Heart-valve sounds obtained with a Laser Doppler Vibrometer

The present work investigates the use of a Laser Doppler Vibrometer (LDV) to record valve sounds and characterizes those recordings. An LDV (Polytec PDV-100) was used to measure the normal component of the velocity of the chest wall at 30 points (grid of 6 × 5 points) in each of seven subjects. The recorded signals were analyzed in the frequency domain and filtered to obtain the SI and S2 heart sounds. From all grid points a center of energy (CoE) was calculated for the signal energy, separately for the SI and S2 sounds. The LDV signal reached a noise floor for a frequency of >80 Hz, whereas 99% of the signal energy was below 80 Hz. The signal to noise ratio was approximately 24 dB if measured directly on the (caucasian) skin, and up to 45 dB if special markers were used. There was little difference in signal amplitudes between measurement points on the ribs as compared with the intercostal spaces. Amplitudes of the valve sounds were below 1 mm/s. The mean centers of energy were to the left of the sternum, with the CoE of the S2 sound about 11 mm superior to the CoE of the SI sound on average. The LDV is an interesting new, non-contact, modality for the recording of heart sounds with excellent signal quality and reproducibility.