Ultrasound-Assist Extrusion Methods for the Fabrication of Polymer Nanocomposites Based on Polypropylene/Multi-Wall Carbon Nanotubes

Isotactic polypropylenes (iPP) with different melt flow indexes (MFI) were used to fabricate nanocomposites (NCs) with 10 wt % loadings of multi-wall carbon nanotubes (MWCNTs) using ultrasound-assisted extrusion methods to determine their effect on the morphology, melt flow, and electrical properties of the NCs. Three different types of iPPs were used with MFIs of 2.5, 34 and 1200 g/10 min. Four different NC fabrication methods based on melt extrusion were used. In the first method melt extrusion fabrication without ultrasound assistance was used. In the second and third methods, an ultrasound probe attached to a hot chamber located at the exit of the die was used to subject the sample to fixed frequency and variable frequency, respectively. The fourth method is similar to the first method, with the difference being that the carbon nanotubes were treated in a fluidized air-bed with an ultrasound probe before being used in the fabrication of the NCs with no ultrasound assistance during extrusion. The samples were characterized by MFI, Optical microscopy (OM), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), electrical surface resistivity, and electric charge. MFI decreases in all cases with addition of MWCNTs with the largest decrease observed for samples with the highest MFI. The surface resistivity, which ranged from 10¹³ to 10⁵ Ω/sq, and electric charge, were observed to depend on the ultrasound-assisted fabrication method as well as on the melt flow index of the iPP. A relationship between agglomerate size and area ratio with electric charge was found. Several trends in the overall data were identified and are discussed in terms of MFI and the different fabrication methods.     

Relationship Between Exhaled Carbon Monoxide and Airway Hyperresponsiveness in Asthmatic Patients

The study objectives were to analyze the changes in exhaled carbon monoxide (COex) induced by histamine provocation challenge in asthmatic patients and to evaluate the relationship between COex and airway sensitivity and reactivity. Levels of COex were measured in 105 nonsmoking mildly asthmatic subjects before and after histamine provocation challenge. Dose-response curves were characterized by their sensitivity (PD₂₀) and reactivity. Dose-response slope (DRS), continuous index of responsiveness (CIR), and bronchial reactivity index (BRI) were determined as reactivity indices. Bronchial challenge was positive for 47 subjects and negative for 58. The COex levels rose significantly after bronchial challenge in the positive response group (4.49 ± 0.4 vs. 5.74 ± 0.57 ppm, p = 0.025) and in the negative response group (2.84 ± 0.25 vs 4.00 ± 0.41 ppm, p = 0.000). An inverse relation between basal COex and PD₂₀ was found (r = - 0.318, p = 0.030). In all subjects, a proportional direct relationship between COex and DRS (r = 0.214, p = 0.015), CIR (r = 0.401, p = 0.000), and BRI (r = 0.208, p = 0.012) was observed. On stepwise multiple linear regression analysis, COex only significantly correlated with CIR (multiple r² = 0.174, p = 0.000). In conclusion, exhaled CO determination is a noninvasive inflammatory marker of the respiratory tract, which shows an acceptable association with airway hyperresponsiveness.     

Carbon Monoxide Mass Exposure in a Pediatric Population

Abstract. Objectives:To describe the outcomes of a mass carbon monoxide (CO) intoxication, and to calculate the CO half-life in a pediatric school-aged population.
Methods:A retrospective chart review was performed based on Regional Poison Center database information, hospital laboratory data, and medical records of the pediatric patients who sought care at one of 3 St. Louis area hospitals, after exposure to high levels of CO. Exposures occurred on January 5, 1996, after evidence of a CO leak was discovered at an area elementary school. Charts were reviewed for major demographics, symptoms reported, carboxyhemoglobin (COHb) levels and times, and level of effect.
Results:Information about 177 (35%) of the 504 children in attendance at school that day was available. Mean age was 8.7 ± 1.8 years (range 4–12 years). Symptoms were present in 155 (88%) of the 177 children for whom data were available. Initial COHb levels were obtained for 147 (83.1%) of the 177 children. First mean COHb level was 7.0% (95% CI = 6.6–7.5%). Second COHb level was obtained for 26 children with a mean of 2.7% (95% CI = 2.2–3.2%). Calculated half-life of COHb, on 100% 0₂ at 1 atm, was 44.0 minutes (95% CI = 39.6–48.2 minutes).
Conclusion:Some children had symptoms at COHb levels that traditionally have been considered nontoxic. The elimination of COHb was found to be more rapid in this population of children than reported in other studies.     

Carbon dioxide recruitment threshold as a predictor of successful weaning in chronic obstructive pulmonary disease patients: A pilot study

Abstract Several methods have been used to predict successful weaning and extubation among chronic obstructive pulmonary disease (COPD) patients. The objective of this study is to determine whether carbon dioxide recruitment threshold (PCO₂RT) can be used as adjunct to conventional weaning parameters to predict early weaning and successful extubation. Twelve COPD patients who were ready to be extubated based on conventional weaning parameters were divided into group A ( n = 7) and group B ( n = 5). Group A were those patients with better weaning parameters and hence a higher probability of successful extubation as compared to group B. Carbon dioxide apnoeic threshold (PCO₂AT) was obtained by hyperventilating the patient using an increment of two breaths per min until apnoea occurs. At this point, the PCO₂AT or the PaCO₂ during said apnoeic period was recorded. A dead space of 150 cc is then added to the circuit until the patient starts to breathe as evidenced by the sensitivity trigger indicator. The PCO₂ obtained at this period is termed PCO₂RT. After weaning for 30 min on a T-tube, another arterial blood gas is determined and this is called the PCO₂SB or the CO₂ level after 30 min on spontaneous breathing. If the PCO₂SB-PCO₂RT difference is high with a sensitivity of 85.71% and specificity of 100% vs sensitivity of 57.14% and specificity of 60% using the conventional weaning parameters. Thus an increase in PCO₂SB at 30 min T-tube is indicative of impending respiratory pump failure and that other causes of failure to wean must be investigated.     

Carbon blacks as EPR sensors for localized measurements of tissue oxygenation.

New electron paramagnetic resonance (EPR) oximetry probes were identified in the class of carbon black materials. These compounds exhibit very high oxygen sensitivity and favorable EPR characteristics for biological applications. At low pO(2), the linewidth is particularly sensitive to changes in oxygen tension (sensitivity of 750 mG/mmHg). The application of the probes for oximetry was demonstrated in vivo: the pO(2) was measured in muscle in which the blood flow was temporarily restricted as well as in tumor-bearing mice during a carbogen breathing challenge. The responsiveness to pO(2) was stable in muscle for at least 3 months. No toxicity was observed using these materials in cellular experiments and in histological studies performed 2, 7, and 28 days after implantation. In view of their EPR characteristics (high sensitivity) as well as the well-characterized production procedure that make them available on a large scale, these probes can be considered as very promising tools for future developments in EPR oximetry.     

Do Electrode and Lead Design Differences for Permanent Cardiac Pacing Translate into Clinically Demonstrable Differences? (Comparison of Sintered Platinum and Activated Vitreous and Porous Carbon Electrodes)

A randomized prospective study was undertaken to compare the electrical performances of three permanent, endocardial, tined pacing leads with different electrode designs--sintered platinum, vitreous carbon, and porous carbon. Ninety-nine patients received one of the leads (S80 31; 423S 32; S100 36). Acute R wave amplitude and ST elevation of the native endocardial electrogram, voltage threshold, impedance, and current flow at four pulse durations (0.25-1.0 msec) were measured. Voltage thresholds were measured noninvasively at each of four pulse durations at 2 days and 1, 3, and 6 months after implantation. No significant differences were found in sensing properties, or current flow at threshold at 0.5 msec pulse duration. The 423S lead had a significantly higher impedance at threshold and both a higher impedance and lower current flow at 5 V. No significant differences in threshold voltages were found between the three leads at any pulse duration, at any of the assessed times after implantation. Six-month thresholds for the S80, 423S, and S100 leads were 1.18 +/- 0.35, 1.17 +/- 0.29, and 1.06 +/- 0.38 V respectively at 0.5 msec pulse duration. Differences between 'high performance' pacing leads need to be of a greater order of magnitude before they can be exploited to give any real clinical advantage to patients.     

儿茶酚胺类药物对感染性休克兔胃肠灌注的影响

Objective To assess the effects of dopamine,dobutamine and norepinephrine on the P(g-a)CO2 and superior mesenteric blood flow in septic shock.Methods Rabbit septic shock model was established by challenging with intravenous injection of lipopolysaccharides from Escherichia coil(2 mg/kg).The rabbits with septic shock were randomly assigned to 3 groups-dopamine group(n = 8),dobutamine group(n = 8) and norepinephrine group(n = 8).Apart from volume resuscitation with normal saline solution [20 ml/(kg· h)]，dopamine[5μg/(kg·min)],dobutamine[(5μg/(kg·min)]and norepinephrine [(1μg/(kg·min)]were infused in dopamine group,dobutamine group and norepinephrine group respeclively.Cardiac index(CI) and superior mesenteric blood flow index(SMBFI) were continuously monitored by doppler flowrneter.Gastric mucosal PCO2 was evaluated by gas tonometry every 10 min.Arterial and venous blood gas analyses and lactate levels were measured every 1 h.Results MAP,CI,and SMBFI significandy decreased and P(g-a) CO2 increased after lipopolysaccharides infusion in three groups.After 2-hour treatment,MAP in norepinephrine group[(70 +3) mm Hg]was higher than that of dopamine group[(66±4) mm Hg]and dobutamine group[(65±4) mm Hg](P ＜0.05).SMBFI in norepinephrine group [(18.7±2.9) ml/(kg·min)]was higher than that of dopamine group[(16.2±1.6) ml/(kg·min)]and dobutamine group[(15.8±1.9) ml/(kg·min)](P＜0.05).P(g-a) CO2 in norepinephrine group [(30±6) mm Hg]was lower than that of dobutamine group[(23±5)mm Hg](P＜0.05).Condnsion As an adjuvant therapy of volume resuscitation,norepinephrine is more effective than low dose dopamine and dobutamine in improving splanchnic perfusion.     

活性炭纤维在地方性氟中毒方面的应用展望

介绍了活性炭纤维（ＡＣＦｓ）的制造，特性及其应用。它具有优异的结耕与性能特征。含碳量高，比表面积大，微孔丰富，从而吸附力强，而且活性炭纤维还可制成纱、布、毡等形状，它可用于去除燃煤氟中毒区室内空气中氟化氢、二氧化硫、氧化氮、氨等污染物，利用它的高吸附性能还可较好的去除饮水中的氟化物及其他有害物质。活性炭纤维是一种新型高效吸附材料。在氟中毒防治方面有广阔的前途。