How does HFCWO work?

High frequency chest wall oscillation (HFCWO) draws its effectiveness from the science of fluid mechanics, the study of fluids and the forces that act upon them. Because mucus is a viscous fluid, it tends to resist movement. But sufficient and sustained airflow creates what physicists call “shear force,” which can cause even high-viscosity fluids to shift and flow.

Marshaling the force of mini coughs


HFCWO applies shear force by producing a “staccato” cough. What feels to the patient like steady, gentle vibration from the Electromed SmartVest® System is actually a series of rapid squeezes. With each oscillation, HFCWO compresses and releases the chest wall, sending a gust of air through the respiratory system. At 15 compressions per second for 20 minutes, HFCWO applies shear force equivalent to 18,000 mini-coughs — with no effort or fatigue for the patient.

Four actions help to clear airways

Clinical and laboratory research finds that HFCWO triggers four distinct actions, all helpful in improving bronchial drainage by mobilizing respiratory secretions:

  • Shearing them away from bronchial walls, as the shear force produced by HFCWO ripples across and through the retained secretions.
  • Causing them to thin and become more fluid. Like other viscous fluids, secretions tend to thin when subjected to consistent force, such as the rapid, repeating mini-coughs of HFCWO.
  • Enhancing the body’s process of moving secretions toward central airways. Replicating what healthy lungs do, HFCWO-induced airflow propels secretions upward, from smaller airways to larger ones.
  • Increasing the velocity and clearance rate of retained secretions. Finally, HFCWO helps transport secretions upward toward the mouth, where they can be coughed, swallowed or suctioned away.