Introduction Obstructive sleep apnoea syndrome (OSAS) independently increases cardiovascular risk and a pro-thrombotic state has been at least partly implicated. Using fractal analysis we have developed a new biomarker called fractal dimension (Df) to assess the microstructure of incipient clot in whole blood. Df relates to the kinetics of clot formation and quantifies clot fibrin network microstructure as it forms. A higher Df represents a more pro-coaguable state. Healthy volunteers have a reproducible Df of 1.74 ±0.07. (1)
Aim To see if Df changes after sleep in OSAS and symptomatic snorers.
Methods 28 patients with newly diagnosed and untreated OSAS: 24 males, mean+SD BMI=38±7.3 kg/m2, age 56.8±10.7 years, 4% Dip-rate (DR)=47.8±32.9 events/hour, Epworth Sleepiness Score (ESS)13.1±5.0. 17 symptomatic Controls with symptoms of OSAS but who had negative sleep studies: 14 males, BMI=32.1±6.8 kg/m2, age 52.7±13.6 years, 4% DR=5.6±3.2 events/hour, ESS 11.3±6.6. We excluded anyone on warfarin, heparin or with a family history of bleeding, thromboses. 36% in the OSAS group and 24% in the Controls were prescribed aspirin but there were no changes in medications throughout the study. Blood was collected at 4pm then 8am the following morning, immediately after an inpatient limited channel overnight sleep study (Visilab, Stowood Instruments, UK). Samples were tested for fractal analysis (AR-G2 Rheometer, TA Instruments, UK) and routine APTT, PT, fibrinogen levels, platelet aggregation. NCT01525160.
Results Df was significantly higher in the early am (post sleep) (p<0.001) than in the afternoon in OSAS but there was no diurnal variation in the Control group (p= NS) Figure 1. There were no statistically significant differences for routine coagulation and platelet function tests both within and between groups.
Conclusion OSAS is associated with a significantly increased prothrombotic state in the morning that is only detected by Df. Larger numbers will allow sub-group analyses (e.g. severity of OSAS, aspirin effects) and seeing possible response to CPAP therapy. This preliminary data suggest Df could be used as a new sensitive biomarker to assess vascular risk.