Influence of blood flow on arteriolar wall-to-lumen ratio in the human retinal circulation in vivo.

OBJECTIVE

We hypothesized that blood flow impacts on arteriolar wall-to-lumen ratio and that vasodilatory capacity is negatively related to arteriolar wall-to-lumen ratio in the human retinal vascular bed.

METHODS

The study cohort comprised 141 non-diabetic untreated male patients with (n=52) or without (n=89) arterial hypertension but without evidence for cardiovascular disease. Retinal capillary blood flow (RCF) before and after exposure to flicker light and to infusion of nitric oxide (NO) synthase inhibitor N-monomethyl-L-arginine (L-NMMA), and parameters of retinal arteriolar morphology, e.g. wall-to-lumen ratio, were assessed non-invasively and in vivo by scanning laser Doppler flowmetry.

RESULTS

The study cohort was grouped according to the median RCF into two groups. Patients with RCF above the median revealed lower wall-to-lumen ratio (0.30 ± 0.1 vs 0.34 ± 0.1 (-), P adjusted=0.023) compared to patients with RCF equal or below the median. In addition, RCF was negatively related to wall-to-lumen ratio independently of cardiovascular risk factors (ß=-0.224, P=0.026). In parallel, the decrease of RCF to L-NMMA infusion was greater in patients with RCF above the median compared to the counter group (-8.95 ± 11 vs. 0.35 ± 15 (%), P adjusted <0.001). The increase in RCF to flicker light exposure was negatively related to wall-to-lumen ratio in hypertensive but not in normotensive or all patients (r=-0.292, P=0.047, r=-0.035, P=0.746 and r=-0.126, P=0.144, respectively).

CONCLUSIONS

In the retinal circulation blood flow impacts on arteriolar wall-to-lumen ratio. Basal NO activity might modulate blood flow and arteriolar morphological changes. In hypertensive, but not in normotensive patients, the vasodilatory capacity is negatively related to arteriolar wall-to-lumen ratio in the human retinal vascular bed.