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1 J. of the Korean Sensors Society Vol. 17, No. 6 (2008) pp Ÿ q(ppg) w y d w y w x Á ¼ Accuracy improvement of respiration rate based on photo-plethysmography by enhancing motion artifact YoungJung Huh and Gilwon Yoon Abstract Respiration rate is one of the important vital signs. Photo-plethysmography (PPG) measurement especially on a finger has been widely used in pulse oximetry and also used in estimating respiration rate. It is well known that PPG contains respiration-induced intensity variation (RIIV) signal. However, the accuracy of finger PPG method has been controversial. We introduced a new technique of enhancing motion artifact by respiration. This was achieved simply by measuring PPG on the thorax. We examined the accuracy of these two PPG methods by comparing with two existing methods based on thoracic volume and nostril temperature changes. PPG sensing on finger tip, which is the most common site of measurement, produced 6.1 % error. On the other hand, our method of PPG sensing on the thorax achieved 0.4 % error which was a significant improvement. Finger PPG is sensitive to motion artifact and it is difficult to recover fully small respiratory signal buried in waveform dominated by absorption due to blood volume changes. Thorax PPG is poor to represent blood volumes changes since it contains substantial motion artifact due to respiration. Ironically, this inferior quality ensures higher accuracy in terms of respiration measurement. Extreme low-cost and small-sized LED/silicon detector and non-constrained reflection measurement provide a great candidate for respiration estimation in ubiquitous or personal health monitoring. Key Words : respiration rate, photo-plethysmography (PPG), motion artifact, finger, thorax 1. Ÿ q(photo-plethysmography, PPG) x ü x y,, w d w y [1], x d PPG y w k x sy d w š [2]. y ú w w ùš, ú w w œw (Electronic & Information Engineering, Seoul National University of Technology) Corresponding author: gyoon@snut.ac.kr (Received : June 26, 2008, Revised : September 9, October 28, 2008 Accepted : November 10, 2008) ù. w y y k» ùkü w y 4 y z (vital sign) wù (heart rate variability, HRV) w, xx y k [3]ù y z l w w ƒ [4]. y š w w y y l w [5]. w w y y d w» w l y š. y d w ƒ š y y ƒ yw ƒ w. x w y d w g 447

2 52 x Á ¼ ù y yk w ú w, y yk d w y e p w [6-9] { w w y w [10] ƒ p ƒ { y w [11]. w g w ù ƒ w y y» w rw w w l w w. y y w» w w š. PPG y l w vl y y y RIIV(respiration-induced intensity variation) w [12]. PPG y w y d Ÿ ( : Ÿ (LED)) Ÿ ( : photo-transistor silicon detector) j»ƒ š, ƒ w w d ƒ w. PPG x y d w. PPG x sy d w š q m jš n ù d w. y x ƒ yx 660 nm yx ƒ 940 nm q d w q w sy w. y d w q d w. { ü w š yw x ƒw, x ƒ x w ù y. ú x w w. PPG y» w ƒ w qx ùkùš,» y y w sw. y y w q ƒ û» PPG qx» y DC(direct current)» xk ùkù. PPG qx y w 0.16 ~ 0.5 Hz vl w. ù PPG y y x ù x, w y y û q yƒ PPG y w š[13], ù Ÿ w» w. w y y ü ƒ.» y y w [14]. w, w wš w w y w w» y wš [15]. PPG y l y w y w,» PPG d y jš w w y d y w k w. ¾ PPG d ƒ ù ² d w x y» w»» PPG y y w ƒ. y w ƒ PPG d w y d y w jš w. 2. l 2.1. w» x PPG d Ÿ Ÿ. PPG d Ÿ Ÿ Ÿ» v w w z n w ù w w [1]. ƒ { w y y y w w. Ÿ 940 nm q EL-23G(Kodenshi ) Ÿ w. Ÿ» ST-23G smp l w ( 1) l» y d w w» w d l 2 w. PPG ƒ w š w PPG { w. { PPG e ƒ w, { š w» w. w y y w» w» ƒ w. BIOPAC y d (TSD201) ƒ x p ƒ y w s y w y y y d w, wz 17«6y,

Ÿ q(ppg) w y d w y w 53 1. (a) PPG d w LED photo-transistor (b) ƒ d x PPG d Fig. 1. (a) LED and phototransistor used in PPG measurement (b) Example of PPG reflectance measurement on a finger. 2.

3 Ÿ q(ppg) w y d w y w (a) PPG d w LED photo-transistor (b) ƒ d x PPG d Fig. 1. (a) LED and phototransistor used in PPG measurement (b) Example of PPG reflectance measurement on a finger. 2. x Fig. 2. Measurement block diagram. (PASCO PS-2135) g w š ú d y y y w. ƒƒ y DC w» w ú x š m vl(0.16 Hz). DC š y ƒ 1.5 V y s» m k z j fp (MCU, ú ADuC842) ADC (analog-to-digital convertor) g. y 3V w MCUü mw q ƒ 0.5 Hz l m vl e š, y y DAC(digital-to-analog convertor) ù. w z w y w d w. y BIOPAC MP100 Acqknowledge(ver 3.7.3) v w ful l w ( 2). 3. x 3.1. e y y LED ƒ w PPG qx 3 ùkù ~ 4.8 Hz PPG y m vl q 0.48 Hz û PPG sw RIIV w PPG y š. LED { w w y 3 3 qx y m vl q 0.48 Hz û y yƒ w. y y» BIOPAC y d (TSD201) w d y qx 3 qx. PPG w RIIV y y ù k w š. A»» e y yƒ» y y j»ƒ. A z PPG y j e y w š, RIIV y ¾ j w 449 J. Kor. Sensors Soc., Vol. 17, No. 6, 2008

4 54 x Á ¼ 3. d y y ( d ) Fig. 3. Simultaneous measurement of respiration using various methods. 4. ƒ» { PPG l y y Fig. 4. Comparison of the respiratory signals between the two references and thorax PPG method. e. Ÿ w w. { w y y»» yƒ wš š. 3.2.» y y d { PPG y l w y y { y w BIOPAC y d (TSD201) w d y y w { w œm. y yƒ y g mw ù œ» w y» e ƒw w. xw» w g y y w e ƒ w 2 w. 4 { PPG w w y yƒ» y y d qx. 3.3.» š y y w» p wz 17«6y,

5 Ÿ q(ppg) w y d w y w 55 5.» š w y Fig. 5. Counting of respiration rate using a period detection algorithm. wý y w» w. p 5 qx t w š, 3 qx l 1 w ƒqx y y p x š. p w ü š y yƒ ƒ ƒ ü ƒ w» w, 1 l r w y ƒ (x l 0.5 )» ó yƒ û p w. p p ¾» y» w, p ù» y ˆ w. 5 A» y ƒ ˆ š. w» y ˆ w» w» yƒ ˆ z 0.5 ˆ w w, y y x» s» s 1/4» yƒ ˆ. y 120 z, ˆ w 0.5 w. w ˆ v w ƒ w. 5 B w» y ˆ. x w» w w û 5 x w. x ƒ k 5 2z d w t 1 v x y wš y y x z w t w. v x s³ ù 24.6 (r 3.6 ), s³ 176 cm(r 7cm) š s³ 70 kg(r 20.5 kg).» y d w BIOPAC y d (TSD201) (PASCO PS-2135) l y y l ƒ ƒ y wš, y s³» w PPG w y d w. ƒ w { w w y yƒ ƒ { š t 1. PPG w y d y t. 5 d y t wš,» TSD201 s³ w Table 1. Accuracy of Respiration Rate Obtained by the PPG Methods. v x TSD 201 ƒ { (%) PPG PPG ƒ { 1-(1) (2) (1) (2) (1) (2) (1) (2) (1) (2) s³ J. Kor. Sensors Soc., Vol. 17, No. 6, 2008

6 56 x Á ¼. 4. š ƒ w PPG y l y y RIIV, y y w f. RIIV y w y sw w, RIIV PPG w PPG yƒ ù y y y j. ƒ d w PPG x x ù x k d w» w y w w w ƒ. y w ƒ x y e w ù y w w. ƒ PPG d w y d y dw w ( %). ƒ PPG q w vl w z y y sw vl w š ƒ y qx w y d. { PPG y ( 0.4 %) d w ù» y d w m ƒ ùkù. { PPG y w x yƒ ùkû. 3 { PPG y w x y» sy d PPG qx j xk š.» ù kù { w yƒ w. TSD201 p {» rw w š, w LED w y š yw d w.» d { w w, LED w j r. { PPG y y w { ƒ ù q w w w y. z y w w w w x ww» w, w ƒ y y d w x ƒ w. PPG d { w y y d w w. w üù w, t 1 w ƒ PPG w y d w y j w g. ƒ PPG w y y d w y ƒ 6.1 % ù { PPG ƒ 0.4 % w. { yù ú d w y d w» w, w ù r wš, wš x d il x l ù w. 2008» (» /w œm t ) ww. š x [1] J. G. Webster, Medical instrumentation, WILEY, New York, pp , [2] J. G. Webster, Design of pulse oximeters, Institute of Physics Publishing Ltd, London, pp , [3] Barry Krakow, Dominic Melendrez, PSG.T., Teddy D. Warner, Richard Dorin, Ronald Harper, and Michael Hollifield, To breathe, perchance to sleep: Sleep-disordered breathing and chronic insomnia among trauma survivors, Sleep and Breathing, vol. 6, pp , [4] F. Scopesi, M.G. Calevo, P. Rolfe, C. Arioni, C. Traggiai, F.M. Risso, and G. Serra, Volume targeted ventilation (volume guarantee) in the weaning phase of premature newborn infants, Pediatric Pulmonology, vol. 42, pp , [5] J. Rosenberg, M. H. Pedersen, T. Ramsing, and H. Kehlet, Circadian variation in unexpected postoperative death, British Journal of Surgery, vol. 79, pp , [6] B. Hok, L. Wiklund, and S. Henneberg, A new respiratory rate monitor: development and initial clinical experience, JU Clinical Monitoring and Computing, vol. 10, pp [7] A. M. Cyna, V. Kulkarni, M. E. Tunstall, J. M. S. Hutchison, and J. R. Allard, Aura: A new respira- wz 17«6y,

Ÿ q(ppg) w y d w y w 57 tory monitor and apnoea alarm for spontaneously breathing patients, Br. J. Anaesth. vol. 67, pp. 341-345. 1991. [8] C. Larsson and P.

Scheer Comparative provocation test of respiratory monitoring methods, J. Clin. Monit., vol. 17, pp. 97-103. 2002. [10] Ÿ, ½,, ½, ½, k,, x y l l, wz, 17«, 2y, pp. 133142, 2008. [11] Eicksson, I.

7 Ÿ q(ppg) w y d w y w 57 tory monitor and apnoea alarm for spontaneously breathing patients, Br. J. Anaesth. vol. 67, pp [8] C. Larsson and P. Staun, Evaluation of a new fibreoptic monitor for respiratory rate monitoring, J. Clin. Monit. Comput., vol 15, pp [9] M. Folke, F. Granstedt, B. Hok, and H. Scheer Comparative provocation test of respiratory monitoring methods, J. Clin. Monit., vol. 17, pp [10] Ÿ, ½,, ½, ½, k,, x y l l, wz, 17«, 2y, pp , [11] Eicksson, I., Berggren, L., and Hallgrem, S., CO 2 production and breathing pattern during invasive and non-invasive respiratory monitoring, Acta anaesthesiologica Scandinavica, vol. 30, pp , x 2002 ~x w œw [12] L. Nilsson, A. Johansson, and S. Kalman, Respiratory variations in the reflection mode photoplethysmographic signal. Relationships to peripheral venous pressure, Medical & Biological Engineering & Computing, vol. 41, pp , [13] A. K. Ahmed, J. B. Harness, and A. J. Mearns, Respiratory control of heart rate, Eur. J. Appl. Physiol., 50, pp , [14] A. Johansson, P..berg, Estimation of respiratory volumes from the photoplethysmographic signal. Part l: experimental results, Medical & Biological Engineering & Computing, vol. 37, pp , [15] M. Folke, L. Cernerud, M. Ekstm, and B. Hk., Critical review of non-invasive respiratory monitoring in medical care, Medical & Biological Engineering & Computing, vol. 41, pp , ¼ University of Texas at Austin Department of Electrical & Computer Engineering w ~ INSERM (France) research fellow 1990 ~1992 Utah Laser Institute (USA) Research engineer 1992 ~2003 ¾ w» x w œw 453 J. Kor. Sensors Soc., Vol. 17, No. 6, 2008

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