CARDIAC-OUTPUT AND MIXED VENOUS OXYGEN-CONTENT MEASUREMENTS BY A TRACER BOLUS METHOD - THEORY

We present a bolus method of inert-gas delivery to the lungs that faci litates application of multiple inert gases and the multiple inert-gas -exchange technique (MIGET) model to noninvasive measurements of cardi ac output (CO) and central mixed venous oxygen content (C (v) over bar (O2)). Reduction in recirculation error is made possible by 1) replace ment of sinusoidal input functions with impulse inputs and 2) replacem ent of steady-state analyses with transient analyses. Recirculation er ror reduction increases the inert-gas selection to include common gase s without unusually high (and difficult to find) tissue-to-blood parti tion coefficients for maximizing the systemic filtering efficiency. Th is paper also presents a practical method for determining the recircul ation contributions to inert expired profiles in animals and determini ng their specific contributions to errors in the calculations of CO an d C (v) over bar(O2) from simulations applied to published ventilation -perfusion ratio ((V) over dot/(Q) over dot) profiles. Recirculation e rrors from common gases mere found to be reducible to the order of 5% or less for both CO and C (v) over bar(O2), whereas simulation studies indicate that measurement bias contributions from recirculation, (V) over dot/(Q) over dot mismatch, and the (V) over dot/(Q) over dot extr action process can be limited to 15% for subjects with severe (V) over dot/(Q) over dot mismatch and high inspired oxygen fraction levels. T hese studies demonstrate a decreasing influence of (V) over dot/(Q) ov er dot mismatch on parameter extraction bias as the number of inert ga ses are increased. However, the influence of measurement uncertainty o n parameter extraction error Limits improvement to six gases.