HEART RATE
Normal heart rate at different phases of life is as under:
Foetus 140-150 per minute
Children 100-110 per minute
Adults 70-80 per minute
Old 65-75 per minute
Heart rate is little higher in woman than in man It normally varies with age metabolic rate and respiration
1. Heart rate is regulated by the autonomic part of the nervous system the vagus nerve which is a parasympathatic inhibitory nerve mainly controls the heart rate it decreases the force and frequency the sympathetic nerve in states of excitement and emotions increase the force and frequency of the heart Hence this is called Cardio-Accelerator mechanism Sympathetic and parasympathetic nerves together balance the heart rate by mutual antagonism (physiological antagonism )
2. Impulses from higher centres of the brain Excitement increases and shock decreases the heart rate
3. Respiration:Inspiration increases and expiration decreases the heart rate at every breath
4.Reflex Stimulation:Stimulation with pain and cold or heat to the skin increase the heart rate but very severe pain decreases the heart rate and sometimes it may even stop the heart
5.Oxygen Lack: Anoxia increases the heart rate but if there is no oxygen supply the heart will stop
6. Co2 Excess: Moderate increase in CO2 increase the heart rate but very high CO2 decreases the rate and may poison the heart
7. Blood pressure: Increase in blood pressure decreases the heart rate especially with increased intracranial pressure
8.Temperature: In fever every degree rise in normal body temperature increases the heart rate by 10 per min
9. Exercise: It increases the heart rate as well as its force
10.Drugs:Drugs like adrenaline and thyroxine increases the heart rate and force of contraction Digitalis decreases the rate but increases the force so as to increase the cardiac output
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