Experimental Assessment of a Variable Orifice Flowmeter for Respiratory Monitoring

Accurate measurement of gas exchanges is essential in mechanical ventilation and in respiratory monitoring. Among the large number of commercial flowmeters, only few kinds of sensors are used in these fields. Among them, variable orifice meters (VOMs) show some valuable characteristics, such as linearity, good dynamic response, and low cost. This paper presents the characterization of a commercial VOM intended for application in respiratory monitoring. Firstly, two nominally identical VOMs were calibrated within ±10 L·min−1, to assess their metrological properties. Furthermore, experiments were performed by humidifying the air, to evaluate the influence of vapor condensation on sensor’s performances. The condensation influence was investigated during two long lasting trials (i.e., 4 hours) by delivering 4 L·min−1 and 8 L·min−1. Data show that the two VOMs’ responses are linear and their response is comparable (sensitivity difference of 1.4%, RMSE of 1.50 Pa); their discrimination threshold is <0.5 L·min−1, and the settling time is about 66 ms. The condensation within the VOM causes a negligible change in sensor sensitivity and a very slight deterioration of precision. The good static and dynamic properties and the low influence of condensation on sensor’s response make this VOM suitable for applications in respiratory function monitoring.

[1]  Gerald L. Morrison,et al.  Response of a slotted orifice flow meter to an air/water mixture , 2001 .

[2]  D. Hess,et al.  Approaches to Conventional Mechanical Ventilation of the Patient With Acute Respiratory Distress Syndrome , 2011, Respiratory Care.

[3]  Peter D. Sly,et al.  Measurement of flow and volume , 1996 .

[4]  Huibert Burger,et al.  Correction factors for oxygen and flow-rate effects on neonatal Fleisch and Lilly pneumotachometers , 2003, Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies.

[5]  Ralph W. Gerard,et al.  Methods in medical research , 1967 .

[6]  E Schena,et al.  A novel control strategy to improve the performances of heated wire humidifiers in artificial neonatal ventilation. , 2012, Physiological measurement.

[7]  Sergio Silvestri,et al.  Non-invasive Estimation of Cardiac Output in Mechanically Ventilated Patients: A Prolonged Expiration Method , 2012, Annals of Biomedical Engineering.

[8]  M. Miller,et al.  Prevention of thermal and condensation errors in pneumotachographic recordings of the maximal forced expiratory manoeuvre. , 1994, The European respiratory journal.

[9]  E. Iso,et al.  Measurement Uncertainty and Probability: Guide to the Expression of Uncertainty in Measurement , 1995 .

[10]  Stephen B. M. Beck,et al.  Experimental study of the pressure drop after fractal-shaped orifices in turbulent pipe flows , 2010 .

[11]  D. Thompson,et al.  Non-invasive automated measurement of cardiac output during stable cardiac surgery using a fully integrated differential CO2 Fick method , 2008, Journal of clinical monitoring and computing.

[12]  M. Heulitt,et al.  Accuracy of small tidal volume measurement comparing two ventilator airway sensors , 2013, Journal of Pediatric Intensive Care.

[13]  Sergio Silvestri,et al.  An orifice meter for bidirectional air flow measurements: Influence of gas thermo-hygrometric content on static response and bidirectionality , 2013 .

[14]  Richard Plavka,et al.  Expired tidal volumes measured by hot‐wire anemometer during high‐frequency oscillation in preterm infants , 2006, Pediatric pulmonology.

[15]  D. Baldwin,et al.  Optimized temperature and deadspace correction improve analysis of multiple breath washout measurements by ultrasonic flowmeter in infants , 2007, Pediatric pulmonology.

[16]  C. K. Yao,et al.  Human intestinal gas measurement systems: in vitro fermentation and gas capsules. , 2015, Trends in biotechnology.

[17]  Sergio Silvestri,et al.  Linearity dependence on oxygen fraction and gas temperature of a novel Fleisch pneumotachograph for neonatal ventilation at low flow rates , 2012 .

[18]  Emiliano Schena,et al.  Flow measurement in mechanical ventilation: a review. , 2015, Medical engineering & physics.

[19]  A. Fleisch.  Der Pneumotachograph; ein Apparat zur Geschwindigkeitsregistrierung der Atemluft , 1925, Pflüger's Archiv für die gesamte Physiologie des Menschen und der Tiere.

[20]  J. Nunn,et al.  Evaluation of metabolic measuring instruments for use in critically ill patients. , 1990, Critical care medicine.

[21]  Emiliano Schena,et al.  Design and Characterization of a Bidirectional, Low Cost Flowmeter for Neonatal Ventilation , 2014, IEEE Sensors Journal.

[22]  Nigel Rankin,et al.  Energy balance in the intubated human airway is an indicator of optimal gas conditioning , 2002, Critical care medicine.