42 Applied Biophysics 



Figure 1 shows a photograph of the apparatus, and figure 2 

 a schematic diagram. The heart sounds are picked up by a 

 piezoelectric microphone, which converts them into electrical 

 pulsations. These are amplified by a thermionic-valve amplifier 

 which has special variable electrical frequency controls incor- 

 porated in it. An electrical stethoscope reconverts the amplified 

 electrical pulsations into sound waves. The phonocardiogram 

 can be directly observed on the long afterglow screen of the 

 double-beam cathode-ray oscilloscope. The electrical variations 

 of the heart can be simultaneously amplified by the second 

 channel, and directly observed as the second trace on the screen. 



The following are some of the uses of the phonoelectrocardio- 

 scope in cardiology : 



1. Simultaneous direct visual observation of the phonocardio- 

 gram and electrocardiogram, plus amplified auscultation. 



3. Simultaneous direct visual observation of the phonocardio- 

 gram and sphygmogram, plus amplified auscultation. 



3. Simultaneous direct visual observation of the electrocardio- 



gram and pneumocardiogram, plus amplified ausculta- 

 tion. 



4. Simultaneous direct visual observation of a logarithmic 



phonocardiogram, and stethoscopic phonocardiogram, or 

 any one of the foregoing with a linear phonocardiogram, 

 plus amplified auscultation. 



5. Simultaneous direct visual observation of the phonocardio- 



gram of one area with that of another, plus amplified 

 auscultation. 



6. Simultaneous direct visual observation of any pair of 



electrocardiogram leads, such as leads I and III. 



7. Photographic registration. 



8. Murmurs or desired sounds can be accentuated and un- 



desirable ones muted by filter controls. 



Figure 3 shows a peculiarity of the double-beam cathode-ray 

 tube. It will be noted that the bottom logarithmic phono- 

 cardiogram is apparently 180 degrees out of phase compared 

 with the similar trace on the top. This can be rectified by 



