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Biomedical subjects

L Vallet

Publications and source records attributed to L Vallet.

At least 19 recordsLinked to original sources
PubMed2003

The fatigue strength of compact bone in torsion.

We have conducted a series of fatigue tests on samples of bovine compact bone loaded in cyclic torsion. The fatigue strength (i.e. the range of stress needed to cause failure in a given number of cycles) was found to be lower than the fatigue strength of the same material in compression by more than a factor of two. We also tested intact chicken metatarsals and found a similar reduction in strength compared to compression testing of chicken tibiae. These results were predicted using a theoretical model in which fatigue failure was assumed to be dependent on the growth of microcracks, oriented approximately parallel to the bone's longitudinal axis but having misorientation angles of up to 30 degrees. An effective stress range was derived which is a function of the normal and shear stresses, and thus of the Mode I and Mode II stress intensities experienced by the crack. These results may have important consequences for the understanding of fatigue in bone in vivo; relatively small amounts of longitudinal shear stress, which are often ignored in analysis, may contribute significantly to fatigue failures. This may shed light on the phenomenon of stress fractures and on the need for repair and adaptation in living bone.

Animals↗
PubMed2001

Vocal cord dysfunction after left lung resection for cancer.

OBJECTIVES: To evaluate the prevalence, the impact-related postoperative complications and the risk factors of vocal cord dysfunction (VCD) after left lung resection for cancer. METHODS: From February 1996 to April 1999, a review of prospectively gathered data was performed on 99 consecutive patients who underwent a pneumonectomy (n=50) or a lobectomy (n=49) with a mediastinal lymph node dissection. A fiber optic laryngeal examination was performed preoperatively for all patients and within the first week postoperatively in patients with symptom(s) or sign(s) of VCD or respiratory complications. RESULTS: Thirty-one patients (31%) had a postoperative VCD (group VCD) and 68 (68%) did not (group non-VCD). Mortality rate was 19% in group VCD and 9% in group non-VCD (P=0.13). Group VCD patients developed more pulmonary complications (P=0.014) and cardiac complications (P<0.001) compared to group non-VCD patients. A higher rate of reintubation (P=0.005), pneumonia (P=0.06), arrhythmia (P=0.002), cardiac failure (P<0.001) was noticeable in group VCD and may account for the higher rate of complications in this group. Using multivariate analysis, preoperative radiotherapy (P=0.001) and pneumonectomy (P=0.008) were predictive of postoperative VCD. Hospital stay was 22+/-16 days in group VCD and 13+/-9 days in group non-VCD (P<0.002). CONCLUSION: VCD is a frequent event that can lead to dramatic pulmonary complications. We would recommend to track it and to treat it as early as possible.

Aged↗
PubMed2001

Concomitant type I thyroplasty and thoracic operations for lung cancer: preventing respiratory complications associated with vagus or recurrent laryngeal nerve injury.

OBJECTIVES: We sought to prevent postoperative swallowing disorder, aspiration, and sputum retention in cases of recurrent laryngeal or vagus nerve section occurring during lung cancer resection. METHODS: In 14 of 25 consecutive patients, type I thyroplasty and thoracic operations were performed during the same period of anesthesia. All patients had a preoperative laryngeal computed tomographic scan providing us with indispensable measurements for vocal fold medialization under general anesthesia (ie, without intraoperative phonatory control). Nine remaining patients had a type I thyroplasty delayed from thoracic operations because of intraoperative doubt about laryngeal innervation injury, and 2 did not need a laryngeal operation. Main postoperative records consisted of swallowing ability, respiratory complications, and quality of voice. RESULTS: No swallowing disorder, aspiration, or sputum retention occurred in cases of concomitant laryngeal and thoracic operations. Of these 14 patients, a single case (7%) of major complication (vocal fold overmedialization) occurred and required an early and successful revision thyroplasty; one case of cervical hematoma that did not require surgical drainage was considered a minor complication (7%). Twelve (86%) patients who underwent the concomitant association of both operations were fully satisfied with their quality of voice. CONCLUSIONS: Type I thyroplasty and thoracic operation can be advantageously associated in case of injury to laryngeal motor innervation to prevent postoperative swallowing disability and dramatic respiratory complications.

Adenocarcinoma↗
PubMed1999

Prediction of hypoxemia and mechanical ventilation after lung resection for cancer.

BACKGROUND: Hypoxemia usually occurs after thoracotomy, and respiratory failure represents a major complication. METHODS: To define predictive factors of postoperative hypoxemia and mechanical ventilation (MV), we prospectively studied 48 patients who had undergone lung resection. Preoperative data included, age, lung volume, force expiratory volume in one second (FEV1), predictive postoperative FEV1 (FEV1ppo), blood gases, diffusing capacity, and number of resected subsegments. RESULTS: On postoperative day 1 or 2, hypoxemia was assessed by measurement of PaO2 and alveolar-arterial oxygen tension difference (A-aDO2) in 35 nonventilated patients breathing room air. The other patients (5 lobectomies, 9 pneumonectomies) required MV for pulmonary or nonpulmonary complications. Using simple and multiple regression analysis, the best predictors of postoperative hypoxemia were FEV1ppo (r = 0.74, p < 0.001) in lobectomy and tidal volume (r = 0.67, p < 0.01) in pneumonectomy. Using discriminant analysis, FEV1ppo in lobectomy and tidal volume in pneumonectomy were also considered as the best predictive factors of MV for pulmonary complications. CONCLUSIONS: These results suggest that the degree of chronic obstructive pulmonary disease in lobectomy and impairment of preoperative breathing pattern in pneumonectomy are the main factors of respiratory failure after lung resection.

Adult↗
PubMed1979

The assay of prekallikrein activator in human blood products.

An assay for the determination of prekallikrein activator (PKA) in human blood products is described. Kallikrein released from a prekallikrein substrate preparation by PKA in the sample is determined using the synthetic substrate S-2302 (H-D-Pro-Phe-Arg-pNA). The PKA content of the sample is quantitated by interpolation from a standard line obtained using a reference preparation of plasma protein fraction (PPF). Endogenous kallikrein is estimated and an adjustment made for its contribution to the apparent PKA content of the sample. The results of determinations on a number of PPF, immunoglobulin and coagulation factor preparations are presented and discussed.

Blood Proteins↗
PubMed1979

Gel filtration in Sephadex G200 for the control of preparations of human immunoglobulin.

Gel filtration in Sephadex G200 has been used in the quality control of normal and specific immunoglobulins at the Blood Products Laboratory, Elstree, for more than eleven years. Eluting from a 140 cm column, polymerised and aggregated protein is excluded by the gel, followed in order of elution by fractions containing the IgG dimer and the monomer. After these, smaller protein impurities such as albumin are eluted and then fragments from the proteolytic breakdown of IgG. On a single chromatogram, possibly five distinct peaks may be recorded and their components quantified. Gel filtration in Sephadex G200 provides an alternative to sedimentary boundary ultracentrifugation, by which fragmentation of IgG can be more readily observed. In addition, the fraction containing the polydisperse aggregates excluded by the gel provides an index of adverse treatment of immunoglobulin during preparation and storage.

Chromatography, Gel↗