Author + information
- Matthias Gorenflo, MDa
In their interesting study (1) the authors report that nebulized iloprost was more potent than inhaled nitric oxide (NO) as a pulmonary vasodilator in patients with primary pulmonary hypertension.
They conclude that iloprost caused a more intense decrease in pulmonary vascular resistance (PVR) and a higher increase in cardiac output (CO) than inhaled NO. However, from a hemodynamic point of view, several findings reported in their study remain to be explained. In Table 1 data for the changes in systemic vascular resistance (SVR) and PVR in response to NO and iloprost are listed. Not only PVR, but also SVR, significantly decreased after iloprost.
As presented in the methods section of their paper, the calculation of PVR and SVR was done according to the following formulas that are widely used (2) to calculate the resistance to pulmonary and systemic perfusion:
As can be seen easily, any increase in cardiac output will lead to a calculatory decrease of PVR and SVR, merely as a result of the way these parameters are calculated (CO in the denominator). Interestingly, the authors report a significant increase in CO after iloprost nebulization (Fig. 1B, Table 1).
Any increase in CO that may result from systemic arterial vasodilation will result in a decrease of calculated values for PVR and SVR without any change of the tone of the pulmonary vasculature itself. Consistent with this interpretation, the authors clearly state that both systemic and pulmonary arterial mean pressures decreased significantly after iloprost compared with NO (Table 1). It would be interesting to see to what extent the ratios of pulmonary/systemic blood pressure and the ratios of calculated PVR/SVR changed after NO or iloprost. Only by reporting data for the ratios of Pp/Ps and PVR/SVR specific changes in pulmonary hemodynamics after exposition to a given drug can be ascertained to be a real effect rather than representing merely a calculatory phenomenon.
- American College of Cardiology
- Hoeper M.M,
- Olschwewski H,
- Ghofrani H.A,
- et al.
- Freed M.D