Flow Interruption Technique Research Articles

Highly Sensitive Determination of Arsenic and Antimony Based on an Interrupted Gas Flow Atmospheric Pressure Glow Discharge Excitation Source.

A novel interrupted gas flow (IF) technique has been proposed for highly sensitive determination of ultratrace levels of arsenic and antimony in water samples by atmospheric pressure glow discharge (APGD) excitation source coupled with HCl-KBH4 hydride generation (HG). It is demonstrated that the gas flow interruption technique provides a dramatic and reproducible enhancement of emission signals of 1-2 orders of magnitude for As and Sb over conventional continuous gas flow (CF) in APGD. The enhanced analyte emission sensitivities in IF-APGD were investigated from the viewpoint of changes in plasma excitation temperature and analyte density. With eight As lines as the thermometric probe, no measurable change in excitation temperature was found, suggesting that the enhancement is caused by an increase in analyte number density in the plasma immediately following the gas flow interruption. Furthermore, the enhancement factor was found to increase with the time interval in between the gas interruption, supporting an analyte adsorption (or trap)-release mechanism hypothesis. Under optimized conditions, the detection limits (DLs) of IF-APGD mode for As and Sb were calculated to be 0.02 and 0.003 μg L-1, which are, respectively, about 27- and 120-fold improved compared to CF-APGD mode. The linearity of calibration for both As and Sb reached R2 > 0.999 in the 0.1-5 μg L-1 range. The accuracy of the proposed method was validated by the determination of certified reference materials (CRMs), and the results agreed well with the certified values.

The Effects of Perfluorocarbon on Respiratory Mechanics and Pulmonary Gas Exchange with Methacholine-induced Bronchoconstriction in Cats

Background: Perfluorocarbon (PFC) liquids have high oxygen carrying capacity and relatively low surface tension allowing them to spread evenly through the diseased lung, especially in the case of adult respiratory distress syndrome. But few studies have demonstrated the effects of PFC on a bronchoconstriction model. The aim of this study was to investigate the effects of PFC on pulmonary mechanics and gas exchange in methacholine-induced bronchoconstricted cats using a flow interruption technique. Methods: Twenty male cats were divided into four groups; control group(group C, n = 5), PFC group (group P, PFC 5 ml/kg, n = 5), methacholine group (group M, 25g/kg/min, n = 5), PFC and methacholine group (group MP, n = 5). Respiratory pressure using a flow interruption technique was measured immediately after stabilizing the heart rate and blood pressure 0, ad 15, 30 and 60 min after the start of the intratracheal administration of PFC and/or methacholine infusion, depending on the group. Arterial blood gas analysis was done to compare arterial partial oxygen pressure among the groups at the time of measuring the pressure values. The pressure data was transferred to a personal computer and analyzed using ANADAT software program. Respiratory, airway and tissue viscoelastic pressure were calculated, Statistical analysis was done by ANOVA and statistical significance was defined as P

Aerodynamic measurements of patients with Parkinson's disease.

Patients with Parkinson's disease commonly complain of voice dysfunction. Most of these complaints can be attributed to the known muscular control disorders that occur with Parkinson's disease. However, the manifestations of Parkinson's disease muscular dysfunction on parameters of phonation such as airflow, laryngeal resistance, and subglottal pressure necessary to sustain phonation have not been reported. The purpose of this study was to examine the aerodynamic characteristics of flow, laryngeal resistance, and phonation pressure threshold in a heterogeneous population of patients with Parkinson's disease who had varying voice complaints and to compare the data to similar studies for human subjects who have no voice complaints. The studies used a noninvasive method of detecting flow and acoustic signal from the lips, oral cavity and nose during phonation and used an external flow interruption technique to estimate subglottal pressure and phonation threshold pressure. About one third of the patients could not produce phonation at regular and loud intensities that were comfortable for normal subjects. The mean subglottal pressure (SGP) of patients with Parkinson disease who could produce 3 levels of intensity comparable to normal subjects was significantly higher than the mean SGPs for normal subjects for the same intensities of vocal production. The mean flow rates measured from patients with Parkinson's disease at the same 3 intensities of phonation was not significantly greater than in normal subjects. This indicated that the mean laryngeal resistance calculated for patients with Parkinson's disease was notably and significantly greater than mean laryngeal resistance calculated for normal subjects at the same intensity levels. The mean vocal efficiency (VE) for normal subjects was not significantly different than the mean VE for patients with Parkinson's disease, because greater pressure was used to generate similar flow and acoustic energy. These findings correlate with the perception of patients with Parkinson's disease that they are working harder to produce phonation. The observation of notably greater laryngeal resistance and phonation threshold pressure in patients with Parkinson's disease suggests that further studies of the glottic aperture in patients with Parkinson' disease may be useful for understanding how this common motor disorder disturbs phonation.

Rate-limited sorption of simazine in saturated soil columns

Column flow experiments under saturated conditions were conducted to investigate the sorption behavior of simazine on a Tujunga sandy loam. The flow interruption technique was used to test whether rate-limited processes were present. The outflow results showed that the simazine sorption was not at equilibrium during the time of the experiment. This non-equilibrium was due to the sorption process, as the bromide tracer concentration did not change during flow interruption. Simazine breakthrough data could be best described by a two-stage, two-rate process, where the first rate is considerably faster than the second. The model predicts slow reaction kinetics, so that equilibrium was not reached even after 185 h of flow interruption. Outflow data of the first simazine breakthrough only could be described well with a one-stage, rate-limited sorption model; flow interruption was necessary to reveal the second sorption stage.

Anaphylactic bronchoconstriction in immunized guinea pigs provoked by inhalation and intravenous administration of hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride.

We established a guinea-pig model of anaphylactic bronchoconstriction provoked in immunized animals by inhalation and intravenous administration of 4,4-methyltetrahydrophthalic anhydride (MTHPA) and hexahydrophthalic anhydride (HHPA). Guinea pigs were immunized intradermally with either MTHPA (n = 8) or HHPA (n = 8) suspended in olive oil. Control animals (n = 8) were injected with olive oil alone. After 4 weeks, the animals were challenged during mechanical ventilation by inhalation or intravenous administration of MTHPA or HHPA conjugated with guinea-pig serum albumin (GPSA). Airway flow, and airway and esophageal pressures were measured. Resistance (R) and static compliance (Cst) of the respiratory system (rs), lung (1), and chest wall were studied with the flow-interruption technique. After challenge with MTHPA-GPSA or HHPA-GPSA, R,rs and R,1 increased dramatically while Cst,rs and Cst,1 decreased, and severe arterial hypoxia developed. The reaction occurred at a well-defined dose of anhydride and lasted about 30 min. When the same dose was repeated after 30 min, the response was much attenuated. MTHPA and HHPA can induce asthma in guinea pigs. The dose-response curve at antigen challenge is steep. Once a threshold dose is reached, a severe reaction occurs. The reactivity is then exhausted. This model may be suitable for assessing occupational asthma caused by acid anhydrides and possibly by other low-molecular-weight chemicals.

Influence of Gas Composition on Recurrence of Atelectasis after a Reexpansion Maneuver during General Anesthesia

Atelectasis, an important cause of impaired gas exchange during general anesthesia, may be eliminated by a vital capacity maneuver. However, it is not clear whether such a maneuver will have a sustained effect. The aim of this study was to determine the impact of gas composition on reappearance of atelectasis and impairment of gas exchange after a vital capacity maneuver. A consecutive sample of 12 adults with healthy lungs who were scheduled for elective surgery were studied. Thirty minutes after induction of anesthesia with fentanyl and propofol, the lungs were hyperinflated manually up to an airway pressure of 40 cmH2O. FIO2 was either kept at 0.4 (group 1, n = 6) or changed to 1.0 (group 2, n = 6) during the recruitment maneuver. Atelectasis was assessed by computed tomography. The amount of dense areas was measured at end-expiration in a transverse plane at the base of the lungs. The ventilation-perfusion distributions (VA/Q) were estimated with the multiple inert gas elimination technique. The static compliance of the total respiratory system (Crs) was measured with the flow interruption technique. In group 1 (FIO2 = 0.4), the recruitment maneuver virtually eliminated atelectasis for at least 40 min, reduced shunt (VA/Q < 0.005), and increased at the same time the relative perfusion to poorly ventilated lung units (0.005 < VA/Q < 0.1; mean values are given). The arterial oxygen tension (PaO2) increased from 137 mmHg (18.3 kPa) to 163 mmHg (21.7 kPa; before and 40 min after recruitment, respectively; P = 0.028). In contrast to these findings, atelectasis recurred within 5 min after recruitment in group 2 (FIO2 = 1.0). Comparing the values before and 40 min after recruitment, all parameters of VA/Q were unchanged. In both groups, Crs increased from 57.1/55.0 ml.cmH2O-1 (group 1/group 2) before to 70.1/67.4 ml.cmH2O-1 after the recruitment maneuver. Crs showed a slow decrease thereafter (40 min after recruitment: 61.4/60.0 ml.cmH2O-1), with no difference between the two groups. The composition of inspiratory gas plays an important role in the recurrence of collapse of previously reexpanded atelectatic lung tissue during general anesthesia in patients with healthy lungs. The reason for the instability of these lung units remains to be established. The change in the amount of atelectasis and shunt appears to be independent of the change in the compliance of the respiratory system.

Mechanics of respiratory system in healthy anesthetized humans with emphasis on viscoelastic properties

The classic model of the respiratory system (RS) is comprised of a Newtonian resistor in series with a capacitor and a viscoelastic unit including a resistor and a capacitor. The flow interruption technique has often been used to study the viscoelastic behavior under constant inspiratory flow rate. To study the viscoelastic behavior of the RS during complete respiratory cycles and to quantify viscoelastic resistance (Rve) and compliance (Cve) under unrestrained conditions, we developed an iterative technique based on a differential equation. We, as others, assumed Rve and Cve to be constant, which concords with volume and flow dependency of model behavior. During inspiration Newtonian resistance (R) was independent of flow and volume. During expiration R increased. Static elastic recoil showed no significant hysteresis. The viscoelastic behavior of the RS was in accordance with the model. The magnitude of Rve was 3.7 +/- 0.7 cmH2O.l-1 x s, i.e., two times R. Cve was 0.23 +/- 0.051 l/cmH2O, i.e., four times static compliance. The viscoelastic time constant, i.e., Cve.Rve, was 0.82 +/- 0.11s. The work dissipated against the viscoelastic system was 0.62 +/- 0.13 cmH2O x 1 for a breath of 0.56 liter, corresponding to 32% of the total energy loss within the RS. Viscoelastic recoil contributed as a driving force during the initial part of expiration.

Relationship of mean alveolar pressure to mean airway pressure: Model analysis and clinical implications

Mean airway pressure (Pao), measured at the oral end of the endotracheal (ET) tube, has been advocated as a major determinant of cardiac output and arterial oxygenation. These associations are based on the assumption that Pao during the breathing cycle closely reflects mean alveolar pressure (Palv). Based on a mathematical model and measurements of respiratory mechanics in normal anesthetized paralyzed subjects (J Appl Physiol 67:2556–2564, 1989) we have calculated Pao and P alv during constant-flow inflation and passive lung deflation. During inspiration Pao markedly exceeds P alv due to resistive pressure losses within the ET tube and the lower airways. This discrepancy increases with decreasing size of the ET tube and with increasing flow. By contrast, during expiration Pao markedly underestimates P alv due to pressure losses within the lower airways and the ET tube. This discrepancy increases with decreasing size of the ET tube. Our analysis indicates that measurements of P ao during the whole breathing cycle cannot be assumed to be a valid index of P alv. Assessment of P alv is feasible using the flow interruption technique.

Effect of valve closure time on the determination of respiratory resistance by flow interruption.

The resistance of the respiratory system to flow may be conveniently assessed by the flow-interruption technique, in which the flow of gas at the mouth of a subject is suddenly interrupted, while the pressure just distal to the point of interruption, is recorded. There is a rapid change in pressure immediately upon interruption, presumably giving the resistive pressure drop across the pulmonary airways. This is followed by a further slow change in pressure reflecting stress relaxation in the respiratory system and possibly gas redistribution between different regions of the lung. The diagnostic potential of the post-occlusion pressure signal is dependent on the airway opening being occluded effectively instantaneously. We present a description of an occlusion valve we have designed and built for performing rapid airway occlusions. We are able to measure the closing characteristics of our valve precisely, and show that its finite closure time of 12 ms causes the initial rapid drop in pressure to be underestimated by about 7 per cent. A simple numerical correction scheme allows us to estimate this pressure drop correctly to within one or two per cent.

Effect of acute exposure to CO 2 on lung mechanics in normal man

The effect of CO 2 on lung mechanics was examined in 10 healthy men at rest. Measurements were begun after each breathed an inspired concentration of 6 % CO 2 in air for 5 min. Lung volumes, expiratory flow-volume curves, static pressure-volume curves of the lung, and pulmonary conductance were measured. CO 2 breathing produced a small but statistically significant increase in total lung capacity. Pulmonary conductance measured by a flow-interruption technique increased markedly in one subject but decreased in all others. The decrease in conductance was not prevented by treatment with a bronchodilator and was considered the result of an increase in laryngeal resistance. There was no consistent effect of CO 2 breathing on any other parameter.

Measurement of Static Lung and Thorax Compliance in Health and Pulmonary Diseases

Automatic flow interruption technique has been utilized for the determination of lung and thorax compliance. The rate of interruption has been fixed at 120 min-1 with a closingtime of 0.36s

Contribution of compliance of airways to frequency-dependent behavior of lungs.

Contribution of compliance of airways to frequency-dependent behavior of lungs.

Mechanical factors in distribution of pulmonary ventilation.

Mechanical factors in distribution of pulmonary ventilation.