Photolethysmograph: An Introduction To Photoplethysmography

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1.1 Introduction to Photoplethysmography
Heart, the key organ of the circulatory system, supplies blood to body parts by rhythmic contraction (systole) and relaxation (diastole) – the heartbeat. Heart rate is the number of beats per minute (BPM) is an important vital signs measurement for cardiovascular health and human’s wellbeing. There are many methods to measure heart rate (or pulse). One simple method is to manually count the pulse by placing finger on Radial pulse (Wrist) or the Carotid pulse (neck). The need for the ceaseless observation of the heart rate motivates for the invention of heart rate monitors. Another essential factor is the Oxygen saturation (So2 or SpO2), the oxygen concentration in hemoglobin. As the name says, we need oxygen to survive. To achieve this, the technique Pulse oximetry is employed. Pulse oximetry produces a graph, called Plethysmogram.
Plethysmograph is a Greek word in which plethynein means to increase and graphein means to record or to write. Photoplethysmograph is a Plethysmograph as a result of light. So, Photoplethysmograghy (PPG) means recording differential portion of blood in human tissue by optical means. Photoplethysmography technique was first described in 1930s [1]. It is a non – invasive method of quantitative extraction of Heart Rate (HR) and SpO2.
1.2 Clinical Relevance:
Heart rate variability (HRV) is one of autonomic responses. In case of ICU’s, Anesthesiology and in Emergency care continuous monitoring of heart rate variability and SpO2 is very essential for the assessment of patients’ health condition. HRV is due to physical, physiological, psycho-emotional activities [2] and other factors. In Pulmonary - respiratory, Cardiac – heart related, Trauma - injured, Paediatric -Ne...

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...e data from the camera is fed to the processing unit in a computer (PC). The raw data is processed and the heart rate and the PPG waveform are displayed on the screen.

[1] Yu Sun, Charlotte Papin, Vicente Azorin-Peris, Roy Kalawsky, Stephen Greenwald and Sijung Hu, Use of ambient light in remote photoplethysmographic systems: comparison between a high-performance camera and a low-cost webcam.
[3] Clinical Use of Pulse Oximetry – Pocket Reference 2010
[2] Anaesthesia Update, Volume 14, June, 2011
[4] Light Tissue Interaction
[5] Photoplethysmography: Beyond the Calculation of Arterial Oxygen Saturation and Heart Rate

[101] http://www.missionignition.net/bms/led_heal_clip_image008.jpg
[102] Oleg Kim, John McMurdy, Collin Lines, Susan Duffy, Gregory Crawford and Mark Alber, Reflectance spectrometry of normal and bruised human skins: experiments and modeling

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