Wood, Earl H.

Thirty-three cases of corrected transposition of the great vessels are analyzed: 31 of corrected transposition in situs solitus, and two of corrected transposition in situs inversus. In 18 of these 33 cases, of which 64% were males, diagnosis was confirmed by necropsy or operation. There was no history of congenital heart disease in the families of any of these patients. The person whose sole anomaly is corrected transposition has no hemodynamic basis for symptoms. Symptoms are the result of associated lesions, the most common of which are anomalies of the left atrioventricular valve usually causing incompetence, ventricular septal defects, pulmonary valvular stenosis, and advanced disturbances of atrioventricular conduction. Physical findings in corrected transposition depend upon these associated defects. Noncardiac associated anomalies are rare. Anteroposterior thoracic roentgenograms may suggest the diagnosis, particularly when a narrow waist is present at the base of the heart, accompanied by the absence of a pulmonary-artery "knob" and the presence of an enlarged left atrium. Electrocardiographic features that should suggest corrected transposition are atrioventricular block (particularly 2:1 or complete heart block), abnormal P waves, absent or low R voltage in aVR, an initial Q wave in leads 3, aVR, aVF and V1, absence of a Q wave in lead V6, upright T waves across the precordium in children, and a clockwise spatial loop in the frontal plane. Cardiac catheterization may be diagnostic in this malformation when careful documentation is made of the location of the atrioventricular valves and their relation to the semilunar valves, together with the position of the great vessels in the anteroposterior and lateral views. Alteration of hemodynamics is secondary to associated malformations. Inability to enter the pulmonary artery during catheterization should arouse suspicion, and in these cases, particularly, angiocardiography can be diagnostic. The decision as to whether the most frequently associated malformations exist as isolated entities, or whether they are present in combination with corrected transposition, appears to be the main differential problem–together with the differentiation of corrected transposition with associated cyanosis from complete (that is, uncorrected) transposition. Surgical treatment of corrected transposition has been difficult because of complete atrioventricular block before or after operation, residual incompetence when deformed left atrioventricular valves were present, and the mirror-image arrangement for the coronary arteries. The most common cause of death was cardiac failure, often with a terminal bout of pulmonary edema. The average age at death in this series was about 14 years, with a median age at death of about 4 years. A review of the literature again emphasizes the association of corrected transposition with some degree of atrioventricular block evidenced on the electrocardiogram. The most frequently reported associated cardiac lesions were ventricular septal defect, pulmonary stenosis or atresia, patent ductus arteriosus, and dextrocardia. The incidence of anomalies of the left atrioventricular valve in these reported cases has probably been underestimated.

Protection against the effects of headward acceleration afforded by immersion in water has been assayed in the human centrifuge on 15 trained subjects. Immersion in water to the xyphoid afforded an average protection of 1.1 ± 0.1 G for vision and ear opacity and of 1.6 ± 0.2 G for ear pulse and heart rate. Deeper immersion, to the level of the third rib at the sternum increased the protection to 1.8 ± 0.1 G for vision and ear opacity and to 2.8 ± 0.2 G for ear pulse and heart rate. The protection afforded the various physiologic variables increased with the magnitude of acceleration tested. Protection against loss of consciousness may be greater than protection against blackout and is probably similar to the protection afforded the ear pulse and heart rate. The cardiovascular reactions produced by headward acceleration are qualitatively similar with and without water immersion. This finding does not support the concept that impediment to venous return is the primary determinant of man's tolerance to headward acceleration. Visual symptoms occurred at greater amplitudes of ear pulse, and presumably also at greater blood pressures at head level, during water immersion than during control runs. vision; arterial pressure; heart rate; venous return; arterial pulse in ear Submitted on May 13, 1963

The inapplicability of Beer's law to densitometry of dyes in whole blood or other nonhomogeneous media has been long known. When using a densitometer whose output is directly proportional to the light transmitted, a simple transformation— log X = log (x – x0)—can be employed to allow rapid, accurate estimation of dye concentration. This is facilitated by use of an optical density ruler. The transformation, X = x – x0, can be made mechanically, by shifting the infinity position of the ruler with reference to the zero light transmission position, or electrically, by appropriate use of zero suppression in the densitometer circuit. The transformation results in an exponential (logarithmic) relationship between light transmitted and concentration of the dye (indocyanine green). Readings of relative optical density obtained by use of the ruler are multiplied by a calibration constant to calculate dye concentration. The principles of the transformation have been applied to the determination of the optimal zero suppression required for maintenance of constant sensitivity of the densitometer in the presence of various levels of background dye. densitometer calibration; indocyanine green densitometer; calibration of dye-dilution curves; correction of dye-dilution curves Submitted on September 13, 1963

The assumption that the rate of blood flow past the sampling site is constant is basic to the Stewart-Hamilton estimation of cardiac output. Pulsatile flow might be expected to cause random and systematic errors. In this study dye-dilution curves were recorded simultaneously from two or three sites (pulmonary artery, aortic root, thoracic aorta, femoral artery) after injections of dye into the inferior vena cava, right ventricle, pulmonary artery, or left atrium of anesthetized dogs. The color of the indocyanine-protein complex formed after injection of the dye stabilized rapidly. Such stabilization is required for continuous photometric quantitation of dilution curves with juxtaposed injection and sampling sites. Areas of curves from the central circulation did not differ significantly from each other; they averaged 2.5% less than areas of curves recorded simultaneously from the femoral artery. Heart rate had no consistent influence. The large variability in estimates of cardiac output from curves recorded from the pulmonary artery after injection into the right ventricle was diminished with injection farther upstream. Submitted on May 29, 1961

Blood is nonhomogeneous; hence, the relationship between light transmission and increasing concentration of dye in whole blood is never the perfect exponential curve predicted by Beer's law. Instead, as the concentration of indocyanine green is increased to high levels (40 mg/liter) the light transmission decreases exponentially toward an asymptote at 6–8% transmission for nearly monochromatic densitometers (half-band width: 13–20 mμ), but at 30–40% for densitometers using light of wide-band width. Consequently, following recording of a dilution curve, circulating background dye reduces the change in transmission per unit increase in dye concentration in subsequent curves. This decrease in sensitivity cannot be compensated for by a simple increase in the sensitivity of the densitometer or in the intensity of its light source. Compensation can be attained, however, if increasing densitometer sensitivity is associated with the automatic scale expansion provided when a suppressed zero point is used. At correct zero suppression, the deflection for zero output of the densitometer coincides with the asymptotic transmission value mentioned above. indicator-dilution in circulation; blood flow measurement; blood optical density; dye dilution technic; cardiac output measurement Submitted on April 15, 1963

In studies on dogs, blood was sampled as for the recording of dye-dilution curves through monochromatic densitometers. Injection of hypertonic media into the superior vena cava caused transient increases in the optical density of blood in the pulmonary and femoral arteries so as to produce apparent “dye” curves. The injection of hypotonic and hemolyzing media produced negative deflections, representing decreases in the optical density of blood, as did brief ventilation with 5% and 50% carbon dioxide in oxygen. Similar changes were demonstrated in vitro. They were compensated for in vivo by the use of a dichromatic densitometer. The changes observed are attributed to altered physical properties of the erythrocytes, which consequently change their light-transmitting and light-reflecting characteristics. Such nonspecific changes in the optical density of blood may constitute an important source of error in monochromatic densitometry done on whole blood. Submitted on January 11, 1961