⚠️ Medical Warning: This tool demonstrates the hemodynamic relationship between Heart Rate and Blood Pressure using physics formulas ($MAP = CO \times SVR$). It is for educational purposes only and cannot replace a sphygmomanometer (BP cuff) for medical diagnosis.
Beats per minute (BPM). Normal resting range: 60-100.
Amount of blood pumped per beat (mL). Average adult: 70 mL.
Resistance to blood flow (dyn·s/cm⁵). Normal range: 800-1200.
function calculateHemodynamics() {
var hrInput = document.getElementById("heartRate").value;
var svInput = document.getElementById("strokeVolume").value;
var svrInput = document.getElementById("vascularResistance").value;
// Validation
if (hrInput === "" || svInput === "" || svrInput === "") {
alert("Please fill in all fields to calculate.");
return;
}
var hr = parseFloat(hrInput);
var sv = parseFloat(svInput);
var svr = parseFloat(svrInput);
if (isNaN(hr) || isNaN(sv) || isNaN(svr) || hr <= 0 || sv <= 0 || svr <= 0) {
alert("Please enter valid positive numbers.");
return;
}
// Step 1: Calculate Cardiac Output (CO) in Liters/minute
// CO = (HR * SV) / 1000
var cardiacOutputL = (hr * sv) / 1000;
// Step 2: Calculate Mean Arterial Pressure (MAP)
// Formula: MAP (mmHg) ≈ (CO (L/min) * SVR (dynes)) / 80
// The factor 80 converts the units properly from hybrid hemodynamic units to mmHg
var map = (cardiacOutputL * svr) / 80;
// Estimating Systolic/Diastolic from MAP is purely theoretical without direct measurement,
// but we can provide a range based on typical pulse pressure (PP) assumptions (PP ≈ SV / Arterial Compliance).
// For educational display, we will focus on MAP as the scientifically derivable metric from these inputs.
var resultDiv = document.getElementById("result");
resultDiv.style.display = "block";
resultDiv.innerHTML = `
Est. Mean Arterial Pressure (MAP):${map.toFixed(1)} mmHg
Analysis: At ${hr} BPM with a stroke volume of ${sv} mL, your heart is pumping ${cardiacOutputL.toFixed(1)} liters of blood every minute.
Given a vascular resistance of ${svr}, the physics requirement suggests a mean pressure of approximately ${map.toFixed(0)} mmHg is needed to sustain this flow.
`;
}
How to Calculate Blood Pressure Using Heart Rate
Understanding the relationship between Heart Rate (HR) and Blood Pressure (BP) requires diving into the physics of hemodynamics. While many people look for a simple conversion calculator to turn their pulse rate into a blood pressure reading, the reality is that heart rate alone cannot determine blood pressure. However, they are mathematically linked through a variable called Cardiac Output.
The Hemodynamic Formula
To calculate Blood Pressure theoretically using Heart Rate, medical physicists use the fundamental equation of blood flow. This is similar to Ohm's Law in electricity (Voltage = Current × Resistance). In the cardiovascular system, the formula is:
BP = Cardiac Output (CO) × Systemic Vascular Resistance (SVR)
Since Cardiac Output is determined by your heart rate, we can expand the formula:
Cardiac Output (CO): Heart Rate × Stroke Volume
Full Equation: BP = (Heart Rate × Stroke Volume) × Resistance
Key Variables in the Calculation
The calculator above uses these three critical inputs to estimate the Mean Arterial Pressure (MAP):
Heart Rate (HR): The speed of the pump, measured in beats per minute (BPM). As HR increases during exercise, BP typically rises to push more oxygen to muscles.
Stroke Volume (SV): The volume of blood pumped with each beat. An average healthy adult pumps about 70 mL per beat at rest. Athletes often have higher stroke volumes.
Systemic Vascular Resistance (SVR): The "tightness" of your arteries. If arteries are constricted (high resistance), the same heart rate will produce higher blood pressure.
Why Can't I Get Just Systolic/Diastolic from HR?
Systolic (top number) and Diastolic (bottom number) pressures depend heavily on arterial stiffness and the timing of the heart's relaxation phase. Two people can have a heart rate of 80 BPM, but if one has stiff arteries (high SVR) and the other has flexible arteries (low SVR), their blood pressures will be drastically different.
For example:
Person A: HR 80, Normal Resistance -> BP might be 120/80.
Person B: HR 80, High Resistance -> BP might be 150/95.
Therefore, while Heart Rate is a component of Blood Pressure, it is not the sole determinant. This calculator helps you visualize how changes in your heart rate or vascular resistance theoretically impact the mean pressure in your circulatory system.
The Role of Rate Pressure Product (RPP)
Another common calculation involving these metrics is the Rate Pressure Product, often used in cardiology to determine the oxygen workload of the heart.
Formula: RPP = Heart Rate × Systolic BP.
While this doesn't calculate BP from HR, it uses both to assess cardiac stress. A lower resting heart rate usually correlates with a more efficient cardiovascular system and often lower blood pressure, but this is a correlation, not a direct calculation rule.