Differences in atherosclerosis according to area level socioeconomic deprivation: cross sectional, population based studyBMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b4170 (Published 27 October 2009) Cite this as: BMJ 2009;339:b4170
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Deans et al have reported the results of a high-tech assessment of
vascular changes which occur in both deprived and in non-deprived
participants. It is noteworthy that although the blood levels of
cholesterol and smoking history were recorded, there was no recognition of
the effects of such variables on the physical properties of the blood, or
on blood flow in the presence of plaques. As plaques reduce the lumenal
diameter, the rate of blood flow distal to the plaque will be reduced,
resulting in thixotropic amplification of blood viscosity. This is
because blood is a thixotropic system in which viscosity is related
directly to rate of blood flow. Blood viscosity is minimal at the
highest rates of blood flow.
A PubMed search for "atherosclerosis and blood viscosity" produced
316 titles, so it is not an unresearched topic.
The significance of blood viscosity is that it is a determinant of
intravascular pressure. The relevance of this was explained by JE French
writing on atherosclerosis in Florey's "General Pathology," 1958. French
drew attention to the fact that, "There are no capillary vessels in the
tunica intima of normal arteries.In general,
the vasa vasorum do not penetrate further than the middle of the tunica
media and the nutrition of the intima and the inner part of the media is
maintained by filtration from the arterial lumen."
It seems reasonable to consider that the nature of the filtrate
entering the intima will be determined by the blood pressure. If this is
so then an elevation of blood pressure would produce a different filtrate
possibly with larger molecules. This could explain the vascular changes
seen in healthy subjects, as French had noted, "...the so-called fatty
streaks may be seen in the posterior wall of the aorta in children, and by
the age of 20, some evidence of atherosclerosis can always be found on
careful inspection of the aorta." It is possible that such deposits
represent non-metabolised substances which had been filtered from the
So what do the observations of French imply for the results of the
Deans et al study ?
Firstly, because of the absence of any measures of blood rheology, they
were unable to explain some of the similarities which linked the deprived
and nondeprived data. For example, blood viscosity could be increased in
both groups, but due to different mechanisms. Stress, smoking, alcohol
intake and dietary factors in different mixes would increase blood
viscosity in both groups.
Secondly, in circumstances where blood viscosity was increased,
plaque score and intima-media thickness measurements could be good
predictors of adverse events.
Thirdly, the recognition of blood viscosity as an important factor,
indicates that lowering of blood viscosity could have beneficial effects.
Dietary changes which lowered the intake of saturated fats, and increased
the intake of oily fish would be beneficial. As 6 grams daily of fish oil
has been found to be effective in hypertension, it is possible that the
effects of 6 grams of fish oil daily on blood viscosity could reduce the
significance of atherosclerosis.
Competing interests: No competing interests