Enhancing Heart Rate-Based Estimation of Energy Expenditure and Exercise Intensity in Patients Post Stroke.

Background: Indirect calorimetry is the gold standard field-testing technique for measuring energy expenditure and exercise intensity based on the volume of oxygen consumed (VO₂, mL O₂/min). Although heart rate is often used as a proxy for VO₂, heart rate-based estimates of VO₂ may be inaccurate after stroke due to changes in the heart rate-VO₂ relationship. Our objective was to evaluate in people post stroke the accuracy of using heart rate to estimate relative walking VO₂ (wVO₂) and classify exercise intensity. Moreover, we sought to determine if estimation accuracy could be improved by including clinical variables related to patients' function and health in the estimation.

Methods: Sixteen individuals post stroke completed treadmill walking exercises with concurrent indirect calorimetry and heart rate monitoring. Using 70% of the data, forward selection regression with repeated k-fold cross-validation was used to build wVO₂ estimation equations that use heart rate alone and together with clinical variables available at the point-of-care (i.e., BMI, age, sex, and comfortable walking speed). The remaining 30% of the data were used to evaluate accuracy by comparing (1) the estimated and actual wVO₂ measurements and (2) the exercise intensity classifications based on metabolic equivalents (METs) calculated using the estimated and actual wVO₂ measurements.

Results: Heart rate-based wVO₂ estimates were inaccurate (MAE = 3.11 mL O₂/kg/min) and unreliable (ICC = 0.68). Incorporating BMI, age, and sex in the estimation resulted in improvements in accuracy (MAE Δ: -36.01%, MAE = 1.99 mL O₂/kg/min) and reliability (ICC Δ: +20, ICC = 0.88). Improved exercise intensity classifications were also observed, with higher accuracy (Δ: +29.85%, from 0.67 to 0.87), kappa (Δ: +108.33%, from 0.36 to 0.75), sensitivity (Δ: +30.43%, from 0.46 to 0.60), and specificity (Δ: +17.95%, from 0.78 to 0.92).

Conclusions: In people post stroke, heart rate-based wVO₂ estimations are inaccurate but can be substantially improved by incorporating clinical variables readily available at the point of care.