ABSTRACT

Objective: To develop and validate a portable volumetric capnograph for collecting data on ventilatory mechanics during spontaneous breathing for outpatient use. Methods: The device was developed by integrating the following commercially available sensors: a Hamilton® flow sensor (variable orifice; Hamilton Medical AG, Graubünden, Switzerland); an SDP810-125PA differential pressure sensor (Sensirion AG, Stäfa, Switzerland); and a Capnostat 5 CO2 sensor (Philips Respironics, Murrysville, PA, USA). An Arduino UNO-R3® microcontroller (Arduino, Monza, Italy) was used as an interface between the sensors and a laptop computer, and a Python application was used to acquire data at 10 ms intervals (100 Hz). Validation included static tests (flow: 0-45 L/min; partial pressure of CO2: 0-100 mmHg) and tests with five healthy volunteers (n = 115 respiratory cycles), in comparison with the reference equipment (a CO2SMO Plus® DX-8100 oxycapnograph; Philips Respironics). Results: The static tests showed excellent linear correlation for flow and CO2 concentration. For the tests conducted with the five volunteers, no significant differences were observed between the portable volumetric capnograph and the reference equipment for any of the variables analyzed. Intracycle variability was observed in the capnography curves, reflecting the physiological characteristics of spontaneous breathing. Conclusions: Our portable volumetric capnograph demonstrated the ability to collect accurate data on flow and partial pressure of CO2 during spontaneous breathing, with performance equivalent to that of the reference equipment. The variability in the capnography curves represents an intrinsic characteristic of spontaneous breathing that must be considered when developing algorithms for calculating physiological indicators.

Keywords: Volumetric capnography, microcontroller, respiratory monitoring, spontaneous breathing, portable device.

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