Vibration patterns of the human chest wall recorded with a microwave interferometer

The vibrational velocity of the anterior chest wall, produced by the cardiac activity within the chest cavity, is recorded with a microwave interferometer. This velocity is cross-correlated with the R wave of the simultaneously recorded EKG and reveals four or five fairly distinct and coherent velocity maxima and minima within each R-R interval. The velocity extrema early in the R-R interval would logically be attributed to ventricular ejection; the mechanical vibration of the chest wall late in the R-R interval is difficult to explain at this time. The instrument operates at 9.3 GHz, which corresponds to a free-space wavelength of 3.1 cm. This wavelength of electromagnetic energy readily passes through normal dry clothing; the vibrational velocity data can be recorded from cooperating subjects who are fully clothed with no physical contact between subject and instrument, The microwave interferometer can thus serve as a noninvasive and noncontacting cardiopulmonary monitor.<>