ADDING OBJECTIVITY TO SUBMAXIMAL EXERCISE TESTING BY ASSESSMENT OF HEART RATE RECOVERY – A HEALTHY VOLUNTEER STUDY III (SEARCH-III)

Abstract

<h3>Objective</h3> Risk prediction is a fundamental component of perioperative medicine. Submaximal exercise tests (SET) are a better-tolerated modality for functional capacity estimation versus maximal tests; but their results are easily influenced by patient motivation and effort. Heart rate recovery (HRR) may be an alternative, objective, modality for cardiopulmonary fitness determination. HRR1 and HRR2 (difference between HR at peak exercise and one/two minutes after exercise cessation) are validated methods for quantifying HRR after maximal testing. Previous work suggests however that HRR1/2 after submaximal exercise may be effort dependent.[1,2] Our group has devised two novel HRR quantification parameters, area under the curve (AUC) and effort correction, both demonstrating good reproducibility in the submaximal setting;[3,4] however, the minimum effort required for reliable HRR quantification during SET remains unknown. We therefore assessed the reproducibility of both existing and novel HRR quantification techniques across different submaximal effort levels. <h3>Design and methods</h3> Following R&D approval and with informed consent, 36 healthy adult volunteers underwent two SETs using a modified Astrand-Rhyming cycle ergometer protocol in a randomised order. Participants exercised briefly to 60% of predicted maximum heart rate (HRmax) and 70% HRmax, with one hour rest between SETs. HR was recorded at 30-second intervals during the recovery period for six minutes. HRR was quantified using HRR1, HRR2, and AUC. Effort-corrected (EC) equivalents of HRR1, HRR2 and AUC were computed by dividing absolute parameters by the effort ratio (HR on exercise cessation divided by HRmax). Intra-individual reproducibility was assessed between SETs using intraclass correlation coefficient (ICC), Spearman's correlation (rs) and Bland-Altman analysis. <h3>Results</h3> Effort-corrected HRR1 proved the best parameter displaying moderate reproducibility (ICC=0.58, 95%CI 0.32-0.76), moderate positive correlation (rs=0.64, p<0.001) and smallest bias (5.2bpm, LoA=-27.0-37.3) between SETs (fig. 1). Similarly, AUC reproducibility improved from poor (ICC=0.46) to moderate (ICC=0.56) after effort-correction. ICC remained poor in HRR2 after effort correction (HRR2 ICC=0.32 vs. EC-HRR2 ICC=0.44). Despite improvement in all parameters following effort correction, reproducibility and correlation were poor-moderate and Bland-Altman analysis demonstrated marked variability of differences across mean values with wide limits of agreement. <h3>Conclusion</h3> Unsatisfactory reproducibility was demonstrated across all HRR parameters at 60% HRmax versus the previously used target of 70% HRmax. Sensitivity analyses revealed a proportion of participants with elevated baseline HR such that minimal effort was required to reach the less demanding 60% HRmax target, producing no HRR as a result. Excluding these "non-responders" improved reproducibility of parameters between SETs. Using "personalised" HR targets based on each participant's resting HR may therefore better standardise effort exerted during testing. Further work should explore the applicability of submaximal HRR in the surgical population.