Intermingled skin grafting: a valid transplantation method at low cost.

The almost forgotten method of intermingled skin grafting of allogeneic material with small autogeneic islets, once developed in the People's Republic of China, proves the feasibility of permanent healing of even extensive burn wounds, at low cost, and therefore an effective treatment possibility in poorer countries, as well as under conditions of a burn disaster. Intermingled skin grafting obtains a better elasticity of the reconditioned skin as elastic fibres of the allodermis survive, and this results in fewer contractures. From the cosmetic point of view the transplantation of autologous keratinocytes results in a better aesthetic homogeneous texture.

Sound localization in the presence of one or two distracters.

Localizing a target sound can be a challenge when one or more distracter sounds are present at the same time. This study measured the effect of distracter position on target localization for one distracter (17 positions) and two distracters (21 combinations of 17 positions). Listeners were instructed to point to the apparent position of a train of 30-ms noise bursts, presented at 1 of 85 positions in virtual free field. A harmonic complex and a frequency-swept complex tone served as distracters. The two distracters were turned on 40 and 80 ms after the target onset, had temporal envelopes similar to that of the target, and did not overlap temporally with the target. Virtual sounds were synthesized with individual HRTFs. Localization performance degraded as the number of distracters increased from 0 to 2. When the horizontal distance between target and a single distracter was small (i.e., the interaural differences were almost the same), the influence on the apparent position was greater than when they were far apart. In the vertical dimension, there was not a systematic effect of distracter position on target localizability. However, there was a substantial increase in localization error for targets at high elevations (above 30 degrees) when distracters were present.

Resolution of front-back ambiguity in spatial hearing by listener and source movement.

Normally, the apparent position of a sound source corresponds closely to its actual position. However, in some experimental situations listeners make large errors, such as indicating that a source in the frontal hemifield appears to be in the rear hemifield, or vice versa. These front-back confusions are thought to be a result of the inherent ambiguity of the primary interaural difference cues, interaural time difference (ITD) in particular. A given ITD could have been produced by a sound source anywhere on the so-called "cone of confusion." More than 50 years ago Wallach [J. Exp. Psychol. 27, 339-368 (1940)] argued that small head movements could provide the information necessary to resolve the ambiguity. The direction of the change in ITD that accompanies a head rotation is an unambiguous indicator of the proper hemifield. The experiments reported here are a modern test of Wallach's hypothesis. Listeners indicated the apparent positions of real and virtual sound sources in conditions in which head movements were either restricted or encouraged. The front-back confusions made in the restricted condition nearly disappeared in the condition in which head movements were encouraged. In a second experiment head movements were restricted, but the sound source was moved, either by the experimenter or by the listener. Only when the listener moved the sound source did front-back confusions disappear. The results clearly support Wallach's hypothesis and suggest further that head movements are not required to produce the dynamic cues needed to resolve front-back ambiguity.

Primary intracerebellar osteosarcoma arising within an epidermoid cyst.

The authors report a case of a primary extraskeletal osteosarcoma arising within an epidermoid cyst in the parenchyma of the cerebellum in a 64-year-old woman. On initial presentation, the tumor involved the midline cerebellum without attachment to the surrounding dura mater or calvarium. Complete medical and radiologic evaluation failed to reveal a primary skeletal or other extraskeletal osteosarcoma. To our knowledge, this is the first reported case of a primary extraskeletal osteosarcoma within the cerebellum. Osteosarcoma as a primary brain tumor is exceedingly rare, and only three cases (all occurring within the cerebral hemispheres) have been reported previously. The histogenesis of primary sarcomas of the brain is not evident. The associated finding of an epidermoid cyst suggests the tumor originated from a teratoma.

Monaural sound localization revisited.

Research reported during the past few decades has revealed the importance for human sound localization of the so-called "monaural spectral cues." These cues are the result of the direction-dependent filtering of incoming sound waves accomplished by the pinnae. One point of view about how these cues are extracted places great emphasis on the spectrum of the received sound at each ear individually. This leads to the suggestion that an effective way of studying the influence of these cues is to measure the ability of listeners to localize sounds when one of their ears is plugged. Numerous studies have appeared using this monaural localization paradigm. Three experiments are described here which are intended to clarify the results of the previous monaural localization studies and provide new data on how monaural spectral cues might be processed. Virtual sound sources are used in the experiments in order to manipulate and control the stimuli independently at the two ears. Two of the experiments deal with the consequences of the incomplete monauralization that may have contaminated previous work. The results suggest that even very low sound levels in the occluded ear provide access to interaural localization cues. The presence of these cues complicates the interpretation of the results of nominally monaural localization studies. The third experiment concerns the role of prior knowledge of the source spectrum, which is required if monaural cues are to be useful. The results of this last experiment demonstrate that extraction of monaural spectral cues can be severely disrupted by trial-to-trial fluctuations in the source spectrum. The general conclusion of the experiments is that, while monaural spectral cues are important, the monaural localization paradigm may not be the most appropriate way to study their role.

Venous stenosis and occlusion in hemodialysis shunts: follow-up results of stent placement in 65 patients.

PURPOSE: To provide follow-up data on the use of self-expanding stents in hemodialysis fistulas to improve the technical success of balloon angioplasty. MATERIALS AND METHODS: Ninety-two self-expanding vascular stents were placed in 65 patients (29 men and 36 women 25-79 years of age; mean, 57.6 years) with failing hemodialysis fistulas or shunts. RESULTS: Stent placement was successful in all patients, but rethrombosis of the shunt occurred in six patients (10%) within 1 week. There were 96 episodes of reobstruction. In 87 cases, percutaneous or combined surgical and percutaneous repeat intervention was performed. The cumulative shunt function rate was 88% after 6 months, 86% after 1 year, and 77% after 2 years. CONCLUSION: Stent placement in hemodialysis fistulas helps treat lesions that cannot be adequately treated with percutaneous transluminal angioplasty (PTA) alone but has a follow-up patency rate similar to that of PTA. Standard central venous stents have a better patency rate than after PTA.

Localization using nonindividualized head-related transfer functions.

A recent development in human-computer interfaces is the virtual acoustic display, a device that synthesizes three-dimensional, spatial auditory information over headphones using digital filters constructed from head-related transfer functions (HRTFs). The utility of such a display depends on the accuracy with which listeners can localize virtual sound sources. A previous study [F. L. Wightman and D. J. Kistler, J. Acoust. Soc. Am. 85, 868-878 (1989)] observed accurate localization by listeners for free-field sources and for virtual sources generated from the subjects' own HRTFs. In practice, measurement of the HRTFs of each potential user of a spatial auditory display may not be feasible. Thus, a critical research question is whether listeners can obtain adequate localization cues from stimuli based on nonindividualized transforms. Here, inexperienced listeners judged the apparent direction (azimuth and elevation) of wideband noisebursts presented in the free-field or over headphones; headphone stimuli were synthesized using HRTFs from a representative subject of Wightman and Kistler. When confusions were resolved, localization of virtual sources was quite accurate and comparable to the free-field sources for 12 of the 16 subjects. Of the remaining subjects, 2 showed poor elevation accuracy in both stimulus conditions, and 2 showed degraded elevation accuracy with virtual sources. Many of the listeners also showed high rates of front-back and up-down confusions that increased significantly for virtual sources compared to the free-field stimuli. These data suggest that while the interaural cues to horizontal location are robust, the spectral cues considered important for resolving location along a particular cone-of-confusion are distorted by a synthesis process that uses nonindividualized HRTFs.

[Treatment of stenosed or occluded hemodialysis shunts. Results of percutaneous angioplasty and combined radiologic-surgical therapy]. / Rekanalisation von stenosierten oder verschlossenen Hämodialyseshunts. Ergebnisse der perkutanen Angioplastie und der kombiniert radiologisch-chirurgischen Therapie.

The results of all recanalisations of stenosed and occluded haemodialysis shunts over a period of three years are reported; there were 112 percutaneous angioplasties and 40 combined radiological-surgical procedures. In 13% of cases a metallic endoprosthesis (wall stent) and in 3% Simpson's atherectomy catheter was used. The functional results were retrospectively evaluated for all 152 interventions which involved 60 orthoptic Brescia-Cimino shunts and 19 PTFE prostheses. In addition, the primary and total functions of the treated shunts were calculated. Cumulative function rate (percentage at a given time of effective shunts) for Brescia-Cimino shunts at one year was 80% and after two years 68.5%; for the PTFE prosthesis the corresponding figures were 83.8 and 75.5% respectively. The average number of interventions per patient was 2.3 with a range of 1-7. Total functional rate of all shunts following the first percutaneous procedure after one year was 78.2%, for combined radiological-surgical procedures for the treatment of acute thromboses it was 68%. Comparison with the results of surgical treatment reported in the literature confirms the effectiveness of percutaneous or combined treatment of stenosed or acutely occluded haemodialysis shunts. The outstanding advantage of radiological intervention is its repeatability.

A computerised machine for the facilitated production of intermingled skin grafts.

The introduction of intermingled allograft/autograft skin grafting in western countries has long been hampered by high costs, due to the personnel requirements to produce this special form of graft. We have solved this problem by designing and constructing a computer-controlled machine, which in one operation punches holes out of strips of allogeneic donor skin and in another cuts fitting islets out of autogenous skin and transfers them into these holes. In comparison to manual preparation, this machine not only accelerates the production of intermingled skin grafts, but it also inserts the islets with superior accuracy, which is very important for the final functional and cosmetic result.

A model of head-related transfer functions based on principal components analysis and minimum-phase reconstruction.

Free-field to eardrum transfer functions (HRTFs) were measured from both ears of 10 subjects with sound sources at 265 different positions. A principal components analysis of the resulting 5300 HRTF magnitude functions revealed that the HRTFs can be modeled as a linear combination of five basic spectral shapes (basis functions), and that this representation accounts for approximately 90% of the variance in the original HRTF magnitude functions. HRTF phase was modeled by assuming that HRTFs are minimum-phase functions and that interaural phase differences can be approximated by a simple time delay. Subjects' judgments of the apparent directions of headphone-presented sounds that had been synthesized from the modeled HRTFs were nearly identical to their judgments of sounds synthesized from measured HRTFs. With fewer than five basis functions used in the model, a less faithful reconstruction of the HRTF was produced, and the frequency of large localization errors increased dramatically.

The dominant role of low-frequency interaural time differences in sound localization.

Two experiments are described in which listeners judge the apparent directions of virtual sound sources-headphone-presented sounds that are processed in order to simulate free-field sounds. Previous results suggest that when the cues to sound direction are preserved by the simulation, the apparent directions of virtual sources are nearly the same as the apparent directions of real free-field sources. In the experiments reported here, the interaural phase relations in the processing algorithms are manipulated in order to produce stimuli in which the interaural time difference cues signal one direction and interaural intensity and pinna cues signal another direction. The apparent directions of these conflicting cue stimuli almost always follow the interaural time cue, as long as the wideband stimuli include low frequencies. With low frequencies removed from the stimuli, the dominance of interaural time difference disappears, and apparent direction is determined primarily by interaural intensity difference and pinna cues.

Follow-up results after stent placement in failing arteriovenous shunts: a three-year experience.

Self-expandable endoprostheses were used in 18 failing arteriovenous shunts after unsuccessful balloon dilatation. Technical success was satisfactory with an early patency in 17 of 18 shunts. Thrombosis right after stenting occurred in three shunts but was successfully treated in two. Follow-up history revealed recurrent events of reobstruction due either to stent or shunt stenoses or thrombosis. Restenosis within the stented segment was responsible for reobstruction in about half the cases. Although patency was low with 27% at 18-month follow-up, repeated intervention established a shunt survival rate of 77% at 18-month follow-up. Stent placement in AV shunts is useful for overcoming acute problems of balloon dilatation but does not prevent restenosis.

Multidimensional scaling analysis of dysphonia in two speaker groups.

The objective of this research was to identify perceptually relevant features of 30 dysphonic female voices. The perceptual dimensions used by listeners in judging the similarity of the dysphonic voices were derived in two multidimensional scaling (MDS) procedures using ALSCAL. Three dimensions were extracted in each MDS solution and accounted for approximately 60% of the total variance in the judgments. The three dimensions were related to measures of intensity, frequency, and perturbation. The results are discussed in relation to how clinicians use perceptual judgments in evaluating dysphonic voices.

Technical aspects and results of percutaneous transluminal angioplasty in Brescia-Cimino dialysis fistulas.

Our experience with percutaneous transluminal angioplasty for treatment of stenoses and occlusions in surgically created arteriovenous fistulas (Brescia-Cimino) is reported. Methodological aspects are emphasized. Forty-nine PTAs were performed in 36 patients, in 3 combined with the use of a vascular metallic endoprosthesis (Wallstent). The initial success rates for stenoses and occlusions were 91% and 77%, respectively. Long stenoses and occlusions (greater than 4 cm) showed significantly worse initial results (55%) as compared to short ones (95%). Of the primarily successfully treated shunts, 90% are still functioning after a mean follow-up time of 8 months. The results indicate that PTA may replace surgical intervention as the primary method for treatment of insufficient flow for internal arteriovenous shunts, provided fresh thrombi are not the cause of the occlusion. Metallic endoprostheses and the use of atherectomy catheters were shown to be a valuable adjunct to classical PTA in selected cases.

The serratus anterior osteocutaneous free flap.

Microvascular transfer of the rib as an osteocutaneous or osseous free flap based on the thoracic branch of the thoracodorsal artery is described. A review of the literature revealed various patterns of rib vascularization in different areas of the body from the periosteum and the endosteal vessels. Reversing the blood flow in the transcortical vessels of the rib is reported to be possible. Injection studies showed a reliable connection between the thoracic branch of the thoracodorsal artery and the endosteal vessels of the sixth and seventh ribs at the origin of the anterior serratus muscle. This approach to free rib transfer has proved to be quick, easy, and reliable in various clinical applications.

[Pathogen spectrum and pathways of infection at an intensive care burn unit]. / Keimspektrum und Infektionswege auf einer Verbrennungsintensivstation.

Coagulase-negative staphylococci have gained increasing importance in burns, whereas interest is no longer focussed on Pseudomonas bacteria. By means of microbiological analysis of swabs taken from patients, environment and staff, we trailed the routes of infection in an intensive-care unit for burns. Analysis of patients: In 27 out of 11 patients the same biotype of Staphylococcus epidermidis could be identified; 22 of these occurred in swabs from wounds. The phagotypification of Staphylococcus aureus showed the same phagotype in 28 out of 41 swabs taken from infected wounds of 10 patients. The pathogen mostly caused the destruction of already healed grafts in a later phase of the treatment. Further microbiological analysis showed a severe infestation of the patients by enterococci. Analysis of environment: Here, greatly increased counts of coagulase-negative staphylococci of the same lysotype as in the patients could be demonstrated. Analysis of staff: The naso-pharyngeal area is of minor importance in the spreading of germs, whereas that of protective clothing and especially the hands should be considered to be more crucial. Regular environmental tests enable rapid detection of hygienic errors so that appropriate countermeasures can be taken.

[Percutaneous vascular endoprotheses for occlusions or stenoses of hemodialysis shunts]. / Perkutane vaskuläre Endoprothesen bei Verschlüssen oder Stenosen von Hämodialyse-Shunts.

In ten patients (four men and six women, mean age 51.7 [26-79] years), with six occlusions and five stenoses of a haemodialysis shunt or shunt-draining subclavian vein, a self-expanding intravascular stent was implanted percutaneously after balloon-dilatation. The implantation was successful in 9 of 11 instances, but the shunt thrombosed in two within 24 hours (in one of the patients, with antithrombin III deficiency, the shunt had to be abandoned). After an average observation period of 7.8 (1-14) months, ten shunts have remained open and suitable for dialysis. A further stent had to be implanted in one of the patients because of stenosis distal to the first stent. In three patients intima hyperplasia within the stent necessitated percutaneous balloon dilatation and/or atherectomy.