Experimental Assessment of a Variable Orifice Flowmeter for Respiratory Monitoring

Abstract

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−1and 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.

Comparison of pneumotachography and anemometery for flow measurement during mechanical ventilation with volatile anesthetics

“…Measurement error may be introduced by variations in gas mixture properties caused by changes in temperature, pressure, and humidity relative to the conditions of the gas mixture during flowmeter calibration. The impact of gas temperature and humidity on measurement error have been characterized for orifice-type flowmeters [21, 22], although such factors minimally influence HWA measurement error [23]. Although gas saturated with water vapor at 37 °C may more closely mimic delivered gases used in clinical practice, the use of humidified gas in our experimental protocol would not alter the general conclusions presented here.…”

Contact-Based Methods for Measuring Respiratory Rate

“…Nevertheless, this aspect is relevant for accurate flow measurements, while it can be neglected for the estimation of fR. Orifice meters . They can be split into fixed orifice meters, where the resistance is an orifice plate, and into variable orifice meters, where the plate composing the resistance increases its passage area with flowrate (e.g., it consists of a flexible flap [42,43]). In both cases, the input-output relationship (ΔP vs. Q ) may be expressed as follows: Qi=d21−β42·ΔPρ where Qi is the flowrate calculated considering ideal conditions, d is the diameter of the orifice, β the ratio between the diameter of the orifice and the internal diameter of the pipe, and ρ the gas density.…”

A Wearable System for Real-Time Continuous Monitoring of Physical Activity

“…These solutions, despite being quite accurate, cannot be adopted in physical training monitoring. A more straightforward direct way to assess only f R consists of measuring the flow expired by the subject by using an accurate flowmeter for low-rate flows positioned over the mouth [ 12 , 20 ]. This solution allows the easy detection of exhalation if the breathing is properly conveyed to the sensor, but it cannot be used to monitor the inspiration phase.…”