Quantification of Retinal Vessel Myogenic Constriction in Response to Blood Pressure Peaks: Implications for Flicker Light-Induced Dilatation

Effects of high-intensity interval training on retinal vessel diameters and oxygen saturation in patients with hypertension: A cross-sectional and randomized controlled trial

INTRODUCTION

Arterial hypertension is a global healthcare burden that affects macrovascular and microvascular structure and function and can promote vascular end-organ damage. This study aimed 1) to evaluate differences in microvascular health between normotensive individuals and patients with arterial hypertension and 2) to assess the effects of short-term high-intensity interval training (HIIT) on microvascular health in the subgroup with arterial hypertension as add-on treatment to antihypertensive medication.

METHODS

In the cross-sectional part, central retinal arteriolar (CRAE) and venular diameter equivalent (CRVE), arteriolar-to-venular diameter ratio (AVR), and retinal oxygen saturation (O2-saturation) were investigated in 19 normotensive healthy controls (mean age 56 ± 7 years) and 41 patients with arterial hypertension (mean age 59 ± 7 years). In the subsequent randomized controlled trial (RCT), patients with arterial hypertension were randomized to an intervention group (HIIT 3×/week) or a control group that received standard physical activity recommendations after baseline assessment. Assessments of retinal vessel biomarkers and patients` characteristics were repeated after the intervention period of 8 weeks.

RESULTS

In the cross-sectional part, individuals with normal blood pressure (BP) showed lower body mass index (BMI), body fat, 24 h systolic and diastolic BP, higher peak oxygen uptake, wider CRAE (174 ± 17 μm vs. 161 ± 17 μm, p = 0.009), and higher AVR (0.84 ± 0.05 vs. 0.79 ± 0.05, p = 0.003) compared to patients with hypertension. In the RCT, patients with arterial hypertension showed reduced BMI and fasting glucose levels after HIIT and control condition. In addition, the intervention group reduced body fat percentage (27.0 ± 5.5 vs. 25.8 ± 6.1, p = 0.023) and increased peak oxygen uptake (33.3 ± 5.7 vs. 36.7 ± 5.1, p < 0.001). No changes in BP were found in either group. The intervention group showed narrower CRVE (β -4.8 [95 % CI, -8.85, -0.81] p = 0.020) and higher AVR (0.03 [0.01, 0.04] p < 0.001) after eight weeks of HIIT compared to the control group. No statistically significant changes in retinal O2-saturation were found in either group.

CONCLUSION

Short-term HIIT proved to be an effective treatment to ameliorate hypertension-induced retinal microvascular abnormalities in patients with hypertension. Retinal vessel diameters may prove to be a sensitive biomarker to quantify treatment efficacy at the microvascular level, at the earliest possible stage in patients with hypertension.

Retinal vessel diameters and function in cardiovascular risk and disease

In the last two decades evidence has gradually accumulated suggesting that the eye may be a unique window for cardiovascular risk stratification based on the assessment of subclinical damage of retinal microvascular structure and function. This can be facilitated by non-invasive analysis of static retinal vessel diameters and dynamic recording of flicker light-induced and endothelial function-related dilation of both retinal arterioles and venules. Recent new findings have made retinal microvascular biomarkers strong candidates for clinical implementation as reliable risk predictors. Beyond a review of the current evidence and state of research, the article aims to discuss the methodological benefits and pitfalls and to identify research gaps and future directions. Above all, the potential use for screening and treatment monitoring of cardiovascular disease risk are highlighted. The article provides fundamental comprehension of retinal vessel imaging by explaining anatomical and physiological essentials of the retinal microcirculation leading to a detailed description of the methodological approach. This allows for better understanding of the underlying retinal microvascular pathology associated with the prevalence and development of cardiovascular disease. A body of new evidence is presented on the clinical validity and predictive value of retinal vessel diameters and function for incidence cardiovascular disease and outcome. Findings in children indicate the potential for utility in childhood cardiovascular disease prevention, and the efficacy of exercise interventions highlight the treatment sensitivity of retinal microvascular biomarkers. Finally, coming from the availability of normative data, solutions for diagnostic challenges are discussed and conceptual steps towards clinical implementation are put into perspective.

Hypertension and retinal microvascular dysfunction (HyperVasc): protocol of a randomised controlled exercise trial in patients with hypertension

INTRODUCTION

Hypertension is a global healthcare burden that affects the structure and function of the macrocirculation and microcirculation and induces disease-specific end-organ damage. Vascular biomarkers are essential to timely diagnose this end-organ damage to improve cardiovascular (CV) risk stratification and medical decision making. Exercise therapy is an effective means to improve vascular health and reduce overall CV risk. However, it is still not clear whether high-intensity interval training (HIIT) is recommendable for patients with hypertension to reduce blood pressure, increase cardiorespiratory fitness and ameliorate vascular health.

METHODS AND ANALYSIS

The 'Hypertension and retinal microvascular dysfunction' trial will investigate macrovascular and microvascular impairments in hypertensive patients compared with healthy controls to investigate hypertension-induced end-organ damage by using gold-standard methods as well as newly developed unique retinal microvascular biomarkers. In addition, this trial will investigate the reversibility of retinal end-organ damage by assessing the effects of an 8-week supervised and walking based HIIT on blood pressure, cardiorespiratory fitness as well as macrovascular and microvascular health, compared with a control group following standard physical activity recommendations. Primary outcome will be the arteriolar-to-venular diameter ratio. Secondary outcomes will be arteriolar and venular diameters as well as the flicker-light-induced dilation. Further outcomes will be other retinal microvascular biomarkers, flow-mediated dilation of the brachial artery as well as blood pressure, cardiorespiratory fitness, microalbuminuria, hypertensive retinopathy and classical CV risk markers. Analysis of variance and analysis of covariance will be used to investigate group differences between healthy controls and hypertensive patients and training effects in hypertensive patients, respectively.

ETHICS AND DISSEMINATION

The Ethics Committee of Northwestern and Central Switzerland approved this study (EKNZ-2021-00086). All participants will give informed consent.

TRIAL REGISTRATION NUMBER

NCT04763005.

Normative data and standard operating procedures for static and dynamic retinal vessel analysis as biomarker for cardiovascular risk

Retinal vessel phenotype is predictive for cardiovascular outcome. This cross-sectional population-based study aimed to quantify normative data and standard operating procedures for static and dynamic retinal vessel analysis. We analysed central retinal arteriolar (CRAE) and venular (CRVE) diameter equivalents, as well as retinal endothelial function, measured by flicker light-induced maximal arteriolar (aFID) and venular (vFID) dilatation. Measurements were performed in 277 healthy individuals aged 20 to 82 years of the COmPLETE study. The mean range from the youngest compared to the oldest decade was 196 ± 13 to 166 ± 17 µm for CRAE, 220 ± 15 to 199 ± 16 µm for CRVE, 3.74 ± 2.17 to 3.79 ± 2.43% for aFID and 4.64 ± 1.85 to 3.86 ± 1.56% for vFID. Lower CRAE [estimate (95% CI): - 0.52 (- 0.61 to - 0.43)], CRVE [- 0.33 (- 0.43 to - 0.24)] and vFID [- 0.01 (- 0.26 to - 0.00)], but not aFID, were significantly associated with older age. Interestingly, higher blood pressure was associated with narrower CRAE [- 0.82 (- 1.00 to - 0.63)] but higher aFID [0.05 (0.03 to 0.07)]. Likewise, narrower CRAE were associated with a higher predicted aFID [- 0.02 (- 0.37 to - 0.01)]. We recommend use of defined standardized operating procedures and cardiovascular risk stratification based on normative data to allow for clinical implementation of retinal vessel analysis in a personalized medicine approach.