The Relation Between Cardiac Output and Body Size

Abstract

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.).

Hemodynamic Findings in Normal Children

“…These children were catheterized for a variety of reasons, including unusual innocent murmurs [13], idiopathic dilatation of the pulmonary artery [4], apparent cardiomegaly [5], pectus excavatum [2], localized pulmonary sequestration [I], and mild pulmonic insufficiency without electrocardiographic evidence of right ventricular hypertrophy [I].…”

“…Indeed thc term 'cardiac index' would secm to imply that this is a satisfactory method for measuring onc aspect of the integrity of the cardiovascular system. I n spitc of common usage, the validity of the cardiac index has been challenged [2, 27, 281 and defended [3,5,13, 291 rcpcatcclly in recent years. 'Thc bcst available surface area estimate, namely the nomogram developed by SENDROY and CI~CCHINI [25], was applied to our data.…”

Diagnostic evaluation of paediatric pulmonary hypertension in current clinical practice

“…At diagnosis, complications were reported in 37 patients (6.7%) (table 7). Of these 37 patients the most frequent events were systemic hypotension (17), requirement of inotropic support was seen (14), and pulmonary hypertensive crisis was observed in (10) patients, unexpected intensive care admission in (seven), cardiac arrest (five) and arrhythmia requiring intervention (four). No significant differences in complications at diagnosis were seen between prevalent and incident patients (p50.86).…”

Calculating vascular resistances

“…[8][9][10][11][12] Recall that estimates of BSA are generally determined from multiple regression-based formulae using height (in cm) and mass (in kg). Using height and mass in a multiple regression-based formula (to calculate BSA) and then using the resultant estimate of BSA in a linear regressionbased formula (to calculate an index) seems redundant.…”