Ventilatory effects of dexmedetomidine, atipamezole, and isoflurane in dogs.

Dexmedetomidine (DMED) is a novel alpha 2 adrenergic agonist that has been shown to have potent analgesic and anesthetic sparing effects. This study was designed to investigate the effects of DMED, both alone and combined with isoflurane, on resting ventilation, the hypercapnic response, and the hypoxic response in dogs. When given alone, 1 microgram/kg decreased resting ventilation by 22% but at larger doses (10, 20, and 100 micrograms/kg) resting ventilation increased, doubling at 100 micrograms/kg. Doses of 10 micrograms/kg and greater caused a maximum depression of 60% in the slope of the hypercapnic response, but no dose had a significant effect on the hypoxic ventilatory response. A dose of 3 micrograms/kg of DMED reduced isoflurane MAC from 1.3% to 0.37%, and the ventilatory effects of this 1 MAC combination were intermediate between the awake values and those of isoflurane-anesthetized (1.3%) dogs. Atipamezole is a specific centrally acting alpha 2 receptor antagonist and when given with DMED in isoflurane-anesthetized dogs prevented the ventilatory depression. However, atipamezole alone also ventilatory stimulating effects, which may indicate tonic alpha 2 adrenergic activity. The ventilatory depression caused by DMED, either alone or combined with isoflurane, at doses that significantly reduce anesthetic requirements are relatively mild.     

A novel, biodegradable polymer conduit delivers neurotrophins and promotes nerve regeneration.

OBJECTIVE/HYPOTHESIS: A wide variety of substances have been shown to promote neuritic extension after nerve injury. An obstacle to achieving the maximal benefit from these substances has been the difficulty in effectively delivering the substances over a protracted time course that promotes maximal, directed growth. In this study the delivery of a growth-promoting substance through a biodegradable conduit, using materials originally designed for drug delivery applications, was hypothesized to promote more robust neural regeneration than through conduits lacking the substance. The objectives of this study were to create a growth factor-loaded biodegradable nerve guidance conduit, and to assess in vivo nerve regeneration through the conduit compared with that through conduits lacking the substance. MATERIALS/METHODS: Inosine, a purine analogue thought to promote axonal extension following neural injury, was loaded into cylindrical polymer foams composed of a polylactide-co-glycolide copolymer. First, in vitro extravasation of inosine was measured over a several week period using spectrophotometry. Second, the foams were fashioned into single-channel cylindrical nerve guidance conduits via a novel, low-pressure injection molding technique. The conduits were then used to bridge 7-mm defects in the rat sciatic nerve (n = 8). Control conduits lacking inosine were implanted into another set of animals as controls (n = 12). RESULTS: In vitro spectrophotometric measurements indicated appreciable leaching of inosine from the loaded foams over a period of at least 9 weeks. In the in vivo model, after 10 weeks, a higher percentage cross sectional area composed of neural tissue existed through the inosine-loaded conduits compared with controls (mean 44%, SD 7.5% vs. 36%, SD 8.6%, respectively). A difference was also found in mean fiber diameter between the two groups, with the inosine-loaded tubes showing a statistically significantly larger diameter than controls (P < .05). CONCLUSIONS: A nerve regeneration conduit was successfully created that delivers growth promoting substances over a protracted time course. In an in vivo model, the presence of inosine, a purine analogue, yielded neural regeneration whose histological features suggest possible superior long-term motor function.     

Estimation of fetal weight with the use of head, body, and femur measurements--a prospective study

In utero estimates of fetal weight were evaluated prospectively in 109 fetuses with the use of sonographic models developed in a previous study. This report confirms that the best in utero weight estimates result from the use of models based on measurements of head size, abdominal size, and femur length. Since the accuracy of these models (1 SD = 7.5%) is significantly better than those based on measurements of head and body (e.g., biparietal diameter, abdominal circumference), we recommend routine use of such models in obstetric sonography.     

Mathematic modeling of fetal growth: development of individual growth curve standards

To provide a more precise means for monitoring individual fetal growth and to improve the detection of growth abnormalities, the Rossavik growth model [P = c(t)k + s(t)] has been used to establish individual growth curve standards. A longitudinal study of the growth of one-dimensional (biparietal diameter, head, and abdominal circumferences), two-dimensional (head and abdominal profile areas), and three-dimensional (head and abdominal volumes) parameters in 18 normal fetuses has revealed that the growth of all parameters can be well-described by the Rossavik model (R2: 97.2 to 99.5%). Strong statistical evidence was obtained indicating that the coefficient k is principally a geometric coefficient having a value determined primarily by the dimension of the parameter being studied. It was also found that the coefficients c and s can be estimated from the data obtained before 28 weeks' conceptual age. Individual growth curve models derived from data obtained before 28 weeks were capable of predicting growth beyond 28 weeks. These models provide growth curve standards for evaluating individual fetal growth beyond 28 weeks.     

Sonographic estimation of fetal weight. The value of femur length in addition to head and abdomen measurements

Sonographic estimation of fetal weight in utero was performed in 167 live-born fetuses examined within one week of delivery. Regression models were based on measurements of abdominal circumference, head circumference, biparietal diameter, and femur length, both alone and in combination. The best results (1 S.D. = 7.5% of actual weight) were obtained by combining measurements of the fetal head, abdomen, and femur, most likely due to the strong linear relationship between femur length and crown-heel length.     

A date-independent predictor of intrauterine growth retardation: femur length/abdominal circumference ratio

The relation between sonographically measured fetal femur length and abdominal circumference (expressed as femur length/abdominal circumference X 100) was studied in 361 normal pregnancies between 15 and 42 weeks. This ratio was found to be independent of menstrual age, with a normal range after 21 weeks (mean +/- 2 SD) of 22 +/- 2. This ratio also was evaluated as a predictor of intrauterine growth retardation in 30 cases using the 90th percentile (23.5) as the upper limit of normal, which resulted in identification of 63% of the growth-retarded fetuses. Because it is independent of menstrual age, this ratio should prove most useful in evaluating high-risk patients who present in the third trimester of pregnancy with no dates. It is also of value in detecting growth retardation in patients with good menstrual history, since it was shown to become abnormal in asymmetrically growth-retarded fetuses before the estimated weight fell below the 10th percentile.     

Baiting the cross-face nerve graft with temporary hypoglossal hookup

BACKGROUND: Cross-face nerve grafting yields inconsistent neural regeneration, and methods that promote more robust axonal traversing of the graft would expand the indications for this procedure. OBJECTIVE: To test the hypothesis that hooking a cross-face nerve graft distally to a source of denervated muscle, rather than leaving it in the subcutaneous space, would positively affect neural ingrowth across the graft, based on elaboration of neurotrophins from the musculature. METHODS: Twenty-four rats underwent cross-face nerve grafting in which the right facial nerve buccal branch was transected and coapted to the graft. The graft was placed across the neck and into the left side of the face. The distal end of the graft was placed either in the left subcutaneous space, coapted to the marginal mandibular branch of the left facial nerve, or coapted to the distal stump of the transected left hypoglossal nerve. Eight control animals underwent right buccal branch transection and placement of a cross-face nerve graft without any proximal and distal hookup. After 12 weeks, all experimental groups underwent hookup of the distal nerve graft to the left facial nerve buccal branch. Vibrissal function was assessed during the ensuing 12 weeks, and then the graft was harvested for histomorphometric analysis. RESULTS: After 12 weeks, there was a significant difference in axon counts between the group coapted distally to the tongue (hypoglossal hookup) and that coapted to the facial musculature (marginal hookup). Twelve weeks later, after distal cross-face nerve graft hookup, this difference was not statistically significant, although the hypoglossally baited group demonstrated statistically significantly greater fiber maturity. Recovery of vibrissal movement did not differ among treatment groups. CONCLUSION: Baiting the cross-face nerve graft via temporary hookup to the distal hypoglossal nerve and tongue musculature appears to improve nerve ingrowth through a nerve graft across the face, although a corresponding improvement in facial muscle function was not observed.