide to be discarded. 

The blood

Each human carries around 5 litres of blood in their bodies at any one time.³ Blood is essential for the delivery of oxygen and nutrients to our organs so that they function efficiently. It is made up of several components:⁴

The blood vessels 

Blood vessels branch from the heart and act as channels for blood to flow around the body. They are categorised into arteries, veins and capillaries, all with different roles to ensure maximum efficiency.⁵

Arteries are tubes that take blood away from the heart to the other organs. The muscular layer of the arteries dilates and constricts the tube to aid the heart in pumping blood around the body.⁵ The largest of the arteries is the aorta, sprouting from the top of the heart and branching into smaller and smaller arteries.

Veins, on the other hand, have much less muscle and bring blood back towards the heart at a low pressure. Because of this low pressure, veins also have valves to prevent blood from flowing backwards or in the wrong direction.⁵ In diagrams, veins are often depicted as blue. This is because the blood on its way back to the heart is ‘deoxygenated’, meaning it is low in oxygen after delivering it around the body.

Capillaries are the smallest type of blood vessels, with their wall being one cell thick. This thin interface is where oxygen and nutrients pass from the blood into the organs.⁵

The heart 

At the centre of the cardiovascular system is the heart, a fist-sized muscular organ that pumps blood around the body to ensure the delivery of oxygen and nutrients. It is split into two halves, with each side having 2 chambers; the upper being the atrium and the lower being the ventricle.⁶

Oxygenated blood flows into the left atrium through the pulmonary veins and then is shunted down into the left ventricle.⁶ It is then pumped out of the heart via the aorta which branches into smaller arteries to distribute oxygenated blood around the body.⁷ On the way back to the heart, deoxygenated blood travels in the veins, and it enters into the right atrium through the vena cava. It then flows into the right ventricle and back out of the heart to the lungs through the pulmonary artery to get re-oxygenated.⁷

How does hypoxia affect the cardiovascular system 

As a result of low oxygen in the tissues, the heart works harder to pump more blood around the body. This results in a faster heart rate and higher blood pressure, which over prolonged periods can put a strain on the cardiovascular system.⁸ In hypoxic conditions, blood is directed to the most oxygen-dependent organs, like the brain and the heart.⁹

However, many athletes choose to expose themselves to hypoxic conditions during training for short-term periods. Whilst seemingly counterintuitive, controlled exercise under hypoxic conditions can strengthen the cardiovascular system when oxygen levels are both normal and low.¹⁰

Diagnosis and cardiovascular implications 

There are several diagnostic tests available for detecting hypoxia. There will be an initial physical exam to check for blue tinges to the skin and nails, which will then be followed by one or more of the following:¹¹

• Noninvasive pulse oximetry: An oxygen monitor placed on your finger to detect oxygen levels in the blood
• Arterial blood gas test (ABG): Blood is drawn using a needle from either the wrist, arm or groin to check oxygen blood levels.
• Pulmonary function test (PFT): involves blowing into a machine to test the capacity of the lungs

Treatment and management 

An individual may experience acute hypoxia as a one-off event or as part of a wider health condition. Therefore, the treatment of hypoxia is very much dependent on the cause. An immediate intervention to help treat acute or short-term hypoxia is the use of a nasal oxygen cannula.¹² This is a simple and reliable way of increasing oxygen intake which should improve the volume of oxygen reaching organs.

Oxygen supply can also be used as a long-term treatment method for individuals who have chronic hypoxia due to lung or heart diseases.¹³ Depending on the level of hypoxia severity, healthcare providers may encourage exposure to hypoxic conditions under supervision to strengthen the cardiovascular system as part of a rehabilitation programme.¹⁰

Summary 

Experiencing either an acute or chronic episode of hypoxia can be dangerous. Despite hypoxic conditioning having the potential to strengthen the cardiovascular system, unprompted hypoxia should be tended to by a medical professional as soon as symptoms are spotted. Without hypoxia treatment, the cardiovascular system can be put under intense strain which may result in permanent damage to the heart and other organs.