Gas exchange and hemodynamics in pulmonary hypertension (PH)

In PH the measure of pulmonary function tests (PFT) and arterial blood gases (ABG) are used to identify underlying lung disease. We wondered if there could be a relationship among indices of PFT, ABG (paO2, paCO2), gas exchange (A-a DO2, a-ADCO2, VDphy/VT) and haemodynamic variables in a population of PH patients. Methods: Sixteen patients with suspicion of PH underwent PFT, diffusing lung capacity (DLCO), ABG, gas exchange, right heart cath; physiological dead space to tidal volume was measured. Mean values and their SD were calculated. The relationships between the observed variables were evaluated by their mutual information. The global network was reconstructed using the ARACNE algorithm (Margolin A, et al.: ARACNE. BMC Bioinformatics, 2006; 20:1-7). Modules in the network were identified applying a multidimensional scaling procedure to the adjaceny matrix and, succesively, clustering the variables with a model-based bayesian approach (Fraley C, et al. JASA, 2002; 97:611-631). We conducted the analyses with R statistical software. Results: Pulmonary gas exchange was on average impaired with increased A-a DO2; a-A DCO2 as well as physiological dead space were abnormal thus indicating impairment of ventilation perfusion distribution ratio. The three most influential variables in the networks were: PCW (betweeness=20), RAP (betweeness=18) and VDphy/VT (betweeness=14). Three modules were identified: a (RAP, FEV1, VDphy/VT, CI, TLC); b (PCW, PVR, mPAP); g (aADO2, aADCO2, DsbHb, PaCO2). The three modules were well separated. VDphy and PVR were significantly correlated (p: 0,042; R: 0.53). Conclusions: It turns out from our results a narrow relationships between VDphy and RAP, CI and PVR.