J. Sleep Res. (2005) 14, 325–327
Letter to the Editor Platelet function (measured by Platelet Function Analyser - 100) and obstructive sleep apnoea
It is known that platelet activation occurs in patients with acute coronary syndromes and antiplatelet drugs provide significant therapeutic benefit in these people (Boersma et al., 2002; Ott et al., 1996; Wodlinger and Pieper, 2003; Yusuf et al., 2003). The platelet function analyser (PFA-100) is a unique device, which simulates high shear-dependent platelet function in vitro (Francis, 2004; Jilma, 2001; Kundu et al., 1995). This is a relatively new test, determining platelet-related primary haemostasis, by measuring the time needed for a platelet plug to form after activation of platelets by pathophysiologically relevant stimuli. Citrated whole blood is aspirated under high shear (5000–6000 s)1) through a capillary tube and onto a collagen-coated membrane, containing a central aperture of 150 lm in diameter. The platelets become activated, adhere to the membrane and slowly close the aperture. The point at which the flow rate stops and occlusion occurs is recorded as the closure time (CT). The membrane is coated with collagen and one of two additional physiological agonists: epinephrine (in the collagen epinephrine, or CEPI, cartridge) or adenosine diphosphate (in the collagen and adenosine diphosphate, or CADP, cartridge). Each cartridge can detect classical platelet defects and von Willebrand’s disease (VWD), but only the CEPI test usually gives prolonged CTs indicating platelet inhibition with aspirin and nonsteroidal anti-inflammatory drugs. Studies have shown PFA100 is easy to use and highly accurate in discriminating normal from abnormal platelet function, with a clinical sensitivity of 81–95% and a specificity of 80–89% (Harrison et al., 2002; Mammen et al., 1998). Two other plasma factors which are implicated in platelet adhesion and activation are von Willebrand factor (VWF) and soluble P-selectin (sP-sel). VWF is a marker of endothelial function and an independent predictor of target organ damage. VWF antigen levels are also an important variable in determining the CT in whole blood. PFA-100 CT inversely correlates with plasma VWF in normals and VWD. sP-sel is a granular molecule expressed on the surface of activated endothelium and platelets and is primarily involved in leucocyte rolling and attachment and is also hypothesized to have a role in the initiation of atherosclerosis. sP-sel expression is also
Correspondence: Sophie West, Sleep Unit, Oxford Centre for Respiratory Medicine, Churchill Hospital, Oxford UK. Tel.: 01865 225 236; fax: 01865 225 205; e-mail:
[email protected] 2005 European Sleep Research Society
a marker for platelet activation as it is expressed and cleaved from the surface of activated platelets. Despite a wealth of data on detection of platelet abnormalities and VWD, there are few papers that yet show evidence of shortened CTs and evidence of platelet hyperfunction. A recent study from Austria however, measured the platelet function of people presenting with acute chest pain and symptoms suggestive of acute coronary syndrome with the PFA-100 (Frossard et al., 2004). Patients with myocardial infarction had significantly shorter CADP-CTs, indicating enhanced platelet function. These shorter times were seen particularly in those people having ST segment elevation myocardial infarction (STEMI), compared with patients with unstable angina, stable coronary artery disease or controls. CADP and CEPI CTs at presentation correlated inversely with markers of cardiac muscle necrosis (troponin-T and creatinine kinase), showing that the shorter the CT, or time needed for platelet plug formation under high shear, the greater the myocardial damage (P < 0.001). Obstructive sleep apnoea (OSA) is associated with nocturnal hypertension, daytime hypertension and increased cardiovascular risk (Davies, 1998; Marin et al., 2005; Peppard et al., 2000). Studies of haematological indices in OSA have sought to demonstrate a hypercoagulable state, which might account for some of the increased vascular risk found in patients with OSA. Studies have shown positive associations between the apnoea–hypopnoea index (AHI) and platelet activation measured by P-selectin (Eisensehr et al., 1998) and respiratory disturbance index and fibrinogen (Wessendorf et al., 2000). Multiple linear regression analysis of several studies showed independent associations between AHI and platelet activity, epinephrine and platelet activity, and average minimal SaO2 and fibrinogen (von Ka¨nel and Dimsdale, 2003). Platelet activation, measured by flow cytometry, was also found to correlate with the apnoea index in patients with OSA and decreased significantly (P < 0.001) compared with controls following continuous positive airway pressure (CPAP) therapy (Hui et al., 2004). Our previous recent study showed normal levels of VWF:Ag in patients with untreated OSA, but raised sP-sel, which was not significantly changed following CPAP treatment (Robinson et al., 2004). This further support that there may be increased platelet activation in OSA. We wanted to establish whether platelet function, as measured by the PFA-100, was potentially enhanced in a
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Figure 1. Scatter plot of 4% SaO2 dip rate against CEPI-CT.
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6–23), mean body mass index was 35.4 kg m)2 (SD 7.8, range 22–59). The mean platelet count of all the patients was 184.5 · 109 L)1 (SD 38.1, range 110–311, normal range ¼ 150–400 · 109 L)1). The mean haematocrit was 38.0% (SD 3.1, range 31.6–44.8%). There was no evidence of platelet hyperfunction or shortened CTs, as measured by the PFA-100. CADP-CTs ranged from 55 to 134 s, mean 91.2 (SD ¼ 18.1, normal range 55– 112 s). CEPI-CTs ranged from 87 to 300 s (SD ¼ 73.0, normal range 79–164 s). 72% of the patients with raised CEPI-CT were known to be taking aspirin or diclofenac. There was no correlation of CADP or CEPI with 4% SaO2 dip rate per hour (Figs 1 and 2), ESS, body mass index or age. The VWF:Ag levels ranged from 58 to 247 IU dL)1, mean 128.8 (SD 44.7, normal range 50–200 IU dL)1). VWF antigen levels showed no correlation with 4% SaO2 dip rate. sP-sel levels ranged from 14 to 62 ng mL)1, mean 38.8 (SD 11.5), which was significantly elevated (P ¼ 0.04, unpaired t-test) when compared with a mean sP-sel of 31.9 ng mL)1 from 23 unmatched control subjects. There was no apparent correlation of sP-sel with 4% dip rate or with BMI. Our previous study (n ¼ 93) showed that BMI was an independent predictor of baseline sP-sel under multiple linear regression (P < 0.002). There was also no correlation of sP-sel with PFA-100 CTs. We conclude that there is no apparent evidence of shortened CTs, measured by the PFA-100, in patients with OSA. However, both this and previous studies have shown evidence of platelet activation in OSA by using a variety of other methods, but presumably this activation is not contributing to a shortening of the PFA-100 CTs. Thus PFA-100 CTs do not appear to be a sensitive way to investigate the platelet abnormalities in OSA. CONFLICT OF INTEREST Dr Harrison is a consultant for Sysmex UK on the PFA-100.
4% dip rate versus CADP
Figure 2. Scatter plot of 4% SaO2 dip rate against CADP-CT.
group of patients with untreated OSA. Patients attending the outpatient sleep clinic with confirmed OSA (diagnosed following an overnight sleep study) and awaiting CPAP treatment, had information regarding Epworth Sleepiness Score (ESS), body mass index and current medication recorded. A citrated blood sample was taken in the morning and analysed within 4 h, using a PFA-100 analyser (Dade Behring, Marburg, Germany), using both CADP and CEPI cartridges. Statistical analysis was with SPSS version 12, using Pearson’s correlation coefficient. Forty-nine patients (40 men) with OSA awaiting CPAP treatment were included in this study. Their mean age was 53.7 years (SD 10.6, range 28–82). The mean severity of OSA was a >4% SaO2 dip rate of 32.9 per hour (SD 22.9, range 3–88). Mean Epworth Sleepiness Score was 13.8 (SD 4.5, range
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Letter to the Editor tool for the assessment of platelet dysfunction. Clin. Lab. Haem., 2002, 24: 225–232. Hui, D. S., Ko, F. W., Fok, J. P., Chan, M. C., Li, T. S., Tomlinson, B. et al. The effects of nasal continuous positive airway pressure on platelet activation in obstructive sleep apnea syndrome. Chest, 2004, 125: 1768–1775. Jilma, B. Platelet function analyzer (PFA-100): a tool to quantify congenital or acquired platelet dysfunction. J. Lab. Clin. Med., 2001, 138: 152–163. von Ka¨nel, R. and Dimsdale, J. E. Hemostatic alterations in patients with obstructive sleep apnea and the implications for cardiovascular disease. Chest, 2003, 124: 1956–1967. Kundu, S. K., Heilmann, E. J., Sio, R., Garcia, C., Davidson, R. M. and Ostgaard, R. A. Description of an in vitro platelet function analyzer- PFA-100. Semin. Thromb. Hemost., 1995, 21 (Suppl. 2): 106–112. Mammen, E. F., Comp, P. C., Gosselin, R., Greenberg, C., Hoots, W. K., Kessler, C. M., Larkin, E. C., Liles, D. and Nugent, D. J. PFA100 system: a new method for assessment of platelet dysfunction. Semin. Thromb. Hemost., 1998, 24: 195–202. Marin, J. M., Carrizo, S. J., Vicente, E. and Agusti, A. G. Long-term cardiovascular outcomes in men with obstructive sleep apnoeahypopnoea with or without treatment with continuous positive airway pressure: an observational study. Lancet, 2005, 365: 1046–1053. Ott, I., Neumann, F. J., Gawaz, M., Schmitt, M. and Schomig, A. Increased neutrophil-platelet adhesion in patients with unstable angina. Circulation, 1996, 94: 1239–1246. Peppard, P. E., Young, T., Palta, M. and Skatrud, J. Prospective study of the association between sleep-disordered breathing and hypertension. N. Engl. J. Med., 2000, 342: 1378–1384.
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Sophie West1, Helen Segal2, Paul Harrison2 and John Stradling1 1 Sleep Unit, Oxford Centre for Respiratory Medicine, Churchill Hospital, Oxford and 2Oxford Haemophilia Centre and Thrombosis Unit, Churchill Hospital, Oxford, UK
