Correlation of the Heart Rate-Minute Ventilation Relationship with Clinical Data: Relevance to Rate-Adaptive Pacing

The heart rate (HR)-minute ventilation (VE) relationship has been shown to be nonlinear and can be expressed as two distinct straight lines. This study is to assess the correlation of the initial HR-VE slope to clinical parameters. Maximum treadmill exercise tests were performed in 100 healthy volunteers (age 19–77 years) using a ramp protocol in which work-rate increases linearly with exercise. Breath-by-breath VO₂, VCO₂, and VE were measured, and HR and RP were monitored throughout the exercise. The HR-VE curve demonstrated nonlinearity with a breakpoint determined by a change point analysis. This breakpoint was significantly higher than that of the anaerobic threshold. The VEat the HB-VE breakpoint was 56.4 ± 19.4 and VE at the VE-VO₂ and VCO₂-VO₂ breakpoints were 48.0 ± 18.3 (P < 0.0001) arid 40.1 ± 16.5 (P < 0.0001). respectively. TheHR at this HR-VE breakpoint was 77.7 ± 12.9% of the HR range. The first slope. Si (1.76 ± 0.64) was steeper than the second slope, S2 (0.66 ± 0.39). Although there was a gender difference for S1, the best clinical predictor on a stepwise multiple regression analysis was body surface area (BSA) which explained 47% of the variance. It was concluded that nonlinearity of the HR-VE curve can be expressed as two straight lines. The breakpoint is beyond the anaerobic threshold and can be estimated to be approximately 75% of the maximal predicted HR. RSA is the only clinical parameter that significantly predicts the initial slope of the HR-VE curve. This can be of great importance in the programming of rate-adaptive pacemakers using a VE.