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Biomedical subjects

L J Larsen

Publications and source records attributed to L J Larsen.

13 recordsLinked to original sources
PubMed1992

Separation of bile vesicles and micelles by gel filtration chromatography: the importance of the intermicellar bile salt concentration.

Micelles and vesicles coexist in native bile. Mixed micelles are composed of bile salt, phospholipid, and cholesterol. Micellar bile salt is in equilibrium with the aqueous phase bile salt (intermicellar bile salt), and mixed micelles can be converted to cholesterol-phospholipid vesicles by depletion of bile salt. To determine the amount of cholesterol carried in vesicles and micelles, these two populations must be separated without altering the relative proportion of each. Based on the size difference between micelles and vesicles, gel filtration chromatography has been used to accomplish this separation. We reasoned that to maintain the proportion of micelles and vesicles in bile, the column must be equilibrated and eluted with buffer containing the intermicellar bile salt concentration (IMBC) and species. To test this hypothesis we created a model bile composed exclusively of micelles, a solution containing micelles and vesicles, and a model bile containing all vesicles, as demonstrated by quasielastic light scattering. Gel filtration on Sepharose 4B demonstrated that model vesicles and micelles could be separated on a column eluted with buffer containing bile salt at the IMBC. However, a modest decrease in the buffer bile salt concentration (less than 1 mmol/L) resulted in complete conversion of micelles to vesicles. A comparable increase in the buffer bile salt concentration converted vesicles to micelles. Using only taurocholate in the eluting buffer at the IMBC caused a complete shift of micelles to vesicles, whereas using only taurochenodeoxycholate resulted in conversion of vesicles to micelles. An initial collection of rat bile separated on a column equilibrated with the measured IMBC demonstrated that 94% of the cholesterol was in the micellar fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Role of the posterior calf muscles in normal gait.

The role of the calf muscles during the single-limb stance phase of gait was assessed in fifteen normal subjects and in seven with either an amputation or a neuromuscular deficit. Normal activity of the muscles, paralysis by nerve blocks, and stability versus instability of the ankle were studied. Pelvic displacement and velocity, step length, and step time were evaluated for each limb during the gait cycle, and the contribution of activity of calf muscles to each was determined. Limb-segment position, lower-limb joint angles, over-all cadence, velocity, and stride length were measured to reveal compensatory mechanisms in the absence of muscle strength in the calf. The results indicate that the force produced by activity of calf muscles is used to restrain the body's own forward momentum and not used to propel it further. Absence of the calf muscle causes an immediate compensatory reaction directed toward maintaining over-all stability rather than speed.

Adolescent↗
PubMed1975

Rectus femoris release in selected patients with cerebral palsy: a preliminary report.

Two theories concerning the effects of surgical release of the proximal origins of the rectus femoris in spastic patients are (1) that release reduces hip flexion contracture and lumbar lordosis and diminishes crouch, and (2) that release primarily enhances early swing-phase knee flexion. A series of eight patients with pre-operative electromyography and pre- and post-operative dynamic knee measurements are reviewed. In these patients, back-knee thrust did not improve because it was not caused by rectus contracture. The effect upon hip was also variable: two patients had increased hip flexion and a third had diminished hip flexion after release. In six of the eight patients knee flexion was improved in early swing phase. Improvement from surgery can be expected when rectus spasticity is sufficient (1) to interfere with the initiation of swing phase, and (2) to decrease the amplitude of knee flexion. Little change occurred in the patients who did not have these functional deficits. A review of the cases supports the primary knee effect theory of Silfvenskiöld; however, insufficient information was obtained from this series to rule out hip and pelvic changes.

Adolescent↗
PubMedDate not supplied

Recurrent hip dislocation in intermediate spinal atrophy.

Recurrent hip dislocation after corrective orthopaedic surgery in children and teenagers with intermediate spinal atrophy has not been reported in the literature. Four cases with long-term follow-up are presented. These represent the only cases surgically treated in 30 years of following spinal atrophy patients. Thus, it seems significant that all hips redislocated after the surgical procedure. In addition, two patients had second operations with subsequent dislocation. Pelvic obliquity should not be the basis for the surgery, as spinal fusion is generally necessary for wheelchair users. The sagacity of performing surgery for hip dislocations is raised.

Adolescent↗