Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Kinesiology

Supervisor

Keir, Daniel A.

Affiliation

School of Kinesiology, University of Western Ontario, London, Ontario, Canada; Lawson Health Research Institute, London, Ontario, Canada; Toronto General Research Institute, Toronto General Hospital, Toronto, Ontario, Canada.

Abstract

The purpose of this thesis was to quantify the proportion of patients whose clinical cardiopulmonary exercise test (CPET) permitted identification of estimated lactate threshold (θLT) and respiratory compensation point (RCP) and to characterize the variability at which these thresholds occur to evaluate the feasibility of “threshold-based” aerobic exercise prescription. We retrospectively analyzed CPET data of 1102 patients (65±12 yrs; 306 females) referred to cardiac rehabilitation. θLT and RCP were identified and reported as oxygen uptake (V̇O2), heart rate (HR), %V̇O2peak, and %HRpeak. Patients were grouped by threshold identification: group 0) neither θLT nor RCP (n=556; 50%); 1) θLT only (n=196; 18%); 2) both θLT and RCP (n=350; 32%). Compared to group 1, θLT in group 2 occurred at a higher V̇O2 and HR, but lower %V̇O2peak and %HRpeak (p

Summary for Lay Audience

Exercise is an important part of managing diseases that affect the heart. When people are diagnosed with heart disease, they are often referred to a cardiac rehabilitation program to perform supervised aerobic (“cardio”) exercise training. At the start of these programs, patients perform an exercise test. These tests are used to assess how good a patient’s aerobic fitness is, and to determine how hard they will work (or “intensity”) on a treadmill or stationary bike during their exercise training program. Current guidelines recommend that patients exercise at a fraction of maximal effort achieved during their first exercise test (e.g., training intensity = 50% of maximal effort). This approach assumes that exercising at the same fraction of maximal effort will feel the same in all patients. A recent statement from European, American, and Canadian cardiac rehab groups suggested that a better way to set exercise training intensity is to separate it into three “domains” (moderate, heavy, and severe) based on two “thresholds” that are seen during exercise. In this thesis, we reviewed over 1000 exercise tests performed by patients referred to cardiac rehab to see how many of these tests showed one threshold, both thresholds, or neither of them. We also compared the fraction of maximal effort where these thresholds occurred between patients. We found that half (50%) of the tests we looked at showed at least one threshold, but only about one-third (32%) of the tests showed both thresholds. This may mean that the exercise tests used in modern cardiac rehab settings may not be designed well enough to allow clinical staff to identify both thresholds. Additionally, we found that in the group of patients showing both thresholds, the fraction of maximal effort where these thresholds occurred was very different between patients. This means that we cannot assume that exercise performed at the same fraction of maximal effort will feel the same in all patients referred to cardiac rehab.

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