How does holding your breath affect heart rate?

Ricky Cheng
23 January 2012

Above: Image © Public Domain

Many people are familiar with David Blaine’s exploits and one of them included holding his breath for over 17 minutes underwater! How is this possible?

Did You Know: David Blaine beat the world record for holding your breath underwater after inhaling pure oxygen (17 minutes and four seconds)!

First, it is important to note that under normal physiological conditions your heart is constitutively activated by the parasympathetic nervous system (PNS), which keeps your heart beat at a constant 75 beats per minute. Under normal conditions, holding your breath has actually been shown to have minimal influences on heart rate but may decrease it ever so slightly. By breathing in and holding your breath, you will further activate the PNS causing a decreased heart rate, known as bradycardia. In addition, holding your breath will create a negative suction pressure in the thorax and inflate the organs. It will then take longer for blood to fill the heart and thus also create a slower heart rate.

Did You Know: The mammalian diving reflex mentioned below is in fact activated when holding your breath on land but to a much lesser degree.

When a person’s face enters water, they will usually enter a state in which the body attempts to conserve oxygen. This is known as the mammalian diving reflex. This conservation of oxygen is done via the activation of the parasympathetic nervous system from nerves on your face and causes bradycardia. Furthermore, the diving reflex stimulates peripheral constriction of the blood vessels in the outer extremities of your body. This will prevent blood circulation to non-vital areas while maximizing the supply of oxygen to vital organs, such as the brain. The diving reflex is sometimes activated to treat ventricular tachycardia, a type of increased rhythm of your heart.

In David Blaine’s case, he inhaled pure oxygen and trained his lungs to inhale air until they filled their physiological capacity using a technique called glossopharyngeal insufflation. Additionally, by doing his stunt underwater, he activated his diving reflex, permitting him to hold his breath longer than on land. So, if you are planning to break his record while dry, don’t hold your breath.

Did You Know Aquatic mammals have as much as 25 to 30 per cent of their oxygen storage in muscle and can keep working long after capillary blood supply is stopped!

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Ricky Cheng

I am currently a fourth year undergraduate student in the honors physiology specialization program at the University of Western Ontario. I enjoy playing multiple sports which primarily include soccer and basketball.  I am applying for medical school this upcoming year.

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