Older individuals experience cardiovascular dysfunction during extended bedridden hospital or care home stays. Bed rest is also used as a model to simulate accelerated vascular deconditioning occurring during spaceflight. This study investigates changes in retinal microcirculation during a ten-day bed rest protocol. Ten healthy young males (22.9 ± 4.7 years; body mass index: 23.6 ± 2.5 kg·m-2) participated in a strictly controlled repeated-measures bed rest study lasting ten days. High-resolution images were obtained using a hand-held fundus camera at baseline, daily during the 10 days of bed rest, and 1 day after re-ambulation. Retinal vessel analysis was performed using a semi-automated software system to obtain metrics for retinal arteriolar and venular diameters, central retinal artery equivalent and central retinal vein equivalent, respectively. Data analysis employed a mixed linear model. At the end of the bed rest period, a significant decrease in retinal venular diameter was observed, indicated by a significantly lower central retinal vein equivalent (from 226.1 μm, CI 8.90, to 211.4 μm, CI 8.28, p = .026), while no significant changes in central retinal artery equivalent were noted. Prolonged bed rest confinement resulted in a significant (up to 6.5%) reduction in retinal venular diameter. These findings suggest that the changes in retinal venular diameter during bedrest may be attributed to plasma volume losses and reflect overall (cardio)-vascular deconditioning.

• MeSH
• Retinal Artery * diagnostic imaging   MeSH
• Fluorescein Angiography MeSH
• Bed Rest adverse effects   MeSH
• Humans MeSH
• Retinal Vessels diagnostic imaging   MeSH
• Retinal Vein * diagnostic imaging   MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

PURPOSE: The aim of the study was to obtain the values of oxygen saturation in retinal vessels and ophthalmic blood flow parameters in a healthy Caucasian population and assess whether the oximetry parameters are affected by the flow rate or the vascular resistance. METHODS: The spectrophotometric retinal oximetry and colour Doppler imaging (CDI) of retinal vessels were successfully performed with 52 healthy subjects (average age 29.7 ± 5.6 years). The retinal oximeter simultaneously measures the wavelength difference of haemoglobin oxygen saturation in retinal arterioles and venules. The arteriolar and venular saturation in both eyes was measured. The peak systolic (PSV) end diastolic (EDV) velocities, resistive (RI) and pulsatility (PI) indices were obtained for both eyes using CDI in the ophthalmic artery. A paired t-test and two sample t-tests were used for statistical analyses. The correlation was assessed using the Pearson coefficient correlation. RESULTS: The mean oxygen saturation level was 96.9 ± 3.0% for the retinal arterioles and 65.0 ± 5.1% for the retinal venules. The A-V difference was 31.8 ± 4.6%. The mean of the measured haemodynamic parameters was PSV 46.6 ± 9.4 cm/s, EDV 12.0 ± 3.5 cm/s, PI 1.68 ± 0.38 and RI 0.74 ± 0.05. No significant difference in oxygen saturation and haemodynamic parameters was found between the left and the right eyes or the dominant and non-dominant eye. The oximetry and ultrasound values were sex independent. The Pearson correlation coefficient demonstrated a significant yet weak negative correlation between A-V difference and RI (r = -0.321, p = 0.020). CONCLUSIONS: A negative correlation between A-V difference and resistance index was observed, suggesting that reduced oxygen consumption may reflect the increased vascular tone of the ophthalmic vessels, which is likely determined by autoregulatory mechanisms.

• MeSH
• Retinal Artery * diagnostic imaging   physiology   MeSH
• Ophthalmic Artery * MeSH
• Adult MeSH
• Hemodynamics MeSH
• Hemoglobins MeSH
• Oxygen MeSH
• Humans MeSH
• Young Adult MeSH
• Oximetry methods   MeSH
• Retina MeSH
• Blood Flow Velocity MeSH
• Oxygen Saturation MeSH
• Healthy Volunteers MeSH
• Check Tag
• Adult MeSH
• Humans MeSH
• Young Adult MeSH
• Publication type
• Journal Article MeSH

• MeSH
• Retinal Artery diagnostic imaging   metabolism   physiopathology   MeSH
• Adult MeSH
• Humans MeSH
• Statistics, Nonparametric MeSH
• Tomography, Optical Coherence methods   MeSH
• Oximetry methods   instrumentation   MeSH
• Pilot Projects MeSH
• Regional Blood Flow MeSH
• Retina diagnostic imaging   metabolism   physiopathology   MeSH
• Retinal Vessels metabolism   ultrasonography   MeSH
• Multiple Sclerosis diagnostic imaging   MeSH
• Ultrasonography, Doppler methods   instrumentation   MeSH
• Optic Neuritis * diagnostic imaging   metabolism   physiopathology   MeSH
• Check Tag
• Adult MeSH
• Humans MeSH
• Male MeSH
• Female MeSH
• Publication type
• Research Support, Non-U.S. Gov't MeSH