Soft Tissue Perfusion Research Articles

The effect of high and low pressure pulsatile lavage on soft tissue and cortical blood flow: a canine segmental humerus fracture model

To determine the effect of high pressure pulsatile lavage (HPPL) and low pressure pulsatile lavage (LPPL) on cortical and soft tissue blood flow in a canine humerus segmental fracture model. Midshaft humeral osteotomies to create a 2-cm segment of diaphyseal bone were performed on bilateral canine humeri. Each osteotomy site was irrigated using either high pressure (n = 6) or low pressure (n = 5) pulsatile lavage prior to stabilization with a 5-mm steinman pin. Perfusion of cortical bone, periosteum, and biceps muscle was measured using Laser Doppler Flowmetry during four intraoperative intervals: pre-osteotomy, post-osteotomy, post-lavage, and post-nailing. Following osteotomy, a significant drop occurred in cortical perfusion (HPPL P = 0.049, LPPL P = 0.021) and in periosteal flow (HPPL P = 0.019, LPPL P = 0.012). Following irrigation there was no significant decrease in blood flow in either group for muscle (HPPL P = 0.249, LPPL P = 0.41), periosteum (HPPL P = 0.381, LPPL P = 0.402), or cortex (HPPL P = 0.398, LPPL P = 0.352) measurements. There was no significant difference between irrigation groups in post-lavage perfusion values for muscle (P = 0.326), periosteum (P = 0.452), and cortex (P = 0.464). Cortical perfusion decreased significantly post-nailing (HPPL P = 0.027, LPPL P = 0.047). Measurements did not differ significantly between groups at any other time interval. Although previous work has demonstrated an association between HPPL and detrimental structural changes in bone, this study demonstrates that HPPL does not adversely affect cortical or soft tissue blood flow acutely. Further, LPPL offers no acute benefit to cortical or soft tissue perfusion.

Increased Ischemic Tissue Survival through Targeting Thrombospondin‐1

Tissue survival requires sustained perfusion. Ischemia secondary to surgery or trauma can limit soft tissue survival, resulting in tissue necrosis and delayed wound healing. Therapeutic interventions to increase soft tissue perfusion have to date met with limited success. The bioactive gas nitric oxide (NO), which is produced by vascular endothelial cells constitutively, can rapidly dilate arteries and increase tissue perfusion. However, under ischemic conditions endogenous NO is insufficient to prevent tissue necrosis. We recently discovered that endogenous thrombospondin-1 (TSP1) is a potent antagonist of NO-induced vasodilation. TSP1 released by activated platelets and produced by vascular cells potently blocks NO driven relaxation of vascular smooth muscle cells at the level of soluble guanylate cyclase via its receptor CD47. In the absence of TSP1 or CD47, survival of ischemic injury is dramatically increased. We are investigating therapeutic approaches to target TSP1 or CD47 to increase wound healing under conditions of ischemia.

Pressure–time cell death threshold for albino rat skeletal muscles as related to pressure sore biomechanics

Deep pressure sores (DPS) are associated with inadequate soft tissue perfusion and excessive tissue deformation over critical time durations, as well as with ischemia-reperfusion cycles and deficiency of the lymphatic system. Muscle tissue shows the lowest tolerance to pressure injuries, compared with more superficial tissues. In this communication, we present new histopathology data for muscle tissue of albino (Sprague–Dawley) rats exposed to pressures for 15 or 30 min. These data are superimposed with an extensive literature review of all previous histopathology reported for albino rat skeletal muscles subjected to pressure. The pooled data enabled a new mathematical characterization of the pressure–time threshold for cell death in striated muscle of rats, in the form of a sigmoid pressure–time relation, which extends the previous pressure–time relation to the shorter exposure periods. We found that for pressure exposures shorter than 1 h, the magnitude of pressure is the important factor for causing cell death and the exposure time has little or no effect: even relatively short exposures (15 min–1 h) to pressures greater than 32 kPa (240 mmHg) cause cell death in rat muscle tissue. For exposures of 2 h or over, again the magnitude of pressure is the important factor for causing cell death: pressures greater than 9 kPa (67 mmHg) applied for over 2 h consistently cause muscle cell death. For the intermediate exposures (between 1 and 2 h), the magnitude of cell-death-causing pressure strongly depends on the time of exposure, i.e., critical pressure levels drop from 32 to 9 kPa. The present sigmoidal pressure–time cell death threshold is useful for design of studies in albino rat models of DPS, and may also be helpful in numerical simulations of DPS development, where there is often a need to extrapolate from tissue pressures to biological damage.

Contrast-enhanced MR angiography and perfusion imaging of the hand.

The goal of this investigation was to develop a technique for producing high-resolution gadolinium-enhanced MR images of the hand that show three-dimensional angiographic anatomy and permit measurement of distal soft-tissue perfusion. High-resolution MR angiograms of the hand, as well as qualitative perfusion information, can be produced using a rapid sequential gadolinium-enhanced three-dimensional gradient-echo technique.

On the relationship between power mode and pressure amplitude decorrelation

Estimation of mean transit time, along with tissue blood volume, are important factors in determining soft tissue perfusion. Recently, power mode decorrelation techniques have been successfully used to estimate mean transit time of red blood cells or contrast material through a region-of-interest (ROI) both in laminar flow phantoms and in vivo. The previously described theory for power mode decorrelation derives from a phenomenological stochastic differential equation (Langevin equation) based on conservation of matter, relating the detected signal power to the measured rate of decorrelation. Given the experimental support for power mode decorrelation as a method to estimate mean transit time, it becomes important to determine the relationship between the phenomenological parameters that appear in the corresponding stochastic equation and system parameters, such as the transducer point response function. With this equation as a starting point, and using the fact that the pressure amplitude is a Gaussianly distributed random process, the following stochastic differential equation for the pressure amplitude p( t) is derived, a necessary first step in establishing the relationship between the measured decorrelation rate and system parameters ( i.e., point response function): dp(t) /dt=−(v/2+2ik·v)p(t)+f(t),(1) where v/2 represents the rate of decorrelation, 2 k· v is the Doppler shift for an insonating wave vector k and particle velocity v.f( t) is a stationary, white noise Gaussian random process. (E-mail: adlerr@hss.edu)

Effects of external thermal manipulation on laminar temperature and perfusion scintigraphy of the equine digit

Aims:To assess the effects of external thermal manipulation on the soft-tissue and vascular perfusion of the equine digit using nuclear scintigraphy and documented tissue temperatures. Methods: Six horses were used in a randomised crossover design. Each horse was treated with external heat (47°C) or external cold (4°C) applied to a digit for 30 minutes. The opposite front foot was untreated and used for control measurements. Nuclear scintigraphy was performed before, during, and after therapy to assess vascular and soft-tissue perfusion to the digit in response to therapy. Dorsal hoof wall laminar-tissue temperatures were recorded before, during, and after therapy using a thermistor. Results: Treatment with topical cold therapy significantly decreased soft-tissue perfusion of the digit to 80.5% of the pre-cooled values. Conversely, the application of external heat significantly increased soft-tissue perfusion of the digit 25.1% above the pre-heated values. Vascular perfusion showed similar, but not statistically significant trends. External cold application to the digit caused a significant mean decrease in laminar-tissue temperatures of 11.6°C during therapy, while external heat application to the digit caused a significant mean increase in laminar-tissue temperatures of 3.9°C. Conclusion: The external application of heat and cold to the normal equine foot could effectively alter soft-tissue perfusion and laminar-tissue temperatures within 30 minutes of treatment. The application of hot water and ice water to the digit was a safe, well-tolerated, and economical therapy. Clinical Relevance: Cooling the foot could decrease enzymatic reactions associated with laminitis, and warming could increase local perfusion when desired.

Vascular occlusion using focused ultrasound surgery for use in fetal medicine

Objective: Focused ultrasound surgery (FUS) is being developed clinically for the non-invasive treatment of soft tissue tumours of the prostate, bladder, liver, kidney, muscle and breast. In the work described in this paper, the application of FUS is extended to investigate the potential to induce vascular occlusion, with the aim of applying the technique to problems in fetal medicine and oncology. Methods: In this feasibility study the occlusion of femoral blood flow in vivo is demonstrated using an array of multiple single exposures of 1.7 MHz focused ultrasound. These were placed in two rows of four lesions at a focal depth of 5 mm. The 4660 W cm−2 (free field spatial peak intensity) 2-s exposures were placed 2 mm apart. Vascular patency was assessed using a Siemens Vision (1.5T) magnetic resonance (MR) imaging scanner with an extremity coil, and intravenous gadolinium contrast agent. FLASH and FISP MR sequences were used to obtain full 3D data sets providing information on soft tissue damage and perfusion. Results and conclusion: Total vascular occlusion was achieved in four of nine cases and significant vascular disruption in five of nine cases. Refinement of the FUS technique and long-term studies are now indicated prior to initial clinical application in fetal medicine.

The relative importance of intramedullary, intracortical, and extraosseous soft-tissue blood flow to the repair of devascularized canine tibial cortex.

Previous studies have not quantified the relative contributions of intracortical and extracortical perfusion to cortical porosity and new bone formation. The current study was performed to determine the relative importance of intramedullary, intracortical, and extraosseous soft-tissue blood flow and type of tissue to the repair of devascularized canine tibial cortex. A 2.5-cm segment of tibia between two standardized osteotomies was devascularized. The segment was replaced anatomically and stabilized with a plate. The animals were divided randomly into two groups: skin coverage (N = 8) and muscle coverage (N = 8). Thirty-one days postoperatively, cerium141 microspheres were injected, prior to sacrifice, to measure blood flow. Extraosseous soft-tissue perfusion was the same in the skin coverage and muscle flap coverage groups. There was no relationship between intramedullary or extraosseous soft-tissue flow and depth of new bone formation and cortical porosity. Intracortical blood flow was directly related to depth of new bone formation (p = 0.0006) and cortical porosity (outer cortex, p = 0.001; inner cortex, p = 0.0001). These findings indicate that the cortical repair process is linked to the restoration of perfusion and that muscle coverage, rather than the quantity of blood flow, determines the extent of cortical repair.

Power Doppler sonography in the assessment of musculoskeletal fluid collections.

Power Doppler sonography is a relatively new technique that has been shown to depict hyperemia associated with musculoskeletal inflammatory disease. We performed this study to evaluate the ability of power Doppler sonography to differentiate musculoskeletal fluid collections of varying etiologies. Gray-scale and power Doppler sonography were performed on 39 patients with joint effusions or appendicular fluid collections. Blood flow (hyperemia) in the soft tissues adjacent to the fluid collections was subjectively analyzed and graded on a scale of 1 to 4 (1, normal flow; 2-4, increasing degrees of hyperemia). All fluid collections were aspirated within 24 hr of the sonographic examination. We found 31 joint effusions and 12 periarticular collections with appropriate imaging and pathologic correlation. Adjacent to 36 effusions and fluid collections, we saw moderate or marked hyperemia. Thirty-five of the 36 had an inflammatory or neoplastic cause, including 15 infected collections. One fluid collection had a degenerative etiology (subdeltoid bursitis secondary to supraspinatus tendon tear). Adjacent to the seven remaining effusions and fluid collections, we saw normal or mildly increased hyperemia; none of these collections had an inflammatory etiology. Power Doppler sonography helps distinguish inflammatory and infectious musculoskeletal fluid collections from those that are noninflammatory, and it may help guide the decision to perform diagnostic aspiration. Power Doppler sonography does not reliably differentiate between inflammatory collections of infectious and noninfectious origin because collections of either origin may significantly increase adjacent soft-tissue perfusion.

Experiences with free and pedicled muscle tissue graft in the treatment of chronic post-traumatic osteomyelitis

A relapse-free condition and/or healing of chronic posttraumatic osteomyelitis is obtained by 1. radical excision of the infected tissue, 2. absolute mechanical immobility in the area of the fracture, 3. optimized blood supply of soft tissues. The perfusion of soft tissues around the osteomyelitic focus is often disturbed due to large scar fields caused by injuries or repeated surgical interventions. It can be improved by means of plastic surgery with local muscle flaps or by transplantation of a free muscle flap with microsurgical connection of vessels. All muscles in which the axial vessels are predominant can be used for plastic surgery with local muscle flaps. In the leg, these are above all the musculi gastrocnemii and the musculus soleus. After having applied this method in six patients, we noticed that infection control could be achieved by this procedure after six to twelve months. When a free muscle flap (musculus latissimus dorsi) is used, the local soft tissue perfusion can be considerably ameliorated by these rather large muscle flaps, irrespective of the local blood flow after epicentric microsurgical connection of vessels. This is the precondition for the healing of the infection. Based on our own results, we discuss the difficulty to indicate exactly the duration and extent of the increased perfusion of transplanted muscles. As is shown by the clinical results available up to now, these two procedures make possible a considerably reduced recurrence rate in chronic posttraumatic osteomyelitis.

Surface quantification of injected fluorescein as a predictor of flap viability.

In a laboratory model, quantitative skin-surface fluorescence has been used to reliably measure skin perfusion in ischemic random flaps and to predict viability. The method is reproducible and allows investigators to sequentially monitor soft-tissue perfusion using a fluorescent indicator. It is superior to the conventional fluorescein test (Wood's lamp method), which allows only a single subjective assessment within a 24-hour period.