Estimulación hipercápnica y respuesta ventilatoria en el síndrome de apnea obstructiva del sueño. Comparación de reinhalación y estado-estable

[A comparative study of patients with chronic obstructive pulmonary disease with and without obstructive sleep apnea syndrome]

We aimed to study whether the presence of obstructive sleep apnea syndrome (OSAS) in patients with chronic obstructive pulmonary disease (COPD) led to differences in clinical picture, gas exchange during awake and sleep states and mechanical ventilation, in comparison with patients with COPD alone. We enrolled 48 COPD patients. In 26 (54.1%), OSAS was ruled out (non-OSAS COPD group) by polysomnography, and in 22 (45.8%) associated OSAS was diagnosed (OSAS COPD group). Patients in the OSAS COPD group experienced greater daytime sleepiness and less dyspnea. Body mass index was not significantly difference. The OSAS COPD group had significantly lower daytime PaO2 (66.4 +/- 10.4 mmHg in the OSAS COPD group and 75.5 +/- 11.2 mmHg in the non-OSAS COPD group; p = 0.01); there were no differences in PaCO2.Pimax in the OSAS-COPD group was 70.6 +/- 23.8 cmH2O, a level that was significantly lower than in the non-OSAS COPD group (Pimax 90.5 +/- 26.1 cmH2O; p = 0.04). Patients in the non-OSAS COPD group experienced longer periods of REM sleep. Nighttime saturation parameters were significantly different in the group with OSAS. We conclude that patients with both OSAS and COPD experience greater oximetric changes than those without OSAS, during both sleep and awake states. The deterioration of respiratory muscle pressures in such patients may play an important role in the changes. The groups also present differences in the intensity of some symptoms, such as degree of daytime sleepiness and dyspnea.

Measuring central-chemoreflex sensitivity in man: rebreathing and steady-state methods compared

We compared the central-chemoreflex sensitivities estimated from steady-state tests with those estimated from rebreathing tests in five subjects. In one laboratory, each subject underwent nine dynamic end-tidal forcing experiments. Three repetitions of 3, 6 and 9 mmHg step changes in the end-tidal partial pressure of carbon dioxide, from a pre-step partial pressure 1.5 mmHg above resting, were used to establish four points of the steady-state ventilatory response to carbon dioxide. In another laboratory, each subject underwent two rebreathing experiments, one using Read's rebreathing technique and the other a modified rebreathing method which included a prior hyperventilation. The central-chemoreflex sensitivities, estimated from the slopes of the ventilatory responses to carbon dioxide using different combinations of the four steady-state points. were compared to those estimated from the slopes of the rebreathing responses. The steady-state sensitivities were significantly lower than the Read rebreathing sensitivities. The ratio of modified rebreathing sensitivities to steady-state sensitivities was closest to one when steady-state sensitivities were estimated from the two middle points of the ventilatory responses. The mean (SE) ratio of the sensitivities was 1.22 (0.21) in this case. We identify a number of factors that may affect the estimation of central-chemoreflex sensitivity using each technique. These include a maximum limit of the ventilation response at high partial pressures of carbon dioxide, an inability to sustain high ventilation for the duration of the steady-state tests and the inclusion of parts of the ventilatory response whose carbon dioxide partial pressures lie below the central-chemoreflex threshold. We conclude that the modified rebreathing method provides the best estimate of central-chemoreflex sensitivity of the three methods.