Resistance vessel growth and remodelling: cause or consequence in cardiovascular disease.

Haemodynamic evidence indicates that in essential hypertension, minimum vascular resistance and vascular pressor response are increased. According to the original concept of Folkow, this is most easily explained in terms of a generalised narrowing of the vasculature and an increase in the ratio of the vessel wall (more specifically, tunica media) thickness to lumen diameter. These predictions have been confirmed, both by histological and in vitro studies of resistance vessels. Moreover, the evidence indicates that these changes are associated mainly with remodelling (rearrangement of the same amount of material) of the vessels rather than growth. However, although the alteration in small artery structure is usually appropriate to the actual blood pressure (BP), the structure is not only a secondary adaptation but is also dependent on other factors, including neurohumoral and genetic factors. Furthermore, although the resistance vessel structure clearly plays an important role in determining BP, it does not appear to be a prime determinant of BP. It thus appears that more emphasis should be placed on Folkow's original idea that resistance vessel structure, like neurohumoral drive, is a mediator of the mechanisms which determine BP. Therefore, although evidence is available that the structure of certain specific parts of the vasculature (namely the renal afferent arterioles) could play a dominant function in the development of hypertension, it is suggested that resistance vessel structure should not in general be considered to have this role.