Wave intensity as a useful modality for assessing ventilation–perfusion imbalance in subclinical patients with hypertension

Wave intensity (WI) is a novel noninvasive index of circulatory dynamics that reflects ventriculo-arterial coupling. It is calculated as the product of the first derivative of blood pressure and that of flow velocity measured by carotid echocardiography. This study aimed to clarify the clinical implications of WI and its relation with carbon dioxide production (VE/VCO₂ slope). Twenty-one healthy volunteers (control group) and 21 patients with hypertension (HT group) underwent cardiopulmonary exercise testing (CPX) and exercise stress echocardiography. WI was assessed in the right carotid artery using an ultrasound system. The first peak of WI (W₁) during the early ejection phase was measured at baseline and mitral annular velocity was assessed by tissue Doppler imaging. Ventilatory kinetics during exercise was assessed using the relation of minute ventilation to VE/VCO₂ slope. VE/VCO₂ slope, W₁, and E/E′ were greater in the HT group than in the control group. PeakVO₂ and VO₂ at the anaerobic threshold were lower in the HT group than in the control group. VE/VCO₂ slope was significantly correlated with W₁ (r = 0.58, p < 0.01) and E/E′ (r = 0.44, p < 0.01). Stepwise multivariate analysis revealed that W₁ was an independent determinant of VE/VCO₂ slope (β = 0.43, p < 0.01). In conclusion, W₁ might be able to predict the severity of heart failure without the need for CPX. Moreover, WI may be a useful modality in assessing heart failure pathophysiology based on ventriculo-arterial coupling.