Pulmonary Doppler signals: a potentially new diagnostic tool

Abstract

To overcome the limitations due to ultrasound attenuation by the air in the lungs, in order to study the pulmonary system using an advanced signal processing technology. Pulsed spectral Doppler signals were obtained over the chest wall using a signal processing and algorithm package (transthoracic parametric Doppler, TPD, EchoSense Ltd, Haifa, Israel) in conjunction with a non-imaging Doppler device (Viasys Healthcare, Madison, WI, USA) coupled with an electrocardiogram. The signals picked up by a transducer positioned at various locations over the chest wall, were treated for noise, analysed parametrically and displayed in terms of both velocity and power originating from moving ultrasound reflectors. Clear reproducible lung Doppler signals (LDS) were recorded. Up to five bidirectional triangular waves with peak velocities of 20-40 cm/s, that survived the 40 dB/cm attenuation of the lung, were recorded during each cardiac cycle. The first signal coincides with early ventricular systole, the second with late systole, the third and fourth with diastole, and the last with atrial contraction. LDS originate from different elements and phases of cardiac activity that generate mechanical waves which propagate throughout the lung and are thus expressed in pulsatile changes in ultrasound reflections. While such signals could originate either from pulsatile blood flow or reflections from movement of the blood vessel--alveolar air interface, the experimental evidence points towards the tissue--air interface movements due to vessel expansion as the origin. The LDS can potentially be an important tool for diagnosing and characterizing cardio-pulmonary physiological states and diseases.