The relationship of heart rate reserve to VO2 reserve in patients with heart disease.

UNLABELLED: Recent reports indicate that among healthy adults, % heart rate reserve (HRR) is more closely related to %VO2 reserve (VO2R) than it is to %VO2max. This finding, in addition to the disparity between %HRR and %VO2max which is greater at low intensities and among low fit individuals, led the American College of Sports Medicine to adopt the use of %VO2R in place of %VO2max when prescribing exercise intensity among healthy adults and persons with heart disease. However, the relationship of %HRR to %VO2R among persons with heart disease has not been described.

PURPOSE: Among patients with a myocardial infarction (MI) and patients with chronic heart failure (HF), test the hypothesis that %VO2R is equivalent to %HRR, while %VO2peak is not.

METHODS: Using a clinical cardiology outcomes database, symptom-limited treadmill tests from 65 patients with MI and 72 patients with HF were identified. Heart rate and VO2 data were measured continuously and averaged every 15 s. For each subject, linear regression was used to calculate the slope and y-intercept of %HRR versus %VO2R (assuming rest VO2 = 3.5 mL x kg(-1) x min(-1)) and %HRR versus %VO2peak. Mean slope and y-intercept were calculated for each group and compared with the line of identity (slope = 1, y-intercept = 0).

RESULTS: For the MI and HF groups, the slope of %HRR versus %VO2R was 0.96 +/- 0.02 (+/-SE; P = NS, slope vs 1) and 0.97 +/- 0.02 (P = NS), respectively. And the y-intercept was -1.9 +/- 2.1% (P = NS, y-intercept vs 0) and -5.9 +/- 2.1% (P < 0.05) for MI and HF, respectively. For both patient groups, the regression of %HRR versus %VO2peak resulted in a line that differed (P < 0.001) in both slope and y-intercept from the line of identity.

CONCLUSIONS: In patients with heart disease, %HRR is a better estimate of %VO2R than %VO2peak. This finding does not affect the current recommended use of %HRR. However, when prescribing exercise based on VO2, relative intensity should be expressed as %VO2R.