AROUSAL, INCREASED RESPIRATORY EFFORTS, BLOOD-PRESSURE AND OBSTRUCTIVE SLEEP-APNEA

The roles of hypoxaemia, of mechanical changes related to partial or c omplete airway obstruction and of arousals during sleep in the haemody namic and heart rate changes seen in association with sleep-disordered breathing have been questioned. Several experiments have been perform ed by these authors to investigate the role of arousals and mechanical changes in the blood pressure changes associated with sleep disordere d breathing. Investigation of the role of arousals. Two different popu lations were used in this study; one of normal, young volunteers witho ut sleep-disordered breathing monitored at baseline (normal sleep) who were submitted to auditory stimulation during sleep, causing sleep fr agmentation, and another of obstructive sleep apnoeic patients who wer e monitored at baseline and after nasal CPAP treatment. Before treatme nt and after one month of treatment while still being treated with nas al CPAP, these subjects were submitted to the same auditory stimulatio n and sleep fragmentation as normal controls. The studied variables we re systolic and diastolic blood pressure and heart rate. In normal con trols, auditory induced arousals lead to an increase in diastolic as w ell as systolic blood pressure. The increase was related to the type o f arousal but was also noted with K complexes to a lesser degree. In O SAS patients under treatment with nasal CPAP, similar increases were n oted with auditory stimulation. Compared to baseline hypoxaemia and hy perventilation periods, however, the haemodynamic increase was, at its highest, only one-third of the mean pressure monitored during the bas eline, end-of-apnoea hyperventilation period with EEG arousals. Invest igation of the role of nasal CPAP on blood pressure (BP) while patient s had no hypoxaemia (SaO(2)>92%) but still showed increased respirator y efforts indicated a persistence of higher systolic and diastolic pre ssures than when nasal CPAP completely eliminated increased efforts. P ossible long-term impact of arousals and mechanical changes. A last st udy was performed on patients with upper airway resistance syndrome (U ARS). Out of 112 patients, 6 were identified using the World Health Or ganization (WHO) protocol and ambulatory monitoring as having borderli ne high BP (140-160//90-98). Subjects were calibrated with nasal CPAP and were asked to use their equipment on a nightly basis. The CPAP mac hines were equipped with counters that could accurately measure the nu mber of hours that the device was used. Patients were their own contro ls and were re-monitored one month later. Four subjects used their nas al CPAP at least 6 nights per week and more than 5 hours per night. On e patient used his CPAP approximately 3 nights per week and more than 4 hours per night. One patient used his CPAP a total of 3 nights in th e whole month. Blood pressure was unchanged in the patient who failed to use his CPAP, but was normalized in the 5 others, as were nocturnal recordings.