Smart Textile Based on Fiber Bragg Grating Sensors for Respiratory Monitoring: Design and Preliminary Trials

Abstract

Continuous respiratory monitoring is important to assess adequate ventilation. We present a fiber optic-based smart textile for respiratory monitoring able to work during Magnetic Resonance (MR) examinations. The system is based on the conversion of chest wall movements into strain of two fiber Bragg grating (FBG) sensors, placed on the upper thorax (UT). FBGs are glued on the textile by an adhesive silicon rubber. To increase the system sensitivity, the FBGs positioning was led by preliminary experiments performed using an optoelectronic system: FBGs placed on the chest surface experienced the largest strain during breathing. System performances, in terms of respiratory period (TR), duration of inspiratory (TI) and expiratory (TE) phases, as well as left and right UT volumes, were assessed on four healthy volunteers. The comparison of results obtained by the proposed system and an optoelectronic plethysmography highlights the high accuracy in the estimation of TR, TI, and TE: Bland-Altman analysis shows mean of difference values lower than 0.045 s, 0.33 s, and 0.35 s for TR, TI, and TE, respectively. The mean difference of UT volumes between the two systems is about 8.3%. The promising results foster further development of the system to allow routine use during MR examinations.Continuous respiratory monitoring is important to assess adequate ventilation. We present a fiber optic-based smart textile for respiratory monitoring able to work during Magnetic Resonance (MR) examinations. The system is based on the conversion of chest wall movements into strain of two fiber Bragg grating (FBG) sensors, placed on the upper thorax (UT). FBGs are glued on the textile by an adhesive silicon rubber. To increase the system sensitivity, the FBGs positioning was led by preliminary experiments performed using an optoelectronic system: FBGs placed on the chest surface experienced the largest strain during breathing. System performances, in terms of respiratory period (TR), duration of inspiratory (TI) and expiratory (TE) phases, as well as left and right UT volumes, were assessed on four healthy volunteers. The comparison of results obtained by the proposed system and an optoelectronic plethysmography highlights the high accuracy in the estimation of TR, TI, and TE: Bland-Altman analysis shows mean of difference values lower than 0.045 s, 0.33 s, and 0.35 s for TR, TI, and TE, respectively. The mean difference of UT volumes between the two systems is about 8.3%. The promising results foster further development of the system to allow routine use during MR examinations.

Keywords: fiber Bragg grating sensors; fiber optic sensors; magnetic resonance-compatible; optoelectronic plethysmography; respiratory monitoring; smart textile.

Figure 1

(a) FBGs position and distance between the two FBGs. Blue lines and markers identify the upper thorax right compartment, red lines and markers identify the upper thorax left compartment, green lines and markers identify the line which separates the two compartments; (b) trend of FBG distance during quiet breathing of a healthy subject.

Figure 2

Picture of the experimental set-up.

Figure 3

(a) Trend of the data provided by the OEP; (b) Trend of the data provided by the two FBGs; (c) three different parameters investigated: Respiratory periods, calculated as the time interval between two consecutive peaks, inspiratory periods, calculated as the time interval that elapses between a maximum and the previous minimum of the signal, and expiratory periods, calculated as the time interval that elapses between a minimum and the previous maximum.

Figure 4

(a,b) Bland Altman plot comparing the respiratory period measured by OEP and by the smart textiles with the automatic method and the manual one, respectively; (c,d) Bland Altman plot comparing the inspiratory period measured by OEP and by the smart textiles with the automatic method and the manual one, respectively; (e,f) Bland Altman plot comparing the expiratory period measured by OEP and by the smart textiles with the automatic method and the manual one, respectively.

Figure 5

Correlation between the FBGs wavelength changes and UT volume considering both left and right side. The best fitting lines are also shown.

Figure 6

Comparison between the FBGs wavelength changes and UT volume considering both left and right side. The best fitting lines are also shown.