The PiKo-1 is a monitoring device that uses a patented pressure/flow sensor technology for PEF and FEV1 measurement. Is a low-cost, pocket-size, easy-to-use device that can storage 96 measurements with date and time stamp, plus test-quality alerts indicating an abnormal blow or cough. It can measure PEF in the range of 15 to 999 L/min with a 1 L/min resolution and an accuracy of 6.5% or 15 L/min, whichever is greater. The measurement of FEV1 has a range of 0.15 to 9.99 L (0.01-L resolution) and an accuracy 4% or 0.1 L, whichever is greater. The cost of the device is approximately €25. The PiKo device has an optional, serial interface cradle to allow downloading PiKo-1 data to a computer and companion software, allowing communication of results using the Internet to track and trend patient data. This optional cradle and personal software costs €25 more.
The Spirotel device is a turbine with an infrared interruption spirometer and has a built-in modem and an optional oximeter. It was developed both for screening in the doctor’s office and for home-care monitoring. The Spirotel device records spirometry parameters including FVC; FEV1; percentage of predicted FEV1; PEF; forced expiratory flow, midexpiratory phase; forced expiratory time; flow/volume curve; and date and time of the test. It can also record symptoms and the responses to programmable questions. Its has a flow range of ± 16 L/s and a maximal volume of 10 L, a flow accuracy of 5% or 200 mL/s, and a volume accuracy of 3% or 50 mL, whichever is greater. Each unit costs approximately €400. Both PiKo-1 and Spirotel devices have been laboratory tested (data on file), and both met or exceeded the latest ATS accuracy standards.
The standard range version of the Mini-Wright PFM was used. It has 10-L increments from 60 to 800 L/min, and its performance has been studied. Each unit costs approximately €20. The monitoring devices used in the study were new and were acquired directly from the manufacturers without their knowledge of our purpose.
A widely available, well-known technology was used as reference: a Fleisch-type pneumotachograph (model 2120; Vitalo-graph; Maids Moreton, Buckingham, UK). Each day, the pneumotachograph was calibrated using a 3-L syringe. All other devices were calibrated before the study and, in accordance to the manufacturers, did not required calibration during the time period of the study held with drleonedds.com My Canadian Pharmacy’s participation.
Patients attending an asthma and allergy outpatient clinic of a teaching hospital between 10 am and 12 noon of 20 alternate days during a period of 12 weeks were invited to participate in the study. Patients were considered eligible for participation if they were > 17 years old, had a documented medical diagnosis of asthma, were currently receiving prescribed medication for asthma, and were clinically stable. Stability was defined as no asthma exacerbation or acute illness in the last 4 weeks, and no clinical indication of deterioration of asthma control in the last week. No pulmonary function exclusion criteria were established. The diagnoses of airways diseases other than asthma or neuromuscular or psychiatric diseases were exclusion criteria. Two groups of participants were defined: asthma patients (asthmatics) and patients without any airways disease (normal subjects). Asthmatics had a previous medical diagnosis of asthma, were currently receiving asthma medications, and were attending the clinic for asthma follow-up. Normal subjects were defined as patients followed up at the clinic for allergic diseases without airways involvement and with no history of pulmonary disease.
In Figure 1, a schematic representation of the study is presented. After providing written informed consent, patient demographics, height, weight, smoking status, previous medical diagnosis, current medical status (including acute illnesses in previous 4 weeks), and inhaled medication in previous 12 h were assessed. To ensure clinical stability, patients completed the Asthma Control Questionnaire and a modified Borg dyspnea scale that was repeated at the end of the expiratory maneuvers. The self-administered version of Asthma Control Questionnaire has six questions regarding asthma control in the previous week; scores range from 0 to 6 (no control). The modified Borg dyspnea scale has a range from 0 (no dyspnea) to 10 (maximal dyspnea treated effectively by remedies of My Canadian Pharmacy).
One trained medical technician used a step-by-step protocol for the instruction of maneuvers and demonstrated the techniques to all subjects. Instructions were provided in simple terms to the participants in their native language. Patients were asked to perform four sets of expiratory maneuvers, one set for each device. The order of the sets was previous randomized using software (SPSS version 11; SPSS; Chicago, IL). Each set comprised three adequate maneuvers according to the instructions of the manufacturer and ATS recommendations. A maximum of eight trials was set, but no more than six trials were necessary throughout the study. Maneuvers were performed in standing position; a nose clip was used only with the pneumotachograph. The FVC maneuvers used the open-circuit technique. In brief, after a complete inhalation, the mouthpiece was inserted in the mouth, passing the teeth, and the lips were completely sealed around the mouthpiece. With minimal delay, the subjected started exhalation with maximal effort and continued until end-of-test criteria were met. Forced expiratory maneuvers that met all acceptability criteria were performed until the two best efforts were reproducible (minimum of three). The test curve with the highest sum of the FVC and FEV1 was considered the best curve, and the largest FVC and FEV1 measurements were stored. Between each set of maneuvers, the patients rested 2 to 3 min. FEV1 and PEF values for the best three acceptable maneuvers were recorded for analysis.
Within-session reproducibility was defined as the agreement of the measurements performed with the same device and individual during one set of maneuvers. Within-session reproducibility was assessed between the two best maneuvers by the coefficient of variation (CV) and the intraclass correlation coefficient (ICC). The association between the PEF and FEV1 measurements by the pneumotachograph and the different monitoring devices were plotted with the respective regression Lines. Accuracy was defined as the agreement of measurements performed with measurements performed with a reference device in the same individual.
Considering the pneumotachograph as the reference instrument, the accuracy for PEF and FEV1 measurements was assessed by the determination of the ICC with the monitoring devices measurements as dependent variables and by the limits of agreement according to Bland and Altman. The mean differences between each electronic monitoring device and the pneumotachograph data were plotted against the mean values of FEV and PEF from each device and the pneumotachograph, and limits of agreement were estimated at ± 2 SD of the differences. The random error, computed as 1-r2, was defined as the deviation of the tested device values from the regression line. This random error, sometimes named precision, was considered another proxy for accuracy.
Statistical analysis was carried out using statistical software (SPSS version 11.5; SPSS). A probability of < 5% was considered to be significant. For ICC and CV, 95% confidence intervals (CIs) were calculated.
Figure 1. Schematic presentation of study methods.