Conversely, the levels of endothelin-1 (ET-1) was higher in patients with PAH than those without or controls suggesting that pulmonary hypertension was a consequence of an imbalance in the output of the two agents by pulmonary epithelium and endothelium.[102] The levels of FENO have been found to correlate to the degree of PAH as assessed by Echo-Doppler studies.[103]. This evidence concerns the gene EDN1 and pulmonary arterial hypertension.