Thermal Dilution Method Research Articles

Model Study of Cardiac Output Measurement by Thermodilution in Thermal Instability

Cardiac output is one of the most valuable hemodynamic parameter. It is measured commonly with intravascular pressures by pulmonary artery catheterization technique. The cardiac output itself is measured by dilution of thermal marker method (thermodilution), which is not resistant for various disturbances. In this paper the influence of blood temperature on metrological properties of thermal dilution method was described.

Aggressive Coiling of Aortopulmonary Collaterals in Single-Ventricle Patients Is Warranted

Aortopulmonary collaterals (APCs) are present in up to 80% of single-ventricle patients undergoing pre-Fontan catheterization [5, 7, 13, 14]. It is theorized that hypoxia is a potent stimulus for the development of APCs [17]. No general consensus exists as to their impact on the midto long-term course of single-ventricle patients. Bradley et al. [2] argued that their presence in the immediate postoperative period after Fontan repair had no impact on the duration of pleural effusions or resource use with regard to length of mechanical ventilation, intensive care unit (ICU), stay, or hospital stay. Although their findings were counterintuitive, even to the authors, this single study has been used as justification to ignore aortopulmonary collaterals not only at the pre-Fontan catheterization but also in the long term at a number of centers (informal polling and personal communication). In the centers performing catheter occlusion of APCs, the criteria for occlusion are subjective and qualitative or based on hemodynamic data that have not been validated in terms of defining what significant APC flow is. Some centers rely on an oxygen step-up from the superior vena cava to branch pulmonary arteries to determine which vessels to occlude in which patients. However, it is clear that many patients would be excluded from catheter occlusion using only this parameter given that collateral flow often enters the lungs distal to the site of sampling. Some centers use filling defects from APC competitive flow noted on pulmonary artery (PA) imaging to discern the degree of negative washout from collaterals (Fig. 1). Some try to gauge the pulsatility of the branch PAs to assess the significance of flow, and some use the PA pressures and end-diastolic pressure measurement of the single ventricle, assuming elevated values are due to volume overloading. Others use the size of APCs, the density of the pulmonary capillary blush (Fig. 2), and opacification of the pulmonary venous return to decide when to occlude. The aforementioned parameters, either singly or in combination, may provide clues as to the volume of collateral flow but can be used only as rough guides. Bradley et al. [2] addressed this issue by quantitating APC flow as the volume of blood returning from the pulmonary venous vent during Fontan surgery [2]. They conceded, however, that their methods were nonphysiologic because flow was measured during hypothermic cardiopulmonary bypass and certainly did not represent a real-life situation. Lim et al. [15] quantitated APC flow using thermal indicator dilution methods in a more physiologic state during the pre-Fontan catheterization, but patients with significant semilunar or atrioventricular valve insufficiency invalidated this technique and were excluded from their study, disqualifying an important subset of patients [10]. In addition, these invasive techniques to evaluate APC flow made it difficult to follow cases in a longitudinal manner. Magnetic resonance imaging (MRI) assessment of PA and pulmonary vein flow using phase-contrast velocity mapping is a promising and accurate noninvasive method for calculating APC flow at the pre-Fontan catheterization and beyond, but it is expensive and time consuming and usually requires general anesthesia [15]. Finally, the long-term impact of permanently occluding vessels off the subclavian arteries and thoracic descending aorta is unknown. A syndrome of chest pain, irritability, and low-grade fevers lasting 3 to 5 days is common after occlusion. Given this backdrop, what is an interventionalist H. J. Stern (&) Cardiology, Stern Cardiology, PC, 4324 Quail View Rd., Charlotte, NC 28226, USA e-mail: tocathu@gmail.com

Measurement of extravascular lung water in patients with pulmonary edema

measurement of extravascular lung water has been a topic of major interest for more than two decades ([1][1], [5][2], [19][3]). In the recent article by Effros et al. ([2][4]), they provide a review of current and past efforts to measure extravascular lung water with thermal and osmotic dilution

Comparison of thermal dilution and electrical impedance dilution methods for measurement of cardiac output in standing and exercising horses

To compare cardiac output measured in the pulmonary artery and a carotid artery by use of thermal and electrical impedance dilution. Animals-7 fit, clinically normal Standardbreds between 2 and 5 years of age. Transient changes in electrical impedance and temperature of blood were induced by bolus injections of ice-cold saline hypertonic (6% and 9% NaCl) solutions. Cardiac output was calculated by applying Stewart-Hamilton principles to the indicator dilution transients. Measurements were made during sequential exercise episodes on a level treadmill over approximately an 8-fold range of cardiac output values. We detected agreement between cardiac output determined by use of electrical impedance dilution at the pulmonary artery and carotid artery. Cardiac output from thermal dilution measured at the carotid artery exceeded that measured at the pulmonary artery. Cardiac output from the thermal dilution technique exceeded cardiac output from the electrical impedance dilution technique at both locations. The electrical impedance indicator is conserved on first transit; therefore cardiac output measured by electrical impedance dilution at the carotid artery is reliable over a large range of values. Thermal dilution provides a larger estimate of cardiac output, compared with the electrical impedance dilution technique, probably because of a loss of indicator. The transpulmonary electrical impedance dilution technique may have potential for clinical application, particularly in animals in which catheterization of the pulmonary artery is not appropriate or blood loss must be minimized.

Enhanced cardiac thermal dilution measurement of cardiac output, volumes, regurgitation, valve effective diameters, ventricular power and efficiency – Feasibility analysis using digital simulation

Cardiac output is measured by the thermal dilution method which uses a quadruple lumen catheter, with a thermistor on the tip, through the right atrium, right ventricle and into the pulmonary artery. Cold saline is injected into the right atrium and the resulting pulmonary artery temperature profile is integrated. The same procedure performed with three thermistors and three pressure sensors located on the catheter to measure temperature and pressure in the atrium, ventricle and artery respectively will produce a set of temperature and pressure curves with shapes determined by injectate temperature, injectate volume, heart rate, systolic time interval, body temperature, cardiac output, volumes, flow rates and valve openings. A digital computer program has been developed to optimize the fit of a lumped parameter model to the thermodilution curves in order to determine heart rate, systolic time as a fraction of cardiac cycle, right atrial systolic and diastolic volumes, ventricular systolic and diastolic volumes, cardiac output, inflow valve forward and reverse flow rates and effective diameters, outflow valve forward and reverse flow rates and effective diameters, ventricular power and efficiency. The program has been tested over a range of operating conditions including noise in the temperature and pressure signals, randomly varying heart rate and cardiac cycle. All of the data for the tests were produced by a digital computer simulation of a pulsatile artificial heart. The results of these tests indicate that the enhanced thermal dilution analysis method is feasible.

Continuous axial rotation and pulmonary fluid balance in acute lung injury

Objective: To investigate the effect of continuous axial rotation (CAR) treatment on the degree of pulmonary oedema (extravascular lung water [EVLW]) and arterial oxygenation in mechanically ventilated patients with acute lung injury (ALI). Design: Prospective investigation in a 12-bed intensive care unit (ICU) of a university hospital. Patients: Sixteen patients with ALI requiring mechanical ventilation. Methods: Random allocation into two groups. In the CAR group (n =8), patients were treated in a kinetic bed for a period of 72 h. In the control group (n =8), patients were treated in a 'conventional' bed. Intrathoracic blood volume (ITBV) and EVLW were assessed by the thermal dye dilution method at baseline (T0) and at 12, 24, 48, and 72 h after baseline. Additionally, arterial oxygenation, serum albumin levels and colloid osmotic pressure values in the serum were measured. Results: After 48 h of treatment, mean EVLW was significantly lower in the CAR group (6.3 ± 1.6 ml/kg [standard deviation, SD]), compared with the control group (11.2 ± 4.9 ml/kg) (p<0.05). In the control group, EVLW tended to increase during the study period. Arterial oxygenation (PaO2/FIO2-ratio) improved continuously during axial rotation therapy and was significantly higher after 24 h of treatment compared with the control group (32 ± 7.5 kPa vs. 21.2 ± 6.6 kPa, p<0.05, respectively). Serum albumin levels, ITBV, and colloid-osmotic pressures in the serum did not show any difference between the two groups during the experimental protocol. Conclusions: Continuous axial rotation caused a reduction of EVLW in patients with ALI. This may be due to continuous changes in intrathoracic pressures during kinetic therapy.

Continuous axial rotation and pulmonary fluid balance in acute lung injury

Objective: To investigate the effect of continuous axial rotation (CAR) treatment on the degree of pulmonary oedema (extravascular lung water [EVLW]) and arterial oxygenation in mechanically ventilated patients with acute lung injury (ALI). Design: Prospective investigation in a 12-bed intensive care unit (ICU) of a university hospital. Patients: Sixteen patients with ALI requiring mechanical ventilation. Methods: Random allocation into two groups. In the CAR group (n =8), patients were treated in a kinetic bed for a period of 72 h. In the control group (n =8), patients were treated in a 'conventional' bed. Intrathoracic blood volume (ITBV) and EVLW were assessed by the thermal dye dilution method at baseline (T0) and at 12, 24, 48, and 72 h after baseline. Additionally, arterial oxygenation, serum albumin levels and colloid osmotic pressure values in the serum were measured. Results: After 48 h of treatment, mean EVLW was significantly lower in the CAR group (6.3 ± 1.6 ml/kg [standard deviation, SD]), co...

Assessment of Hemodynamics in Hemodialysis Shunts: From Catheter Probe to Magnetic Resonance Imaging

This article reviews the different types of modalities that can assess the hemodynamics in hemodialysis shunts. Discussion focuses on indicator and thermal dilution methods, measurement of pressure and gradients, magnetic resonance flow measurements, and intervascular Doppler flow mapping techniques. Each specific technique is discussed with concentration on the technique, results, and usefulness of the modality.

Usefulness of sodium chloride as a nondiffusible indicator in the measurement of extravascular lung thermal volume in dogs.

The authors examined the usefulness of sodium chloride as a nondiffusible indicator during the first passage through dogs' lungs, before and after increased-permeability pulmonary oedema produced by an intravenous injection of alloxan. With an injection of a mixture of ice-cold 3 per cent sodium chloride and indocyanine green dye (a nondiffusible reference indicator), the authors simultaneously recorded three dilution curves from the aortic root: dye dilution, thermal and blood electrical conductivity dilution curves in six dogs. The mean transit time of sodium chloride in the conductivity dilution curve was significantly different from, but fairly equal to, that of indocyanine green dye (6.2 +/- 1.4 s (mean +/- SD) against 6.5 +/- 1.4 s (p < 0.01) in the baseline period, and 7.6 +/- 1.9 s against 8.4 +/- 2.1 s (p < 0.01) in the oedema period, respectively). The calculated extravascular lung thermal volume with the thermal and conductivity dilution method (Y, ml kg-1) correlated well with the gravimetrically determined extravascular lung mass in a total of 12 dogs, including six other dogs without intervention (x, g kg-1) (y = 0.72 x +3.03, r = 0.96). The authors conclude that sodium chloride is useful as a nondiffusible indicator in the first passage through the lungs, and that the thermal and conductivity dilution method is also useful for measuring extravascular lung water mass.

Increased extravascular lung water in patients with low pulmonary artery occlusion pressure after acute myocardial infarction

To evaluate the clinical characteristics of increased extravascular lung water (EVLW) in patients with low pulmonary artery occlusion pressure (PAOP) in the early phase of acute myocardial infarction. Consecutive sample for descriptions of the clinical features of medical disorders. A general medicine group practice in a university hospital. Sixteen patients with low PAOP (less than 18 mm Hg) on the initial measurement obtained within 12 hr of chest pain onset. EVLW was measured by the thermal indocyanine green dye double-indicator dilution method. QRS score was obtained on hospital day 7 from the Selvester's QRS Scoring System. Eleven (69%) patients had increased EVLW greater than 7 mL/kg despite low PAOP. EVLW had no significant correlation with PAOP and the difference between plasma colloid osmotic pressure and PAOP, but did have a significant correlation with pulmonary vascular resistance index (r2 = .31, p less than .05), and QRS score (r2 = .45, p less than .005). Larger infarcts led to increased EVLW even with low PAOP, and the accumulation of increased EVLW around the small arterioles might have led to increased pulmonary vascular resistance.

Local cerebral blood flow is increased in rapid-eye-movement sleep in fetal sheep

Behavioral state-induced changes in fetal cerebral blood flow were continuously monitored with a simple thermal dilution method. Thermojunctions were heated 1.5 degrees C above reference thermojunctions implanted contralaterally in various cerebral cortical and subcortical structures of four near-term fetal sheep. Temperature difference in rapid-eye-movement sleep was lower than in non-rapid-eye-movement sleep (p = 0.014), reflecting convective heat loss from increased blood flow. Temperature difference also varied significantly with the locus of placement in the brain (p = 0.003), reflecting, in part, regional differences in cerebral blood flow. The thermocouple method gives qualitative, continuous information on local cerebral blood flow that could be useful in monitoring the vascular response to changing functional activity during prenatal brain development.

Effects of non-shunting operation on azygos venous blood flow in cirrhotic patients.

Azygos venous blood flow and other haemodynamic parameters were measured in 14 cirrhotic patients to investigate the effects of a non-shunting operation, oesophageal transection with paraoesophagogastric devascularisation. Azygos venous blood flow measured by the local continuous thermal dilution method was significantly reduced by 13.8% after the operation (428 (41) v 369 (33) ml/min). Hepatic venous pressure gradient (HVPG) was also significantly decreased from 14.5 (0.8) to 12.8 (0.7) mmHg (-11.8%). Cardiac output and routine liver tests did not change remarkably postoperatively. In this haemodynamic study before and after non-shunting operation, moderate but significant decreases were seen in azygos venous blood flow and portal pressure (HVPG), without substantial changes in systemic circulation. This suggests that blood flow through the portosystemic collaterals other than oesophageal varices may be decreased but still adequate after the operation. Well preserved portosystemic collaterals without oesophageal varices are thus considered an optimally balanced state after non-shunting operation.

Measurement of left ventricular ejection fraction and volumes with three-dimensional reconstructed transesophageal ultrasound scans: Comparison to radionuclide and thermal dilution measurements

A transesophageal, ultrasonic cardiac imaging probe was built that incorporated a mechanism for changing the angle of the imaging plane of a conventional phased array in a precise and known manner. This probe was used to acquire an angular spatial sequence of two-dimensional images of the left ventricular cavity over a series of cardiac cycles by sweeping the imaging plane through it stepwise. The endocardial borders of these images were manually outlined off-line and the application of a threedimensional reconstruction algorithm was then used to compute the left ventricular end-diastolic and end-systolic volumes and ejection fraction. A study was conducted with seven anesthesized dogs to compare ultrasonic determinations by this method with determinations and measurements made using radionuclide and thermal dilution methods. Comparison of 33 ejection fractions, measured by the ultrasonic volume method and by the gated blood pool radionuclide approach, yielded a correlation coefficient of 0.87 and a standard error of the estimate of 5.7% measured over a range of 10% to 58% (average, 40%). Comparison of the ultrasonically measured volumes with those calculated from stroke volume (derived from thermal dilution cardiac output measurement) and ejection fraction (measured by radionuclide technique) produced a correlation coefficient of 0.92 and a standard error of the estimate of 10.3 mL over a range of 18 to 130 mL (average, 56 mL). The accuracy of volume and ejection fraction measurements with this new ultrasonic method seems comparable to that of other currently used clinical approaches such as radionuclide and angiography.

Theoretical and practical considerations of measuring extravascular lung water.

The volume of extravascular lung water is currently measured in vivo from the difference in mean transit times of the extrapolated first-pass dilution curves of two indicators, one diffusible and the other confined to the intravascular space. To overcome the limitations of this method, one can prolong the measurement interval, introduce a highly diffusible indicator, or both. In the first case, recirculating indicators are measured and included in the computation by deconvolution of the mean transit time through the lung. In the second case, heat is used as the water indicator. In the third case, not yet explored, recirculating heat would be measured and long thermal transit times uncovered. In view of the complexity of the deconvolution method and the pitfalls of the thermal dilution method, a radiographic score of pulmonary edema may be more useful clinically to assess the volume of extravascular lung water in patients with heart disease or adult respiratory distress syndrome.

Hemodynamic and Endocrine Parameters in the Anesthetized Cynomolgus Monkey: A Primate Model

Hemodynamic and endocrine parameters were determined in nine anesthetized adult male cynomolgus monkeys. Simultaneous phasic and mean pressures were measured in the right atrium, pulmonary artery, and abdominal aorta. Intermittent pulmonary artery wedge pressures and mean cardiac output measured by the thermal dilution method were used to calculate stroke volume, systemic vascular resistance, and pulmonary vascular resistance. Plasma adrenocorticotropic hormone (ACTH), cortisol, and plasma renin activity were measured throughout the procedure. Technical aspects, data in the anesthetized monkey, and comparison with previously reported data are presented.

Thermal and cardiovascular changes during three methods of resuscitation from mild hypothermia.

The interrelations among core temperatures (cardiac, esophageal, tympanic, rectal), skin temperature, and cardiovascular function (cardiac output, arterial pressure, heart rate, total peripheral resistance) were studied in a conscious subject during entry into mild hypothermia through cold water (10 degrees C) immersion, and during rewarming by three basic procedures: peripheral heat donation (bath); core heat donation (inhalation); and no exogenous heat (spontaneous). Swan-Ganz catheterization of the heart enabled measurement of cardiac temperature as well as cardiac output by the thermal dilution method. During cooling, all sites of core temperature measurement showed similar rates of entry into hypothermia. However, during the rewarming procedures, divergent patterns of temperature change among the four sites occurred. Rectal and tympanic temperatures were not representative of cardiac temperature, but esophageal temperature was, and is therefore most suitable as a criterion for experimental evaluation of the thermal benefit of various core rewarming techniques. During the first 30 min of rewarming, rates of increase in cardiac temperature for bath, inhalation, and spontaneous procedures varied according to the proportions 4:2:1, respectively. No afterdrop of cardiac temperature occurred with the inhalation or spontaneous procedures, but an afterdrop at this site did occur during the first 15 min of bath rewarming as soon as skin temperature was greater than 30 degrees C. This afterdrop coincided with cardiovascular changes including abrupt decreases in arterial pressure and total peripheral resistance, along with increases in heart rate and cardiac output. Such evidence of increased peripheral circulation was not observed with the inhalation and spontaneous methods. The findings relate to experimental evaluation of rewarming techniques and principles for resuscitation of hypothermia victims, especially in the first-aid situation.

Measurement of Extravascular Renal Water by the Thermal Dye Indicator Dilution Technique

Simple mechanical swelling of the renal parenchyma against an unyielding renal capsule may be responsible in part for the development of oliguria and acute tubular necrosis. However, until now, renal swelling was difficult to measure, except by postmortem gravimetric techniques.A new in vivo technique, the thermal dye double indicator dilution technique, was used to assess renal swelling by measuring extravascular renal water. Ice cold indocyanine green dye solution was injected rapidly into the renal artery of 5 mongrel dogs, and the thermal dilution and dye dilution curves were recorded simultaneously by means of a thermistor catheter in the renal vein. The curves were corrected for the response time of the measuring systems, then the extravascular renal water was computed (renal blood flow multiplied by the difference in mean transit times of the thermal dilution and dye dilution curves). The results were compared to the gravimetrically determined extravascular renal water. A high correlation was found to exist between the thermal dye dilution method and the gravimetric method (r = 0.92, X = 0.65Y + 19.8, p <0.05). These preliminary results are encouraging and warrant further trials, inasmuch as this technique would allow the sequential in vivo measurement of renal edema. It is therefore feasible to quantitate the effect of clinical insults, such as hypovolemic shock or sepsis, on the kidney, and to assess the value of different therapeutic interventions. A small body of evidence attempts to relate the role of simple mechanical swelling of the kidney to the pathogenesis of acute renal failure.

Correlation of blood temperature fluctuations with blood pressure waves.

Constant blood temperature in the pulmonary artery is assumed when the thermal dilution method is used for cardiac output determination. In some cases, however, slow temperature fluctuations (2-6 cycles per min.) occur in arterial and venous blood and interfere in the measurement. Those thermal fluctuations were investigated in the pulmonary artery and venae cavae of dogs. The temperature variations were found to be correlated with blood pressure waves: an increase of blood pressure was accompanied by an increase in the blood temperature in the pulmonary artery and a decrease in the blood temperature in the venae cavae. Therefore, measurement of the temperature of the pulmonary artery relative to that of the venae cavae does not rule out those fluctuations, and will not improve the thermal dilution method.

Theoretical validation of the thermal dilution method for cardiac output determination.

The basic formula of the thermal dilution method for the measurement of cardiac output is proven for pulsatile flow, assuming constant stroke rate, equal stroke volumes, and ideal ventricular mixing. Firstly, for an ideal thermistor of negligible response time which presents the temperature of the blood in the pulmonary artery as a step function; then it is shown that the area under the curve of temperature versus time is independent of the response time of the thermistor; hence, the formula holds for all thermistors.

A COMPARISON OF METHODS FOR THE MEASUREMENT OF CARDIAC OUTPUT AND BLOOD OXYGEN CONTENT

A comparison has been made between the recently introduced thermal dilution method for measurement of cardiac output and the standard dye dilution technique. Two relatively new methods of measurement of blood oxygen content, one involving the measurement of oxygen tension after release of oxygen by carbon monoxide, and the other the measurement of current flow upon reduction of oxygen in a galvanic cell, have been compared with a standard indirect method of measurement of blood oxygen content. All three new methods fulfilled the criteria of accuracy and simplicity and compared favourably with the standard methods. Of the two new methods for measurement of oxygen content, that involving reduction of oxygen in a galvanic cell was superior by virtue of compactness and speed of operation.