A new method for the assessment of tissue hemoglobin oxygenation in patients with chronic venous insufficiency

Venous overload choroidopathy: A hypothetical framework for central serous chorioretinopathy and allied disorders

In central serous chorioretinopathy (CSC), the macula is detached because of fluid leakage at the level of the retinal pigment epithelium. The fluid appears to originate from choroidal vascular hyperpermeability, but the etiology for the fluid is controversial. The choroidal vascular findings as elucidated by recent optical coherence tomography (OCT) and wide-field indocyanine green (ICG) angiographic evaluation show eyes with CSC have many of the same venous patterns that are found in eyes following occlusion of the vortex veins or carotid cavernous sinus fistulas (CCSF). The eyes show delayed choroidal filling, dilated veins, intervortex venous anastomoses, and choroidal vascular hyperpermeability. While patients with occlusion of the vortex veins or CCSF have extraocular abnormalities accounting for the venous outflow problems, eyes with CSC appear to have venous outflow abnormalities as an intrinsic phenomenon. Control of venous outflow from the eye involves a Starling resistor effect, which appears to be abnormal in CSC. Similar choroidal vascular abnormalities have been found in peripapillary pachychoroid syndrome. However, peripapillary pachychoroid syndrome has intervortex venous anastomoses located in the peripapillary region while in CSC these are seen to be located in the macular region. Spaceflight associated neuro-ocular syndrome appears to share many of the pathophysiologic problems of abnormal venous outflow from the choroid along with a host of associated abnormalities. These diseases vary according to their underlying etiologies but are linked by the venous decompensation in the choroid that leads to significant vision loss. Choroidal venous overload provides a unifying concept and theory for an improved understanding of the pathophysiology and classification of a group of diseases to a greater extent than previous proposals.

An investigation of skin perfusion in venous leg ulcer after exercise

INTRODUCTION

A venous leg ulcer (VLU) has a major impact on the quality of life and functional ability of individuals, but no single treatment is yet effective. This study investigates the changes induced by dorsiflexion exercise on skin perfusion in VLU patients to achieve a better understanding of venous ulcer pathophysiology.

METHODS

Seventy-eight venous leg ulcer patients were randomised into four groups. The non-exercise groups included a control group (n = 18) and a compression therapy group (n = 20) and the exercise groups included an exercise-only group (n = 20) and a compression and exercise group (n = 20). The exercise groups were expected to perform exercise for three months. Measurements included transcutaneous oximetry (tcPO₂) and laser Doppler flowmetry (LDF). Skin perfusion measurements for all groups were taken twice: at the beginning and end of the three-month period.

RESULTS

Initially, all participants showed a low level of tcPO₂. The exercise groups showed a significant increase after three months of exercise (p<0.001), the tcPO₂ level remained the same in the non-exercise groups. The LDF parameters decreased significantly (p<0.001) in the compression and exercise group and decreased to a lesser extent in the exercise-only group. There were no LDF changes in the non-exercise groups.

CONCLUSIONS

Perfusion measurements showed significant changes after three months of regular exercise. We conclude that exercise has a significant effect on tissue perfusion parameters in venous leg ulcer and this effect may play a role in understanding the pathophysiology of VLU.

Optical Measurement of Tissue Oxygen Saturation

Advances in opto-electronic systems have meant that optical spectroscopy can now be used for noninvasive measurements in tissue in patients. A number of techniques have evolved over the last 15 years that make use of the characteristic differences in the absorption spectrum of deoxygenated and oxygenated hemoglobin to measure oxygen saturation. This article summarizes, in particular, those techniques that may prove to be applicable to measurements relating to lower extremity wounds. A short introduction is given about existing electrode methods before describing applications of near infrared and visible wavelength spectroscopy to measurements in tissue. The advantages and limitations of these methods are discussed. An example of an area where tissue spectroscopy is now in routine clinical use for tissue healing viability assessment is presented.

A Review of Microvascular Measurements in Wound Healing

The microcirculatory evaluation in patients affected by arteriopathic or venous ulcers is usually carried out using laser Doppler flowmetry, transcutaneous oxygen (transcutaneous pressure of oxygen, TcPO2), and carbon dioxide (transcutaneous pressure of carbon dioxide, TcPCO2) measurements and capillaroscopy. These techniques provide significant pathophysiologic and prognostic information. TcPO2 and TcPCO2 diagnose and classify the extent of arterial disease in the leg ulcers caused by arterial disease; the prognostic value is recognized, though doubts about its prognostic potential exist in the case of leg ulcer. Laser Doppler flowmetry is able to identify the first functional impairment in the early stages of the arterial disease and in the complicated venous insufficiency. Capillaroscopy gives us morphological and quantitative parameters of the capillary bed that is damaged in arteriopathic and venous ulcers; nevertheless, it does not provide us with definite prognostic indexes. Combining the 3 methods may contribute to yield objective measures in the clinical management of lower extremity ulcers.

Techniques to assess tissue oxygenation in the clinical setting

The microcirculation plays an essential role in health and disease. Microvascular perfusion can be assessed directly using laser Doppler flowmetry and various imaging techniques or indirectly using regional capnometry and measurement of indicators of mismatch between oxygen delivery and oxygen consumption or indices of disturbed cellular oxygen utilization. Assessment of microvascular oxygen availability implies measurement of oxygen pressure or measurement of hemoglobin oxygen saturation. Microvascular function is assessed using other methods, including venous plethysmography. In this paper, I review current knowledge concerning assessment of the microcirculation with special emphasis on methods that could be used at the bedside.