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Biomedical subjects

C Scheer

Publications and source records attributed to C Scheer.

10 recordsLinked to original sources
PubMed2000

Development of an opto-electronic positioning device for serial direct digital images of oral structures.

The aim of this study was to develop and test in vitro an opto-electronic positioning device for serial direct digital images of oral structures, i.e. to associate direct digital imaging with the principles of computer-aided surgery. This system registered positions of infrared light emitting diodes (LED) on carriers, establishing local coordinate systems. With LED markers attached on the sensor holder, the X-ray tube and a fix reference, the opto-electronic camera (Optotrak) registered the geometric source/detector relation. A specially designed tracking and guidance software was developed which enabled the operator to reposition the X-ray source. A graphical user interface guided the operator in aligning 2 circles to the reference axis, one indicating the origin of the beam, the other its tip. In addition, depth control was provided. An in vitro calibration was performed. A sensor holder/bite block carried the Sens-A-Ray sensor with a hair-cross. In front of the object a second hair-cross was fixed. A steel ball fixed to the center of the X-ray cone allowed to verify the alignment. The mean angulation error in the vertical plane was 0.06 degrees and 0.04 degrees in the horizontal one. Translation mean errors were small and ranged between -0.02 mm and 0.37 mm. The translation in the Z axis is negligible. This resulted in pairs of images suitable for digital subtraction. Although still in an experimental state, the results showed that opto-electronic navigation was useful to standardize projection geometry without any mechanical link and to achieve digital subtraction images based on direct digital imaging.

Equipment Design↗
PubMed1998

Angiotensin II and intracellular calcium of adult cardiac fibroblasts.

In various cardiovascular disorders, circulating or myocardial angiotensin II (Ang II) levels are increased, leading to excess collagen synthesis of cardiac fibroblasts. To characterize signal transduction mechanisms of Ang II, we examined changes in intracellular Ca2+ concentration ([Ca2+]i) of fura-2-loaded cultured adult rat cardiac fibroblasts by fluorescence photometry. [Ca2+]i was increased by Ang II via AT1 receptors in a dose-dependent manner (EC50 = 2.4 x 10(-8) mol/l) involving two distinct phases, an initial Ca2+ peak and a sustained elevated plateau phase. The initial Ca2+ peak occurred transiently and independently of the duration of Ang II application. While the magnitude of the transient Ca2+ peak did not differ in a nominally Ca(2+)-free (3 mmol/l EGTA) solution, the Ang II-mediated sustained plateau phase of [Ca2+]i was dependent on extracellular Ca2+. Thus, the initial transient Ca2+ peak appears to arise from intracellular Ca2+ stores, whereas the plateau phase involves an external Ca2+ influx. Since collagen synthesis of cardiac fibroblasts is maximally stimulated by Ang II or by fetal bovine serum (FBS), the effects of Ang II and FBS on [Ca2+]i were compared. The magnitude of the transient Ca2+ peak induced by 10(-7) mol/l Ang II was comparable to that of 10% FBS indicating that the rise in [Ca2+]i might be involved in the signal transduction pathway of Ang II-mediated collagen synthesis of cardiac fibroblasts.

Angiotensin II↗
PubMed1997

[Spironolactone: renaissance of anti-aldosterone therapy in heart failure?].

Mortality of patients with severe congestive heart failure (CHF) is still high despite combined treatment with angiotensin-converting enzyme (ACE) inhibitors, diuretics, and digitalis. Further therapeutic regimens are needed which include reversal of adverse myocardial remodeling and subsequent ventricular dysfunction. One third of all patients with CHF have diastolic left ventricular (LV) dysfunction with preserved systolic function. In these patients myocardial collagen matrix is the major determinant of myocardial stiffness and therefore diastolic function. Cardiac fibroblasts, expressing mRNA for types I and III collagens which are the major fibrillar proteins of the myocardial collagen network and for matrix metalloproteinase (MMP) 1 which is the key enzyme for interstitial collagen degradation, are controlled by the renin-angiotensin-aldosterone (RAAS) system irrespective of hemodynamics and cardiac myocyte growth. In the rat with primary or secondary hyperaldosteronism, myocardial fibrosis occurs in the pressure overloaded, hypertrophied left and in the normotensive, nonhypertrophic right ventricle. In contrast, no fibrosis is found in either ventricle of rats with infrarenal aortic banding, when the RAAS is not activated, despite comparable systemic hypertension and LV hypertrophy. In cultured cardiac fibroblasts, either effector hormone of the RAAS, angiotensin (Ang) II and aldosterone (Aldo) stimulate collagen synthesis measured by 3H-proline incorporation under serum-free conditions. Aldo is able to stimulate collagen synthesis normalized per total protein synthesis in a dose-dependent manner and at concentrations (10(-9) M) which are comparable to stimulated states in vivo (e.g., CHF). While Aldo does not affect collagen degradation AngII significantly inhibits, MMP 1 activity that would lead to further accumulation of collagen in the myocardium. Specific AngII type I or Aldo receptor antagonists are able to abolish the AngII or Aldo-mediated increase in collagen synthesis, respectively. In vivo in rats with primary or secondary hyperaldosteronism, the Aldo antagonist spironolactone has been shown to prevent myocardial fibrosis in both ventricles irrespective of the development of LV hypertrophy and hypertension. Thus, in vivo and in vitro evidence could be provided that the mineralocorticoid. Aldo, plays a pivotal role in promoting myocardial fibrosis and can be antagonized by its competitive receptor blocker, spironolactone. This may be of particular clinical relevance in treating patients with CHF where the RAAS is activated leading to myocardial fibrosis with subsequent deterioration of myocardial function. Clinical trials are needed to confirm these experimental data. If the ongoing RALES mortality study will prove that survival and/or morbidity of patients with CHF are improved by combined ACE inhibitor/spironolactone treatment a renaissance of anti-aldosterone therapy in patients with CHF would occur.

Animals↗
PubMed1997

Man-machine interfaces in computer assisted surgery.

The clinical potential of computer assisted surgery (CAS) has been more and more widely acknowledged since CAS systems have been introduced into the operating room (OR) theater. Especially the improvements in safety and accuracy are remarkable and strengthen the ties between surgeons and engineers. Tumor stereotaxis was introduced to neurological surgery in the early 1980s, and currently systems with and without robotic navigation are in use for specific medical indications. Recently, solutions for computer assisted orthopedic surgery were developed and applied to various anatomical regions. However, with the establishment of CAS in vivo, a new complex of problems, which was not present in the laboratory setup, was introduced: the man-machine interface. Currently, the complexity of available CAS systems requires the presence of at least one system engineer (often called the "operator") in the OR. As a consequence, there is no possibility for direct communication between the surgeon and the machine or software. Most of the program steps involved in CAS and choices to be made intraoperatively have to be transferred to the software by means of communication of the surgeon with the operator. Particularly, the establishment of a relation between the virtual object (i.e., a medical image) and the surgical object (i.e., the patient), often denoted as "matching" or "skeletal registration," requires intensive interaction of the surgeon with the computer. A literature survey revealed that no CAS system in clinical use exists without a system engineer or a comparable person, and our clinical experience indicated that the matching process is a weak point in most systems. Because it appears to be contradictory to cost-reduction efforts in health care to have a highly paid specialist in the OR, this research evaluates strategies to facilitate the man-machine interface with the final goal of establishing a direct control of the system by the surgeon or the medical personnel traditionally present at surgery. Options to be investigated include 1) a CAS control panel (virtual keyboard) as an integrated component of the existing navigation system and 2) introduction of a commercial voice-recognition system. The implementation of these strategies into the existing CAS setup at the Department of Orthopaedic Surgery at the Inselspital (University of Bern) and clinical experience gained are reported.

Biomedical Engineering↗
PubMed1997

The first twelve cases of computer assisted periacetabular osteotomy.

Image guided freehand navigation of surgical instruments has been applied to the Bernese periacetabular osteotomy, a complex surgical technique for the treatment of dysplastic hips. This navigation system has been introduced into the operating room and has so far been used for 12 patients. Image data from computed tomography (CT) scans are presented in various ways to support the preoperative plan and to provide optimized control of surgical action. Special attention has been paid to the implementation of a sophisticated surgeon-machine interface. This paper describes the features of this novel surgical navigation system and its introduction into the clinical environment.

Acetabulum↗
PubMed1997

Renin-angiotensin system and myocardial collagen matrix: modulation of cardiac fibroblast function by angiotensin II type 1 receptor antagonism.

BACKGROUND: Left ventricular hypertrophy is an adaptive process to increased loading of the left ventricle. This condition becomes pathologic with impaired myocardial function if the various tissue compartments of the myocardium (myocyte, interstitial and vascular compartments) are inhomogeneously altered, particularly if myocardial fibrosis occurs. In arterial hypertension, myocardial fibrosis is known to occur in association with activated circulating or local renin-angiotensin systems and includes reactive perivascular and interstitial fibrosis in both the pressure-overloaded hypertrophied left ventricle and the normotensive non-hypertrophied right ventricle. Therefore, it appears that hemodynamics are not primarily responsible for the adverse myocardial collagen matrix remodeling in hypertensive heart disease. Accordingly, we studied the interaction between cultured adult rat cardiac fibroblasts, which express messenger (m)RNAs for types I and III collagens, the major fibrillar collagens in the heart, and angiotensin II (Ang II), the effector hormone of the renin-angiotensin system. OBJECTIVES: Specifically, we sought to determine whether Ang II stimulates total collagen synthesis and the expression of type I collagen mRNA in cultured adult rat cardiac fibroblasts, and to investigate the effects of Ang II on intracellular Ca2+ levels. MATERIALS AND METHODS: Adult rat cardiac fibroblasts were cultured in Dulbecco's Modified Eagle's Medium + 10% fetal calf serum and incubated for 24 h with Ang II with or without specific Ang II type 1 or type 2 receptor antagonists. Collagen synthesis was measured using a 3H-proline incorporation assay, and type I collagen mRNA was determined using reverse-transcriptase polymerase chain reaction. Intracellular Ca2+ transients were measured by fast fluorescence photometry using the fluorescent dye fura-2-acetoxymethylester. RESULTS: We found a 76% increase in type I collagen mRNA in cultured cardiac fibroblasts after a 24-h incubation with Ang II, and this was abolished by simultaneous incubation with the Ang II type 1 (AT1)-receptor antagonist candesartan. Likewise, total collagen synthesis was stimulated by Ang II in a dose-dependent manner, and this stimulation was also counteracted by candesartan. Additionally, incubation with Ang II resulted in a significant dose-dependent increase in intracellular Ca2+ transients which was also abolished by treatment with candesartan. CONCLUSIONS: Ang II stimulates collagen synthesis in cultured adult rat cardiac fibroblasts via AT1 receptors, most likely using Ca2+ as a second messenger. These findings suggest a direct interaction between Ang II and cardiac fibroblasts in mediating myocardial fibrosis in arterial hypertension, leading to pathologic left ventricular hypertrophy with initially impaired diastolic and ultimately reduced systolic function of the left ventricle. The AT1-receptor antagonist candesartan cilexetil, which is the prodrug of the active compound candesartan, may prove valuable in preventing or regressing myocardial fibrosis in hypertensive heart disease.

Angiotensin II↗
PubMed1997

Rheumatic manifestations of scurvy. A report of two cases.

Bleeding into the muscles and joints can be the presenting manifestation of scurvy, as illustrated by two case-reports. One patient presented with hemarthrosis of the tibiotalar joint due to an insufficiency fracture and was suspected to have scurvy based on the presence of purpura and hypertrophy of the gums with loss of teeth. In the other patient, multiple hematomas in the lower limbs were found at presentation and the presence of coiled hairs suggested the diagnosis. Both patients had completely eliminated fruit and vegetables from their diet. Low levels of ascorbic acid were found in serum and urine. A full recovery was achieved in both cases under ascorbic acid supplementation.

Adult↗
PubMed1987

Development and implementation of a quality assurance program for mammography.

As a pilot study for a national campaign to promote the use of screening mammography, the Virginia Division of the American Cancer Society conducted a breast cancer awareness project with mammography screening. An important part of the program was the development of a quality assurance program for mammography. Guidelines were established for equipment, image recorders, processing, dose, and patient positioning. A survey of information about the mammographic equipment was conducted, and the mammograms from each facility were reviewed. A total of 63 mammographic units in 56 facilities statewide were included in the month-long program during which approximately 9,000 women were screened.

Breast Neoplasms↗