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

Recent reports indicate that among healthy adults, % heart rate reserve (HRR) is more closely related to %(V) over dot O-2 reserve ((V) over dot O2R) than it is to %(V) over dotO(2max). This finding, in addition to the disparity between %HRR and %(V) over dot O-2max which is greater at low intensities and among low fit individuals, led the American College of Sports Medicine to adopt the use of %(V) over dotO(2)R in place of %(V) over dotO(2max) when prescribing exercise intensity among healthy adults and persons with heart disease. However, the relationship of %HRR to %(V) over dotO(2)R 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 %(V) over dotO(2)R is equivalent to %HRR, while %(V) over dot O-2peak 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 (V) over dot O-2 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 %(V) over dotO(2)R (assuming rest (V) over dot O-2 = 3.5 mL.kg(-1).min(-1)) and %HRR versus %(V) over dot O-2peak. 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 %(V) over dot O2R 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 %(V) over dot O-2peak 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 %(V) over dotO(2)R than %(V) over dot O-2peak. This finding does not affect the current recommended use of %HRR. However, when prescribing exercise based on (V) over dot O-2, relative intensity should be expressed as %(V) over dot O2R.