Information AboutHeart Rate |
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Heart rate is a term used to describe the frequency of the Cardiac Cycle . It is considered one of the four Vital Signs . Usually it is calculated as the number of contractions ('''heart beats''') of the Heart in one Minute and expressed as "beats per minute" (bpm). See " Heart " for information on embryofetal heart rates. The heart beats up to 120 times per minute in childhood. When resting, the adult Human heart beats at about 70 bpm (males) and 75 bpm (females), but this rate varies among people. However, the resting heart rate can be significantly lower in athletes. The infant/neonatal rate of heartbeat is around 130-150 bpm, the toddler's about 100–130 bpm, the older child's about 90–110 bpm, and the adolescent's about 80–100 bpm. The Pulse is the most straightforward way of measuring the heart rate, but it can be deceptive when some heart beats do not have much cardiac output. In these cases (as happens in some Arrhythmia s), the heart rate may be considerably higher than the pulse rate. Auscultation is also a method of heart rate measurement. CONTROL OF HEART RATE The heart contains two Cardiac Pacemaker s that spontaneously cause the heart to beat. These can be controlled by the Autonomic Nervous System and circulating Adrenaline . The Vagus Nerve (which is pneumogastric nerve or cranial nerve X) which governs heart rate can be controlled through breathing. Heart rate variability (HRV) is the variation of beat-to-beat intervals. A healthy heart has a large HRV, while decreased or absent variability may indicate cardiac disease. HRV also decreases with exercise-induced Tachycardia . HRV has been the focus of increased research to use it as a physiological marker to classify different pathological disorders. One aspect of heart rate variability can be used as a measurement of fitness, specifically the speed at which one's heart rate drops upon termination of vigorous exercise. The speed at which a person's heart rate returns to resting is considerably faster for a fit person than an unfit person. A drop of 20 beats in a minute is typical for a healthy person. A drop of less than 12 beats per minute after maximal exercise has been correlated with a significant increase in mortality Erna Obenza Nishime, MD; Christopher R. Cole, MD; Eugene H. Blackstone, MD; Fredric J. Pashkow, MD; Michael S. Lauer, MD: "Heart Rate Recovery and Treadmill Exercise Score as Predictors of Mortality in Patients Referred for Exercise ECG", ''JAMA'', 2000;284:1392-1398. MEASURING HEART RATE The Pulse Rate (which in most people is identical to the heart rate) can be measured at any point on the body where an Artery 's pulsation is transmitted to the surface - often as it is compressed against an underlying structure like bone. Some commonly palpated sites are as listed. #The Wrist ( Radial Artery ) on the thumb side, (and less commonly Ulnar Artery on the pinky side which is deeper and harder to Palpate ) #The Neck ( Carotid Artery ), #The inside of the Elbow , or under the biceps muscle ( Brachial Artery ) #The Groin ( Femoral Artery ), #Behind the Medial Malleolus on the feet ( Posterior Tibial Artery ) #Middle of Dorsum of the foot ( Dorsalis Pedis ). #Behind the knee ( Popliteal Artery ) #Over the Abdomen ( Abdominal Aorta ) #The chest. ( Aorta )This can be felt with one's hands or fingers but it is possible to Auscultate the heart by utilizing a Stethoscope . ''NOTE: The thumb should never be used for measuring heart rate, as its strong pulse may interfere with discriminating the site of pulsation, and you may count the thumb's pulse accidentally when measuring' Regulation of Human Heart Rate . Serendip. Retrieved on June 27 , 2007 . Producing an Electrocardiogram , or ECG (also abbreviated EKG), is one of the most precise methods of heart rate measurement. Continuous electrocardiographic monitoring of the heart is routinely done in many clinical settings, especially in Critical Care Medicine . Commercial Heart Rate Monitor 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). MAXIMUM HEART RATE Maximum heart rate (also called MHR, or HRmax) is the maximum heart rate that a person should achieve during maximal physical exertion. Research indicates it is most closely linked to a person's age; a person's HRmax will decline as they age. Physical Activity for Everyone . Department of Health and Human Services, Centers for Disease Control and Prevention. Retrieved on May 1 , 2007 . People who have participated in sports and athletic activities in early years will have a higher MHR than those less active as children. Measuring HRmax The most accurate way of measuring HRmax for an individual is via a Cardiac Stress Test . In such a test, the subject exercises while being monitored by an Electrocardiogram (ECG). During the test, the intensity of exercise is periodically increased (if a Treadmill is being used, through increase in speed or slope of the treadmill) until the subject can no longer continue, or until certain changes in heart function are detected in the ECG (at which point the subject is directed to stop). Typical durations of such a test range from 10 to 20 minutes. Since the HRmax declines with age, this test does not hold permanent value. Conducting an accurate maximal exercise test requires expensive equipment, and should only be performed in the presence of medical staff due to risks associated with high heart rates. Instead, people typically use predictive formulae to estimate their individual Maximum Heart Rate. The most common formula encountered is: :HRmax = 220 − age (can vary) This is attributed to various sources, often "Fox and Haskell". While the most common (and easy to remember and calculate), this particular formula is not considered by some to be a good predictor of HRmax. A 2003 study {Link without Title} 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 , and prescription of exercise training HR ranges) 2) The most accurate formula of those examined was:
This was found to have a standard of error that, although large (6.4 bpm), was still deemed to be acceptable for the use of prescribing exercise training HR ranges. Other often cited formulae are:
(Often attributed to "Londeree and Moeschberger from the University Of Missouri–Columbia ")
(Often attributed to "Miller et al. from Indiana University ") , 2007 . :For males: 210 - 1/2 your age - 5% of total body weight (in pounds) + 4 = HRmax :For females: 210 - 1/2 your age - 5% of total body weight (in pounds) + 0 = HRmax RECOVERY HEART RATE The recovery heart rate is that taken 2–10 minutes after exercise. It is measured over a 15-second sampling interval. The goal is not to exceed 150 Bpm. NOTE: The thumb should never be used for measuring heart rate, as it has a pulse of its own. {Link without Title} A drop of 20 beats in a minute is typical for a healthy person. A drop of less than 12 beats per minute after maximal exercise has been correlated with a significant increase in mortality {Link without Title} . TARGET HEART RATE Target heart rate (THR), or training heart rate, is a desired range of heart rate reached during Aerobic Exercise which enables one's Heart and Lungs to receive the most benefit from a workout. This theoretical range varies based on one's physical condition, age, and previous training. Below are two ways to calculate one's Target Heart Rate. In each of these methods, there is an element called "intensity" which is expressed as a percentage. THR can be calculated by using a range of 50%–85% intensity. Karvonen method The Karvonen method factors in Resting Heart Rate (HRrest) to calculate Target Heart Rate (THR): :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 = 130; ± 5 → 125 to 135 bpm Zone 4 (tough exercise): 180 - 20 = 160; ± 5 → 155 to 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 reserve. :HRR = HRmax − HRrest HEART RATE ABNORMALITIES Tachycardia See Also: 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 adults. Bradycardia See Also: Bradycardia Bradycardia is defined as a heart rate less than 60 beats per minute although it is seldom symptomatic until below 50 bpm. Trained Athlete s 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. Again, this number can vary as smaller people and children have faster heart rates than adults. , 2007 . SEE ALSO REFERENCES |
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