The effect of experimental hypertension on retinal vascular autoregulation in humans: a mechanism for the progression of diabetic retinopathy

Abstract

SUMMARYSince the retinal vessels have no sympathetic innervation, blood flow in response to raised blood pressure is dependent on autoregulation. To determine the effect of hypertension on retinal haemodynamics and the autoregulatory capacity of the retinal circulation under conditions of normoglycaemia and hyperglycaemia, retinal blood flow was measured before and after raising the systemic blood pressure in ten normal control subjects, ten diabetic subjects with blood glucose < 10 mmol 11 and ten diabetic subjects with blood glucose > 15 mmol 1-'. A controlled nse in systemic blood pressure was achieved using an intravenous infusion of tyramine. Retinal volume flow was determined from red cell velocity using laser Doppler velocimetry and from retinal vessel diameter measurements using digital image analysis of fundus photographs. With a 40 % increase in mean arterial blood pressure (MAP), there was a significant increase in retinal blood flow of 32.9 + 7-1 % in non-diabetic controls. In diabetics at the low blood glucose level, the increase in retinal blood flow was significant at 30% increase in MAP (23.6 + 87 %, P = 0-032) and at 40 % increase (49-9 + 12-03 %, P = 0-004). Diabetics with high blood glucose failed to autoregulate at any of the increased levels of MAP (15 % increase, 27 0 + 11 1 %; 30 % increase, 66.9 + 19.8 %; and 40 % increase, 101 9 + 21 4 %; P < 0.022). The coefficients of autoregulation showed that in non-diabetic controls, retinal vascular autoregulation broke down with increases in MAP of between 30 and 40 %. In diabetic subjects, it broke down between 15 and 30 % in normoglycaemia and at less than 15 % in hyperglycaemia. This study demonstrates an impairment in retinal vascular autoregulation in response to raised systemic blood pressure in diabetic subjects, more so at an elevated blood glucose level, thus providing a mechanism for the detrimental effect of hypertension on diabetic retinopathy.

The contribution of hypertension to diabetic nephropathy and retinopathy: the role of inflammation and oxidative stress

“…29 Loss of autoregulation in diabetes has also been discovered in human retinal vasculature. 30 This alteration would facilitate transmission of systemic hypertension to the retinal capillary bed, thus contributing to the mechanism of exacerbation of DR by hypertension. 30 Interestingly, there is a positive correlation between loss of autoregulation and levels of glucose in the human retinal vasculature.…”

“…30 This alteration would facilitate transmission of systemic hypertension to the retinal capillary bed, thus contributing to the mechanism of exacerbation of DR by hypertension. 30 Interestingly, there is a positive correlation between loss of autoregulation and levels of glucose in the human retinal vasculature. 30 Recently, molecular studies have identified several mechanisms that may be involved in the process of renal and retinal damage associated with hypertension and hyperglycemia.…”

“…30 Interestingly, there is a positive correlation between loss of autoregulation and levels of glucose in the human retinal vasculature. 30 Recently, molecular studies have identified several mechanisms that may be involved in the process of renal and retinal damage associated with hypertension and hyperglycemia. Most of these studies were based on an in vitro model of mechanical stimuli, such as stretch, mimicking the effect of increased pressure in glomerular and retinal cells in vivo.…”

Retrobulbar circulation in patients with age-related maculopathy

“…Hypertension is known to be prevalent among ARM patients and blood pressure and posture have been found to affect central retinal circulation. 18,19 However, blood pressure and posture during measurement have not been reported in the above mentioned studies. Except for the inclusion criteria, we suspect these to be among the possible reasons why the results from the present and the mentioned studies differ with respect to the results of the central retinal artery circulation.…”

Unilateral macular oedema secondary to retinal venous congestion without occlusion in patients with diabetes mellitus

“…Indeed, impaired autoregulation with increasing retinal perfusion following an increase in blood pressure and hyperperfusion in response to acute hyperglycaemia have previously been demonstrated (Grunwald et al 1992;Rassam et al 1995). A more widespread role of retinal venous pressure elevation in diabetic retinopathy may be suspected, because it explains why retinal hyperperfusion may induce retinopathy.…”