The heart rate is affected by many factors, so much so that people often don't realize how much the heart rate fluctuates during the day. The simple act of rising from a chair causes a change in heart rate. Emotions, actions, medications and things we eat, drink and smoke such as cigarettes and caffeine all affect heart rate.
Stress
Stress can be emotional or physical in nature. Both forms of stress create changes in the body which affect the heart rate. Donna D. Ignatavicius, MS RN, and M. Linda Workman, Ph.D, authors of "Medical-Surgical Nursing---Critical Thinking for Collaborative Care," explain that, when under stress, the body releases hormones that make the heart pump faster and harder to provide the muscles, lungs, heart and brain with necessary energy for self defense or escape.
A healthy heart can respond to the increased demands for more oxygen rich blood and adequately increase the heart rate. But an unhealthy heart will fatigue under the added strain and bradycardia, or slow heart rate below 60 beats per minute, occurs.
Vagus Nerve Stimulation
The vagus nerve is the 10th cranial nerve and innervates more than 20 different parts of the body including the heart. With regard to the heart, stimulation of the vagus nerve causes bradycardia. For example, when a person bears down to have a bowel movement, or holds his breath to lift something heavy, the increased pressure in the body stimulates the cardiac branch of the vagus nerve which signals the heart to slow down its rate.
Drugs
Drugs, be they illicit, prescription, over-the-counter or herbal preparations, are factors that affect the heart rate. Stimulants such as caffeine, nicotine, cocaine and ephedrine increase the heart rate and cause tachycardia which is a rapid heart rate greater than 100 beats per minute. Other drugs such as beta blockers slow down the heart rate. Use caution when taking more than one medication at a time, a situation called polypharmacy, as this can cause drug interactions and subsequent severe heart complications such as heart block. Heart block can be partial or complete---it is the disruption in electrical impulse transmission through the heart muscle. In heart block, the signal for the heart to beat is slowed down or lost altogether; severe bradycardia or cardiac arrest results.
Diseased Heart
The Mayo Clinic discusses how damage to the heart muscle from conditions such as a heart attack or an infection can lead to arrhythmias. Arrhythmias are irregular heart rhythms that affect the heart rate. Arrhythmias make the heart beat too fast or too slow. A diseased heart valve or a diseased sinus node, which is the pacemaker of the heart, affects the heart rate, either increasing or decreasing it.
References
- "Medical-Surgical Nursing: Critical Thinking for Collaborative Care"; Donna D. Ignatavicius MS RN, & M. Linda Workman Ph.D; 2006
- The Mayo Clinic: Heart Arrhythmias: Causes
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