A prerequisite in the study of abnormal body function is the ability to establish the limits of normal. In the case of parameters such as cardiac output that vary with the size of the subject, it has become an accepted practice to standardize values in relation to the body surface area. Thus the cardiac index describes the cardiac output per square metre of body surface area, and the stroke index describes the volume of blood per heart beat per square metre of body surface area. The validity of these expressions depends on the premise that there is a constant or straight line relation between body surface area on the one hand, and cardiac output and stroke volume on the other, over the whole range of body size to be studied, and that the relation can be described by a simple regression equation cutting the intercept at zero. Only where this is so is it meaningful to refer to "the normal" cardiac index or stroke index. Though this premise is backed by observations in the case of adult or adolescent subjects, it was until recently entirely unsupported in the case of children and is still unsupported by any data for infants. This report is an attempt to supply the necessary data. SUBJECTS AND METHODSThe study concerns 77 subjects divided into three age-groups, one consisting of 22 children 3 weeks to 4 years in age, one of 31 children 5 to 15 years of age, and the third of 24 healthy adult volunteers ranging between 20 and 52 years of age. The two younger groups consisted of children without cardiovascular abnormality, in whom minor elective surgery was about to be performed. Physical data regarding 46 of these subjects have been reported elsewhere . Light anvsthesia was used in the two younger age-groups. This was induced without premedication with 80 per cent nitrous oxide in oxygen and was maintained with 50 per cent nitrous oxide, in some cases with the addition of 0 25 per cent halothane. The adult group received no sedation but the subjects were rested for half an hour before the procedure. The local pain of venepuncture was minimized by infiltrating the area with 2 per cent "novocaine." These subjects were thus not truly basal and, in an attempt to eliminate the most tense, data were arbitrarily rejected when heart rates exceeded 84 beats a minute.The cardiac output was calculated from dye dilution curves (Hamilton et al., 1928) using a directly calibrated ear oximeter. Injections were made into an antecubital vein, or in the case of young children into the external jugular vein, and were immediately and forcefully flushed in with 5-10 ml. normal saline, a technique that gives identical results to injections made into the central circulation (Bousvaros et al., 1962). In earlier studies the indicator was Evans blue dye (T 1824) in a dose of 0-2-0-3 mg./kg., the concentration of which was recorded by an automatic computing ear oximeter (Sekelj et al., 1958). Subsequently, the oximeter was simplified McGregor, Sekelj, and Adam, 1961) and the dye changed to Coomassie blue (0-3-0-7 mg./kg.).

Experiences with three patients with cor triatriatum illustrate the urgent need for early recognition of this obstructing diaphragm in the left atrium. A 4-month old infant died with severe and progressive heart failure before cardiac studies were completed. A 3-year-old girl was under observation for one year prior to death in acute pulmonary edema. In spite of extensive studies the diagnosis was not established. A 16-month-old male had increasing dyspnea and fatigue for 3 weeks prior to referral. The hemodynamic studies revealed marked elevation of pulmonary capillary and pulmonary artery pressures. Unusual features included a continuous murmur high in the left axilla and striking enlargement of the left atrium. Excision of the obstructing membrane was accomplished at open operation with cardiopulmonary bypass, and striking clinical improvement has been maintained for 3 years.

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