Our study aims to evaluate the effect of 100 % oxygen on the pulmonary vascular hemodynamics in pulmonary arterial hypertension(PAH) and to analyse the main determinants of this response.
Fifty-four PAH patients (11 male, 43 female)underwent right heart catheterisation. Mean pulmonary artery pressure (mPap) and pulmonary capillary wedge pressure were measured. Arterial and mixed venous saturations and oxygen pressures were obtained from the femoral and pulmonary artery. All measurements were performed at baseline and after reversibility testing. Cardiac output was calculated by the Fick method and the pulmonary vascular resistance (PVR) was calculated from the cardiac output and pressure measurements. Reversibility was tested by means of inhaling 100% oxygen for a time period of 5 minutes followed by a refractory time of 5 minutes. In addition, 20 ppm Nitric Oxide (NO) was inhaled for 5 minutes. Reversibility to 100% oxygen was defined as a decrease of the PVR (dPVR) more than 20%. Differences between the groups were statistical analysed by use of the non parametric Mann Witney t test.
Thirty-three patients showed reversibility to 100% oxygen inhalation(dPVR= 37 ± 11%). Arterial oxygen pressure was at baseline (PaO2 = 77 ± 16 mmHg) for the patients showing reversibility and (PaO2 = 66 ± 16 mmHg) for the non reversible patients(p < 0.02). Mixed venous oxygen pressure (PvO2)did not differ significantly between the two groups. PaO2 showed a weak relation with dPVR (r=0.34, p < 0.02). PvO2 was not related to dPVR. Oxygen caused a significant larger (p < 0.001) decrease of the PVR (dPVR = 26 ± 14%) than NO (dPVR = 13 ± 16%).
These data show that the higher the systemic arterial oxygen pressure the greater the respons to oxygen therapy and that the improvement of pulmonary hemodynamics in PAH is more pronounced for 100% oxygen inhalation than for NO.
The extent of the systemic arterial oxygen pressure might be the main determinant for the decision to initiate oxygen therapy in PAH patients.
A. Vonk-Noordegraaf, None.