Introduction

With each heartbeat, an electrical signal spreads across the heart, causing it to contract in order to pump blood throughout the body. The pressure wave that is generated by the contraction of the heart and travels through the arterial system is called a pulse. The rate at which pulses occur is the Pulse Rate (PR).

Pulse rate is a vital sign, and its measurement is a standard clinical procedure. It is typically measured as the average number of pulses that occur per minute. This is the Pulse Rate Average (PRA), and is expressed in units of /min – pulses per minute. The PR is usually regular in nature; however, there are beat-to-beat variations. This change in the PR, called Pulse Rate Variability (PRV), is measured as the standard deviation of the beat-to-beat variations, and is expressed as a percentage of the PRA. These two measures of PR are displayed as part of the results for each Pulsewave reading.

 

Pulse Rate Measurement

A discussion of PR measurement first requires a differentiation of PR and heart rate (HR). While the former is determined based on the heart’s ability to generate a pressure wave (pulse), the latter is determined by the heart’s electrical activity that occurs prior to the pulse. In fact, the electrical activity of the heart is the precursor to the generation of the pulse. Under normal circumstances, the PR coincides with the HR.

Heart rate is typically measured based on heart sounds via auscultation, or based on the heart’s electrical activity via electrocardiography. Pulse rate, on the other hand, is typically measured based on tactile feedback via palpation; blood volume changes via photoplethysmography; or based on changes in cuff pressure during BP measurement. These changes in cuff pressure occur as the pressure wave, which travels through the arterial system, causes a displacement of the arterial walls that is transferred to the cuff. This results in the pulse waveform that is displayed during each Pulsewave reading. The measures of PR, PRA and PRV, are then measured from this waveform.

 

Pulse Rate Classification

Normal adult resting PRA is considered to be in the range of 60 to 100 /min. Outside of this range exist categories of high and low PRs. A consistently high PRA, greater than 100 /min, is known as tachycardia, while a consistently low PRA, less than 60 /min, is known as bradycardia. Although there are levels of risk associated with these conditions, it is very important that your physician determine this for you. This is because a high or low PRA may be normal for some people. Healthy young adults and trained athletes, for instance, may have a normal resting PRA of 40 /min.

Tachycardia and bradycardia may both have the same consequence: blood may not be effectively pumped throughout the body, and organs and tissues may be deprived of oxygen, thus increasing the risk of heart and brain damage. These conditions may be caused by underlying problems that disrupt the heart’s normal electrical activity, e.g., heart damage, high BP, and thyroid problems. They may also be a result of drug use, or adverse reactions to medication. Symptoms of these conditions include dizziness, shortness of breath, and chest pain.

Pulse Rate Variability

Pulse rate variability, which is displayed as part of the results for each Pulsewave reading, refers to a measure of the beat-to-beat variations that occurs within the reading. In general, PR can vary between readings (i.e., there can be changes in PRA across multiple readings) due to various factors, including activity and fitness level, air temperature, emotions, and medication. However, the term PRV refers to variations in PR that occur within a single reading.

The PRV is an indicator of the rhythm of the pulse. Highly rhythmic pulse waveforms will result in a low PRV value, less than 2 %, while highly arrhythmic pulse waveforms will result in a high PRV value, greater than 20 %. Although there are levels of risk associated with these conditions, it is very important that your physician determine this for you. This is because a high or low PRV may be normal for some people. The breathing process, for instance, results in beat-to-beat variations that are associated with respiration and cause an increase in PRV. This phenomenon, known as respiratory sinus arrhythmia, is normal.

Most arrhythmias, which include high, low, or irregular PRs, are harmless; however, some can result in serious complications, such as heart and brain damage, and indicate underlying problems that disrupt the heart’s normal electrical activity. These conditions include heart damage, high BP, and diabetes. Arrhythmias can also be caused by dietary supplements, drug use, and medication. A high PRV value indicates the occurrence of irregular beat-to-beat variations within the reading. These occurrences of arrhythmic pulses can be observed on the pulse waveform, typically appearing as missing, delayed or premature pulses. A high PRV value does not indicate the severity or risk, if any, associated with the arrhythmic pulse occurrences, nor does it indicate the type of electrical disruption that resulted in the arrhythmic pulse occurrences.

 

Relationship to Blood Pressure

Circumstances exist in which PR and Blood Pressure (BP) change in response to one another. For instance, the sudden fall in BP associated with standing up, known as orthostatic hypotension, may initiate a sudden increase in PR, known as reflex tachycardia. However, in general, the correlation between PR and BP is low. Measurement of PR does not give an indication of BP, and vice versa. Furthermore, a change in PR does not give an indication of the change in BP, and vice versa. One reason for this is that the characteristics of arteries, e.g., diameter, may change to accommodate changes in other biological parameters.

Additional Resources

Introduction:

National Heart Lung and Blood Institute. How the heart works [Online]. Available: http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_pumping.html. Accessed: 2011-02-07.

Wikipedia. Pulse [Online]. Available: http://en.wikipedia.org/wiki/Pulse. Accessed: 2011-02-07.

Wikipedia. Vital signs [Online]. Available: http://en.wikipedia.org/wiki/Vital_signs, Accessed:

2011-02-07.

Pulse Rate Measurement:

Wikipedia. Heart rate [Online]. Available: http://en.wikipedia.org/wiki/Heart_rate. Accessed:

2011-02-07.

Wikipedia. Pulse [Online]. Available: http://en.wikipedia.org/wiki/Pulse. Accessed: 2011-02-07.

Pulse Rate Classification:

Mayo Clinic. Heart rate: What’s normal? [Online]. Available: http://www.mayoclinic.com/health/heart-rate/AN01906. Accessed: 2011-02-07.

Mayo Clinic. Tachycardia [Online]. Available: http://www.mayoclinic.com/health/tachycardia/DS00929. Accessed: 2011-02-07.

Mayo Clinic. Bradycardia [Online]. Available: http://www.mayoclinic.com/health/bradycardia/DS00947. Accessed: 2011-02-07.

Wikipedia. Pulse [Online]. Available: http://en.wikipedia.org/wiki/Pulse. Accessed: 2011-02-07.

Pulse Rate Variability:

Task Force of the European Society of Cardiology and The North American Society of Pacing and Electrophysiology, “Heart rate variability: Standards of measurement, physiological interpretation, and clinical use”, European Heart Journal, vol. 17, pp. 354-381, 1996.

Mayo Clinic. Heart rate: What’s normal? [Online]. Available: http://www.mayoclinic.com/health/heart-rate/AN01906. Accessed: 2011-02-07.

Mayo Clinic. Heart arrhythmias [Online]. Available: http://www.mayoclinic.com/health/heart-arrhythmias/DS00290. Accessed: 2011-02-07.

National Heart Lung and Blood Institute. Arrhythmia [Online]. Available: http://www.nhlbi.nih.gov/health/dci/Diseases/arr/arr_whatis.html. Accessed: 2011-02-07.

American Heart Association. Arrhythmia [Online]. Available: http://www.heart.org/HEARTORG/Conditions/Arrhythmia/Arrhythmia_UCM_002013_SubHomePage.jsp. Accessed: 2011-02-07.

Wikipedia. Cardiac dysrhythmia [Online]. Available: http://en.wikipedia.org/wiki/Cardiac_dysrhythmia. Accessed: 2011-02-07.

Wikipedia. Heart rate variability [Online]. Available: http://en.wikipedia.org/wiki/Heart_rate_variability. Accessed: 2011-02-07.

Relationship to Blood Pressure:

American Heart Association. Blood pressure vs. heart rate [Online]. Available: http://www.heart.org/HEARTORG/Conditions/HighBloodPressure/AboutHighBloodPressure/Blood-Pressure-vs-Heart-Rate_UCM_301804_Article.jsp. Accessed: 2011-02-07.

Wikipedia. Tachycardia [Online]. Available: http://en.wikipedia.org/wiki/Tachycardia. Accessed: 2011-02-07