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Breathing rate and heart rate are directly connected. This is because the heart is connected to the lungs via the pulmonary artery.

I first thought that breathing rate would be half of the heart rate since half of the heart cycle occurs in the lungs.

But I know that is not true with a normal 12 BPM(breaths per minute) breathing rate.

So what is the ratio of breathing rate to heart rate?

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"This is because the heart is connected to the lungs via the pulmonary artery." It's not like heart rate or breathing rate are regulated by pulmonary arteries. The relation is more sophisticated than that. For example heart rate is controlled by nerves and hormones, and neither comes straight from the lung. But fast breathing leads to changes in blood oxygen and pH, which are picked up by sensors such as the carotid body, which informs the medulla, which then talks to the sinoatrial node. There is also more direct influence, because ample breathing increases pressure in the thorax.

But at each step, there are many other factors interfering, meaning the correlation between the two gets ever looser. There isn't really a "normal" ratio of heart rate to respiration rate. There is a healthy heart rate and a healthy respiratory rate, but they are both wide intervals (60-100 and 12-20, respectively). Dividing one by the other, you get a very wide interval, from 60 beats per minute / 20 breaths per minute = 3, to 100 beats per minute / 12 breaths per minute = 8.

Perhaps in practice the most common values for beats per breath are in a narrower interval. But "normal" values are defined in relationship to abnormal conditions, and there is no disease in which a change in this ratio is a cardinal feature. It makes little sense for clinicians to define a normal range for beats per breath, and therefore it makes little sense for epidemiologists to estimate most common values.

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    $\begingroup$ did you mean "breathing rate" in it's not like heart rate or bleeding rate are regulated by pulmonary arteries? $\endgroup$ – bonCodigo Aug 23 '14 at 3:51
  • $\begingroup$ yes, that was a typo $\endgroup$ – Nick Alexander Aug 23 '14 at 4:10
  • $\begingroup$ but a disease that changes the HR most likely also changes the BR(breathing rate) and it probably also changes the ratio in lots of people even though the exact ratio varies from individual to individual. One example of something that is beneficial sometimes and changes the HR is ventricular hypertrophy. When caused by excersize it increases stroke volume and thus increases O2 transport which is always a plus. It also lowers the HR in response to the high BP that there is at first so that high BP becomes normal BP so that resting HR is anywhere in the normal range as well as down to 40 BPM. $\endgroup$ – Caters Aug 23 '14 at 11:15
  • $\begingroup$ As I said above, the chances are that when one is high, the other one is high too, and the interval may be narrower than 3-8 beats per breath. But, because it is of limited clinical importance, the ratio was not the focus of high-scale epidemiological studies. To my knowledge, scientists did not look for a "most common", nor for a "healthy" ratio. In the absence of actual data, I was only speculating. $\endgroup$ – Nick Alexander Aug 23 '14 at 12:39
  • $\begingroup$ but if breathing rate is clinically important and HR is too than why wouldn't the ratio be important? Cardiovascular disease and Respiratory disease can both change the ratio to where it is out of the normal range of 3-8 beats per breath. And it is important to know whether you have cardiovascular disease, respiratory disease, or both. $\endgroup$ – Caters Aug 23 '14 at 17:37
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I feel that ideally a healthy adult, under normal static conditions, should breathe 15 times per minute and his pulse rate is should be 60 per minute.

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  • $\begingroup$ Welcome to SE BIology. I think your answer is plausible but this is a science website so most other uses will like to see data/evidence. Can you update your answer to include some evidence? Thanks. $\endgroup$ – Michael_A Sep 16 '18 at 22:39

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