SpO2 and Oxygen Saturation Estimator
Estimated Results
Note: This is a mathematical estimation based on the Severinghaus equation and Bohr effect. Always use a medical-grade pulse oximeter for clinical accuracy.
Understanding the Relationship Between Heart Rate and SpO2
Many people search for a way to calculate SpO2 from heart rate because they notice their heart rate increases when oxygen levels drop. While there is no direct linear formula that says "Pulse X equals SpO2 Y," there is a deep physiological connection between the two. This calculator uses the Oxyhemoglobin Dissociation Curve to estimate saturation based on oxygen pressure, while allowing you to log heart rate as a contextual data point.
The Role of Heart Rate (HR)
The heart rate is a delivery mechanism. When your blood oxygen saturation (SpO2) drops (hypoxemia), your body compensates by increasing your heart rate (tachycardia) to pump the existing oxygenated blood faster to vital organs. If your heart rate is 100+ BPM at rest and your SpO2 is below 94%, it indicates your cardiovascular system is under stress.
The Science: Severinghaus Equation
To mathematically determine SpO2 without a pulse oximeter, clinicians look at the partial pressure of oxygen (PaO2). The relationship follows a sigmoidal (S-shaped) curve. The formula used in this tool is the Severinghaus equation:
SpO2 = (((PaO2³ + 150·PaO2)⁻¹ · 23400) + 1)⁻¹ · 100
Practical Examples
- Normal Health: A PaO2 of 95 mmHg typically yields an SpO2 of 97-99% with a resting heart rate of 60-80 BPM.
- Mild Hypoxia: A PaO2 of 60 mmHg (the "knee" of the curve) results in an SpO2 of approximately 90%. You will often see the heart rate climb to 90-110 BPM to compensate.
- Acidosis (pH shift): If your blood pH drops (becomes more acidic), the curve shifts to the right (Bohr effect), meaning your SpO2 will be lower for the same amount of oxygen pressure.
Why Heart Rate Doesn't Give the Whole Story
Heart rate can be affected by caffeine, stress, exercise, and dehydration, even if your oxygen levels are perfect. Conversely, during carbon monoxide poisoning, your SpO2 might appear high on a standard pulse oximeter, but your tissues are starving for oxygen. Always consult a healthcare professional for persistent symptoms of shortness of breath or rapid pulse.