Influence of skin type and wavelength on light wave reflectance

Abstract

DedicationIn dedication to my family, friends, and Jessie for whom I could of not done this without.Their constant support, faith and encouragement provided me with the strength and passion that allowed me to pursue my dreams. They are my foundation and worked just as hard as I did being here for me. Thank you with all my heart and love.v Acknowledgements A very special thanks to Dr. Tanaka my primary investigator and advisor, whom kept me on track and taught me that research, is more than just knowledge; it is a complete pursuit and dedication. His ability to drive and teach were great examples and helped me grow as a graduate student and researcher but also as a person. Thanks to Dr.Brothers for being my second reader and providing a second set of eyes to my ideas. Heart rate monitoring (HRM) is an essential tool for monitoring physical activity and as a diagnostic tool in the clinical setting. The ability to monitor heart rate gives users and clinicians vital information about the current condition of the cardiovascular system before, during, and after exercise. However, HRM requires a telemetric chest strap, and comfort, transmission and fit can become problems with the chest strap. New technology using photoplethysmography (PPG) has emerged recently to provide the possibility of HRM without a telemetric chest strap during exercise. The aim of this study was to determine if a new device could detect heart rate over a broad range of skin types (I-V), and whether what wavelength would be most suitable for detecting the signals. A light emitting diode (LED) based PPG system was used to determine heart rate by change in pulsatile blood flow on 22 apparently healthy individuals (11 male and 11 female, 20-59 years old) of varying skin type. Skin type was classified according to a questionnaire in combination with digital photographs with a skin type chart. Each subject was exposed to four different wavelengths (470 nm, 520 nm, 630 nm, and 880 nm) and multiple trials were conducted on each wavelength. Heart rate detection was vii represented by modulation of the incident light wave and normalized by saturation into a pulsatile waveform represented as modulation average. The 520nm wavelength classified as visible green light provided a significantly greater (p<0.001) ability to detect heart rate. Increasing levels of melanin, or darker skin type (Type V) showed decreased modulation however this trend was not significant (p<0.067). There was no significant interaction between the wavelength of light and the skin type. In conclusion, a PPG based device can detect heart rate across skin types and use of a green light wavelength provides an even greater resolution.viii

Validation of photoplethysmography as a method to detect heart rate during rest and exercise

“…Although this would seem to be an obvious area of scrutiny of such devices, data on the accuracy of instantaneous heart rate in people of varied skin pigment using a photoplethysmograph is scarce. These current data agree with Fallow et al [38], who found that green light wavelengths of 530 nm demonstrated the greatest modulation compared to all other wavelengths tested in resting and exercise conditions, regardless of skin type.…”

“…These data suggest that future research of this nature include a measurement of device proximity to the wrist. Discrepancy may also be owed to the light wavelength used in each device and how they detect heart rate in participants with varied skin types [38]. These concerns will be addressed in the discussion section.…”

Evaluation of Baroreflex Function Using Green Light Photoplethysmogram in Consideration of Resistance to Artifacts

“…5 indicates that the IRPTT cannot be calculated accurately because of its susceptibility to noise or motion artifacts, despite the subject being in a resting condition. This advantage of the green PPG is consistent with the conclusions from previous studies [13][14][15]. We speculate that this is due to the fact that the light path length of green LED is shorter than that of near-infrared LED.…”

“…Previous studies indicate that green PPG sensors are more resistant to motion artifacts than near-infrared PPG sensors [13][14][15]. Therefore, a green PPG sensor is often used to estimate the state of blood ow and to measure heart rate.…”

Effect of Ambient Humidity on the Transmission of UV/Visible Light through Model Human Epidermis

“…Most recently, light scattering properties of surface of human skin are theoretically studied using Maxwell's equation [10]. The effects of varying level of melanin in light reflectance of a wide range of wavelength are investigated for its applications in biomedical optics such as heart rate monitoring devices [11]. However, the impact of ambient humidity on the optics of the skin is poorly understood.…”