Stethoscope
Transform your smartphone into a digital stethoscope
Author:
Title 4
Learning objectives :
This activity allows students to transform their smartphone into a stethoscope to visualize their heart rate. It establishes a fascinating link between digital technology and human physiology.
Concepts covered
Heart sounds; Signal processing; Filtering; Cardiac cycle; Systole and diastole
What students will do :
The student uses their smartphone's microphone as an acoustic sensor to detect heartbeats. By placing the device against their chest and activating signal filtering in FizziQ, the student can record the sound waves produced by their heart, observe their characteristic shape and then calculate their heart rate from the number of peaks identified.
What is required :
Smartphone with the FizziQ application; A calm environment; FizziQ experience notebook
Scientific background :
Heart sounds, commonly called "lub-dub", are produced by the closing of heart valves during the heart's cycle of contraction and relaxation. The first sound ("lub") is duller and prolonged, caused by the closure of the atrioventricular valves (mitral and tricuspid) during ventricular contraction (systole). The second sound ("dub") is shorter and higher, produced by the closure of the semilunar valves (aortic and pulmonary) when the pressure in the arteries exceeds that of the ventricles at the end of systole. A smartphone's microphone, although designed to pick up the human voice, has sufficient sensitivity to detect these acoustic vibrations, particularly when placed firmly against the sternum, where sounds are best transmitted through the rib cage. The main challenge is the signal-to-noise ratio: heartbeats are of low amplitude compared to ambient noise and body movements. This is why filtering is crucial. The low-pass filter set at 70 Hz in FizziQ attenuates high frequencies (including most breathing and ambient noise) while preserving heart sounds which are primarily between 20 and 150 Hz. To optimize the measurement, it is recommended to: 1) Maintain constant but not excessive pressure of the phone against the chest; 2) Hold your breath briefly to reduce interference; 3) Remain perfectly still while recording. Signal visualization allows one to observe not only the heart rate, but also the separation between the two characteristic sounds, providing a window into the dynamics of the cardiac cycle. This simple but powerful technique illustrates how everyday devices can be hijacked for rudimentary medical applications.