EFFECT OF NITRIC-OXIDE INHALATION ON RESPIRATORY SYSTEM RESISTANCE INCHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Nitric oxide (NO) has been identified as a neurotransmitter of nonadre nergic noncholinergic bronchodilator nerves. To investigate whether in haled NO exerts a bronchodilator effect in patients with chronic obstr uctive pulmonary disease (COPD), we measured the resistance of the res piratory system, using the forced oscillation technique, while breathi ng NO. Eight patients with COED (7 men and 1 woman; aged 66+/-7 yrs (m ean+/-SD); forced expiratory volume in one second (FEV1) 37+/-17% of p redicted) and eight healthy subjects (7 men and 1 woman; 33+/-4 yrs; F EV1 108+/-14% pred) were studied. Nitric oxide, at a concentration of 40 parts per million (ppm) in air, was inhaled for 20 min. Total resis tance (Rrs) and reactance (Xrs) of the respiratory system, arterial ox ygen saturation, heart rate, tidal volume, and breathing frequency wer e continuously recorded at baseline, and during and after ceasing NO i nhalation. Methaemoglobin levels were additionally measured in healthy subjects. At baseline, patients with COPD showed higher Rrs than heal thy subjects (Rrs at 10 Hz (Rrs,lo) 4.97+/-2.19 vs 2.29+/-0.65 hPa . L (-1). s). During NO inhalation, no significant change in Rrs or in Xrs was observed. Mean variation in Rrs,10 while breathing NO was negligi ble and similar in the two groups (-0.10+/-0.13 hPa . L(-1). s in COPD patients and -0.02+/-0.13 hPa . L(-1). s in healthy subjects), Moreov er, there were no differences in oxygen saturation, heart rate, tidal volume and breathing frequency during NO inhalation, Methaemoglobinaem ia increased at the end of NO inhalation (from 0.48+/-0.18 to 0.81+/-0 .16%), and this increment remained 10 min later (0.86+/-0.31%). From t hese results, we conclude that inhaled nitric oxide, at a concentratio n of 40 ppm, exerts no effect on respiratory system resistance in pati ents with chronic obstructive pulmonary disease or in healthy subjects .