424 



HANDBOOK OF PHVSIOLOGV 



CIRCULATION I 



valuable in assessing the hemodynamic and patho- 

 logic alterations occurring in congenital heart disease. 

 Sodi-Pallares (225) has developed to a high degree 

 the use of the electrocardiogram in evaluating systolic 

 and diastolic overload patterns of the right and left 

 ventricles. Disturbances in conduction are best 

 evaluated by electrocardiographic studies. Intra- 

 cardiac electrocardiograms (130) have pro\-ed of value 

 in this regard and can also give information as to the 

 site in the heart in which the catheter-tip electrode 

 is located. 



The accuracy of radiologic examination has also 

 benefited from the elucidation that has occurred in 

 the past decade regarding the hemodynamic and 

 pathologic alterations associated with given defects. 

 One example is the ability of the radiologist, by 

 e.xamination of the peripheral lung fields, to estimate 

 with some degree of confidence whether increased 

 or decreased blood flow through the pulmonary 

 arterial segments is present. 



In general, as a result of increased knowledge of 

 the hemodynamic alterations that occur in congenital 

 heart disease and the correlation of these alterations 

 \\ ith clinical findings, clinicians have gready increased 

 their ability to evaluate these defects. With certain 

 exceptions, however, these clinical techniques are of 

 limited value to the physiologist in carrying out basic 

 studies of the hemodynamic alterations, and in the 

 patient with complicated or unusual defects the 

 clinician must resort to hemodynamic studies to ob- 

 tain a diagnosis of the defect or defects present. 



Intracardiac Catheterization 



Cardiac catheterization has played an in\aluable 

 role in the diagnosis of congenital cardiac defects as 

 well as in providing the means for accurate investiga- 

 tion of the hemodynamic alterations associated with 

 various disease complexes. The increased ability of 

 clinicians to diagnose many cardiac detects that has 

 resulted from correlation of clinical findings with 

 objective hemodynamic studies and surgical findings 

 has made it unnecessary for many patients with 

 congenital cardiac defects to undergo cardiac cathe- 

 terization. The skilled clinician reserves the procedure 

 of diagnostic cardiac catheterization chiefly for two 

 types of patients: /) the patient who is relatively 

 asymptomatic and in whom the clinician is unai:)le 

 to decide whether a congenital cardiac defect is 

 present, and 2) the patient with a complex combina- 

 tion of defects in whom, because of the complicated 

 nature of the resulting hemodvnamic alterations, the 



clinician is unable to make a definitive diagnosis. 

 These patients also present a challenge to the hemo- 

 dynamic laboratory and require the best equipment 

 as well as highly trained individuals to attain a defini- 

 ti\e diagnosis in a high percentage of the patients 

 studied. 



Since cardiac catheterization is a basic and valu- 

 able technique for many hemodynamic and other 

 studies in human as well as animal investigations, a 

 rather detailed discussion of various aspects of this 

 procedure will be presented. 



PRESSURE RECORDING. Measurement of phvsiologic 

 variables directly concerned with the heart and cir- 

 culation in man requires that these variables be 

 determined on the intact, preferably unanesthetized 

 person. Therefore, direct measurements of many 

 of the variables must commonly be made through 

 small needles or long, narrow-bore flexible tubes. 

 Since variables such as blood pressure have both 

 static and dynamic components, high-fidelity re- 

 cording of them under such circumstances requires 

 close attention to the frequency and damping char- 

 acteristics of the instruments used. Adequate instru- 

 mentation must be capable of faithfvil reproduction 

 of both the static component and all dynamic com- 

 ponents of a maainitude to be of practical importance. 



The highest frequencies of the dynamic components 

 of practically important magnitudes in a complex 

 wa\'e form, such as an arterial pressure pulse, are 

 not accurately known. It is generally considered, 

 however, that instruments with a uniform dvnamic 

 sensitivity to the tenth harmonic of the fundamental 

 frequency of such complex \\ave forms are suitable 

 for high-fidelit\' recording of the wa\'e concerned. 

 By this criterion, since the heart rate of human beings 

 seldom exceeds 240 beats per min, an instrument 

 with a uniform sensitivity from o to 40 cycles per 

 sec should be adequate for the recording of arterial 

 blood pressure and most other physiologic variables 

 a.ssociated with the cardiovascular system. Recent 

 direct evidence indicates that manometer systems 

 with a uniform dynamic response over the frequency 

 range from o to 10 cycles per sec will record the 

 pressure variations in the circulatory system in man 

 without significant amplitude distortion (235, 267). 



A manometer system suitable lor direct recording of 

 blood pressure should possess the following charac- 

 teristics: high natural frequency; high stability; 

 linear calibration; usability with long leads; insen- 

 sitivity to mo\ement, temperature, and humidity; 

 imperviousness to electrolyte solutions; simplicity 



