heart rate

Examples of heart rate in the following topics:

• Pulse

  • Pulse is a measurement of heart rate by touching and counting beats at several body locations, typically at the wrist radial artery.
  • Pulse is often used as an equivalent of heart rate due to the relative ease of measurement; heart rate can be measured by listening to the heart directly through the chest, traditionally using a stethoscope.
  • Pulse varies with age; a newborn or infant can have a heart rate of about 130-150 bpm.
  • The heart rate may be greater or less than the pulse rate depending upon physiologic demand.
  • In this case, the heart rate is determined by auscultation or audible sounds at the heart apex, not the pulse.

• Cardiac Cycle

  • Heart rate is a term used to describe the frequency of the cardiac cycle.
  • Usually heart rate is calculated as the number of contractions (heartbeats) of the heart in one minute and expressed as "beats per minute" (bpm).
  • Resting heart rates can be significantly lower in athletes and significantly higher in the obese.
  • The body can increase the heart rate in response to a wide variety of conditions in order to increase the cardiac output, the blood ejected by the heart, which improves oxygen supply to the tissues.
  • Exercise, environmental stress, or psychological stress can cause the heart rate to increase above the resting rate.

• Electrical Events

  • The SA and AV nodes act as a pacemaker for the heart, determining the rate at which it beats, even without signals from the larger nervous system of the human body.
  • Without autonomic nervous stimulation, the SA node will set the heart rate itself, acting as the primary pacemaker for the heart.
  • The SA node fires to set a heart rate in a range of 60-100 beats per minute (bpm), a normal range that varies from person to person.
  • Sympathetic nervous stimulation still increases heart rate, while parasympathetic nervous stimulation decreases heart rate by acting on the AV node.
  • The system of nerves that work together to set the heart rate and stimulate muscle cell depolarization within the heart.

• Arrhythmia

  • The sinoatrial node is a single specialized location in the atrium which has a higher automaticity (a faster pacemaker) than the rest of the heart and, therefore, is usually responsible for setting the heart rate and initiating each heart beat.
  • In adults the normal resting heart rate ranges from 60 to 80 beats per minute.
  • The resting heart rate in children is much faster.
  • Arrhythmias - types: Arrhythmia may be classified by rate (normal, tachycardia, bradycardia), or mechanism (automaticity, reentry, fibrillation).
  • Arrythmias arising from pathologies at the AV node (AV blocks): First degree heart block, which manifests as PR prolongation, Second degree heart block, and Third degree heart block, also known as complete heart block.

• Aging and the Heart

  • As a person ages, the walls of the heart thicken, the heart becomes heavier, valves stiffen and leak, and the aorta becomes larger.
  • As a person ages, the heart goes through certain structural changes: the walls of the heart thicken and the heart becomes heavier, heart valves stiffen and are more likely to calcify, and the aorta, the major vessel carrying blood out of the heart, becomes larger.
  • The heart muscle becomes less efficient with age, and there is a decrease in both maximum cardiac output and heart rate, although resting levels may be more than adequate.
  • A weak ventricle is not an efficient pump, and may progress to congestive heart failure.
  • The heart valves may become thickened by fibrosis or calcification, leading to heart murmurs and less efficient pumping.

• Anatomy of the Heart

  • Each side contains an atria which receives blood into the heart and flows it into a ventricle, which pumps the blood out of the heart.
  • The left heart deals with systemic circulation, while the right heart deals with pulmonary circulation.
  • These nodes can send impulses to the heart without central nervous system stimulation, but may be influenced by nervous stimulation to alter heart rate.
  • The heart also has its own blood supply, the cardiac arteries that provide tissue oxygenation to the heart as the blood within the heart is not used for oxygenation by the heart.
  • This composite sac protects the heart, anchors it to surrounding structures, and prevents the heart from overfilling with blood.

• Congestive Heart Failure

  • Heart failure is a common, costly, disabling, and potentially deadly condition.
  • Heart failure is the leading cause of hospitalization in people older than 65.
  • Heart failure can result from any one, or combinations of, cardiomyopathies or problems within the heart muscle, and these problems can result in heart failure.
  • Increased heart rate in CHF is stimulated by increased sympathetic activity in order to maintain cardiac output.
  • Binding to beta-1 receptors in the myocardium increases the heart rate and make contractions more forceful, in an attempt to increase cardiac output.

• Electric Activity in the Heart

  • Electric energy stimulating the heart occurs in the sinoatrial node, the heart's pacemaker, and is transmitted partially by Perkinje fibers.
  • The reason Purkinje cells do not normally control the heart rate is that they generate action potentials at a lower frequency than the AV or SA nodes.
  • Purkinje fibers also have the ability of automatically firing at a rate of 15-40 beats per minute if left to their own devices.
  • In contrast, the SA node outside of parasympathetic control can fire a rate of almost 100 beats per minute.
  • In short, they generate action potentials, but at a slower rate than sinoatrial node and other atrial ectopic pacemakers.

• Heart Failure

  • Heart failure is defined as the inability of the heart to supply blood to the organs of the body.
  • Heart failure (HF) often called congestive heart failure (CHF) is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body.
  • Common causes of heart failure include myocardial infarction and other forms of ischemic heart disease, hypertension, valvular heart disease, and cardiomyopathy.
  • The term "heart failure" is sometimes incorrectly used to describe other cardiac-related illnesses, such as myocardial infarction (heart attack) or cardiac arrest, which can cause heart failure but are not equivalent to heart failure.
  • Common respiratory signs are tachypnea (increased rate of breathing) and increased work of breathing (non-specific signs of respiratory distress).

• Heart Sounds

  • The closing of the heart valves produces a sound.
  • Heart sounds are a useful indicator for evaluating the health of the valves and the heart as a whole.
  • The time between A2 and P2 is variable depending on the respiratory rate, but the split is generally only prominent in children during inspiration.
  • Heart murmurs are common and generally not serious, but some may be more severe and/or caused by severe underlying problems within the heart.
  • Third and fourth heart sounds, S3 and S4, differ from S1 and S2 because they are caused by abnormal contraction and relaxation of the heart instead of the closure of valves and are more often indicative of more severe problems than are heart murmurs.