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Altered blood rheology
- Les Simpson (25 January 2008)
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Aspirin resistance in cardiovascular disease: Muddy waters?
- Ashok I Handa, Ediri Sideso (20 February 2008)
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Les Simpson, retired experimental pathologist Dunedin, New Zealand
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According to the “BMJ : What’s new on line,” of Jan 23,2008, editorials discussed, “Aspirin resistance in cardiovascular disease, “ and, “The cardiovascular risks of calcium supplements in women.” Probably as a lack of appreciation of the pathophysiological significance of altered blood rheology, it seems not to be recognised that key factors in both situations are increased blood viscosity and reduced red cell deformability, both of which may be worsened by treatment. According to Ajmani and Rifkind (1), the aging process is associated with reduced red cell deformability and increased blood viscosity, with raised levels of fibrinogen increasing plasma viscosity. They noted, “ It has been found in a number of clinical observations for various groups of patients and in case-control studies that the rheological properties of the red cell change in the course of aging.” This could relate to changes in the shape populations of red cells as Simpson and O’Neill (2) reported that immediately fixed blood samples from 76 males and 91 females aged between 60 and 96 years, showed a prevalence of non- discocytic cells with flat cells being the most common change, when studied by scanning electron microscopy. As change in the internal environment stimulates change in the shape populations of red cells, this could reflect the age-related changes in the composition of blood. As non-discocytic red cells are poorly deformable and contribute to blood viscosity, it should be noted that there are many reports concerning the increased blood viscosity which has been found in association with cardiovascular disorders. Therefore it seems possible that “aspirin resistance,” might become explicable in terms of blood viscosity and/or reduced red cell deformability, drawing attention to the possibility of other treatment options. Ajmani and Rifkind (1) discussed the studies of the effects of menopausal changes on blood rheology, which showed changes in the composition of the blood with increased fibrinogen levels as a major feature. They stated, “ Elevated blood viscosity factors for postmenopausal women are indicative of a high risk of cardiovascular mortality.” As calcium has been shown to stiffen red cells, calcium supplements would amplify the effects of poorly deformable red cells, and increase the possibility of an adverse event in postmenopausal women. The apparent failure to recognise the relevance of blood rheology in both editorials, draws attention to a paper by Professor John Dormandy (3), who organised the Second European Conference on Clinical Haemorheology under the auspices of the Royal Society of Medicine. In 1982 he stated, “ …practising clinicians have tended to be unjustifiably resistant to new ideas. The continuing collaboration between haemorheologists and clinicians, which was the theme of this Conference, is the essential next step in establishing clinical haemorheology in its proper place.” It should be a major concern that the “essential next step” has not been taken, and the published information concerning altered blood rheology in the major causes of morbidity and mortality, cardiovascular disorders, cerebrovascular disease and stroke, diabetes, hypertension etc., has failed to gain clinical recognition. As the first review on blood viscosity was published in 1911, surely it is time to recognise the clinical significance of the topic. Les Simpson (retired experimental pathologist) Dunedin, New Zealand. References. 1. Ajmani RS, Rifkind JM. Hemorheological changes during human aging. Gerontology 1998;44: 111-20. 2. Simpson LO, O’Neill DJ. Red cell shape changes in the blood of people 60 years of age and older imply a role for blood rheology in the aging process. Gerontology 2003;49:310-5. 3. Dormandy JA. Second European Conference on Clinical Haemorheology. J Roy Soc Med 1982;75:581-3. Competing interests: None declared |
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Ashok I Handa, Clinical Tutor in Surgery and Consultant Surgeon Nuffield Department of Surgery,University of Oxford, John Radcliffe Hospital,Oxford OX3 9DU, Ediri Sideso
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We read with interest the editorial article on Aspirin “resistance” in cardiovascular disease by Professor Biondi-Zoccai and Marzia Lotrionte. The authors state that clopidogrel should be substituted for aspirin, for people at intermediate thrombotic risk and low risk of bleeding, as a more effective alternative. Given the observed significant heterogeneity in the subgroup analysis from CAPRIE, we contend that clopidogrel and aspirin are only equivalent in efficacy in patients suffering a myocardial infarction and that Clopidogrel is not superior. We agree with the authors that Aspirin resistance may be a reflection of the normal variability to drug response however the issue of patient concordance with therapy must be a paramount concern . Medication concordance data in transplant patients demonstrates that up to a third of patients do not adhere to their prescribed regimen. Finally, we agree that the underlying issue may well be that drug regime in most cases assumes a “one size fits all” approach, but switching to a different medication may result in a similar phenomenon. More clinical trials with other drugs therefore, may only serve to muddy the waters. 1. Caprie steering committee. A randomised, blinded, trial of clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE). Lancet 1996; 348: 1329 – 39 2. M Dew, A Di Martini, A De Vito Dabbs, L Myaskovsky, J Steel, M Unruh, C Switzer, R Zomak, R Kormos and J Greenhouse. Rates and risk factors for nonadherence to the medical regimen after adult solid organ transplantation. Transplantation 2007 ; 83 (7) : 858-873 Competing interests: None declared |
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