PubMed Health⌕ Search

Biomedical subjects

K S Jensen

Publications and source records attributed to K S Jensen.

At least 19 recordsLinked to original sources
PubMed1992

Standardization of tibial fractures in the rat.

The influence of the fracture level on the biomechanical properties of healing rat tibial fractures has not been investigated so far, despite the widespread use of rats in fracture healing studies. Fractures were produced in four different zones in the right rat tibia and immobilized with a K-wire. A fifth group of rats was not fractured. After 40 days of healing the fractures and the non-fractured bones were tested in three-point bending. A distinct correlation was found between fracture level and mechanical parameters: maximum load, maximum stiffness, and maximum stress decreased the more distal the fracture was located. In the non-fractured bones, maximum load and maximum stress were constant in all four zones tested, whereas energy absorption increased in the distal part of the tibia. No influence of the healing fracture was found on the contralateral, non-fractured tibia, compared with the animals left undisturbed, and the mechanical properties of the right and the left tibia were found to be symmetrical in terms of mean values. Four different methods of determining the area moment of inertia were investigated, and the simple method of approximating the cross section to an elliptical annulus was found to correlate well with the area moment of inertia, determined from computer tracings of bone slices prepared from the test specimens after the bending test. The computer tracings were corrected for the compression of the specimens caused by the mechanical test.

Animals↗
PubMed1992

Rapid onset of hypoxic vasoconstriction in isolated lungs.

A fast-response O2 analyzer that samples air at low flow rates allows the quasi-instantaneous measurement of O2 concentration change in the airways of isolated blood-perfused rat lungs. This instrument and an oximeter were used to measure the stimulus-response delay time of hypoxic pulmonary vasoconstriction when the lungs were challenged with 10, 5, or 3% O2. The estimate for the shortest delay time between accomplished fall in airway O2 concentration and the onset of hypoxia-induced vasoconstriction was approximately 7 s. We found that the slope of pressure rise, but not the stimulus-response delay time, correlated with the magnitude of hypoxic vasoconstriction. Oscillations in pulmonary arterial pressure were observed when the lungs were challenged with 10% O2 but not when the challenge was 12, 5, or 3%, indicating perhaps that these oscillations were a threshold phenomenon. Established hypoxic vasoconstriction was sensitive to brief changes in airway O2 concentration. Vasodilation occurred when the gas mixture was switched from 3 to 21% O2 for two to five breaths, and vasoconstriction occurred when the gas was changed during a single breath from 5 to 3% O2.

Animals↗
PubMed1990

A model of vertebral trabecular bone architecture and its mechanical properties.

An idealized, structural model of vertebral trabecular bone is presented. The architecture of the model (thick vertical columns and thinner horizontal struts) is based on studies of samples taken from the central part of vertebral bodies from normal individuals aged 30 to 90 years. With trabecular diameters and spacings typical for persons aged 40, 60, and 80 years respectively, the model accounts reasonably well for age-related changes in vertical and horizontal stiffness and trabecular bone volume, as seen in experimental data. By introducing a measure for the randomness of lattice joint positions in the modeled trabecular network, it is demonstrated that the apparent stiffness varies by a factor of between 5 and 10 from a perfect cubic lattice to a network of maximal irregularity, even though trabecular bone volume remains almost constant. A considerable change in mechanical behaviour is also seen, without changing the overall trabecular bone volume, when the bone material is slightly redistributed among vertical and horizontal trabeculae. It is concluded that measured bone mass should not be the sole indicator of trabecular bone biomechanical competence (stiffness and stress). It is crucial that measurements of bone density are considered in combination with a detailed description of the architecture.

Adult↗
PubMed1989

Modeling absorption kinetics of subcutaneous injected soluble insulin.

Absorption of subcutaneously injected soluble insulin deviates markedly from simple first-order kinetics and depends both on the volume and concentration of the injected solution. This paper presents a model of the absorption process in which insulin is presumed to be present in subcutis in a low molecular weight form, a high molecular weight form, and an immobile form where the molecules are bound to the tissue. The model describes how diffusion and absorption gradually reduce the insulin concentrations in the subcutaneous depot and thereby shift the balance between the three forms in accordance with usual laws of chemical kinetics. By presuming that primarily low molecular weight insulin penetrates the capillary walls, the model can account for experimentally observed variations in the absorption rate over a wide range of volumes and of concentrations. The model is used to determine the effective diffusion constant D for insulin in subcutis, the absorption rate constant B for low molecular weight insulin, the equilibrium constant Q between high and low molecular weight insulin, the binding capacity C for insulin in the tissue, and the average life time T for insulin in its bound state. Typical values for a bolus injection in the thigh of fasting type I diabetic patients are D = 0.9 x 10(-4) cm2/min, B = 1.3 X 10(-2)/min, and Q = 0.13 (ml/IU)2. Binding of insulin in the tissue is significant only at small concentrations. The binding capacity is of the order of C = 0.05 IU/cm3 with a typical average life time in the bound state of T = 80.0 min. Combined with a simplified model for distribution and degradation of insulin in the body, the absorption model is used to simulate variations in plasma free insulin concentrations with different delivery schedules, i.e., bolus injection and dosage by means of an infusion pump. The simulations show that a pump repetition frequency of 1-2 per hr is sufficient to secure an almost constant plasma insulin concentration.

Absorption↗
PubMed1983

Lignocaine test and detrusor instability.

Detrusor instability in infravesical obstruction is well recognised and often resolves after surgery. The aetiology is not clearly understood but is probably due to increased vesical sensory input. Since intravesical lignocaine has been proved to have an effect (although shortlived) on detrusor instability in some patients, we have used it in order to differentiate between idiopathic detrusor instability and detrusor instability caused by infravesical obstruction. Our study showed that in patients with a positive lignocaine test pre-operatively, the detrusor instability and micturition disorder disappeared after operation, and in patients with a negative lignocaine test, it persisted. The differences were statistically significant (P less than 0.5).

Aged↗
PubMed1983

Improvement of detrusor instability following repeated bladder distension with cystomat. A case report.

Treatment of idiopathic detrusor instability with drugs and prolonged distension of the bladder is often unsatisfactory. Some amelioration of symptoms was previously described after 24-hour bladder distension with use of the cystomat. A case is presented in which detrusor instability was successfully treated with continuous infusion via the cystomat, and thereby repeated bladder distension, for one week. The symptoms subsided, the cystometric bladder capacity was increased and there was no side effects. The improvement has persisted for six months. Though the mechanism by which the bladder distension exerts its effect is poorly understood, the technique of repeated distension offers an alternative in the treatment of patients with idiopathic detrusor instability.

Aged↗