Question

2. Download a free heart-rate monitoring app onto your smartphone or tablet, such as Azumio’s Instant...

2. Download a free heart-rate monitoring app onto your smartphone or tablet, such as Azumio’s Instant Heart Rate (available for iPhone and Android, search for it). Or borrow a friend’s. This app measures your heart rate by shining light (from your camera flash) through your skin, and measuring light transmission with your phone’s camera. Cool! a. From your finger, what is your measured heart rate? What were you doing/feeling when you took the reading, e.g. were you resting, standing, actively moving around, calm, nervous, etc.? b. Where else can you measure heart rate with this method? You could try your palm, arm, leg, forehead, etc. Did you measure a similar heart rate to your finger? Many fitness trackers use a similar optical method to measure instantaneous heart rate, like the Fitbit and Apple Watch. These shine a green light onto the skin. Why might green light be best? Consider the color of blood, what that means about absorbance, and how it relates to sensitivity.

Homework Answers

Answer #1

a. From your finger, measured heart rate is 78 /min. (while resting.

b. hand palm and foot palm are the possible options where it seems to work; ie has similar reading as the finger tips.

Green light is used primarily because the human body is a very good absorber of green light. Since the body naturally reduces the amount of green light penetrating the skin from external light sources, the noise floor produced by ambient light is significantly reduced–thus making it easier to measure a meaningful signal from the device.

Our skin color is produced by a natural pigment found in most organisms called melanin. This pigment is produced by a specialized group of cells in the skin known as melanocytes. Melanin is a very good absorber of green light, meaning that darker skin absorbs more green light, producing an obvious problem when the device can’t get its signal through.

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