Interpretation of Changes in “Central” Blood Volume and Slope Volume During Exercise in Man*

Abstract

Under certain circumstances, the volume of a vascular compartment may be estimated by the indicator dilution technic (1, 2). The method usually has been applied to measure the "central" blood volume (CBV). For The first series of observations was made on 4 subjects lying supine, standing, and then exercising with varying grades of severity on a treadmill inclined at an angle of 120 from the horizontal. The cardiac output was measured by the indicator dilution method. A no. 5 Lehman cardiac catheter was introduced into a brachial vein by percutaneous puncture and advanced until its tip lay at the lower end of the superior vena cava. The catheter was kept filled with cardio-green dye,' and successive injections of 7.5 mg of the dye were made by displacement. The duration of each injection (0.5 to 1.0 second) was signaled on the record. The right arm was kept at rest throughout the procedure. Blood was sam-1)led from the right radial artery at a rate of 30 to 50 ml per minute through a Wood cuvet densitometer and was reinfused after each curve. Samples of blood were taken before and after each complete study; known amounts of dye were added to 10-mIl aliquots and drawn through the densitometer to obtain calibrations for the dilution curves. At any given concentration of dye, the deflection obtained with the latter blood sample was 0 to 6 per cent less than that with the former because of the persistence of small amounts of background dye in the blood. Allowance for these minor changes in calibration were made in calculating the area subtended by each indicator dilution curve.The mean transit time of the recorded dilution curve was corrected for delay owing to the sampling system as follows. By means of the apparatus described by Fox, Sutterer and Wrood (11), undyed blood followed by a square wave front of dyed blood was drawn through the sampling system at a rate similar to that used in the experiments. The first derivative of the resulting timeconcentration curve was identical in contour with that which would have been obtained had the sampling system been tested with a sudden single inj ection of dye (11,12). The mean transit time of this curve was calculated; subtraction from that of the recorded curve gave the corrected mean transit time between injection and sampling sites. The CBV was calculated as the product of cardiac output (milliliters per second) and the "true" mean transit time (seconds).In other studies, the cardiac output and the CBV were measured during leg exercise in the supine position. In two subjects a blood pressure cuff was applied to the right arm; this was inflated to a pressure of 250 mm Hg for 3 minutes while the subject performed leg ex-'Kindly supplied by Hynson, Westcott and Dunning, Inc., Baltimore, Md. 375

Reductions in cardiac output, central blood volume, and stroke volume with thermal stress in normal men during exercise.

“…In addition to elimination of problems cited above, central sampling prevented the large errors in determination of CBV due to gross disparities between aortic and peripheral transit times induced by peripheral vasoconstriction during exercise (7,8). Indeed, Schlant and associates (20) observed a close correlation between a direct measurement of CBV and this volume as determined by the Stewart-Hamilton method with central injection and sampling.…”

“…To decrease the large variability of multiple determinations of cardiac output with sampling of diluted indicator from peripheral arteries (6), we selected a central sampling site in the aortic arch. In addition, aortic sampling allowed more accurate measurements of central blood volume (CBV) by eliminating artifactual changes attending peripheral measurement of this volume (7,8).…”

Cardiovascular Adjustments to Gravitational Stress

“…Regional partition of the overall compliance is difficult because of nonlinearities of the basic vascular pressure-volume relationship, discontinuities in the distribution of venous pressures, and the inaccuracies inherent in in vivo measurements of regional blood volumes (138,223,277). The potential of volume measurements based on scintigraphic techniques is yet to be fully explored.…”

Behavior of Normal Pulmonary Circulation during Changes of Total Blood Volume in Man*

“…These pressure alterations are generally thought to occur in association with changes of the pulmonary blood volume, which is believed to increase or decrease simultaneously with a rise or fall in total circulating volume (1-3, 7, 8). However, in the majority of reports published on this subject, the pulmonary blood volume was either not measured (1,5,6) or estimated from "central" blood volume determinations (2,3,7), which are known to encompass many drawbacks and pitfalls (9,10). More recently, Oakley and associates (11) studied four patients with rheumatic heart disease during the intravenous administration of dextran or saline solutions and found an increase of the pulmonary blood volume measured by the method of Milnor, Jose, and McGaff (12).…”