Heart rate
Overview
 
Heart rate is the number of heartbeat
Cardiac cycle
The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages...

s per unit of time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

, typically expressed as beats per minute (bpm). Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep.

The measurement of heart rate is used by medical professionals to assist in the diagnosis
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...

 and tracking of medical conditions. It is also used by individuals, such as athletes, who are interested in monitoring their heart rate to gain maximum efficiency from their training.
Encyclopedia
Heart rate is the number of heartbeat
Cardiac cycle
The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages...

s per unit of time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

, typically expressed as beats per minute (bpm). Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep.

The measurement of heart rate is used by medical professionals to assist in the diagnosis
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...

 and tracking of medical conditions. It is also used by individuals, such as athletes, who are interested in monitoring their heart rate to gain maximum efficiency from their training. The R wave to R wave interval (RR interval) is the inverse of the heart rate.

Measurement

Heart rate is measured by finding the pulse
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...

 of the body. This pulse rate can be measured at any point on the body where the artery's
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 pulsation is transmitted to the surface by pressuring it with the index and middle fingers; often it is compressed against an underlying structure like bone. The thumb should not be used for measuring another person's heart rate, as its strong pulse may interfere with correct perception of the target pulse.

Possible points for measuring the heart rate are:
  1. The ventral aspect of the wrist
    Wrist
    In human anatomy, the wrist is variously defined as 1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand;...

     on the side of the thumb (radial artery
    Radial artery
    In human anatomy, the radial artery is the main blood vessel, with oxygenated blood, of the lateral aspect of the forearm.-Course:The radial artery arises from the bifurcation of the brachial artery in the cubital fossa. It runs distally on the anterior part of the forearm...

    ).
  2. The ulnar artery
    Ulnar artery
    The ulnar artery is the main blood vessel, with oxygenated blood, of the medial aspect of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins with the superficial branch of the radial artery...

    .
  3. The neck
    Neck
    The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...

     (carotid artery
    Carotid artery
    Carotid artery can refer to:* Common carotid artery* External carotid artery* Internal carotid artery...

    ).
  4. The inside of the elbow
    Elbow
    The human elbow is the region surrounding the elbow-joint—the ginglymus or hinge joint in the middle of the arm. Three bones form the elbow joint: the humerus of the upper arm, and the paired radius and ulna of the forearm....

    , or under the biceps muscle (brachial artery
    Brachial artery
    The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...

    ).
  5. The groin
    Groin
    In human anatomy, the groin areas are the two creases at the junction of the torso with the legs, on either side of the pubic area. This is also known as the medial compartment of the thigh. A pulled groin muscle usually refers to a painful injury sustained by straining the hip adductor muscles...

     (femoral artery
    Femoral artery
    The femoral artery is a general term comprising a few large arteries in the thigh. They begin at the inguinal ligament and end just above the knee at adductor canal or Hunter's canal traversing the extent of the femur bone....

    ).
  6. Behind the medial malleolus on the feet (posterior tibial artery
    Posterior tibial artery
    The posterior tibial artery of the lower limb carries blood to the posterior compartment of the leg and plantar surface of the foot, from the popliteal artery...

    ).
  7. Middle of dorsum
    Dorsum
    Dorsum is a Latin word. In science, it could mean:* Dorsum , the posterior side of an animal* Dorsum , a term used in astrogeology for a ridge* Theta Capricorni, a star on the back of the Goat...

     of the foot (dorsalis pedis).
  8. Behind the knee (popliteal artery
    Popliteal artery
    In human anatomy, the popliteal artery is defined as the extension of the "superficial" femoral artery after passing through the adductor canal and adductor hiatus above the knee...

    ).
  9. Over the abdomen
    Abdomen
    In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

     (abdominal aorta
    Abdominal aorta
    The abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta .-Path:...

    ).
  10. The chest (apex of heart), which can be felt with one's hand or fingers. However, it is possible to auscultate the heart using a stethoscope
    Stethoscope
    The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds. It is also used to listen to intestines and blood flow in arteries and veins...

    .
  11. The temple
    Temple (anatomy)
    Temple indicates the side of the head behind the eyes. The bone beneath is the temporal bone as well as part of the sphenoid bone.-Anatomy:Cladists classify land vertebrates based on the presence of an upper hole, a lower hole, both, or neither in the cover of dermal bone which formerly covered the...

     (superficial temporal artery
    Superficial temporal artery
    In human anatomy, the superficial temporal artery is a major artery of the head. It arises from the external carotid artery when it bifurcates into the superficial temporal artery and maxillary artery....

    ).
  12. The lateral edge of the mandible (facial artery
    Facial artery
    The facial artery is a branch of the external carotid artery that supplies structures of the superficial face.-Structure:...

    ).
  13. The side of the head near the ear (basilar artery)

A more precise method of determining pulse involves the use of an electrocardiograph, or ECG (also abbreviated EKG). Continuous electrocardiograph monitoring of the heart is routinely done in many clinical settings, especially in critical care medicine
Critical Care Medicine
Critical Care Medicine is a peer-reviewed medical journal in the field of intensive care medicine. It is the official publication of the Society of Critical Care Medicine, and is published by Lippincott Williams & Wilkins. The editor-in-chief is Joseph E. Parrillo....

. Commercial heart rate monitor
Heart rate monitor
A heart rate monitor is a personal monitoring device which allows a subject to measure his or her heart rate in real time or record his or her heart rate for later study...

s are also available, consisting of a chest strap with electrodes. The signal is transmitted to a wrist receiver for display. Heart rate monitors allow accurate measurements to be taken continuously and can be used during exercise when manual measurement would be difficult or impossible (such as when the hands are being used).

At rest

The resting heart rate (HRrest) is a person's heart rate when they are at rest, that is lying down but awake, and not having recently exerted themselves. The typical resting heart rate in adults is 60-90 bpm,with rates below 60 bpm referred to as bradycardia
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...

, and rates above 100 bpm referred to as tachycardia
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...

. Conditioned athletes often have resting heart rates below 60 bpm, with values of below 40 bpm not unheard of. For instance, cyclist Lance Armstrong
Lance Armstrong
Lance Edward Armstrong is an American former professional road racing cyclist who won the Tour de France a record seven consecutive times, after having survived testicular cancer. He is also the founder and chairman of the Lance Armstrong Foundation for cancer research and support...

 has been known to have resting heart rates to as low as around 32 bpm, cyclist Miguel Indurain
Miguel Indurain
Miguel Ángel Indurain Larraya is a retired Spanish road racing cyclist. He won five consecutive Tour de Frances from 1991 and 1995, the first to do so, and the fourth athlete to win five times. He won the Giro d'Italia twice, becoming one of only seven people in history to achieve the Giro Tour...

 had a resting heart rate of 28 bpm. The low pulse in conditioned athletes is due to hypertrophy
Hypertrophy
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It should be distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number...

 of the cardiac muscles, therefore enabling a higher volume of blood being pumped at each beat (i.e. higher stroke volume).

In children

The normal heart rate in children is variable and depends on the child's age. The ranges that should be considered normal are controversial.

Maximum

The maximum heart rate (HRmax) is the highest heart rate an individual can safely achieve through exercise stress, and depends on age. The most accurate way of measuring HRmax is via a cardiac stress test
Cardiac stress test
Cardiac stress test is a test used in medicine and cardiology to measure the heart's ability to respond to external stress in a controlled clinical environment....

. In such a test, the subject exercises while being monitored by an EKG. During the test, the intensity of exercise is periodically increased (if a treadmill
Treadmill
A treadmill is an exercise machine for running or walking while staying in one place. The word treadmill traditionally refers to a type of mill which was operated by a person or animal treading steps of a wheel to grind grain...

 is being used, through increase in speed or slope of the treadmill), continuing until certain changes in heart function are detected in the EKG, at which point the subject is directed to stop. Typical durations of such a test range from ten to twenty minutes.

Standard textbooks of physiology and medicine mention that heart rate (HR) is readily calculated from the ECG as follows: HR = 1,500/RR interval in millimeters, HR = 60/RR interval in seconds, or HR = 300/number of large squares between successive R waves. In each case, the authors are actually referring to instantaneous HR, which is the number of times the heart would beat if successive RR intervals were constant.

Conducting a maximal exercise test can require expensive equipment. People just beginning an exercise regimen are normally advised to perform this test only in the presence of medical staff due to risks associated with high heart rates. For general purposes, people instead typically use a formula to estimate their individual maximum heart rate.

Formula

Various formulas are used to estimate individual maximum heart rates, based on age, but maximum heart rates vary significantly between individuals.
Even within a single elite sports team, such as Olympic rowers in their 20s, maximum heart rates can vary from 160 to 220. This variation is as large as a 60 or 90 year age gap by the linear equations given below, and indicates the extreme variation about these average figures.

The most common formula encountered, with no indication of standard deviation, is:
HRmax = 220 − age


The formula has been attributed to various sources, but is widely thought to have been devised in 1970 by Dr. William Haskell and Dr. Samuel Fox. Inquiry into the history of this formula reveals that it was not developed from original research, but resulted from observation based on data from approximately 11 references consisting of published research or unpublished scientific compilations. It gained widespread use through being used by Polar Electro
Polar Electro
Polar Electro, or in brief Polar, is a manufacturer of advanced training computers and heart rate monitoring equipment. The company is based in Kempele, Finland. Founded in 1977, Polar introduced the world's first wireless heart rate monitor...

 in its heart rate monitors, which Dr. Haskell has "laughed about", as it "was never supposed to be an absolute guide to rule people's training."

While the most common (and easy to remember and calculate), this particular formula is not considered by reputable health and fitness professionals to be a good predictor of HRmax. Despite the widespread publication of this formula, research spanning two decades reveals its large inherent error (Sxy = 7–11 b/min). Consequently, the estimation calculated by HRmax = 220 − age has neither the accuracy nor the scientific merit for use in exercise physiology and related fields.

A 2002 study of 43 different formulae for HRmax (including the one above) concluded the following:
  1. No "acceptable" formula currently existed, (they used the term "acceptable" to mean acceptable for both prediction of VO2
    VO2 max
    VO2 max is the maximum capacity of an individual's body to transport and use oxygen during incremental exercise, which reflects the physical fitness of the individual...

    , and prescription of exercise training HR ranges)
  2. The formula deemed least objectionable was:
HRmax = 205.8 − (0.685 × age)

This was found to have a standard deviation
Standard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...

 that, although large (6.4 bpm), was still considered to be acceptable for the use of prescribing exercise training HR ranges.


Other often cited formulae are:
  • HRmax = 206.3 − (0.711 × age)

(Often attributed to "Londeree and Moeschberger from the University of Missouri
University of Missouri
The University of Missouri System is a state university system providing centralized administration for four universities, a health care system, an extension program, five research and technology parks, and a publishing press. More than 64,000 students are currently enrolled at its four campuses...

")

  • HRmax = 217 − (0.85 × age)

(Often attributed to "Miller et al. from Indiana University
Indiana University Bloomington
Indiana University Bloomington is a public research university located in Bloomington, Indiana, in the United States. IU Bloomington is the flagship campus of the Indiana University system. Being the flagship campus, IU Bloomington is often referred to simply as IU or Indiana...

")

  • HRmax = 208 − (0.7 × age)

(Another "tweak" to the traditional formula is known as the Tanaka method. Based on a study of thousands of individuals, a new formula was devised which is believed to be more accurate).


In 2007, researchers at the Oakland University analysed maximum heart rates of 132 individuals recorded yearly over 25 years, and produced a linear equation very similar to the Tanaka formula—HRmax = 206.9 − (0.67 × age)—and a nonlinear equation—HRmax = 191.5 − (0.007 × age2). The linear equation had a confidence interval of ±5–8 bpm and the nonlinear equation had a tighter range of ±2–5 bpm. Also a third nonlinear equation was produced — HRmax = 163 + (1.16 × age) − (0.018 × age2).

These figures are very much averages, and depend greatly on individual physiology and fitness. For example an endurance runner's rates will typically be lower due to the increased size of the heart required to support the exercise, while a sprinter's rates will be higher due to the improved response time and short duration. While each may have predicted heart rates of 180 (= 220 − age), these two people could have actual HRmax 20 beats apart (e.g., 170–190).

Further, note that individuals of the same age, the same training, in the same sport, on the same team, can have actual HRmax 60 bpm apart (160 to 220): the range is extremely broad, and some say "The heart rate is probably the least important variable in comparing athletes."

The 2010 research conducted at Northwestern University revised the maximum heart rate formula for women. According to Martha Gulati, et al., it is:
HRmax = 206 − (0.88 × age)


A study from Lund, Sweden gives reference values (obtained during bicycle ergometry) for men:
HRmax = 203.7 / (1 + exp (0.033 x (age - 104.3)))

and for women:
HRmax = 190.2 / (1 + exp (0.0453 x (age - 107.5)))

Target rate

The Target Heart Rate or Training Heart Rate (THR) is a desired range of heart rate reached during aerobic exercise
Aerobic exercise
Aerobic exercise is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism...

 which enables one's heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 and lungs
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

 to receive the most benefit from a workout. This theoretical range varies based mostly on age; however, a person's physical condition, gender, and previous training also are used in the calculation. Below are two ways to calculate one's THR. In each of these methods, there is an element called "intensity" which is expressed As a percentage. The THR can Be calculated As a range of 65%–85% intensity. However, it is crucial to derive an accurate HRmax to ensure these calculations are meaningful (see above).

Example for someone with a HRmax of 180(age 40, estimating HRmax As 220 − age):
65% Intensity: (220 − (age = 40)) × 0.65 → 117 bpm
85% Intensity: (220 − (age = 40)) × 0.85 → 153 bpm

Karvonen method

The Karvonen method factors in resting heart rate (HRrest) to calculate target heart rate (THR), using a range of 50–85% intensity:
THR = ((HRmax − HRrest) × % intensity) + HRrest


Example for someone with a HRmax of 180 and a HRrest of 70:
50% Intensity: ((180 − 70) × 0.50) + 70 = 125 bpm
85% Intensity: ((180 − 70) × 0.85) + 70 = 163 bpm

Zoladz method

An alternative to the Karvonen method is the Zoladz method, which derives exercise zones by subtracting values from HRmax:
THR = HRmax – Adjuster ± 5 bpm
Zone 1 Adjuster = 50 bpm
Zone 2 Adjuster = 40 bpm
Zone 3 Adjuster = 30 bpm
Zone 4 Adjuster = 20 bpm
Zone 5 Adjuster = 10 bpm


Example for someone with a HRmax of 180:
Zone 1(easy exercise): 180 − 50 ± 5 → 125 – 135 bpm
Zone 4(tough exercise): 180 − 20 ± 5 → 155 – 165 bpm

Heart rate reserve

Heart rate reserve (HRR) is a term used to describe the difference between a person's measured or predicted maximum heart rate and resting heart rate. Some methods of measurement of exercise intensity measure percentage of heart rate reserve. Additionally, as a person increases their cardiovascular fitness, their HRrest will drop, thus the heart rate reserve will increase. Percentage of HRR is equivalent to percentage of VO2
VO2 max
VO2 max is the maximum capacity of an individual's body to transport and use oxygen during incremental exercise, which reflects the physical fitness of the individual...

 reserve.
HRR = HRmax − HRrest


This is often used to gauge exercise intensity (first used in 1957 by Karvonen).

Karvonen's study findings have been questioned, due to the following:

- The study did not use VO2 data to develop the equation.

- Only six subjects were used, and the correlation between the percentages of HRR and VO2 max was not statistically significant.

Recovery heart rate

Recovery heart rate is the heart rate measured at a fixed (or reference) period after ceasing activity, typically measured over a one minute period.

A greater reduction in heart rate after exercise during the reference period indicates a better-conditioned heart. Heart rates that do not drop by more than 12 bpm one minute after stopping exercise are associated with an increased risk of death.

Training regimes sometimes use recovery heart rate as a guide of progress and to spot problems such as overheating or dehydration. After even short periods of hard exercise it can take a long time (about 30 minutes) for the heart rate to drop to rested levels.

Tachycardia

Tachycardia is a resting heart rate more than 100 beats per minute. This number can vary as smaller people and children have faster heart rates than average adults.

Bradycardia

Bradycardia is defined as a heart rate less than 60 beats per minute although it is seldom symptomatic until below 50 bpm when a human is at total rest. Bradycardia may be associated with medical conditions such as hypothyroidism.

Trained athletes tend to have slow resting heart rates, and resting bradycardia in athletes should not be considered abnormal if the individual has no symptoms associated with it. For example Miguel Indurain
Miguel Indurain
Miguel Ángel Indurain Larraya is a retired Spanish road racing cyclist. He won five consecutive Tour de Frances from 1991 and 1995, the first to do so, and the fourth athlete to win five times. He won the Giro d'Italia twice, becoming one of only seven people in history to achieve the Giro Tour...

, a Spanish cyclist and five time Tour de France
Tour de France
The Tour de France is an annual bicycle race held in France and nearby countries. First staged in 1903, the race covers more than and lasts three weeks. As the best known and most prestigious of cycling's three "Grand Tours", the Tour de France attracts riders and teams from around the world. The...

 winner, had a resting heart rate of 28 beats per minute, one of the lowest ever recorded in a healthy human. Again, this number can vary as children and small adults tend to have faster heart rates than average adults.

Arrhythmia

Arrhythmias are abnormalities of the heart rate and rhythm (sometimes felt as palpitation
Palpitation
A palpitation is an abnormality of heartbeat that causes a conscious awareness of its beating, whether it is too slow, too fast, irregular, or at its normal frequency. The word may also refer to this sensation itself...

s). They can be divided into two broad categories: fast and slow heart rates. Some cause few or minimal symptoms. Others produce more serious symptoms of lightheadedness, dizziness and fainting.

Ventricular assist device

A body with a ventricular assist device
Ventricular assist device
A Ventricular assist device, or VAD, is a mechanical circulatory device that is used to partially or completely replace the function of a failing heart...

, or VAD, installed as an aid to a failing heart will sometimes have no heart beat or pulse and therefore no heart rate, because many VADs are continuous flow pumps.

As a risk factor

A number of investigations indicate that faster resting heart rate has emerged as a new risk factor for mortality in homeothermic mammals, particularly cardiovascular mortality in human beings. Faster heart rate may accompany increased production of inflammation molecules and increased production of reactive oxygen species in cardiovascular system, in addition to increased mechanical stress to the heart. There is a correlation between increased resting rate and cardiovascular risk. This is not seen to be "using an allotment of heart beats" but rather an increased risk to the system from the increased rate.

An Australian-led international study of patients with cardiovascular disease has shown that heart beat rate is a key indicator for the risk of heart attack. The study, published in The Lancet (September 2008) studied 11,000 people, across 33 countries, who were being treated for heart problems. Those patients whose heart rate was above 70 beats per minute had significantly higher incidence of heart attacks, hospital admissions and the need for surgery. University of Sydney professor of cardiology Ben Freedman from Sydney's Concord hospital, said "If you have a high heart rate there was an increase in heart attack, there was about a 46 percent increase in hospitalizations for non-fatal or fatal heart attack."

Standard textbooks of physiology and medicine mention that heart rate (HR) is readily calculated from the ECG as follows:
HR = 1,500/RR interval in millimeters, HR = 60/RR interval in seconds, or HR = 300/number of large squares between successive R waves. In each case, the authors are actually referring to instantaneous HR, which is the number of times the heart would beat if successive RR intervals were constant. However, because the above formula is almost always mentioned, students determine HR this way without looking at the ECG any further.

External links

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