Nonlinear absorbance amplification using a diffuse reflectance cell: total organic carbon monitoring at 214 nm.

We present an absorption spectrometric method using a polytetrafluoroethylene (PTFE) cell as a diffuse reflector. The system was used for monitoring ultrapure water. All compounds absorb to some degree at low UV wavelengths, and the absorption at 214 nm from a zinc lamp source was monitored using a charge-coupled device (CCD) spectrometer. The absorption was interpreted in terms of total organic carbon present. The cell acts as a nonlinear absorbance amplifier, improving both the limit of detection (LOD) and the dynamic range. Potassium hydrogen phthalate (KHP) and glucose were used to evaluate the system and provided respective LODs of 46.5 ng/L and 4.5 mg/L as carbon. Although the physical path length was 25 cm, a maximum effective path length of 280 cm was observed at the lowest tested KHP concentrations. The system is intended for real-time monitoring of ultrapure water.

Cavity-enhanced absorption measurements across broad absorbance and reflectivity ranges.

Cavity-enhanced spectrometry constitutes an important and highly sensitive technique for absorbance measurements. The current practice generally involves very high reflectivity mirrors and hence intense light sources (typically lasers) to have enough light transmitted. Available theory describes the situation only for high-finesse cavities (high-reflectance mirrors) and generally for systems with very low absorbances. We develop the general expression for absorbance regardless of mirror reflectivity or the absorbance and show that in the limit of high reflectivities and low absorbances it predicts the same numerical values as that derived by O'Keefe (Chem. Phys. Lett. 1998, 293, 331-336; Chem. Phys. Lett. 1999, 307, 343-349). Signal to noise in any photometric system is also dependent on the amount of light reaching the detector because of shot noise limitations. We show that a small aperture in the entrance mirror greatly improves light throughput without significant departure from the theoretically predicted amplification of absorbance; such simple modifications result in real improvement of detection limits, even with mirrors of modest reflectivity and inexpensive detectors. This allows the merits of cavity enhancement measurements to be demonstrated for pedagogic purposes.

Novel phosphorescent hydrogels based on an Ir(III) metal complex.

Novel phosphorescent hydrogels have been explored by immobilizing an Ir(III) metal complex into the matrices of hydrogels. FTIR spectra demonstrate that the Ir(III) -PNaAMPS hydrogel is achieved by irreversible incorporation of positively charged [Ir(ppy)(2)(dmbpy)]Cl (ppy = 2-phenylpyrine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine) into negatively charged poly(2-acrylamido-2-methylpropane sulfonic acid sodium) (PNaAMPS) hydrogel via electrostatic interaction. The photoluminescent spectra indicate that the Ir(III)-PNaAMPS hydrogel exhibits stable phosphorescence. In vitro cultivation of human retinal pigment epithelial cells demonstrates the cytocompatibility of the Ir(III)-PNaAMPS hydrogel. This work herein represents a facile pathway for fabrication of phosphorescent hydrogels.

[Phrenic nerve conduction of obstructive sleep apnea-hypopnea syndrome patients].

OBJECTIVE: To investigate the significance of phrenic nerve conduction time (PNCT) and diaphragm compound muscle action potential (CMAP) detection in the assessment of severity and response to treatment in obstructive sleep apnea-hypopnea syndrome (OSAHS) patients. METHODS: Sixteen healthy volunteers (control group), 8 primary snorers (snorer group), 14 mild-moderate OSAHS patients (mild-moderate group) and 18 severe OSAHS patients (severe group) were recruited for the study from January to July in 2005. Multi-pair esophageal electrodes were used to measure PNCT and CMAP of diaphragm in response to unilateral magnetic stimulation. The study was repeated in 5 OSAHS patients after effective nCPAP treatment for at least 2 months. RESULTS: The PNCT in severe OSAHS group was (8.9 +/- 1.2), (7.9 +/- 1.5) ms respectively, which was significantly longer than those in the control group (6.5 +/- 0.7), (6.0 +/- 0.5) ms, snorer group (6.5 +/- 1.2), (6.0 +/- 0.8) ms and mild-moderate group (7.3 +/- 1.0), (6.3 +/- 0.7) ms. The amplitude of diaphragm CMAP was (1.4 +/- 0.4), (1.4 +/- 0.3) mV in mild-moderate group and (0.9 +/- 0.4), (1.1 +/- 0.6) mV in severe group, which was significantly lower than those in the control group (2.3 +/- 0.9), (2.1 +/- 0.9) mV and snorer group (1.9 +/- 0.5), (2.1 +/- 0.7) mV, and severe patients have significantly lower CMAP than mild-moderate patients. The PNCT and CMAP of both sides for all subjects correlated significantly with oxygen desaturation index and apnea-hypopnea index. The PNCT shortened significantly after effective nCPAP treatment, which was (8.6 +/- 0.6) ms, (7.4 +/- 0.5) ms for left side and (7.8 +/- 0.6) ms, (6.5 +/- 0.5) ms for right side. CONCLUSION: PNCT and CMAP detection with multi-pair esophageal electrodes in response to unilateral magnetic stimulation may be useful for the severity assessment and evaluation of response to effective treatment in OSAHS patients.

[Effects of inhaled short-acting bronchodilators on diaphragm function and neural respiratory drive during maximal isocapnic ventilation in patients with chronic obstructive pulmonary disease].

OBJECTIVE: To investigate the effects of inhaled short-acting bronchodilators on diaphragm function and neural respiratory drive in patients with chronic obstructive pulmonary disease (COPD) during maximal isocapnic ventilation (MIV). METHODS: Forty-seven patient with moderate to severe COPD were randomized into 4 groups: placebo group (n=12), salbutamol group (n=13), ipratropium group (n=10), and combined group (salbutamol and ipratropium, n=12). Each subject received an initial MIV for 3 min at baseline and inhaled placebo (400 µg), salbutamol (400 µg), ipratropium (80 µg), or both salbutamol and ipratropium, followed 30 min later by another 3 min of MIV. The parameters of diaphragm function and neural respiratory drive were monitored continuously and calculated during MIV. RESULTS: During the initial MIV, all the patients experienced a linear increase in root mean square (RMS) of diaphragm electromyogram with a gradual decrease in transdiaphragmatic pressure (Pdi), minute ventilation (VE), and VE/RMS, and these parameters all improved significantly after inhalation of the bronchodilators. Compared with the placebo group at the same time point, the 3 bronchodilator-treated groups showed significantly decreased RMS and Borg score and increased Pdi, VE and VE/RMS; VE/RMS was the highest in the combined treatment group (P<0.05). The Delta Borg was significantly correlated with Delta Pdi, Delta VE, Delta RMS, and Delta VE/RMS (P<0.05). CONCLUSIONS: In COPD patients, inhaled short-acting bronchodilators can alleviate diaphragm fatigue during MIV, increase lung ventilation, reduce neural respiratory drive, and improve neuro-ventilatory coupling to relieve dyspnoea, and the combination of ß-2 agonists and anti-muscarinic antagonists produces a stronger efficacy.

Efficiency of neural respiratory drive for the assessment of bronchodilator responsiveness in patients with chronic obstructive pulmonary disease: an exploratory study.

BACKGROUND: Conventional lung function parameters, such as forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1) and inspiratory capacity (IC) are often used to assess the therapeutic outcomes of bronchodilators, but they lack sensitivity. A novel indicator, namely efficiency of neural respiratory drive (NRD), may objectively evaluate the physiological changes in patients with chronic obstructive pulmonary disease (COPD). We investigated whether this indicator could be used to more accurately assess the responsiveness to inhaled bronchodilators. METHODS: Thirty-six subjects with moderate-to-severe COPD were randomized into group A (n=18) and group B (n=18). Participants in group A inhaled 400 µg placebo, 400 µg salbutamol and 80 µg ipratropium in sequence whereas those in group B had the salbutamol and ipratropium reversed. At different time points after administration of placebo or bronchodilators, evaluated indices included FEV1, FVC, IC, root mean square (RMS) of diaphragm electromyogram (EMGdi), and efficiency of NRD [herein defined as the ratio of minute ventilation (VE) to RMS, or VE/RMS]. RESULTS: FEV1, FVC, IC, RMS, and VE/RMS significantly improved after inhaled bronchodilators and VE/RMS had the largest improvement among five indices. The detection efficiency of VE/RMS was greater than FEV1, FVC, IC (all P<0.05), but not different from RMS. The accuracy and sensitivity of VE/RMS were significantly higher than FEV1, FVC, IC, and RMS (all P<0.05). CONCLUSIONS: Efficiency of NRD may be a sensitive tool to evaluate the efficacy of inhaled bronchodilators in COPD.

[Physiologic response to proportional assist ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease].

OBJECTIVE: To investigate the effect of different assist levels during proportional assist ventilation (PAV) on patients with acute exacerbation of chronic obstructive pulmonary disease (COPD). METHODS: Nine patients with acute exacerbation of COPD received different levels of assist ventilation during PAV. The change of inspiratory muscle effort and breathing pattern of the patients were observed. RESULTS: (1) The average tidal volume (V(T)), minute ventilation (V.(E)) and respiratory frequency (RR) were slightly higher during PAV, as compared to spontaneous breathing (SB). The change of breathing pattern of the patients was not significant at different assist levels during PAV. (2) The transdiaphragmatic pressure (Pdi), the pressure-time product (PTP) and work of breathing (Wi) reduced significantly during PAV as compared with SB (differently reduced 8.36 cm H2O, 11.49 cm H2O.s(-1).L(-1) and 0.53 J/L). The change in Pdi, PTP and Wi was small among different levels during PAV. (3) Dyspnea was improved during PAV. CONCLUSIONS: The present study confirms the feasibility of noninvasive ventilation PAV in treating patients with acute exacerbation of COPD. Based on the patient's assessment, the ventilatory support level which the patients could comfortably tolerate was (57 +/- 11)%. noninvasive ventilation PAV set at a level of comfort determined by the patient can unload inspiratory muscles; at the comfortable level of ventilatory support, Wi, Pdi and PTP decreased by 57%, 72% and 65% respectively. It also improved breathing pattern and dypnea.