PubMed Health⌕ Search

Biomedical subjects

C M Pedersen

Publications and source records attributed to C M Pedersen.

18 recordsLinked to original sources
PubMed2006

Frequency response in surface-potential driven electrohydrodynamics.

Using a Fourier approach we offer a general solution to calculations of slip velocity within the circuit description of the electrohydrodynamics in a binary electrolyte confined by a plane surface with a modulated surface potential. We consider the case with a spatially constant intrinsic surface capacitance where the net flow rate is, in general, zero while harmonic rolls as well as time-averaged vortexlike components may exist depending on the spatial symmetry and extension of the surface potential. In general, the system displays a resonance behavior at a frequency corresponding to the inverse time of the system. Different surface potentials share the common feature that the resonance frequency is inversely proportional to the characteristic length scale of the surface potential. For the asymptotic frequency dependence above resonance we find a omega(-2) power law for surface potentials with either an even or an odd symmetry. Below resonance we also find a power law omega(alpha) with alpha being positive and dependent of the properties of the surface potential. Comparing a tanh potential and a sech potential we qualitatively find the same slip velocity, but for the below-resonance frequency response the two potentials display different power-law asymptotics with alpha=1 and alpha approximately 2, respectively.

Journal Article↗
PubMed1998

Haemolysis following rapid experimental red blood cell transfusion--an evaluation of two infusion pumps.

BACKGROUND: The vast majority of infusion pumps used for rapid transfusion of large amounts of blood have never been properly examined regarding their influence on the quality of the red blood cells (RBCs) infused. In this study, we evaluated the effect of two different infusion pumps on the degree of RBC destruction following rapid experimental blood transfusion. METHODS: Divided into 2 groups according to age, 30 u of SAGM RBCs were infused through an experimental transfusion model by either a manual roller pump (MRP) or a pressure infusor pump (PIP). Fresh (i.e stored for 8-11 d) RBCs, 20 u, and 10 u of older (i.e. stored for 25-33 d) RBCs were randomly allocated to infusion with either of the two pumps. The rate of infusion was as fast as possible with the MRP, and with the PIP adjusted with an external applied pressure of 300 mm Hg. RBC samples collected before and after infusion were analyzed for total haemoglobin, free haemoglobin, haematocrit, total free potassium, lactate dehydrogenase (LDH) and the percentage of haemolysis. The time spent for each transfusion was measured by a stop watch. RESULTS: Following infusion, a marginal increase (i.e. considerably below 0.8%) in the percentage of haemolysis and LDH content was seen with both pumps. This increase was only statistically significant when RBCs stored for 8-11 d were used (P = 0.002 for both parameters). Irrespective of the age of the RBCs, no differences between the two pumps could be detected. Compared to the PIP, infusion with the MRP could be accomplished significantly faster, i.e. median 5.9 ml/s (5.2-6.4 ml/s) versus 2.9 ml/s (2.5-3.2 ml/s), (P < 0.0001). CONCLUSIONS: Both the pumps used in this study are safe alternatives for rapid transfusion of RBCs; however, with MRP this can be accomplished approximately twice as fast as with the PIP.

Adenine↗
PubMed1997

[Persistent pulmonary hypertension in newborn infants].

On the basis of a review of the literature, a survey is presented concerning persistent pulmonary hypertension of the newborn. In this article the authors focus on the pathophysiology, diagnostic criteria and treatment, including mechanical ventilation, pharmacological vasodilation and extracorporal membrane oxygenation. Particular emphasis is placed on the treatment of the condition with inhaled nitric oxide. Nitric oxide is a selective pulmonary vasodilator and able to improve ventilation/ perfusion mismatching in cases where there is an affection of the pulmonary parenchyma. Data from randomized trials with close long-term follow-up is necessary before routine nitrogen oxide treatment can be recommended.

Humans↗
PubMed1996

[Sedation and analgesia in ventilator-treated children].

Ventilator-treated children often require sedation in order to facilitate the ventilation. Sedatives alone or in combination with analgesics are commonly used for this purpose. In some cases, however, the addition of a neuromuscular blocking agent (NMB) may be necessary. In this article a survey is presented regarding both pharmacological and non-pharmacological means of improving the ventilator treatment in ventilated children. The most commonly employed sedatives, opioids and NMB's are discussed. The authors stress that whichever drug is used, it should be administered to the children guided by its effects rather than by a rigid scheme. In that respect monitoring of the treatment is important.

Analgesia↗
PubMed1994

[Bronchodilating inhalation anesthetics in bronchial asthma and status asthmaticus].

On the basis of a review of the literature, a survey is presented concerning the use of halogenated inhalational anaesthetics (halothane, enflurane, isoflurane) in anaesthesia of asthmatic patients and in intensive care units in the treatment of status asthmaticus refractory to maximal standard therapy. Particular emphasis is placed on the bronchospasmolytic, cardiovascular and organotoxic effect of the anaesthetics. It is concluded that halogenated inhalational anaesthetics are established as bronchospasmolytics, and that their use in bronchospastic disease should be individualized to the patient and his other specific disease process.

Anesthesia, Inhalation↗
PubMed1994

[Severe bronchospasm in a 1-year old child treated with halothane].

A case of severe bronchospasm in a one-year old mechanically ventilated girl which in spite of maximal conventional bronchodilatory treatment only responded to halothane inhalation is presented. The benefits and limitations of this therapy are discussed.

Administration, Inhalation↗
PubMed1993

Smooth muscle relaxant effects of propofol and ketamine in isolated guinea-pig trachea.

The effects of anesthetics on airway smooth muscle tone are important in the management of patients with asthma. In the present study we evaluated the effect of propofol and ketamine on isolated guinea-pig tracheal preparations mounted for recording isometric contractile force. In a concentration-dependent way both drugs produced 100% relaxation irrespective of whether tracheal tone was spontaneous or induced by carbachol, histamine, prostaglandin F2 alpha, 30 mM K+ or 124 mM K+. The relaxant potency of propofol was dependent of the formulation of the drug used. Propofol showed an about 3 times higher potency when solubilized with hydroxypropyl-beta-cyclodextrin compared with an oil-in-water emulsion of the drug (Diprivan). Propofol had the greatest potency on tracheal preparations with spontaneous tone (EC50 = 4.0 +/- 0.9 microM). Ketamine preferentially relaxed contractions elicited by carbachol (EC50 = 120.8 +/- 5.2 microM) and had a lower potency than propofol when tone was spontaneous or induced by other tracheal spasmogens. Since propofol was a more effective tracheal relaxant in vitro than ketamine, the possibility that propofol, like ketamine, may inhibit bronchoconstriction during anesthesia should be studied further.

Animals↗
PubMed1992

[Failure of the pacemaker in electric cardioversion of atrial fibrillation].

A 72-year-old man with an AAI-rate-responsive pacemaker (Siemens-Elema Sensolog III; unipolar pacing electrode) was admitted for cardioversion of atrial fibrillation. Electrical defibrillation was followed by severe nodal bradycardia and pacemaker malfunction characterized by loss of atrial capture. The pacemaker failure was due to an acute rise in the stimulation threshold, possibly secondary to current-induced tissue damage at the electrode-endomyocardial interface. It is recommended that a pacemaker is reprogrammed to maximum pulse voltage amplitude prior to elective DC-cardioversion and that serial measurements of the myocardial stimulation threshold are performed after defibrillation. Other factors essential for the management of the pacemaker patient who requires electrical defibrillation are outlined.

Aged↗
PubMed1992

Bone graft incorporation around titanium-alloy- and hydroxyapatite-coated implants in dogs.

To evaluate cancellous allogenic bone graft incorporation into porous-coated implants, the fixation of titanium alloy-(Ti) and hydroxyapatite-(HA) coated implants with and without bone graft was compared. An unloaded model with unilateral carragheenin-induced osteopenia of the knee was used in 12 mature dogs. Ti- and HA-coated cylinders were implanted in the distal femoral condyles and centralized in 2-mm overreamed drill holes. Allogenic, fresh-frozen (-80 degrees) cancellous bone graft was packed around the implants in six dogs. In a matched group of six other dogs, the implants were left in overreamed canals without bone graft. After six weeks the interface shear strength of grafted Ti-coated implants had significantly increased compared to the nongrafted Ti implants. However, HA coating used without bone graft was capable of enhancing the bone-implant interface shear strength to nearly the same degree. The fixation of grafted Ti- and HA-coated implants was equal. No significant difference in implant fixation was found between osteopenic and control bone. Histomorphometric evaluation of mineralizing surfaces in direct contact with the implant confirmed the results from the push-out test. Bone-implant fixation when using allogeneic fresh-frozen cancellous bone graft in osteopenic and control bone was enhanced by hydroxyapatite coating but the HA coating alone appeared to offer almost the same improvement in anchorage in 2-mm defects. Loss of bone stock around loose prosthetic implants often requires bone grafting. However, because of anatomic constraints in joint prosthetic surgery, a complete filling of defects with bone graft is difficult, and areas of gaps between bone and implant will remain. Provided mechanical stability of the prosthesis, the results reported here suggest that these areas will probably be filled early with new mineralizing bone if the prosthesis is coated with a thin layer of hydroxyapatite.

Animals↗
PubMed1991

[Splenectomy and Haemophilus influenzae meningitis].

The case of a boy aged 13 years with Haemophilus influenzae type b meningitis is presented. Six years previously, splenectomy was performed on account of trauma. He died from the meningitis after ten days despite the recommended antibiotic treatment. Splenectomized patients should always seek medical advice at the first of any infection. If there is any doubt about the severity of infection, these patients should be admitted to hospital. Some countries recommended administration of Haemophilus influenzae type b vaccine to patients at risk.

Adolescent↗
PubMed1991

Physical bone changes in carragheenin-induced arthritis evaluated by quantitative computed tomography.

Repeated non-invasive measurements were performed in dogs of trabecular bone density (TBD), low density bone area (LDBA), and high density bone area (HDBA) in chronic arthritis using quantitative computed tomography (QCT). Unilateral chronic arthritis of the knee had been induced by weekly instillation of 2 ml carragheenin into the right knee joint for 12 weeks with the left knee serving as a control. CT scanning of the distal femoral condyles was performed in 12 mature dogs with chronic arthritis. Another 6 dogs underwent a longitudinal CT study starting immediately prior to induction of arthritis. During induction of arthritis TBD decreased (P less than 0.01), LDBA increased (P less than 0.05) and HDBA decreased (P less than 0.01) in the arthritic bone. Opposite changes were found on the control side, i.e. TBD increased (P less than 0.01), LDBA decreased (P less than 0.01) and HDBA increased (P less than 0.01). The chronic arthropathic bone showed 20% lower TBD (P less than 0.0001), greater LDBA (P less than 0.0001) and lower HDBA (P less than 0.0001) as compared with the control bone. Reproducibility tests of TBD showed a coefficient of variation of 0.8%. Indentation tests and histomorphometric analyses confirmed the bone density changes as measured by CT.

Animals↗
PubMed1991

Fixation of titanium and hydroxyapatite-coated implants in arthritic osteopenic bone.

Retrieval studies of porous-coated prostheses have demonstrated deficient bony ingrowth in high percentages. Possible reasons for this are lack of initial mechanical stability and the presence of osteopenia. The authors studied ingrowth of osteopenic bone into titanium alloy (Ti) porous-coated implants with and without hydroxyapatite (HA) coating in an experimental dog model. Unilateral osteopenia of the knee with a 20% reduced bone density as judged by computed tomography (CT) scanning (P less than .001) was induced in 12 mature dogs by weekly intraarticular injections of Carragheenin into the right knee for 12 weeks, with the left knee serving as control. Ti porous-coated cylinders were inserted in press-fit bilaterally in the lateral femoral condyles in six dogs. HA-coated titanium plugs were implanted similarly in another sex-, age-, and weight-matched group of six dogs. Bony ingrowth after 4 weeks was significantly reduced for Ti implants in osteopenic bone compared to control bone, but HA-coated implants were covered by equal amounts of bone tissue. Bone-implant shear strength of Ti implants also was reduced in osteopenic bone compared to control bone. In control bone, the anchorage of Ti implants was stronger than HA-coated implants, whereas the fixation of Ti and HA-coated implants was equal in the osteopenic bone. The results demonstrate that the bony fixation of Ti porous-coated implants is weakened by the presence of experimentally induced osteopenia. However, the fixation of HA-coated implants was not affected by the osteopenic condition in the surrounding bone. The fixation of Ti and HA-coated implants was equal in osteopenic bone, whereas the fixation of Ti porous-coated implants was superior to that of HA-coated implants in control bone.

Animals↗
PubMed1991

Gap healing enhanced by hydroxyapatite coating in dogs.

During prosthetic implantation, gaps between the implant surface and the surrounding bone may occur resulting in reduced implant stability. In these instances bone-conductive materials might augment the formation of hosting bone into the pores of the implant and insure earlier implant stabilization and fixation by bony ingrowth. Titanium-alloy cylinders with a porous-titanium-alloy plasma spray coating were implanted into the medial femoral condyles in six mature dogs. In another group of six dogs, matched in age, weight, and gender, hydroxyapatite (HA) coated implants were used. All implants were surrounded by a 1-mm gap. Unilateral osteopenia of the knee, with a 20% reduction of bone density as judged by computed tomography scanning, was induced by 12 weekly intraarticular injections of carrageenin into the right knee before surgery. Four weeks after implantation, the HA-coated implants were compared to the parent porous-titanium implants by mechanical testing and histomorphometry. A marked positive influence of HA coating on bone mineralization and the strength of the interfacial bone between the bone and implant was found. The increment in interface shear strength and shear stiffness was three- to fivefold in osteopenic bone and two-fold in control bone. Coating of an unloaded porous-titanium-coated implant with HA accelerates the rate of bone ingrowth and thereby provides relatively high, early interfacial shear strengths in the presence of an initial gap between bone and implant even in the presence of osteopenic host bone.

Animals↗
PubMed1990

Hydroxyapatite coating enhances fixation of porous coated implants. A comparison in dogs between press fit and noninterference fit.

Intimate contact at the bone-porous surface interface is not always achievable in noncemented prosthetic implantation. We investigated the effect of hydroxyapatite (HA) coating on skeletal attachment in noninterference fit 4 weeks after implantation in 6 mature dogs. The push-out test of HA-coated implants surrounded by a 1-mm gap showed a twofold increased shear strength and fivefold increased shear stiffness compared with titanium alloy (Ti) coated implants. The fixation of Ti implants was reduced by two thirds when inserted in a gap as compared with press fit, whereas HA-coated implants in gap showed anchorage close to implants in press fit. Only minor differences were found between HA and Ti implants in press fit. Histomorphometric analysis showed a significant increase in bone in direct contact to HA-coated implant as compared with Ti implants inserted both in gap and press fit. The study indicates that tightness of surgical fit is an important factor for sufficient fixation of the implant. However, our results demonstrate that hydroxyapatite coating almost eliminates the negative influence of noninterference fit between bone and unloaded implant.

Animals↗
PubMed1989

Density changes at the proximal tibia after medial meniscectomy.

Trabecular bone density changes at the proximal tibia were studied after total and partial meniscectomy using quantitative computerized tomography. Thirty-seven medially meniscectomized patients (5- and 10-year follow-up) and 10 control persons were included. In the partially and the totally meniscectomized knees, the area of maximal density in the medial tibial condyle was displaced approximately 4 mm in a posteromedial direction relative to the position in the intact knees. In both partially and totally meniscectomized knees, the density in the region of tibiofemoral contact in the medial tibial condyle was higher compared with the density in the same region in the contralateral intact knees. This difference was of the same order in the 5- and 10-year follow-up groups. The density difference between the meniscectomized and the intact knees in the region of tibiofemoral contact in the medial condyle was significantly higher in totally than in partially meniscectomized patients. It is concluded that not only total but also partial medial meniscectomy is followed by density changes, occurring within the first 5 years after meniscectomy. The results emphasize the importance of the utmost conservatism in surgery on the meniscus.

Adult↗
PubMedDate not supplied

Bone strength and material properties of the glenoid.

The quality of the glenoid bone is important to a successful total shoulder replacement. Finite element models have been used to model the response of the glenoid bone to an implanted prosthesis. Because very little is known about the bone strength and the material properties at the glenoid, these models were all based on assumptions that the material properties of the glenoid were similar to those of the tibial plateau. The osteopenetrometer was used to assess the topographic strength distribution at the glenoid. Strength at the proximal subchondral level of the glenoid averaged 66.9 MPa. Higher peak values were measured posteriorly, superiorly, and anteriorly to the area of maximum concavity of the glenoid joint surface known as the bare area. One millimeter underneath the subchondral plate, average strength decreased by 25%, and at the 2 mm level strength decreased by 70%. The contribution of the cortical bone to the total glenoid strength was assessed by compression tests of pristine and cancellous-free glenoid specimens. Strength decreased by an average of 31% after the cancellous bone was removed. The material properties of the glenoid cancellous bone were determined by axial compression tests of bone specimens harvested from the central part of the glenoid subchondral area. The elastic modulus varied from approximately 100 MPa at the glenoid bare area to 400 MPa at the superior part of the glenoid. With the elastic constants used a predictor of the mechanical anisotropy, the average anisotropy ratio was 5.2, indicating strong anisotropy. The apparent density was an average 0.35 gr. cm-3, and the Poisson ratio averaged 0.263. According to our findings the anisotropy of the glenoid cancellous bone, details concerning the strength distribution, and the load-bearing function of the cortical shell should be considered in future finite element models of the glenoid.

Adult↗