Dyspnea in Eisenmenger syndrome and its amelioration by sildenafil: role of J receptors

Background In Eisenmenger syndrome (ES), oral phosphodiesterase type-5 inhibitors, which are preferential pulmonary vasodilators, reduce the elevated pulmonary artery pressure and pulmonary vascular resistance index by increasing cyclic guanosine monophosphate (cGMP). However, no information is available as to how pulmonary vasodilatation alleviates the accompanying dyspnoea and improves patient's exercising ability. Objectives As the natural stimulus of juxtapulmonary capillary (J) receptors is an increase in interstitial pressure, the aim was to estimate their threshold level stimulation chemically by intravenous lobeline, before and after 6weeks of sildenafil therapy in treatment-naive ES patients. Methods Nine Eisenmenger syndrome patients [mean age=26 (SD=1.6) years] underwent 6MWT and an exercise test before and 6weeks after oral sildenafil (20mg 3× D). Their respiratory responses to threshold doses of intravenous lobeline were determined at both these stages. Results After 6weeks of sildenafil therapy, the 6MWD [from 453.3 (SD=50.9) m to 516.6 (SD=48.9) m; P =0.001] and the duration of exercise with the modified Bruce protocol from 7min 53s (SD=0.04) to 10min 44s (SD=0.88) ( P =0.001) improved significantly. However, the improvement in oxygen saturation was not noteworthy. The lobeline dose required to produce threshold level of respiratory effects was higher in ES patients [37.5 (SD=3.4) μg/kg] and with sildenafil therapy it fell significantly [20.6 (SD=1.8) μg/kg; P =0.001]. Conclusions J receptor threshold doses were elevated in ES patients and fell significantly with sildenafil therapy that was associated with improved exercise tolerance, implying thereby a role of J receptors in producing dyspnea in ES patients.