J receptor activity in idiopathic pulmonary hypertension and its expected change in the presence of pulmonary bed vasodilators.

Juxtapulmonary receptors (J) lying in the lung parenchyma are stimulated naturally by any condition that produces interstitial oedema, transient increases in interstitial volume and pressure or raised pulmonary capillary pressure. There is no information available about the level of their stimulation in patients with idiopathic pulmonary hypertension (IPH) who have high levels of pulmonary artery systolic pressures. The aim of the present study therefore was to find the level of these receptors activity in these patients at their prevailing pulmonary artery systolic pressures. This was done by the established method of determining the dose of i.v. lobeline that gives rise to threshold levels of sensations in the upper chest areas and accelerates respiration. In IPH patients it was found to be as high as 31.6 ± 5.6 μg/kg i.e., twice as much as that known for healthy individuals which is 15 μg/kg. This shows an enhanced stimulation of J receptors in IPH patients. Expectedly when pulmonary artery systolic pressure falls with pulmonary bed vasodilator medication given to IPH patients, a reduction in the natural stimulus of J receptors would also occur leading to a fall in their activity and hence that of the quantum of their reflexes of respiratory acceleration and inhibition of exercise. This finding provides the first insight of a neural mechanism that could be influenced to produce its effects when pulmonary artery systolic pressure falls by pulmonary vasodilator medication.