Retinal capillary rarefaction in patients with untreated mild-moderate hypertension

Abstract

Background: Microvascular rarefaction influences peripheral vascular resistance, perfusion and metabolism by affecting blood pressure and flow pattern. In hypertension microvascular rarefaction has been described in experimental animal studies as well as in capillaroscopy of skin and biopsies of muscle tissue in patients. Retinal circulation mirrors cerebral microcirculation and allows non-invasive investigations. We compared capillary rarefaction of retinal vessels in hypertensive versus normotensive subjects.

Methods: In this study retinal capillary rarefaction in 70 patients with long time (more than 67 month of disease duration) and 64 patients with short time hypertension stage 1 or 2 has been compared to 55 healthy control subjects, who participated in clinical trials in our Clinical Research Center ( www.clinicaltrials.gov : NCT01318395, NCT00627952, NCT00152698, NCT01319344). Retinal vascular parameters have been measured non-invasively and in vivo in perfusion image by scanning laser Doppler flowmetry (Heidelberg Engineering, Germany). Capillary rarefaction was assessed by capillary area (CapA) (in pixel-number) and intercapillary distance (ICD) (in μm). Additionally retinal capillary flow (RCF) was measured.

Results: ICD was greater in the long time hypertensive group compared to healthy individuals (24.2 ± 6.3 μm vs 20.1 ± 4.2 μm, p = 0.001) and compared to short time hypertensive patients (22.2 ± 5.2 μm, p = 0.020). Long time hypertensive patients showed less CapA compared to healthy people (1462 ± 690 vs 1821 ± 652, p = 0.005). Accordingly, RCF was significantly lower in the long time hypertensive group compared to the healthy control group (282 ± 70 AU vs 314 ± 60 AU, p = 0.032). Our data indicate a lower level of retinal capillary density in hypertensive patients, especially in those with long time hypertension.

Conclusion: Patients with hypertension stage 1 or 2 showed retinal capillary rarefaction in comparison to healthy normotensive subjects. Retinal capillary rarefaction was intensified with duration of disease.

Keywords: Capillary density; Capillary rarefaction; Hypertension; Microcirculation; Retina.

Conflict of interest statement

Ethics approval and consent to participate

The study protocol of each trial was approved by the Local Ethics Committee (University of Erlangen-Nürnberg), and the studies were conducted in accordance with the Declaration of Helsinki and the principles of good clinical practice guidelines. Subjects were recruited by advertising in local newspapers in the area of Erlangen-Nürnberg, Germany, and eligible subjects were enrolled consecutively. Written informed consent was obtained before study inclusion.

Consent for publication

Not applicable

Competing interests

The authors declare that they have no competing interests.

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Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1

Correlation of retinal capillary density and wall-to-lumen ratio in hypertensive patients. 1a: Intercapillary distance and wall-to-lumen ratio (r = 0.185, p = 0.033). 1b: Capillary area and wall-to-lumen ratio (r = −0.185, p = 0.035)

Fig. 2

Correlation of retinal Intercapillary distance and 24 h ambulatory BP. 2a: Intercapillary distance and systolic 24 h ambulatory BP (r = 0.238, p = 0.010). 2b: Intercapillary distance and diastolic 24 h ambulatory BP (r = 0.219, p = 0.018)

Fig. 3

Correlation of capillary density and duration of hypertension. 3a: Intercapillary distance and duration of hypertension (r = 0.263, p = 0.002). 3a: Capillary area and duration of hypertension (r = −0.243, p = 0.006)

Fig. 4

Correlation of capillary density and HDL. 4a: Intercapillary distance and HDL-cholesterol (r = −0.174, p = 0.018). 4b: Capillary area and HDL-cholesterol (r = 0.136, p = 0.070)