Lumbar dura mater biomechanics: experimental characterization and scanning electron microscopy observations.

UNLABELLED: There is no consensus about the anatomical structure of human dura mater. In particular, the orientation of collagen fibers, which are responsible for biomechanical behavior, is still controversial. The aim of this work was to evaluate the mechanical properties and the microstructure of the lumbar dura mater. We performed experimental mechanical characterization in longitudinal and circumferential directions and a scanning electron microscopy observation of the tissue. Specimens of human dura mater were removed from the dorsal-lumbar region (T12-L4/L5) of six subjects at autopsy; specimens of bovine dorsal-lumbar dura mater were obtained from two animals at slaughter. Human and bovine tissues both exhibited stronger tensile strength and stiffness in the longitudinal than in the circumferential direction. Scanning electron microscopy observations of dura mater showed that the collagen fibers are mainly oriented in a longitudinal direction, which accounts for its stronger tensile strength in this direction. We conclude that dura mater has a different mechanical response in the two directions investigated because the fiber orientation is predominantly longitudinal. IMPLICATIONS: In this experimental work, we studied the structural and functional relationship of human lumbar dura mater. We performed mechanical tests and microscopic observations on dura mater samples. The results show that the dura mater is mainly composed of longitudinally oriented collagen fibers, which account for higher tissue resistance in this direction.

Spinal anesthesia using hyperbaric 0.75% versus hyperbaric 1% bupivacaine for cesarean section.

UNLABELLED: Although 0.75% hyperbaric bupivacaine is commonly administered to provide spinal anesthesia for cesarean section in the United States, in some countries, only the 1% hyperbaric solution of spinal bupivacaine is available. The aim of this study was to compare 0.75% with 1% hyperbaric spinal bupivacaine for cesarean section. In this prospective study, 50 patients undergoing elective cesarean section were randomized to receive a spinal anesthetic with either 1.5 mL of 0.75% bupivacaine (n = 25) or 1.125 mL of 1% bupivacaine (n = 25). There were no statistically significant differences in patient demographics, time to onset of block, or intraoperative pain. All patients had a successful block for surgery. The time from injection of the spinal anesthetic to first request for pain medication in the postanesthesia care unit was longer in the women who received 0.75% bupivacaine (4.3 vs 3 h; P < 0.05). Six women (24%) who received 1% bupivacaine versus one woman (4%) who received 0.75% bupivacaine complained of postoperative backache (P < 0.05). In addition, postdural puncture headache occurred in four women, all of whom received 1% bupivacaine (P = 0.04). In conclusion, our data suggest that 0.75% bupivacaine results in fewer postoperative problems and offers several significant benefits compared with the 1% concentration. IMPLICATIONS: Although 0.75% bupivacaine is usually used to provide spinal anesthesia for cesarean section in the United States, a more concentrated solution is popular in Europe. In this study, we compared 0.75% bupivacaine with 1% bupivacaine when administered for cesarean section and found that the 0.75% solution offers several significant benefits.

[Effects of intravenous diltiazem in acute myocardial infarction: hemodynamic evaluation]. / Effetti del diltiazem per via endovenosa nell'infarto miocardico acuto: valutazione emodinamica.

The acute hemodynamic effects of intravenous Diltiazem were studied in 20 pts. with acute myocardial infarction, admitted to Coronary Care Unit within 24 hours from onset of Symptoms--19 men, 1 woman, aged from 46 to 83 years, 14 with anterior myocardial infarction, 6 with inferior myocardial infarction. All, but one, where at the time of their admission to CCU in first Forrester's hemodynamic subset (CI greater than 2.2 L/min/m2, WP less than 18 mmHg); in the last patient WP was 21 mmHg, CI 2.6 L/min/m2. Hemodynamic measurements were performed before (no drugs with hemodynamic effects were allowed during 4-6 hours before the study protocol) and after the administration of Diltiazem, 0,3 mg/kg i.v. administered in 2 min. (bolus) in 12 patients, Group A. In 8 pts--Group B--the bolus was followed by continuous infusion of Diltiazem at the rate of 5 mcg/Kg/min for three hours. The hemodynamic measurements were repeated: in Group A 2-5-30-60-120 min. after the end of the bolus; in the Group B at the same time as Group A, at the end of infusion (180 min) and 60 min after the end of infusion. Diltiazem induced no significant changes of HR, CVP, WP, CI, LVSWI and Triple product, in both groups of pts., at any time. Systolic and diastolic blood pressure decreased significantly (P less than 0.01) only 2 min. after Diltiazem administration (Group A: SBP 125.0 +/- 15.8----114.0 +/- 16.0 mmHg, DBP 85.4 +/- 6.5----76.6 +/- 10.5 mmHg; Group B: SBP 123.0 +/- 20.0----113.0 +/- 11.0 mmHg, DBP 78.1 +/- 7.0----75.0 +/- 4.9 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)