Blood pressure and heart rate are often measured together during a medical examination, leading many people to assume they are the same measurement or directly linked. However, these two metrics are fundamentally distinct indicators of cardiovascular function. Heart rate measures the speed of the heart, while blood pressure measures the force the blood exerts against the vessel walls. While they are outputs of the same system, they represent different physiological processes within the body.
What Blood Pressure Measures
Blood pressure (BP) is the physical force exerted by the circulating blood against the walls of the body’s arteries. This measurement is a reflection of how hard the heart is working to pump blood and the resistance the blood flow meets in the vessels. It is always reported as two numbers, measured in millimeters of mercury (mm Hg), such as 120/80 mm Hg.
Systolic Pressure
The top number is the systolic pressure, which is the maximum pressure recorded when the heart muscle contracts, pushing blood out into the body. This contraction phase is known as systole, and the reading reflects the peak force on the artery walls.
Diastolic Pressure
The bottom number is the diastolic pressure, which is the lowest pressure recorded when the heart is at rest between beats. During this relaxation phase, known as diastole, the heart refills with blood. This measurement indicates the residual pressure within the arteries when the heart is not actively pumping blood. Both the systolic and diastolic numbers are necessary to provide a complete picture of the pressure dynamics.
What Heart Rate Measures
Heart rate (HR) is a count of the number of times the heart beats in one minute, commonly expressed as beats per minute (BPM). This metric is a measure of frequency, indicating how quickly the heart is cycling through its contraction and relaxation phases. It can be easily measured by finding the pulse at the wrist or neck.
Heart rate is a single number, unlike the dual reading required for blood pressure. A typical resting heart rate for an adult ranges between 60 and 100 beats per minute. Athletes often have lower resting rates due to increased cardiac efficiency.
The heart rate is dynamic and can change rapidly in response to immediate factors like physical activity, emotional stress, or body position. While a consistently elevated resting heart rate can indicate underlying health issues, it is primarily a measure of the heart’s rhythm and pace. It does not directly indicate the force or pressure of the blood against the vessel walls.
The Connection Between These Two Measurements
Blood pressure and heart rate are interdependent because they are both regulated by the body’s autonomic nervous system to maintain adequate blood flow to organs. When the body requires more oxygen, such as during exercise, the heart rate increases to pump more blood per minute. This increased cardiac output usually causes both the heart rate and the blood pressure to rise in tandem.
However, the two metrics do not always rise and fall together in a synchronized fashion. When the body experiences stress, such as dehydration or severe infection, blood pressure may drop because of reduced blood volume or widespread vessel dilation. To compensate for the low pressure, the body signals the heart to beat faster, resulting in a high heart rate paired with low blood pressure.
Medications can also intentionally cause a dissociation between the two measurements. For example, beta-blockers are drugs designed to slow the heart rate, reducing the workload on the heart. This reduction in heart rate can help lower blood pressure, but the effect on each metric is regulated by different physiological mechanisms. The fact that these two measurements can move independently emphasizes that they are distinct physiological indicators.