Biomedical subjects

A Vasavada

Publications and source records attributed to A Vasavada.

25 records · Page 2Linked to original sources

PubMed1994

Disc degeneration affects the multidirectional flexibility of the lumbar spine.

STUDY DESIGN: An in vitro biomechanical investigation using human lumbar cadaveric spine specimens was undertaken to determine any relationship between intervertebral disc degeneration and nonlinear multidirectional spinal flexibility. SUMMARY OF BACKGROUND DATA: Previous clinical and biomechanical studies have not established conclusively such a relationship. METHODS: Forty-seven discs from 12 whole lumbar spine specimens were studied under the application of flexion-extension, axial rotation, and lateral bending pure moments. Three flexibility parameters were defined (neutral zone (NZ), range of motion (ROM), and neutral zone ratio (NZR = NZ/ROM)) and correlated with the macroscopic and radiographic degeneration. RESULTS AND CONCLUSIONS: In flexion-extension, the ROM decreased and NZR increased with degeneration. In axial rotation, NZ and NZR increased with degeneration. In lateral bending, the ROM significantly decreased and the NZR increased with degeneration. In all three loading directions, the NZR increased, indicating greater joint laxity with degeneration.

Adult↗

PubMed1994

Anular incision technique on the strength and multidirectional flexibility of the healing intervertebral disc.

STUDY DESIGN: This study used a sheep model to biomechanically analyze the healing strength of the anulus fibrosus after two types of anular incisions. OBJECTIVE: This study evaluated whether the type of anular incision made at the time of lumbar discectomy plays a role in the subsequent healing strength of the anulus and the biomechanical flexibility of the corresponding motion segment. METHODS: Two types of anular incision, a full thickness removal of a box or window of anulus and a full thickness straight transverse slit through the anulus, were made in the intervertebral discs of 18 adult sheep. After healing times of 2, 4, and 6 weeks, the intervertebral discs were tested versus control levels for strength of anular healing and biomechanical flexibility of the corresponding motion segment. RESULTS: The box incised discs showed a significantly greater loss in strength during the early healing phase (2 to 4 weeks) and a longer response before recovering anular strength when compared with the slit-incised discs. The type of incision also affected the multidirectional flexibility of the motion segments in a differentiated manner. Larger amounts of motion were seen with the box incision when compared with the slit incision at all time periods and in all pure moments. CONCLUSION: The technique of anular incision plays a definite role in the timing and strength of subsequent anular healing. The box incision through the anulus led to significantly weaker healing than did the slit incision in the early healing phase (2-4 weeks). Also, larger amounts of motion were seen in the vertebral motion segments of those discs undergoing box incision when compared with slit or control levels.

Animals↗

PubMed1994

Intraocular lens implantation in infants with congenital cataracts.

We evaluated 21 eyes of 13 infants between two and eight months old who had primary posterior chamber intraocular lens (IOL) implantation for congenital cataracts between 1988 and 1993. Twelve eyes had a posterior capsulorhexis or plaque peeling at the time of implantation and one eye had a vitrectomy. Eight eyes had no posterior capsule procedure during the initial surgery. Follow-up ranged from six months to five years. All eyes developed one or multiple posterior synechias and all, except one, required secondary capsulectomy and vitrectomy between one month and one year. Twenty eyes attained stable IOL fixation and a clear visual axis. In one eye, the IOL decentered downward. Patients with bilateral cataracts had greater visual improvement than those with a cataract in one eye only. No patient could manage spectacles postoperatively. Our findings show the benefits of posterior capsulectomy and anterior vitrectomy done in the early postoperative period and that IOL implantation in infants is a reasonable treatment in some parts of the world.

Cataract↗

PubMed1994

Kinematics of the cervical spine canal: changes with sagittal plane loads.

Spondylotic myelopathy is a result of decreased spinal canal space due to degeneration. The space also may change with physiological movements. The knowledge of the normal physiological changes is necessary for a better understanding of the clinical symptoms. Using a novel technique, we measured the changes in disk bulge, ligamentum flavum bulge, and anteroposterior canal diameter in response to tension-compression forces (up to 40 N each) and combined loading: 2 Nm of flexion or extension moment combined with 20 N compression force in five human cadaveric lower cervical spine specimens (C4-C7). From tension to compression, the average disk bulge changed 1.13 mm or 10.1% of the original canal diameter. The ligamentum flavum bulge changed 0.73 mm or 6.5% of the canal diameter. From flexion to extension the average disk bulb changed 1.16 mm or 10.8% of the canal diameter, whereas the ligamentum flavum bulge changed 2.68 mm or 24.3% of the canal diameter. Most of the changes in the bulges occurred with a small load application around the neutral position of the spine. The results of this study demonstrate that ligamentum flavum bulge can contribute significantly to canal encroachment in extension and that a flexed posture increases the sagittal diameter of the spinal canal.

Aged↗

PubMed1994

[The unstable spine--an "in vitro" and "in vivo study" on better understanding of clinical instability].

In cases of suspected painful instability of a cervical segment, temporary external fixation by means of external fixator was applied. The segmental immobilization caused immediate relief of pain. The pain reoccurred after removal of the immobilization. The effect of immobilization by external fixation was investigated in biomechanical tests using fresh cadaveric C4-7 specimens. Multidirectional flexibility was measured before and after application of the fixator at C4/C5, C5/C6 and C4-6. We measured the reduction in motion between the different segments. In every situation the neutral zone decreased more than the range of motion. The findings are helpful to understand the clinical instability of the spine and support the hypothesis that the neutral zone is more closely associated with clinical instability than range of motion. The combination of clinical application and biomechanical investigation allowed us to establish a direct correlation between instability and pain.

Accidents, Traffic↗

PubMed1991

Fermentation of a yeast producing A. niger glucose oxidase: scale-up, purification and characterization of the recombinant enzyme.

We have developed a fermentation process to produce up to 3 grams per liter of active, secreted glucose oxidase from a recombinant Saccharomyces cerevisiae. Real-time size-exclusion HPLC analysis is used to monitor enzyme production during fermentation, and purification to more than 95 percent is obtained using only filtration methods. The recombinant enzyme is stable to higher temperatures and a wider pH range than the native Aspergillus niger enzyme, and is free of contaminating amylase, cellulase and catalase.

Aspergillus niger↗

PubMed1990

Glucose oxidase from Aspergillus niger. Cloning, gene sequence, secretion from Saccharomyces cerevisiae and kinetic analysis of a yeast-derived enzyme.

The gene for Aspergillus niger glucose oxidase (EC 1.1.3.4) has been cloned from both cDNA and genomic libraries using oligonucleotide probes derived from the amino acid sequences of peptide fragments of the enzyme. The mature enzyme consists of 583 amino acids and is preceded by a 22-amino acid presequence. No intervening sequences are found within the coding region. The enzyme contains 3 cysteine residues and 8 potential sites for N-linked glycosylation. The protein shows 26% identity with alcohol oxidase of Hansenuela polymorpha, and the N terminus has a sequence homologous with the AMP-binding region of other flavoenzymes such as p-hydroxybenzoate hydroxylase and glutathione reductase. Recombinant yeast expression plasmids have been constructed containing a hybrid yeast alcohol dehydrogenase II-glyceraldehyde-3-phosphate dehydrogenase promoter, either the yeast alpha-factor pheromone leader or the glucose oxidase presequence, and the mature glucose oxidase coding sequence. When transformed into yeast, these plasmids direct the synthesis and secretion of between 75 and 400 micrograms/ml of active glucose oxidase. Analysis of the yeast-derived enzymes shows that they are of comparable specific activity and have more extensive N-linked glycosylation than the A. niger protein.

Amino Acid Sequence↗