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PubMed1982

Effects of mechanical ventilation on the measurement of cardiac output by thermodilution.

Phasic variation in cardiac output (CO) of 10-50% during mechanical ventilation was documented in dogs, and in 1 patient by injection of thermal indicator at 1-sec intervals throughout the ventilation cycle. Measured flow variation increased with inflation pressure when other variables were unchanged, and was not influenced to a significant degree by the injection of iced vs room temperature injectate. Such variation can occur in adult patients requiring only minimally increased airway pressure for ventilation. The technique of injecting indicator at a particular moment of the ventilation cycle is not appropriate to monitor absolute or even relative changes in CO because of occasional changes in the phase relation between the ventilation cycle and the flow variation. The mean CO by thermodilution technique is approximately best by the mean of values taken at regularly spaced intervals through the ventilation cycle.

Animals↗

PubMed1989

Instantaneous and continuous cardiac output obtained with a Doppler pulmonary artery catheter.

A newly developed, flow-directed, Doppler pulmonary artery catheter, capable of measuring instantaneous and continuous cardiac output, was evaluated in both an in vitro pump model and an animal model. Quantitative flow was calculated with use of the instantaneous, space-average velocity (obtained from the velocity profile) and the instantaneous area (obtained from the vessel diameter) and compared with electromagnetic flow. Additionally, simultaneous thermodilution flow measurements were obtained. Doppler catheter-determined flow was highly predictive of electromagnetic flow in both continuous and pulsatile pump models (r2 = 0.98, slope or m = 1.04, SEE = 0.44; and r2 = 0.97, m = 1.04 and SEE = 0.33, respectively). Thermodilution was less predictive and appeared to underestimate electromagnetic flow in both the continuous and the pulsatile model (r2 = 0.99, m = 0.91, SEE = 0.20 and r2 = 0.95, m = 0.84 and SEE = 0.34, respectively). In the animal model, Doppler catheter-determined cardiac output appeared to modestly underestimate electromagnetic flow (r2 = 0.80, m = 0.87, SEE = 0.61). However, Doppler determinations of flow remained more accurate than did simultaneous thermodilution measurements (r2 = 0.73, m = 0.79, SEE = 0.72). Accurate, continuous and instantaneous cardiac output measurements appear possible with use of a flow-directed, Doppler pulmonary artery catheter. This catheter system also provides instantaneous diameter measurements and mapping of instantaneous velocity profiles within the main pulmonary artery and may lead to more accurate Doppler-derived assessment of cardiac output in humans.

Animals↗

PubMed1979

Effect of non-carbonic acidosis on total splanchnic perfusion and cardiac output during anaesthesia with O2-N2O-halothane.

Six dogs, premedicated with pethidine 10 mg kg-1 b.w, were anaesthetized with mebumal natrium (NFN) 25 mg kg-1 b.w. and 80 mg gallamoni jodidum (NFN). Anaesthesia was continued with O2-N2O-halothane and artificial ventilation. Non-carbonic acidosis was induced by i.v. infusion of hydrochloric acid, during which the related values of pulse, blood pressure, cardiac output, total splanchnic prefusion and portal pressure were measured. The pulse remained unchanged down to pH 7.0. At this pH, arrhythmia suddenly occured and developed into ventricular fibrillation. Before this occured falling cardiac output was observed (cardiac output 1 min-1 = -21.49+3.21 x pH, N = 23, r = 0.75, P less than 0.001) and rising oxygen consumption (O2 ml min-1 kg-1 = 25.79--2.96 x pH, N =28, r = 0.52, P less than 0.01), rising oxygen extraction and rising peripheral resistance, while the mean pressure in the aorta was almost unaltered. During this course towards circulatory failure, an unchanged to slightly rising total splanchnic perfusion (Qsp1) was demonstrated, which with the lowest pH, represented up to 40% of the cardiac output (Qtot): Qsp1/Qtot = 3.11--0.39 x pH (N = 28, r = 0.52, P less than 0.01). Portal pressure rises slightly during acidosis, and oxygen saturation in the portal vein is high. It is probable that the retained splanchnic blood flow is caused by retention of the portal flow. This is quite different from observations during anaesthesia with barbiturates. It is concluded that halothane modifies considerably the circulatory response in the systemic circulation and the splanchnic region during non-carbonic acidosis.

Abdomen↗

PubMed2004

Comparison of cardiac outputs of major burn patients undergoing extensive early escharectomy: esophageal Doppler monitor versus thermodilution pulmonary artery catheter.

BACKGROUND: After major burn injury, severe hemodynamic fluctuations occur in a relatively short time, requiring invasive hemodynamic monitoring. The noninvasive esophageal Doppler monitor offers an alternative to the pulmonary artery catheter. This study compares the cardiac output of the esophageal Doppler monitor with that of a pulmonary artery catheter during the large volume shifts seen in extensive early escharectomy. METHODS: This study recruited 20 critically ill, major burn patients scheduled for elective early escharectomy. A thermodilution pulmonary artery catheter and esophageal Doppler monitor probes were inserted to measure cardiac output simultaneously at regular intervals. The results were analyzed by simple linear regression and Bland and Altman plots. RESULTS: The analysis included 92 data pairs from 20 patients, most of whom were critically ill with major burns. Escharectomy caused large intraoperative fluid shifts. The cardiac output of the esophageal Doppler monitor correlated moderately well with the cardiac output of the pulmonary artery, although it showed a mean of 15% less than the output of the pulmonary artery catheter. The mean bias was 0.77 L/minute, and the limits of agreement were +/-2.74 L/min. CONCLUSIONS: For major burn patients undergoing early escharectomy, the esophageal Doppler monitor allows changes in hemodynamics to be followed, but does not accurately measure the absolute values of cardiac output.

Adult↗

PubMed1986

[Determination of cardiac output under PEEP-respiration with the "NCCOM 3" non-invasive bioimpedence monitor in comparison with the thermodilution method. A study in anesthetized dogs].

A new noninvasive cardiac output (CO) computer ("NCCOM 3") based on the bioimpedance principle was compared to a CO computer based on standard thermodilution measurements. Simultaneous measurements were made on dogs who were ventilated with or without positive end expiratory pressure (PEEP). There was no correlation of cardiac output measurements with the two methods (r = 0.10, n = 60). Comparing only measurements without PEEP yielded r = 0.41. Thermodilution measurements showed the well-known decline in cardiac output during PEEP, whereas the bioimpedance device recorded an increase in cardiac output. These differences were statistically significant. We conclude that the NCCOM 3 cannot at present replace the invasive standard methods of CO measurement in ventilated patients. A lack of differentiation of circulatory effects, thoracic gas volume, and intrathoracic fluid content is the most likely cause of the discrepancies seen.

Anesthesia↗

PubMed1985

Redistribution of cardiac output in anesthetized thermally dehydrated rats.

Cardiac output (CO) and its distribution were studied in dehydrated (37 degrees C) anesthetized (Na thiopentone) rats prior to and following heat acclimation (at 34 degrees C), using 57Co 15 micron microspheres. In non-acclimated dehydrated rats, CO decreased while heart rate (HR) increased significantly. Following acclimation CO increased without any change in HR; during dehydration CO remained elevated together with a significant increase in HR. In non-acclimated rats at low dehydration blood perfusion to peripheral thermoregulatory areas increased while perfusion of splanchnic area decreased; at high dehydration level peripheral blood flow decreased whereas splanchnic blood flow was augmented. In acclimated dehydrated rats, CO distribution to thermoregulatory areas did not change while perfusion of the splanchnic area decreased. It is suggested that following acclimation, the increased CO contributes to maintenance of thermoregulatory peripheral blood flow; in non-acclimated rats severe dehydration leads to augmented blood flow in the permeable splanchnic vascular bed, increasing efflux of plasma protein and failure of plasma volume conservation.

Acclimatization↗

PubMed1997

[Continuous measurements of cardiac output in the perioperative period].

Management of critically ill patients is based on knowledge of fundamental physiological variables. Automatized and continuous measurement of these variables is preferable. A new system based upon the thermodilution method has been developed to measure cardiac output automatically and continuously. We evaluated the system in the potentially unstable perioperative period with possible great and rapid changes in cardiac output. Twenty patients, scheduled for open heart or abdominal aortic aneurysm surgery, were included into the study, which was approved by the local ethical committee. The patients were monitored for up to 30 hours. At random intervals five iced bolus thermodilution cardiac output (BCO) determinations were made and compared to the continuous measurements (CCO). Two hundred and thirty-one pairs of data were obtained. The cardiac outputs ranged from 2.5-14.9 l/min. The absolute bias was 0.31 l/min (95% limits of agreement -1.4 l/min to 2.0 l/min). The mean relative error was 4.7% with a standard deviation of the relative error of 15.4%. The linear regression was represented by: CCO = 11.352 x BCO - 0.36. The correlation coefficient R was 0.90 (p < 0.001). In conclusion, the CCO measurement technique is a promising clinical method. The method is straightforward, requires no calibration, is independent of vascular geometry and measures with its limitations volumetric flow. Finally automatic and continuous patient monitoring provides more information and has potential to reveal previously undetected haemodynamic events.

Aged↗

PubMed1975

Comparison of the cardiac output measurements with electromagnetic flowmeter and dye-dilution technique in dogs, with a note on the comparison between radiocardiography and ear-dye method in man.

There are relatively few studies and opinions are still divided as to the agreement between the electromagnetic flowmeter and dye-dilution technique in measurements of cardiac output in animals. Of 22 pairs of cardiac output measurements performed with an electromagnetic flow probe applied to the root of aorta in open-chest, anesthetized dogs and with peripheral venous injection of indocyanine green dye and an arterial cuvette, the measured points fell within the range of plus or minus 20% on both sides of the line of identity in 19 instances. Studied on 8 human subjects with radiocardiography and ear-dye method performed simultaneously with peripheral venous injection of a mixture of R131ISA and indocyanine green, cardiac output given by ear-dye method was higher than that given by radiocardiography by an average of 9 plus or minus 11 (SD)%. Agreement and disagreement in cardiac output measurements given by electromagnetic flow probe, dye-dilution method with arterial cuvette, dye-dilution method with ear-piece densitometer and radiocardiography were discussed.

Animals↗

PubMed1996

Effect of inhaled nitric oxide on venous admixture depends on cardiac output in patients with acute lung injury and acute respiratory distress syndrome.

BACKGROUND: It has been shown that inhaled nitric oxide (NO) reduces intrapulmonary venous admixture (QVA/QT) and improves oxygenation in patients suffering from acute respiratory distress syndrome (ARDS). The change in QVA/QT during NO inhalation varies individually. Factors known to influence the respiratory response to NO are the NO concentration and the level of shunt before NO administration. Other factors that may modify the effect on gas-exchange during NO breathing are unknown. METHODS: We studied the effect of 40 ppm inhaled NO on pulmonary gas-exchange and haemodynamics in 37 patients with acute lung injury (ALI) and ARDS, respectively, and factors that may influence the respiratory response to NO. RESULTS: Inhalation of 40 ppm NO produced a decrease in mean pulmonary artery pressure (MPAP) from 33.1 +/- 7.2 to 30.2 +/- 6.8 (mean +/- SD) mmHg (P < 0.0001) while pulmonary artery wedge pressure (PAWP), cardiac output and mean arterial pressure remained constant. Change in QVA/QT during NO inhalation depended on the preinhalation cardiac output and had no association with mixed venous oxygen tension, MPAP-PAWP, and QVA/QT before NO delivery. QVA/QT decreased in 26 patients (group 1) and increased in 11 patients (group 2) during NO inhalation. In group 1, cardiac output was lower than in group 2 (8.6 vs 12.2 l.min-1; P < 0.0005). CONCLUSION: We conclude that the change in venous admixture during inhalation of 40 ppm NO depends on cardiac output. If preinhalation cardiac output is high, 40 ppm NO can adversely affect gas exchange in patients with ALI and ARDS.

Acute Disease↗

PubMedDate not supplied

Evaluation of the CO2 rebreathing method for the non-invasive measurement of resting cardiac output in man.

We have compared the indirect Fick, a non-invasive CO2 rebreathing method for measuring resting cardiac output, with the thermodilution method in eleven subjects including some with cardiac and pulmonary disease. Three alternative methods for calculating veno-arterial CO2 content difference were used: (i) from end-tidal and rebreathing bag equilibrium PCO2 modified from the equations developed for use during exercise by Jones et al. (1975); (ii) by using the uncorrected difference between end-tidal and equilibrium PCO2 and the standard CO2 dissociation curve; (iii) by direct measurement of arterial PCO2. Each method was satisfactory in that reproducibility was similar to thermodilution (5-10%) and the equations relating thermodilution to indirect Fick cardiac output were linear with slope and intercept, close to 1 and 0, respectively. End-tidal PCO2 accurately predicted arterial PCO2 except in five patients with liver disease. Direct measurement of arterial PCO2 is recommended in such patients. In other subjects there was no advantage in either correcting non-invasive measurements of alveolar gas to obtain veno-arterial CO2 content difference, or in direct measurement. The indirect Fick is an accurate method for measuring cardiac output at rest in normal subjects and those with cardiovascular disease. Its use can be extended to other groups by a single arterial blood sample.

Adult↗

PubMed1983

Volume loading improves low cardiac output in experimental right ventricular infarction.

To evaluate the effect of volume loading in the low output state associated with right ventricular infarction, isolated right ventricular infarction was produced in seven dogs with the pericardium intact. Volume loading and pericardiotomy were then sequentially performed. After the production of right ventricular infarction, right ventricular systolic pressure decreased by 25%, aortic pressure by 36% and cardiac output by 32%. Right ventricular ejection fraction decreased by 57%, but left ventricular ejection fraction did not change significantly. Left ventricular transmural pressure and diastolic size decreased, and right ventricular diastolic size increased. Intrapericardial pressure increased and equalization of diastolic pressures was noted. Volume loading resulted in increased right ventricular systolic pressure and stroke work, increased aortic pressure and cardiac output and increased transmural pressure and diastolic size in both ventricles. Pericardiotomy resulted in further increases in right and left ventricular filling, stroke work and cardiac output, as well as resolution of equalized diastolic pressures. These results indicate that cardiac output in experimental right ventricular infarction increases with volume loading, which enhances left ventricular preload by augmenting right ventricular output. Elevated intrapericardial pressure affects filling of both ventricles and may play a role in the pathophysiology of low cardiac output in right ventricular infarction.

Animals↗

PubMed1989

Measurement of cardiac output by carbon dioxide rebreathing methods.

Cardiac output may be measured noninvasively by applying the Fick principle to CO2; CO2 output is measured by expired gas analysis and the veno-arterial CO2 content difference is obtained from estimates of PVCO2 and PaCO2. PVCO2 is determined using the lung as a tonometer for the equilibration of CO2; two main methods are available. In the Defares or exponential method, a low concentration of CO2 is initially rebreathed. Complete equilibration is not reached between the lung and rebreathing bag and the PvCO2 is calculated as the asymptote of the exponential rise in PETCO2 during rebreathing and prior to recirculation. Even though several mathematical methods can be used to calculate PvCO2, the most precise is an iterative statistical analysis to obtain the best-fit curve for PETCO2 with time, from which PvCO2 is obtained from PETCO2 at 20 seconds after the start of rebreathing. In the Collier or equilibrium method, a bag having CO2 concentration higher than PvCO2 is rebreathed. If an appropriate initial bag volume CO2 has been selected, equilibration will occur in the lung-bag system, recognized as a plateau in the PCO2 rebreathing record. If a plateau is not obtained, PvCO2 can be estimated by extrapolating the line joining the points of expired PCO2 during the 8th and 12th seconds of rebreathing to that of the 20th second. With the equilibrium method, the plateau PCO2 is systematically higher than PvCO2 (downstream effect) and a correction is applied to obtain PvCO2. PaCO2 can be estimated from PETCO2 or from the mixed-expired PCO2 and an assumed physiologic dead space, except in patients with abnormal lung function, in whom PaCO2 must be measured directly. The content of CO2 in blood may be calculated from PCO2 by the equation: In(CCO2) = [0.396 X In(PCO2)] + 2.38 More complex algorithms are available to calculate CCO2 if the pH, hemoglobin, and arterial O2 saturation are widely divergent from resting values. The indirect Fick method applied to CO2 during exercise can be used to obtain a valid and reproducible measurement of Q comparable to that obtained by invasive methods.

Carbon Dioxide↗

PubMed2006

Comparisons between electromagnetic and X-beam transit-time flow measurements for evaluating drug actions on cardiac output in the conscious dog.

INTRODUCTION: Cardiac output remains an important preclinical measurement for evaluating the cardiovascular effects of drugs. We evaluated the performance of the Triton Active Redirection Transit-Time, ART(2), which represents a new class of X-beam flow systems and compared it in vivo and in vitro to an electromagnetic flow (EMF) system for measuring large vessel flow. METHODS: In vivo, simultaneous aortic flow measurements were obtained during alpha- and beta-adrenergic receptor stimulation in 5 conscious dogs instrumented with both ART(2) and EMF probes on their ascending aortas. In vitro, simultaneous measurements of volume flow using the ART(2), EMF, and timed-volume collection were made using a novel benchtop flow apparatus that ensured probe alignment and precise timed-volume flow measurements. Accuracy and sensitivity of both systems were assessed by recording flow measurements while varying rates, temperature and hematocrit. RESULTS: In vivo aortic flow measurements between ART(2) and EMF were closely correlated (linear regression r(2) values ranged from 0.84 to 0.99), with the ART(2) system recording lower flow values than the EMF. In vitro ART(2) flow rates were in excellent agreement with timed-volume flow, while EMF flow rates were lower (p<0.05) and exhibited more variation and dependency upon temperature or hematocrit than the ART(2). Saline flows measured by ART(2) and EMF averaged 97+/-2% and 91+/-5% accuracy, respectively, over the temperature range 32 degrees C to 42 degrees C. For blood hematocrit values between 35% and 45%, ART(2) accuracy averaged 98+/-2%, compared to 89+/-5% accuracy with the EMF. DISCUSSION: The ART(2) flow measurements in conscious dogs correlated closely to concurrent measurements obtained with the EMF over a wide range of flow rates, even though the absolute aortic flow values differed. Since it accurately measured flow in vitro, the ART(2) system is an appropriate alternative for evaluating cardiovascular effects of disease progression or drug administration in experimental animals.

Adrenergic alpha-Agonists↗

PubMed1990

Clinical evaluation of a diameter sensing Doppler cardiac output meter.

A concentric beam Doppler ultrasonic flowmeter has been developed. This instrument has capacity for independent assessment of volumetric flow, as it determines flow cross-section area, stroke length, and pulse rate from the Doppler signals alone. The method is practically independent of the angle of interrogation. We used this device and obtained noninvasive estimates of cardiac output in 54 patients undergoing invasive assessment of cardiac output by thermodilution, Fick, or indicator dye methods (x). Correlations against pooled cardiac output reference standards ranged from r = .86 (y = .86x + 1.03) in 26 studies of high confidence to r = .45 (y = .30x + 2.62) in 17 studies under difficult conditions. The overall correlation was r = .68 (y = .63x + 1.49, n = 87). Noninvasive results of experienced and inexperienced operators were similar (r = .87). The instrument returned accurate assessments of heart rate (r = .83), but underestimated stroke length (r = .72) and appeared to be limited in the assessment of aortic diameters less than 28 or greater than 31 mm (r = .23). We conclude that stand-alone Doppler assessment of cardiac output is appealing and feasible, but difficult or impossible in many ICU scenarios. Further evolution of the concentric beam Doppler approach is needed and anticipated.

Aorta↗

PubMed1978

Measurements of cardiac output in seriously ill patients using a CO2 rebreathing method.

A CO2 rebreathing method for the measurement of cardiac output was evaluated by comparison with the direct Fick O2 method in 26 studies performed in 18 patients who were critically ill. The method requires measurement of CO2 output by collection of expired gas, of arterial PCO2, and of mixed venous PCO2 by rebreathing. Twenty-five comparisons were within +/- 20% of the direct Fick measurements, at cardiac outputs varying between 1.4 and 6.4 L/min. Knowledge of the cardiac output increased the quality of the interpretation of arterial blood PO2 measurements in the assessment of pulmonary gas exchange disturbances.

Blood Gas Analysis↗

PubMed1975

[Determination of cardiac output using impedance-cardiography in comparison with conventional methods during rest and under pharmacological stress].

A recording of the changes in the transthoracic resistance as a function of the cardiac cycle enables--in connection with the ejection time--a non-invasive determination of the cardiac output (impedance cardiography). On volunteers without heart diseases the cardiac output according to the Fick principle, the impedance-cardiographic and sphygmographic method at rest and under pharmacological influence is synchronously measured and statistically compared with the found cardiac output according to Fick. Especially under pharmacological influence the impedance-cardiographically determined values do not show a sufficient correlation. The range of error, is causes as well as the limited possibility of application of the method are being discussed.

Cardiac Output↗

PubMed1991

Post-prandial worsening of angina: all due to changes in cardiac output?

BACKGROUND: The precise mechanism leading to the post-prandial worsening of angina has yet to be adequately defined. It has been attributed to an increase in double product but is perhaps more likely to be related to an increase in cardiac output after food. This study was designed to evaluate the effects of food on patients' exercise tolerance and compare these with changes in haemodynamic variables. METHODS: 23 patients with chronic stable angina who had post-prandial worsening of their angina were studied. The patients were evaluated on two occasions and at each visit they underwent two symptom limited treadmill exercise tests. They remained fasting on the first visit and were given a 1400 kcal meal 60 minutes before the second exercise test on the second visit. Time to onset of 1 mm ST segment depression, heart rate, systemic arterial blood pressure, and cardiac output were measured at rest and during exercise. RESULTS: There were no differences in any of the variables during the two exercise tests on the day the patients remained fasting. After the meal exercise tolerance fell significantly by 136 seconds and the stage at which 1 mm ST segment depression was first seen was also significantly reduced. Resting cardiac output increased significantly by 0.86 1/min with the patients sitting and by 0.89 1/min standing. The exercise times after food were significantly related to cardiac output even when fasting times were taken into account. Resting heart rate increased significantly by 8.3 beats per minute sitting and 10.4 beats per minute standing. There was little change in blood pressure and no evidence that the double product predicted the post-prandial exercise time. CONCLUSIONS: Worsening of angina was related to the increase in cardiac output after a meal and successful treatment will depend upon the prevention of this increase.

Aged↗

PubMed1989

Endothelin induces an initial increase in cardiac output associated with selective vasodilation in rats.

The systemic and regional hemodynamic effects of endothelin (ET), a novel endothelial derived vasoconstrictor peptide were studied in Wistar Kyoto rats. A bolus of 1 nmol/Kg ET intravenously induced a transient 43% decrease in blood pressure associated with a 57% decrease in systemic resistance and a 30% increase in cardiac output (p less than 0.01 for all parameters). This was followed by an increase of 20% in arterial pressure and of 71% in systemic resistance and a decrease of 30% in cardiac output at 10 minutes. The initial fall in blood pressure was not abolished by pretreatment with verapamil, captopril, indomethacin, ketanserin, atropine, methylene blue or ethanol. Verapamil abolished the hypertensive phase by markedly decreasing cardiac output. ET had selective effects on the arterial tree; during the hypotensive phase it caused a transient increase in blood flow in the carotid and femoral arteries (+41% and +83% respectively, p less than 0.01) but a decrease in flow in the renal and mesenteric arteries (-53% and -44% respectively, p less than 0.05). Accordingly, there was a decrease in resistance in the carotid and femoral beds (-55% and -67% respectively, p less than 0.01) and an increase in resistance in the renal and mesenteric beds (+102%; p less than 0.01 and +23%; p = N.S. respectively). Subsequently there was an increase in resistance in all vascular beds to variable degrees. The maximal increase in resistance was in the renal bed (+156%). Thus, ET causes initially a potent systemic vasorelaxation and an increase in cardiac output later progressing to systemic vasoconstriction and a decrease in cardiac output. The initial vasodilation is selective, appearing in musculocutaneous beds but not in visceral beds.

Animals↗