Amplitude modulation issues in Doppler radar heart signal extraction

Medical Doppler radar research has largely been limited to obtaining respiratory and heart rates. While this information is vital for many applications, medical Doppler radar signatures carry significant other information that could lead to cardiopulmonary volume assessments, including cardiac stroke volume (SV), and cardiac output (CO). Accurate recovery of heart signal amplitude is required for these assessments. This paper presents the first analysis of amplitude modulation artifacts on heart signal recovery in Doppler radar systems. The sources of amplitude modulation artifacts are identified, including limitations of linear demodulation, and inherent affects of respiratory signal harmonics on heart signals. Experimental and simulation results demonstrate the validity of this analysis, and outline the path towards successful heart signal amplitude recovery.