Ventilatory efficiency improvement after cardiac rehabilitation in dysautonomia: an independent physiological adaptive mechanism

Background Postural orthostatic tachycardia syndrome (POTS) and inappropriate sinus tachycardia (IST) are forms of dysautonomia characterized by exercise intolerance and abnormalities in ventilatory regulation, among other symptoms. Ventilatory inefficiency, reflected by alterations in the ventilation–carbon dioxide production relationship (VE/VCO₂), represents a key physiological marker. Although cardiac rehabilitation has been proposed as a therapeutic strategy, the impact of structured training on ventilatory efficiency in this population has not been extensively investigated. Purpose To evaluate the physiological impact of a structured cardiac rehabilitation program on ventilatory efficiency and to determine whether improvement in VE/VCO₂ represents an autonomous adaptive mechanism independent of aerobic capacity and clinical evolution in patients with dysautonomia. Methods A total of 104 patients with a diagnosis of dysautonomia who completed a structured cardiac rehabilitation program were included. Functional capacity was assessed by cardiopulmonary exercise testing (CPET) at baseline and after 6 months. Physical fitness components were also evaluated. Changes in VE/VCO₂, peak oxygen uptake (VO₂ peak), resting heart rate, and symptomatic relapse were analyzed. Results Mean age was 27.9 ± 5.5 years; 92.3% were female. A mean reduction of 18.99% in VE/VCO₂ was observed (SD 8.87%), representing a physiologically meaningful change exceeding thresholds considered clinically significant in heart failure populations. Approximately 25% of patients achieved reductions greater than 27%. Improvement in VE/VCO₂ showed no significant correlation with the increase in VO₂ peak (r = 0.053; p = 0.595) nor with the reduction in resting heart rate (r = −0.068; p = 0.490). Furthermore, VE/VCO₂ improvement did not predict symptomatic relapse (OR 1.02; p = 0.587) and was consistent across diagnostic subgroups (POTS vs IST; p = 0.282). VO₂ peak increased significantly from 21.42 to 29.95 mL/kg/min (Δ +8.53 mL/kg/min; +39.8%; p<0.001). Resting heart rate decreased from 94.9 to 72.3 bpm (Δ −22.6 bpm; p<0.001). Program adherence was 82.8%, and symptomatic relapse occurred in 8.7% of patients. Conclusion Cardiac rehabilitation in patients with dysautonomia is associated with a significant improvement in ventilatory efficiency. The absence of correlation with aerobic capacity, chronotropic reduction, and clinical evolution suggests that the decrease in VE/VCO₂ may represent an autonomous adaptive mechanism within the rehabilitation process. Ventilatory efficiency emerges as an objective physiological marker of cardiorespiratory adaptation in this population, potentially reflecting relevant central and peripheral physiological remodeling.VE_VCO2_vs_VO2VE_VCO2_vs_RestingHR