Diabetic oxygen-hemoglobin equilibrium curves evaluated by nonlinear regression of the Hill equation

Two-dimensional mathematical modelling of retinal oxygen transport and recommending treatment options

This paper presents a novel two-dimensional (2D) computational modeling of the retinal oxygen delivery, transport, and consumption analysis. The 2D modeling allows the division of the retina into four layers to address different flow profiles. The retina domain was meshed using the ICEM CFD mesher, while the ANSYS Fluent was used to calculate the transport phenomena for the four different layers. Clinical cases such as diabetes and sickle cell anaemia denoting the effects of decreasing retinal blood flow and hemoglobin's oxygen affinity were investigated. The simulation results showed that for a healthy retina in light and dark conditions, the outer retina is in danger of hypoxia at thickness >197.56μm. However, the treatment of severe ischaemia using extreme hyperoxia seems beneficial for retinal thickness >197.56μm but harmful for thickness <122.75μm. The reduction of hemoglobin's oxygen affinity at low blood flow regimes could not improve the retina's oxygen levels. The study supports the oxygen toxicity hypothesis that hypoxia causes retina degeneration and estimates the retinal thickness and lighting conditions (dark or light) this may occur.

Influence of oxygen on wound healing dynamics in healing-impaired diabetic mice

A previous experiment using an in vivo mouse model has proved that hypoxia increased angiogenesis during wound healing. It was hypothesised that one of the mechanisms for wound healing impairment in diabetes includes insufficient angiogenic ability in response to hypoxia. The current study aims to investigate the influence of hypoxia on wound healing in diabetic mice. Oxygen-impermeable (hypoxic group) and -permeable membranes (normoxic group) were used to control topical oxygen tension. Membranes were applied to symmetrical excisional wounds on diabetic mice. Wound area, granulated tissue thickness, and vascular density were analyzed. As results, a decrease in wound size on day 7 was observed in the normoxic group (20.7 ± 3.64%) compared with the hypoxic group (34.1 ± 4.98%). The normoxic group also showed significantly thicker granulated tissue than the hypoxic group (225.7 ± 54.7 vs 128.7 ± 42.4 µm). There was no significant difference in mean vascular density between normoxic and hypoxic groups (0.046 ± 0.022 vs 0.038 ± 0.017 mm(2)/mm(2), p = 0.80). Contrary to healthy mice, diabetic mice have shown no enhancement of angiogenesis in hypoxic condition. The findings illustrate that neovascularisation in response to hypoxia is diminished in diabetic wounds.

Retinal oxygen tension in diabetic dogs following insulin infusion

We measured preretinal oxygen tensions using a microelectrode in dogs made diabetic with alloxan. The intravenous administration of insulin did not affect preretinal oxygen tension over the two hours it could be continuously accurately measured. Furthermore, the oxygen-hemoglobin equilibrium curves measured before and two hours after insulin administration did not change.