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Biomedical subjects

A B Christensen

Publications and source records attributed to A B Christensen.

31 records · Page 2Linked to original sources
PubMed1987

Assessment of tibial stiffness by vibration testing in situ--III. Sensitivity of different modes and interpretation of vibration measurements.

Post mortem vibration measurements on one human tibia during gradual transection reveal the vibration modes and frequencies of a tibia during a simulated healing. The modes are identified in a tibia in an above knee amputation specimen with the leg in two positions: hanging down with the knee flexed (90 degrees) and supported in a special designed bone clamping splint (knee flexed 45 degrees). The vibration measurements are analysed using Modal Analysis and are translated to mechanical stiffness by mathematical modelling. The single bending 'free-free' mode turned out to be more sensitive to weakening of one cross-section than the 'rigid body' and single bending 'hinged-spring' modes. The error on the assessed value of the stiffness is a multiple of the error on the measured frequencies. This multiplication factor decreases for more sensitive modes. In this experiment, the results are accurate enough to reflect the asymmetric weakening imposed upon the tibia. Attempts are made towards automatization of the measurement and analysis in order to get a system for clinical use. The actual system is still too cumbersome and time consuming for standard clinical use.

Humans↗
PubMed1986

Acute and long-term nephrotoxicity of cis-platinum in man.

To detect whether the nephrotoxicity of cis-diamminedichloroplatinum (DDP) is acute and can be demonstrated at an early stage in man, a method for estimating the function of the kidneys during intensive hydration was devised. The method includes a calculation of the clearance of 125I-orthoiodohippurate and an estimation of the glomerular filtration rate (GFR) from fast changes of the extracellular volume (ECV) and the mean transit time of 99mTc-DTPA in this volume. We examined nine patients with testicular cancer on 2 consecutive days for acute nephrotoxicity while they were undergoing treatment with cis-platinum. Placebo was given on day 1, cis-platinum on day 2. On both days the patients were hydrated with 4 l saline, glucose, and mannitol (0.51) over a period of 4 h, which resulted in an increase of 125I-orthoiodohippurate clearance on both days (P less than 0.01). The increase was, however, lower on the day of treatment with cis-platinum than on the day with placebo (P less than 0.05). There were no acute changes in the GFR. This indicates that treatment with DDP inhibits the active transport of 125I-orthoiodohippurate in the tubules; that is to say there is an acute effect on the kidney function. There were no acute changes in the GFR, but in the long-term followup study we found that the GFR had decreased significantly (P less than 0.05) after 2 months of treatment. During the first year after the initiation of treatment the GFR changes were found to progress. A significant increase in se-creatinine was not observed until 6 months after the initiation of treatment (P less than 0.05). The degree of chronic nephrotoxicity did not correlate in individual patients with the acute changes in kidney function.

Acute Disease↗
PubMed1986

Assessment of tibial stiffness by vibration testing in situ--I. Identification of mode shapes in different supporting conditions.

Vibrational methods to monitor fracture healing, the BRA and the IFR, are compared under different supporting conditions, excitation technique and signal processing. Mode shapes are identified by modal analysis. A wet excised human tibia and an amputation specimen are investigated. Excitation technique and signal processing caused only minor differences in the resonance frequencies. The supporting conditions had an important influence on the single bending modes changing both mode-shapes and frequencies. Thus the BRA-splint imposed a node at the malleolus. Modal analysis revealed the following modes in the two supporting conditions: BRA-splint: A 'rigid body' mode of 165 Hz in the sagittal plane. A single bending mode of 315 Hz close to the sagittal plane. IFR-hanging leg: A 'rigid-body' mode of 167 Hz close to the sagittal plane. Two single bending modes ('free-free'), a mode of 303 Hz close to the frontal plane and a mode of 470 Hz in the sagittal plane.

Biomechanical Phenomena↗
PubMed1986

Assessment of tibial stiffness by vibration testing in situ--II. Influence of soft tissues, joints and fibula.

The influence of soft tissues and joints on the vibration of the human tibia was examined by modal analysis on amputated lower limbs, where the soft tissues and the fibula were dissected gradually. Measurements were made in two different set ups, IFR and BRA, which were both designed to monitor fracture healing. In IFR, vibrations are generated by hammer impact on a relaxed hanging lower leg, with the knee flexed. Resonant frequencies are determined by a computer Fourier transform procedure. In BRA, a steady state vibration is induced in a lower leg, supported near the ankle and the tibial tuberosity, using an electromagnetic shaker. Resonant frequencies are determined from the maxima in vibration amplitudes. In both set ups the soft tissues have a similar influence on the vibration of the tibia: the skin hardly influences the determined modal parameter. The mass of the muscles influences both the resonant frequency and the damping. The fibula has a stiffening effect on the tibia. The influence of the joints is small in the IFR-set up: the tibia vibrates in conditions close to those for the free-free vibration. In the BRA-set up, the supports determine the boundary conditions.

Biomechanical Phenomena↗
PubMed1986

Determination of 99mTc-DTPA clearance by a single plasma sample method.

To derive a formula for determination of 99mTc-DTPA clearance (Cl) from the radioactivity in a single plasma sample, the relation Cl = ECV/t was used, where ECV is the extracellular volume and t is the mean transit time of the tracer in the organism. By studying 99mTc-DTPA time activity curves of 45 consecutive patients we found that ECV could be estimated from the body surface area, and that t could be calculated from the radioactivity in a single plasma sample. Cl calculated by the single sample method was almost identical to Cl calculated by a standard multiple sample method (r = 0.987). It is concluded that the single sample method is accurate and that it may prove useful as a routine method provided that the method is not used in patients with 99mTc-DTPA clearance less than 30 ml min-1, since this investigation includes only patients with Cl greater than 30 ml min-1; the method is not used for children, since the test material did not contain any children; the method is only used for plasma samples drawn at 180 less than or equal to t less than or equal to 300 min.

Adult↗
PubMed1985

Arterial embolism of the legs. A follow-up study of 252 patients.

This retrospective study of 279 embolectomies in 252 patients shows a mortality of 27%, and an amputation rate of 15% within the first month after the embolectomy. The mortality as well as the rate of amputations decreased through the first year. After this period the mortality was comparable to that of a normal population and the rate of amputation was negligible. The mortality rate as well as the number of amputations increased with increasing time-lag of the embolectomy. In addition, the rate of amputation increased with preexisting intermittent claudication. There was no significant difference in amputation rate between limbs with and without palpable pulsations in the groin on admission, but 8 out of 103 limbs without groin pulsations had successful major vascular reconstruction performed after failing embolectomy in contrast to none in the group where pulsations were present. In 28 patients the embolectomy was followed by impairment of renal function and 14 of these died. It is concluded that embolectomy must be performed as early as possible, vascular reconstruction must be considered if the embolectomy fails to revascularize the limb, preventive measures should be taken against renal failure, i.e. the myonephropathic-metabolic syndrome.

Acute Kidney Injury↗
PubMed1983

CdTe-detector registration of 99mTc-DTPA clearance. An assessment of kidney function without blood sampling.

Since the most essential function of the kidneys is to regulate the composition and volume of the extracellular fluids the ratio of the extracellular volume (ECV) to the glomerular filtration rate (GFR) seems to be a relevant index of kidney function. This ratio is equal to the mean transit time (t) of an injected ECV-distributed tracer that is exclusively eliminated from the body by glomerular filtration. In 26 patients t was estimated by means of standard methods after an intravenous injection of 99mTc-DTPA and was found to be correlated (r = 0.98) to the reciprocal final slope of the time-activity curve obtained by means of small CdTe-detectors pasted laterally on the crus, 10-12 cm below the knee joint. It is concluded that this external measurement of kidney function, without blood sampling, may shorten the usual procedure from 4 to 1 h. Furthermore, due to the constant detection geometry throughout the investigation it may provide the means for prolonged continuous monitoring of the kidney function at steady state and when rapid changes are expected.

Adolescent↗
PubMed1980

Experimental nonsuture colonic anastomoses.

A comparative study of sutured colonic anastomoses and anastomoses made by isobutylcyanoacrylate was performed in 60 rats. No difference in the strength of the anastomoses, as expressed by the bursting pressure, was found, and there was no difference in the frequency of adhesions or stenoses, provided the cyanoacrylate was meticulously covered by omentum. Histologic evidence of delayed healing was observed in the cyanoacrylate group; however, this did not seem to reduce the strength of the anastomosis. Provided it is covered with an omental tag, isobutylcyanoacrylate may prove to be a valuable adjunct to conventional suture techniques under special circumstances.

Animals↗
PubMed1977

Bile peritonitis due to spontaneous perforation of the common hepatic duct. Report of a case.

A 55-year-old female, previously cholecystectomized, was admitted to hospital with signs of severe acute abdomen. At laparotomy, bile peritonitis was found, but the site of leakage could not be discovered. The biliary tree was otherwise normal and without stones. The treatment was confined to drainage of the common bile duct by inserting a T-tube. In spite of intensive postoperative care the patient died. Autopsy showed a perforation opening in the common hepatic duct on the posterior wall and a solitary stone was detected in the adjacent retroperitoneal tissue. The mechanism to this rare condition is discussed and a review of earlier similar cases is given. The benefit of routine cholegraphy in order to avoid retained stones is briefly mentioned.

Biliary Tract Diseases↗
PubMed1975

25-Hydroxycholecaliferol and fractures of the proximal.

Plasma 25-hydroxycholecalciferol (25-H.C.C.) has been measured in 67 consective cases of fracture of the proximal femur. The values found in these patients were not different from values found in these patients were not different from those in control groups at the same time of the year. Plasma 25-H.C.C. was not correlated to plasma calcium or phosphorus, the Ca times P product, or the alkaline phosphatase. X-rays showed Looser zones in only 1 patient, in whom the lowest plasma 25-H.C.C. was found. Osteomalacia is not uncommon among elderly people in Denmark, but it is more likely to depend on a decline in the renal efficiency to convert 25-H.C.C. to 1,25-dihydroxycholecalciferol than a low dietary intake of vitamin D.

Adult↗