Alveolar-derived exhaled nitric oxide is reduced in obstructive sleep apnea syndrome.
BACKGROUND
Obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular diseases, in particular systemic arterial hypertension. We postulated that intermittent nocturnal hypoxia in OSAS may be associated to decreased fractional exhaled nitric oxide (FENO) levels from distal airspaces.


METHODS
Multiple flow rate measurements have been used to fractionate nitric oxide (NO) from alveolar and bronchial sources in 34 patients with OSAS, in 29 healthy control subjects, and in 8 hypertensive non-OSAS patients. The effect of 2 days of treatment with nasal continuous positive airway pressure (nCPAP) on FENO was examined in 18 patients with severe OSAS.


RESULTS
We found that the mean [+/- SE] concentrations of exhaled NO at a rate of 50 mL/s was 21.8 +/- 1.9 parts per billion (ppb) in patients with OSAS, 25.1 +/- 3.3 ppb in healthy control subjects, and 15.4 +/- 1.7 ppb in hypertensive control patients. The mean fractional alveolar NO concentration (CANO) in OSAS patients was significantly lower than that in control subjects (2.96 +/- 0.48 vs 5.35 +/- 0.83 ppb, respectively; p < 0.05). In addition, CANO values were significantly lower in OSAS patients with systemic hypertension compared to those in normotensive OSAS patients and hypertensive patients without OSAS. The mean values of CANO significantly improved after nCPAP therapy (2.67 +/- 0.41 to 4.69 +/- 0.74 nL/L, respectively; p = 0.01).


CONCLUSIONS
These findings suggest that alveolar FENO, and not bronchial FENO, is impaired in patients with OSAS and that this impairment is associated with an increased risk of hypertension. NO production within the alveolar space is modified by treatment with nCPAP.
Foresi
Antonio
A
Unit of Respiratory Medicine, Sesto San Giovanni Hospital, Sesto San Giovanni, Italy.
Leone
Clementina
C
Olivieri
Dario
D
Cremona
George
G
D000328:Adult; D000368:Aged; D001944:Breath Tests; D001980:Bronchi / Q000378:metabolism*; D016022:Case-Control Studies; D045422:Continuous Positive Airway Pressure; D045853:Exhalation / Q000502:physiology; D005260:Female; D006801:Humans; D006973:Hypertension / Q000150:complications / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000378:metabolism*; D020181:Sleep Apnea, Obstructive / Q000150:complications / Q000378:metabolism* / Q000628:therapy
D009569:Nitric Oxide