Clinical Studies

The goal of the clinical studies in human subjects is to investigate acoustic changes due to pathologies such as pneumothorax (PTX).

Experiment Setup

Piezoelectric sensor for measuring transmitted sound on skin surface

 

 

  • PTX was induced in 12 patients during video assisted thoracic surgery where lung collapse is a part of the procedure.
  • Broad band acoustic signals (0-2000 Hz) were introduced into the endotracheal tube of mechanically ventilated patients in the OR.
  • Transmitted sounds measured at the right chest surface at the intersection of the mid axillary line and nipple line for the normal and PTX states were acquired by a in-house-developed piezoelectric sensor.

Clinical Breath Sound Recording

After IRB approval, an electronic stethoscope was used to record sounds at the chest surface of a patient who underwent Video Assisted Thoracic surgery.

During this surgery, the patient rested on his side with the right side up and the right lung was collapsed as a routine part of the procedure. The stethoscope was placed at the intersection of the right mid axillary line and the nipple line. Sound recordings were performed before lung collapse (called the control state, abbreviated as CRL) and after lung collapse (called the pneumothorax, PTX, state).

For each condition, two different sounds were recorded. The first are normal occurring breath sounds (called the passive case) and the second are sounds introduced in the trachea and were transmitted to the chest surface (called the active case). The sound recordings for each case showed a drop in the sound amplitude when lung collapse was introduced.

Active and passive sound recordings for test patients one and four were then analyzed and can be displayed below. The time domain data for the passive case can be seen below:

The above trends show a decreased normalized response for PTX-induced patients.
Below are two similar responses for active cases, shown in the time domain:

The above active cases show a similar trend to the passive cases: in an induced PTX state, the normalized response decreases.

Spectra of Transmitted Acoustic Energy

A drop in acoustic energy with PTX is observed, but sometimes not clearly shown.

 

Energy Ratio for normal and PTX

PTX leads to a drop in acoustic energy ratio.