Respiratory drive at rest and during exercise in obstructive sleep apnea patients before and after CPAP treatment

Respiratory drive at rest and during exercise has not been fully investigated in obstructive sleep patients. The aim of this study is to enlighten the response of respiratory drive to CPAP treatment in obstructive sleep apnea patients.

Methods

Fifteen consecutive patients (14 males/one female, aged 53 ± 6 years) with newly diagnosed disease were enrolled in this study. Diagnosis was made by all-night polysomnography using standard criteria. Blood gases, body mass index measurement (BMI) and spirometry were performed in all patients. P_0.1 and the mean inspiratory flow (V_T/T_I) were used as indices of respiratory drive. All parameters of the respiratory cycle were measured during the P_0.1 procedure (V_T, f, V_E, T_I, T_TOT, T_I/T_TOT). We measured the parameters at rest and during two stages of submaximal exercise. We evaluated all the parameters before and 6 months after CPAP treatment.

Results

Our patients seem to have moderate to severe disease as indicated by polysomnographic data (apnea hypopnea index 34–120). There was no significant difference in BMI, FEV₁ and FVC before and after treatment. PO₂ was significantly increased (76 ± 11 mmHg vs 82 ± 9 mmHg, P < 0.01) and PCO₂ was significantly reduced (45 ± 6 mmHg vs 41 ± 2 mmHg, P < 0.01). At rest there was no difference in respiratory drive and respiratory cycle parameters. At the first stage of submaximal exercise P_0.1 was significantly reduced (6.7 ± 2.7 cmH₂O vs 5.0 ± 2.2 cmH₂O, P < 0.05) and V_T/T_I was reduced (75 ± 29 l/min vs 61 ± 12 l/min, P < 0.05). At the second stage of submaximal exercise P_0.1 was unchanged, V_T/T_I was significantly reduced (99 ± 33 l/min vs 85 ± 17 l/min, P < 0.05) and T_I was significantly increased (0.9 ± 0.3 min vs 1.3 ± 0.2 min, P < 0.05).

Conclusion

Respiratory drive indices and respiratory cycle parameters at rest did not change in our population, although mild hypoxemia and hypercapnia significantly improved. Changes in respiratory drive during submaximal exercise could possibly explain changes of ventilatory control after CPAP treatment, which may not be detected at rest.