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PubMed1979

Cardiac output during rest and exercise in desert heat.

Cardiac output and stroke volume were measured in two environments and at metabolic rates ranging from rest to the maximum rate that could be sustained for 25 minutes. One environment was indoors at about 23 degrees C, the other outdoors in desert sunshine and low water vapor pressure. The age range of the one female and four of the male subjects was from 19 to 40; the fifth male subject was 85 years old. Cardiac output was the same in the two environments; stroke volume was less at higher metabolic rates in the heat. The cardiac output for the old man was about one-tenth less and stroke volume about 20 ml less than that observed for the same work 50 years earlier.

Adult↗
PubMed2006

Comparison of invasive and less-invasive techniques of cardiac output measurement under different haemodynamic conditions in a pig model.

BACKGROUND AND OBJECTIVE: Despite the introduction of various less-invasive concepts of cardiac output measurement, pulmonary arterial thermodilution is still the most common measurement technique. METHODS: This prospective controlled study was designed to compare different methods of cardiac output measurement simultaneously. Pulmonary arterial thermodilution, transpulmonary thermodilution (PiCCO), trans-oesophageal echo-Doppler probe (HemoSonic) and partial carbon dioxide rebreathing technique (NICO monitor) were evaluated against a peri-aortic transit-time flow-probe as reference method in a clinically relevant animal model. After approval from the Local Ethics Committee on Animal Research, the investigations were conducted in nine anesthetized domestic pigs. Systemic haemodynamics were modulated systematically by the application of catecholamines, caval occlusion and exsanguination. Statistical analysis was performed with Bland-Altman and linear regression. RESULTS: A total of 366 paired cardiac output measurements were carried out at a reference cardiac output between 0.5 and 7 L min(-1). The correlation coefficients for pulmonary arterial and transpulmonary thermodilution against reference were 0.93 and 0.95, for trans-oesophageal Doppler and partial rebreathing technique 0.84 and 0.77. Pulmonary arterial thermodilution and transpulmonary thermodilution showed comparable bias and limits of agreement. Where HemoSonic showed an overestimation of cardiac output at a higher precision, NICO overestimated low and underestimated higher cardiac output values. CONCLUSIONS: Our data suggest that pulmonary arterial thermodilution and PiCCO may be interchangeably used for cardiac output measurement even under acute haemodynamic changes. The method described by Bland and Altman demonstrated an overestimation of cardiac output for both thermodilution methods. HemoSonic and NICO offer non-invasive alternatives and complementary monitoring tools in numerous clinical situations. Trend monitoring and haemodynamic optimizing can be applied sufficiently, when absolute measures are judged critically in a clinical context. The use of the NICO system seems to be limited during acute circulatory changes.

Algorithms↗
PubMed1985

The nursing diagnosis of decreased cardiac output.

This descriptive study validated the nursing diagnosis of decreased cardiac output in a critical-care population. A cardiac output assessment tool was developed. Nursing interventions associated with decreased cardiac output were identified and classified as independent, collaborative, and dependent.

Adult↗
PubMed1993

[Measurement of cardiac output by CO2 rebreathing technique. A study of reproducibility in the normal subject; application to cardiac insufficiency].

A feasibility and reproducibility study of cardiac output measurement by CO2 rebreathing was performed in normal subjects and in patients with compensated cardiac failure. The measurements were performed at rest and at the second stage of the Bruce protocol in normal subjects (N = 12) with a good reproducibility (r = 0.81) after an interval of two days. In patients with stable cardiac failure (N = 17), the cardiac outputs were 9.4 +/- 3.9 l/min and 9.3 +/- 3.1 l/min by measuring the arterial pCO2 and end-expiratory CO2 compared with the theoretical value of 9.9 +/- 2 l/min. The non-invasive measurement of cardiac output by the CO2 rebreathing method was well tolerated by patients and is reliable and reproducible.

Adult↗
PubMed1988

Thermodilution cardiac output measurements during conventional and high-frequency ventilation.

The thermodilution method for cardiac output determinations correlates well with Fick and dye dilution methods. Experimental work with thermodilution techniques has shown that individual measurements of right heart cardiac output during conventional ventilation vary throughout the respiratory cycle. The aims of this study were to compare thermodilution cardiac output determinations made at a fixed point (zero end-expiratory pressure [ZEEP]) with those made randomly throughout the respiratory cycle during conventional controlled positive pressure ventilation (CPPV) and high-frequency jet ventilation (HFJV) with up to 10 cm H2O positive endexpiratory pressure (PEEP). There were no statistically significant differences between the cardiac output determinations made at ZEEP and randomly in the ventilation cycle in any group and all correlations were significant. The clinical implications of these results are discussed, and it is concluded that it is not necessary to time the measurements of thermodilution cardiac output determinations during CPPV or HFJV with up to 10 cm H2O of PEEP.

Adult↗
PubMed2000

Spontaneous variability of cardiac output in ventilated critically ill patients.

OBJECTIVE: To define the magnitude of spontaneous cardiac output variability over time in sedated medical intensive care unit patients attached to a continuous cardiac output monitor, and to determine whether high level positive end-expiratory pressure or inverse inspiratory-to-expiratory (I:E) ratio ventilation resulted in greater variability over time than low positive end-expiratory pressure with conventional I:E ratio ventilation. DESIGN: Prospective study. SETTING: Medical intensive care unit in a tertiary medical center. PATIENTS: A total of 22 hemodynamically stable acute respiratory failure patients with a pulmonary artery catheter inserted for hemodynamic monitoring INTERVENTIONS: After being sedated, patients were randomized ultimately to receive pressure control ventilation first at setting A (high positive end-expiratory pressure [15 cm H2O] with conventional I:E ratio [1:2]) and then at setting B (low positive end-expiratory pressure [5 cm H2O] with inverse I:E ratio [2:1]), or vice versa, and then at setting C (low positive end-expiratory pressure [5 cm H2O] with conventional I:E ratio [1:2]). Each ventilation setting period lasted 1 hr. MEASUREMENTS AND MAIN RESULTS: Cardiac output (CO) was measured continuously. The continuous CO value displayed was updated every 30-60 secs. The updated value reflected an average of the previous 3-6 mins. The coefficient of variation (CV) of CO for each setting in each patient was calculated to represent the spontaneous variability. The mean CO+/-SD and CV of each setting was 5.7+/-1.8 L/min and 4.4% for setting A, 5.6+/-1.5 L/min and 4.6% for setting B, and 5.9+/-1.7 L/min and 4.8% for setting C. Analysis of variance revealed no significant differences between the CVs of the three settings. The 95% confidence interval for the COs for each setting was approximately the mean CO+/-0.1 x mean CO measured. CONCLUSIONS: In critically ill sedated medical intensive care unit patients with stable hemodynamics, the spontaneous variability of cardiac output over time was not significant. High positive end-expiratory pressure (15 cm H2O) and inverse ratio ventilation (2:1) did not contribute to increased spontaneous variability of cardiac output.

APACHE↗
PubMed1982

Differences between directly measured and calculated values for cardiac output in the dogfish: a criticism of the Fick method.

Cardiac output has been measured directly, and calculated by the Fick method, during normoxia and hypoxia in six artificially perfused dogfish (Scyliorhinus canicula) in an attempt to estimate the accuracy of this method in fish. The construction and operation of a simple extra-corporeal cardiac bypass pump is described. This pump closely mimics the flow pulse profiles of the fish's own heart and allows complete control of both cardiac stroke volume and systolic and diastolic periods. During normoxia (PO2 = 21 kPa) there was no significant difference between directly measured and calculated values for cardiac output. However, some shunting of blood past the respiratory surface of the gills may have been obscured by cutaneous oxygen uptake. In response to hypoxia (PO2 = 8.6 kPa) there is either a decrease in the amount of blood being shunted past the respiratory surface of the gills and/or an increase in cutaneous oxygen uptake such that the Fick calculated value for cardiac output is on average 38% greater than the measured value. It is proposed that the increase in the levels of circulating catecholamines that is reported to occur in response to hypoxia in this species may play an important role in the observed response to hypoxia. The results are discussed in terms of their implications for the calculation of cardiac output by the Fick principle in fish.

Animals↗
PubMed2007

Mechanisms of a reduced cardiac output and the effects of milrinone and levosimendan in a model of infant cardiopulmonary bypass.

OBJECTIVES: A low cardiac output state is an important cause of morbidity after pediatric cardiopulmonary bypass. The objectives of our study were to define the early precipitants of the reduced cardiac output and to investigate the effects on these of milrinone and levosimendan in a model of pediatric cardiopulmonary bypass. DESIGN: Experimental study. SETTING: : Research laboratory at a university-affiliated, tertiary pediatric center. SUBJECTS: Eighteen piglets. INTERVENTIONS: Piglets, instrumented with systemic, pulmonary arterial, and coronary sinus catheters, pulmonary and circumflex arterial flow probes, and a left ventricular conductance-micromanometer-tipped catheter, underwent cardiopulmonary bypass with aortic cross-clamp and cardioplegic arrest. At 120 mins, they were assigned to control, milrinone, or levosimendan groups and studied for a further 120 mins. MEASUREMENTS AND MAIN RESULTS: In controls, between 120 and 240 mins, cardiac output decreased by 15%. Systemic vascular resistance was unchanged, but pulmonary vascular resistance increased by 19%. Systemic arterial elastance increased by 17%, indicating increased afterload. End-systolic elastance was unchanged, and coronary sinus oxygen tension decreased by 4.0 +/- 1.7 mm Hg. In animals receiving milrinone cardiac output was preserved, and in animals receiving levosimendan cardiac output increased by 14%. Both drugs prevented an increase in arterial elastance and pulmonary vascular resistance after cardiopulmonary bypass. Systemic vascular resistance decreased by 31% after levosimendan, and end-systolic elastance increased by 48%, indicating improved contractility. Both agents prevented a decrease in coronary sinus oxygen tension. CONCLUSIONS: Increased afterload, which is not matched by an equivalent elevation in contractility, contributes to the reduced cardiac output early after pediatric cardiopulmonary bypass in this model. This increase is prevented by milrinone and levosimendan. Both agents exert additional beneficial effects on pulmonary vascular resistance and myocardial oxygen balance, although levosimendan has greater inotropic properties.

Age Factors↗
PubMed1982

Cardiac output measured by transthoracic impedance cardiography at rest, during exercise and at various lung volumes.

1. Cardiac output measured by transthoracic impedance cardiography has been compared with simultaneous measurements made by the indirect Fick CO2 rebreathing method in nine adults and 14 children. All were healthy normal volunteers. Sixty-six comparisons were made at rest and during steady exercise at work loads up to 100 W. 2. Impedance measurements of cardiac output were consistently higher than indirect Fick measurements of cardiac output, but after application of a correction factor related to packed cell volume there was close correlation between the results obtained by the two methods (r = 0.94). 3. The mean coefficient of variation of impedance measurements of cardiac output was 13% at rest and 5% during steady-state exercise. 4. Changes of lung volume due to breath holding or resulting from addition of an expiratory resistance did not affect the measurement of cardiac output by impedance. 5. Transthoracic impedance cardiography is a rapid, non-invasive technique for measurement of cardiac output. It requires very little active co-operation from the subject. The method would probably give reliable results for patients with respiratory illnesses such as acute asthma or bronchiolitis, during which changes of lung volume may be expected to occur.

Adult↗
PubMed1987

Assessment of beat to beat changes in cardiac output during the Valsalva manoeuvre using electrical bioimpedance cardiography.

Beat to beat changes in cardiac output during standardized Valsalva's manoeuvres were recorded using electrical bioimpedance cardiography in 13 normal subjects. Cardiac output increased by 12 +/- 5% after 1 s of straining solely because of an increase in heart rate. Subsequently, cardiac stroke volume and cardiac output fell during the strain to lows of -40 +/- 6% and -21 +/- 3% respectively at 15 s. There was a sustained increased in cardiac output (maximum +17 +/- 4%) in the late post strain period. The mean coefficient of variation in impedance measurements of cardiac output was 6.8% during all parts of Valsalva's manoeuvre, with no single value exceeding 10%.

Adult↗
PubMed1985

Validation of radionuclide cardiac output measurements during exercise.

A nongeometric radionuclide technique with correction for attenuation was used for the determination of cardiac output and stroke volume during exercise in nine normal subjects and in ten hypertensive patients. Simultaneous reference stroke volume (range 48-159 ml) and cardiac output (range 3.6-23.8 l/min) measurements were obtained by the Fick method. Data were collected at rest and during 60 degrees upright exercise, at two or three levels of increasing severity. Three statistical measurements were used for the comparison of both methods: correlation, precision, and accuracy. Radionuclide and Fick cardiac output measurements (n = 67, rest and exercise data) correlated well (r = 0.90). For stroke volume, the correlation was less (r = 0.64); however, the precision or random variability of both methods was similar for stroke volume (radionuclide: 8 ml or 9%; Fick: 16 ml or 16%). The accuracy or systematic error was defined as the mean difference between radionuclide and Fick measurements. The radionuclide method underestimated the Fick measurements. The systematic error was 18 +/- 18 ml for stroke volume and 2.4 +/- 2.4 l/m for cardiac output. A similar comparison of both methods was made on the absolute changes of stroke volume (r = 0.61; range -19 + 70 ml) and cardiac output (r = 0.82; range +1.6 + 16.4 l/m) between rest and exercise. The precision of the two methods was similar; the systematic error was 1.9 +/- 2.2 l/m for cardiac output and 6 +/- 17 ml for stroke volume. Thus, in these two groups of patients, although radionuclide and Fick cardiac output measurements at rest and during exercise correlated well, the radionuclide values were systematically and significantly lower.

Adult↗
PubMed1992

Room-temperature thermodilution cardiac output: central venous vs right ventricular port.

OBJECTIVE: To assess the accuracy of room-temperature thermodilution cardiac output measurements from the right ventricular port. In addition, waveform patterns were evaluated to determine the actual location of the right ventricular port. DESIGN: Central venous port cardiac output measurements were compared with right ventricular port cardiac output measurements using the same right-heart catheter. SETTING: The general intensive care unit of Memorial Sloan-Kettering Cancer Center. PATIENTS: Thirty-seven critically ill cancer patients with 38 different right-heart catheters were evaluated. INTERVENTION: Four injections of 10 mL normal saline at room temperature were made through each port; the results of the last three injections were averaged. Cardiac output determinations from both ports were completed in less than 10 minutes. The order of port injection was random. RESULTS: No difference was noted between cardiac output determinations from the two ports in a paired t test. Of 38 right-heart catheters, 17 were in the right ventricle and the other 21 in the right atrium. A comparison of ports in the 17 right ventricle catheters showed no difference with a significant (P < .01; R2 = 0.96) correlation. CONCLUSION: Thermodilution cardiac output measurements using 10 mL normal saline at room temperature can be determined accurately using the right ventricular port if the central venous port becomes nonfunctional.

Adult↗
PubMed1992

Reliability of first-pass radionuclide determination of cardiac output in the upright position at rest and during exercise.

The reliability of non-invasive determination of cardiac output using first-pass radionuclide cardiography at rest and during exercise in the upright position was evaluated in 20 patients with coronary artery disease. Cardiac output values ranged from 2.97 to 5.99 l/min at rest and from 5.08 to 10.82 l/min during exercise. Cardiac output results obtained by the radionuclide method were compared with those derived from the thermodilution technique performed simultaneously. The mean difference between the two techniques was 0.02 l/min at rest and -0.34 l/min during exercise; the limits of agreement (mean +/- 1.96 SD) were -1.29 to 1.33 l/min and -1.97 to 1.29 l/min, respectively, indicating an acceptable level of agreement. A high reproducibility of the radionuclide technique was found, with a mean difference between determinations by two observers of 0.03 l/min at rest and 0.21 l/min during exercise, the corresponding limits of agreement being -0.75 to 0.81 l/min and -0.79 to 1.21 l/min, respectively. With the aid of a variance component analysis of two determinations by each of four observers, 95% confidence intervals of +/- 10% at rest and +/- 12% during exercise were computed for the radionuclide cardiac output measurements. The observer variation was most pronounced for the part of the cardiac output determination related to measurement of left ventricular equilibrium activity during exercise. First-pass radionuclide cardiography is a reliable method for determination of cardiac output in cardiac patients at rest and during exercise in the upright position.

Aged↗
PubMed2005

[Comparison of cardiac output measurement in critical patients using transesophageal Doppler or thermodilution: a preliminary report].

BACKGROUND: Cardiac output can be measured non invasively by transesophageal Doppler. This is an alternative to measure it by thermodilution with a catheter in the pulmonary artery. AIM: To compare both methods of cardiac output measurement. MATERIAL AND METHODS: Simultaneous measurement of cardiac output by transesophageal Doppler and thermodilution with a catheter in the pulmonary artery in four male critical patients, aged 60+/-12 years, hospitalized in a University Hospital. The Bland and Altman method to compare the concordance between two measurements, was used. RESULTS: Forty measurements were performed. The results of both methods had a correlation coefficient of 0.98. According to the Bland and Altman method, the difference between both methods was -0.5 L with a precision of 0.52 L/min (95% confidence interval -1.51 to 0.52 L/min). Considering that a change between two sequential measurements is considered significant when the difference is more than 15%, both measurements agreed in 83% of cases, that there was a change in cardiac output. CONCLUSIONS: Transesophageal Doppler is a promising non invasive technique to measure cardiac output in critical care patients. It becomes a valid alternative to the thermodilution technique. This preliminary experience must be confirmed in a larger series.

Cardiac Output↗
PubMed1975

Serial determination of cardiac output during prolonged work by a CO2-rebreathing technique.

Cardiac outputs were calculated on eight male college students while walking on a treadmill at controlled heart rate levels. The heart rate levels were maintained through the use of a heart rate controller (Quinton Model AI-607), standard deviations for heart rate in beats/min ranged from +/-2.1 at the heart rate level 110 to +/-3.2 at 170. Test-retest correlations of the cardiac output values at the various heart rate levels were: at heart rate 110, 0.66 after 7 min and 0.85 at 30 min; at heart rate 150, 0.92 after 7 min and 0.68 at 30 min; at heart rate 130, 0.97 after 7 min, and at heart rate 170, 0.85 after 7 min. The calculated cardiac output values when plotted against oxygen uptake compare favorably with published reports. The data collected demonstrate that the CO2-rebreathing method used in the present investigation provides a reliable bloodless technique for determining multiple cardiac output during prolonged work of varied intensities.

Adult↗
PubMed1996

Evaluation of the tracking potential of a noninvasive estimator of cardiac output.

A robust, automatic measurement system for calculating cardiac output noninvasively has recently been developed. The proposed method relies on fast Fourier transform (FFT) analysis of pulses measured externally at the carotid and femoral pressure points. A transfer function of the aorta is computed from these (calibrated) pressure measurements, and a tapered model of the aorta is parametrically adapted so that its transfer function matches that derived experimentally. Incorporated in the system are a custom routine for digitally filtering pressure data and a simplex optimization algorithm for identification of aortic parameters essential to the calculation of impedance and aortic flow. Once flow has been reconstructed in the time domain it is averaged to a stroke volume and multiplied by the heart rate to yield cardiac output. Flow measurements are computed over several pulses and compared against the standard, invasive procedure of thermodilution. Preliminary results for a dynamic investigation of the method indicate a strong potential for tracking changes in cardiac output over time, thus advocating its use in monitoring hemodynamically unstable patients.

Algorithms↗
PubMed2004

The effects on arterial haemoglobin oxygen saturation and on shunt of increasing cardiac output with dopamine or dobutamine during one-lung ventilation.

Theoretically, if the cardiac output were increased in the presence of a given intrapulmonary shunt, the arterial saturation should improve as the venous oxygen extraction per ml of blood decreases if the total oxygen consumption remains constant. Previous work demonstrated that this was not achieved with adrenaline or isoprenaline as increased shunting negated any benefit from improved cardiac output and mixed venous oxygen content. However pharmacological stimulation of cardiac output and venous oxygen without any increase in shunt should achieve the goal of improved arterial oxygenation. To test this hypothesis, seven pigs were subjected to one-lung ventilation and infused on separate occasions, with dopamine and with dobutamine in random order to increase the cardiac output. The mixed venous oxygen content, shunt fraction, oxygen consumption and arterial oxygen saturation were measured. With both dopamine and dobutamine there was a consistent rise in venous oxygen content. However, with dopamine, the mean shunt rose from 28% to 42% and with dobutamine, the mean shunt rose from 45% to 59% (both changes P<0.01). With dopamine, the mean arterial oxygen saturation fell by 4.7%, and with dobutamine by 2.9%, but neither fall was statistically significant. It is concluded that any benefit to arterial saturation which might occur from a dopamine- or dobutamine-induced increase in mixed venous oxygen content during one-lung ventilation is offset by increased shunting. During one-lung anaesthesia, there would appear to be no benefit to arterial saturation in increasing cardiac output with an infusion of either dopamine or dobutamine.

Adrenergic beta-Agonists↗
PubMed1997

Continuous cardiac output monitoring during adult liver transplantation: thermal filament technique versus bolus thermodilution.

UNLABELLED: Continuous thermodilution (CT) using a pulmonary artery (PA) catheter with a thermal filament has the potential for intraoperative on-line monitoring of cardiac output. Liver transplantation frequently requires rapid fluid administration and often includes the use of an extracorporeal veno-venous bypass. To assess the agreement between CT and bolus thermodilution (BT) in such a setting, we conducted a prospective intraoperative study in 14 liver transplant patients. Throughout the operation, CT cardiac output was recorded and paired with BT measurements taken every 30 min and whenever indicated for clinical reason. Corresponding data were assigned to acquisition periods when patients were on or off veno-venous bypass (flow rate 2.5 +/- 0.2 L/min) and were discriminated by the various range of intravenous infusion rates (< 150 mL/h, 150-1000 mL/h, 1000-2000 mL/h, and 2000-4000 mL/h) and the magnitude of cardiac output (< or = 7.5 L/min, 7.5-10.0 L/min, > 10.0 L/min). A total of 270 data pairs was obtained and examined by analysis of agreement (mean difference +/- SD), variance, error, and weighted regression. Trend analysis was performed for significant CT and BT cardiac output changes, defined as changes greater than 15%. Agreement of both methods was best at peripheral intravenous fluid infusion rates < or = 1000 mL/h and BT cardiac output > 10 L/min (0.0 +/- 0.6 L/min) and was unaffected by veno-venous bypass. Discrepancy was most evident at intravenous fluid infusion rates > 2000 mL/h and BT cardiac output < or = 7.5 L/min (2.1 +/- 1.7 L/min). Correlation of CT and BT cardiac output was excellent (r = 0.95, P < 0.001) for combined data from all patients. Changes in CT cardiac output > 15% (n = 116) correctly indicated the direction in 93% of BT cardiac output changes and were 74% sensitive and 75% specific for significant BT cardiac output changes. The thermal filament technique enhances the usefulness of PA catheterization during liver transplantation but reflects BT cardiac output with clinically acceptable error only at low peripheral intravenous fluid infusion rates. IMPLICATIONS: Cardiac output determines organ perfusion. In clinical practice, it is measured by intermittent thermodilution using right heart catheterization. This intraoperative study compared the intermittent method with a technique based on continuous thermodilution. The new technique provides logistical advantages and challenges the accuracy of the intermittent method during liver transplantation.

Adult↗