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PubMed1997

Gastric intramucosal pH: a predictor of survival in cardiac surgery patients with low cardiac output?

OBJECTIVE: To assess the value of gastric intramucosal pH measurement in patients with low output after cardiac surgery. DESIGN: Prospective clinical study. SETTING: University hospital. PARTICIPANTS: Fifteen patients with low output after cardiac surgery were included. Those who survived the first postoperative day (n = 14) remained in the study. INTERVENTIONS: Gastric intramucosal pH and arterial lactate concentrations were measured 6, 12, and 24 hours after admission to the intensive care unit. Intravenous infusion of buffer solutions was strictly avoided during the equilibration period and in the half hour before injection of saline into the gastric balloon of the tonometer. MEASUREMENTS AND MAIN RESULTS: Eight patients survived during the 28-day observation period, and six patients died. On admission to the intensive care unit, no difference in cardiac index (1.56 v 1.54 L/min/m2) or pulmonary capillary wedge pressure (17.3 v 17.7 mmHg) was found between survivors and nonsurvivors. During the first 24 hours after surgery, arterial lactate was significantly higher in the nonsurvivor group (61 v 23 mg/dL), but there was no difference between the gastric intramucosal pH of survivors and nonsurvivors (7.41 v 7.42 on admission). CONCLUSIONS: Calculated gastric mucosal pH is not an early predictor of survival in cardiac surgery patients with postoperative low cardiac output syndrome. Further studies are required to assess whether the gradient between arterial and intramucosal partial pressure of carbon dioxide (PCO2) might be a more useful predictive value.

Adult↗
PubMed1987

[Peritoneal dialysis in the treatment of the low cardiac output after extracorporeal circulation].

Low cardiac output after cardiopulmonary bypass is not uncommon. This per- and postoperative cardiac depression is accompanied by an impairment of renal function, which recovers with the improvement of the low cardiac output. These two correlated failures may become resistant to cardiotonic and diuretic drugs. Indeed the fluid balance is strongly disturbed, although venous pressure is only moderately increased. The only possible treatment could be water withdrawal. Nine patients are reported, all suffering from cardiac and renal failure after cardiopulmonary bypass. They were successfully treated with the method of continuous ambulatory peritoneal dialysis. This method allowed us to stop all intravenous cardiac drugs within 36 h, whilst diuresis reappeared together with a better efficacy of diuretic drugs. This beneficial haemodynamic effect of water withdrawal is discussed. This phenomenon may be related to an influence of right ventricular filling on the left ventricle. Low cardiac output may occur as a result of septal displacement, especially if there is concomitant myocardial suffering. Withdrawing a small volume of water may have modified the septal displacement, and improved cardiac output. Continuous ambulatory peritoneal dialysis was simple and well tolerated; it seemed to have contributed to the haemodynamic recovery of all the nine patients.

Aged↗
PubMed1991

Effects of augmenting cardiac contractility, preload, and heart rate on cardiac output during enflurane anesthesia.

Changes in cardiac output in response to augmenting cardiac contractility, preload, and heart rate during enflurane anesthesia were examined in 12 open-chested dogs. Cardiac contractility was assessed by the slope of the end-systolic pressure-volume relation (Emax). Dobutamine (3, 6, and 9 micrograms.kg-1.min-1) was administered to augment cardiac contractility. Autologous blood (5.0 and 10 mL/kg) was infused to increase preload. Atrial pacing was used to increase the heart rate by about 30%. Cardiac output decreased from 96 +/- 4 (0% enflurane) (mean +/- SE) to 73 +/- 5 (1.7% enflurane) and to 46 +/- 7 mL.kg-1.min-1 (3.4% enflurane), concomitantly with decreases in Emax from 6.0 +/- 1.2 (0% enflurane) to 4.5 +/- 1.2 (1.7% enflurane) and to 2.5 +/- 0.5 mm Hg/mL (3.4% enflurane). Dobutamine (3, 6, and 9 micrograms.kg-1.min-1) increased Emax from 69% +/- 7% (compared to 0% enflurane with no dobutamine) to 139% +/- 15%, 167% +/- 25%, and 183% +/- 35% at 1.7% enflurane, and from 43% +/- 8% to 78% +/- 7%, 137% +/- 20%, and 157% +/- 22% at 3.4% enflurane, respectively. The decreases in cardiac output by 1.7% and 3.4% enflurane were reversed by the intravenous administration of 3 micrograms.kg-1.min-1 of dobutamine. Cardiac output was significantly increased by administration of 10 mL/kg of autologous blood at 1.7% enflurane, but did not significantly increase at 3.4% enflurane. Increasing the heart rate did not significantly increase cardiac output at 1.7% and 3.4% enflurane. The results of this study suggest that increasing cardiac contractility is the most effective therapeutic means of reversing circulatory depression during enflurane anesthesia.

Anesthesia↗
PubMed1993

Use of noninvasive bioelectric impedance to predict cardiac output in open heart recovery.

Cardiac outputs (CO) measured by bioelectric impedance (Z) and thermodilution (TD) were compared in ten stable, non-ventilated male coronary artery bypass patients (mean age 59 +/- 12 years) in an open heart recovery unit. The measurements were obtained blindly in three sequential body positions (supine, 45 degrees, final supine) using either a calculated value for resistivity (p) (based upon hematocrit with blood sampled at the time of the study) to estimate CO(Z), or assumed values of p = 135.5 omega cm and p = 150 omega cm. The results indicate high correlations between the two measurement methods (range: r = 0.97 to 0.99) in the initial supine position for all resistivity conditions followed by a progressive decline when body position was changed to 45 degrees and supine (range: r = 0.74 to 0.90). The highest overall correlations and closest absolute mean cardiac output values were obtained when p was calculated from actual hematocrit values obtained at the time of the study. Applying a two-way ANOVA to assess the simultaneous effects of method (TD vx. Z) and position change (supine, 45 degrees, supine), no significant main effects or interactions were found when cardiac output values were estimated using the calculated measurement of p. However, significant main effects of method were found when p was assumed to be either 135.5 omega cm (p > or = 0.005) or 150.0 omega cm (p > or = 0.0001), with impedance showing a tendency to overestimate cardiac output. In conclusion, our findings suggest that impedance is a valid method to estimate cardiac output in this subpopulation of patients in open heart recovery provided that p is calculated at the time the study is performed.

Adult↗
PubMed1987

Cardiac output during labour.

Serial measurements of cardiac output and mean arterial pressure were performed in 15 women during the first stage of labour and at one and 24 hours after delivery. Cardiac output was measured by Doppler and cross sectional echocardiography at the pulmonary valve. Basal cardiac output (between uterine contractions) increased from a prelabour mean of 6.99 l/min to 7.88 l/min at greater than or equal to 8 cm of cervical dilatation as a result of an increase in stroke volume. Over the same period basal mean arterial pressure also increased. During uterine contractions there was a further increase in cardiac output as a result of increases in both stroke volume and heart rate. The increment in cardiac output during contractions became progressively greater as labour advanced. At greater than or equal to 8 cm of dilatation cardiac output increased from a basal mean of 7.88 l/min to 10.57 l/min during contractions. There were also further increases in mean blood pressure during contractions. One hour after delivery heart rate and cardiac output had returned to prelabour values, though mean arterial pressure and stroke volume remained raised. By 24 hours after delivery all haemodynamic variables had returned to prelabour values. Haemodynamic changes of the magnitude found in this series are of considerable clinical relevance in managing mothers with complicated cardiovascular function.

Adult↗
PubMed1993

Transgastric continuous-wave Doppler to determine cardiac output.

A new method to measure cardiac output using transgastric continuous-wave Doppler was evaluated in 31 consecutive patients undergoing cardiac surgery with simultaneous measurement of cardiac output by the thermodilution technique. A 5 MHz single-plane imaging/5 MHz continuous-wave Doppler transesophageal transducer was used to image the left ventricular outflow tract, aortic valve and ascending aorta from a modified transgastric short-axis plane. The continuous-wave Doppler cursor was aligned parallel with blood flow across the aortic valve to obtain the maximal Doppler velocity spectra. Stroke volume was obtained by multiplying the mean Doppler flow velocity integral by the aortic annulus area, which was calculated from its diameter measured from the esophageal 5-chamber view. The stroke volume was multiplied by heart rate to yield cardiac output. A total of 57 simultaneous thermodilution and Doppler studies were attempted. Doppler data were technically limited for 2 patients both before and after cardiopulmonary bypass and for 3 patients before cardiopulmonary bypass with a result of 50 adequate studies of 57 (88%) attempted. The Doppler-derived cardiac outputs were correlated with the simultaneous measurements of cardiac output by the thermodilution technique. Linear regression analysis revealed a close correlation with R = 0.91, SEE = 0.8 liter/min, and y = 1.01x + 0.2 (p < 0.001). In conclusion, transgastric continuous-wave Doppler across the aortic valve is a promising new technique that may be used in selected patients for accurate measurement of cardiac output.

Cardiac Output↗
PubMed1993

Errors in the measurement of cardiac output by thermodilution.

Cardiac output (CO) determination by thermodilution, which was introduced by Fegler in 1954, has gained wide acceptance in clinical medicine and animal experiments because it has several advantages over other methods with respect to simplicity, accuracy, reproducibility, repeated measurements at short intervals, and because there is no need for blood withdrawal. However, errors in determination of CO by thermodilution may be introduced by technical factors and the patients' pathological conditions. The current review summarizes these issues and provides our recommendations, based on the medical literature published between 1954-1992. To obtain more reproducible and accurate CO values by thermodilution, one should make several determinations (1) by using 10 ml injectate at room temperature for adults and 0.15 ml.kg-1 injectate for infants and children; (2) at evenly spaced intervals of the ventilation cycle; (3) when rapid intravenous fluid administration is discontinued; (4) by observing thermodilution curves so that baseline pulmonary artery temperature drift or the existence of intra- and extracardiac shunts are noticed. Finally, CO determination by thermodilution may be unreliable or impossible in patients with low CO states and tricuspid or pulmonary regurgitation. Since non-invasive CO monitoring has not replaced CO determination by thermodilution, intimate knowledge of this method is crucial for anaesthetists to prevent errors in the management of patients.

Adult↗
PubMed1996

A comparison of the use of transoesophageal Doppler and thermodilution techniques for cardiac output determination.

Doppler cardiac output (CO) determination is discussed as a non-invasive alternative to CO estimation by thermodilution. This study was designed to compare the accuracy of a new transoesophageal Doppler device with the thermodilution technique. In 24 patients undergoing coronary artery bypass surgery, CO was determined simultaneously by the oesophageal Doppler (OD) and thermodilution (TD) method in triplicate for three sample episodes: after induction of anaesthesia during clinical steady-state conditions (A), after start of surgery (B), and after sternotomy (C). The agreement between ODCO and TDCO estimations was assessed by analysing the mean difference, indicating the systematic error, and analysing the distribution of differences between the two methods. The bias between ODCO and TDCO estimations was 0.38 (-0.06 to +0.81) L min-1 (mean and 95% confidence interval) for sample episode A, 0.48 (-0.11 to +1.1) L min-1 for sample episode B, and 0.69 (+0.08 to +1.3) L min-1 (P < 0.05 vs. zero) for sample episode C. Bias analysis of the log-transformed data revealed that 95% of the ODCO values differed from TDCO values by 43% below to 50% above for sample episode A, by 39% below to 95% above for sample episode B, and by 32% below to 96% above for sample episode C. Analysis of the changes in CO from sample episode A to B and from sample episode B to C, expressed as percentage values, showed a non-significant bias between the methods, but the 2 SD limits were +/-44% and +/-36% respectively. Our findings suggest that CO estimation by OD cannot replace estimation by the TD method.

Adult↗
PubMed1995

Effect of analyzer on determination of mixed venous PCO2 and cardiac output during exercise.

Cardiac output (CO) during exercise can be determined noninvasively by using the indirect Fick CO2-rebreathing technique. CO2 measurements for this technique are usually performed with an infrared analyzer (IA) or mass spectrometer (MS). However, IA CO2 measurements are susceptible to underreading in the face of high O2 concentrations because of collision broadening. We compared an IA (Ametek model CD-3A) with a MS (Marquette model MGA-1100) to see the effect this would have on mixed venous PCO2 (PVCO2) and CO measurements. After calibration with room air and a gas mixture of 5% CO2-12% O2-83% N2, both devices were tested with three different gas mixtures of CO2 in O2. For each gas mixture, IA gave lower CO2 values than did the MS (4.1% CO2: IA, 3.85 +/- 0.01% and MS, 4.13 +/- 0.01%; 9.2% CO2: IA, 8.44 +/- 0.07% and MS, 9.19 +/- 0.01%; 13.8% CO2: IA, 12.57 +/- 0.15% and MS, 13.82 +/- 0.01%). Warming and humidifying the gases did not alter the results. The IA gave lower values than did the MS for eight other medical gases in lower concentrations of O2 (40-50%). Equilibrium and exponential rebreathing procedures were performed. Values determined by the IA were > 10% higher than those determined by the MS for both rebreathing methods. We conclude that all IAs must be checked for collision broadening if they are to be used in environments where the concentration of O2 is > 21%. If collision broadening is present, then either a special high O2-CO2 calibration curve must be constructed, or the IA should not be used for both arterial PCO2 and PVCO2 estimates because it may produce erroneously low PVCO2 values, with resultant overestimation of CO.

Blood Gas Analysis↗
PubMed2004

Comparison of esophageal Doppler, pulse contour analysis, and real-time pulmonary artery thermodilution for the continuous measurement of cardiac output.

OBJECTIVE: Continuous measurement of cardiac output (CCO) is of great importance in the critically ill. However, pulmonary artery thermodilution has been questioned for possible complications associated with right heart catheterization. Furthermore, measurements are delayed in the continuous mode during rapid hemodynamic changes. A new pulmonary artery catheter CCO device (Aortech, Bellshill, Scotland) enabling real-time update of cardiac output was compared with 2 different, less-invasive methods of CCO determination, esophageal Doppler and pulse contour analysis. DESIGN: Prospective, observational study. SETTING: University hospital, single institution. PARTICIPANTS: Patients scheduled for elective coronary artery bypass grafting (CABG). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: CCO measurements were analyzed using a Bland-Altman plot. Bias between CCO and pulse contour cardiac output (PCCO), and Doppler-derived cardiac output (UCCO) was (mean +/- 1 SD) -0.71 +/- 1 L/min versus -0.15 +/- 1.09 L/min, and between UCCO and PCCO -0.58 +/- 1.06 L/min. Bias was not significantly different among methods, nor were comparative values before and after cardiopulmonary bypass (p > 0.05). CONCLUSIONS: Agreement between the CCO method and both less-invasive measurements was clinically acceptable. There were no adverse events associated with the use of either device.

Aged↗
PubMed2004

Measurement of cardiac output with indocyanine green transcutaneous fluorescence dilution technique.

BACKGROUND: Cardiac output is an essential parameter for the hemodynamic assessment of patients with cardiovascular disease. The authors tested in an animal model the feasibility of measuring cardiac output by transcutaneous fluorescence monitoring of an intravenous bolus injection of indocyanine green. METHODS: Fluorescence dilution cardiac output was measured in 10 anesthetized rabbits and compared with cardiac output measured with a pulmonary thermodilution catheter and to aortic velocity measured by Doppler ultrasound. Indocyanine green fluorescence was excited with a near-infrared laser and measured with an optical probe positioned on the central ear artery. Measurements were obtained during baseline conditions as well as during short-term decreases and increases of the cardiac output. RESULTS: The fluorescence of circulating indocyanine green detected transcutaneously varied proportionally to that of arterial blood samples, which allowed for calibration in terms of blood concentration of indocyanine green. Average values of fluorescence dilution cardiac output and thermodilution cardiac output measured in baseline conditions were 412 (+/- 13) and 366 (+/- 11) ml/min, respectively. Fluorescence dilution cardiac output showed a close, one-to-one linear relation with thermodilution cardiac output in each animal and in the pooled data from all animals (slope = 0.95 x 0.03; R = 0.94). Fluorescence dilution cardiac output overestimated thermodilution cardiac output by an average of 46 (+/- 6) ml/min during baseline conditions. Fluorescence dilution cardiac output was tightly correlated with aortic velocity. CONCLUSIONS: The proposed technique yielded accurate estimates of the cardiac output in experimental animals. This study should provide an initial framework for clinical testing of this new minimally invasive method for measuring cardiac output.

Animals↗
PubMed1985

Doppler echocardiographic measurement of cardiac output using the mitral orifice method.

Cardiac output was determined in 20 patients with various cardiac conditions by measuring the cross sectional area of the mitral orifice by echocardiography and the transmitral flow by the Doppler technique. Cardiac output was calculated by multiplying the corrected mitral orifice area by the maximum diastolic velocity integral recorded by the pulsed mode. The results were compared with that obtained by the Fick method. The correlation for cardiac output by the two techniques was high in the whole group, particularly in patients without mitral regurgitation. There was also a good correlation for stroke volume determined by the two methods. Cardiac output was significantly overestimated by the continuous mode and in patients with mitral regurgitation. These results show that the mitral orifice method provides a new and reliable approach to the non-invasive measurement of cardiac output.

Adolescent↗
PubMed1993

Pulsed Doppler transesophageal echocardiographic determination of cardiac output in human beings: comparison with thermodilution technique.

Measurement of cardiac output is a clinically valuable and widely used index of cardiac function. Although transesophageal echocardiography has been used to assess left ventricular function, little data exist on the accuracy of this technique in the measurement of cardiac output. Therefore cardiac output derived by pulsed Doppler transesophageal echocardiography and thermodilution methods were compared in adult patients being mechanically ventilated. The left ventricular outflow tract diameter was determined from a transgastric long-axis view of the left ventricle by using the transverse plane and longitudinal plane of the transesophageal scope. The cross-sectional area of the left ventricular outflow tract was calculated from the diameter assuming a circular shape. Pulsed Doppler recordings were obtained at the left ventricular outflow tract. Doppler time-velocity integrals were measured from the leading edge of the velocity curve. Cardiac output derived by transesophageal echocardiography was calculated as time-velocity integral multiplied by left ventricular outflow tract area and heart rate. Cardiac output derived by transesophageal echocardiography from the transverse plane (n = 26) and longitudinal plane (n = 22) were correlated with simultaneous thermodilution measurements. Thermodilution-derived cardiac output demonstrated excellent correlation with cardiac output measured by using transesophageal echocardiography from the transverse plane (r = 0.97, SEE = 0.84 L/min; p < 0.0001) and longitudinal plane (r = 0.95, SEE = 0.97 L/min; p < 0.0001). Transesophageal echocardiography is a promising technique in the measurement of cardiac output and expands the clinical use of this modality in the assessment of cardiac function.

Adult↗
PubMed1992

[Direct effects of prostaglandin E1 on renal blood flow and renal function during acute reduction of cardiac output in dogs].

During low cardiac output state induced by inflating the balloons inserted into both superior and inferior caval veins, direct effects of PGE1 (10 ng.kg-1.min-1, infused into renal artery) on renal blood flow and renal function were investigated. In control group, acute reduction of cardiac output resulted in decrease of renal blood flow (RBF) and significant increase of filtration fraction (FF), suggesting tight constriction of the efferent arteriole by activation of renin-angiotensin system and sympathetic nervous system. In PGE1 group, glomerular filtration rate (GFR) and FF decreased significantly although there was no decrease in RBF. No significant change was seen in distribution of intrarenal blood flow during low cardiac output state in both groups. These results indicate that decrease in GFR by direct infusion of PGE1 into renal artery during low cardiac output state is probably due to reduction of glomerular filtration pressure produced by dominant inhibition of the efferent arteriole constriction rather than the inhibition of the afferent arteriole by PGE1.

Acute Disease↗
PubMed1984

Exercise cardiac output is maintained with advancing age in healthy human subjects: cardiac dilatation and increased stroke volume compensate for a diminished heart rate.

To assess the effect of age on cardiac volumes and function in the absence of overt or occult coronary disease, we performed serial gated blood pool scans at rest and during progressive upright bicycle exercise to exhaustion in 61 participants in the Baltimore Longitudinal Study of Aging. The subjects ranged in age from 25 to 79 years and were free of cardiac disease according to their histories and results of physical, resting and stress electrocardiographic, and stress thallium scintigraphic examinations. Absolute left ventricular volumes were obtained at each workload. There were no age-related changes in cardiac output, end-diastolic or end-systolic volumes, or ejection fraction at rest. During vigorous exercise (125 W), cardiac output was not related to age (cardiac output [1/min] = 16.02 + 0.03 [age]; r = .12, p = .46). However, there was an age-related increase in end-diastolic volume (end-diastolic volume [ml] = 86.30 + 1.48 [age]; r = .47, p = .003) and stroke volume (stroke volume [ml] = 85.52 + 0.80 [age]; r = .37, p = .02), and an age-related decrease in heart rate (heart rate [beats/min] = 184.66 - 0.70 [age]; r = -.50, p = .002). The dependence of the age-related increase in stroke volume on diastolic filling was emphasized by the fact that at this high workload end-systolic volume was higher (end-systolic volume [ml] = 3.09 + 0.65 [age]; r = .45, p = .003) and ejection fraction lower (ejection fraction = 88.48 - 0.18 [age]; r = -.33, p = .04) with increasing age. These findings indicate that although aging does not limit cardiac output per se in healthy community-dwelling subjects, the hemodynamic profile accompanying exercise is altered by age and can be explained by an age-related diminution in the cardiovascular response to beta-adrenergic stimulation.

Adult↗
PubMed1990

[Continuous measurement of cardiac output based on the Fick principle in cardiac anesthesia].

With the development of fiberoptic and pulse oximetry, as well as the development of the more modern methods of oxygen consumption measurements, the online monitoring of Fick cardiac (FCO) output has become possible in the clinical treatment routine. The aim of this study was to compare fiberoptically measured mixed venous oxygen saturation with values from blood samples and continuously determined Fick cardiac output with intermittent thermodilution cardiac output (TCO). Ten patients undergoing coronary artery bypass grafting were measured during the perioperative period. Total body oxygen consumption was determined with a metabolic monitor (Deltatrac Datex) from respiratory gases. Arterial oxygen saturation was assessed by pulse oximetry (Nellcor). Mixed venous oxygen saturation was measured by a balloon tipped pulmonary artery fiberoptic catheter (Opticath) attached to an electronic device based on three wavelengths (Oximetrix cardiac output monitor). Hemoglobin, Methemoglobin and CO-hemoglobin were determined from intermittent blood samples by in vitro analysis. FCO was calculated from corresponding differences in arterial mixed venous oxygen and total body oxygen consumption. TDCO values were calculated from microcomputer recordings of the thermodilution data by monoexponential curve-fitting with respect to baseline drift. A significant systematic difference between FCO and TCO was observed. FCO exceeded TCO on average by 0.42 +/- 0.12 l/min. The limits of confidence (95%) were 0.18 to 0.66 l/min. There was no systematic difference between mixed venous saturation measurements with the fiberoptic system and from blood samples. The cardiac output values derived from fiberoptic and pulse oximetry can be considered sufficiently reliable for clinical purposes.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1987

Thermodilution cardiac output determination in the guinea pig.

Thermodilution cardiac output was compared with simultaneously determined aortic flow in 5 guinea pigs during thoracotomy. Total cardiac output was affected by volume expansion, adrenergic stimulation, and the volume of hemorrhage. For the equation y = mx, where y is aortic flow, x is thermodilution cardiac output, and m is the slope of the regression line, m = 0.88 +/- 0.02 (95% confidence interval). The SE of the regression was 27.8 ml/min. Thermodilution may have been overestimated because the aortic flow measurement did not take into account the coronary arterial blood flow, which is approximately 4% of total cardiac output in the guinea pig. Indicator loss (ie, temperature) also may be an important factor in the calculation of cardiac output, as determinations of thermodilution cardiac output were affected by sampling site in the guinea pig. Thermodilution appears to be a useful and reliable means of determining cardiac output in the guinea pig.

Animals↗
PubMed1983

A removable extraluminal Doppler probe for continuous monitoring of changes in cardiac output.

To address the problem of monitoring cardiac output in postoperative cardiac patients, a removable, extraluminal pulsed Doppler probe has been constructed which continuously reflects changes in cardiac output by monitoring blood velocity in the ascending aorta. Velocity is related to the frequency of the Doppler shift and the angle at which the ultrasound beam intersects the vessel. A 1 mm2 piezoelectric crystal mounted at a 45 degree angle on the tip of the probe is activated with a 20-MHz range-gated pulsed Doppler, and velocity is determined from Fourier analysis of quadrature data using computer software with a 50-KHz processing range. The device is designed for application to the ascending aorta at the conclusion of a cardiac surgical procedure; and, since mean diameter changes in the ascending aorta have been shown to be very small over a wide range of mean aortic pressures, cardiac output is linearly related to velocity. To test this technique, simultaneous recordings were made from the pulsed Doppler probe and an electromagnetic flow probe in five mongrel dogs over a range of cardiac outputs from 0.5 to 6 l/min for a total of 136 data points. Excellent correlation was found between the electromagnetic flow probe and pulsed Doppler probe data (average r = .98 +/- .006). Average slope between the two was 1.004 and average zero intercept was -0.025 l/min. The catheter is small, stable, has no baseline drift, and continuously and accurately reflects pulsatile changes at high and low flows.

Animals↗