ASSESSMENT OF VENTILATORY NEUROMUSCULAR DRIVE IN PATIENTS WITH OBSTRUCTIVE SLEEP-APNEA

The presence of abnormalities of the respiratory center in obstructive sleep apnea (OSA) patients and their correlation with polysomnographi c data are still a matter of controversy. Moderately obese, sleep-depr ived OSA patients presenting daytime hypersomnolence, with normocapnia and no clinical or spirometric evidence of pulmonary disease, were se lected. We assessed the ventilatory control and correlated it with pol ysomnographic data. Ventilatory neuromuscular drive was evaluated in t hese patients by measuring the ventilatory response (VE), the inspirat ory occlusion pressure (P.(1)) and the ventilatory pattern (VT/TI, TI/ TTOT) at rest and during submaximal exercise, breathing room air. Thes e analyses were also performed after inhalation of a hypercapnic mixtu re of CO2 (Delta P(.1)Delta PETCO2, Delta VE/Delta PETCO2) Average res t and exercise ventilatory response (VE: 12.2 and 32.6 l/min, respecti vely), inspiratory occlusion pressure (P-.1: 1.5 and 4.7 cmH(2)O, resp ectively), and ventilatory pattern (VT/TI: 0.42 and 1.09 l/s; TI/TTOT: 0.47 and 0.46 Vs, respectively) were within the normal range. In resp onse to hypercapnia, the values of ventilatory response (Delta VE/Delt a PETCO2: 1.51 l min(-1) mmHg(-1)) and inspiratory occlusion pressure (Delta P-.1/Delta PETCO2: 0.22 cmH(2)O) were normal or slightly reduce d in the normocapnic OSA patients. No association or correlation betwe en ventilatory neuromuscular drive and ventilatory pattern, hypersomno lence score and polysomnographic data was found; however a significant positive correlation was observed between P-.1 and weight. Our result s indicate the existence of a group of normocapnic OSA patients who ha ve a normal awake neuromuscular ventilatory drive at rest or during ex ercise that is partially influenced by obesity.