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PubMed1987

Influence of cardiac output on thermal-dye extravascular lung water (EVLW) in cardiac patients.

The influence of varying cardiac output (CO) on thermal-dye extravascular lung water (EVLW) was investigated in a total of 40 cardiac surgery patients before the onset of the operation. EVLW was measured by means of the double indicator dilution technique with indocyanine green as the non-diffusible indicator and a microprocessed lung water computer 15 min and 30 min after change of CO. CO was varied from -45% to +70% of the baseline value by nifedipine infusion (CO increases, n = 20) or halothane application (CO decreases, n = 20), respectively. CO was measured from the femoral artery instream thermistor tipped lung water catheter and, simultaneously, from the pulmonary artery. In spite of a highly significant decrease (-45%) and increase (+70%) in CO no change in EVLW could be observed. CO estimation was comparable for both methods used. Regression analysis revealed no relationship between CO and EVLW as well as between EVLW and various hemodynamic parameters. We conclude that thermal-dye technique for estimation of EVLW may be accurate in spite of changing cardiac output over a wide range.

Cardiac Output↗
PubMed1996

Transgastric, pulsed Doppler echocardiographic determination of cardiac output.

OBJECTIVE: The aim of this study was to evaluate the accuracy of cardiac output measurement with transesophageal echocardiography (TEE) using a transgastric, pulsed Doppler method in acutely ill patients. DESIGN: Cardiac output was simultaneously measured by thermodilution (TD) and a transgastric, pulsed Doppler method. SETTING: The study was carried out in a surgical intensive care unit as part of the management protocol of the patients. PATIENTS: Thirty consecutive acutely ill patients with a Swan-Ganz catheter, mechanically ventilated, sedated and with a stable hemodynamic condition were included. MEASUREMENTS: Pulsed Doppler TEE was performed using a transgastric approach in order to obtain a long axis view of the left ventricle. Cardiac output was calculated from the left ventricular outflow tract diameter, the velocity time integral of the blood flow profile and heart rate. RESULTS: One patient was excluded because of the presence of aortic regurgitation and another, because of the impossibility of obtaining a transgastric view. Twenty-eight simultaneous measurements were performed in 28 patients. A clinically acceptable correlation and agreement were found between the two methods (Doppler cardiac output = 0.889 thermodilution cardiac output +0.74 l/min, r = 0.975, p <0.0001). CONCLUSION: Transgastric pulsed Doppler measurement across the left ventricular outflow tract with TEE is a very feasible and clinically acceptable method for cardiac output measurement in acutely ill patients.

Adult↗
PubMed2000

A comparison of bolus versus continuous cardiac output in an experimental model of heart failure.

OBJECTIVE: The majority of studies examining cardiac output measurement have been done in physiologically stable models with low thermal background noise. Research comparing continuous cardiac output (CCO) with bolus thermodilution cardiac output (COTD) measures in human and animal models have reported high correlations, negligible bias, but large limits of agreement. The purpose of this project was to compare CCO with COTD measures in an experimental model of heart failure where the cardiac output values were low and the range was narrow. DESIGN: A one-group experimental design with preintervention control measures and repeated CCO and COTD measures across nine time points. SETTING: Cardiovascular research laboratory. SUBJECTS: Thirty dogs. MEASURES AND MAIN RESULTS: Univariate and multivariate versions of repeated-measures analysis were used to assess the influences of temperature, weight, and stage of the experimental protocol on CCO, COTD, and the differences between them. The two measures CCO and COTD were assessed for agreement by using methods proposed by Bland and Altman. Two hundred and fifty pairs of measurements were obtained during sinus rhythm. The range for COTD measures was 0.5-4.67 L/min and for CCO measures 1.0-5.40 L/min. Of the 250 cardiac outputs estimated by the continuous method, 73.4% of the values were within +/-15% of that estimated by the repetitive, single thermodilution method. The mean bias for the entire protocol was 0.01 (SD = 0.51) with a range of 4.33 L/min. CONCLUSION: Agreement between the two measures may be the function of biological variability, responses to anesthesia, and technique. Bland and Altman evaluation demonstrated low bias and precision and similar levels of agreement when compared with previous studies in an experimental model where the cardiac output was low and the range was narrow.

Animals↗
PubMed1995

Effect of measurement errors on cardiac output calculated with O2 and modified CO2 Fick methods.

We have investigated the effect of measurement errors on cardiac output, calculated via three different Fick methods. In method 1, the classic O2 Fick equation is expressed in terms of oxygen uptake (VO2), arterial pulse (SaO2) and venous oximetry (SVO2) saturations. The second method, a modified CO2 Fick method, is obtained by replacing VO2 in method 1 with carbon dioxide production (VCO2) divided by the respiratory quotient. In method 3, cardiac output is expressed as VCO2 divided by the product of the SaO2-SVO2 difference and a constant. This constant is determined from initial measurements of VCO2, SaO2, SVO2, and thermodilution cardiac output (Qth). This determination of the constant results in equality of the initial cardiac output of method 3 with the simultaneously determined Qth and, therefore, is similar to performing an autocalibration. For each of the three preceding Fick methods, we derive general expressions that explicitly show how measurement errors (random and systematic) in the Fick variables (VO2, VCO2, SaO2, and SVO2) propagate into errors in calculated cardiac output. The errors in theoretically calculated cardiac output decrease as the SaO2-SVO2 difference increases, except for the systematic error in method 3. The systematic error of method 3 is constant and depends only upon the accuracy of the initial Qth. Analytic expressions for the sensitivity of calculated cardiac output to errors in individual Fick variables are also obtained. Using estimates from the literature for typical systematic and random measurement errors in the Fick variables, the resultant errors in cardiac output are numerically calculated. The effect of random measurement errors on errors in calculated cardiac output was comparable among the three methods. However, the systematic error was least with method 3. Total errors (random and systematic) were comparable among the three methods. Using these numerical measurement errors, we conclude that continuous cardiac output may be calculated with comparable accuracy with each of these methods.

Bias↗
PubMed1994

The effect of Trendelenburg and modified trendelenburg positions on cardiac output, blood pressure, and oxygenation: a preliminary study.

BACKGROUND: Although we have insufficient knowledge about the effects of Trendelenburg positions on various hemodynamic parameters, these positions are frequently used to influence cardiac output and blood pressure in critically ill patients. OBJECTIVES: To determine the effect of Trendelenburg and modified Trendelenburg positions on five dependent variables: cardiac output, cardiac index, mean arterial pressure, systemic vascular resistance, and oxygenation in critically ill patients. METHODS: In this preliminary study subjects were 23 cardiac surgery patients (mean age, 55; SD, 8.09) who had a pulmonary artery catheter for cardiac output determination and who were clinically stable, normovolemic and normotensive. Baseline measurements of the dependent variables were taken in the supine position. Patients were then placed in 10 degrees Trendelenburg or 30 degrees modified Trendelenburg position. The dependent variables were measured after 10 minutes in each position. A 2-period, 2-treatment crossover design with a preliminary baseline measurement was used. RESULTS: Five subjects were unable to tolerate Trendelenburg position because of nausea or pain in the sternal incision. In the 18 who were able to tolerate both position changes, no statistically significant changes were found in the five dependent variables. Changes in systemic vascular resistance over time approached statistical significance and warrant further study. CONCLUSIONS: This preliminary study does not provide support for Trendelenburg positions as a means to influence hemodynamic parameters such as cardiac output and blood pressure in normovolemic and normotensive patients.

Bed Rest↗
PubMed1976

Measurement of cardiac output by electrical impedance at rest and during exercise.

A comparison was made between cardiac output values determined by the dye dilution and electrical impedance methods in ten subjects at rest and during graded exercise on a bicycle ergometer. The cardiac output values determined by the two methods were linearly related and significantly (P less than 0.001) correlated (r = 0.90). Movement artifact associated with exercise at maximum or near-maximum work loads caused severe distortion of the dZ/dt wave form and prevented calculation of impedance cardiac output at these levels of work. Use of the lowest value of L (distance between mean value of L in the impedance stroke volume equation (SV = p(L2/ZO2) (dZ/dt)mt), resulted in nearly identical values for the least-squares line and equalvalue line of impedance and dye cardiac outputs. Although absolute values of cardiac output determined by the two methods were not identical in all subjects the changes in cardiac output were nearly identical during the different levels of exercise. The data support the validity of the impedance method as a noninvasive, atraumatic measure of cardiac output at rest and during graded exercise.

Adult↗
PubMed1986

Comparison between ultrasonic and thermodilution cardiac output measurements in intensive care patients.

The reliability of ultrasonic cardiac output measurement was assessed using a commercial device that combines A-mode aortic root diameter determination and continuous wave (CW) Doppler flow velocity measurement in the ascending aorta. We compared this method with thermodilution (TD) cardiac output in 41 intensive care patients. Aortic root diameter measurement with A-mode was not possible in four (10%) patients. Using strictly defined criteria based upon our initial experience, we could not obtain acceptable CW Doppler flow signals in nine (22%) patients. Thus, ultrasonic cardiac output measurement was possible in 28 (68%) patients in whom there was an excellent correlation with cardiac output (r = 0.97; p less than .001). This study demonstrates that the transcutaneous CW Doppler method for measuring cardiac output is accurate and reliable in a limited percentage of ICU patients. Combining the CW Doppler with B-mode echocardiogram increases the applicability when an A-mode measurement is not possible.

Adult↗
PubMed1999

Semicontinuous cardiac output monitoring using a neural network.

OBJECTIVES: This study compared 2-mL bolus thermodilution cardiac output measurements with standard 10-mL bolus measurements. DESIGN: Cardiac output was measured with the new 2-mL bolus technique and the 10-mL standard thermodilution technique in a perspective series. We describe a system that automatically cools and injects 2-mL boluses of saline into a standard pulmonary artery catheter. It uses a Peltier effect solid-state cooler and pneumatically driven syringe injector to measure cardiac output once per minute. SETTING: Animal laboratory. ANIMALS: Eight adult Duroc swine weighing between 38.0 and 57.5 kg. INTERVENTIONS: Once each minute, 2 mL of cooled 5% dextrose was injected through the pulmonary catheter. Once every 8 mins, four sequential measurements of cardiac output were made using 10-mL injections. MEASUREMENTS AND MAIN RESULTS: A total of 1249 paired waveforms were processed with both a conventional algorithm and with a neural network. For the conventional algorithm, the correlation coefficient was r2 = .92 and the SD of the difference was 1.30 L/min. For the neural network, the correlation coefficient was r2 = .94 and the SD of the difference was 0.88 L/min. Output filtering improved the results in both cases. CONCLUSION: Neural networks accurately derive cardiac output from 2-mL bolus thermodilution injections, allowing cardiac output to be monitored automatically once per minute in many patients. The technique is convenient and uses standard low-cost catheters.

Algorithms↗
PubMed1990

[Intraoperative cardiac output monitoring by the transtracheal Doppler method].

We investigated the cardiac output measured with a transtracheal doppler (TTD) tube in surgical patients and evaluated its usefulness during operations. This tube was located at the point where maximum velocity of blood flow was obtained in the ascending aorta. At this point the cross-sectional area of the ascending aorta was calculated and the cardiac output was obtained by multiplying this area with average blood flow velocity which had been ultrasonically determined. The cardiac output by the TTD method was compared with that of the thermodilution method in 10 patients. The results with both groups showed a direct linear correlation. We obtained the following linear equation: TTD C.O. = 0.61 Thermo C.O. + 1.3 C.O.: cardiac output. The direct correlation coefficient proved to be 0.85 at a risk factor of 0.01. The result suggests that this non-invasive TTD method is easily available and useful in monitoring the intraoperative cardiac output.

Aged↗
PubMed1990

Measurement of extravascular lung water by thermal-dye dilution technique: mechanisms of cardiac output dependence.

The extent to which extravascular lung water (EVLW) is dependent on cardiac output was analysed in anaesthetized and mechanically ventilated pigs. EVLW was measured by thermal-dye dilution technique, by a fibreoptic thermistor catheter system (system 1), and by a thermistor catheter-external optical cuvette system (system 2). During baseline conditions, at which cardiac output was 3.65 l/min, and EVLW was 11.7 and 7.7 ml/kg b.w. with systems 1 and 2 respectively. A reduction of cardiac output to a mean of 1.90 l/min by the addition of halothane to the inspired gas did not significantly affect EVLW with system 1 (-5%) but increased EVLW by 39% (p less than 0.05) with system 2. An increase of cardiac output to a mean of 4.78 l/min by intravenous infusion of isoproterenol caused a small increase in EVLW with system 1 (14%; p less than 0.05) and a decrease with system 2 (10%; p less than 0.05). The dependence on cardiac output was the same whether the catheters were positioned centrally (aortic root) or peripherally (abdominal aorta). With system 1 the CO dependence was due to different time constants in thermistor and optical systems, and with appropriate phasing the dependence could be eliminated. With system 2 a large overestimation of the mean transit time difference between the two indicators was seen when cardiac output was low, resulting in overestimation of EVLW. It is concluded that the dependence of EVLW volume on cardiac output is an artefact due to technical problems in the design of the recording equipment rather than a reflection of pulmonary or vascular effects.

Animals↗
PubMed1980

Distribution of cardiac output in the unstressed pregnant guinea pig.

Cardiac output (CO) and organ flows were measured in five nonpregnant and 14 pregnant unstressed guinea pigs between the thirty-ninth and sixty-fifth postconceptional day by means of radionuclide-labeled microspheres. Blood pressure, heart rate, and cardiac output in nonpregnant animals were 60 torr, 234 bpm, and 248 ml/min, respectively. These parameters did not change significantly during pregnancy. The uterine fraction of cardiac output increased to approximately 18% at term and there was an equivalent decrease in the CO fractions to the carcass and skin. Blood flow per gram of wet weight increased during pregnancy by approximately 140% and 70% for the thyroid and gastrointestinal tract, respectively, but did not change significantly for the heart, brain, kidneys, and adrenals. In pregnant animals near term the weight of the heart, kidneys, intestines, and lungs was approximately 25% lower than that observed in nonpregnant guinea pigs.

Animals↗
PubMed1983

The mitral valve orifice method for noninvasive two-dimensional echo Doppler determinations of cardiac output.

We developed and validated a mitral valve orifice method for Doppler cardiac output determination. In 15 open-chest dogs, cardiac output was controlled and measured by a roller pump interposed between the right atrium and pulmonary artery as a right-heart bypass. Left heart flows were measured in the open-chest dog model by Doppler measurements at the mitral valve orifice and compared not only to volume flow measured by the roller pump, but to electromagnetic flow meters as well. The maximum mitral valve orifice area was measured off short-axis two-dimensional echocardiographic views by planimetry. The maximal orifice was then adjusted for its diastolic variation in size by calculating a ratio of mean-to-maximal mitral valve separation on a derived M-mode echocardiogram. Flow was sampled parallel to mitral valve inflow in a four-chamber plane. The multiplication of mean flow throughout the cardiac cycle by the mean mitral valve area after correction for diastolic size variation yielded a cardiac output determination that could be compared to the roller pump measurement. Fifty-two cardiac output determinations over roller pump values of 1-5 l/min yielded a high correlation between roller pump flows and Doppler (r = 0.97 +/- 0.23 l/min). Our study shows that the mitral valve orifice provides an accurate site for Doppler cardiac output measurements.

Animals↗
PubMed1994

Injectate port selection affects accuracy and reproducibility of cardiac output measurements with multiport thermodilution pulmonary artery catheters.

OBJECTIVE: To compare the accuracy and reproducibility of thermodilution cardiac output measurements obtained from the injectate and infusion ports of a multilumen pulmonary artery catheter. The thermodilution results were compared with an independent measure of flow obtained from an electromagnetic flow meter. METHODS: In an experimental study conducted at an animal research laboratory of a health sciences university, two virgin western breed ewes were surgically instrumented with an inferior vena cava occluder, which reduced venous return and thus lowered cardiac output, and an ascending aortic electromagnetic flow probe, which provided an independent reference measure of cardiac output. On the day of study, a multilumen pulmonary artery catheter was inserted. Cardiac output was manipulated over a range of 2.9 to 12.1 L/min with i.v. isoproterenol or inferior vena cava occlusion. Approximately 30 simultaneous thermodilution and electromagnetic flow meter measurements of cardiac output were obtained from both the infusion and injectate ports in each of the two subjects. RESULTS: Correlation coefficients were lower and standard error of the estimates was higher for the infusion port (r = .83; SEE = 1.19 L/min) vs the injectate port (r = .94; SEE = .74 L/min), indicating reduced reproducibility with infusion port thermodilution cardiac output determinations. Accuracy was also adversely influenced in the infusion port results. The linear regression for the infusion port data intercepted the Y axis at +2.64 L/min, indicating significant overestimation of cardiac output at flows of less than 5 L/min and underestimation of flow when cardiac output exceeded 8 L/min. CONCLUSIONS: The use of the infusion port for the measurement of thermodilution cardiac output measurements may result in nonreproducible and inaccurate results.

Animals↗
PubMed2002

Comparison of continuous, stat, and intermittent cardiac output measurements in patients undergoing minimally invasive direct coronary artery bypass surgery.

OBJECTIVE: To compare intermittent cardiac output (ICO) with continuous cardiac output (CCO) and stat cardiac output (SCO) measurements in patients undergoing minimally invasive direct coronary artery bypass (MIDCAB) surgery. DESIGN: Prospective, clinical study. SETTING: Single, tertiary referral center. PARTICIPANTS: Twenty adult patients undergoing off-pump MIDCAB surgery from January through June 2000. INTERVENTIONS: Each patient had a 7.5F 5-lumen pulmonary artery thermodilution catheter (CCO catheter, Baxter Healthcare Corporation, Irvine, CA) inserted for measurement of cardiac output (CO). ICO, CCO, and SCO were compared at 10 predefined time points. RESULTS: A total of 400 data pairs for CO were obtained. ICO values ranged from 1.8 to 8.4 L/min; CCO, 1.9 to 7.5 L/min; and SCO, 2.25 to 6.35 L/min. Correlation between ICO and CCO was significant (correlation coefficient, r = 0.78, p < 0.001), accompanied by a bias of -0.095 L/min and precision of 0.729 L/min. Similarly, the correlation between ICO and SCO was significant (r = 0.79, p < 0.001), accompanied by good accuracy (bias, 0.084 L/min) and precision (0.843 L/min). There were statistically significant decreases in mean arterial pressure, CO, cardiac index, stroke volume, stroke volume index, and left and right ventricular stroke work indices during anastomosis of the left internal mammary artery to left anterior descending artery. These parameters returned to baseline preinduction values 1 minute after completion of the anastomosis. CONCLUSION: Excellent correlation, accuracy, and precision were found among the 3 methods of measuring CO in patients undergoing MIDCAB surgery. Further studies are needed to assess their accuracy in multivessel off-pump coronary artery bypass graft surgery and in patients with poor left ventricular function.

Cardiac Output↗
PubMed1981

Thermodilution technique for measurement of cardiac output during artificial ventilation.

The feasibility of using the thermodilution method to monitor cardiac output during artificial ventilation was studied in anesthetized pigs. Normal saline (0.5 ml) at room temperature was injected into the left ventricle or the right atrium. The dilution curves were detected in the aortic arch and the pulmonary artery, respectively. The ventilation rate was 10 cycles/min at end-expiratory pressures of 0, 5, 10, and 15 cmH2O. For each level, 50 measurements of cardiac output were performed at regular intervals over the ventilatory cycle. The order of measurements were randomly selected. The average of each series of 50 measurements showed excellent correlation with the estimates of cardiac output based on the direct Fick method for oxygen. The maximum difference between the values of cardiac output randomly measured by the thermodilution method was 40% for the left side of the heart and 70% for the right side. However, when the values of cardiac output were sorted according to the specific phases of the respiratory cycle, there was a systematic variation with a small random error. For the left side of the heart, a satisfactory moment of injection for estimation of mean cardiac output appeared to be at the end of the spontaneous expiration. On the other hand, the analysis of cardiac output values at the right side did not reveal any satisfactory moment for injectate administration under changing circumstances, e.g., positive end-expiratory pressure.

Animals↗
PubMed1984

[Continuous measurement of cardiac output during ergometer exercise using an ultrasonic pulsed Doppler flowmeter].

A method for determining cardiac output was developed, which provided the product of the absolute blood flow rate at the aortic arch (as measured non-invasively from the suprasternal notch by an ultrasonic pulsed Doppler flowmeter: UPDF) and the cross-sectional area of the aorta at that level, as estimated from two-dimensional echograms. Using this method, non-invasive continuous measurements of cardiac output were made during bicycle ergometer exercise. The results were summarized as follows: Resting cardiac output values obtained by this method correlated reasonably well with those by the thermodilution method (correlation coefficient r = 0.76). Eight healthy male volunteers exercised for 2 min on a bicycle ergometer at 250 kpm/min, and serial cardiac outputs were determined by this method for five of these subjects during and after the loading. The cardiac output curves thus obtained clearly demonstrated abrupt increases in cardiac outputs initially, followed by rapid returns to resting cardiac output levels after the end of exercise. We intend to conduct additional studies for larger groups of subjects to further evaluate and to establish this method for use in cardiac examinations.

Adult↗
PubMed1987

Augmentation of cardiac output with intravenous catecholamines in unanesthetized hypoxemic newborn lambs.

We compared the effects of three different sympathetic-type agonist drugs upon cardiac output (pump function) and its determinants during hypoxemia, a condition of increased endogenous catecholamines. At 1-3 days after birth, 15 lambs were instrumented with catheters in the aorta, the left atrium, and a vein, and thermistors were placed in the abdominal aorta for cardiac output sampling. In eight animals, a pressure transducer was placed in the left ventricle. After a 2- to 3-day recovery, sequential measurements were made of blood gases, cardiac output, aortic and left atrial pressure and left ventricular maximal first derivative of pressure with respect to time (LV dP/dtmax) in room air and in hypoxemia (FiO2 = 0.08-0.10). Measurements were repeated during continued hypoxemia with increasing doses of isoproterenol (0.1, 0.4, 0.7, and 1.0 microgram/kg/min) and dopamine and dobutamine (10, 20, 40, and 80 micrograms/kg/min). Hypoxemia alone was associated with no significant change in cardiac output, but cardiac output rose significantly during continued hypoxemia with each drug (maximum increases-dobutamine 58%, isoproterenol 51%, dopamine 31% all p less than 0.05). Studies with continued hypoxemia alone showed no rise in cardiac output over time. Augmentation of contractility, demonstrated by a doubling of LV dP/dtmax by each of the drugs, contributed to the increases in cardiac output. Differences in cardiac output responses could not be explained by contractile effects of the drugs alone, since LV dP/dtmax increased in similar fashion for all three. The relatively limited cardiac output response and downward trend at the highest dosage of dopamine occurred with a reduction in heart rate and an increase in systemic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Monitoring of cardiac output by pulse contour method.

A pulse contour method for cardiac output determination was evaluated in sixteen cardiac surgery patients. Stroke volume was derived from the aortic pressure waveform by means of a formula developed by Wesseling and was calculated with an in-built computer (Philips cardiac output module). The method was used for continuous postoperative monitoring and was compared with thermodilution cardiac output determinations. The overall comparison of data (71 simultaneous measurements) yielded a correlation coefficient of 0.78 (regression y = 0.81 x + 1.07 liter) (p less than 0.001). Advantages and disadvantages of the pulse contour method are discussed.

Cardiac Output↗