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PubMed1987

Mixed venous oxygen tension as an estimate of cardiac output in anesthetized horses.

The relationship between mixed venous O2 tension and cardiac output was studied in six anesthetized horses breathing 100% O2. Cardiac output, O2 consumption, mean arterial pressure, heart rate, and arterial and venous blood gases were measured after administration of xylazine or dobutamine to horses in lateral, sternal, and dorsal recumbencies. After approximately 3 hours, Escherichia coli endotoxin was administered while horses were in dorsal recumbency, and all measurements were repeated. Relationships between cardiac index (CI) and PVO2, heart rate, mean arterial pressure, jugular PVO2, and PVO2 of blood from a superficial limb vein were evaluated by linear regression analysis. Mean arterial pressure was significantly (P less than 0.05) correlated with CI in horses in all positions and after endotoxin administration. However, data points were poorly grouped. Heart rate and CI were significantly correlated in horses in all positions, but not after endotoxin administration. Correlations between jugular PVO2 and PVO2 of blood from a superficial limb vein were not significant in horses in sternal recumbency, and PVO2 of blood from a superficial limb vein was not significantly correlated with CI in horses in lateral recumbency. There was a significant and tight correlation between PVO2 and CI in horses in all positions and after endotoxin administration.

Anesthesia, General↗
PubMed2006

Variation in preoperative assessment of cardiac output reserve and likelihood of transfusion among anaesthetists: a pilot study.

The aim of this pilot study was to investigate anaesthetists' assessment of the ability of patients to increase cardiac output over a range of clinical scenarios and of their perceived 'likelihood of transfusion' in these scenarios. Specialist anaesthetists were given a questionnaire with clinical cues in the form of diagnoses about theoretical patients. They were asked to use 100 mm visual analogue scales (VAS) for their assessments of each patient's cardiac reserve and their 'likelihood of transfusion' of these patients; the endpoints of the VAS being 'Very low' (0 mm) to 'High' (100 mm), and 'Do not transfuse' (0 mm) to 'Transfuse' (100 mm) respectively. The assessment of patients' cardiac output reserve by anaesthetists (n = 54) showed great variation; for example, a patient with severe aortic stenosis was perceived overall to have a limited ability to increase cardiac output (mean VAS 16 mm) but there was considerable variation between anaesthetists (25-75 percentiles 10 mm to 21 mm). Assessment of 'likelihood of transfusion' (n = 42) also had great variation; as an example a patient with 'angina' with a haemoglobin of 95 g l(-1) was perceived overall to have an average likelihood of transfusion of 50 mm, but the 25-75 percentiles ranged from 33 mm to 71 mm. This study suggests that inter-anaesthetist variability in the assessment of a patient's 'cardiac output reserve' and his 'likelihood of transfusion' is large.

Anesthesia↗
PubMed1998

A noninvasive method for estimating cardiac output using lung to finger circulation time of oxygen.

To develop a safe, noninvasive, simple, inexpensive, and clinically adaptable method for estimating cardiac output, we evaluated the potential of lung to finger circulation time (LFCT) and buildup time (Tb) of oxygen as measured by pulse oximetry to estimate cardiac output. Significant correlation was found between cardiac output as measured by thermodilution and the inverse of LFCT (R = 0.76, p < 0.001, SEE = 0.9 L/min) as well as the inverse of Tb (R = 0.72, p < 0.001, SEE = 0.9 L/min).

Cardiac Catheterization↗
PubMed1984

Control of cardiac output in thyrotoxic calves. Evaluation of changes in the systemic circulation.

The contribution of peripheral vascular factors to the high output state in thyrotoxicosis was examined in 11 calves treated with daily intramuscular injections of L-thyroxine (200 micrograms/kg) for 12-14 d. Thyroxine treatment increased cardiac output from 14.1 +/- 1.4 to 24.7 +/- 1.4 liters/min (P less than 0.001) and decreased systemic vascular resistance from 562 +/- 65 to 386 +/- 30 dyn-s/cm5 (P less than 0.01). Blood volume was increased from 65 +/- 4 ml/kg in the euthyroid state to 81 +/- 6 ml/kg when the animals were thyrotoxic (P less than 0.05). The role of low peripheral vascular resistance in maintenance of the high output state was evaluated by infusion of phenylephrine at two dosages (2.5 and 4.0 micrograms/kg per min). In the euthyroid state, no significant decrease in cardiac output was observed at either level of pressor infusion. In the thyrotoxic state, the higher dosage of phenylephrine increased peripheral resistance to the euthyroid control level and caused a small (6%) decrease in cardiac output (P less than 0.05). This small decrease in cardiac output probably could be attributed to the marked increase in left ventricular afterload caused by the pressor infusion as assessed from measurements of intraventricular pressure and dimensions. Changes in the venous circulation were evaluated by measurement of mean circulatory filling pressure and the pressure gradient for venous return in six animals during cardiac arrest induced by injection of acetylcholine into the pulmonary artery. Mean circulatory filling pressure increased from 10 +/- 1 mmHg in the euthyroid state to 16 +/- 2 mmHg (P less than 0.01) during thyrotoxicosis, while pressure gradient for venous return increased from 10 +/- 1 to 14 +/- 2 mmHg (P less than 0.02). These changes in venous return curves were not affected significantly by ganglionic blockade with trimethapan (2.0 mg/kg per min) before cardiac arrest. Thus, the high output state associated with thyrotoxicosis is not dependent upon a low systemic vascular resistance, but is associated with increases in blood volume, mean circulatory filling pressure, and pressure gradient for venous return.

Animals↗
PubMed1985

Cardiac output distribution and regional blood flow during hypocarbia in monkeys.

Cardiac output distribution and regional blood flow were studied during hypocarbia independent of changes in ventilatory parameters. Fifteen cynomolgus monkeys were anesthetized with methohexital sodium (8 mg/kg im) and hyperventilated through an endotracheal tube. Hypocarbia at two levels, 28 +/- 1.8 and 17 +/- 0.6 Torr, was achieved by a stepwise decreasing CO2 flow into the semiclosed system. Regional blood flow was determined with labeled microspheres. At each stage of experiments two sets of microspheres (9 and 15 microns diam) were used simultaneously. The use of two microsphere sizes allowed evaluation of the relationship between total (nutritive and nonnutritive) tissue blood flow, determined with 15-microns spheres, and nutritive blood flow, determined with 9-microns spheres. There was no change in cardiac output or arterial pressure during both degrees of studied hypocarbia. Hypocarbia was accompanied by a decrease in myocardial blood flow determined with 15-microns spheres and preservation of the flow determined with 9-microns spheres. Splenic blood flow was decreased, whereas hepatic arterial blood flow was increased during both levels of hypocarbia. Blood flow through the brain, renal cortex, and gut showed a biphasic response to hypocarbia: during hypocarbia at 28 +/- 1.8 Torr, blood flow determined with 15-microns spheres was unchanged (in the gut) or decreased (in the brain and kidneys), whereas blood flow determined with 9-microns spheres was decreased. During hypocarbia at 17 +/- 0.6 Torr, blood flow determined with 9-microns spheres had a tendency to restore to base-line values.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Reliability of the thermodilution method in the determination of cardiac output in clinical practice.

The thermodilution (TD) method of determining cardiac output (CO) is widely used in clinical practice, but its reliability in this setting is not well understood and may be poor. This is especially true when dealing with unstable patients and using commercial TD devices. Numerous published reports have shown markedly variable results when comparing simultaneously the TD method and the Fick or dye-dilution methods in catheterization laboratories, intensive care units, or operating rooms. In order to assist clinicians in interpreting the reliability of the TD method in measuring CO, we analyzed all available published data (14 reports). The differing results in these reports were evaluated by standard statistical methods and by an extension of the influence function method of structural analysis developed to differentiate reproducibility and accuracy errors of each technique. Comparing the accuracy of the TD method with that of the Fick or the dye-dilution methods reveals that the 3 methods are of equal merit and can be used as independent references. Our reproducibility data show that when using commercial TD devices there must be a minimal difference of 12 to 15% (average, 13%) between determinations of cardiac output (3 measurements per determination) to suggest clinical significance. Minimal differences of 20 to 26% (average, 22%) are required between determinations when using 1 measurement per determination. There was no difference in the quality of the TD method when comparing rapid injection of iced or room temperature thermal indicator.

Cardiac Output↗
PubMed1978

Some aspects of the clinical use of thermodilution in measuring cardiac output. With particular reference to the Swan-Ganz thermodilution catheters.

Accuracy of the thermodilution method in measuring cardiac output was tested in a model and against Fick in ten patients. Reproducibility was determined from 573 thermodilution curves. The influence of catheter position, catheter irrigation, post-injection aspiration, and the substitution of rectal temperature for central blood temperature was also studied. The thermodilution method showed very good correlation to direct measurements in the model (corr. coeff. 1.00) and the Fick method in patients (corr. coeff. 0.97). Mean standard deviation for cardiac outputs calculated from individual thermodilution curves was 5%. Post-injection aspiration and variation in catheter tip location did not influence the results. Catheter irrigation during recordings and the use of rectal temperature for TB resulted in underestimation of cardiac output.

Calibration↗
PubMed1987

Cardiac output by rebreathing in patients with cardiopulmonary diseases.

Noninvasive estimates of cardiac output by rebreathing soluble gases (Qc) can be unreliable in patients with cardiopulmonary diseases because of uneven distribution of ventilation to lung gas volume and pulmonary blood flow. To evaluate this source of error, we compared rebreathing Qc with invasive measurements of cardiac output performed by indicator-dilution methods (COID) in 39 patients with cardiac or pulmonary diseases. In 16 patients with normal lung volumes and 1-s forced expiratory volumes (FEV1), Qc measured with acetylene [Qc(C2H2)] overestimated COID insignificantly by 2 +/- 9% (SD). In subjects with mild to moderate obstructive lung disease, Qc(C2H2) slightly overestimated COID by 6 +/- 15% (P = 0.11). In patients with restrictive disease or combined obstructive and restrictive disease, Qc(C2H2) underestimated COID significantly by 9 +/- 14% (P less than 0.04). The magnitude of the discrepancy between Qc and COID correlated with size of the volume rebreathed and an index of uneven ventilation calculated from helium mixing during rebreathing that determined a dead space to inspired volume ratio (VRD/VI). Rebreathing volumes less than 40% of the predicted FEV or VRD/VI of 0.4 or greater identified all subjects with a discrepancy between Qc(C2H2) and COID of 20% or greater.

Cardiac Output↗
PubMed1985

Influence of airway pressure waveform on cardiac output during positive pressure ventilation of healthy newborn dogs.

During positive pressure ventilation, increases in mean airway pressure produced by increases in end expiratory pressure are associated with reductions in cardiac output. Mean airway pressure may be increased not only by increasing end expiratory pressure, but also by increasing the inspiratory pressure or the inspiratory to expiratory time ratio. During positive pressure ventilation of 10 healthy newborn dogs, cardiac output and left ventricular dimensions were measured using radioactive microspheres and echocardiography, respectively. Baseline ventilation was produced using the least inspiratory pressure to maintain normocarbia (rate = 50 min-1, inspiratory to expiratory time ratio = 1:3, end expiratory pressure = 2 cm H2O). The mean airway pressure was increased 3-fold by independently changing the airway pressure waveform through increases in inspiratory pressure, inspiratory to expiratory time ratio, or end expiratory pressure. Despite differences in airway pressure waveform, similar reductions in left ventricular dimension, cardiac output, and stroke volume were seen. We conclude that at a given increased mean airway pressure during positive pressure ventilation, the reduction in cardiac output is independent of the airway pressure waveform.

Animals↗
PubMed1978

Cardiac output during submaximal exercise in New Guineans: the relation with body size and habitat.

Cardiac performance in moderate bicycle exercise has been measured in five groups of New Guineans (N = 161). Men and women in both coastal and highland (2000 m) locations were studied, as well as a group of highland men after migration to the coast. The results have all been standardized to an oxygen consumption of 1 1.min(-1). Cardiac output values are similar to those previously quoted for Europeans; a significant positive correlation with body size is found, and resident highlanders appear to have slightly larger cardiac outputs (+4%) and larger stroke volumes (+10%) after adjustment for body size, but this is not because they have larger hearts. The highland migrants at sea-level share none of the 'altitude' characteristics of the highland residents and, after size-adjustment, correspond with the lowlanders. The cardiac frequencies of the lowland women are higher than the other groups (+15 beats.min(-1)) after adjustment for differences in body size. Their values are close to those found previously for moderately active Europeans, while all the other New Guinean subjects have lower cardiac frequencies probably because of their greater habitual activity.

Adaptation, Physiological↗
PubMed1996

Delayed time response of the continuous cardiac output pulmonary artery catheter.

Previous studies of the accuracy of pulmonary artery catheters (PAC) which provide continuous cardiac output (CCO) monitoring have investigated the performance during steady-state conditions. We compared the response time to hemodynamic change using a CCO PAC and an ultrasonic flow probe (UFP). In five sheep, a CCO PAC was inserted, and an UFP for measurement of CCO was placed around the pulmonary artery via a left thoracotomy. Six interventions which rapidly alter cardiac output were studied: crystalloid bolus, balloon inflation in the inferior vena cava (IVC), IVC balloon deflation, dobutamine infusion, hemorrhage, and reinfusion of blood. Cardiac output measured before and after each intervention was used to calculate the total change caused by the intervention, and the time intervals from intervention to 20%, 50%, and 80% of that change were noted. For all interventions, the time response of CCO was significantly slower than UFP. The largest differences were seen with the rapid infusion of lactated Ringer's solution for which the time interval for 20% change was 7.3 +/- 2.3 min (mean +/- SD) for CCO versus 0.5 +/- 0.3 min for UFP. The time interval for 80% change was 14.5 +/- 4.1 min for CCO versus 1.8 +/- 0.9 min with UFP. The current study demonstrates clinically important time delays in the response of the CCO catheter. This delay must be considered when rapid alterations of the hemodynamic state may occur.

Adrenergic beta-Agonists↗
PubMed1985

Cardiac output changes in newborns with hyperbilirubinemia treated with phototherapy.

Phototherapy is known to increase peripheral blood flow in neonates, but information on the associated cardiovascular effects is not available. Using pulsed Doppler echocardiography we evaluated cardiac output and stroke volume in 12 preterm and 13 term neonates during and after phototherapy. We concomitantly measured arterial limb blood flow by strain gauge plethysmography and skin blood flow by photoplethysmography. Cardiac output decreased by 6% due to reduced stroke volume during phototherapy, whereas total limb blood flow and skin blood flow increased by 38% and 41%, respectively. Peripheral blood flow increments tended to be higher in the preterm than in the term infants. The reduced stroke volume during phototherapy may be an expression of reduced activity of the newborn during phototherapy. For healthy neonates the reduction in cardiac output is minimal, but for sick infants with reduced cardiac output, this reduction may further aggravate the decrease in tissue perfusion.

Blood Circulation↗
PubMed1982

Beat-by-beat control of cardiac output in awake dogs with atrioventricular block.

In dogs with atrioventricular block and implanted ascending aortic flow probes, cardiac output can be controlled on each beta. The procedure is implemented through on-line use of a digital computer. The algorithm has three steps: 1) aortic flow is measured and integrated to give stroke volume; 2) at the end of ejection, the program computes how long the current beat must be to keep cardiac output at a target level; and 3) the ventricle is stimulated at the proper time. Cardiac output can be controlled over a range of 60-110% of normal in a resting dog. This range can be expanded by combining hemorrhage or volume infusion with the control procedure.

Animals↗
PubMed1989

Effect of cardiac output on pulmonary hemodynamics.

The purpose of this study was to test the hypothesis that there is a direct relation between pulmonary arterial input resistance and compliance in seven anesthetized cats. Cardiac output was altered by varying the direction and flow through an arteriovenous fistula with a roller pump. Pulmonary arterial input impedance was calculated from the Fourier analysis of the pressure and flow waveforms. Input resistance, pulmonary arterial compliance and characteristic impedance were estimated from the impedance spectra with a lumped parameter model. We found that pulmonary arterial compliance increased with cardiac output (P less than 0.002) but characteristic impedance was independent of flow. The observed response has the effect of reducing the hydraulic power lost by the pulmonary vasculature due to wave reflection. In three additional cats we measured the diameter of the main pulmonary artery by sonomicrometry. We found a linear relation between mean pulmonary arterial pressure and pulmonary arterial diameter during alterations of cardiac output. This result suggests that the increase of pulmonary arterial compliance with cardiac output is due to geometric factors rather than changes in vascular elastic properties.

Animals↗
PubMed1984

Effects of nifedipine on total cardiac output distribution in conscious rat.

The purpose of this study was to determine the effects of the "calcium channel blocker" nifedipine (NF) on cardiocirculatory dynamics and the total distribution of cardiac output in the conscious rat preparation. Animals were instrumented for right atrial, left ventricular, arterial and venous pressure recordings and the radioactive microsphere technique was used to measure regional blood flow and cardiac output before (control) and during the i.v. infusion of either NF at three dosage levels [0.1, 0.6 and 1.5 mg (kg X hr)-1] or vehicle (ethyl alcohol and polyethylene glycol) at rates matching those of the NF protocol [0.015, 0.1 and 0.5 ml(min)-1]. The maximum rate of infusion represented approximately a 2% increase in blood volume per minute. Systemic vascular resistance, stroke volume, regional vascular resistances and the regional percentage of distribution of total cardiac output were calculated. In the experimental group (N = 7), NF at the highest dosage level lowered mean arterial pressure by 20% and resulted in a significantly lower systemic vascular resistance and left ventricular end diastolic pressure compared with the parallel vehicle control data. The parallel vehicle only slightly but significantly lowered heart rate. The most predominant circulatory effect of NF was a significant 64% reduction in coronary vascular resistance also reflected in a substantial increase in coronary blood flow. NF also dilated the hepatic arterial circulation. The net effects of NF on cardiac output distribution involved a significant fractional shift away from the cutaneous and splenic circulatory beds in favor of the coronary, hepatic arterial and gastrointestinal circulations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Thermodilution cardiac output. Cold vs room temperature injectate and the importance of measuring the injectate temperature in the right atrium.

BACKGROUND: The feasibility of thermodilution cardiac output measurements with the more convenient room temperature thermal indicator instead of cold injectates has been repeatedly investigated. However, the issue has not been addressed with the appropriate statistical approach advocated by Altman and Bland. Furthermore, we wished to determine if the incorporation of a second thermistor in the thermodilution catheter, to measure the temperature of the thermal indicator where it is delivered into the right atrium/superior caval vein, would result in more precise cardiac output measurements. METHODS: Fifty patients were randomized to receive a single or dual thermistor pulmonary artery thermodilution catheter. Cardiac output was calculated as the average of four injections of 10 ml of isotonic saline. Precision (2 x SD of differences in replicate measurements) for the two catheters and injectate temperatures, and bias and limits of agreement between measurements, with cold and room temperature injectates, were determined. RESULTS: Precision was (0 degrees C) 0.42 l/min and (20 degrees C) 0.90 l/min, and bias and limits of agreement -0.83 l/min and -1.93-0.27 l/min for the single thermistor catheter. For the dual thermistor system precision was (0 degrees C) 0.34 l/min and (20 degrees C) 0.58 l/min. Bias and limits of agreement were -0.03 l/min and -0.61-0.55 l/min. CONCLUSION: The second thermistor is redundant if cold injectates are used. If one wishes to use room temperature injectates the single thermistor system is inadequate. A dual thermistor catheter is, on the other hand, acceptable.

Adult↗
PubMed1969

The redistribution of cardiac output on cold exposure in new-born rabbits.

1. In anaesthetized new-born rabbits isotope-labelled microspheres were injected into the left ventricle to investigate the distribution of cardiac output.2. On cold exposure the proportion of radioactivity (and hence of cardiac output) distributed to brown adipose tissue rose from 6 to 19%. Similar results were obtained in ten rabbits in which the distribution of microspheres labelled with two different isotopes was examined both in a neutral thermal and cold environment.3. The perirenal, inguinal, pectoral and axillary adipose tissue deposits showed a trivial increase in the proportion of cardiac output (from 1.2 to 1.9%) on cold exposure as compared with the cervical and interscapular deposits.4. The small intestine of new-born rabbits received 24% of the cardiac output while renal flow was only 8%. There were large changes in the proportions of body weight and in the distribution of cardiac output with age from 1 to 6 days from birth.5. The results support the contention that brown adipose tissue is the principal site of additional thermogenesis in anaesthetized new-born rabbits exposed to cold.

Adipose Tissue, Brown↗
PubMed1993

Haemodynamic changes associated with thermodilution cardiac output determination during metabolic acidosis or hypoxic hypoxia in dogs.

Haemodynamic alterations elicited by iced injectate during thermodilution cardiac output measurements were evaluated in the presence of metabolic acidosis or hypoxic hypoxia in 14 instrumented anaesthetized dogs. The alterations in some haemodynamic variables during slowing of the heart rate following injection of 3 ml iced injectate were slightly greater in metabolic acidosis and hypoxic hypoxia as compared to animals without metabolic acidosis or hypoxic hypoxia (P < 0.05), but the changes were clinically insignificant. No serious haemodynamic changes were found during any cardiac output measurement by thermodilution in the presence of metabolic acidosis or hypoxic hypoxia. The values of cardiac output measured by thermodilution correlated closely with those of pulmonary blood flow measured by an electromagnetic flowmeter in the metabolic acidosis and hypoxic hypoxia groups (r > 0.9). It is concluded that thermodilution using iced injectate will estimate right ventricular output accurately in conditions of metabolic acidosis and hypoxic hypoxia.

Acidosis↗