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 facilitates application of multiple inert gases and the multiple inert-gas-exchange technique (MIGET) model to noninvasive measurements of cardiac output (CO) and central mixed venous oxygen content Reduction in recirculation error is made possible by 1) replacement of sinusoidal input functions with impulse inputs and 2) replacement of steady-state analyses with transient analyses. Recirculation error reduction increases the inert-gas selection to include common gases without unusually high (and difficult to find) tissue-to-blood partition coefficients for maximizing the systemic filtering efficiency. This paper also presents a practical method for determining the recirculation contributions to inert expired profiles in animals and determining their specific contributions to errors in the calculations of CO and from simulations applied to published ventilation-perfusion ratio (V/Q) profiles. Recirculation errors from common gases were found to be reducible to the order of 5% or less for both CO and whereas simulation studies indicate that measurement bias contributions from recirculation, V/Q mismatch, and the V/Q extraction process can be limited to 15% for subjects with severe V/Q mismatch and high inspired oxygen fraction levels. These studies demonstrate a decreasing influence of V/Q mismatch on parameter extraction bias as the number of inert gases are increased. However, the influence of measurement uncertainty on parameter extraction error limits improvement to six gases.

An assessment of the radiological module of NEONATE as an aid in interpreting chest X-ray findings by nonradiologists.

NEONATE is a prototype of an expert system for the Newborn Intensive Care Unit developed at the Primary Children's Medical Center in Salt Lake City, Utah. A pilot study was undertaken to see if the addition of radiological frames to the NEONATE software could aid attending Neonatologists to interpret chest X-ray films. A set of radiological frames was created from rules generated by a radiologist. The performance of these radiological frames was compared to the performance of other radiologists using the Kappa statistic to measure agreement. There is a good agreement between the computer's decisions and the radiologists' decisions. The radiological frames were also tested to see if they help physicians who are not trained in radiology. A system that compares the residents' interpretation and the computer's interpretation to a gold standard interpretation was developed. It shows that the computer helps the first and second year residents, but not the third year residents. This article suggests that NEONATE's interpretation of chest X-ray findings are close to the radiologists' interpretations. While NEONATE's radiological frames help novice physicians in reaching better chest X-ray interpretation, the current study suggests that they are not likely to help a Neonatologist.

"NEONATE"--an expert application for the "HELP" system: comparison of the computer's and the physician's problem list.

NEONATE is a prototype of an expert application for the HELP Hospital Information System. Its goal is to improve documentation in the Newborn Intensive Care Unit. The decision module of NEONATE is designed to produce an admission problem list. In this paper, the admission problem list that NEONATE generates was compared to the admission problem list of the current CETUS system for 30 patients. These were compared to a retrospectively constructed gold standard problem list. Of 101 problems in the gold standard list, 56 were on the current admission reports; 82 were found by NEONATE. NEONATE found 31 problems missed on the current admission reports; the current admission reports contained 5 problems missed by NEONATE. The current admission reports contained 9 false positives; whereas NEONATE's reports contained 27. Of the 27, 16 were caused by a single rule in NEONATE. We conclude that an expert system has great potential for improving the documentation of the patient problem list.

Gas-blood Pco2 and Po2 equilibration in a steady-state rebreathing dog preparation.

Alveolar gas and mixed venous blood PCO2 and PO2 were compared in a steady-state rebreathing dog preparation, during spontaneous breathing and mechanical ventilation, by a new null-balancing method that removes potential biases in the comparison of measurements in the blood and gas phases and includes an inert gas test to verify the equilibration between the rebreathing lung and the bag. No systematic PCO2 and PO2 differences were observed under equilibrium conditions. However, inert gas studies suggested that a high percentage of measurements obtained during spontaneous breathing were unreliable because of inadequate equilibration between blood and rebreathing bag (attributable to reduced ventilation or perfusion) and that all mechanical ventilation measurements were acceptable. The present data support the view that no PCO2 or PO2 gradients exist when the pulmonary capillary blood and alveolar gas are in equilibrium; the data also suggest that the steady-state rebreathing dog preparation may not be completely stable and that the time course of PCO2 and PO2 in the rebreathing bag may not be reliable as a means of assessing the equilibration between blood and bag.

Analysis of left and right ventricular size and shape, as determined from human casts. Description of the method and its validation.

A method is described to produce life-like left and right ventricular casts of 22 human hearts and to store their surface coordinates on magnetic tape for the analysis of ventricular shape and of angiocardiographic volume determination methods. According to their shape, experienced cardiologists divided these casts into diastolic, systolic and intermediate subgroups. On the basis of X-ray silhouettes and computer-simulated projections, single-plane as well as biplane model volumes were calculated with the multiple-slices and the area--length methods for various ventricular orientations. The mean correction factors (CF), relating actual and model volumes vary considerably with respect to cardiac phase and orientation. The systolic CFs are smaller than the diastolic ones, their averaged ratio being 0.74 for the left and 0.86 for the right ventricular casts. In general, the reported CFs are smaller than those published by other authors, which is attributed to different cast-production procedures. The described method uses selective, equql, and simultaneous filling of both ventricles, which prevents an unphysiologic shift of the interventricular septum.

Angiocardiographic left ventricular volume determination. Accuracy, as determined from human casts, and clinical application.

On the basis of 21 life-like human casts (the method is described in the first paper of this series) the influence of (a) spatial orientation, (b) cardiac phase, and (c) biplane and single-plane methods of volume calculation on the accuracy of left ventricular (LV) angiocardiographic volume determination was quantitated. The best results are obtained, when a biplane approach is utilized and when position and cardiac phase appropriate correction factors (CF) are applied to the model volumes (area--length (AL) and multiple-slices (MS) methods). Thus the statistical error is decreased and a more important larger systematic error avoided. The AL and the MS methods perform equally well; on the average, however, the AL method is slightly favored. The application of this concept of differentiated CFs to 83 normal left ventricles of infants and children resulted in nonlinear relationships between LV volumes and their respective body surface areas (BSA) (EDV = 65.1 . BSA1.219, r = 0.961, SV = 46.7 . BSA1.219, r = 0.949). The ejection fraction (71.8%) does not correlate with the BSA (r = -0.036).

Angiocardiographic right ventricular volume determination. Accuracy, as determined from human casts, and clinical application.

On the basis of 22 life-like human casts (the method is described in the first paper of this series) the influence of (a) spatial orientation, (b) cardiac-phase and (c) biplane (BP) and single-plane (SP) methods of volume calculation on the accuracy of right ventricular (RV) angiocardiographic volume determination was quantitated. The best results are obtained, when a BP approach is utilized and when position and cardiac-phase appropriate correction factors (CF) are applied to the model volumes (multiple-slices (MS) and area--length (AL) methods). Thus the statistical error is decreased and a more important larger systematic error (especially for SP) avoided. The MS and AL methods perform equally well; on the average, however, the MS method is slightly favored. The application of this concept of differentiated CFs to 100 normal right ventricles of infants and children resulted in nonlinear relationships between RV volumes and their respective body surface areas (BSA) (EDV = 73.1 . BSA1.219, r = 0.961,SV = 46.2 . BSA1.219, r = 0.937). The ejection fraction (63.3%) does not correlate with the BSA (r = -0.292). The right ventricle accomplishes the same SV (with respect to BSA) as the left ventricle from a higher enddiastolic and endsystolic level.