Highly integrated catalytic burner with laser-additive manufactured manifolds

This paper describes a highly integrated catalytic burner for auxiliary power units based on PEM-fuel cells.

Flap perfusion after free musculocutaneous tissue transfer: the impact of postoperative complications

In a previous study, the authors found persistence of pedicle blood flow up to 10 years after uncomplicated free latissimus dorsi transfer. In this study, the impact of postoperative complications (hematoma, thrombosis, infection) and successful surgical revision was tested. Since 1982, more than 1200 free tissue transfers have been performed at the authors' institution (Hannover Medical School). Of these, the authors selected two groups of 30 patients each who had received a free latissimus dorsi transfer to the lower leg without microsurgical nerve coaptation for wound coverage. All patients included in this study were carefully selected for clinical homogeneity, with one difference: group I comprised patients who had no postoperative complications after free latissimus dorsi transfer. Group II included only patients with major postoperative complications after the procedure. All flaps in group II survived after successful surgical revision. The arteries, which nourished the lower leg, were visualized and documented by means of a duplex scanner in both groups. Three different time intervals were chosen for measurements of blood flow: 4 to 6 months (groups I.I and II.I), 4 to 6 years (groups I.II and II.II), and 8 to 10 years (groups I.III and II.III). Quantitative measurements of local flap perfusion in milliliters per minute per 100 g tissue were performed by means of the hydrogen clearance technique. In each patient, a total of nine measurements was performed in three phases: phase A, before closing the vascular pedicle by manual compression (n = 3); phase B, with a closed pedicle (n = 3); and phase C, after releasing the vascular pedicle from manual compression (n = 3). Each measurement took approximately 10 minutes. One hundred percent closure of each pedicle in phase B was confirmed by the duplex scanner. Furthermore, all patients were monitored both clinically and by means of the hydrogen clearance technique during phase B for adequate blood supply to the lower leg. Lower leg perfusion showed no statistical differences for phases A, B, and C in all groups of patients. In group I, no statistical differences in local flap perfusion were encountered for phases A and C. In phase B, however, a statistically significant (p < 0.01) complete extinction of local flap perfusion was registered in all patients of group I at the site of the flap's skin paddle. In group II, however, persistent flap perfusion was registered during phase B in up to 50 percent of cases in one subgroup (II.III). No statistically significant alterations of local blood flow were registered in the surrounding tissue of group II during phases A, B, and C. Patients with thrombosis of the venous anastomosis (n = 7) seemed to have the highest incidence of loss of autonomous blood supply through the vascular pedicle (5 out of 11 cases). No inconstant results were found during the repetitive measurements (n = 3) for each patient in each phase. After uncomplicated free tissue transfer, the flap's intact vascular pedicle seems to play an important role in permanent flap survival up to 10 years after the procedure. Postoperative complications after free tissue transfer with successful surgical revision, especially venous thrombosis of the vascular anastomosis, may lead to loss of vascular flap autonomy over time.

[Does tissue perfusion after free microvascular tissue transplantation remain autonomous?]

In a retrospective study, including 60 patients, after free latissimus dorsi transplantation (FLDT) to the lower leg, we found persistent pedicle blood flow up to ten years postoperatively. After uncomplicated FLDT, the pedicle supported the flap in all cases. After complicated FLDT (hematoma, thrombosis, infection) only 50% of all flaps after ten years were perfused by the vascular pedicle.

[Does tissue perfusion after free microvascular tissue transplantation stay autonomous?]

In a prospective study including 60 patients after free latissimus dorsi transfer (FLDT) to the lower leg, we found persistence of pedicle blood flow up to 10 years postoperatively. After uncomplicated FLDT the pedicle supported the flap in all cases, whereas after complicated FLDT (hematoma, thrombosis, infection) we found only 50% of all flaps autonomously perfused by the vascular pedicle.

Persistence of pedicle blood flow up to 10 years after free musculocutaneous tissue transfer

The hypothesis of whether or not flap perfusion remains persistent through its vascular pedicle up to 10 years after free tissue transfer was tested. Since 1982, more than 1,000 free tissue transfers have been performed at this institution. Of these, 40 patients were selected with comparable posttraumatic soft-tissue defects of the lower leg and surgical repair by a latissimus dorsi myocutaneous free flap. All patients had a postoperative course free of complications. Measurements of flap perfusion were started in groups 1 through 4 (each 10 patients) 3 to 5 weeks, 5 to 7 months, 4 to 6 years, and 8 to 10 years after free tissue transfer, respectively. Quantitative measurements of local flap perfusion were performed by means of the hydrogen clearance technique (Ameda, Switzerland) at definite sites intracutaneously and subcutaneously within the flap's skin paddle as well as in the adjacent intracutaneous and subcutaneous skin of the surrounding soft tissue. Simultaneously, the vascular pedicle of the flap was visualized by a duplex scanner (Toshiba, Japan). In each group nine measurements were performed before (phase A), during (phase B), and after closing the pedicle (phase C) by manual compression. Each measurement took about 10 minutes. Statistical evaluation of the obtained values was achieved by the Mann-Whitney U test and the Wilcoxon signed rank test. Local flap perfusion showed no statistical differences for phase A and C in all four groups of patients. In phase B, however, a statistically highly significant (p < 0.01) absence of local flap perfusion was registered in all four groups at the site of the flap's skin paddle. No statistically significant alterations of intracutaneous and subcutaneous blood flow was found in the surrounding soft tissue. In our clinical-experimental setting, flap perfusion persisted by means of its vascular pedicle even 10 years after free tissue transfer. Our findings support the importance of an intact vascular pedicle for permanent flap survival after free tissue transfer.

Measurements of tissue blood flow by the hydrogen clearance technique (HCT): a comparative study including laser Doppler flowmetry (LDF) and the Erlangen micro-lightguide spectrophotometer (EMPHO)

The purpose of this study was to compare the hydrogen clearance technique (HCT) with two different, well-established techniques, i.e., the laser Doppler flowmetry (LDF) and the Erlangen micro-lightguide spectrophotometer (EMPHO), for tissue blood flow measurements in an experimental setting. For the animal experiments, we chose a rat model for arterial and venous flap thrombosis, using the epigastric groin flap. Forty male dark Aguty rats were included in the study. The animals were divided into eight groups, each with a different vascular thrombotic model. HCT was used to collect 1,467 measurements, and 2,934 graphs were recorded; 27 measurements (54 graphs) had to be discarded due to faulty electrode placements and electronic noise. In 19 of the 27 discarded measurements the cause of failure was moving of the awaking animal with disruption of the decay signal. The LDF and EMPHO measurements were performed continuously during each measuring phase. Simple and multiple linear regression and paired t-tests were used to compare the three techniques. The reproducibility of registered blood flow values in phases 1, 3, 6 and 7 varied between 7.8% and 13.6% which is in about the same range as LDF and EMPHO. We could not find a significant difference between the three techniques in this regard. The correlation coefficient for HCT and LDF was r = 0.89. For HCT and EMPHO we found r = 0.67. Sensitivity and specificity values for HCT were both 1.0 in detecting arterial and venous flap thrombosis; for LDF we found values of 0.89 and 0.92, respectively. Sensitivity and specificity values for EMPHO were 0.92 and 0.95, respectively. After careful evaluation of three different techniques (HCT, LDF, and EMPHO) for measurements of local tissue blood flow we came to the conclusion that HCT must be favoured as a reliable tool for quantitative measurement of local tissue blood flow and early diagnosis of arterial and venous flap thrombosis.