Severe obstructive sleep apnoea exacerbates the microvascular impairment in very mild hypertensives

Different studies have shown that obstructive sleep apnoea syndrome (OSAS), frequently associated with hypertension, represents a harmful and independent risk for cardiovascular diseases. The aim of our study was to ascertain whether the occurrence of OSAS could worsen microcirculatory impairment in very mild hypertensives.

One hundred untreated very mild hypertensives underwent polysomnography and subdivided into 32 non-OSAS, 33 mild OSAS and 35 severe OSAS patients on standardized criteria. They underwent routine blood chemistry, ambulatory blood pressure monitoring and anthropometric analysis. Skin capillary density (n mm(-2)) of forearm (FAC) and periungueal (PUC) fields was obtained through videocapillaroscopy. By a venous congestion manoeuvre, PUC was maximized (CVC) and secondary capillary recruitment (GAIN) was calculated. These measurements served as indices of structural and functional capillary rarefaction, respectively.

Severe OSAS hypertensives showed reduced FAC (P < 0.001) and PUC (P < 0.001) as compared to those with mild OSAS and non-OSAS, but a greater CVC (P < 0.01) and GAIN (P < 0.001). Multiple regression analysis showed that PUC was inversely related to total sleep time with oxyhaemoglobin saturation at < 90% (TST90) (P < 0.001) and FAC to the apnoea-hypopnoea index (AHI) (P < 0.001) and to the sleep propensity (P < 0.01). CVC was positively associated to AHI (P < 0.001) and GAIN to TST90 (P < 0.05).

The findings suggest that OSAS, by means of reduced basal and functional capillarity rarefaction, might pose an additional risk of impaired peripheral perfusion in very mild hypertensives. A microcirculation study therefore should be a part of the clinical approach in patients at high cerebro-cardiovascular risk such as hypertensives and patients with OSAS.