Cardiopulmonary exercise testing for identification of patients with hyperventilation syndrome

INTRODUCTION: Measurement of ventilatory efficiency, defined as minute ventilation per unit carbon dioxide production (V(E)/VCO(2)), by cardiopulmonary exercise testing (CPET) has been proposed as a screen for hyperventilation syndrome (HVS). However, increased V(E)/VCO(2) may be associated with other disorders which need to be distinguished from HVS. A more specific marker of HVS by CPET would be clinically useful. We hypothesized ventilatory control during exercise is abnormal in patients with HVS. METHODS: Patients who underwent CPET from years 2015 through 2017 were retrospectively identified and formed the study group. HVS was defined as dyspnea with respiratory alkalosis (pH >7.45) at peak exercise with absence of acute or chronic respiratory, heart or psychiatric disease. Healthy patients were selected as controls. For comparison the Student t-test or Mann-Whitney U test were used. Data are summarized as mean ± SD or median (IQR); p<0.05 was considered significant. RESULTS: Twenty-nine patients with HVS were identified and 29 control subjects were selected. At rest, end-tidal carbon dioxide (P(ET)CO(2)) was 27 mmHg (25–30) for HVS patients vs. 30 mmHg (28–32); in controls (p = 0.05). At peak exercise P(ET)CO(2) was also significantly lower (27 ± 4 mmHg vs. 35 ± 4 mmHg; p<0.01) and V(E)/VCO(2) higher ((38 (35–43) vs. 31 (27–34); p<0.01)) in patients with HVS. In contrast to controls, there were minimal changes of P(ET)CO(2) (0.50 ± 5.26 mmHg vs. 6.2 ± 4.6 mmHg; p<0.01) and V(E)/VCO(2) ((0.17 (-4.24–6.02) vs. -6.6 (-11.4-(-2.8)); p<0.01)) during exercise in patients with HVS. The absence of V(E)/VCO(2) and P(ET)CO(2) change during exercise was specific for HVS (83% and 93%, respectively). CONCLUSION: Absence of V(E)/VCO(2) and P(ET)CO(2) change during exercise may identify patients with HVS.