SUMMARY The roles of hypoxaemia, of mechanical changes related to partial or complete airway obstruction and of arousals during sleep in the haemodynamic and heart rate changes seen in association with sleep-disordered breathing have been questioned. Several experiments have been performed by these authors to investigate the role of arousals and mechanical changes in the blood pressure changes associated with sleep disordered breathing.
Investigation of the role of arousals. Two different populations were used in this study; one of normal, young volunteers without sleep-disordered breathing monitored at baseline (normal sleep) who were submitted to auditory stimulation during sleep, causing sleep fragmentation, and another of obstructive sleep apnoeic patients who were monitored at baseline and after nasal CPAP treatment. Before treatment and after one month of treatment while still being treated with nasal CPAP, these subjects were submitted to the same auditory stimulation and sleep fragmentation as normal controls. The studied variables were systolic and diastolic blood pressure and heart rate.
In normal controls, auditory induced arousals lead to an increase in diastolic as well as systolic blood pressure. The increase was related to the type of arousal but was also noted with K complexes to a lesser degree. In OSAS patients under treatment with nasal CPAP, similar increases were noted with auditory stimulation. Compared to baseline hypoxaemia and hyperventilation periods, however, the haemodynamic increase was, at its highest, only one-third of the mean pressure monitored during the baseline, end-of-apnoea hyperventilation period with EEG arousals. Investigation of the role of nasal CPAP on blood pressure (BP) while patients had no hypoxaemia (SaO2>92%) but still showed increased respiratory efforts indicated a persistence of higher systolic and diastolic pressures than when nasal CPAP completely eliminated increased efforts.
Possible long-term impact of arousals and mechanical changes. A last study was performed on patients with upper airway resistance syndrome (UARS). Out of 112 patients, 6 were identified using the World Health Organization (WHO) protocol and ambulatory monitoring as having borderline 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 machines were equipped with counters that could accurately measure the number of hours that the device was used. Patients were their own controls and were re-monitored one month later. Four subjects used their nasal CPAP at least 6 nights per week and more than 5 hours per night. One 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 the 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.
Despite the absence of SaO2 drops, there were chronic changes in BP readings that appear to be related to arousals and mechanical changes.