Hypercapnia and respiratory drive in obstructive sleep apnea patients before and after CPAP treatment

Objective

To investigate the respiratory drive and the response to CPAP treatment in obstructive sleep apnea patients.

Methods

Twenty-one consecutive patients (19 males/2 females) with newly diagnosed disease with polysomnography were enrolled in this study. Blood gases, body mass index measurement (BMI) and spirometry were performed in all patients. Respiratory drive was evaluated by using the P_0.1 technique and the mean inspiratory flow (V_T/T_I). P_0.1 was also measured during sub maximal exercise by using the same technique. 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 evaluated all the parameters before and 2 days after CPAP treatment.

Results

There was no significant difference in BMI, PO₂, FEV₁, FVC, respiratory cycle indices and P_0.1 at rest. PCO₂ was significantly reduced (44 ± 5 vs 42 ± 6 mmHg) after treatment. At exercise P_0.1and V_T/T_I were significantly reduced (6.6 ± 2.7 vs 4.9 ± 1.6 cmH₂O, P < 0.01 and 72 ± 16 vs 64 ± 10, P < 0.05, respectively).

Conclusion

The unchanged respiratory drive at rest may not reduction in explain the PCO₂ reduction in our population. The significantly reduced respiratory drive and mean inspiratory flow during exercise could possibly explain change of ventilatory control, which may not be detected at rest.