CHAPTER 21 



Technical aspects of the study of 

 cardiovascular sound 



VICTOR A. McKUSICK 



SAMUEL A. TALBOT 



GEORGE N. WEBB 



EDWARD J . B A T T E R S B Y 



Dejiaiiment of Medicine, Johns Hopkins University 

 Scliool of Medicine, Baltimore, Maryland 



CHAPTER CONTENTS 



The Nature of the Phenomenon 



Physiologic Considerations 



Physical Considerations 

 Transducers 



Filtration, Including Amplification and Low-Frequency At- 

 tenuation (Equalization) 



Filter Systems in Spectral Phonocardiography 

 The Display 



Oscillography 

 Physiologic Data for Correlation 

 Some Practical Aspects of Recording, with a Discussion of 



Artifacts 

 Storage of Cardiovascular .Sound and Correlated Information 

 Special Techniques 

 Calibration of Intensity 



THE FIRST PHONOCARDIOGRAMS in anything approacli- 

 ing the modern sense were made by Einthoven and 

 Gehik (1894) using Lippmann's capillary electrom- 

 eter. Otto Frank of Munich (1904) devised the tech- 

 nique of direct phonocardiography, that is, recording 

 of the precordial vibrations with optical amplifica- 

 tion. The so-called Frank segment capsule was im- 

 proved on and used by workers such as Wiggers, and 

 Orias and Braun-Menendez. The fragility of the 

 capsule membranes and unsatisfactory frequency 

 response characteristics led to the replacement of 

 this technique by others. Einthoven (1907) applied 

 the string galvanometer to phonocardiography. The 



tremendous range of intensities found in cardiovascu- 

 lar sound, far exceeding that of the electrocardiogram, 

 led to frequent accidents with fracture or other dam- 

 age of the string. The development of the vacuum 

 tube for electronic amplification and of various 

 galvanometers opened a new era of phonocardiog- 

 raphy. The review of Rappaport & Sprague (14) in 

 1942 marked the end of earlier techniques in phono- 

 cardiography. 



Concern with the frequency dimension of cardio- 

 vascular sound led to the use of microphones of differ- 

 ing frequency response and to multichannel recording 

 with various filtration and amplification applied in 

 each channel. A number of different systems have 

 been suggested (e.g., Mannheimer, Leatham, Luisada, 

 Maass, Bekkering, and others), each aiming to encom- 

 pass the wide frequency-intensity range of cardio- 

 vascular sound and to permit analysis of faint com- 

 ponents in the presence of intense ones. Satisfactory 

 display of all frequencies in a single record was accom- 

 plished by spectral phonocardiography, an adaptation 

 of the Bell Telephone Laboratories' method of sound 

 spectrography. A development of the 1950's, spectral 

 phonocardiography was a major departure from all 

 previous phonocardiography which had been oscillo- 

 graphic in nature. Also a development of the 1950"$ 

 was intracardiac phonocardiography, the recording 

 of vibrations in the audible frequency range using 

 miniature transducers introduced into the heart on 

 the tip of catheters. The barium titanate catheter 



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