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 s tudied less. Twenty-three male and 16 female subjects, mean age 52 +/- 7 years, were selected in whom complete heart catherization and exten sive noninvasive studies excluded major cardiopulmonary disease. Semis upine bicycle exercise testing with analysis of respiratory gas exchan ge was performed using a ramping work rate protocol with work incremen ts of 20 watts/min. At the respiratory AT, determined by the V slope m ethod, oxygen uptake (VO2-AT) was 15.2 +/- 3.0 mL/kg in males versus 1 3.8 +/- 2.3 mL/kg in females and heart rate (HR-AT) was 109 +/- 18 bea ts/min versus 119 +/- 20 beats/min, respectively. Heart rate was highl y correlated (r greater-than-or-equal-to 0.9) to VO2 and minute ventil ation (VE). A linear regression for HR-VO2, however, was found only in 16139 and for HR-VE in 11/39 subjects. Assuming the AT as the breakpo int of two linear curves, it could be demonstrated that compared to lo w exercise HR appeared to increase at maximal exercise more in relatio n 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). Similarly, in women the individual slopes for HR-VO2 were 3 .7 +/- 1.4 below but 4.3 +/- 1.4 above AT (P < 0.05) and the slopes fo r HR-VE were 2.1 +/-0.9 below but 1.3 +/- 0.4 above AT (P < 0.05). The differences between male and female subjects were significant. The no nlinear behavior of the HR-VO2 and HR-VE relation from rest to maximal exercise should have a particular impact in respiratory controlled pa cing systems.