Page 180 - Assessing right ventricular function and the pulmonary circulation in pulmonary hypertension Onno Anthonius Spruijt

10
RVESP. It is possible that in a pressure overloaded RV, RVESP is more closely related to the systolic RV pressure (RVSP) [39] which would have led to an overestimation of Ees. However, mPAP and RVSP were strongly related both at rest and during exercise, implying that the choice of pressure will not influence the direction of the rest-to-exercise response.
Although the single beat method has been developed and validated for the left ventricle [12], validation of the method in PH has been restricted to animals [11]. The results of that study showed, in a wide range of Pmax values, that an excellent relation exist between Pmax determined by the single beat method and the Pmax values determined after clamping of the pulmonary artery.
We used relatively deconditioned control subjects, as the primary indication to perform iCPET in these subjects was unexplained dyspnea. Based on the literature [3, 40-42], including a previous study from our institute [3], we did not expect to find an unchanged SV in healthy subjects during submaximal exercise. The difference in SV response in control subjects between the current study and our previous study [3] can probably be explained by the fact that the control subjects in our previous study were healthy volunteers in good condition. Several previous studies showed physiological explanations for an unchanged SV from rest-to-exercise. A reduced filling time due to an increase in HR can result in an inability to increase SV in healthy subjects. Furthermore, in the upright position, the venous return is increased from rest-to-exercise via the muscle pump. When exercise is performed in the supine position, the venous return is already increased at rest due to the return of pooled blood due to gravity, resulting in an inability to increase SV during exercise [6, 43-49]. Since we already found large differences in the hemodynamic rest-to-exercise responses between PH patients and relatively deconditioned control subject, the inclusion of relatively deconditioned control subjects only strengthens our findings.
Conclusions
PH patients had no RV exertional contractile reserve, which resulted in RV-arterial uncoupling during submaximal exercise. Rest-to-exercise responses in pulmonary artery pressures rather reflected the rest-to-exercise response in heart rate, than an exertional contractile reserve and should therefore not be used as a surrogate measure of exertional contractile reserve.