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PubMed1994

Continuous thermodilution measurement of cardiac output: in-vitro and in-vivo evaluation.

The current study was designed to evaluate a method for continuous measurement of cardiac output. The system consists of a modified pulmonary artery catheter that uses the thermodilution principle for determination of cardiac output. The evaluation was performed in vitro and in vivo. In-vitro evaluation was performed using a simple flow bench model (flow 2-9 L/min). Both continuous and bolus thermodilution methods were compared. Both methods showed good correlation with the pump flow calibrated using a volumetric tank and timer (correlation coefficient (r) for bolus thermodilution = 0.92, r for continuous thermodilution = 0.90). In-vivo evaluation was performed in six bovine experiments. Data from a total of 87 pairs of bolus versus continuous measurements were obtained. The cardiac output ranged from 1.9 to 8.9 L/min. The absolute measurement bias was not significant (mean: -0.07 L/min; 95% confidence limits: -0.87 and 0.73 L/min). The squared correlation coefficient from linear regression was 0.92. The results from this study suggest that the new continuous thermodilution measurement system for cardiac output provides accurate data in vitro and in vivo. Continuous monitoring of cardiac output adds a new dimension for evaluation of the patient's hemodynamic profile. Furthermore, significant volume load due to bolus thermodilution measurements can be avoided.

Animals↗
PubMed1987

Cardiac output and its distribution in peritonitis. (Septic) shock in the rat.

Cardiac output and its distribution were studied in rats made septic by an i.p. injection of live E. coli bacteria and in controls given an equivalent amount of saline. The E. coli injection was followed by signs of severe shock in eight of 12 rats. Control animals all survived with only minor changes in cardiac output and peripheral hemodynamics. Blood flow in shocked animals was characterized by a reduction of cardiac output, while myocardial and cerebral flows were not reduced. The intact circulation to the brain and to the heart in the shocked rats was at the expense of kidney, spleen, and skin blood flows.

Animals↗
PubMed1991

Thermodilution estimation of cardiac output at high flows in anesthetized horses.

The purpose of this study was to compare the thermodilution technique for estimation of cardiac output with the indocyanine green dye dilution technique at flows between 10 and 39 L/min in halothane-anesthetized horses. The estimation of area of dye dilution cardiac output curves was made by using the fore-'n-aft (FA) triangle method. This shorthand technique was compared with logarithmic exponential extrapolation and summation (extrapolated area), using 64 cardiac output curves. Then, 256 simultaneous thermodilution measurements were compared with dye dilution measurements calculated by use of the FA technique. Forty milliliters of iced 0.9% NaCl solution containing 15 mg of indocyanine green dye was used as the indicator. This was delivered in less than 1 second to the right atrium, using a power injector. A thermistor positioned in the pulmonary artery detected the thermal indicator. Blood was withdrawn from the carotid artery through a densitometer cuvette to measure the dye concentration. The FA estimations of area were higher than those determined by use of extrapolated area. A multiplicative adjustment of 0.837 was estimated. On average, thermodilution estimates of cardiac output exceeded the adjusted FA determinations. Using a weighted linear regression, we determined the following calibration adjustment: thermal dilution cardiac output/1.048 = indocyanine green dye dilution cardiac output.

Anesthesia↗
PubMed1988

Cardiac output by MR imaging: an experimental study comparing right ventricle and left ventricle with thermodilution.

Cardiac output was measured by gated magnetic resonance imaging (MRI) and by thermodilution in four mongrel dogs. The entire heart was examined in contiguous slices at end-diastole and end-systole in a plane parallel to the interventricular septum. Each set of images was analyzed for chamber volume using a custom computer program to evaluate each pixel. No geometric assumptions were made. Cardiac output was calculated for right and left ventricles and compared with the thermodilution data. We found that the cardiac output of the right ventricle compared well with that of the left ventricle and that both fell within the range measured by thermodilution. Cardiac-gated MRI has the potential to assess the cardiac output of both the right and left ventricles. Comparison between right ventricular and left ventricular function will permit quantification of left to right shunting or unilateral ventricular volume overload.

Animals↗
PubMed1997

Effect of independent changes in mixed-venous PCO2 or PO2 on cardiac output in anesthetized sheep.

To determine whether changes mixed-venous PCO2 or PO2 affect cardiac output independent of changes in arterial blood gases, we used extracorporeal gas exchange to increase mixed-venous PCO2 or decrease mixed-venous PO2 in adult sheep. Sheep were anesthetized, mechanically ventilated, and connected to a veno-venous extracorporeal circuit. The circuit included a gas exchanger which was used to increase mixed-venous PCO2 or decrease mixed-venous PO2; the native lungs were ventilated to maintain arterial PCO2 and PO2 at control levels. When mixed-venous PCO2 was increased by 32% above control levels for a period of 60 min, cardiac output increased significantly to 28% above control levels. Cervical vagotomy abolished this response. In contrast, decreasing mixed-venous PO2 by 29% did not increase cardiac output. These results demonstrate that increasing mixed-venous PCO2 can increase cardiac output independent of changes in arterial blood gases and that intact vagus nerves are necessary for this response to occur.

Anesthesia↗
PubMed1976

Changes in distribution of cardiac output by surface-induced deep hypothermia in dogs.

The effects of surface-induced deep hypothermia on organ blood flow and on the distribution of cardiac output were investigated in the anesthetized dog. Organ flows were determined by the radioactive microsphere technique. Phenoxybenzamine (POB) was administered prior to hypothermia to minimize vasoconstriction and hence facilitate cooling. Measurements were made before POB, on stabilization after POB, and during hypothermia. Cardiac output was reduced by POB as was blood flow to the pancreas, small intestine, and skeletal muscle. Hypothermia, following POB, produced a further fall in Q and during this maneuver blood flow fell in all organs and vascular beds studied. The relative distribution of Q during hypothermia was essentially the same as in the control except the brain, kidneys, and pancreas received a smaller fraction of the total output. The relatively normal distribution of a reduced cardiac output during hypothermia was in marked contrast to distribution of comparable low cardiac output induced by hemorrhage. In the latter condition, the fraction of the cardiac output perfusing the brain, kidneys, adrenals, and hepatic artery was increased.

Acid-Base Equilibrium↗
PubMed1993

Hydrocortisone-induced hypertension in men. The role of cardiac output.

In previous studies we have shown that administration of 200 mg/day hydrocortisone (cortisol) to normal subjects raises blood pressure and cardiac output, with no change in total peripheral resistance or resting forearm vascular resistance. We have tested the hypothesis that this rise in cardiac output is essential for the rise in blood pressure (BP). Six normal volunteer men, aged 22 to 34 years, took part in two studies of 10 days, in random order, at least 4 weeks apart. Placebo (Study A) or 50 mg atenolol orally, 12 hourly (Study B), was given on days 1 to 10 and 50 mg cortisol orally, 6 hourly, on days 5 to 10. Blood pressure and cardiac output (Fick technique, alternative Doppler) were measured on days 4 and 10. In Study A (placebo and cortisol) systolic BP rose from 116 to 125 mm Hg (standard error of the difference, SED 1.5), P < .01, and in Study B (atenolol and cortisol) from 109 to 120 mm Hg (SED 1.5), P < .01. Cardiac output (indirect Fick) rose from 4.8 +/- 0.01 to 5.9 +/- 0.2 L/min, P < .01, in A, and was unchanged in Study B, 4.4 +/- 0.1 to 4.4 +/- 0.2 L/min. Cardiac output measured by Doppler method was similar in pattern, 5.1 +/- 0.2 to 6.7 +/- 0.2 L/min (P < .01) in A and 5.7 +/- 0.2 to 5.8 +/- 0.2 in B. Calculated peripheral resistance fell in Study A and increased in Study B.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Analysis of uncertainty in theoretical methods of cardiac output measurement using the "Monte Carlo" technique.

We have developed three models which describe the relationship between cardiac output and the uptake of volatile anaesthetic agents, based on the Fick equation, and determined if these models could provide useful methods of cardiac output measurement. Because many variables are involved in the calculation of cardiac output using these methods, a "Monte Carlo" simulation was performed to investigate the combined effect of uncertainties in several variables on the resultant cardiac output estimate. We found that the single-breath model was most accurate when the inspired concentration was large, while the rebreathing model was better with smaller inspired concentrations. The three-breath model was the least accurate under all conditions studied. Volatile anaesthetics were generally more accurate than nitrous oxide, with both enflurane and halothane more accurate than isoflurane. The "Monte Carlo" technique provides a valuable tool for analysis of errors in measurement methods.

Anesthetics↗
PubMed1993

Impedance cardiography for cardiac output estimation in pacemaker patients: review of the literature.

Impedance cardiography permits noninvasive beat-to-beat determination of cardiac output, the product of the amplitude of the first derivative of thoracic impedance signal (dZ/dt), the ventricular ejection time, and heart rate corrected by the distance between the measuring electrodes. Its use is based on: (1) the dZ/dt signal that originates from the upper thorax; (2) the ventricular ejection period measured by the dZ/dt curve that occurs between the opening and closing of the aortic valve; (3) the dZ/dt curve is similar in morphology and timing to the aortic flow curve measured by an electromagnetic flowmeter with a significant linear correlation (r = 0.9) between dZ/dt and peak aortic flow; (4) similarity of the linear correlation between stroke volume, determined by the flowmeter and the impedance signal; and (5) significant reduction of the dZ/dt signal by 90% follows simultaneous occlusion of the aorta and the pulmonary artery. The rapid systolic portion of the impedance signal occurs only when blood is ejected into the aorta and is independent of right ventricular ejection. Most studies comparing impedance cardiography results with standard cardiac output determination have shown a correlation of 0.7-0.9. While the accuracy of impedance cardiography remains controversial and can be affected by the inherent limitations of the technique and by low cardiac output, intracardiac shunts, and valvular regurgitation, the high reproducibility of the method is established and may be comparable or superior to other commonly used techniques. When accurate determination of cardiac output is crucial, impedance cardiography may be used in conjunction with a standard technique to establish a baseline reference, thereby permitting further analysis. If only the trend need be followed, the high reproducibility of impedance cardiography measurements allows small changes in cardiac output to be detected on a frequent and ongoing basis. The ease and precision of this technique warrants its more widespread use in the assessment of pacemaker patients. Further use of this promising technique will allow a better definition of its role in the assessment of a wide range of cardiac patients.

Cardiac Output↗
PubMed1990

Determination of cardiac output during positive end-expiratory pressure--noninvasive electrical bioimpedance compared with standard thermodilution.

Many investigators have demonstrated the accuracy and reliability of thoracic electrical bioimpedance (TEB) in spontaneously breathing patients and under mechanical intermittent positive-pressure ventilation. Most of these studies showed a good correlation between TEB and invasive methods, such as thermodilution (TD) or the Fick method. But during PEEP, contrary results occur when comparing TEB and TD. In six patients undergoing neurosurgical interventions, TEB cardiac output measurements were compared during zero end-expiratory pressure (ZEEP) and during PEEP at 8 cm H2O with a low respiratory rate. The data revealed a good correlation during ZEEP (r = .93) and during PEEP (r = .91). There was no significant statistical difference when measuring cardiac output by TEB during ventilation with PEEP. During normal or decreased cardiac output, TEB overestimated cardiac output compared with TD, whereas TEB underestimated cardiac output compared with TD during increased cardiac output, especially during PEEP.

Brain Neoplasms↗
PubMed1980

INfluence of interposed ventilation pressure upon artificial cardiac output during cardiopulmonary resuscitation in dogs.

This study was conducted to determine the effects of high pressure interposed ventilations during cardiopulmonary resuscitation (CPR). Cardiac output was measured by a modified indicator dilution technique in eight anesthetized, intubated mongrel dogs. Positive pressure ventilations (12/min, 80% O2) were interposed after every five chest compressions (performed at 62/min) by a mechanical chest compressor (Thumper). On repeated trials in the same animal, ventilation pressures from 10--50 cm of H2O were tested in randomized sequence, while the technique of chest compression was held constant. Arterial blood gases immediately after resuscitation were monitored. Increasing ventilation pressure had surprisingly little effect on cardiac output curing CPR, although blood gases were profoundly altered. For ventilation pressures of 10, 20, 30, 40, and 50 cm of H2O, producing mean tidal volumes 23, 38, 61, 83, and 94 ml/kg; cardiac output remained nearly constant, averaging 21, 25, 23, 26, and 24 ml/min . kg. Corresponding mean postresuscitation pH was 7.24, 7.41, 7.51, 7.56, and 7.53; PCO2 was 41, 26, 18, 16, and 15 torr. The postresuscitation arterial oxygen tension was greater than 100 torr at all ventilation pressures except 10 cm of H2O. Interposed ventilations of pressure and volume more than adequate to prevent acidosis during CPR did not impair artificial cardiac output. If anything, cardiac output was slightly improved by more forceful ventilation.

Animals↗
PubMed1978

[Determination of cardiac output and ejection fraction using radionuclide angiography. A comparsion with conventional diagnostic methods in cardiology (author's transl)].

Cardiac output and ejection fraction of left and right ventricle were determined in 75 patients with different heart diseases applying a newly developed method which combines radionuclide angiography and triggered blood pool scintigraphy. The comparison of cardiac output and ejection fraction as determined by dye-dilution or thermodilution technique and left ventricular angiography is excellent (coefficient of correlation r equal to 0.86 and r equal to 0.91). Cardiac output and ejection fraction can be determined with this method in single non-invasive operation, i.e. under physiological conditions. The ejection fractions can be determined with high statistical accuracy from time-activity curves of both ventricles. Similar to cine-angiography it is possible to evaluate the ventricular volume, the regional contraction patterns and aneurysmata. Outpatients can be investigated in 30 min. Since the radiation dose in comparison to cine-angiography is very low, this investigation can be repeated several times without harm to the patient. There are no risks as described for cardiac catheterization and contrast angiography. Patients with low cardiac output and ejection fraction can be classified as "high risk patients". In these patients cardiac catheterization can be avoided by applying the described method.

Cardiac Output↗
PubMed1992

[Measurement of cardiac output by invasive methods: methods and variability].

Invasive techniques for the measurement of cardiac output include the Fick method, the marker dilution method and radiological ventriculography. The principles, methods and accuracy of these techniques are described. The reference method remains that of Fick, despite its being less widely used now because of its complicated nature and its technical limitations (need for strict baseline conditions, precision of sampling). The thermodilution method is often performed. It is easy and provides reliable results, except in conditions of low cardiac output or when there is severe tricuspid insufficiency. Radiological ventriculography is used less for the measurement of cardiac output, since it is heavily dependent upon heart rate and theoretical geometrical models. It remains valuable for the quantification of mitral and aortic regurgitation.

Cardiac Output↗
PubMed1994

Effects of insertion depth and use of the sidearm of the introducer sheath of pulmonary artery catheters in cardiac output measurement.

OBJECTIVE: To investigate the effects of various insertion depths and sidearm functions of the introducer sheath of pulmonary artery flotation catheters on cardiac output measurement. DESIGN: Prospective, randomized, crossover study. SETTING: A general intensive care unit. PATIENTS: Ten patients who had a pulmonary artery flotation catheter placed in the right internal jugular vein as part of their clinical management. INTERVENTIONS: Cardiac output was measured at three insertion depths of the pulmonary artery catheter, each with a different rate of flow into the introducer sheath. MEASUREMENTS AND MAIN RESULTS: Significant differences of up to 23% occurred in the measurement of cardiac output under the various conditions. Cardiac output measurement is greater, the closer the injection port lies to the introducer sheath and the more open the introducer sheath sidearm. CONCLUSIONS: All users of pulmonary artery catheters should be alert to this problem. For reliable measurements of cardiac output by thermodilution, the cold saline injection port of the pulmonary artery catheter must be downstream of the introducer sheath, and the introducer sidearm must be closed.

Adult↗
PubMed1989

A comparative study of cardiac output in neonates supported by mechanical ventilation: measurement with thoracic electrical bioimpedance and pulsed Doppler ultrasound.

In newborn infants supported by mechanical ventilation, cardiac output was measured simultaneously with thoracic electrical bioimpedance and pulsed Doppler ultrasound to determine whether the impedance technique is reliable and accurate in this age group. The mean difference between paired measurements with the two techniques in 26 subjects was negligible (less than 1 ml/kg/min), with 95% confidence limits being approximately 11% of the mean Doppler-derived cardiac output. In addition, the two techniques related well (correlation coefficient r = 0.94) over a wide range of Doppler-derived cardiac output measurements (120 to 530 ml/kg/min). In 8 of the 26 subjects, cardiac output was observed for 7 to 12 hours. The mean difference between the Doppler and impedance techniques was 6.1% to -0.7% of the Doppler value. Thoracic electrical bioimpedance is applicable to newborn infants and offers a continuous noninvasive method of cardiac output measurement.

Cardiac Output↗
PubMed2003

Noninvasive cardiac output measurement using partial carbon dioxide rebreathing is less accurate at settings of reduced minute ventilation and when spontaneous breathing is present.

BACKGROUND: Although evaluation of cardiac output by the partial carbon dioxide rebreathing technique is as accurate as thermodilution techniques under controlled mechanical ventilation, it is less accurate at low tidal volume. It is not clear whether reduced accuracy is due to low tidal volume or low minute ventilation. The effect of spontaneous breathing on the accuracy of partial carbon dioxide rebreathing measurement has not been fully investigated. The objectives of the current study were to investigate whether tidal volume or minute ventilation is the dominant factor for the accuracy, and the accuracy of the technique when spontaneous breathing effort is present. METHODS: The authors enrolled 25 post-cardiac surgery patients in two serial protocols. First, the authors applied three settings of controlled mechanical ventilation in random order: large tidal volume (12 ml/kg), the same minute ventilation with a small tidal volume (6 ml/kg), and 50% decreased minute ventilation with a small tidal volume (6 ml/kg). Second, when the patient recovered spontaneous breathing, the authors applied three conditions of partial ventilatory support in random order: synchronized intermittent mandatory ventilation-pressure support ventilation, pressure support ventilation with an appropriately adjusted rebreathing loop, and pressure support ventilation with the shortest available loop. After establishing steady state conditions, the authors measured cardiac output using both partial carbon dioxide rebreathing and thermodilution methods. The correlation between the data yielded by the two methods was determined by Bland-Altman analysis and linear regression. RESULTS: Cardiac output with the carbon dioxide rebreathing technique correlated moderately with that measured by thermodilution when minute ventilation was set to maintain normocapnia, regardless of tidal volumes. However, when minute ventilation was set low, the carbon dioxide rebreathing technique underreported cardiac output (y = 0.70x; correlation coefficient, 0.34; bias, -1.73 l/min; precision, 1.27 l/min; limits of agreement, -4.27 to +0.81 l/min). When there was spontaneous breathing, the correlation between the two cardiac output measurements became worse. Carbon dioxide rebreathing increased spontaneous tidal volume and respiratory rate (20% and 30%, respectively, during pressure support ventilation) when the rebreathing loop was adjusted for large tidal volume. CONCLUSIONS: During controlled mechanical ventilation, minute ventilation rather than tidal volume affected the accuracy of cardiac output measurement using the partial carbon dioxide rebreathing technique. When spontaneous breathing is present, the carbon dioxide rebreathing technique is less accurate and increases spontaneous tidal volume and respiratory rate.

Adult↗
PubMed2006

The relationship between cardiac output, cerebral electrical activity, cerebral fractional oxygen extraction and peripheral blood flow in premature newborn infants.

Cardiac output is a determinant of systemic blood flow and its measurement may therefore be a useful indicator of abnormal hemodynamics and tissue oxygen delivery. The purpose of this study was to investigate in very premature newborn infants the relationships between cardiac output (left and right ventricular outputs), systemic blood pressure, peripheral blood flow (PBF) and two indicators of cerebral oxygen delivery (cerebral electrical activity and cerebral fractional oxygen extraction (CFOE)). This was a prospective observational study performed on 40 infants of less than 30 wk gestation. Digital electroencephalograms (EEGs) were recorded for one hour every day during the first four days after birth and subjected to qualitative and quantitative analysis. Left and right ventricular outputs, mean blood pressure (MBP), CFOE, PBF and arterial blood gases were measured at the same time. Within the ranges studied, there was no apparent relationship between left or right ventricular output (RVO), PBF and indicators of cerebral perfusion (cerebral electrical activity and CFOE). The EEG was normal in infants with low left and right ventricular outputs (<150 mL/kg/min) and MBP > 30 mm Hg. Infants with low cardiac output and normal MBP seem able to maintain cerebral perfusion, possibly through vasodilatation of the cerebral microvasculature.

Blood Circulation↗
PubMed1985

The influence of verapamil on dopamine's ability to augment cardiac output.

Calcium channel blockers are used in the treatment of angina pectoris, cardiac arrhythmia, and hypertension. Sporadic reports of hypotensive reactions to verapamil have indicated that these reactions are not reversed readily by catecholamine administration. This study was conducted to test the hypothesis that verapamil pretreatment does not alter the ability of dopamine in conventional doses to augment cardiac output. Twelve mongrel dogs, weighing 19 to 25 kg, were anesthetized with pentobarbital and placed on a respirator. Heart rate, cardiac output, and the right atrial, pulmonary artery, pulmonary capillary wedge, and central aortic pressures were measured directly. Dopamine, 10 micrograms/kg/min, increased cardiac index by 52.4 mL/kg/min over baseline. The dopamine was stopped and the animals were allowed to return to baseline. Dopamine, 10 micrograms/kg/min, was administered again after pretreatment with 0.15 mg/kg verapamil, and it increased cardiac index by 47.9 mL/kg/min over the second baseline control. The results were not statistically different using the Student t test for paired data (P greater than .05). It is concluded that verapamil does not affect dopamine's ability to augment cardiac output in the dosages tested.

Animals↗