Over recent years, there has been renewed interest in the multiple breath wash-out (MBW) technique for assessing ventilation inhomogeneity (VI) as a measure of early lung disease in children. While currently considered the gold standard, use of mass spectrometry (MS) to measure MBW is not commercially available, thereby limiting widespread application of this technique. A mainstream ultrasonic flow sensor was marketed for MBW a few years ago, but its use was limited to infants. We have recently undertaken intensive modifications of both hardware and software for the ultrasonic system to extend its use for older children. The aim of the current in vivo study was to compare simultaneous measurements of end-tidal tracer gas concentrations and lung clearance index (LCI) from this modified ultrasonic device with those from a mass spectrometer. Paired measurements of three MBW, using 4% sulfur hexafluoride (SF(6)) as the tracer gas and the two systems in series, were obtained in nine healthy adult volunteers. End-tidal tracer gas concentrations (n = 675 paired values) demonstrated close agreement (95% CI of difference -0.23; -0.17%, r(2) = 1). FRC was slightly higher from the MS (95%CI 0.08;0.17 L), but there was no difference in LCI (95%CI -0.10; 0.3). We conclude, that this ultrasonic prototype system measures end-tidal tracer gas concentration accurately and may therefore be a valid tool for MBW beyond early childhood. This prototype system could be the basis for a commercial device allowing more widespread application of MBW in the near future.

Background: Diagnosis of chronic obstructive pulmonary disease (COPD) and its severity determination is based on spirometry. The quality of spirometry is crucial. Objectives: Our aim was to assess the quality of spirometry performed using a spirometer with automated feedback and quality control in a general practice setting in Switzerland and to determine the prevalence of airflow limitation in smokers aged ≧40 years. Method: Current smokers ≧40 years of age were consecutively recruited for spirometry testing by general practitioners. General practitioners received spirometry training and were provided with an EasyOne™ spirometer. Spirometry tests were assigned a quality grade from A to D and F, based on the criteria of the National Lung Health Education Program. Only spirometry tests graded A–C (reproducible measurements) were included in the analysis of airflow limitation. Results: A total of 29,817 spirometries were analyzed. Quality grades A–D and F were assigned to 33.9, 7.1, 19.4, 27.8 and 11.8% of spirometries, respectively. 95% required ≤5 trials to achieve spirometries assigned grade A. The prevalence of mild, moderate, severe and very severe airway obstruction in individuals with spirometries graded A–C was 6, 15, 5 and 1%, respectively. Conclusion: Spirometries in general practice are of acceptable quality with reproducible spirometry in 60% of measurements. Airway obstruction was found in 27% of current smokers aged ≧40 years. Office spirometry provides a simple and quick means of detecting airflow limitation, allowing earlier diagnosis and intervention in many patients with early COPD.

The construction and specific function of a new ultrasonic flowmeter are described. The mean velocity of the respiratory airflow is calculated by measuring the transit times of short ultrasonic pulse trains, simultaneously transmitted upstream and downstream at a 500-Hz rate. The flowmeter system consists of a control unit and a separate flow head. The former includes the power supplies, a controlling microprocessor, most of the signal-processing circuitry, and three analog outputs for flow, volume, and temperature. The flow head contains the respiratory tube with a constant circular cross section (length 90 mm, diam 20 mm, dead space 35 ml), a fast temperature sensor, two electronic circuits for processing of flow and temperature data, and a sound transmission channel with two capacitive ultrasonic wide-band transducers. This respiratory airflow meter, suitable for spirometric maneuvers (vital capacity, forced vital capacity) as well as for long-term breath-by-breath respiratory analysis, is extremely fast (response time 1-2 ms) and accurate (volume accuracy with room air +/- 0.7%), with low noise (below 9 ml/s), a wide flow range (bidirectional from 0 to 9 l/s), and a flat frequency response up to 70 Hz.

No abstract

The measurement of the tracer gas concentration with the molar mass signal of the ultrasonic flow meter provides a good and simple alternative to respiratory mass spectrometer for FRC measurements in ventilated subjects.