Artificial neural network discovery of a switchable metasurface reflector.

Optical materials engineered to dynamically and selectively manipulate electromagnetic waves are essential to the future of modern optical systems. In this paper, we simulate various metasurface configurations consisting of periodic 1D bars or 2D pillars made of the ternary phase change material Ge2Sb2Te5 (GST). Dynamic switching behavior in reflectance is exploited due to a drastic refractive index change between the crystalline and amorphous states of GST. Selectivity in the reflection and transmission spectra is manipulated by tailoring the geometrical parameters of the metasurface. Due to the immense number of possible metasurface configurations, we train deep neural networks capable of exploring all possible designs within the working parameter space. The data requirements, predictive accuracy, and robustness of these neural networks are benchmarked against a ground truth by varying quality and quantity of training data. After ensuring trustworthy neural network advisory, we identify and validate optimal GST metasurface configurations best suited as dynamic switchable mirrors depending on selected light and manufacturing constraints.

Effects of clarithromycin, azithromycin and rifampicin on terbutaline-induced sweating in foals.

BACKGROUND: Erythromycin (ERY) induces anhidrosis in foals. Azithromycin (AZI) and clarithromycin (CLA), often combined with rifampicin (RIF), are commonly used to treat Rhodococcus equi infections, but effects on sweating have not been investigated. OBJECTIVE: To determine the effects of AZI, CLA and RIF on sweat responses in normal foals. STUDY DESIGN: Each experiment was a blinded, duplicated, six foal × three period counterbalanced within subjects design (12 foals/experiment). METHODS: Antimicrobials were given orally for 5 days. In Experiment 1, ERY, AZI and CLA were given. In Experiment 2, ERY, RIF and ERY/RIF combination were used. Quantitative intradermal terbutaline sweat tests were performed daily for 3 days before and 1, 2, 5, 9, 24, and 39 days after treatment. Data were analysed by repeated measures analysis of variance procedures. Significance was P≤0.05. RESULTS: In Experiment 1, all macrolides suppressed sweating although CLA and AZI were less potent than ERY. In Experiment 2, significant sweat suppression occurred in foals given ERY with or without RIF, but there was no effect of RIF alone. Rifampicin reduced sweat suppression by ERY on Day 1 of treatment but not thereafter. MAIN LIMITATIONS: Because ERY blood concentrations were not measured, effects of RIF on ERY-induced anhidrosis could not definitively be ascribed to altered ERY bioavailability. CONCLUSIONS: All macrolides commonly used to treat R. equi pneumonia, i.e. ERY, AZI and CLA, induce anhidrosis in foals. The potent anti-sudorific effect of ERY is delayed, but not substantially affected by concurrent RIF administration.

Macrolide-induced hyperthermia in foals: Role of impaired sweat responses.

REASONS FOR PERFORMING STUDY: The mechanism of hyperthermia, a potentially fatal adverse effect of erythromycin treatment of foals, is unknown. OBJECTIVES: To determine the cause of erythromycin-associated hyperthermia. It was hypothesised that the normal sweat response of foals is impaired by treatment with erythromycin. STUDY DESIGN: Blinded, crossover study in 10 healthy pony foals. METHODS: Foals kept in stalls were given either erythromycin (25 mg/kg bwt orally, 3 times daily) or control for 10 days then turned out for a further 10 days. Quantitative intradermal terbutaline sweat tests were performed on Days 1 (baseline), 3, 10 and 20. The effects on terbutaline-induced sweating of erythromycin, terbutaline concentration and treatment day were analysed by repeated-measures ANOVA with Bonferroni-corrected pairwise post hoc comparisons. Peak temperatures were compared by Wilcoxon's signed rank test and proportions by McNemar's related samples test. Significance was set at P<0.05. RESULTS: There were significant 2-factor interactions for treatment × terbutaline after baseline, treatment × day at every terbutaline concentration, and day × terbutaline for erythromycin (P<0.001) but not control (P = 0.9) treatment. Sweating was significantly reduced from baseline in erythromycin-treated foals at all subsequent days. Erythromycin-treated foals produced less sweat at all time-points than did control-treated foals (P<0.05). Peak rectal temperatures of erythromycin-treated foals were significantly higher (P = 0.02) than those of controls. During the first 3 days outside more erythromycin-treated than control-treated foals required treatment for hyperthermia (6 vs. 0; P = 0.03). CONCLUSIONS: We believe drug-induced anhidrosis is the likely cause of hyperthermia in some foals treated with erythromycin.

Effect of GastroGard and three compounded oral omeprazole preparations on 24 h intragastric pH in gastrically cannulated mature horses.

REASONS FOR PERFORMING STUDY: Ulceration of the squamous gastric mucosa is commonly associated with intensive training programmes in horses, but only one compound ('Gastrogard') has been subjected to controlled scrutiny as to therapeutic efficacy. OBJECTIVES: To compare the gastric acid inhibitory efficacy of one manufactured ('GastroGard') and 3 generic pharmacy-compounded preparations of the proton pump inhibitor omeprazole (OME) in the mature horse. HYPOTHESIS: All OME preparations tested would induce a clinically acceptable effect. METHODS: Six healthy mature gastrically cannulated horses of various breeds, 3 mares and 3 geldings, were used. Each product was administered per os once daily (0730 h) at an equivalent dose of 4 mg OME/kg bwt, in a randomised complete repeated measures design for sequence of individual preparation treatment per horse. There was a minimum of 14 days between treatment regimens. A portable unit that recorded pH continuously was attached to a recording electrode fixed within the gastric lumen via the gastric cannula. Three 24 h recordings were made one day before and during Days 2 and 7 after commencement of a 7 day treatment with each of the 4 individual preparations. The horses were fed as usual throughout the study. RESULTS: Only the GastroGard and one other preparation induced a significant increase over baseline in mean percentage of time that the pH was > 4.0 and mean median intragastric pH, during the first 14 and 12 h post treatment respectively, for both Days 2 and 7 post treatment. Both these products had a vehicle pH > 8.0, in contrast to the 2 less effective products, where the vehicle pH was < 6.0. CONCLUSIONS: OME at 4 mg/kg per os s.i.d. can effectively maintain intragastric pH at an accepted anti-ulcerogenic level for at least 12 h post administration in mature horses. In contrast to GastroGard, it should not be expected that all compounded preparations of OME are equally effective in achieving this performance. It appears that vehicle pH might play an important part in determining preparation efficacy. POTENTIAL RELEVANCE: Optimal timing for daily dosing of athletic horses with an effective OME preparation, in order to suppress gastric squamous ulceration, might be 4-8 h prior to a training session.

Histamine-induced gastric acid secretion in horses.

OBJECTIVE: To determine gastric secretory responses in horses treated with histamine and to determine the dose of histamine needed to elicit maximal gastric secretion. ANIMALS: 6 adult horses with an indwelling gastric cannula. PROCEDURE: Gastric contents were collected in 15-minute periods, and volume, pH, hydrogen ion concentration, hydrogen ion output, sodium concentration, and sodium output were determined. Values were determined without any treatment (baseline), after administration of pyrilamine maleate (1 mg/kg of body weight, i.v., given during a 15-minute period), and during 1-hour infusions of histamine at 3 rates (7.5, 15, and 30 microg/kg/h, i.v.). RESULTS: Volume and hydrogen ion concentration of gastric contents and hydrogen ion output were significantly increased, compared with baseline values, during histamine infusion. Mean hydrogen ion concentration and hydrogen ion output were significantly greater during infusion of histamine at a rate of 15 or 30 microg/kg/h than at a rate of 7.5 microg/kg/h. Sodium concentration was significantly decreased, compared with baseline value, during histamine infusion, but sodium output was unchanged. CONCLUSIONS: Histamine at doses of 15 and 30 microg/kg/h, i.v. stimulated maximal gastric secretion in horses. Histamine appeared to induce only parietal secretion. CLINICAL RELEVANCE: This study provides additional information related to equine gastric physiology, which may benefit further understanding of the pathogenesis of peptic ulcer disease.

Effect of xylazine, detomidine, and a combination of xylazine and butorphanol on equine duodenal motility.

OBJECTIVE: To evaluate the effect on equine duodenal motility of some analgesic agents commonly used to treat colic. ANIMALS: 4 healthy adult healthy horses--2 mares and 2 geldings--which were carrying an indwelling gastric cannula made of silastic rubber. One horse also carried 2 long-term indwelling bipolar electrodes that had been sutured onto the duodenum and jejunum. PROCEDURE: To ensure an empty stomach, solid food was withheld from horses for around 20 hours prior to an experiment. Using videoendoscopic guidance, an 8-F catheter with 3 small, discrete pressure sensors was passed through the gastric cannula and directed into the proximal portion of the duodenum. Deflection of the recording pen, to which the catheter was attached, indicated a motile event in that section. Drugs (treatment) were given into the jugular vein in a randomized block design, 1 treatment/experiment, after a 1-hour baseline recording. Treatments were: 2 ml of 0.9% NaCl, xylazine (XYL, 0.5 mg/kg of body weight), detomidine (DET, 0.0125 mg/kg), or a xylazine/butorphanol combination (XYB, 0.5/0.05 mg/kg). Each horse received each treatment twice. All positive pressure peaks > 5 mm of Hg recorded from the most proximal sensor on the catheter were counted in 15-minute blocks. Each mean 15-minute posttreatment value was compared with the baseline value for that specific treatment. RESULTS: There was no significant difference between baseline values. All treatments significantly (P < 0.05) reduced frequency of pressure peaks below their respective pretreatment values, but to variable degrees and durations. Comparatively, XYL had the least effect, with mild, though significant, reduction for only the first 30 posttreatment minutes; DET and XYB caused a significant marked reduction for 1 hour after treatment. CONCLUSIONS: The profound suppressive effect of a routine dose of detomidine or xylazine/butorphanol combination on equine duodenal motility must be considered when using these agents for management of colic, especially when encouragement of intestinal motility is desirable.

Effect of pyloric blockade and infusion of histamine or pentagastrin on gastric secretion in horses.

OBJECTIVE: To determine the origin of the nonacid (nonparietal) component of gastric secretions in horses induced by pentagastrin infusion. ANIMALS: 6 horses. PROCEDURE: A Latin square design was used, involving 6 horses, 3 treatments, and 2 duodenal intubation conditions (catheter with balloon to obstruct pylorus [B] or without balloon allowing movement of contents between stomach and duodenum [NB]). Each horse had an indwelling gastric cannula and a catheter positioned in the duodenum. Gastric and duodenal contents were collected during 15-minute periods. Each experiment consisted of serial collection periods: baseline; infusion of pyrilamine maleate (1 mg/kg of body weight, IV); not treated; and IV infusion of saline (0.9% NaCl) solution alone, saline solution containing pentagastrin (6 microg/kg x h), or saline solution containing histamine (30 microg/kg x h). Volume of samples was recorded, and electrolyte concentrations were measured. RESULTS: Pentagastrin and histamine stimulated maximal acid output; however, during NB conditions, pentagastrin-induced concentration of hydrogen ions was significantly less than during histamine or pentagastrin infusions during B conditions. The large volume produced in response to pentagastrin during NB conditions was accompanied by increased sodium ion output that was greater than for pentagastrin during B conditions, but both values were significantly greater than values for histamine during B or NB conditions. CONCLUSIONS AND CLINICAL RELEVANCE: Nonparietal secretions collected during IV infusion of pentagastrin are duodenal in origin. Reflux of duodenal contents into the stomach of horses is enhanced by pentagastrin. Flow of duodenal contents into the stomach could have implications in the pathogenesis of ulcers in horses.

Effect of omeprazole on sodium and potassium output in pentagastrin-stimulated equine gastric contents.

OBJECTIVE: To better characterize the source of the large nonparietal secretory response to pentagastrin (PG) expressed in gastric contents of cannulated horses. ANIMALS: Adult cross-bred horses: 4 geldings and 1 mare. PROCEDURE: Horses were prepared by surgical insertion of a silastic gastric cannula from which gastric contents after feed was withheld could be continuously collected by gravity drainage. During experiments, the horses were lightly restrained in stocks, the gastric cannula was opened, and a catheter was inserted into a jugular vein. Over the next 5 hours, gastric contents were collected in 15-minute aliquots for which volume, pH, [Na+], and [K+] were measured. During the first hour, treatment was not administered. At the start of the second hour, either 0.5 mg of omeprazole (OME; dissolved in glycerol formal)/kg of body weight, or 0.9% NaCl (PSS) of comparable volume, was given IV at random as a bolus. At the start of the third hour, IV infusion of PG (6 micrograms/ kg/h) was started and continued for the next 2 hours. RESULTS: The response to PG in the PSS-treated horses was similar to that previously seen-significant decrease in pH and increase in volume of gastric contents, and no change in [K+] and [Na+], but a modest volume-related increase in their respective outputs. After OME treatment, pH of the contents increased sharply and remained between 5 and 6 throughout PG infusion. Sodium concentration significantly increased after OME and virtually paralleled the pH response throughout the rest of the experiment; volume of gastric contents significantly increased in response to PG infusion and resulted in a significant increase in Na output. There was no change in K output in OME-treated animals. CONCLUSIONS: PG induces a marked, nonparietal, secretory response into the gastric contents of cannulated horses. The volume and [Na+] of this response was maintained after pretreatment with OME, although the pH of the contents became basic, indicating that this nonparietal response is not mediated by an OME-sensitive proton pump.

Effect of aluminum hydroxide/magnesium hydroxide antacid and bismuth subsalicylate on gastric pH in horses.

OBJECTIVE: To assess the effect of aluminum hydroxide/magnesium hydroxide antacid and bismuth subsalicylate on gastric pH in clinically normal horses and to develop guidelines on the use of these agents for treatment of peptic ulcer disease in horses. DESIGN: Prospective, randomized, controlled trial. ANIMALS: 5 clinically normal adult horses with chronically implanted gastric cannulas. PROCEDURE: Each horse received all 5 treatments (30 g of aluminum hydroxide/15 g of magnesium hydroxide, 12 g of aluminum hydroxide/6 g of magnesium hydroxide, 10.5 g of bismuth subsalicylate, 26.25 g of bismuth subsalicylate, and 5% methylcellulose control) with only 1 experiment performed each day. Gastric pH was measured via a glass electrode inserted through the gastric cannula for 1 hour before treatment and continued for 2 hours after treatment. Food or water was not given to the horses during the experiment. Measurements of gastric pH obtained during posttreatment hours were compared with pretreatment gastric pH values. RESULTS: Only a dose of 30 g of aluminum hydroxide/ 15 g of magnesium hydroxide resulted in a significant increase in gastric pH over baseline or control values. Mean pH was 5.2 +/- 0.62 and 4.59 +/- 0.48 for posttreatment hours 1 and 2, respectively. CLINICAL IMPLICATIONS: Oral administration of 30 g of aluminum hydroxide/15 g of magnesium hydroxide to adult horses should result in a mean hourly gastric pH > or = 4.0 for at least 2 hours.

Systemic, renal, and colonic effects of intravenous and enteral rehydration in horses.

BACKGROUND: Intravenous (IV) and intragastric (IG) administration of fluid therapy are commonly used in equine practice, but there are limited data on the systemic, renal, and enteric effects. HYPOTHESIS: IV fluid administration will increase intestinal and fecal hydration in a rate-dependent manner after hypertonic dehydration, but will be associated with significant urinary water and electrolyte loss. Equivalent volumes of IG plain water will result in comparatively greater intestinal hydration with less renal loss. ANIMALS: Six Thoroughbred geldings. METHODS: Experimental study. 6 by 6 Latin square design investigating constant rate IV administration at 50, 100, and 150 mL/kg/d over 24 hours in horses dehydrated by water deprivation. Equivalent volumes of IG plain water were administered by 4 bolus doses over 24 hours. RESULTS: Water deprivation resulted in a significant decrease in the percentage of fecal water, and increases in serum and urine osmolality. IV fluids administered at 100 and 150 mL/kg/d restored fecal hydration, but increasing the rate from 100 to 150 mL/kg/d did not confer any additional intestinal benefit, but did result in significantly greater urine production and sodium loss. Equivalent 24-hour volumes of plain water resulted in greater intestinal water and less urine output. CONCLUSIONS AND CLINICAL IMPORTANCE: IV polyionic isotonic fluids can be used to hydrate intestinal contents in situations where enteral fluids are impractical. IV fluids administered at three times maintenance are no more efficacious and might be associated with adverse physiological findings after withdrawal. Bolus dosing of IG water can be used to restore intestinal water with minimal adverse effects.

Equine pelvic flexure myoelectric activity during fed and fasted states.

The pelvic flexure is the midpoint of the equine large colon that marks the junction of dorsal and ventral components. Previous studies of intraluminal pressure in this region indicate that it could be an important motility control center. The present study was undertaken to expand our knowledge of normal myoelectric activity around the pelvic flexure region. Eight bipolar silver wire electrodes were surgically fixed at 5-cm intervals to the colonic serosa of five adult horses, starting 30 cm oral to the pelvic flexure on the left ventral colon and ending 15 cm aboral to the pelvic flexure on the left dorsal colon (LDC). Recordings of myoelectric activity were done after feed had been withheld for 20 h or when the horses had been allowed to eat hay up to the time of the recording session. The activity was recorded on a polygraph, digitized, processed through a commercial graphics software package, and stored on magnetic tape for later analysis. Action potential activity was basically separated into long spike bursts (LSB) that were > or = 4 s duration and short spike bursts (SSB) that were < 4 s duration and quantified by a software program developed exclusively for the equine large intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the antisecretory effects of omeprazole when administered intravenously, as acid-stable granules and as an oral paste in horses.

The antisecretory activity of omeprazole on gastric acid when administered i.v., intragastrically or per os, was evaluated in 2 female and 3 castrated male horses. Each horse had been prepared with a chronic indwelling gastric cannula. A single i.v. administration of omeprazole (1.5 mg/kg bwt) was effective in abolishing basal and pentagastrin (PG)-stimulated acid secretion. Once daily, nasogastric administration of omeprazole in acid-stable granules for 5 days inhibited acid secretion in a dose-dependent manner: 57% (1.5 mg/kg bwt) and 98% (5.0 mg/kg bwt) reduction of PG-stimulated acid secretion. The degree of inhibition was maintained over a 19 day treatment period with once daily dosing. A prototype oral paste formulation containing either acid-stable omeprazole granules or uncoated omeprazole powder was equipotent when compared to a similar dosage of acid-stable omeprazole granules administered by nasogastric tube. A dose-dependent inhibition was seen with the oral paste formulation containing omeprazole powder: 55% (1.5 mg/kg bwt) and 77% (3.0 mg/kg bwt) reduction of PG-stimulated acid secretion after 5 days. Therefore, a paste formulation of omeprazole powder may offer an effective, easily administered, once daily acid inhibitory treatment for gastric ulcer disease in horses.