On-Road Evaluation of Unobtrusive In-Car Respiration Monitoring

Abstract

This paper introduces and evaluates an innovative sensor for unobtrusive in-car respiration monitoring, mounted on the backrest of the driver's seat. The sensor seamlessly integrates into the vehicle, measuring breathing rates continuously without requiring active participation from the driver. The paper proves the feasibility of unobtrusive in-car measurements over long periods of time. Operation of the sensor was investigated over 12 participants sitting in the driver seat. A total of 107 min of driving in diverse conditions with overall coverage rate of 84.45% underscores the sensor potential to reliably capture physiological changes in breathing rate for fatigue and stress detection.

Keywords: automotive sensors; breathing rate; continuous health monitoring; unobtrusive monitoring; vital signs.

Figure 1

Schematic of the Colpitts CMOS Oscillator circuit of the MI sensor.

Figure 2

Photograph of the coil of the MI sensor.

Figure 3

Photograph of the MI sensor postioned on the driver seat’s backrest in a BMW 320 car.

Figure 4

Acquired data during on-road measurement: street view, driver view, and sensor signals ((top) gold standard (bottom) custom sensor signal).

Figure 5

Exemplary excerpt of the signal and the reference breathing rate in idle conditions.

Figure 6

Bland-Altman plot over all twelve subjects comparing breath-to-breath intervals derived from the MI sensor and reference breathing rate monitor during driving.

Figure 7

Driving route—highway drive.

Figure 8

Bland-Altman plot comparing breath-to-breath intervals derived from the MI sensor and reference breathing rate monitor during highway drive.

Figure 9

Extracted breath-to-breath intervals over the entire highway drive.

Figure 10

Driving route—rural drive.

Figure 11

Bland-Altman plot comparing breath-to-breath intervals derived from the MI sensor and reference breathing rate monitor during rural drive.

Figure 12

Extracted breath-to-breath intervals over the entire rural drive.

Figure 13

The signal of the unobtrusive respiration signal while driving. (Upper diagram): raw signal; (middle diagram): filtered signal; (lower diagram) reference signal.

Figure 14

The signal of the unobtrusive respiration signal with engine in idle mode. (Upper diagram): raw signal; (lower diagram): filtered signal.

Figure 15

Effect of road conditions on the sensor signal. The red line indicates the transition from rural road to highway.

Figure 16

The signal of the MI sensor over the course of one stop and start. red: start decelaration; black: total stop; magenta: start of acceleration; violet: end of acceleration. (Upper diagram): raw signal; (middle diagram): filtered signal; (lower diagram): reference signal.

Figure 17

The signal of the MI sensor over the course of one turn. The start of turn is indicated by the red line. (Upper diagram): raw signal, (middle diagram): filtered signal, (lower diagram): reference signal.