Why does your heart rate decrease when you take a deep breath?

Csilla
23 January 2012

Above: Image © Public Domain

Your heart rate is actually tied in to your breathing rate in a phenomenon called "respiratory sinus arrythmia (RSA)". When you normally breathe in (inhalation), your heart rate increases slightly and then decreases again when you breathe out (exhalation). Scientists aren't really sure as to why your heart rate is linked with your breathing, but some studies suggest that the human body saves energy in this way, by increasing the efficiency of oxygen and carbon dioxide exchange in your lungs.

Link between respiration and heart rate

Energy efficiency may be increased by lowering your heart rate during an exhalation, as unnecessary heart beats are inhibited during periods of lower oxygenated blood. If we know RSA to be true, then why does your heart rate decrease during a deep breath? The deep breath in this case is what is referred to as the "valsalva maneuver" — taking a big breath in and then attempting to forcibly exhale with your nose and mouth closed (think of trying to lift or push a really heavy object).

During the early phase of the valsalva maneuver, the pressure inside your rib cage is so great that it compresses blood vessels, like the aorta, as well as the walls of the heart, decreasing the amount of blood flow to the heart and decreasing the cardiac output (how much blood is pumped by the heart). This can be seen by a rise in aortic blood pressure and decrease in heart rate (Phase I). Heart rate and aortic blood pressure are very closely linked, so as soon as the heart rate falls, blood pressure decreases. This causes heart rate to increase again (phase II). Once you start breathing normally and the pressure is released, your heart rate and blood pressure eventually return back to normal.

This answer was written by Csilla Egri, a Master's student in Biomedical Physiology and Kinesiology at Simon Fraser University in British Columbia.

Csilla

My interest in science and learning dates back probably to the first time I saw a baking soda volcano, but ever since then its been the ooey gooey inner workings of the human body that excite me. The natural progression for me after asking more questions than the teacher could answer in grade school biology was to get my Bachelor of Science Degree in Kinesiology; studying the movement and physiology of the human body. And it didn't end after that either! I undertook a two year research endeavour to obtain a Master's Degree in the same field. I explored the world under the microscope, investigating how tiny proteins invisible to the naked eye are crucial and maintaining human health and function. Ta da! There you have it, my educational timeline in about 100 words. And now here I am, continuing my love of the sciences and of the miraculous human body by answering your curious questions!


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Comments

Avatar  Ann Bywater

This is very interesting. My dad, who has COPD and a heart murmur and is of a very anxious disposition, is repeatedly becoming breathless even when his blood is fully oxygenated. We know ghost because he is in hospital being treated for a lung infection. I have a theory that his brain is being tricked into thinking he needs oxygen by his irregular heart. Do you think there could be any truth in this?

Avatar  D.B

For me, it's the other way around. My heartbeat slows up when I inhale and goes back to normal when I exhale. ?? Especially when I Work out.

Avatar  Dan

This article has many mistakes. A big one is the inaccurate description of the causal a maneuver. That is an increase in abdominal pressure, not chest pressure.