Improved accuracy and extended flow range for a Fleisch pneumotachograph

• Published in: Medical & biological engineering & computing 1999-07, Vol.37 (4), p.456-460
• Main Authors: Stromberg, NOT, Gronkvist, MJ
• Format: Article
• Language: English
• Subjects: Accuracy; Biological and medical sciences; Calibration; Conductance; Electric conductivity; Equipment Design; Extended flow range; FIowmeter; Flow calibration; Flow measurement; Flow measuring instruments; Flow of fluids; Humans; Investigative techniques of respiratory function; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; MEDICIN; MEDICINE; Pressure effects; Respiratory Function Tests - instrumentation; Respiratory Function Tests - methods; Respiratory mechanics
• ISSN: 0140-0118; 1741-0444; 1741-0444
• DOI: 10.1007/BF02513330

A large linear flow range and a small instrumental dead space volume are incompatible properties for a pneumotachometer (PTM). The linearity of a Fleisch number 2 PTM is studied for flows up to 6 litre s-1 (nominal range 0-2 litre s-1) with various up- and downstream geometries. It is hypothesised that using an array of calibration factors (conductance; flow/pressure), instead of a single calibration factor over the entire flow range, could improve accuracy and also extend the applicable flow range. The conductance against pressure characteristics are calculated with a previously described weighted averaging technique based on multiple strokes from a precision syringe. A single conductance value gives stroke volume errors in the range of -5 to 3% (0-2 litre s-1) and -6 to 11% (0-6 litre s-1) for validation using the same geometry as for calibration. The pressure dependent conductance improves accuracy to within -3% and 1% independent of flow range. However, for validation using a different geometry than for calibration, errors range from -5% to +8%. The degree of non-linearity varies between the geometries (range 3-15%) and is highest when using a one-directional valve upstream of the PTM and a Y-shaped connector. In conclusion, a pressure-dependent conductance improves accuracy and can also be used to extend the applicable flow range up to at least three times the nominal flow range.