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PubMed1990

Autoregulation of cardiac output by passive elastic characteristics of the vascular capacitance system.

After a change in cardiac output, the magnitude of potential blood volume redistribution was investigated in 10 dogs anesthetized with chloralose. All of the venous return was pumped into a reservoir, using servocontrolled pumps to maintain fixed superior and inferior vena cava pressures. The cardiac output was set at various levels by pumping from the reservoir into the right atrium. Changes in reservoir volume were assumed to reflect the changes in vascular blood volume. After measuring the control responses, cardiovascular reflexes were blocked with hexamethonium. Reducing the cardiac output, for example, from 110 to 80 ml/(min.kg) with reflexes intact, caused a 9.2-ml/kg transfer of blood from the dog to the reservoir. With reflexes blocked, the same change in cardiac output caused 6.8 ml/kg of the blood to be transferred. Under the control conditions, throughout the range of 50-140 ml/(min.kg), an increase or decrease of cardiac output of 1 ml/(min.kg) elicited a 0.304 +/- 0.086 (mean +/- SD) ml/kg change in dog blood volume; with reflexes blocked, the flow sensitivity was 0.239 +/- 0.062 ml/kg. Thus, only 21% of the total blood volume redistribution was attributable to active reflex responses. Deterioration of the preparation may have attenuated the magnitude of active reflex activity. Neither the systemic vascular compliance of 1.80 +/- 0.35 ml/mm Hg.kg nor the fraction of venous return from the superior vena cava of 26.5 +/- 4.6% was significantly changed by reflex blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Changes in mean airway pressure during HFOV influences cardiac output in neonates and infants.

BACKGROUND: Changes in mean airway pressure affect cardiac output during conventional positive pressure ventilation. The effect of high-frequency oscillation ventilation (HFOV) on cardiac output is less studied. METHODS: A prospective study in a university hospital pediatric intensive care unit. Fourteen patients aged <1 year and weighing <10 kg who were on HFOV were included. All patients had been on HFOV for >12 h and were considered to be in a stable condition. In the study group (n = 9) the mean proximal airway pressure (Paw) was increased and decreased by +5 and -3 cmH2O, respectively, from baseline in each patient. Measurements were made at each level including baseline settings between each change. In a control group (n = 5) no changes in ventilatory parameters were made. Cardiac output was assessed with echocardiography and the Doppler technique at each level of Paw and at similar intervals in the control group. RESULTS: Cardiac output changed significantly when Paw was changed in the study group (P = 0.02), with the greatest change at the highest Paw at -11% (range: -19 to -9) compared with baseline. We found no significant changes over time in the control group. CONCLUSION: This study shows that CO is affected by changes in mean airway pressure during HFOV in concordance with the known effects of mean airway pressure during conventional positive pressure ventilation. The mean changes are smaller than expected compared with earlier studies of conventional mechanical ventilation. Further studies are needed to better understand these relationships.

Cardiac Output↗
PubMed1993

Validity of thermal dilution technique for measurement of cardiac output in rats.

The validity of the thermal dilution technique for the measurement of cardiac output was verified in experiments on a circulation model and on anesthetized rats under open- and closed-chest conditions. In the circulation model thermal dilution was compared with direct (Fdir) and electromagnetic (F(elm)) flowmetry. Flow values measured in the circulation model with the thermal dilution (Fth) technique correspond well with direct flowmetry (Fth = 0.92 Fdir + 7.0; r = 0.888) and with electromagnetic flowmetry (Fth = 0.95 F(elm) + 1.2; r = 0.990). In the anesthetized rat cardiac output was determined with thermal dilution and simultaneously with Fick's method and/or with electromagnetic flowmetry. Fick's method and electromagnetic flowmetry resulted in identical cardiac output values (COFick = 0.95 COelm; r = 0.865), whereas the thermal dilution technique yielded unequivocally higher values. The extent of overestimation is much more pronounced at low cardiac output than at a high output. The study clearly demonstrates that this overestimation is due to heat diffusion, which is obviously of greater significance in small animals than in large animals or humans. Therefore, the thermal dilution technique is not appropriate for the measurement of cardiac output in the rat.

Animals↗
PubMed1993

Continuous cardiac output monitoring by the Fick method.

Current methods for longitudinal assessment of cardiac output in severely ill patients are intermittent only and in many respects appear unsatisfactory. We have developed a computerized on-line system for continuous Fick cardiac output monitoring, utilizing fiberoptic arterial and pulmonary arterial probes with a metabolic analyzer for VO2. In 15 patients, cardiac output ranged 1.9-6.8 L/min and 12 were within 5% of thermodilution values. Continuous output monitoring during interventions in two patients (saline infusion and coronary angioplasty) illustrate the utility of the technique. Two additional patients had unsatisfactory VO2 data due to low airflow velocity. The results of this pilot study suggest that cardiac output monitoring by the Fick method may have clinical and investigational uses in intensive care units and during cardiac catheterization or surgical procedures.

Adult↗
PubMed2004

Evaluation of a new continuous cardiac output monitor in off-pump coronary artery surgery.

We evaluated a new, ultra-fast response continuous cardiac output monitor in 34 adult patients undergoing off-pump coronary artery bypass graft surgery. Cardiac output was measured with the TruCCOMS continuous cardiac output monitor (Aortech International plc, Lanarkshire, UK), using triplicate cold bolus thermodilution as the criterion standard, at fixed time points during surgery and during dobutamine infusion. The two techniques were compared using linear regression and Bland-Altman analysis. Overall, the study device displayed a bias of 0.4 l.min(-1) with limits of agreement of +2.5 l.min(-1) and -1.7 l.min(-1). The study device failed to detect the change in cardiac output caused by dobutamine accurately (y = 0.18x + 0.45; r(2) = 0.13), with an error linearly related to the magnitude of the change measured. We conclude that the device's failure to detect changes in cardiac output could be a major limitation in its clinical use in its current form.

Aged↗
PubMed1990

Prevalence and clinical characteristics of a high cardiac output state in patients with multiple myeloma.

PURPOSE: This study was undertaken to define the prevalence and clinical characteristics of patients with a high cardiac output state associated with multiple myeloma. PATIENTS AND METHODS: Specifically, we evaluated clinical, laboratory, and two-dimensional and Doppler echocardiographic data in 36 patients with multiple myeloma. Cardiac output was determined noninvasively by a pulsed Doppler technique. RESULTS: A high cardiac output state, defined as a cardiac index greater than or equal to 4.0 L/minute/m2, was present in eight of 34 (23.5%) subjects in whom cardiac output was measurable. None of the known causes of high output states could be identified in these patients. Four patients developed high output congestive heart failure, two of whom died. Age, sex, degree of anemia, serum calcium level, immunoglobulin type, or disease stage did not differ significantly between subjects with or without high output states. However, severe bone involvement was significantly more frequent in those patients with high cardiac output states, occurring in all eight patients with high cardiac indexes compared with nine of 26 patients with low or normal cardiac indexes (p = 0.001). CONCLUSION: These data demonstrate that high cardiac output states are relatively common in patients with multiple myeloma and are associated with the presence of extensive bone disease.

Bone and Bones↗
PubMed2003

Non-invasive assessment of cardiac output during exercise in healthy young humans: comparison between Modelflow method and Doppler echocardiography method.

AIMS: The Modelflow method can estimate cardiac output from arterial blood pressure waveforms using a three-element model of aortic input impedance (aortic characteristic impedance, arterial compliance, and systemic vascular resistance). We tested the reliability of a non-invasive cardiac output estimation during submaximal exercise using the Modelflow method from finger arterial pressure waveforms collected by Portapres in healthy young humans. METHODS: The Doppler echocardiography method was used as a reference method. Sixteen healthy young subjects (nine males and seven females) performed a multi-stage cycle ergometer exercise at an intensity corresponding to 70, 90, 110 and 130% of their individual ventilatory threshold for 2 min each. The simultaneous estimation of cardiac output (15 s averaged data) using the Modelflow and Doppler echocardiography methods was performed at rest and during exercise. RESULTS AND CONCLUSION: The Modelflow-estimated cardiac output correlated significantly with the simultaneous estimates by the Doppler method in all subjects (r = 0.87, P < 0.0001) and the SE of estimation was 1.93 L min-1. Correlation coefficients in each subject ranged from 0.91 to 0.98. Although the Modelflow method overestimated cardiac output, the errors between two estimates were not significantly different among the exercise levels. These results suggest that the Modelflow method using Portapres could provide a reliable estimation of the relative change in cardiac output non-invasively and continuously during submaximal exercise in healthy young humans, at least in terms of the relative changes in cardiac output.

Adult↗
PubMed1985

Effect of flecainide on cardiac output.

The effect of intravenous flecainide (2 mg/kg) on cardiac output was evaluated by a dye dilution method in six healthy nonsmokers. The study was of a double-blind, crossover, placebo-controlled, randomized, and balanced design. Cardiac output, heart rate, and stroke volume were measured 0, 10, 30, 60, 90, 120, 150, 180, and 240 minutes after the beginning of the flecainide infusion. Flecainide reduced cardiac output and stroke volume during the first 90 minutes and heart rate increased during the first 30 minutes after flecainide. Visual analog scales for alertness and dry mouth were determined 0, 10, 60, and 240 minutes after dosing. Alertness was reduced 60 minutes after flecainide, but there was no increase in dryness of the mouth.

Adult↗
PubMed1982

Cardiac output in normal pregnancy measured by impedance cardiography.

Impedance cardiography was used to study cardiodynamic changes throughout normal pregnancy. Stroke volume, heart rate and cardiac output were determined in fourteen normal primigravidae from early pregnancy until 6-25 weeks after delivery. To elucidate the influence of the patient's position on cardiac output, measurements were made in the supine as well as in the left and right lateral positions. Stroke volume and cardiac output increased up to the 28th week of pregnancy and then decreased during late pregnancy. These changes seemed to be independent of the patient's position. After delivery a further reduction in cardiac output due to a significant decrease in heart rate was found. No significant differences in cardiac output were found between right and left lateral position. However, during pregnancy as well as after delivery, cardiac output measured by impedance cardiography was significantly higher in the supine position than in the lateral positions. Thus, the impedance method does not seem to be reliable in measuring absolute values of stroke volume and cardiac output but may be used for relative measurements during pregnancy.

Adult↗
PubMed1977

Noninvasive determination of cardiac output by a modified acetylene rebreathing procedure utilizing mass spectrometer measurements.

A modified acetylene rebreathing technique for measuring cardiac output has been developed utilizing a mass spectrometer for measuring gas concentrations. Helium serves as an indicator of mixing and system volume. The disappearance rate of acetylene is proportional to pulmonary capillary blood flow, which is taken as an index of cardiac output. The method also provides an estimate of pulmonary tissue volume. The technique was assessed by comparing 22 simultaneous acetylene and dye-dilution cardiac outputs measured at rest and during exercise in six healthy subjects. There was no significant difference between the mean acetylene and dye-dilution cardiac output values (11.5 l/min vs. 11.24 l/min, respectively). The correlation coefficient was 0.94 and the S.E.M. difference was 0.53 l. The effect of the procedure on cardiac output was evaluated in a separate study of six subjects. There was a significant positive correlation between respiratory rate and cardiac output; but the magnitude of this effect was small, indicating that accurate measurements may be made at spontaneous respiratory rates.

Acetylene↗
PubMed1997

Noninvasive assessment of cardiac output in critically ill patients by analysis of the finger blood pressure waveform.

OBJECTIVE: To assess whether the measurement of cardiac output by computer-assisted analysis of the finger blood pressure waveform can substitute for the thermodilution method in critically ill patients. DESIGN: Prospective data collection. SETTING: Emergency department in a 2000-bed inner city hospital PATIENTS: Forty-six critically ill patients requiring invasive monitoring for clinical management were prospectively studied. INTERVENTIONS: Under local anesthesia a 7-Fr pulmonary artery catheter was inserted via the central subclavian or jugular vein. Cardiac output was determined by the use of a cardiac output computer and injections of 10 mL ice-cold glucose 5%. Noninvasive cardiac output was calculated from the finger blood pressure waveform by the use of the test software program. MEASUREMENTS AND MAIN RESULTS: Three hundred twenty-three pairs of invasive and noninvasive hemodynamic measurements were collected in intervals of 30 mins from 46 patients (mean age 61.9 +/- 12.4 yrs; 35 male, 11 female). The average cardiac index during the study period was 2.83 L/min/m2 (range 0.97 to 5.56). The overall discrepancy between both measurements was 0.14 L/min/m2 (95% confidence interval: 0.10-.018, p < .001). Seventy-five (23.2%) measurements had an absolute discrepancy > +/- 0.50 L/min/m2. Noninvasive and invasive comparisons of mean differential cardiac output were out of phase for 9.7% of all readings. CONCLUSION: Computer-assisted analysis of finger blood pressure waveform to assess cardiac output is not a substitute for the thermodilution method due to a high percentage (23.2%) of inaccurate readings; however, it may be a useful tool for the detection of relative hemodynamic trends in critically ill patients.

Adult↗
PubMed1989

Transtracheal Doppler: a new procedure for continuous cardiac output measurement.

An endotracheal tube with a 5 mm diameter ultrasonic transducer incorporated into its distal end was inserted into the tracheas of six anesthetized dogs. The device provides for ultrasound measurement of aortic diameter and blood velocity in the ascending aorta to obtain cardiac outputs. Because measurements are made proximal to the origins of the aortic arch vessels, total cardiac output is obtained. Procedures for measurement of aortic diameter, aortic blood velocity, and cardiac output are discussed. The resulting data were used to empirically determine the angle of incidence of the ultrasound beam that gave the best least squares fit over a range of thermodilution cardiac outputs. For an angle of incidence of 62.3 degrees, the relationship between cardiac output determined by thermal dilution and by transtracheal Doppler was transtracheal Doppler cardiac output = -.69 + 1.19 thermal dilution cardiac output. R2 = .82. The results from this preliminary assessment of the feasibility of measuring cardiac output in dogs using transtracheal Doppler suggest that additional studies should be pursued. Additional issues that require investigation include confirmation of constancy of human anatomy and demonstration of lack of tracheal trauma from the Doppler equipped endotracheal tube.

Animals↗
PubMed1988

Cardiac output and regional myocardial contraction in anorexia nervosa.

The study measured cardiac output and assessed regional myocardial contraction in 14 patients with anorexia nervosa, some of whom also had bulimia, and in 15 controls. The experimental and control groups were not significantly different in age or body surface area (p = greater than 0.05). To evaluate regional myocardial contraction, 12 of 14 anorexia nervosa-bulimia (ANB) patients were studied in the acute phase and once serially at a mean interval of 1.5 years by assessing the movement of each left ventricular wall segment toward the center of the ventricle as imaged in the precordial short axis. Cardiac output was measured in the ascending aorta by pulsed Doppler for control subjects and for 13 ANB patients. Regional myocardial contraction was normal for all controls, but eight of 14 ANB patients showed regional myocardial contraction abnormalities. Between studies, four of these eight demonstrated improved regional myocardial contraction, three remained unchanged, and one was worse. Mean cardiac output was markedly reduced in ANB patients (2.6 L/min) compared to controls (4.5 L/min) (p = less than 0.001). The low cardiac output in ANB patients was reflected as reduced mean ascending aortic velocity/second (18.5 cm/s) compared to a mean of 22.8 cm/s for controls (p = less than 0.02). Mean ascending aortic area was slightly smaller for ANP patients. Mean peak ascending aortic velocity was significantly lower in ANB patients than in controls (p = less than 0.02). Mitral valve prolapse was seen during at least one examination in seven of 14 ANB patients (0/15 controls) and disappeared in two of three patients following hydration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

[Clinical importance of cardiac output dissociation between the right and left ventricle without evidence of an anatomical shunt].

Authors took note of transitoric cardiac output dissociation between the right and left ventricle during the treatment of the acute myocardial infarction controlled hemodynamically, without the presence of a provable anatomical shunt. They demonstrate some kinds of clinical appearances and call the attention to the clinical importance of the progressive cardiac output dissociation. The re-establishment of balance of the right and left cardiac output in resting position at the most optimal level of the oxygen demand, simultaneously the correction of the blood pressure and blood volume correlation can help the treatment of such acute cardiovascular cases which are complicated hemodynamic disturbances. The authors demonstrate a simple method for the registration of the cardiac output in the left and right ventricles. It has been found that the right cardiac output determined by the thermodilution method cannot be referred to the left one in such cases when the dissociation of cardiac output is present, because it can cause damage.

Blood Pressure↗
PubMed1981

The relationship of cardiac output and arterial pressure control.

Many basic concepts of cardiac output and arterial pressure control have changed considerably in the past few years. In general, each tissue controls its own local resistance and blood flow regardless of the level of arterial pressure; the sum of the local flows then determines the venous return and cardiac output. However, the arterial pressure is normally controlled by separate mechanisms that do not significantly alter the cardiac output. During acute circulatory stresses, such as exercise, the arterial pressure is controlled almost entirely by nervous reflex mechanisms; but over long periods, there reflex mechanisms fade away because they adapt. The arterial pressure is then controlled mainly by a renal-volume-endocrine pressure control system, in which the blood volume and total peripheral resistance are manipulated slowly to adjust the pressure.

Animals↗
PubMed2000

End-tidal CO2 pressure decreases during exercise in cardiac patients: association with severity of heart failure and cardiac output reserve.

OBJECTIVES: We measured end-tidal CO2 pressure (PETCO2) during exercise and investigated the relationship between PETCO2 and exercise capacity, ventilatory parameters and cardiac output to determine the mechanism(s) of changes in this parameter. BACKGROUND: It is unclear whether PETCO2 is abnormal at rest and during exercise in cardiac patients. METHODS: Cardiac patients (n = 112) and normal individuals (n = 29) performed exercise tests with breath-by-breath gas analysis, and measurement of cardiac output and arterial blood gases. RESULTS: PETCO2 was lower in patients than in normal subjects at rest and decreased as the New York Heart Association class increased, whereas the partial pressure of arterial CO2 did not differ among groups. Although PETCO2 increased during exercise in patients, it remained lower than in normal subjects. PETCO2 in relation to cardiac output was similar in patients and normal subjects. PETCO2 at the respiratory compensation point was positively correlated with the O2 uptake (r = 0.583, p < 0.0001) and the cardiac index at peak exercise (r = 0.582, p < 0.0001), and was negatively correlated with the ratio of physiological dead space to the tidal volume. The sensitivity and specificity of PETCO2 to predict an inadequate cardiac output were 76.6% and 75%, respectively, when PETCO2 at respiratory compensation point and a cardiac index at peak exercise that were less than the respective control mean-2 SD values were considered to be abnormal. CONCLUSIONS: PETCO2 was below normal in cardiac patients at rest and during exercise. PETCO2 was correlated with exercise capacity and cardiac output during exercise, and the sensitivity and specificity of PETCO2 regarding decreased cardiac output were good. PETCO2 may be a new ventilatory abnormality marker that reflects impaired cardiac output response to exercise in cardiac patients diagnosed with heart failure.

Anaerobic Threshold↗
PubMed1986

Cardiac output measurements. A review of current techniques and research.

Cardiac output is the volume of blood ejected by the heart per unit time. It is a useful measurement in that it can be used to evaluate overall cardiac status in both critically ill patients and patients with suspected cardiovascular disease. An ideal cardiac output measurement system would have automated continuous output capability, be minimally invasive, accurate, fast, small, low cost and clinically adaptable. This paper presents a theoretical and practical description of the variety of clinical techniques in use today and lists their advantages and shortcomings with respect to the ideal system. Included are the Fick method, indicator dilution techniques, velocity measurements and transthoracic impedance and combined Doppler ultrasound as noninvasive techniques. In addition, several experimental methods are described along with their desirable features and possible constraints. These include intravascular heating/recording, thermistor tracking of cardiac output, ejection fraction measurements and magnetic susceptibility plethysmography.

Biomedical Engineering↗
PubMed1986

Evaluation of a modified acetylene rebreathing method for the determination of cardiac output.

In order to evaluate a computerized modified acetylene rebreathing method for the determination of cardiac output, 15 healthy subjects were studied at different levels of their maximal oxygen uptake (VO2max). Submaximal exercise was performed on a cycle ergometer and maximal exercise on a treadmill. Oxygen uptake, heart rate, and cardiac output (acetylene method) were determined in all test situations. In seven subjects simultaneous determinations of cardiac output were made by a modified acetylene rebreathing method (QA) and a dye dilution method (QD). Furthermore, a new resting rebreathing technique was used. The methodological error for QA (means of double samples) was 0.37 litre min-1 (2.8%) in the same individual at 150 W. The corresponding values between individuals were 0.71 (rest), 0.41 (50 W), 0.69 (150 W), and 0.40 litre min-1 (VO2max). Thus the methodological error of the modified acetylene method was very low. There was a significant difference (P less than 0.01), however, between the acetylene method and the dye dilution method, which showed a lower value for QA at all levels. This was probably due to the long response time of the mass spectrometer combined with anatomical and physiological arteriovenous shunt effects in the lungs during exercise. When these factors were considered the correcting formula was: QAc = QA + 0.005 X Q2A. There was no significant difference between the corrected cardiac output values (QAc), and the corresponding QD values. In conclusion, this modified acetylene rebreathing method is a very useful non-invasive method for measuring cardiac output at rest as well as during heavy exercise.

Acetylene↗