Saturday, July 4, 2015

What influence heart rate?

Basically, the heart rate, or cardiac frequency, depends on the inhibitory activity of the vagus nerve (CN X), that is to say on its variable tone. If this parasympathetic nerve gets completely paralyzed (due to atropine, for example), the heart can accelerate to a top frequency of 150 beats per minute. Although supplementary acceleration produced during strenuous physical exercises (up to 180 beats per minute), is probably due to additional active excitation of sympathetic fibers. Vagal tone is little accentuated in children, whose rate can reach 120 beats per minute; however, it gets accentuated with age to the point that the adult's heart rate is 70 beats per minute, but it can be as low as 40 o 50 beats.

In general, heart rate is influenced or altered by a number of factors, such as:

1- nervous impulses coming from superior centers
2- breathing
3- blood content of O2 and CO2
4- reflexes from the cardioaortic zone and carotid sinus, from right atrium and the big veins
5- body temperature
6- intracraneal pressure
7- thyroid hormone (specially Tyroxine)
8- muscular exercise