R.M. Dunn

Valvular Density Alone Cannot Account for Sites of Chronic Venous Insufficiency and Ulceration in the Lower Extremity

Objective: Class 6 chronic venous stasis is associated with abnormal venous hemodynamics and ulceration. Ulcers primarily occur over bones and tendon prominences but very rarely over muscular compartments. We hypothesized that the anatomical distribution of venous stasis ulcers in the lower extremity is related to a lower density of venous valves.

The microvenous valvular anatomy of the human dorsal thoracic fascia.

&NA; The use of free scapular fasciocutaneous flaps for reconstruction of recalcitrant grade 6 venous stasis ulcers has shown excellent early success rates. Venous refilling times measured postoperatively over the flaps by photoplethysmography have noted improvements to normal levels. Preliminary anatomic studies have demonstrated valves in the circumflex scapular veins of flaps used in reconstruction. The purpose of this study was to investigate and document the number, morphology, size, and location of valves in the human dorsal thoracic fascia. Ten scapular flaps were obtained from unembalmed cadavers and injected with methyl methacrylate. Each flap cast was divided into four parts: proximal, right and left, and distal, right and left. We reduced the size of specimens (the largest being 24 × 11 mm) and studied them in a scanning electron microscope. We identified all valves, estimated the diameter of the corresponding vein, calculated the depth of the valvular sinus, and related it to the corresponding venous size. Light microscopy and transmission electron microscopy were used as assisting tools applied to glutaraldehyde‐fixed specimens. Analysis of injected specimens showed that valves were most abundant in veins with a luminal diameter of 30 to 120 μm (59.3 percent of 905 valves). The depth of valves became larger with increasing venous diameter. The sizes of valve sinuses were not different for individual valves. Except for veins larger than 1000 μm in diameter, there was no significant difference between the number of valves in different parts of an individual flap, nor were there significant differences between the valve numbers in different flaps. Most valves were bicuspid; only in the vein category of 30 to 120 μm were unicuspid valves encountered. Valves sometimes were located in series in a short segment of a vein; occasionally, they were found at the merging site of two veins. Transmission electron microscopy showed that valve leaflets had collagen fibers that ascended toward the tip of the leaflet and occasionally were accompanied by elastic fibers. Myofibroblasts were regularly present in the valve leaflets. These data show that fasciocutaneous flaps from the scapular region have numerous valves (90 valves on average in each flap) in the venous microcirculation. The microvenous valves in the dorsal thoracic fascia appear to be structurally similar to valves in larger veins. These valves may play a role in the improved hemodynamics and promising clinical outcome of patients with chronic venous insufficiency who have undergone free scapular flap reconstruction.

Morphological and clinical aspects of scapular fasciocutaneous free flap transfer for treatment of venous insufficiency in the lower extremity

We have recently shown that free scapular fasciocutaneous flaps transferred to the lower extremities of patients with chronic venous insufficiency and cutaneous ulcers have resulted in improvement in venous refilling times measured by photoplethysmography in the flap areas and that recurrent ulceration does not recur for up to 7 years. We hypothesized that the transferred flaps contained valves in their microvascular bed, which facilitated venous return, and using scanning electron microscopy of vascular corrosion casts and light and transmission electron microscopy of tissue sections prepared from human dorsal thoracic fascia, we showed that valves were most abundant in veins with a luminal diameter of 30–120 μm (59.3% of 905 valves). The depth of these valves increased with venous diameter, but the size of valve sinuses was not different for individual valves. Except for veins >1,000 μm in diameter, there was no significant difference in the number of valves in different parts of an individual flap or between different flaps. Most valves were bicuspid; only in the vein Category 30–120 μm were unicuspid valves encountered. Valves were sometimes located in series in a short segment of a vein; occasionally they were found at the merging of two veins. Transmission electron microscopy showed that valve leaflets had collagen fibers that ascended toward the tip of the leaflet and were occasionally accompanied by elastic fibers. Myofibroblasts were regularly present in the valve leaflets. The present report reviews and updates these anatomic data about the human scapular region, focusing on venous valvular microstructure, and suggests that the high number of smaller‐size valves contributes to improved hemodynamic of the leg and thus the clinical success of free scapular flaps used to treat cutaneous ulcerations in the lower extremity. Clin. Anat. 11:38–46, 1998.

Development of a minimally invasive microvascular ischemia monitor: drift reduction results

The objective of the authors research is to develop a pH based, ischemia measuring system which will be used for postoperative monitoring of transplanted tissue over a four day period. Currently, most pH monitors are difficult for hospital personnel to operate and lack sufficient long-term stability, resulting in false readings of tissue pH (drifts >/spl plusmn/0.48 pH units per 100 hours). An electronic multi-channel pH measuring device which interfaces with a laptop computer was constructed. The system uses an algorithm to compensate for inherent pH measurement instabilities. This is accomplished using separate pH reference electrode channels from which multiple measurements are averaged. The authors system provides tissue pH measurements that are sufficiently stable during 96 hour postoperative monitoring periods.

Design of a screw-plate system to minimize loosening in sternal fixation

The use of screw-plate fixation devices after open heart sternotomy surgeries are becoming more prevalent with studies showing the devices mechanical superiority. However, there is no current device that is capable of supplying both a compressive and locking force needed to optimally fixate the plate to the bone. This can lead to screw loosening and wobbling within the plate, potentially compromising the integrity of the overall system. The goal of the design is to create an “anti-wobble” screw-plate sternal fixation device capable of reducing sternal displacement post sternotomy plate fixation more efficiently than current market devices. The device will supply “rigid sternal fixation” in the stabilization of two full hemi-sterna, and will allow for minimal screw loosening and back out. The device contains both a locking and compressive mechanism, enhancing the bone-plate interface. Validation testing on the device is currently being completed using an Instron Electroplus E-1000 uniaxial testing device to conduct low loading cyclic testing on human cadaveric sterna.

Development of a pH based tissue ischemia monitor: hardware realization

The objective of the authors research is to develop a pH measuring system which will be used for accurate postoperative monitoring of transplanted tissue. Currently, most pH monitors that are used for this purpose are difficult to operate for hospital personnel and do not possess sufficient long-term stability, resulting in false readings of tissue pH. To resolve these problems, an electronic multichannel pH measuring device, that interfaces with a laptop computer, was constructed. The system makes use of an algorithm to compensate for instabilities that are inherent to pH measurements. This is accomplished using separate pH reference electrode channels from which multiple measurements are taken and averaged. Preliminary tests show that this system accurately measures pH and remains stable during 96 hour test periods.

Muscle tissue ischemia monitoring using impedance spectroscopy: preliminary animal studies

Tissue ischemia detection can be performed using several methods, however, neither of them is writable for non-invasive, long term, and continuous tissue ischemia monitoring. Tissue impedance measurement presents a simple method for monitoring certain tissue characteristics and it can be used for ischemia monitoring because ischemia of tissues causes changes in tissue impedance. The overall goal of this research is to develop a muscle tissue ischemia monitoring system, based on tissue impedance measurements at various frequencies (impedance spectroscopy). For this purpose, an instrument for complex tissue impedance measurements, over a wide frequency range (10 Hz-1 MHz) was built and tested. The acquisition system uses digital demodulation principles to improve performance, several in-vivo animal experiments were done to obtain data on impedance of healthy and ischemic muscle tissue. The collected data provided the authors with a new knowledge on tissue ischemia-impedance relationship. Also, specific tissue impedance behavior and artifacts were observed. Results indicate that impedance spectroscopy can be used for qualitative ischemia monitoring.

Development of a pH based tissue ischemia monitor: preliminary clinical results

The objective of the authors research is to develop a pH measuring system which will be used for accurate postoperative monitoring of transplanted tissue. Currently, most pH monitors that are used for this purpose are difficult to operate by hospital personnel and do not possess sufficient long-term stability, resulting in false readings of tissue pH. To resolve these problems, an electronic multi-channel pH measuring device, that interfaces with a laptop computer, was constructed. The system makes use of an algorithm to compensate for instabilities that are inherent to pH measurements. This is accomplished using separate pH reference electrode channels from which multiple measurements are taken and averaged. Preliminary tests show that this system accurately measures tissue pH and remains stable during the 96 hour postoperative monitoring period.

Determination of a relationship between bacteria levels and tissue pH in wounds: animal studies

The objective of this research is to develop a methodology and means for achieving instantaneous and objective estimations of wound properties. The level of bacterial contamination in wounds is a well known indicator of the condition of a wound; however, clinicians do not currently have the methodology or instrumentation to quantitatively measure the amount of bacteria in the wound without significant time delays. Tissue pH levels have been found to correlate to a wounds properties, including tissue perfusion and bacteria levels. A custom-made electronic pH monitor which interfaces to a laptop computer is used for measurement of tissue pH. A micro-pH combination electrode along with special software algorithms are utilized to obtain accurate measurements. The main hypothesis of the project is that a correlation exists between bacteria and tissue pH levels in chronic wounds. A rat model was designed for animal testing. Preliminary results support the principal hypothesis.

Management of Venous Ulceration: Excision, Skin Grafting and Microsurgical Flaps

A regimen of leg elevation, compression bandaging and local wound care is successful in healing the majority of venous ulcers. Failure of a venous ulcer to heal with appropriate wound care or recurrence despite these measures leaves the physician with a challenge in which multiple factors must be addressed in order to achieve long-term wound closure. Most surgical interventions employed to address refractory venous ulceration have been directed at correcting underlying venous hypertension with the assumption that this would lead to resolution of the ulcer. However, even if successful control of venous hypertension in the extremity is achieved, a chronically scarred wound with compromised healing capacity may remain and require surgical reconstruction. Thus, the approach to reconstruction of the tissue defect associated with chronic venous ulceration is the subject of this chapter.