The Ultrasonic Directional Tidal Breathing Pattern Sensor: Equitable Design Realization Based on Phase Information

Abstract

Pulmonary ailments are conventionally diagnosed by spirometry. The complex forceful breathing maneuver as well as the extreme cost of spirometry renders it unsuitable in many situations. This work is aimed to facilitate an emerging direction of tidal breathing-based pulmonary evaluation by designing a novel, equitable, precise and portable device for acquisition and analysis of directional tidal breathing patterns, in real time. The proposed system primarily uses an in-house designed blow pipe, 40-kHz air-coupled ultrasound transreceivers, and a radio frequency (RF) phase-gain integrated circuit (IC). Moreover, in order to achieve high sensitivity in a cost-effective design philosophy, we have exploited the phase measurement technique, instead of selecting the contemporary time-of-flight (TOF) measurement; since application of the TOF principle in tidal breathing assessments requires sub-micro to nanosecond time resolution. This approach, which depends on accurate phase measurement, contributed to enhanced sensitivity using a simple electronics design. The developed system has been calibrated using a standard 3-L calibration syringe. The parameters of this system are validated against a standard spirometer, with maximum percentage error below 16%. Further, the extracted respiratory parameters related to tidal breathing have been found to be comparable with relevant prior works. The error in detecting respiration rate only is 3.9% compared to manual evaluation. These encouraging insights reveal the definite potential of our tidal breathing pattern (TBP) prototype for measuring tidal breathing parameters in order to extend the reach of affordable healthcare in rural regions and developing areas.

Keywords: 3D printed blow pipe; AD8302; pulmonary assessment; tidal breathing; ultrasonic phase detection.

Figure 1

The entire system architecture comprising the flow pipe, the electronic circuitry and acquisition in laptop through Python-based bespoke software GUI. TBP: tidal breathing pattern.

Figure 2

The 3D printed flow pipe.

Figure 3

The custom-made TBP acquisition software interface (a) the initial screen to enter the subject and trial information; (b) the data visualization window depicting the acquired TBP waveform.

Figure 4

The flow pipe arrangement for phase detection to comprehend respiration flow.

Figure 5

The change in V_Phase with change in phase difference at 40 kHz.

Figure 6

Change in phase $\partial {\phi }_{\max }$ with respect to the angle θ (v_max = 10 m/s).

Figure 7

The TBP signal preprocessing steps.

Figure 8

Tidal breathing pattern signal with respiratory parameters annotated. PIF: peak inspiratory flow; PEF: peak expiratory flow; t_PEF: Time to peak expiratory flow; t_PIF: peak inspiratory flow.

Figure 9

(a) The setup comprising a 3-L syringe (fitted at the mouthpiece of the blowpipe) in series with a TBP sensor during the calibration phase; (b) variation in the output of TBP device (V_OUT) during slow, medium and fast rate of syringe-piston push (EXP expiration) and pull (INSP: inspiration).

Figure 9

(a) The setup comprising a 3-L syringe (fitted at the mouthpiece of the blowpipe) in series with a TBP sensor during the calibration phase; (b) variation in the output of TBP device (V_OUT) during slow, medium and fast rate of syringe-piston push (EXP expiration) and pull (INSP: inspiration).

Figure 10

Subject breathes through the blowpipes of TBP and spirometer (connected in series) during the system validation phase.

Figure 11

Breathing rates computed by the experimenter (BR_manual) and by calculating the TI and TE (BR_calculated) from the TBP signal.

Figure 12

Tidal, forced, and nasal breathing acquired by the developed TBP device.