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PubMed1984

An evaluation of the pulse-contour method of measuring cardiac output.

The pulse-contour (PC) method continuously derives the cardiac output in litres per minute from the arterial pressure wave form by using a portable analogue computer. The reliability of the PC method in determining cardiac output was studied in 6 patients during anaesthetic induction for cardiac surgery. The results obtained with the PC method using the radial artery to register the arterial pulse wave were compared with cardiac output measurements using the more conventional thermodilution technique. The PC method would seem to offer a simple, clinically useful method for on-line monitoring of short-term variations in cardiac output.

Adult↗
PubMed1991

Norepinephrine kinetics and cardiac output during nonhypotensive lower body negative pressure.

Recently we have shown that arterial norepinephrine (NE) concentration increases significantly during lower body negative pressure (LBNP) of -15 mmHg. Interestingly, the increase was found to be related predominantly to a decrease in arterial NE clearance. We postulated that this reduction in clearance would be related to a reduction in cardiac output. Accordingly, we measured both cardiac output (2-dimensional echocardiographic/Doppler technique) and arterial NE kinetics ([3H]NE continuous infusion radiotracer technique) during LBNP of -15 mmHg. These measures of cardiac output and arterial NE spillover and clearance were obtained in 12 normal subjects at baseline, 5 and 10 min (Early) and 25 and 30 min (Late) of LBNP. We found that arterial NE concentration increased significantly, by 25% Early and 22% Late (P = 0.001). Spillover, however, did not change (P = 0.258), whereas clearance decreased by 12% Early and 19% Late (P = 0.014), and cardiac output decreased by 15% Early and 19% Late (P = 0.001). These reductions in clearance and cardiac output correlated significantly (r = 0.61, P = 0.001). No correlation was noted between spillover and cardiac output (r = 0.027, P = 0.874). We conclude that the increases in arterial NE concentration during nonhypotensive LBNP are predominantly due to decreased cardiac output with resultant decreases in systemic clearance of NE. These findings suggest that the ability to clear NE from the circulation is linked to the level of cardiac output and that low cardiac output states by themselves may lead to an elevation in arterial plasma NE concentrations.

Adult↗
PubMed1984

Regulation of cardiac output during upright exercise in patients with aortic regurgitation.

The change in cardiac output during upright exercise in patients with aortic regurgitation (AR) is not well known. We measured left ventricular (LV) ejection fraction (EF) and volume, regurgitant fraction (RF), total cardiac output and forward cardiac output at rest, and peak upright exercise by means of radionuclide angiography in ten normal subjects and 15 patients with AR. In the normal subjects, there was no significant change in the end-diastolic volume but there was a significant decrease in the end-systolic volume (p = 0.0001) and a significant increase in EF (p = 0.0001). The increase in cardiac output during exercise was due to increases in both stroke volume and heart rate. In patients with AR, there was a significant decrease during exercise in RF (53 +/- 15% at rest, and 45 +/- 15% during exercise; p = 0.03), and in end-diastolic and end-systolic volume (p = 0.02, and p = 0.003, respectively). The EF increased during exercise (p = 0.003). The total stroke volume did not change (68 +/- 19 ml/m2 at rest, and 67 +/- 14 ml/m2 during exercise; p, NS). Thus, in patients with AR, individual changes in EF, RF, and volume are quite variable, but as a group a decrease in RF and an increase in heart rate contribute to the increase in forward flow. The total stroke volume may not increase during exercise, despite an increase in EF and a decrease in end-systolic volume because of a concomitant decrease in end-diastolic volume.

Adolescent↗
PubMed2000

Clinical evaluation of the non-invasive cardiac output (NICO) monitor in the intensive care unit.

The Non-invasive Cardiac Output (NICO) monitor (Novametrix Medical Systems Inc., Wallingford, CT, U.S.A.) utilizes a minimally-invasive partial rebreathing method to determine cardiac output by means of a differential form of the Fick equation. We evaluated the NICO monitor by comparing its output to paired measurements obtained by the standard thermodilution (TD) technique in patients who had recently undergone cardiac surgery. Forty-two paired measurements were carried out in 12 patients. The correlation between the two methods was moderate with a correlation coefficient of 0.691. Repeated measures ANOVA showed that TD measures of cardiac output were significantly higher than those obtained by the NICO monitor (P = 0.0003). Comparison of the two techniques using the method described by Bland and Altman showed decreased correlation at higher values of cardiac output. We conclude that the NICO monitor may well have a place in intensive care monitoring, provided patients are not breathing spontaneously and are able to tolerate a 4 mmHg rise in PaCO2. It is less suitable for use in patients with a high cardiac output state.

Analysis of Variance↗
PubMedDate not supplied

Original insight into continuous cardiac output monitoring: "TruCCOMS". Correlation with other methods.

AIM: Of all technical devices used for continuous or intermittent monitoring of cardiac output, in our clinical practice during the last year, we tested a new system, the true continuoas cardiac output monitoring system (TruCCOMS), for the continuous real time measurement of cardiac output. The purpose of this study was to compare the accuracy, reliability and promptness of TruCCOMS with other systems and methods of cardiac output (CO) measurement such as pulsion continuous cardiac output (PiCCO) and end diastolic Area (EDA) determination by trans-esophageal-echocar-diography (TEE), keeping as gold standard for CO measurement the thermodilution method by Swan-Ganz. METHODS: Sixteen male patients, aged 50 to 60 years, with ejection fraction (FE) >50%, EUROSCORE=1, who underwent CABG surgery with circulation extra corporeal (CEC), were analysed with all methods mentioned above. The measurements were obtained at different phases: pre-CEC; post-CEC; and Intensive Care Unit (ICU). In the ICU setting, 5 patients classified as under-filled with a pulmonary capillary wedge pressure (PCWP) =/<8 mmHg were filled until a PCWP gs;13 mmHg in order to evaluate the promptness of the various systems to detect the new condition. RESULTS: The statistical analysis of data obtained in our survey, clearly demonstrates that TruCCOMS is at least equivalent to average thermo-dilution cardiac output (AvTDCO), with the advantage of being continuous, real time and, furthermore, with no need for physician intervention/interference. CONCLUSION: In our experience the TruCCOMS seems to be an ideal method for continuous cardiac output (CCO) monitoring compared with the other bedside systems challenged.

Cardiac Catheterization↗
PubMed1999

Evaluation of a new advanced thoracic bioimpedance device for estimation of cardiac output.

OBJECTIVE: This study is an evaluation of a new thoracic bioimpedance cardiac output monitoring system which incorporates a modified form of the Kubicek equation and a method of estimating the left ventricular ejection time from the time derivative bioimpedance signals. METHODS: The performance of the new system was compared with conventional thermodilution in a porcine model. One hundred and ninety nine (n = 199) paired measurements of thermodilution cardiac output (TDCO) (range 1.20-18.00 L/min) and thoracic bioimpedance cardiac output (BICO) were collected in 7 pigs. The bioimpedance measurements were adjusted for the animal's weight and chest circumference, thus compensating for the differences in the anatomy of pigs when compared to humans. Data were compared using weighted correlation coefficient and Bland-Altman analysis. RESULTS: The weighted correlation coefficient between TDCO and BICO values was 0.87 (n = 199). The Bland-Altman technique yielded a precision of the device of +/-1.69 L/min with a bias of 0.11 L/min. CONCLUSION: The results from the porcine study show that the new system performed well over a wide range of cardiac outputs, comparing favorably with data from other new bioimpedance cardiac output devices currently available in the market.

Animals↗
PubMedDate not supplied

Factors influencing the accuracy of the cardiac output monitoring and diagnostic unit for pneumatic artificial hearts.

The Cardiac Output Monitor and Diagnostic Unit (COMDU) has been the most widely used method to noninvasively determine cardiac output in pneumatic ventricles for the past 10 years. Clinical observation has suggested a discrepancy between the COMDU and expected cardiac outputs. In vivo tests verified and quantified this error. The error sources were examined using in vitro test conditions, with both the inflow and outflow, as well as COMDU flow readings, being analyzed. Transducer and calibration error sources were also identified, and the accuracy of the method for determining cardiac output for the in vitro test conditions was quantified. With a more accurate calibration scheme, the in vitro average error was reduced from -16.2% (range of 0.1% to -41.1%) to 0.1% (range 4.8% to -3.65). The major error sources were identified as missed inflow, transducer calibration and drift, and system variance.

Animals↗
PubMed1996

Predictors of low cardiac output syndrome after coronary artery bypass.

The purpose of this study was to identify patients at risk for the development of low cardiac output syndrome after coronary artery bypass. Low cardiac output syndrome was defined as the need for postoperative intraaortic balloon pump or inotropic support for longer than 30 minutes in the intensive care unit to maintain the systolic blood pressure greater than 90 mm Hg and the cardiac index greater than 2.2 L/min per square meter. The preoperative patient characteristics that were independent predictors of low cardiac output syndrome were identified among 4558 consecutive patients who underwent isolated coronary artery bypass at The Toronto Hospital between July 1, 1990, and December 31, 1993. The overall prevalence of low cardiac output syndrome was 9.1% (n = 412). The operative mortality rate was higher in patients in whom low cardiac output syndrome developed than in those in whom it did not develop (16.9% versus 0.9%, p < 0.001). Stepwise logistic regression analyses identified nine independent predictors of low output syndrome (percent frequency in parentheses) and calculated the factor-adjusted odds ratios associated with each predictor: (1) left ventricular ejection fraction less than 20% (27%, odds ratio 5.7); (2) repeat operation (25%, odds ratio 4.4); (3) emergency operation (27%, odds ratio 3.7); (4) female gender (16%, odds ratio 2.5); (5) diabetes (13%, odds ratio 1.6); (6) age older than 70 years (13%, odds ratio 1.5); (7) left main coronary artery stenosis (12%, odds ratio 1.4); (8) recent myocardial infarction (16%, odds ratio 1.4); and (9) triple-vessel disease (10%, odds ratio 1.3). Low cardiac output syndrome is a clinical outcome that may result from inadequate myocardial protection or perioperative ischemic injury. Patients at high risk for the development of low cardiac output syndrome should be the focus of trials of new techniques of myocardial protection to resuscitate the ischemic myocardium.

Aged↗
PubMed1992

Clinical evaluation of transtracheal Doppler for continuous cardiac output estimation.

A newly developed transtracheal Doppler (TTD) computer for cardiac output determination was studied in nine patients after open heart surgery (coronary artery bypass grafting, n = 4; mitral valve replacement, n = 5). The measurements were compared with those simultaneously obtained by thermodilation. Doppler signals were adequate in 78% of the patients studied. Limited correlation between both methods (r = 0.248; r2 = 0.0615; mean of difference, 1.714 +/- 1.67 L/min; limits of agreement, -1.6 to 5.0 L/min) was found. The large difference in cardiac output readings between TTD and thermodilation may be due to (a) false angles of the ultrasound beam in relation to the aortic wall and blood flow or (b) misplacement of the ultrasound head and underestimation of the aortic lumen. Patients must be completely sedated and paralyzed to prohibit artifacts. Routine patient care can interfere with continuous measurements. Cardiac output determinations by TTD are limited to the period during which the trachea is intubated with the special TTD tube. We conclude that the TTD system does not offer accurate cardiac output determinations and that the routine use of this device is not practical.

Aged↗
PubMed1985

Cardiac output measured by impedance cardiography during maximal exercise tests.

The overall accuracy of cardiac output measurements made by impedance cardiography during maximum exercise was studied in man. Initially, the systematic error of the technique was assessed over the range 3.5 to 18 litre . min-1 by comparing with simultaneous measurements of cardiac output made using the direct Fick method. No systemic error was demonstrated in 40 estimations made in 20 subjects. The random error was assessed in 4 subjects in a steady state at rest and during exercise at 80 and 130 W and found to be less than 5% in each subject. The reproducibility of maximum exercise response was assessed in six healthy male subjects (age 26.2 +/- 4.4 years, +/- SEM) who underwent maximum exercise tests twice, 1 week apart, on a bicycle ergometer. Simultaneous recordings of cardiac output and oxygen uptake (VO2) at rest and during each 3 min stage of exercise were made. Highly significant correlations were obtained in the stroke volume (r = 0.84, p less than 0.001), cardiac output (r = 0.98, p less than 0.001) and VO2 (r = 0.98, p less than 0.001) between the two tests. Average maximum cardiac output was 27.0 +/- 1.2 litre . min-1 (+/- SEM) and maximum VO2 was 4.4 +/- 0.2 litre . min-1 (+/- SEM). These results show that measurements of cardiac output were reproducible over one week. Impedance cardiography is non-invasive technique which is as accurate as invasive methods and can be used for maximal exercise testing.

Adult↗
PubMed1992

Esophageal electrodes allow precise assessment of cardiac output by bioimpedance.

OBJECTIVES: To analyze the impact of the position of the thoracic external electrodes on the values of cardiac output measured by electrical bioimpedance and to compare the results obtained by bioimpedance with those values determined by thermodilution in critically ill patients. DESIGN: Open, prospective, comparative trial. SETTING: ICU of a teaching hospital. PATIENTS: Twenty healthy volunteers and ten critically ill patients. INTERVENTIONS: Measurements of cardiac output by bioimpedance at rest and after physical activity in normal volunteers and after changing the neck or xiphoid electrodes. Comparisons of cardiac output obtained by thermodilution and bioimpedance with internal and external electrodes in patients. MEASUREMENTS AND MAIN RESULTS: Mean +/- SD values are presented. Cardiac output values at rest and after exercise were 6.7 +/- 1.3 and 10.8 +/- 2.6 L/min at rest and after exercise, respectively (p less than .001). Displacement of the xiphoid electrodes 3 cm in the caudal direction was accompanied by a decrease of the mean cardiac output from 7.1 +/- 1.2 to 5.8 +/- 1.3 L/min (p less than .001) and displacement 3 and 6 cm cranially was accompanied by increases in cardiac output from 7.1 +/- 1.2 to 8.1 +/- 1.4 L/min (p less than .001) and 8.6 +/- 1.5 L/min (p less than .001), respectively. In the ten patients, cardiac output measurements were virtually identical when results obtained by thermodilution (6.7 +/- 3.1 L/min) were compared with those results obtained by bioimpedance using internal esophageal (6.6 +/- 3.1 L/min), but not external (4.7 +/- 1.6 L/min) electrodes. CONCLUSIONS: a) The values of cardiac output derived from measurements obtained by bioimpedance using internal electrodes were comparable with those values derived from thermodilution. b) Values of cardiac output from bioimpedance studies with external electrodes were dependent on the position of the xiphoid electrodes.

Adult↗
PubMed1994

Continuous invasive cardiac output monitoring--the Baxter/Edwards Critical-Care Swan Ganz IntelliCath and Viligance system.

We evaluated the Baxter/Edwards Critical-Care Swan Ganz IntelliCath continuous cardiac output catheter and Vigilance continuous cardiac output monitor in critically ill adult intensive care patients, and compared cardiac output measurements obtained from this new system with those from a standard bolus thermodilution technique using cold normal saline. Nine Swan Ganz IntelliCath catheters were inserted into patients selected at random, following the decision that pulmonary artery catheter monitoring was required. A total of 100 comparisons were made in nine patients. We found the Swan Ganz IntelliCath catheter to be both easy to insert and position, and simple to use. There were no complications or technical difficulties. The mean cardiac output measured by the continuous system was 8.00 l/min (SD 1.66/min) compared to 8.02 1/min (SD 1.74 l/min) using bolus techniques. Continuous cardiac output values correlated well with bolus measurements (r = 0.87), there was excellent accuracy (bias of 0.02 l/min) and precision was acceptable (limits of agreement of -1.71 to 1.75 l/min). These larger than anticipated limits of agreement may not reflect any inaccuracy in the continuous measurement system, rather they may highlight the extent of well recognised potential errors inherent in the intermittent bolus technique. The availability of a system to measure cardiac output continuously provides a major improvement in intensive care monitoring. This system will permit the rapid and accurate assessment of the response of patients to therapy while providing increased diagnostic facilities and a new research tool.

Adult↗
PubMed1997

Whole-body impedance cardiography in the measurement of cardiac output.

OBJECTIVE: To evaluate the reliability of whole-body impedance cardiography with electrodes on wrists and ankles in the measurement of cardiac output compared with the thermodilution method. DESIGN: Prospective, clinical investigation. SETTING: Surgical intensive care unit and operating room at a university hospital. PATIENTS: Simultaneous cardiac output measurements by thermodilution and whole-body impedance cardiography were performed in 74 patients undergoing a coronary artery bypass grafting operation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A total of 97 triplicate, simultaneous cardiac output measurements were carried out with thermodilution and whole-body impedance cardiography: 74 measurements were conducted in patients who were awake and 23 measurements were conducted during anesthesia but before the commencement of surgery. The mean cardiac output difference (bias) between the two methods was 0.25 +/- 0.81 (SD) L/min; the limits of agreement (2 SD) were-1.37 and 1.87 L/min, respectively. The repeatability value (rv = 2.83 x SD) for whole-body impedance cardiography (rv = 0.46 L/min) was considerably better than for the thermodilution method (rv = 1.05 L/min). Whole-body impedance cardiography reliably detected cardiac output changes induced by head-up tilt before anesthesia, by anesthesia induction, and by intubation. Two factors predicted the between-methods stroke volume difference: hematocrit (correlation coefficient r = -.36, r2 = .13; p < .001); and body mass index (r = .29, r2 = .08; p < .01). Using the multiple linear regression equation for correcting the stroke volume by hematocrit and body mass index, the limits of agreement (2 SD) between the methods studied were reduced to +/-1.28 L/min for cardiac output and +/-0.72 L/min/m2 for cardiac index. CONCLUSIONS: There was close agreement between whole-body impedance cardiography and thermodilution in the measurement of cardiac output in patients with coronary artery disease without cardiac shunts and valvular lesions. The repeatability of the impedance method was significantly better than the repeatability of thermodilution. Whole-body impedance cardiography can be recommended for the assessment of cardiac output and its changes in the resting state. Whole-body impedance cardiography is a feasible and handy method for noninvasive and continuous measurement of cardiac output.

Cardiac Output↗
PubMedDate not supplied

New method of electrode placement for determination of cardiac output using impedance cardiography.

In thirty eight young healthy adult subjects, cardiac output was determined non-invasively by using two methods of electrode placement viz. vertical (uses silver braided wires in a band shape) and horizontal (conventional stick-on type surface ECG electrodes), using the technique of Impedance Cardiography. The recordings were taken in supine position on the same day in two separate sets with 30.0 min interval between two sets. In each set of recording, five successive recordings, each at an interval of five minutes were taken. The mean values of cardiac out put by two methods were compared. For the set I, the respective values (Mean +/- SD) of cardiac output by horizontal and vertical methods for the each of the five recordings were 4.87 +/- 0.77 and 5.03 +/- 0.64 for the first, 4.87 +/- 0.71 and 4.91 +/- 0.66 for the second, 4.99 +/- 0.67 and 5.00 +/- 0.70 for the third, 4.78 +/- 0.69 and 4.98 +/- 0.61 for the fourth, 4.84 +/- 0.69 and 4.98 +/- 0.62 for the fifth recording in supine position. The respective P values for these pairs for between the group comparisons were 0.33, 0.50, 0.96, 0.17, and 0.36. In addition, to see the repeatability for each method, within the group comparison was done, the P values were 0.71 and 0.91 for the horizontal and vertical methods, respectively. The mean value of cardiac output did not differ significantly between two methods for recordings of set II in supine position. The cardiac output measurement by placing four spot electrodes horizontally, gave consistent result on repeated measurements and their values showed concordance with the cardiac output values obtained by conventional four band electrodes tied around the chest.

Adult↗
PubMed1976

Effects of reserpine, guanethidine and methyldopa on cardiac output and its distribution.

In anaesthetized rats with a renal model of hypertension, effects of reserpine, guanethidine and methyldopa on cardiac output (the dye-dilution method) and its distribution among the heart, the lung, the kidney, the large and small intestine, the stomach, the liver, the spleen, skeletal muscle and skin (the rubidium method) were studied. Several hours administration of all three drugs under study, a definite decrease in cardiac output was observed. Cardiac output then escaped from the influence of the drugs despite a reduction in heart rate. Fall of arterial pressure 24 hr after administration of the drugs was only due to the decrease in total peripheral resistance. Effects of the drugs on distribution of cardiac output were studied at the time when cardiac output was not changed to any significant extent. Under this condition the features common to all the drugs were an increase of the cardiac output fractions to the gastro-intestinal tract and a decrease to the heart and the spleen. This fact indicates that decrease in resistance of gastro-intestinal vascular region plays a basic role in the hypotensive effect of reserpine, guanethidine and methyldopa.

Animals↗
PubMed1999

Effects of injectate volume on thermodilution measurements of cardiac output in patients with low ventricular ejection fraction.

OBJECTIVE: To determine the effect of 5-mL injectate on cardiac output measurements in critically ill patients with low ventricular ejection fraction (< 35%). METHODS: Thermodilution cardiac output measurements obtained with three 5-mL and three 10-mL (randomly ordered) iced injectates in 50 patients with low ejection fraction were averaged if the measurements were within 10% of the median. If the 3 measurements were not within those limits, additional measurements were obtained. RESULTS: Cardiac output measured with the 5-mL injectate (mean, 4.63 L/min) and cardiac output measured with the 10-mL injectate (mean, 4.52 L/min) were not significantly different (P = .64). Lower and upper limits of agreement were -1.7 L/min to +1.6 L/min. The bias (mean difference between 10- and 5-mL measurements) of all measurements was -0.09, and the precision was 1.43 L/min, with a 95% confidence limit (mean difference +/- 2 SD) of -1.7 to +1.6 L/min. An additional measurement was necessary in 77% of patients in the 5-mL group but in only 48% of the 10-mL group (P = .006). CONCLUSIONS: Cardiac outputs measured with 5- and 10-mL injectates do not differ significantly. The greater variability of measurements obtained with a 5-mL injectate suggests that more measurements, and thus more time, are needed to measure cardiac output accurately. Clinicians must weigh the benefit of minimizing fluid volume used against the potential decreased reliability of cardiac output measurements.

Adult↗
PubMed1980

Optimization of the regular frequency of the heart in atrial fibrillation in relation to the cardiac output.

In atrial fibrillation an optimal frequency value has been derived to give the maximum cardiac output. A multiple, non-linear regression analysis of phasic aortic flow velocity in 12 patients with atrial fibrillation yields the parameters: (i) upper limiting frequency, fc; and (ii) 'optimal' frequency of the heart fo = fc/2. fo is defined at maximum cardiac output in resting conditions. An estimate of fc may be obtained from the carotid pulse tracing in a non-invasive way for the individual patient. The maximum cardiac output at fo ranges between 100% and 125% of the cardiac output was measured in the atrial fibrillatory state with irregular excitation of the ventricles. The greater the degree of irregularity of atrial fibrillation, the more expressed was the potential rise in cardiac output at the optimal regularization frequency. In chronic atrial fibrillation a regular excitation of the ventricles could be achieved by pharmacological agents, such as Verapamil or by ventricular pacing, without restitution of normal sinus rhythm. In critically ill patients with atrial fibrillation and the low cardiac output syndrome the heart rate should be adjusted to the individual cardiac output-related optimal frequency.

Aorta↗