validation of subjective exercise intensity prescription for stringent blood pressure control in cardiac rehabilitation: comparing the borg scale and anaerobic threshold with real-time blood pressure

Abstract Background Cardiac rehabilitation (CR) is a crucial intervention for improving long-term prognosis. However, specific patient groups, such as those post-mitral valve repair, require extremely stringent blood pressure (BP) control during exercise. Historically, BP monitoring during CR has been limited to pre- and post-exercise readings, leaving a gap in understanding intra-exercise BP fluctuations. Furthermore, determining appropriate exercise intensity is challenging, as the gold standard, Cardiopulmonary Exercise Testing (CPX), is often unavailable prior to CR initiation. Consequently, physical therapists rely on subjective assessments like the Borg Rating of Perceived Exertion (RPE), leading to concerns that exercise wattage might be set too low, resulting in a sub-therapeutic effect. Purpose This study aimed to: (1) Evaluate the safety of conventional RPE-based intensity prescription by measuring BP during exercise to assess the risk of exertional hypertension. (2) Validate the therapeutic optimality of this subjective prescription by comparing the prescribed Watts with the objective Anaerobic Threshold (AT) in Watts derived from CPX. Methods The study involved frequent automated BP measurements taken throughout the exercise duration to assess exertional hypertension. The Watts determined by the physical therapist based on the Borg RPE scale (subjective intensity) were quantitatively compared against the AT-level Watts predetermined by pre-rehabilitation CPX (objective intensity). Results The study cohort consisted of 55 patients instructed to undergo stringent BP management during CR (39 males, 70.9%). This included 18 patients (32.7%) post-mitral valve repair. Mean resting systolic BP was 117.9 ±17.1 mmHg, with a mean ceiling BP during rehabilitation of 135.2±9.9 mmHg. Real-time BP monitoring confirmed that BP during rehabilitation was generally well-controlled, suggesting RPE-based intensity did not induce dangerous exertional hypertension. In a subset of 35 patients, the quantitative comparison of Watts between the RPE-based prescription and the AT-level from CPX showed no statistically significant difference (p value = 0.214). This suggests the conventional subjective RPE use enables the setting of an appropriate wattage that effectively reaches the objective AT. Conclusion(s) Objective data validates that the conventional subjective method of exercise intensity prescription, based on the Borg RPE scale, safely guides patients to a therapeutically optimal AT-level wattage without significantly exacerbating the risk of hypertension. This result strongly justifies the validity of traditional clinical judgement. The findings assure that an adequate and non-sub-therapeutic wattage is safely delivered, even in resource-constrained CR environments where pre-rehabilitation CPX is difficult to perform, supporting the continued, confident application of RPE-based prescription.