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PubMed1995

[Comparison of 2 modified Fick methods and thermodilution for determining the cardiac output in patients with mechanical ventilation].

OBJECTIVE: To evaluate the effectiveness of two cardiac output measurement methods based on a modified Fick equation, that calculate the O2 consumption (VO2) dividing the CO2 production (VCO2) by a fixed respiratory quotient (RQ). DESIGN: Comparative study. SETTING: One 5 beds general intensive care unit in a 500 beds general hospital. PATIENTS: Ten mechanically ventilated critically ill patients requiring the right heart catheterization. The mean age was 65.5 years and the mean APACHE II score at admission was 24. MEASUREMENTS: The cardiac output was measured using two modified Fick methods. The VO2 was calculated dividing VCO2 by 0.9, while the arteriovenous O2 content difference was calculated using the mixed venous O2 content in the first method (COF), and the central venous O2 content in the second one (COFra). Moreover the cardiac output was measured with the thermodilution technique (COTD) as gold standard. RESULTS: The mean difference between the COTD and COF determinations was 0.571 L +/- 1.81 L, with limits of agreement ranging from -3.057 to +4.200 L. The mean difference between the COTD and COFra determinations was -0.322 L +/- 2.05 L, with limits of agreement ranging from -4.430 to +3.785 L. Both differences were nonsignificant. The correlation coefficients with COTD were: COF determinations 0.72, COFra determinations 0.70. In the group of COFra determinations less than 7 L the mean difference between COTD and COFra was 0.495 L with limits of agreement ranging from +2.208 L to -1.218 L. CONCLUSIONS: The correlation coefficients of the two modified Fick methods with COTD are good, and the mean differences between their results and the gold standard are small, but the low precision of both tested methods demonstrated by the very large limits of agreement, severely reduce the clinical reliability of the measurements. Only for the less than 7 L cardiac outputs the COFra limits of agreement with COTD are narrow enough, and in this range the technique can be useful e.g. revealing a low cardiac output.

Adult↗
PubMed1992

[A study of measuring cardiac output in patients during mechanical ventilation with CO2 rebreathing method].

Measurement of cardiac output with CO2 rebreathing method and thermodilution method was carried out in seven COPD patients undergoing mechanical ventilation. Mixed venous PCO2 could be measured reasonably well with CO2 rebreathing method. There was a very significant positive correlation between the CO2 method and thermodilution method for measuring cardiac output (r = 0.9130, P < 0.01). The change of cardiac output before and after infusion of sodium nitroprusside could be reflected by CO2 rebreathing method. We conclude that the cardiac output in COPD patients undergoing mechanical ventilation could be measured reasonably well with CO2 rebreathing method.

Aged↗
PubMed1987

The effect of a low-dose infusion of ritodrine on cardiac output distribution and uteroplacental blood flow in unanaesthetized pregnant guinea pigs.

Cardiac output and its distribution were measured using the microsphere technique before and at 2 and 6 h during the infusion of ritodrine, 1.5 microgram X min-1 X kg-1 i.v., into near-term pregnant guinea pigs. Average cardiac output increased 16 and 25%, and total peripheral resistance decreased 16 and 19% after 2 and 6 h of ritodrine infusion. The carcass and gastrointestinal tract together received two-thirds of the extra cardiac output. Uteroplacental blood flow and uteroplacental vascular resistance were not significantly different from the preinfusion values after 2 h of ritodrine treatment, but were increased 35% and decreased 31%, respectively (p less than 0.05 and less than 0.01), after 6 h of infusion. The increase in uteroplacental blood flow between the 2- and 6-h measurements was positively, and the decrease in uteroplacental vascular resistance negatively correlated with the increase in cardiac output during the same period.

Animals↗
PubMed1980

Determination of cardiac output from pulse pressure contour during intra-aortic balloon pumping.

The reliability of cardiac output determinations from radial pulse pressure contour during intra-aortic balloon pumping (IABP) has been tested and compared with thermodilution measurements. During IABP the pulse pressure curve is distorted by preset volume changes in the aorta. The pressure decrease following balloon deflation was compared with pressure increase following systolic ejection to determine stroke volume and cardiac output. The analysis and calculations were computerized. Measurements were made in thirteen patients with left ventricular failure. The algorithmic analyser failed to produce any results at all in two patients and in ten other patients if failed to produce results more often in some of the patients than others. This made the algorithmic calculation of cardiac output useless in the care of the individual patients. In thirteen patients on IABP seventy-seven comparisons were obtained, and a fair covariation (r = 0.86) was found. The ratio between the two methods of cardiac output measurements did not change significantly with increasing cardiac output.

Assisted Circulation↗
PubMed1996

A new automatic cardiac output control algorithm for moving actuator total artificial heart by motor current waveform analysis.

A new automatic cardiac output control algorithm for an implantable electromechanical total artificial heart (TAH) was developed based on the analysis of motor current waveform without using any transducer. The basic control requirements of an artificial heart can be described in terms of three features: preload sensitivity, afterload insensitivity, and balanced ventricular output. In previous studies, transducers were used to acquire information on the hemodynamic states for automatic cardiac output control. However, such a control system has reliability problems with the sensors. We proposed a novel sensorless automatic cardiac output control algorithm (ACOCA) providing adequate cardiac output to the time-varying physiological demand without causing right atrial collapse, which is one of the critical problems in an active filling device. In vitro tests were performed on a mock circulatory system to assess the performance of the developed algorithm and the results show that the new algorithm satisfied the basic control requirements of the cardiac output response.

Algorithms↗
PubMed1982

Automatic vs manual injections for thermodilution cardiac output determinations.

To investigate the effects of operator variability on thermodilution cardiac output determinations, a group of physicians and nurses made a series of manual indicator injections and automatic injections using a gas powered injector in a simulated clinical situation. The data show significant variability in injection time, injectate flow rate, consistency of injection, and cardiac output values obtained during manual injections. There was little variability in these parameters during automatic injections. When other variables are properly controlled, the automatic injector may improve the precision of cardiac output measurements by controlling the consistency of injection and variables introduced by different operators performing manual injections. However, despite significant variation in parameters associated with manual injection, it is interesting to note that 8 out of 10 operators obtained cardiac output values by hand injection using room temperature injectate, which did not differ significantly from those obtained by automatic injection.

Animals↗
PubMed1986

Treatment of low cardiac output complicating acute pulmonary hypertension in normovolemic goats.

In eight anesthetized ventilated goats, the hemodynamic effect of isoproterenol (ISU), dopamine (DOP), norepinephrine (NE), nitroglycerin (NTG), and Ringer's lactate (RL) infusion was evaluated after inducing acute pulmonary hypertension (PHN) to decrease cardiac output. Therapy with ISU significantly (p less than .05) increased cardiac output, but also increased transmural right ventricular end-diastolic pressure (RVEDPTM) and heart rate (HR) and decreased stroke volume (SV) and right ventricular ejection fraction (RVEF). NE increased cardiac output, mean arterial pressure (MAP), systemic vascular resistance (SVR), and RVEF. DOP decreased pulmonary vascular resistance (PVR) and increased cardiac output, MAP, and RVEF, but also significantly increased HR. NTG increased cardiac output and RVEF while decreasing SVR and PVR. Intravascular volume expansion by RL infusion increased cardiac output, SV, and RVEDPTM and decreased HR and PVR. The results of this study indicate that volume loading may be the treatment of choice to restore cardiac output in the face of acute PHN. NE and NTG may be effective as an adjunct therapy. Although ISU and DOP increase cardiac output, the concomitant elevation in HR is undesirable.

Animals↗
PubMed1980

Reliability of the cardiac output measurement with the indirect Fick-principle for CO2 during exercise.

Cardiac output measurements were performed during 50 exercise tests in 16 normal subjects employing the indirect Fick principle for CO2. During sub-maximal steady state exercise the plateau CO2 tension (PplatCO2) was estimated with a rebreathing procedure. The mixed venous CO2 tension (PvCO2) was calculated by subtracting the alveolocapillary CO2 tension difference from the PplatCO2. Compared with data from the literature the most valid calculation of the cardiac output was obtained by using the PvCO2. Cardiac output values, calculated via the PplatCO2 turned out to be too low. The reproducibility was tested by repitition of 18 exercise tests at least after 5 days. The relative standard error of a single observation was 4.1% for the cardiac output, which was found to be as good as that of invasive measurements.

Adult↗
PubMed2004

Non-invasive measurement of cardiac output in patients with chronic heart failure.

OBJECTIVES: The measurement of cardiac output by thoracic bioimpedance has been previously assessed in several studies. However, there continues to be disagreement as to whether this technique is sufficiently accurate for use in clinical practice or research. The current study aimed to compare thoracic bioimpedance (COTB) with thermodilution (COTD) in patients with stable chronic heart failure. METHODS AND RESULTS: A total of 282 paired measurements of cardiac output from 11 patients were analysed. There was good correlation between COTB and COTD (r=0.76, P<0.0001). However, Bland-Altman analysis revealed an average difference between values of 0.3 (2.2) l/min (P=0.02), suggesting a small average bias but marked variability in results. There was no significant correlation when results were expressed as percentage change from baseline and a significant average difference between values of 10.1 (30.1)%. There was no difference in between-day repeatability between thermodilution and thoracic bioimpedance [-0.2 (1.2) versus 0.1 (1.0) l/min, P=0.7]. CONCLUSIONS: This study demonstrates a correlation between the techniques but shows a poor level of agreement. The method of COTB underestimated cardiac output compared with COTD, and this difference appeared greater with higher cardiac outputs. Agreement was worse when results were expressed as change from baseline. The present study does not support the use of thoracic bioimpedance in its current form as an alternative to thermodilution in stable patients with chronic heart failure.

Aged↗
PubMed1999

Changes in stroke volume cause change in cardiac output in neonates and infants when mean airway pressure is altered.

BACKGROUND: Based on early studies in the lamb, and in spite of more recent studies in humans, it has been the received opinion that neonates and infants can not change their stroke volume significantly, but are mainly dependent on changes in heart rate, to change cardiac output. To further evaluate the relationship between cardiac output and stroke volume during mechanical ventilation of neonates and infants, we have studied the effects on cardiac output and stroke volume by two different ways of changing mean airway pressure. METHODS: In one group, mean airway pressure was decreased by using a patient triggered mode: pressure support ventilation; in the other, mean airway pressure was increased by increasing positive end-expiratory pressure (PEEP). Changes in cardiac output, heart rate and stroke volume were assessed with the Doppler technique, measuring blood flow velocity in the ascending aorta. RESULTS: Without a significant change in heart rate, we found a significant increase in cardiac output of +16+/-2% (P<0.01) with a decrease in mean airway pressure and a decrease in cardiac output of -13+/-4%, (P<0.02) with an increase in mean airway pressure, depicting a change in stroke volume of +17+/-2% (P<0.02) and -14+/-5%, (P<0.01) respectively. CONCLUSIONS: We conclude that neonates and infants are able to regulate cardiac output by changing the stroke volume to a greater extent than presumed, at least when cardiac output is influenced by changes in the mean airway pressure.

Airway Resistance↗
PubMed2001

Mean cardiac output by thermodilution with a single controlled injection.

OBJECTIVE: A new method to estimate mean cardiac output by thermodilution with a single duration-controlled injection was evaluated in patients. DESIGN: Prospective criterion standard study. SETTING: University hospital cardiac surgical intensive care unit and cardiac operation room. PATIENTS: Of 33 patients, 24 underwent coronary bypass graft surgery, four had a valve replacement, and five were treated in the intensive care unit. INTERVENTIONS: Interventions consisted of thermodilution cardiac output measurements. One single duration-controlled injection of cold fluid was used to calculate cardiac output. This controlled injection was performed with a duration equal to one whole ventilation cycle of the ventilator. An algorithm adapted to this duration-controlled injection calculated cardiac output. Moreover, this algorithm has properties to reduce errors caused by artificial ventilation and thermal noise. MEASUREMENTS AND MAIN RESULTS: In 33 patients, the averaged values of four measurements equally spread over the ventilatory cycle (phase-controlled) were compared with the values of two single duration-controlled measurements. The measurements were performed during periods of stable respiration and circulation. No significant difference was observed between the mean of four phase-controlled measurements and the mean of the two duration-controlled measurements. The cardiac output values in the intensive care patients were significantly higher compared with the two other patient groups (p <.05). The difference between the two methods could not be subdivided for the three patient groups (p >.05). The coefficient of variation of the single duration-controlled thermodilution measurements was significantly lower than the single phase-controlled measurements, 3% vs. 6% (p <.01). CONCLUSIONS: One single duration-controlled injection thermodilution measurement is as accurate and repeatable as the mean of four phase-controlled measurements and is clinically feasible.

Adult↗
PubMedDate not supplied

[Intraoperative measurement of cardiac output by transesophageal echocardiography of transmitral flow].

INTRODUCTION: Intraoperative transesophageal echocardiography is used to study cardiac structure and function. Cardiac output is measured by calculating the velocity with which a volume of blood travels a predetermined area. Output can be assessed at the mitral valve by parallel alignment of the Doppler transducer to measure flow velocity. OBJECTIVE: To compare cardiac output measurements from transesophageal echocardiography with measurements performed by the standard clinical technique of thermodilution. PATIENTS AND METHODS: Cardiac output measurements obtained by thermodilution and by echocardiography at the mitral valve were compared in a prospective study during 34 cardiac surgery procedures. RESULTS: Cardiac output measurements ranged from 2.3 L min(-1) to 7.8 L min(-1) (mean 4.27 +/- 0.125 L min(-1) for measurements made by Doppler echocardiography and from 1.9 L min(-1) to 8.1 L min(-1) (mean 4.36 +/- 0.124 L min(-1)) for measurements made by thermodilution. The correlation between the methods was high (r = 0.926, p = 0.00001). CONCLUSION: Intraoperative measurement of cardiac output by transesophageal Doppler echocardiography at the mitral valve is easy and correlates highly with the clinical method of thermodilution used at present. Use of the technique will widen the spectrum of information provided by echocardiography, which is a safe, minimally invasive technique.

Aged↗
PubMed1986

The effect of pericardiectomy on maximal oxygen consumption and maximal cardiac output in untrained dogs.

To test the hypothesis that the pericardium limits maximal oxygen consumption by limiting stroke volume and cardiac output, we studied 10 untrained dogs during submaximal and maximal exercise before and after pericardiectomy. Seven additional dogs were studied before and after a sham operation. All dogs were instrumented chronically with aortic and pulmonary artery catheters. Dogs were tested by running on a motor-driven treadmill, 4-6 times before and after pericardiectomy or sham operation. We measured cardiac output (dye dilution), heart rate, and arteriovenous oxygen difference. Oxygen consumption and stroke volume were calculated from these variables. After pericardiectomy, there were significant (P less than 0.01) increases in maximal oxygen consumption, maximal cardiac output, and maximal stroke volume. Maximal oxygen consumption decreased significantly in the sham group. There was no change in maximal heart rate following pericardiectomy, or in maximal cardiac output, heart rate, or stroke volume following sham operation. Both groups of dogs experienced similar significant decreases in hematocrit, arterial and venous oxygen contents, and arteriovenous oxygen difference. Neither pericardiectomy nor sham operation had any effect on oxygen consumption during submaximal exercise. However, the sham group had significant increases in cardiac output and heart rate during submaximal exercise, and the pericardiectomy group demonstrated a trend toward an increased cardiac output during submaximal exercise. These results support the hypothesis that the pericardium limits maximal oxygen consumption by limiting stroke volume and cardiac output during maximal exercise in untrained dogs. Further, these findings suggest that maximal oxygen consumption is limited by the oxygen transport capacity of the cardiovascular system, and not by the oxidative capacity of skeletal muscle in the untrained dog.

Animals↗
PubMed2000

Reduced maximal cardiac output at altitude--mechanisms and significance.

When a lowlander ascends to altitude and acclimatizes over days to weeks, both maximal exercise capacity and maximal cardiac output are reduced compared to sea level. Of the several possible mechanisms underlying this reduction of maximal cardiac output, the available data are interpreted as supporting the simplest hypothesis--that this merely reflects the reduced requirement for muscle blood flow that results from the arterial hypoxemia of altitude (which reduces muscle O2 availability and thus maximal muscle function). The competing hypotheses, that increased blood viscosity, reduced blood volume, autonomic nervous system changes or myocardial hypoxic dysfunction reduce maximal cardiac output, are not well supported by existing data. However, critical tests of some of these hypotheses remain to be devised and undertaken. When it comes to the question of the importance of reduced maximal cardiac output to V(O2) MAX at altitude, the available evidence suggests that cardiac output is not a major limiting variable. This is because as cardiac output rises, gains in convective flow of O2 in the circulation are offset by losses from greater diffusion impairment of O2 transfer in the lungs and muscles, and vice versa. However, just as with the mechanism of cardiac output reduction itself, clear-cut experimental tests of its role in limiting exercise at altitude remain to be conducted.

Adaptation, Physiological↗
PubMed1984

Doppler ultrasound measurement of cardiac output in patients with physiologic pacemakers. Effects of left ventricular function and retrograde ventriculoatrial conduction.

Dual-chamber cardiac pacing (DDD) offers obvious theoretical advantages over traditional ventricular demand (VVI) pacing. Nevertheless, no widely agreed upon criteria exist for the selection of patients for physiologic DDD pacemakers compared with the simpler VVI systems. Accordingly, a non-invasive method for measuring cardiac output (Doppler ultrasound) was used to identify candidates for pacing who would derive the greatest hemodynamic benefit from DDD vs VVI pacing. Among 29 patients studied at rest during VVI-mode pacing, the average cardiac output by Doppler ultrasound was 4.3 +/- 0.3 liters/min (mean +/- standard error of the mean). In the DDD mode, the average cardiac output was 5.0 +/- 0.3 liters/min (p less than 0.001). Baseline left ventricular ejection fraction did not identify a group that improved more with DDD pacing. Patients who showed either retrograde ventriculoatrial conduction or described symptoms consistent with the "pacemaker syndrome" during VVI pacing, however, showed greater increases in cardiac output during DDD pacing. In these patients, the mean improvement in cardiac output was 30.4 +/- 8.6% with DDD vs VVI pacing, as opposed to an average increase of only 14.4 +/- 3.4% in the remaining 20 patients (p = 0.02). Thus, Doppler ultrasound can be used to quantitate the change in cardiac output at rest that occurs with DDD vs VVI pacing. The change is independent of the level of left ventricular function but is substantially higher when there is evidence of ventriculoatrial conduction or the pacemaker syndrome.

Adult↗
PubMed2003

Noninvasive monitoring of cardiac output during exercise by inductance cardiography.

INTRODUCTION/PURPOSE: Inductance cardiography is a noninvasive technique that monitors changes in cardiac output from an inductance plethysmographic transducer encircling the chest at the level of the heart. The method has been previously validated in supine patients at rest by comparisons to thermodilution. Our purpose was to investigate whether the technique can be employed during bicycle exercise. METHODS: We simultaneously measured cardiac output by inductance cardiography and by two gas exchange methods based on the Fick principle during upright cycle ergometry in healthy volunteers. RESULTS: In 11 subjects, comparisons of changes in cardiac output by inductance cardiography agreed well with values measured by carbon dioxide rebreathing during a steady-state exercise protocol. In 12 subjects, cardiac output changes measured by inductance cardiography and an oxygen uptake method agreed closely during a progressive ramp exercise protocol to exhaustion. The bias (mean difference to reference methods) and limits of agreement (+/-2 SD of bias) for estimation of relative changes in cardiac output by inductance cardiography were 1% +/- 21% in 67 comparisons to the carbon dioxide rebreathing technique, and 0% +/- 22% in 98 comparisons to the oxygen uptake method. CONCLUSION: In healthy subjects, inductance cardiography accurately and unobtrusively estimates changes in cardiac output during bicycle exercise in comparison to gas exchange methods.

Adult↗
PubMedDate not supplied

A new constant infusion radioisotopic technique for the noninvasive determination of cardiac output.

A constant infusion radioisotopic method for the noninvasive determination of cardiac output is introduced and validated in a series of 22 patients by comparison with simultaneous dye dilution or Fick measurements. The new bedside radioisotopic technique utilizes peripheral venous infusion of indium-113m, detection by a single external probe, and analysis of the time-concentration curve by a specially designed, multivariate computer model. The technique is entirely atraumatic, requiring neither injection into the central circulation nor intra-arterial cannulation. The correlation coefficient was 0.72 (p less than 0.001) between the radioisotopic and standard methods for cardiac output determinations. In addition, results in five patients with valvular regurgitation or intracardiac shunts support the validity of the constant infusion radioisotopic technique in these clinical settings in which the standard dye dilution methods for determining cardiac output are invalid. The techniques is applicable in a variety of clinical conditions in which the invasive techniques for cardiac output measurement are either impractical or not available.

Adult↗
PubMed1990

The Doppler method for measuring cardiac output in conscious rabbits: validation studies, uses, and limitations.

The velocity of blood in the rabbit aorta is very fast, approaching the limits of some pulsed directional Doppler flow meters. Therefore, we thoroughly evaluated a 20- and a 10-MHz device for measuring cardiac output in rabbits. Flow probes were implanted around the ascending aorta and catheters were implanted into the left atrium (for microsphere injection), femoral artery, and vein. About 2 weeks later, cardiac output was determined with the Doppler method and simultaneously with tracer microspheres. Cardiac output was manipulated with isoproterenol, dihydralazine, guanfacine, or alinidine, intravenously. With the 20-MHz device, only normal and decreased cardiac output could be measured accurately, even with a 60 degrees implantation angle of the crystals. The 10-MHz device yielded accurate measurements also at very high flow. Surprisingly, at high aortic flow rates, both the 10- and the 20-MHz devices were unable to measure correctly diastolic flow, which is close to zero. It was necessary to adjust the position of the late diastolic Doppler signal manually to the electrical zero line. With this precaution, the 10-MHz device yielded an excellent correlation between mean Doppler signal and cardiac output. Cardiac output can be measured in absolute flow units if the flow-probe can be calibrated in vivo with an independent, accurate method about 2 wk after implantation. The baroreflex was not affected by the implanted flow probes. Within these limits, Doppler flow meters are good tools to assess drug effects on cardiac output in conscious rabbits.

Animals↗