[The VO2 performance index for evaluation of cardiopulmonary capacity in respiratory minute volume controlled VVI-R stimulation].

This study was designed to assess the effect of acute minute ventilation sensing, rate-responsive pacing on cardiopulmonary exercise capacity in 27 patients (mean age 60 years) with chronotropic incompetence. The exercise protocol consisted of bicycle exercise in semisupine position with breath-to-breath analysis of gas exchange. At the anaerobic threshold heart rate increased from 75 +/- 9 in the VVI-mode to 113 +/- 21 beats/min in the VVI-R-mode (p < 0.001), oxygen uptake from 9.3 +/- 3.4 to 10.9 +/- 4.3 ml/kg/min (p < 0.001) and work rate from 52 +/- 20 to 65 +/- 24 watts (p < 0.001). Compared to 41 normal subjects, VVI-R pacing increased oxygen uptake up to 75% and work rate up to 79% of normal values, while heart rate increased similarly in both groups. The VO2 to work rate ratio (dVO2/dWR), calculated as the slope of the relation of oxygen uptake to work rate below the anaerobic threshold, improved from 7.9 +/- 2.3 to 10.2 +/- 2.4 ml/min/watts (p < 0.001) in the VVI-R-mode; so it did not differ from normal values. Thus, acute respiratory dependent rate-responsive pacing results in substantial improvement in cardiopulmonary exercise capacity in patients with chronotropic incompetence. The VO2 to work rate ratio demonstrated to be a reliable parameter for assessing this improvement.