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PubMed2004

Respiratory measurements of cardiac output: from elegant idea to useful test.

The measurement of cardiac output was first proposed by Fick, who published his equation in 1870. Fick's calculation called for the measurement of the contents of oxygen or CO2 in pulmonary arterial and systemic arterial blood. These values could not be determined directly in human subjects until the acceptance of cardiac catheterization as a clinical procedure in 1940. In the meanwhile, several attempts were made to perfect respiratory methods for the indirect determination of blood-gas contents by respiratory techniques that yielded estimates of the mixed venous and pulmonary capillary gas pressures. The immediate uptake of nonresident gases can be used in a similar way to calculate cardiac output, with the added advantage that they are absent from the mixed venous blood. The fact that these procedures are safe and relatively nonintrusive makes them attractive to physiologists, pharmacologists, and sports scientists as well as to clinicians concerned with the physiopathology of the heart and lung. This paper outlines the development of these techniques, with a discussion of some of the ways in which they stimulated research into the transport of gases in the body through the alveolar membrane.

Cardiac Output↗
PubMed1984

Cardiac output, oxygen consumption and renal blood flow in essential hypertension.

Cardiac output, oxygen consumption, total blood volume and mean circulatory transit time were investigated at rest in men with sustained essential hypertension in comparison with normal subjects of the same age and sex. In normal subjects and in patients with hypertension, oxygen consumption was positively correlated to cardiac output. In hypertensives, the slope of the curve was significantly shallower with an increase in arteriovenous oxygen difference. Oxygen consumption in both populations was negatively correlated with mean circulatory transit time but not with total blood volume. In normal subjects, mean circulatory transit time and arteriovenous oxygen difference were positively correlated. The correlation was not significant in hypertensive patients. The study suggests important abnormalities in the transport and cost of energy in erythrocytes of patients with sustained essential hypertension.

Adult↗
PubMed1993

Relationship of oxygen consumption and cardiac output to work of breathing.

This study examined the relationship between work of breathing and estimated blood flow to and oxygen consumption by the respiratory muscles. Five subjects performed inspiratory loaded breathing and voluntary hyperpnea while ventilatory work, cardiac output, and oxygen consumption were measured. Blood flow to and oxygen consumption by the respiratory muscles were estimated by subtracting the resting from the working values of cardiac output the oxygen consumption, respectively. Loaded breathing increased cardiac output, but there was no significant correlation with work of breathing, while oxygen consumption was significantly correlated with work of breathing. During hyperpnea both cardiac output and oxygen consumption were correlated with work of breathing. Our results indicate that blood flow and oxygen consumption are increased in a regular pattern with increases in work of breathing. These results may be significant in estimating the demand of the respiratory muscles in disease and exercise.

Analysis of Variance↗
PubMed1981

Thermodilution cardiac output--a systematic error.

The purpose of this study was to examine the mechanism and magnitude of a systematic error in thermodilution cardiac output measurement. One hundred and seventy-one thermodilution cardiac output measurements in dogs using a Swan-Ganz catheter were compared with simultaneously made dye dilution measurements under different conditions over a wide range of cardiac outputs. A systematic error with the thermodilution technique was confirmed and was almost identical to that observed in the literature. It is proposed that its mechanism is loss of thermal indicator between the injectate orifice and detection. Application of a further correction factor for thermal indicator loss is suggested.

Animals↗
PubMed1992

Accuracy of the BoMED NCCOM3 bioimpedance cardiac output monitor during induced hypotension: an experimental study in dogs.

Changes in thoracic electrical bioimpedance during the cardiac cycle are utilised by the BoMed NCCOM3 monitor to measure cardiac output (COTEB). The technique provides a continuous noninvasive measurement but it has not been widely accepted. To determine the accuracy of the monitor, we compared its measurement with cardiac output measured by dye dilution (CODD) during induced hypotension and recovery in 23 dogs. After calibration of the NCCOM3 monitor during a resting state in each dog [mean blood pressure 112 +/- 17 (SD), mean CODD 3.22 +/- 0.99 l/min], the mean difference (COTEB-CODD) between paired measurements at the nadir of hypotension (blood pressure 55 +/- 24 mmHg) was 0.29 +/- 0.47 l/min whose limits of agreement (mean difference +/- 2 SD) were + 111.8% and -59.1% of the mean hypotensive CODD (1.10 +/- 0.66 l/min). Upon recovery from hypotension (mean blood pressure 102 +/- 20 mmHg), the mean difference between paired measurements was -0.28 +/- 0.66 l/min, whose limits of agreement were +44.1% and -67.8% of the mean CODD (2.36 +/- 1.01 l/min). The mean difference between the two techniques is too variable and excessive to permit substitution of one technique for the other. These results do not support the accuracy and reliability of the BoMed NCCOM3 cardiac output monitor.

Animals↗
PubMed1999

Non-invasive cardiac output determination: state of the art.

This review deals with recent developments in non-invasive cardiac output measurement. In the past few years significant progress has been made with semi-invasive transoesophageal echocardiography; the method now provides advanced facilities to measure cardiac output and other important characteristics of cardiac function. The method is, however, operator-dependent and the equipment used is expensive, which means that large-scale use on intensive care patients is not feasible. Whole-body impedance cardiography has recently shown good accuracy and flexibility in use, and seems to be the most promising method for the non-invasive measurement of cardiac output.

Journal Article↗
PubMed1991

[Evaluation of maintenance of cardiac output during DDD and VVI pacing by exercise Doppler echocardiography].

To evaluate the efficacy of DDD pacing for cardiac reserve, we assessed increases in the stroke volume and cardiac output during randomized treadmill exercise in 16 patients by DDD and fixed-rate ventricular (VVI) pacing. The stroke volume index and cardiac index were determined using suprasternal Doppler measurements. Ten patients who showed sinus rhythm during exercise were excluded from this study. Compared with the findings during VVI pacing, those during DDD pacing showed: 1) a greater exercise-induced positive chronotropic response (mean maximum heart rate 122 +/- 22 beats/min vs 70 beats/min, p < 0.01), 2) a lesser increase in the stroke volume index (34 +/- 7 to 39 +/- 9 ml/m2 vs 31 +/- 7 to 49 +/- 11 ml/m2, p < 0.05), 3) a greater increase in the cardiac index (2.43 +/- 0.45 to 4.48 +/- 1.36 L/min/m2 vs 2.22 +/- 0.47 to 3.43 +/- 0.45 L/min/m2, p < 0.05), and 4) prolongation of exercise duration (6.35 +/- 2.00 min vs 5.97 +/- 1.81 min, NS). These findings indicated that VVI pacing promoted a greater stroke volume than DDD pacing, which provides a compensatory increase in contractility and the preload in cases without an increase in heart rate during exercise, however, the increase in cardiac output was insufficient due to the absence of a chronotropic response. In conclusion, a DDD pacemaker could effectively increase heart rate, causing a significant increase in cardiac output and extending exercise duration.

Adult↗
PubMed1999

Cardiac output can be reliably measured noninvasively after coronary artery bypass grafting operation.

OBJECTIVE: To evaluate the reliability of whole-body impedance cardiography in the measurement of cardiac output after coronary artery bypass grafting operation in comparison with the thermodilution method. DESIGN: Prospective, consecutive sampling. PATIENTS: A total of 82 patients undergoing coronary artery bypass surgery were investigated. In a group of 41 patients who were intubated, cardiac output measurements were taken simultaneously with whole-body impedance cardiography and the thermodilution method within the first 3 hrs after the operation (early intensive care unit [ICU] period). In another group of 41 patients, the measurements were taken before the operation and in the second 12 hrs after cardiac surgery (late ICU period). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The agreement between the thermodilution and whole-body impedance cardiography cardiac output measurements was good before the operation, bias 0.04 +/- 1.64 L/min (n = 41), and in the late ICU period, bias 0.00 +/- 1.84 L/min (+/-2 SD) (n = 41). The results were within 20% in 81%-85% of the cases. The agreement was satisfactory in the early ICU period, bias 0.38 +/- 2.74 L/min (n = 41). It was presumed that thermal instability of the patients was one possible source of measurement errors in the thermodilution method, causing reduced agreement between the methods in this period. The repeatability values (rv = 2.83 x SDs) for whole-body impedance cardiography were 0.44 L/min before the operation, 0.30 L/min in the early ICU period, and 0.65 L/min in the late ICU period, being significantly better than for the thermodilution method (0.79, 0.51, and 1.11 L/min, respectively) in all phases of the investigation (p < .001). The agreement between the thermodilution method and whole-body impedance cardiography is similar to reported comparisons between invasive methods in analogous settings. CONCLUSIONS: Whole-body impedance cardiography reliably measures cardiac output in patients after coronary artery bypass grafting operation. The excellent repeatability of whole-body impedance cardiography enhances the value of the method in continuous monitoring of patients after the operation.

Aged↗
PubMed1981

Cardiac output during cardiopulmonary resuscitation at various compression rates and durations.

Cardiac output during cardiopulmonary resuscitation (CPR) was measured by a modified indicator-dilution technique in 20 anesthetized dogs (6-12 kg), during repeated 1- to 2-min episodes of electrically induced ventricular fibrillation, by a mechanical chest compressor and ventilator. With compression rates from 20 to 140/min and compression durations (duty cycles) from 10 to 90% of cycle time, cardiac output (CO) was predicted by the equation: CO = CR . SVmax . [DC/(k1 . CR + DC)] . [(1 -- DC)/k2 . CR + 1 - DC)], where CR is compression rate, DC is duty cycle, SVmax (19 ml) is the effective capacity of the pumping chamber, and k1 (0.00207 min) and k2 (0.00707 min) are ejection and filling constants. This expression predicts maximal CO for DC = 0.40 and cR = 126/min and 90-100% of maximal CO for 0.3 less than DC less than 0.5 and 70 less than CR less than 150/min. Such mathematical analysis may prove useful in the optimization of CPR.

Animals↗
PubMed1979

The 24 hour cycle and nocturnal depression of human cardiac output.

The NASA-developed version of the impedance plethysmographic method for the determination of left ventricular stroke volume was applied to the investigation of daily variation of cardiovascular function. Hourly determinations of cardiac output and arterial pressure (auscultation) were obtained from two male subjects over the course of a 48-h period in the laboratory. Cardiac output displayed a strong 24-h cycle of nearly 1 1/min, peak-to-peak, cresting in the late evening hours. Nocturnal sleep was associated with a reduction of cardiac output characterized by a minimum in the early morning hours. It was concluded that a nocturnal, 24-h cyclic depression of waking cardiac output is exacerbated during sleep periods, and mechanisms for this exacerbation were suggested.

Adult↗
PubMed1986

Effect of injectate volume and temperature on thermodilution cardiac output determination.

Six combinations of injectate volume (10, 5, and 3 ml) and temperature (0 degree C and room temperature [RT]) are recommended by the manufacturers of thermodilution cardiac output catheters and computers. We prospectively studied the accuracy and variability associated with these six combinations in critically ill patients requiring intermittent mandatory ventilation. The six methods were similar in their average estimation of cardiac output but differed markedly in their reproducibility. The 10 ml 0 degree C and 10 ml RT combinations produced the least variability. The 5 ml 0 degree C and 5 ml RT combinations produced more variability. Variability was much greater with the remaining two combinations. The 3 ml RT combination resulted in an average range of 1.71 1/min within each set of three repeat measurements and an average absolute difference of 1.51 1/min from the values obtained with 10 ml 0 degree C (each the mean of three injections). We recommend the use of 10 ml 0 degree C or 10 ml RT for cardiac output determinations in critically ill patients. If it is important to minimize volume administration, the use of 5 ml injectate is acceptable for an estimation of cardiac output. The use of 3 ml injectate volumes is rarely, if ever, justified because the small reduction in volume administration results in a large increase in variability.

Adult↗
PubMed2004

Load dependence of cardiac output in biventricular pacing: right ventricular volume overload in pigs.

BACKGROUND: Previous work from our laboratory has demonstrated that optimization of biventricular pacing is load dependent. During acute pulmonary stenosis and right ventricular pressure overload in swine, cardiac output was maximized by pacing the right ventricle 40 ms before the left ventricle. To extend those studies, this experiment examined biventricular pacing optimization during right ventricular volume overload. METHODS: After median sternotomy in 6 anesthetized domestic pigs, complete heart block was induced by ethanol ablation. A conduit was grafted from the right ventricle to the right atrium to simulate tricuspid insufficiency. During epicardial, atrial tracking DDD biventricular pacing, atrioventricular delay was varied between 60 and 180 ms in 30-ms increments. Right ventricular-left ventricular delay was varied at each atrioventricular delay from +80 ms (right ventricle first) to -80 ms (left ventricle first) in 20-ms increments. Aortic flow, right ventricular pressure, and electrocardiogram were measured at each pacemaker setting with the graft clamped and unclamped. RESULTS: Atrioventricular and right ventricular-left ventricular delays had no significant effect on cardiac output with the graft clamped. With the graft unclamped, however, there was a statistically significant (P =.003 by mixed modeling repeated measures analysis of variance) trend toward higher cardiac output with left ventricle-first pacing. CONCLUSION: Left ventricle-first biventricular pacing in swine significantly increased cardiac output during acute tricuspid insufficiency but not during the control state. Trials are warranted to develop clinical biventricular pacing for treatment of perioperative right ventricular dysfunction.

Animals↗
PubMed1998

[Estimation of cardiac output by first-pass data with technetium-99m-labeled myocardial perfusion imaging agent].

Technetium-99m-tetrofosmin, a myocardial perfusion imaging agent was used for estimation of cardiac output by means of first-pass radionuclide angiography performed in the anterior projection. Region of interests (ROIs) were assigned over right ventricle, left ventricle and whole chest, and time activity curves (TACs) were obtained. Cardiac output indices (COIs) were calculated by the following equation; COI = p3/2. Qc/[symbol: see text] A(s)ds, where p = number of pixels of the ventricular ROI, Qc = the peak count rate of the TAC obtained from the whole chest's ROI and [symbol: see text] A(s)ds = the area under ventricular TAC. The COI (y) determined by ROI over the left ventricle yield the best correlation with the cardiac output by conventional radionuclide method (x) (y = 0.0381x + 6.22, r = 0.828, n = 48, p < 0.001). In conclusion, cardiac output can be easily measured with first pass data using myocardial perfusion imaging agent.

Adult↗
PubMed1986

Continuous noninvasive estimation of cardiac output by electrical bioimpedance: an experimental study in dogs.

A new device has been developed to estimate continuously and noninvasively cardiac output from the thoracic electrical bioimpedance (CObi). CObi was compared to cardiac output by thermodilution (COtd) in five anesthetized dogs. Blood pressure, blood volume, and blood flow were manipulated by hemorrhage and infusions of sodium nitroprusside and phenylephrine. These data were used to determine the correlation between CObi and COtd under conditions of hypotensive normal flow and normotensive low flow, as well as during hemorrhagic shock and resuscitation. The CObi device was calibrated in vivo to COtd for each dog at the beginning of each experiment. CObi had a significant positive correlation with COtd throughout the experiments (r = 0.84, slope = 0.91, intercept = 0.55, p less than 0.01), and CObi predicted COtd with a standard error of the estimate of 0.81 L/min. Neither heart rate nor mean arterial pressure was significantly correlated with COtd or CObi. During severe hemorrhagic shock, CObi could not determine cardiac output in two of the dogs when COtd averaged 1.7 L/min. These data indicate that CObi is a blood-flow related variable that can be monitored continuously.

Animals↗
PubMed2005

Temporal stability of ambulatory stroke volume and cardiac output measured by impedance cardiography.

UNLABELLED: Recently, devices have become available that allow non-invasive measurement of stroke volume and cardiac output through ambulatory thorax impedance recording. If such recordings have adequate temporal stability, they offer great potential to further our understanding of how repeated or chronic cardiovascular activation in response to naturalistic events may contribute to cardiovascular disease. In this study, 24 h ambulatory impedance-derived systolic time intervals, stroke volume and cardiac output were measured in 65 healthy subjects across an average time span of 3 years and 4 months. Stability was computed separately for sleep and daytime recordings. To avoid confounding by differences in posture and physical activity across measurement days, temporal stability was computed using sitting activities only. During the day intraclass correlations were moderate for stroke volume (.29-.46) and cardiac output (.33-.46) and good for systolic time intervals (.55-.81). When test-retest comparison was limited to two comparable days (two work days or two leisure days), correlations for both SV (.42-.46) and CO (.43-.50) improved. CONCLUSION: Moderate long-term temporal stability is found for individual differences in ambulatory stroke volume and cardiac output measured by impedance cardiography.

Adult↗
PubMed1990

Influence of splanchnic intravascular volume changes on cardiac output during muscarinic receptor stimulation in the anaesthetized dog.

The direct influence of systemic muscarinic receptor stimulation on total splanchnic intravascular volume and the splanchnic organs responsible for the total splanchnic volume change associated with muscarinic receptor stimulation in the animal with an intact circulation are unknown. Furthermore, the subsequent effect of these volume changes on cardiac output is not known. Thus, acetylcholine was infused at 5 micrograms kg-1 min-1 in 25 anaesthetized dogs in which nicotinic blockade of the ganglia was achieved with mecamylamine, while total and regional splanchnic intravascular volume changes were determined with a radionuclide imaging technique. Total splanchnic volume decreased by 4.9 +/- 1.0% (P less than 0.0001), splenic volume decreased by 10.3 +/- 2.0% (P less than 0.0001), hepatic volume increased by 5.8 +/- 1.4% (P less than 0.01), extrahepatosplenic volume increased by 6.6 +/- 1.6% (P less than 0.01) and cardiac output increased from 1960 +/- 190 to 2290 +/- 230 ml min-1 (P less than 0.001). After splenectomy (n = 13), the hepatic and extrahepatosplenic volume increments were abolished, and the increase in cardiac output was not attenuated (1600 +/- 260 to 2040 +/- 370 ml min-1). After subsequent evisceration (n = 5), the cardiac output increment associated with acetylcholine was still not attenuated. Acetylcholine-associated splanchnic volume changes were abolished after muscarinic receptor blockade with atropine. Thus, muscarinic receptor stimulation causes a decrease in total splanchnic volume due entirely to a decrease in splenic volume. The splanchnic volume changes do not influence cardiac output.

Acetylcholine↗
PubMed1995

Influence of simulated microgravity on cardiac output and blood flow distribution during exercise.

Rats exposed to simulated conditions of microgravity by head-down suspension (HDS) exhibit reductions in aerobic capacity. This may be due to an impaired ability to augment cardiac output and to redistribute blood flow during exercise. The purpose of this investigation was to measure cardiac output and blood flow distribution in rats that were exposed to 14 days of HDS or cage control conditions. Measurements were obtained at rest and during light-intensity (15 m/min) and heavy-intensity (25 m/min; 10% grade) treadmill exercise. Cardiac output was similar in HDS and cage control rats at rest and light exercise but was significantly lower in HDS rats (-33%) during heavy exercise. Soleus muscle blood flow (ml/min) was lower at rest and during exercise in HDS rats; however, when expressed relative to muscle mass (ml.min-1.100 g-1), soleus blood flow was lower only during light exercise. Plantaris muscle blood flow was lower in HDS rats during heavy exercise. Blood flow to the ankle flexor, knee extensor, and knee flexor muscles was not altered by HDS. Blood flow to the spleen and kidney was significantly higher in HDS rats. It was concluded that the reduction in aerobic capacity associated with HDS is due in part to an impaired ability to augment cardiac output during exercise.

Animals↗
PubMed2000

Is the placement of a pulmonary artery catheter still justified solely for the measurement of cardiac output?

OBJECTIVE: The authors compared four clinical techniques of measuring cardiac output (CO) in critically ill patients: pulmonary artery thermodilution (CO[PA]), transpulmonary aortic thermodilution (CO[AORTA]), Fick principle-derived (CO[FICK]), and continuous pulmonary artery (CCO) measurements. DESIGN: Prospective clinical study. SETTING: Surgical intensive care unit of a university hospital. PARTICIPANTS: Twelve adult patients suffering from sepsis or septic shock. INTERVENTIONS: All patients were deeply sedated and mechanically ventilated in a pressure-controlled mode. Each patient received a 7.5F five-lumen pulmonary artery catheter for the continuous measurement of cardiac output and a 4F aortic catheter with an integrated thermistor. The thermistors of the two different catheters were connected to one computer system (COLD-Z021, Pulsion Medical Systems, Munich, Germany). Whole-body oxygen consumption was measured by indirect calorimetry using a metabolic cart (Deltatrac, Datex-Engstroem, Helsinki, Finland) over a 5-minute period, at the end of which arterial and mixed venous blood gases were taken and measured by co-oximetry. During each measuring period, three bolus CO measurements were performed. A total number of 51 CO measurements was analyzed. RESULTS: Linear regression analysis revealed the highest correlation between CO(AORTA) and CO(PA) (r = 0.98), whereas agreement between these two techniques and CCO was lower (r = 0.92 and r = 0.93). All three techniques correlated comparably with CO(FICK) (r = 0.85, r = 0.83, and r = 0.83). CONCLUSION: The correlations among the four CO techniques were high and similar, with CO(PA) and CO(AORTA) techniques showing the highest agreement. Because CO with similar accuracy can be obtained from transpulmonary aortic thermodilution in a less-invasive manner, it appears that the placement of a pulmonary artery catheter solely for the measurement of CO is no longer justified, unless continuous CO measurements are needed.

Adult↗