Chronotropic Response Index Calculator

The Chronotropic Response Index (CRI) is used to evaluate the adequacy of heart rate response during exercise. It is defined as the ratio of the percentage of heart rate reserve achieved during exercise to the percentage of metabolic reserve achieved.

Key Concepts:

• Predicted Maximum Heart Rate: Typically estimated as 220 minus age.
• Heart Rate Reserve: The difference between the predicted maximum heart rate and the resting heart rate.
• Achieved Heart Rate Reserve: The difference between the peak heart rate during exercise and the resting heart rate.

Calculation Formula:

\[ \text{Chronotropic Index} = \frac{\text{Achieved Heart Rate Reserve}}{\text{Heart Rate Reserve}} \]

Example Calculation:

For a 40-year-old with a resting heart rate of 70 bpm and a peak heart rate of 160 bpm during exercise:

• Predicted Maximum Heart Rate: 220 - 40 = 180 bpm
• Heart Rate Reserve: 180 - 70 = 110 bpm
• Achieved Heart Rate Reserve: 160 - 70 = 90 bpm
• Chronotropic Index: \( \frac{90}{110} = 0.82 \)

Clinical Relevance:

A CRI below 0.8 may indicate chronotropic incompetence, where the heart does not appropriately increase its rate with exercise, which can be associated with cardiovascular issues.

This calculator aids clinicians and patients in assessing cardiovascular fitness and exercise response.