Current limits for flowmeter resistance in metabolic carts can negatively affect exercise performance.

PURPOSE: To investigate whether a metabolic cart using a flowmeter in the upper range of accepted resistance to airflow (<1.5 cmH2 O∙L-1 ∙s-1 for flows up to 14 L∙s-1 , American Thoracic Society) negatively impacts exercise performance in healthy individuals. METHODS: 16 recreationally active males (age 25 ± 1 years, height 180 ± 6 cm, weight 73.5 ± 5.8 kg, all mean ± SD) performed two incremental tests on a bicycle ergometer on each of two visits, using a metabolic cart with a flowmeter of either low (Oxycon Pro) or high (Innocor) airflow resistance. Mouth pressures, gas exchange, blood lactate concentration [La- ], perception of breathlessness, respiratory, and leg exertion were assessed throughout the tests. RESULTS: Tests performed with the Innocor were significantly shorter (15.3 ± 3.2 vs. 15.8 ± 3.3 min, p < 0.0001) and showed higher maximal flow resistance (1.3 ± 0.2 vs. 0.3 ± 0.0 cmH2 O∙L-1 ∙s-1 , p < 0.0001). At end-exercise, peak oxygen consumption (-200 ± 220 ml.min-1 , p < 0.0001), minute ventilation (-19.9 ± 10.5 L.min-1 , p < 0.0001), breathing frequency (-5.4 ± 5.2 breaths.min-1 , p < 0.0001), heart rate (-2.1 ± 3.6 bpm, p = 0.002) and [La- ] (-0.7 ± 1.0 mmol.L-1 , p < 0.0001), but not tidal volume (-0.1 ± 0.2 L, p = 0.172) were lower with the Innocor, while the perception of breathlessness was higher (+3.8 ± 5.1 points, p < 0.0001). CONCLUSIONS: Airflow resistance in the upper range of current guidelines can significantly affect exercise performance and respiratory pattern in young, healthy males during incremental exercise. The present results indicate the need to revisit guidelines for devices used in ergospirometry.

On accuracy and precision of flowmeters used for oxygen therapy in a veterinary teaching hospital.

OBJECTIVE: To determine the accuracy and precision of flowmeters used for oxygen therapy in a veterinary teaching hospital. STUDY DESIGN: An observational study. METHODS: A total of 50 flowmeters used for oxygen therapy were evaluated using Defender 530 gas flow analyzers to measure flow. For each flowmeter, a minimum of seven flow settings were tested in random order and in triplicate. Flow measured at ambient conditions was converted to standardized flow specifications (21.1 °C and 760 mmHg) and analyzed using general linear mixed models. Flowmeters were considered accurate at a given flow setting when the targeted mean flow was within the corresponding 95% confidence interval. Precision of flow was characterized based on the magnitude of variance component estimates. RESULTS: Flowmeters of 1.0, 3.5 and 8.0 L minute-1 were considered accurate across flow settings corresponding to their capacity range. Flowmeters of 7.0 and 15.0 L minute-1 were accurate at flow settings ≤2.0 L minute-1. For flow settings ≥3.0 L minute-1, average oxygen flow was consistently below reference values. Precision varied with the capacity of the flowmeter, ranked by decreasing precision as 1.0 > 3.5 > 8.0 > 7.0 > 15.0 L minute-1. CONCLUSIONS AND CLINICAL RELEVANCE: A flowmeter of the smallest maximum capacity within the desired flow range is more appropriate for smaller patients where accurate, precise flow delivery is needed. Although 15.0 L minute-1 flowmeters were accurate at flow settings ≤2.0 L minute-1, the graduated increments do not allow exact flow settings <0.5 L minute-1. Flowmeters of 15 L minute-1 capacity should be useful for high-flow oxygen delivery for which accuracy and precision are not critical.

Effect of cleaning status on accuracy and precision of oxygen flowmeters of various ages.

OBJECTIVE: To evaluate oxygen flowmeters for accuracy and precision, assess the effects of cleaning and assess conformity to the American Society for Testing Materials (ASTM) standards. STUDY DESIGN: Experimental study. METHODS: The flow of oxygen flowmeters from 31 anesthesia machines aged 1-45 years was measured before and after cleaning using a volumetric flow analyzer set at 0.5, 1.0, 2.0, 3.0, and 4.0 L minute-1. A general linear mixed models approach was used to assess flow accuracy and precision. RESULTS: Flowmeters 1 year of age delivered accurate mean oxygen flows at all settings regardless of cleaning status. Flowmeters ≥5 years of age underdelivered at flows of 3.0 and 4.0 L minute-1. Flowmeters ≥12 years underdelivered at flows of 2.0, 3.0 and 4.0 L minute-1 prior to cleaning. There was no evidence of any beneficial effect of cleaning on accuracy of flowmeters 5-12 years of age (p > 0.22), but the accuracy of flowmeters ≥15 years of age was improved by cleaning (p < 0.05). Regardless of age, cleaning increased precision, decreasing flow variability by approximately 17%. Nine of 31 uncleaned flowmeters did not meet ASTM standards. After cleaning, a different set of nine flowmeters did not meet standards, including three that had met standards prior to cleaning. CONCLUSIONS: Older flowmeters were more likely to underdeliver oxygen, especially at higher flows. Regardless of age, cleaning decreased flow variability, improving precision. However, flowmeters still may fail to meet ASTM standards, regardless of cleaning status. CLINICAL RELEVANCE: Cleaning anesthesia machine oxygen flowmeters improved precision for all tested machines and partially corrected inaccuracies in flowmeters ≥15 years old. A notable proportion of flowmeters did not meet ASTM standards. Cleaning did not ensure that they subsequently conformed to ASTM standards. We recommend annual flow output validation to identify whether flowmeters are acceptable for continued clinical use.

Accuracy of portable devices in measuring peak cough flow.

Peak cough flow (PCF) measurements can be used as indicators of cough effectiveness. Portable peak flow meters and spirometers have been used to measure PCF, but little is known about their accuracy compared to pneumotachograph systems. The aim of this study was to compare the accuracy of four portable devices (Mini-Wright and Assess peak flow meters, SpiroUSB and Microlab spirometers) in measuring PCF with a calibrated laboratory based pneumotachograph system. Twenty healthy volunteers (mean (SD) age 45 (16) years) coughed through a pneumotachograph connected in series with each portable device in turn, and the differences in PCF readings were analysed. In addition, mechanically generated flow waves of constant peak flow were delivered through each device both independently and when connected in series with the pneumotachograph. Agreement between PCF readings obtained with the pneumotachograph and the portable devices was poor. Peak flow readings were on average lower by approximately 50 L min(-1) when measured using the portable devices; 95% limits of agreement spanned approximately 150 L min(-1). The findings highlight the potential for inaccuracy when using portable devices for the measurement of PCF. Depending on the measurement instrument used, absolute values of PCF reported in the literature may not be directly comparable.

A curvilinear nomogram of peak expiratory flow rate for the young.

OBJECTIVE: Peak expiratory flow rates (PEFRs) differ among populations and between times. The new EU scale of the mini-Wright flow-meter has been introduced since 2004. This study updated the PEFR nomograms with the new scale for Chinese children and adolescents (aged 6-19 years) in Hong Kong. METHODS: A convenience sample was recruited from 34 primary care practices (patients' companions/children) and four schools. Standardization workshops were run for the physicians, and the proper use of the flow-meter was demonstrated to students prior to the data collection. Brand new meters were used. For each sex, the linear regression model was used to determine the relationship between PEFR and the variables of age and body height. The open-source software PyNomo was used to generate the nomograms. RESULTS: After excluding 66 participants with past/current history of respiratory tract diseases, heart disease, incomplete data, and poor effort, PEFRs were collected from 798 males and 794 females. The PEFR had a linear relationship with age but a curvilinear relationship with height. The regression equations for predicted PEFR were ln(PEFR) = 1.810256*ln(height) + 0.038297*age - 3.734139 for males and ln(PEFR) = 1.525509*ln(height) + 0.033275*age - 2.368592 for females. The corresponding nomograms were constructed. They were tested with 230 patients in primary care; 9.6% (12 males and 10 females) had PEFR less than the predicted value by ≥20%. CONCLUSION: The body height was a stronger determinant than age for PEFR. The predicted PEFR with these determinants bear a curvilinear relationship.

Precision and accuracy of oxygen flow meters used at hospital settings.

BACKGROUND: Oxygen therapy is an important therapeutic resource for patients with hypoxemia. When changing oxygen flow meters, we have observed that sometimes, even with the same oxygen flow setting as before, a different S(pO(2)) is obtained. OBJECTIVE: To analyze the precision and accuracy of flow meters used in hospital settings. METHODS: An experimental study was performed to test oxygen flow meters from a tertiary hospital, by using a calibrated flow analyzer. Used and new flow meter accuracy was tested by reading in the gas analyzer a single measurement at flow rates of 1, 3, 5, and 10 L/min in 91 flow meters, and they were compared using the Student t test or Mann-Whitney U test. Flow meter precision was tested by reading in the flow analyzer 3 repetitive measurements set at flow rates of 1, 3, 5, and 10 L/min in 11 flow meters, and the reproducibility of these measurements was conducted by using the intraclass correlation coefficient and the Friedman test. RESULTS: The mean measured flow rates were slightly lower than the stipulated flow rate at 1 L/min, very close for 3 L/min, and higher for the 5 and 10 L/min flow rates. There was a large variability among the measurements from different flow meters, mainly at low flow rates (1 and 3 L/min). There was no difference between new and used flow meters at the flow rates measured, except at 10 L/min. Flow meters precision analysis showed a good reproducibility in 3 repetitive measurements for each flow rate (minimum 0.95, maximum 0.99 intraclass correlations). CONCLUSIONS: The flow meters tested showed good precision and poor accuracy.

Comparison of the ATS versus EU Mini Wright peak flow meter in normal volunteers.

OBJECTIVES: The American Thoracic Society (ATS) and European Union (EU) have precise and accurate Mini Wright peak flow meters. The purpose of this investigation was to compare both 1) for accuracy using a pneumotachometer, 2) in volunteers to determine whether they are interchangeable, and 3) to spirometrically predicted peak flows. METHODS: Lab testing: A pneumotachometer was connected in series with each peak flow meter and varying flows pushed through both meters for comparison. Human subjects: Nonsmoking adult volunteers did three standing peak flows. The order of peak flow meter used was random. The best of three efforts was used for analysis. The t-test, concordance correlation coefficient (CCC), Deming regression, and Bland-Altman plot were the analytic strategies used to determine agreement. Peak flow results were compared to spirometrically predicted values. RESULTS: Fifty-seven volunteers, average age 37 ± 12 years and mean BMI 24.9 ± 2.5 years, were included. The average peak flows were different at 541 ± 114 and 526 ± 112 L/min for the ATS and EU meters, respectively (p < .01). Both peak flow meter values were significantly different than spirometrically predicted values of 483 ± 86 L/min (p < .01). The CCC was 0.98 (0.97-0.99) and regression revealed a slope and y-intercept consistent with 1 and 0, respectively. The Bland-Altman plot revealed no increase in scatter of values over the range of peak flows versus the difference with a mean bias of 15 ± 15 L/min. Laboratory testing revealed that the ATS and EU peak flow meters read 3.0 ± 2.1% above and -2.0 ± 1.5% below the comparison pneumotachometer, respectively. The pneumotachometer comparison was significantly different for both meters at p < .01, paired t-test. CONCLUSIONS: The ATS peak flow meter reads 2.8% higher than the EU peak flow meter across a range of flows. Both meters have similar accuracy with a different bias compared with a pneumotachometer. Finally, both peak flow meters read slightly and significantly higher than spirometrically derived peak flows. Therefore, the peak flow meters are not interchangeable and both may obtain slightly higher values than those determined using current spirometrically derived prediction equations.

Avoid cruising on the uroflowmeter: evaluation of cruising artifact on spinning disc flowmeters in an experimental setup.

AIMS: The aim of our study was to access the variability of maximum flow rate (Q(max)), average flow rate (Q(av)) and flow pattern while varying the point of impact of flow on the flowmeter. METHODS: Water was delivered through a motorised tube holder in a standardised experimental set up. Flow was directed in 4 different directions on the funnel; 1) Periphery, 2) Base, 3) Centre and, 4) in a cruising motion from the periphery of the funnel to the centre and back again. The variation in the Q(max), Q(av) and the flow pattern were studied at 4 different flow rates. The variables recorded when the flow was directed at the centre of the funnel was taken as baseline. RESULTS: There was a significant difference in the Q(max) and Q(av)when the point of impact was at the periphery or in a cruising motion compared to the centre. The difference was more marked with cruising motion with a characteristic flow pattern. The maximum percentage difference in Q(av) was 4.1%, whereas the difference in Q(max) was higher at 16.6% on comparing crusing motion with the values from the centre. CONCLUSION: We have demonstrated a significant variation in Q(max), Q(av) and flow pattern with change in the point of impact on the flowmeter. Though the changes in Q(av) were statistically significant, the alteration in the recorded Q(max) values was more striking. Our study emphasizes the importance of combining Q(av) and flow pattern along with Q(max) in interpretation of results of uroflowmetry.

Constructed wetlands for wastewater and activated sludge treatment in north Greece: a review.

Constructed wetlands used for the treatment of urban, industrial and agricultural wastewater have become very popular treatment systems all over the world. In Greece, these systems are not very common, although the climate is favourable for their use. During recent years, there have been several attempts for the implementation of these systems in Greece, which include, among others, pilot-scale systems used for research, and full-scale systems designed and/or constructed to serve settlements or families. The purpose of this paper is the presentation of systems operating in Northern Greece, which have been studied by the Laboratory of Ecological Engineering and Technology of Democritus University of Thrace and others. A comparison is made of different system types, and the effect of various design and operational parameters is presented. Current research shows the good and continuous performance of these systems.

Optimized temperature and deadspace correction improve analysis of multiple breath washout measurements by ultrasonic flowmeter in infants.

BACKGROUND: Assessment of lung volume (FRC) and ventilation inhomogeneities with ultrasonic flowmeter and multiple breath washout (MBW) has been used to provide important information about lung disease in infants. Sub-optimal adjustment of the mainstream molar mass (MM) signal for temperature and external deadspace may lead to analysis errors in infants with critically small tidal volume changes during breathing. METHODS: We measured expiratory temperature in human infants at 5 weeks of age and examined the influence of temperature and deadspace changes on FRC results with computer simulation modeling. A new analysis method with optimized temperature and deadspace settings was then derived, tested for robustness to analysis errors and compared with the previously used analysis methods. RESULTS: Temperature in the facemask was higher and variations of deadspace volumes larger than previously assumed. Both showed considerable impact upon FRC and LCI results with high variability when obtained with the previously used analysis model. Using the measured temperature we optimized model parameters and tested a newly derived analysis method, which was found to be more robust to variations in deadspace. Comparison between both analysis methods showed systematic differences and a wide scatter. CONCLUSION: Corrected deadspace and more realistic temperature assumptions improved the stability of the analysis of MM measurements obtained by ultrasonic flowmeter in infants. This new analysis method using the only currently available commercial ultrasonic flowmeter in infants may help to improve stability of the analysis and further facilitate assessment of lung volume and ventilation inhomogeneities in infants.

[Effects of nonlinear error correction of measurements obtained by peak flowmeter using the Wright Scale to assess asthma attack severity in children].

INTRODUCTION: Monitoring of peak expiratory flow (PEF) is recommended in numerous guidelines for management of asthma. Improvements in calibration methods have demonstrated the inaccuracy of original Wright scale of peak flowmeter. A new standard, EN 13826 that was applied to peak flowmeter was adopted on 1st September 2004 by some European countries. Correction of PEF readings obtained with old type devices for measurement is possible by Dr M. Miller's original predictive equation. OBJECTIVE: Assessment of PEF correction effect on the interpretation of measurement results and management decisions. METHOD: In children with intermittent (35) or stable persistent asthma (75) aged 6-16 years, there were performed 8393 measurements of PEF by Vitalograph normal-range peak flowmeter with traditional Wright scale. Readings were expressed as percentage of individual best values (PB) before and after correction. The effect of correction was analysed based on The British Thoracic Society guidelines for asthma attack treatment. RESULTS: In general, correction reduced the values of PEF (p < 0.01). The highest mean percentage error (20.70%) in the measured values was found in the subgroup in which PB ranged between 250 and 350 l/min. Nevertheless, the interpretation of PEF after the correction in this subgroup changed in only 2.41% of measurements. The lowest mean percentage error (15.72%), and, at the same time, the highest effect of correction on measurement results interpretation (in 22.65% readings) were in children with PB above 450 l/min. In 73 (66.37%) subjects, the correction changed the clinical interpretation of some values of PEF after correction. In 13 (11.8%) patients, some corrected values indicated the absence or a milder degree of airflow obstruction. In 27 (24.54%) children, more than 10%, and in 12 (10.93%), more than 20% of the corrected readings indicated a severe degree of asthma exacerbation that needed more aggressive treatment. CONCLUSION: Correction of PEF values obtained by peak flowmeters with traditional Wright scale shows a possibility of overtreatment in younger or short stature children and undertreatment in older or taller ones if we use old type of metres. The correction of peak flowmeter for non-linear error is a prerequisite in the application of asthma guidelines in PEF measurements.

Functional residual capacity measurements in healthy infants: ultrasonic flow meter versus a mass spectrometer.

Accurate, reproducible and portable bedside monitoring of lung volume could potentially facilitate the early recognition of both under and overinflation of the lungs in ventilated and nonventilated subjects. This study asked whether a prototype portable ultrasonic flow meter provided valid and reliable measurements of functional residual capacity (FRCUS) when compared to those obtained using a mass spectrometer (FRCMS) in nonventilated healthy infants. Paired, randomised measurements of FRCMS and FRCUS were obtained using the sulphur hexafluoride (SF6) multiple-breath washout technique in 23 healthy infants with a median (range) postnatal age of 34.6 (1.3-92.6) weeks and weight of 8.3 (3.9-11.7) kg. FRCUS was on average 5.7%, (95% CI: 1.0-10.4%) less than FRCMS equating to a difference of approximately 1 mL x kg(-1). The 95% limits of agreement (LA) between the two techniques were relatively wide (95% LA: -17.5% to 29%), although in keeping with previously reported within-patient variability for lung volume measurements. There was no significant difference between the within subject coefficient of variation for FRCMS (3.7%) and FRCUS (5.2%). The ultrasonic flow meter used in this study provides repeatable measurements of functional residual capacity in spontaneously breathing healthy infants that approximate those obtained during mass spectrometry.