Ventilation and heart rate response during exercise in normals: relevance for rate variable pacing.

The observation of a close relationship of heart rate to oxygen uptake (HR-VO2) and heart rate to minute ventilation (HR-VE) has been shown to be of particular value in rate variable pacing. However, the impact of anaerobic threshold (AT) for the HR-VO2 and HR-VE slope has been studied less. Twenty-three male and 16 female subjects, mean age 52 +/- 7 years, were selected in whom complete heart catherization and extensive noninvasive studies excluded major cardiopulmonary disease. Semisupine bicycle exercise testing with analysis of respiratory gas exchange was performed using a ramping work rate protocol with work increments of 20 watts/min. At the respiratory AT, determined by the V slope method, oxygen uptake (VO2-AT) was 15.2 +/- 3.0 mL/kg in males versus 13.8 +/- 2.3 mL/kg in females and heart rate (HR-AT) was 109 +/- 18 beats/min versus 119 +/- 20 beats/min, respectively. Heart rate was highly correlated (r > or = 0.9) to VO2 and minute ventilation (VE). A linear regression for HR-VO2, however, was found only in 16/39 and for HR-VE in 11/39 subjects. Assuming the AT as the breakpoint of two linear curves, it could be demonstrated that compared to low exercise HR appeared to increase at maximal exercise more in relation to VO2 but less in relation to VE; in men the individual slopes for HR-VO2 were 2.6 +/- 0.7 below but 3.2 +/- 1.0 above AT (P < 0.05) and the slopes for HR-VE were 1.6 +/- 0.5 below but 1.0 +/- 0.4 above AT (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)