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Sleep disordered breathing (SDB) is associated with an increased prevalence of hypertension and cardiovascular disease independent of age, sex, and body mass index. The adverse cardiovascular effects are thought to be due to combinations of overnight hypoxaemia, hypercapnia, and sympathetic nervous system overactivity. There is limited research that has addressed the influence of these variable overnight physiological changes on the endothelial function. Brachial artery ultrasonography is a reliable non-invasive surrogate marker of endothelial function which allows repetitive dynamic assessment of both arterial diameter and velocity. Reduced flow mediated dilation (FMD) of the brachial artery in response to increased stress correlates with angiographically proven coronary artery disease. The percentage increase in peak blood flow (PBF) in response to transient arterial occlusion and hypoxia has also been reported as a measure of resistance vessel endothelial function.
Families affected with SDB were identified and neighbourhood control families were also recruited. Of the 2462 members, 700 underwent in-depth studies of cardiovascular and metabolic risk factors and 193 participants aged 16 years and older were studied. Individuals with known cardiovascular disease or diabetes were excluded. Participants underwent overnight polysomnography and brachial artery ultrasonography the following morning.
The authors concluded that increasing severity of SDB is associated with decreasing FMD and PBF. However, these relationships were observed only in women. This was unexpected but previous studies have suggested that there may be gender differences in endothelial function. This suggests that women with SDB may be more vulnerable to early SDB related cardiovascular disease than men with relatively mild levels of SDB, but we do not yet know what mechanisms are involved in this difference.