Calibration Checks Research Articles

Potential for Calibrating Airborne Video Imagery Using Preflight Calibration Coefficients

The low-cost Multispectral Airborne Video System (MAVS), developed using off-the-shelf components, is predominantly being used for agricultural and environmental monitoring applications in Australia. In order to guarantee quality of operational imagery, regular radiometric calibration checks, under both preflight and in-flight environments, are a necessity. While preflight calibration is conducted in the field with relative ease, to conduct in-flight calibration checks during operational missions is difficult, especially when onboard calibration instrumentation is not available. The calibration of MAVS imagery in flight requires a radiative transfer code such as the 6S to simulate the radiation signal at the operational altitude. A comparison of the simulated in-flight calibration equation with the corresponding preflight calibration equation showed a statistically significant agreement for every MAVS band, demonstrating the stability of response of the instrument in the air. This MAVS response stability indicates a potential for calibrating operational airborne imagery using preflight calibration equations. A few simulated in-flight calibration checks, in addition to regular preflight calibrations, could still be carried out during the flight season to verify system radiometric response in the air.

Análise da aferição dos tonômetros de aplanação de Goldmann em serviços oftalmológicos de Recife

OBJETIVOS: Verificar a freqüência de tonômetros de Goldmann descalibrados e a influência das seguintes variáveis: modelo, idade, número de utilizações diárias e freqüência de aferição. Avaliar o conhecimento dos oftalmologistas sobre a checagem da calibração. MÉTODOS: O estudo foi desenvolvido em Recife, Brasil. Foram identificados 79 tonômetros de Goldmann. O funcionamento dos tonômetros foi checado nas posições 0, 20 e 60 mmHg. Erros maiores que ± 2 mmHg foram considerados significativos. Numa ficha foram registrados: modelo (fixo à lâmpada de fenda ou removível), tempo de fabricação, número de utilizações diárias e freqüência de aferição. Um terço (92) dos oftalmologistas da cidade foram entrevistados e responderam um questionário perguntando se sabiam como fazer a checagem de calibração do tonômetro e se realizavam-na pessoalmente. RESULTADOS: Vinte tonômetros (25,3%) estavam descalibrados. Trinta e oito aparelhos (48,1%) eram fixos à lâmpada de fenda e 41 (51,9%) eram removíveis. Vinte e oito aparelhos (35,4%) tinham menos de 5 anos de fabricação. Quarenta e oito aparelhos (60,8%) eram utilizados em 20 ou menos pacientes por dia. A freqüência da checagem da calibração era anual ou mais freqüente em 36 (45,6%) aparelhos. Aparelhos descalibrados foram mais freqüentes entre os removíveis e entre os com mais de 5 anos de uso (p=0,008 e p=0,050, respectivamente). Apenas 37 (40,2%) oftalmologistas sabiam checar a calibração dos tonômetros. CONCLUSÕES: Um quarto dos tonômetros es-tava descalibrado. Os aparelhos removíveis e aqueles com mais de 5 anos de fabricação foram mais propensos à descalibração. A maioria dos oftalmologistas não sabe aferir o tonômetro.

Assessment of the Calibration of the Intoxilyzer® 5000C Following Extensive use of an Alcohol Standard

ABSTRACTThe assessment of the accuracy of the Intoxilyzer® 5000C relies on the use of an aqueous alcohol standard placed in a simulator to form a closed, re-circulating system. This study was designed to evaluate the ability of the alcohol standard to correctly assess the calibration of the instrument as the alcohol concentration of the standard decreases through extensive use. The conducting of an average of 218 calibration checks per calibrated instrument over a 12 day period resulted in a 5% decrease in the actual concentration of the alcohol standard. While the mean of the calibration check results also decreased, 99.7% of the calibration check results were within the acceptable range of 90 to 110 mg/100 mL used to show the instrument is calibrated. Thus, while alcohol depletion does occur through use of the Intoxilyzer® 5000C, the alcohol standard remains suitable for the assessment of the calibration of the instrument under conditions of expected field use.

Using temporal averaging to decouple annual and nonannual information in avhrr ndvi time series

As regularly spaced time series imagery becomes more prevalent in the remote sensing community, monitoring these data for temporal consistency will become an increasingly important problem. Long-term trends must be identified, and it must be determined if such trends correspond to true changes in reflectance characteristics of the study area (natural), or if their source is a signal collection and/or processing artifact that can be identified and corrected in the data (artificial). Spectrally invariant targets (SITs) are typically used for sensor calibration and data consistency checks. Unfortunately, such targets are not always available in study regions. The temporal averaging technique described in this research can be used to determine the presence of artificial interannual value drift in any region possessing multiyear regularly sampled time series remotely sensed imagery. Further, this approach is objective and does not require the prior identification of a SIT within the region of study. Using biweekly Advanced Very High Resolution Radiometer (AVHRR) normalized difference vegetation index (NDVI) data from 1990 to 2001 covering the conterminous United States, an interannual trend present in the entire scene was identified using the proposed technique and found to correspond extremely well with interannual trends identified using two SITs within the region.

Alcohol Depletion in Simulator Solutions used with the Intoxilyzek® 5000C System Calibration Check

ABSTRACTUsing alcohol-water solutions in wet bath simulators for calibration verification of breath alcohol testing instruments is a commonly employed safeguard in breath test programs. The forensic value of this practice is critically dependent on the simulator solution maintaining a correct alcohol concentration over the time it is applied for this purpose. Alcohol depletion is a recognized phenomenon with simulator solution use. The purpose of this study was to evaluate the extent of alcohol depletion occurring in simulator solutions used in performing repeated calibration checking of an Intoxilyzer® 5000C instrument operated in recirculation mode. Measurements of alcohol depletion were made on simulator solutions used in trials involving 50 to 100 calibration checks performed over periods of 14 to 33 days. In three of the four trials, alcohol depletion was found to be significant at the 99% Confidence Interval (CI) with solution concentrations decreasing more than 3 percent from the original target values. The use of recirculation for calibration checks of the Intoxilyzer® 5000C provides a conserving effect on the amount of alcohol lost from the solution. However, the results of this study suggest that even with recirculation, significant decreases in alcohol concentration occur when repeated tests are performed over time with the same solution. Where recirculation is used, alcohol depletion appears to remain a factor that should be monitored as one part of maintaining the overall quality assurance in a breath alcohol program.

Thermoluminescent dosimeters (TLD) quality assurance network in the Czech Republic

The Czech thermoluminescent dosimeters (TLD) quality assurance network was established in 1997. Its aim is to pursue a regular independent quality audit in Czech radiotherapy centres and to support state supervision. The audit is realised via mailed TL dosimetry. The TLD system consists of encapsulated LiF:Mg,Ti powder (type MT-N) read with Harshaw manual reader model 4000. Basic mode of the TLD audit covers measurements under reference conditions, specifically beam calibration checks for all clinically used photon and electron beams. Advanced mode consists of measurements under both reference and non-reference conditions using a solid multipurpose phantom ('Leuven phantom') for photon beams. The radiotherapy centres are instructed to deliver to the TLD on central beam axis absorbed dose of 2 Gy calculated with their treatment planning system for a particular treatment set-up. The TLD measured doses are compared with the calculated ones. Deviations of +/-3% are considered acceptable for both basic and advanced mode of the audit. There are 34 radiotherapy centres in the Czech Republic. They undergo the basic mode of the TLD audit regularly every 2 years. If a centre shows a deviation outside the acceptance level, it is audited more often. Presently, most of the checked beams comply with the acceptance level. The advanced TLD audit has been implemented as a pilot study for the present. The results were mostly within the acceptance limit for the measurements on-axis, whereas for off-axis points they fell beyond the limit more frequently, especially for set-ups with inhomogeneities, oblique incidence and wedges. The results prove the importance of the national TLD quality assurance network. It has contributed to the improvement of clinical dosimetry in the Czech Republic. In addition, it helps the regulatory authority to monitor effectively and regularly radiotherapy centres.

Expanding the sensitivity of conventional analytical techniques in quality control using sensory technology

To conduct a quality control program, a company can utilize professional sensory panels, analytical techniques, and newer computer technologies. Choosing the right method(s) can be a complex task in which strengths and weaknesses of each method, budget constraints, and other resource issues must be weighed. Human sensory panels provide the most sensitive measure of quality, detecting trace-to-ultra-trace concentrations of compounds. Panelists can incorporate quantitative information with qualitative nuances of the whole product. Analytical techniques can be efficient, fatigue-free, and helpful in monitoring potentially toxic chemicals. Identifying a specific quality-degrading constituent can be difficult solely through instrumental methods. Sensory-directed chemical analysis can sort through the hundreds to thousands of compounds that may cause a quality problem in a food product. New technological advances, such as electronic noses, also require human direction to “learn” the limits of acceptability and conduct periodic calibration checks.

Ultrasonic method for the whole blood coagulation analysis

The developed ultrasonic method is based on the experimentally established fact that the ultrasound velocity in a blood sample is changing in a specific way during the blood clotting process. For ultrasound velocity measurements pulse echo method was selected. Implementation of this approach has a few problems caused by small dimensions of the measurement cell. All elements of the cell contacting with the blood are made of biologically compatible materials. The length of Pd coated chamber is 5 mm, volume 0.2 ml. Data of measurements are stored and processed by PC. The ultrasound velocity in a sample is displayed as it changes in time during the experiment; the temperature is monitored as well. Application of the digital filtering allows to smooth the coagulation curve and reach the sensitivity up to ±3 cm/s. The coagulation curves were obtained at frequency 5 MHz and they represent peculiar stages of blood clotting characterised by their duration and ultrasound velocity differences. Fine structure of ultrasonic velocity changes is registered from the very beginning of the clotting to lysis. Such experiments were carried out using blood samples taken from a few hundred volunteers. For dynamic calibration and periodic checking of the measuring system the liquid medium in which acrylamide polymerisation reaction takes place is proposed as a reference liquid. Such a liquid mimics clotting blood from the point of view of ultrasonic velocity changes.

Objective measurement of nasal airway dimensions using acoustic rhinometry: methodological and clinical aspects.

Nasal congestion is an important symptom in many diseases of the upper airways. Nasal congestion may also affect personal well-being and quality of life. Furthermore, as the nasal mucosa is the first part of the airways in contact with the environment, objective evaluation of nasal congestion or nasal patency is important. Systematic evaluation of nasal patency was described in the last part of the 19th century by Zwaardemaker. Measurement of the pressure drop over the nasal cavity at a passive dow has been described in 1903 by Courtade and is one of first descriptions rhinomanometry. The technique is still in use and computer technology has made the measurements much easier but the method has not yet been accepted for wide clinical use. Acoustic methods have also been used for evaluation of nasal patency. A qualitative method was the hum-test by Spiess (1902), where external occlusion of the nonocciuded side of the nasal cavity is experienced as a change in the timbre of the sound during humming. Acoustic reflections have been used in geophysical investigations especially with regard to search for oil. The use of acoustic reflections from the airways gained special interest in 1960-70 for determining the geometry of the vocal tract shape with regard to speech reconstruction. A method described by A. Jackson (1977) was adopted and for the first time applied to the nasal cavity. The method for determining the cross-sectional area as function of distance in the airways by acoustic reflections is impulse or relatively simple. The incident sound pseudorandom noise in the audible frequency range is compared with the response - the reflections from the airways. Intuitively, if the size of the entrance to the airways is known, the size of the reflections may represent changes of the airway size and the time between reflections may give the distance between the changes, dependent on the speed of sound. In this way it is possible to determine the area as function of distance in the airways. The technique has some assumptions and the major effort has been to validate use in the nose and elucidate aspects with regard to sound loss in the airways and resolution. Therefore, the acoustic reflection technique - named acoustic rhinometry - was compared with other methods like MRI, CT, and rhinomanometry. Allergic and nonallergic subjects were also compared. Acoustic rhinometry showed reasonable correlation with CT in a cadaver and in 10 subjects in comparison with MRI for the first 6 cm of the nasal cavity. Models based on MRI scannings of subjects also showed good correlation for the first 6 cm of the nasal cavity. Posteriorly in the nasal cavity and the epipharynx, differences were found mainly due to 'sound loss' to the paranasal sinuses. Sound loss due to viscous loss or friction at increasing surface/area ratio (the complex geometry in the nose) and loss due to nonrigidity the nasal mucosa were also examined. Neither these factors affected the area-distance function significantly. Acoustic rhinometry seems to reflect the area-distance function in the nose reasonably accurately. In allergic subjects acoustic rhinometry has been used to evaluate hypersensitivity. More pronounced spontaneous variation in nasal mucosa congestion was found in patients suffering from hay fever compared to nonallergic subjects. Furthermore, a tendency to a more swollen mucosa in the allergic subjects compared to the normal state, and increased sensitivity to histamine was found. This and reduction in swelling of the mucosa in allergic subjects during nasal steroid treatment out of the pollen season indicate an ongoing inflammatory process or hypersensitivity in allergic subjects out ot the pollen season. During allergen challenge the change in nasal cavity dimension as well as inflammation may affect olfaction in hay fever patients. Acoustic rhinometry has not only been used to examine hay fever patients but in many different aspects of rhinology. Since the introduction of the acoustic reflection technique in the nose more than papers using the technique have been published. Most of the papers find the technique valuable for evaluation of nasal patency. Fortunately, some critical papers have drawn attention to some practical aspects of the technique. Standard operating procedures, and calibration checks as well as training operators will enhance the accuracy and reproducibility of results. A decade after its introduction acoustic rhinometry is a well-established method for evaluation of nasal patency, but further improvement can be obtained by continued validation and adjustments of the technique.

Quality-control issues on high-resolution diagnostic monitors.

Previous literature indicates a need for more data collection in the area of quality control of high-resolution diagnostic monitors. Throughout acceptance testing, which began in June 2000, stability of monitor calibration was analyzed. Although image quality on all monitors was found to be acceptable upon initial acceptance testing using VeriLUM software by Image Smiths, Inc (Germantown, MD), it was determined to be unacceptable during the clinical phase of acceptance testing. High-resolution monitors were evaluated for quality assurance on a weekly basis from installation through acceptance testing and beyond. During clinical utilization determination (CUD), monitor calibration was identified as a problem and the manufacturer returned and recalibrated all workstations. From that time through final acceptance testing, high-resolution monitor calibration and monitor failure rate remained a problem. The monitor vendor then returned to the site to address these areas. Monitor defocus was still noticeable and calibration checks were increased to three times per week. White and black level drift on medium-resolution monitors had been attributed to raster size settings. Measurements of white and black level at several different size settings were taken to determine the effect of size on white and black level settings. Black level remained steady with size change. White level appeared to increase by 2.0 cd/m2 for every 0.1 inches decrease in horizontal raster size. This was determined not to be the cause of the observed brightness drift. Frequency of calibration/testing is an issue in a clinical environment. The increased frequency required at our site cannot be sustained. The medical physics division cannot provide dedicated personnel to conduct the quality-assurance testing on all monitors at this interval due to other physics commitments throughout the hospital. Monitor access is also an issue due to radiologists' need to read images. Some workstations are in use 7 AM to 11 PM daily. An appropriate monitor calibration frequency must be established during acceptance testing to ensure unacceptable drift is not masked by excessive calibration frequency. Standards for acceptable black level and white level drift also need to be determined. The monitor vendor and hospital staff agree that currently, very small printed text is an acceptable method of determining monitor blur, however, a better method of determining monitor blur is being pursued. Although monitors may show acceptable quality during initial acceptance testing, they need to show sustained quality during the clinical acceptance-testing phase. Defocus, black level, and white level are image quality concerns, which need to be evaluated during the clinical phase of acceptance testing. Image quality deficiencies can have a negative impact on patient care and raise serious medical-legal concerns. The attention to quality control required of the hospital staff needs to be realistic and not have a significant impact on radiology workflow.

Office Spirometry for Lung Health Assessment in Adults: A Consensus Statement From the National Lung Health Education Program

COPD is easily detected in its preclinical phase using spirometry, and successful smoking cessation (a cost-effective intervention) prevents further disease progression. This consensus statement recommends the widespread use of office spirometry by primary-care providers for patients >/= 45 years old who smoke cigarettes. Discussion of the spirometry results with current smokers should be accompanied by strong advice to quit smoking and referral to local smoking cessation resources. Spirometry also is recommended for patients with respiratory symptoms such as chronic cough, episodic wheezing, and exertional dyspnea in order to detect airways obstruction due to asthma or COPD. Although diagnostic-quality spirometry may be used to detect COPD, we recommend the development, validation, and implementation of a new type of spirometry-office spirometry-for this purpose in the primary-care setting. In order to encourage the widespread use of office spirometers, their specifications differ somewhat from those for diagnostic spirometers, allowing lower instrument cost, smaller size, less effort to perform the test, improved ease of calibration checks, and an improved quality-assurance program.

TIMED Solar EUV experiment

The Solar EUV Experiment (SEE) on the NASA Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) mission will measure the solar vacuum ultraviolet (VUV) spectral irradiance from 1 to 195 nm. To cover this wide spectral range two different types of instruments are used: a grating spectrograph for spectra above 25 nm and a set of silicon photodiodes with thin film filters for the soft x-ray (XUV) below 35 nm. Redundant channels of the spectrograph and XUV photodiodes provide in-flight calibration checks on the time scale of a week, and annual rocket underflight measurements provide absolute calibration checks traceable to radiometric standards. Both types of instruments have been developed and flight proven as part of a NASA solar EUV irradiance rocket experiment. The SEE instrument is currently on the NASA TIMED spacecraft at the Johns Hopkins University (JHU) Applied Physics Laboratory (APL). The TIMED launch is planned for October 2000 as a two year mission.

Evaluation of a New Fiberoptic Catheter for Monitoring Jugular Venous Oxygen Saturation

OBJECTIVE: The purpose of this study was to evaluate three modified, fiberoptic, oxygen saturation catheters as monitors of jugular venous oxygen saturation (SjvO2). METHODS: Three modified fiberoptic catheters, designated Catheters 1, 2, and 3, were evaluated. After preinsertion calibration, the catheters were inserted in the dominant jugular vein of patients with severe head injuries. The catheter reading for SjvO2 was compared with the SjvO2 value measured in a blood sample drawn through the catheter, at intervals up to 72 hours. RESULTS: Catheter 3 (a modified version of the pediatric Swan-Ganz catheter) showed significantly better performance than the other two catheters. Both the initial calibration of the catheter and the calibration with time were significantly better for Catheter 3 than for the other two catheters tested. The Catheter 3 value for SjvO2 was more than 4% different from the co-oximeter value in only 6% of the 4-hour calibration checks, compared with 26% and 29% for Catheters 1 and 2, respectively. CONCLUSION: Catheter 3, which is now being marketed as the Opticath P540-H catheter, represents a significant improvement in performance and may make SjvO2 monitoring in the intensive care unit more practical.

Reliability of Bench Press Velocity-Spectrum Testing

Evaluations were made of the stability reliability of force measurements obtained from an Ariel dynamometer, the test -- retest reliability of force and power data for bench presses using the same dynamometer at multiple velocities, and the logical (face) validity of force and power output using the same instrument and exercise. Stability reliability of the dynamometer was determined from daily duplicate force calibration checks using two standard loads. Intra- and intertest coefficients of variation ranged from 0.07% to 1.16%. The test -- retest reliability of the bench press force and power outputs of 33 young men as well as the logical validity of their bench press force and power outputs were assessed at 0.0, 0.124, 0.496, and 0.868 m · sec-1, respectively. Intraclass correlation coefficients for force and power ranged from .95 to .99. Plots for both force and power were similar to those expected for analogous single-joint exercises. Therefore, data presented here support the stability reliability of the dynamometer for force measurements, the reliability of the bench press protocol, and the face validity of force outputs over a velocity spectrum.

Performance characteristics of an automated gas chromatograph‐ion trap mass spectrometer system used for the 1995 Southern Oxidants Study field investigation in Nashville, Tennessee

A trailer‐deployed automated gas chromatograph‐mass spectrometer (autoGC‐MS) system capable of making continuous hourly measurements was used to determine volatile organic compounds (VOCs) in ambient air at New Hendersonville, Tennessee, and Research Triangle Park, North Carolina, in 1995. The system configuration, including the autoGC‐MS, trailer and transfer line, siting, and sampling plan and schedule, is described. The autoGC‐MS system employs a pair of matched sorbent traps to allow simultaneous sampling and desorption. Desorption is followed by Stirling engine cryofocusing and subsequent GC separation and mass spectral identification and quantification. Quality control measurements described include evaluating precision and accuracy of replicate analyses of independently supplied audit and round‐robin canisters and determining the completeness of the data sets taken in Tennessee. Data quality objectives for precision (±10%) and accuracy (±20%) of 10‐ to 20‐ppbv audit canisters and a completeness of >75% data capture were met. Quality assurance measures used in reviewing the data set include retention time stability, calibration checks, frequency distribution checks, and checks of the mass spectra. Special procedures and tests were used to minimize sorbent trap artifacts, to verify the quality of a standard prepared in our laboratory, and to prove the integrity of the insulated, heated transfer line. A rigorous determination of total system blank concentration levels using humidified scientific air spiked with ozone allowed estimation of method detection limits, ranging from 0.01 to 1.0 ppb C, for most of the 100 target compounds, which were a composite list of the target compounds for the Photochemical Assessment Monitoring Station network, those for Environmental Protection Agency method TO‐14, and selected oxygenated VOCs.

Improving Indoor Air Quality Through the Use of Continual Multipoint Monitoring of Carbon Dioxide and Dew Point

This article summarizes an approach for improving the indoor air quality (IAQ) in a building by providing feedback on the performance of the ventilation system. The delivery of adequate quantities of ventilation to all building occupants is necessary for the achievement of good IAQ. Feedback on the performance includes information on the adequacy of ventilation provided, the effectiveness of the distribution of this air, the adequacy of the duration of operation of the ventilation system, and the identification of leakage into the return plenum, either of outdoor or supply air. Keeping track of ventilation system performance is important not only in terms of maintaining good IAQ, but also making sure that this system continues to perform as intended after changes in building use. Information on the performance of the ventilation system is achieved by means of an automated sampling system that draws air from multiple locations and delivers it to both a carbon dioxide monitor and dew point sensor. The use of single shared sensors facilitates calibration checks as well as helps to guarantee data integrity. This approach to monitoring a building's ventilation system offers the possibility of achieving sustainable performance of this important aspect of good IAQ.

Improving indoor air quality through the use of continual multipoint monitoring of carbon dioxide and dew point.

This article summarizes an approach for improving the indoor air quality (IAQ) in a building by providing feedback on the performance of the ventilation system. The delivery of adequate quantities of ventilation to all building occupants is necessary for the achievement of good IAQ. Feedback on the performance includes information on the adequacy of ventilation provided, the effectiveness of the distribution of this air, the adequacy of the duration of operation of the ventilation system, and the identification of leakage into the return plenum, either of outdoor or supply air. Keeping track of ventilation system performance is important not only in terms of maintaining good IAQ, but also making sure that this system continues to perform as intended after changes in building use. Information on the performance of the ventilation system is achieved by means of an automated sampling system that draws air from multiple locations and delivers it to both a carbon dioxide monitor and dew point sensor. The use of single shared sensors facilitates calibration checks as well as helps to guarantee data integrity. This approach to monitoring a building's ventilation system offers the possibility of achieving sustainable performance of this important aspect of good IAQ.

Slug flow regime identification from dynamic void fraction measurements in vertical air-water flows

An existing design of conductivity probe for the measurement of void fraction has been developed and tested. Calibration checks showed that the time averaged output of the instrument was close to linear over the whole range of void fraction, with a tendency to overestimate the true value. Computer modelling of the probe's response to different void distributions supported the calibration results. Two meters were used to examine the dynamic variation of void fraction in air water flows in a vertical 32 mm diameter tube. Flow patterns ranging from bubbly to annular were observed. Examination of the void fraction traces and their probability distribution functions enabled the identification of six flow regimes: discrete bubble flow, spherical cap bubble flow, stable slug flow, unstable slug flow, churn flow and annular flow. The locations of flow regime transition boundaries on a flow pattern map, deduced from this objective analysis, are in agreement with the data of other workers. The unstable slug flow regime corresponds to a region some workers have identified as churn flow, it provides explanations for some of the apparent anomalies concerning the location of the slug to churn flow boundary. Cross-correlation of the signals from the two probes has provided statistical data on the lengths of slugs and Taylor bubbles which suggested modifications to the previous theories enabling the entry to and exit from the unstable slug flow regime to be predicted.

Kontrollmessungen zur Verlängerung der Gültigkeitsdauer der Eichung von Therapiedosimetern – ein Dreijahresbericht

The period required for recalibration of therapy dosimeters in Germany is two years. According to the legislation, however, the user is permitted to extend the time for recalibration up to six years under certain conditions. For this purpose test measurements must be carried out at least every six months, and their results must be recorded. In the following the performance, the results and the documentation of these calibration checks are described.

Long-term performance of a hand held spirometer.

A study was undertaken to test the long term performance of a small hand held spirometer for self-administered serial spirometric testing. Thirty turbine pocket spirometers (MicroMedical DiaryCard) were used in a clinical trial on 22 emphysematous patients with severe alpha 1-antitrypsin deficiency. The spirometers were able to store the date, time, forced expiratory volume in one second (FEV1), forced vital capacity (FVC), peak expiratory flow (PEF), and flow-volume loop for each blow. Every four weeks when the patients came for alpha 1-antitrypsin infusions the performance of their spirometer was checked before and after retrieval of the data from the spirometer. Calibration checks were threefold and included volume calibration with a 1.0 litre and 3.0 litre syringe, and flow calibration with a decompression calibrator. After two years of study the mean number of spirometric recordings performed per spirometer was 693 (range 237-1178), and the mean number of calibration checks was 33 (range 2-57). The coefficient of variation of the calibration signal was 1-2% for syringes and 0.5-1% for the decompression calibrator. The bearings of one turbine exhibited excessive friction after 17 months. None of the other 29 instruments showed drift, and a general drift of all spirometers towards larger or smaller readings could not be shown. However, unforeseen problems in the stability of the calibrating devices were observed. The small hand held turbine spirometers are suitable for long term patient-administered serial spirometric testing. The two year durability is acceptable and the long term reproducibility excellent.