[LOGNORMAL-NLSQ-technique. Evaluation of a new mathematical method for determining blood volume]

This paper describes the investigation of a new mathematical method of calculating blood volume. The new method determines the blood volume by calculating the product of the mean circulation transit time. The mean transit time is calculated from the body transport function. To examine the accuracy of the LOGNORMAL-NLSQ technique, 45 concentration time curves were measured in an in vitro recirculation model with variable clearance. The calculated volume was 4% smaller than the actual volume. This may be attributed to the functional dead space within the model, and is tolerable for clinical situations. The LOGNORMAL-NLSQ technique might acquire considerable importance in future, especially since it provides accurate results very quickly.

Influence of high-dose ketamine on the vascular reactivity of human and porcine isolated coronary artery segments

The influence of ketamine on the vasomotor effect of histamine and serotonin was studied in isolated human and porcine coronary artery rings. Ketamine (10(-3) mol L-1) attenuated the contractile response to both mediators significantly (P < 0.05 for histamine concentrations of 3 x 10(-5) mol L-1 and above as well as for serotonin concentrations of 3 x 10(-8) mol L-1 and above). This effect of ketamine was observed in intact and endothelial denuded porcine rings (difference n.s.) as well as in coronary arteries from explanted human hearts of patients undergoing heart transplantation. It is concluded that this reduction of the contractile response to histamine and serotonin caused by ketamine is not dependent on the endothelial function (e.g. endothelium-derived relaxing factor).

Modelling of non-linear pharmacokinetics in sheep after short-term infusion of cardiotoxic doses of imipramine

Imipramine was administered to sheep (n = 10) by intravenous infusion in high doses (450 mg-900 mg) to elicit cardiovascular shock. A cardiac assist device was then employed to manage the acute overdose situation. The concentration-time course of imipramine and its metabolite desmethylimipramine in plasma was measured by HPLC. As an indicator of imipramine's cardiotoxic effect, cardiac output was monitored. The aim of the study was to evaluate the pharmacokinetics under these conditions and to assess the efficiency of a cardiac assist device with (n = 5) and without (n = 5) an integrated haemoperfusion unit in removing drug from the circulation. The kinetics of imipramine could be described by a three compartment body model with concentration-dependent clearance resulting in non-linear kinetics. The changes in cardiac output with time could be linked to the pharmacokinetic model by a linear relationship. The cardiac assist device was found to contribute to the overall elimination of imipramine whereas the haemoperfusion unit had no clinically relevant impact.

[Asymptotic behavior of calculated concentration time curves]

The measured concentration time curve of an injected substance is often used as a basis for calculating the distribution volume. For the first time, the present paper describes a generally applicable formula for calculating the asymptote of a concentration time curve in medical applications. With a knowledge of this formula, previously unexplained phenomena (varying results obtained from two different methods of calculating the distribution volume) can now be understood. At the same time, errors of methodology (choice of injection and measuring sites) can be avoided.

Local mechanics of the lung tissue determined by functional EIT

A new functional EIT (f-EIT) evaluation technique providing information on the local dynamic behaviour of the lung is presented. Out of a series of single EIT thoracic images local time courses of the impedance change are extracted. To detect regional differences in the dynamic behaviour of the lung tissue the local time courses at different locations are related to the average time course of the impedance change over the whole thoracic cross section. The time shifts between this reference signal and the signals from separate positions are calculated from the phase information of the complex cross spectra and evaluated in terms of the local phase angle. The computed phaseshifts are imaged over the cross section creating an 'f-EIT phase image' characterizing the local dynamic properties. To relate the observed differences to the proper lung location the resulting images are presented as a combination of the f-EIT ventilation images, which represent the local amplitude of ventilation and the f-EIT phase images. The new imaging technique was tested in spontaneously breathing humans. Alterations to pulmonary dynamics were induced by changing the body posture of the subjects. The f-EIT phase imaging procedure was shown to identify lung regions with different dynamics and it is expected that this technique will also distinguish pathologically determined alterations.

Gravity-dependent phenomena in lung ventilation determined by functional EIT

Gravity exerts an effect on the distribution of intrapulmonary ventilation. A study on the detection of gravity-dependent inhomogeneity of ventilation by a functional EIT technique is presented. The study was performed on five human subjects, whose ventilation distribution was modified by changes in body position. The subjects were studied during spontaneous tidal breathing. The qualitative and quantitative analysis of the functional EIT images revealed that the ventilation is higher in the dependent lung regions when compared with the non-dependent ones. These EIT findings correspond to current knowledge of the physiological behaviour of the lungs as derived from the radioactive-gas methods and raise the possibility of applying the less complicated functional EIT in future studies on ventilation distribution in the lungs. This may be of major interest in the monitoring of intensive care patients with severe pulmonary disorders.

Myocardial extraction of bupivacaine in anaesthetized sheep and by hearts of sheep and rats in vitro

We observed the in vivo kinetics of bupivacaine in the cardiopulmonary system, particularly in the pulmonary artery, the upper part of the descending aorta and the coronary sinus of anaesthetized sheep, each of which received a high dose infusion into the central vein. In some experiments dilution curves were monitored for the non-extracted dye, indocyanine green. Concentrations of bupivacaine were approximately 20% lower in the aorta than in the pulmonary artery. This gradient of bupivacaine was present across the lung for 5-10 min. Concentrations of bupivacaine in the coronary venous plasma were also markedly lower than at the arterial site. Initially more than 50% of the amount of bupivacaine at the arterial site was removed by the heart. Later, the myocardial extraction ratio decreased and plateaued at a value of 0.30-0.40. At this time, concentrations of bupivacaine in the pulmonary artery were approximately 12 micrograms ml-1. Therefore, approximately 0.3-0.6 mg of bupivacaine were extracted per minute by the sheep heart in vivo. On the other hand, isolated perfused rat hearts did not substantially remove bupivacaine (2 micrograms ml-1) from the medium. Approximately one-third of 14C-bupivacaine was retained in slices of rat and sheep myocardial tissue. However, there was no evidence that metabolism played a substantial role in the cardiac kinetics of bupivacaine.

Computation of the initial distribution of a drug by repetitive convolution with a circulatory transport function

Hereby we present a widely applicable computational method for the description of recirculation and distribution phenomena occurring immediately after intravenous injection of a substance. The intravascular concentration-time course, r, is described as r = c0 + g * r, where the asterisk denotes the convolution operation, c0 is the concentration-time course during the first passage of the substance at an arterial measuring site and g is the transport function of the body. If the body transport function is known, then the arterial concentration-time course of a substance can be predicted for different amounts, injection times and elimination rates. The site of interest can be chosen arbitrarily, i.e. the concentration-time course in the arterial circulation supplying any organ can be described. This might be of special interest for the optimal design of intravenous injections of contrast media, where initial concentrations at the region of interest determine the success of the diagnostic procedure.

Changes in the thoracic impedance distribution under different ventilatory conditions

The present study was performed with the aim of checking the suitability of EIT in imaging regional thoracic impedance variations during lung ventilation under predefined conditions and to compare EIT with established reference techniques. A new technique of functional EIT imaging designed to visualize physiologically relevant information from the sequentially registered series of thoracic distributions was introduced. Experiments were performed on five spontaneously breathing healthy subjects and on 12 anaesthetized supine pigs. 16 electrodes were placed around the thorax and consecutive transthoracic impedance distributions were measured at a rate of 1 Hz (Sheffield APT system mark I, IBEES, Sheffield, UK). Several voluntary breathing manoeuvres were performed in human subjects and the tracings of local impedance were compared with standard spirometry. In animal experiments EIT was applied during artificial ventilation at different ventilation rates and during stepwise passive emptying and filling of either one or both lungs while the respiratory muscles were relaxes. Further, selective blockade of lung regions resulting in regionally reduced ventilation was performed and the capability of EIT to follow and differentiate local ventilatory disturbances was checked by reference techniques (x-ray and staining methods). The experiments revealed an overall agreement between the spirometric and impedance data in all breathing patterns performed. A linear relationship between changes of the air content of the lungs and the regional thoracic impedance was shown (intraindividual correlation coefficient range, 0.986-0.999; n = 12 animals). The functional images of the impedance distribution across the thorax reproduced adequately the typical anatomical characteristics of the pig and the human thorax. The spatial resolution of EIT functional images was sufficient to differentiate lung areas corresponding to approximately 20 ml tissue volume. EIT with the additional evaluation procedure of functional imaging was shown to be a suitable and reliable method of imaging different ventilatory conditions with the potential to become a useful tool for monitoring respiratory function.

[Anesthesia with propanidid in a liposomal preparation. An experimental study in swine]

BACKGROUND

Propanidid was widely used as a short-acting i.v. anaesthetic until it was withdrawn due to severe haemodynamic side effects. It was presumed that anaphylactoid reactions with massive histamine release were caused by the solvent cremophor rather than by propanidid itself. A new liposomal preparation of propanidid was examined in this animal study and compared with propanidid in cremophor solution and with propofol.

METHODS

Eighteen pigs were randomly assigned to one of the following groups: Group 1 (n = 6): Propanidid in liposomal preparation (PropaLip; Braun Melsungen, Germany). Anaesthesia was induced with 60 mg/kg, followed by continuous infusion of 400 mg/kg.h. Group 2 (n = 6): Propanidid in cremophor solution (PropaCrem; Sombrevin, Gedeon Richter, Budapest) 15 mg/kg, 100 mg/kg.h. Group 3 (n = 6): Propofol (Disoprivan, Zeneca, Plankstadt, Germany) 5 mg/kg, 20 mg/kg.h. After induction and tracheal intubation, the animals were ventilated with 50% oxygen in air. Basic monitoring included noninvasive blood pressure measurements, electrocardiographic monitoring, and capnography. In a short surgical procedure, arterial and pulmonary artery catheters were placed via the right carotid artery and right internal jugular vein, respectively. As soon as the animals responded to a pain stimulus a second anaesthetic induction was performed, followed by a 60-min continuous infusion of the agent studied with invasive haemodynamic monitoring including arterial and pulmonary arterial pressures and cardiac output. Blood samples were taken for the measurement of serum levels of adrenaline, noradrenaline, cortisol, aldosterone, adrenocorticotropic hormone, and histamine.

RESULTS

Intubation conditions and quality of anaesthesia were best in propofol animals, followed by PropaCrem animals. In spite of the large dose of 410 mg/kg.h, resulting in a volume load of as much as 16.4 ml/kg.h, the PropaLip animals showed evidence of poor anaesthetic quality. In group 1 we recorded the highest increases in heart rate (91 vs. 115/min), cardiac output (5.4 vs. 7.7 l/min), plasma catecholamine levels, and histamine concentrations (124-268 ng/ml).

CONCLUSIONS

In our animal study, propanidid in liposomal preparation failed to show promise as a new anaesthetic agent. Our results are discussed in view of a drug targeting the cells of the reticuloendothelial system, especially the liver, where liposomes are eliminated from the blood. This may result in the transport of propanidid to one of its major places of inactivation.

Pulmonary and left ventricular decompression by artificial pulmonary valve incompetence during percutaneous cardiopulmonary bypass support in cardiac arrest

BACKGROUND

In cardiac arrest, use of percutaneous cardiopulmonary bypass support (PCPS) may lead to left ventricular loading, with deleterious effects on the myocardium, and is often accompanied by an increase in pulmonary artery pressure. The present study was designed to assess the potential of artificially induced pulmonary valve incompetency to retrogradely decompress the left ventricle during PCPS in ventricular fibrillation.

METHODS AND RESULTS

Studies were performed using a standardized experimental animal model in sheep (n = 12; body weight, 77 to 112 kg). When PCPS was used during fibrillation, an increase in left ventricular pressure (from 21.4 +/- 5.0 mm Hg after 1 minute to 28.4 +/- 9.5 mm Hg after 10 minutes of fibrillation) was observed in all animals, with a simultaneous increase in pulmonary artery pressure in 6 animals, from 15.5 +/- 3.8 to 24.3 +/- 5.4 mm Hg (group A). In these animals, artificial pulmonary valve incompetency, which was induced by a special "pulmonary valve spreading catheter," led to effective decompression of both the pulmonary circulation (decrease in pulmonary artery pressure from 24.3 to 11.3 mm Hg) and the left ventricle (decrease in left ventricular pressure from 30.5 to 17.7 mm Hg). We simultaneously measured a decrease in the myocardial release of lactate (increase in arterial coronaryvenous difference in lactate content from -0.01 to 0.14 mmol/L), demonstrating the myocardial protective effect of the procedure. In contrast, in 6 animals without an increase in pulmonary artery pressure during PCPS (group B), artificial pulmonary valve incompetency did not reduce left ventricular loading, which was probably because of competent mitral valves in these animals.

CONCLUSIONS

In case of increasing pulmonary artery pressure during PCPS in cardiac arrest, artificial pulmonary valve incompetency might be a useful tool for effective pulmonary and retrograde left ventricular decompression.

[Concomitant hemodynamic effects of intracoronary injections of a new transpulmonary contrast medium]

AIM

A new transpulmonary echo contrast agent (SH U 508) was injected intracoronally to six anaesthetised sheep to examine its possible direct cardiac effects.

METHOD

SH U 508 was injected in randomised order in three different volumes (2, 4 and 8 ml; n = 12, 10, 9) with the same drug concentration of 200 mg/ml.

RESULTS

The 2 ml and 4 ml injections had no relevant effect on the arterial, pulmonary-arterial and ventricular pressures, on the left ventricular contraction velocity and on the myocardial blood flow (less than +/- 10% of the control value). The left ventricular relaxation velocity decreased by 20%. The disturbance of the left ventricular relaxation at a volume of 8 ml was pronounced (about 40% decrease). Slight left ventricular dysfunction further manifested itself in a decreased systolic pressure (-15%) and increased left ventricular enddiastolic pressure (20%).

CONCLUSION

In summary the overall effect of the intracoronary injections of SH U 508 exhibited only minor cardiac side effects. If the current results are extrapolated to peripheral-venous application, the clinically required central-venous 8 ml injection of a 400 mg/ml suspension is not expected to produce any coronary haemodynamic side effects, due to drug dilution in the pulmonary circulation and resulting low intra-coronary concentrations.

Peripheral and cardiac effects of a new phosphodiesterase inhibitor in comparison with enoximone

The effect of the new phosphodiesterse inhibitor R80122 (E)-N-cyclohexyl-N-methyl-2-[[[phenyl(1,2,3,5-tetrahydro-2-oxoimidazo [2,1-b]-quinazolin-7-yl)methylene] amino]oxy]acetamide, (CAS 133718-29-3) on haemodynamic parameters and myocardial oxygen consumption were intraindividually compared with those of enoximone, a clinically established phosphodiesterase inhibitor. In 12 anaesthetised sheep the drugs were given in randomized order as i. v. infusions for 6 min at each setting (10, 20 and 30 micrograms.kg-1.min-1 (R80122) and 32, 64 and 96 micrograms.kg-1.min-1 (enoximone)). R 80122 as well as enoximone caused a significant increase in cardiac inotropism with a simultaneous increase of myocardial oxygen consumption. The peripheral resistance was significantly decreased by both drugs. The haemodynamic effects elicited by the application of equieffective doses of R80122 and enoximone did not show any differences.

Efficiency of a new radiant heater for postoperative rewarming

Effective rewarming devices have only become available recently. This investigation compares the efficiency of an new overhead radiant heater (ARAGONA Thermal Ceilings TM, CTCX, 1000 W) with that of an electric blanket (50 W) or a standard hospital blanket. 35 patients undergoing postoperative assisted ventilation and continued sedation were randomly assigned to one of the treatments. Shivering, oxygen uptake, heart rate and invasive blood pressure were measured and the increase in total body heat minus body heat production was calculated as heat balance. Results are given as medians (range). Subcutaneous temperatures were taken to calculate the mean skin temperature. The evaluation was undertaken for an oesophageal temperature interval of 35 degrees to 37 degrees C. All groups exhibited a similar mean oxygen uptake i.e. thermogenesis (3.5 (2.7-4.0) ml.kg-1.min-1, 3.3 (2.7-4.9) ml.kg-1.min-1;3.2 (2.4-5.1) ml.kg-1. min-1) which correspond to a resting energy expenditure. The time of rewarming of the radiant heat treated group (n = 12) (100 (76-143) min) for this interval was significantly reduced in comparison to both other groups (183 (116-320) min; 231 (115-340) min). A slightly positive heat balance was only achieved in the group treated by radiant heat, indicating that all metabolic heat was conserved or heat losses were compensated by transfer of external heat. Shivering was significantly reduced in the radiant heater group whereas the rate pressure product was insignificantly higher. We did not find any significant effect for the electric heating blanket in comparison to the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine-dependent diastolic dysfunction in moderate hypothermia

We designed an experimental animal study to study the effects of dopamine (DA) on diastolic function in hypothermia. DA was applied at five incremental infusion rates in 6 sheep during normothermia and moderate hypothermia (29 degrees C). Left ventricular end-diastolic pressure (LVEDP) was increased during hypothermia as compared with normothermia at all doses of DA. Contraction and relaxation velocity were changed only slightly during hypothermia; during normothermia, both velocities were markedly increased. The pronounced hemodynamic effect observed during hypothermia was further intensified by occurrence of aftercontractions, which disappeared at very high DA doses. These paradoxic results were considered the result of hypothermia-induced reduction in active transport mechanisms responsible for regulation of the cytoplasmic CA2+ concentration. The generally reduced inotropic effect of DA, the risk of paradoxic reactions, and the occurrence of aftercontractions must be taken into account when emergency drugs are administered clinically during hypothermia.

[Dynamic blood volume determination using the body transport function]

This paper describes a dynamic blood volume determination which is faster and more accurate than the classic method. The new method determines blood volume by means of the product of the mean transit time of the circulation and the cardiac output. The mean transit time is calculated from the body transport function. To examine the precision of the dynamic method the blood volume of 24 patients was determined in both the dynamic and the classical way, using radioactively labelled erythrocytes. The comparison of the two methods resulted in a correlation coefficient of r = 0.77. The dynamic method of blood volume determination will be helpful especially in risk patients to accurately determine the quantities of fluids to be administered.

Need for active left-ventricular decompression during percutaneous cardiopulmonary support in cardiac arrest

During ventricular fibrillation, myocardial hemodynamic and metabolic effects of percutaneous cardiopulmonary support (PCPS) were analyzed in 11 adult sheep (body weight 77-112 kg). During supported fibrillation, an abrupt increase in left-ventricular pressures with alignment to aortic pressures was observed in 2 animals, which was probably due to spontaneous aortic regurgitation, and resulted in deterioration of coronary perfusion. In 9 animals, left-ventricular pressures rose from 22.9 +/- 4.9 to 31.2 +/- 7.9 mm Hg elevating left ventricular wall stress from 16,750 +/- 8,745 to 28,835 +/- 8,892 dyn/cm2 after 10 min of PCPS-supported fibrillation (mean flow rate 4.5 +/- 0.7 liters/min). Simultaneously, myocardial perfusion pressures decreased from an average of 32.4 +/- 11.7 to 22.3 +/- 9.4 mm Hg and myocardial lactate release was observed. Additional transapical LV venting using a 9-Fr catheter led to a decrease in both LV pressure (to 25.7 +/- 5.3 mm Hg) and wall stress (to 20,612 +/- 7,499 dyn/cm2). Left-ventricular decompression decreased myocardial oxygen consumption (from 5.3 +/- 1.4 to 4.8 +/- 0.9 ml/min.100 g), and reduced myocardial lactate release, which indicates myocardial protection. Protective effects were most pronounced using 12-Fr-, and 21-Fr-venting cannulas (with 21 Fr: decrease in myocardial oxygen consumption to 2.7 +/- 0.6 ml/min.100 g, and reversal of myocardial lactate release to lactate uptake during fibrillation). Conclusions. Hemodynamic and metabolic data clearly demonstrate the deleterious effects of PCPS to the unvented left ventricle during cardiac arrest. The results emphasize the need for active left-ventricular decompression during PCPS in ventricular fibrillation.

Mechanical left ventricular unloading during high risk coronary angioplasty: first use of a new percutaneous transvalvular left ventricular assist device

A new catheter mounted, transvalvular left ventricular assist device has been designed for percutaneous transfemoral access. The device, the Hemopump [14 French (Fr.) outer diameter], is based on a mixed flow rotary pump and is capable of flow rates of 1.5-2.2 l/min. The pump is inserted using a specialized 16 Fr. femoral introducer sheath. The first application of the percutaneous Hemopump in man was performed in two patients with hemodynamic compromise during high risk coronary angioplasty. In these patients, Hemopump support resulted in hemodynamic stabilization (increase in aortic pressure from 60/42 to 87/61 and from 80/60 to 100/70 mm Hg, respectively) and marked left ventricular unloading (decrease in pulmonary capillary wedge pressure from 25 to 10 and from 14 to 10 mm Hg) during balloon inflation. In both patients, percutaneous transluminal coronary angioplasty (PTCA) could be accomplished successfully. Using the system for periods of about 2 hr in each patient, we observed no vascular, hemorrhagic, or embolic complications. In both patients, only a minor increase in both plasma free hemoglobin and lactate dehydrogenase levels was noted. Our preliminary experiences suggest that the percutaneous Hemopump is safe and effective and may be a powerful alternative to other devices used for supported angioplasty.

Simulation of arterial drug concentration after intravenous application

The aim of this study was to develop a widely applicable model for circulatory indicator dispersion which could describe the pharmacokinetics of early drug distribution. The model assumes that the substance is injected into the right atrium and measured in the aorta. The dilution curve results from the dispersion and recirculation of the indicator in the body. The concentration time curve in the aorta, r, can be described as r = c0 + g* r, where g is the transport function of the body and c0 is the concentration time course, which is measured for the first time in the aorta. If the body transport function is known, then the aortic dilution curve of a drug can be predicted for different elimination rates and injection times. The site of interest can be chosen arbitrarily, i.e. the concentration of inflow into the kidney or any other organ can be described.

Left-ventricular unloading by transvalvular axial flow pumping in experimental cardiogenic shock and during regional myocardial ischemia

The efficacy of the transfemoral left-ventricular assist device Hemopump (HP; 21 Fr outer diameter) was examined in experiments with adult sheep in two different models of cardiogenic shock (tachycardia shock; ischemia shock), and during ventricular fibrillation. During tachycardia (high frequency pacing-induced; n = 14), HP assist led to a significant increase in cardiac output (from 2.2 to 2.8 liters/min), mean aortic pressure (from 47.6 to 65.6 mmHg), and myocardial perfusion pressure (from 25.5 to 59.0 mmHg). Simultaneously, a normalization of body oxygen-uptake (from 1.4 to 2.5 ml/min.kg), a decrease in myocardial oxygen consumption (from 6.1 to 4.8 ml/min.100 g), and a normalization of myocardial lactate metabolism were observed during HP assist. During regional myocardial ischemia (PTCA balloon occlusion of the proximal LAD (3.5 min; n = 12), HP assist led to significant decrease in LV end-diastolic pressure (from 21.1 to 12.1 mmHg), and increase in diastolic aortic pressure (from 58 to 67 mmHg) resulting in significant increase in coronary perfusion pressure. In the early reperfusion period, myocardial release of both lactate and potassium was significantly lowered with HP assist. During ventricular fibrillation (induced by electrical stimulation; n = 9), HP flow rates decreased from 2.5 (after 10 min) to 2.1 liters/min (after 30 min). Mean aortic pressures simultaneously decreased from 64.0 to 54.6 mmHg. Perfusion conditions were sufficient for maintenance of aerobic myocardial metabolism, but were borderline for peripheral circulation. Our hemodynamic and metabolic data demonstrate beneficial effects of cardiac assist with the Hemopump 21 Fr in both tachycardia-induced severe cardiogenic shock and during acute regional myocardial ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

[The use of the RACE technique for quantitative flow measurements. Evaluation using a clinically relevant flow model]

A phantom has been designed for measuring flow velocities; using pipes of specified diameter and selectable pulse rates, flow rates varying from 0-250 cm/s can be determined. The measurements are made in a superconductive magnet with a field strength of 1.5 Tesla, employing a RACE technique. The reference technique was electromagnetic flow measurement. There was good linear correlation between the electromagnetic and the MRT results with a correlation coefficient of 0.98. It is necessary in the first place to estimate flow speed; if flow velocity is unknown initially, there is no correlation. Hence, in everyday use erroneous results may be obtained, particularly since one cannot always demonstrate vessels in all parts of the body without superimposition. Further clinical studies are required in various vascular territories to evaluate the usefulness of the RACE technique for flow measurements.

Investigation of cardiac metabolism using stable isotopes and mass spectrometry

The technique described in this communication enables detailed investigations of cardiac metabolism using 13C-labeled substrates and mass spectrometric measurements of 13CO2 in the coronary effluent. To validate this technique for further studies isolated working rat hearts were perfused with 13C-labeled substrates in a bicarbonate-free perfusion fluid. The fraction of CO2 produced by oxidation of labeled substrate was calculated by the 13CO2/CO2 ratio in the coronary perfusate. The oxidation of 13C-acetate showed a linear correlation with 13C-acetate concentrations between 0.015 and 0.16 mmol/l. An inhibitor of acylcarnitine translocase, 2-(3-methylcinnamylhydrazono)-propionate (BM42.304) decreased CO2 production from 13C-palmitate from 48% +/- 4% to 31% +/- 3% (n = 11, SEM). Taking into account considerations of tracer kinetic theory rapidly accessible intracellular palmitate stores were estimated to be less than 900 nmol/g ww. This technique allows specific investigations of the oxidation of labeled substrates in the heart and may be useful for basic research and/or clinical diagnosis, thus avoiding the hazards of radiolabeled substrates.

Influence of pH management on hemodynamics and metabolism in moderate hypothermia

In moderate hypothermia, three different concepts of pH management have been described to date: pH-stat, alpha-stat, and alkalinity. In our study these pH strategies were compared in adult sheep, with animals serving as their own controls for direct comparability. Hemodynamic parameters, such as mean aortic pressure (from 109 +/- 12 to 72 +/- 23 mm Hg), cardiac output (from 5.55 +/- 1.25 to 4.5 +/- 0.82 L/min), and systemic oxygen consumption (from 3.73 +/- 0.8 to 1.81 +/- 0.4 ml/kg/min), decreased significantly with alpha-stat at 28 degrees C from values for normothermia. No marked or even significant differences were found among the three pH strategies in any value, with the exception of body oxygen consumption. The difference of 2% between pH-stat and alpha-stat, at 0.06 ml oxygen/kg/min, was significant (p < or = 0.05), however of no practical relevance because hypothermia itself caused a decrease of nearly 52%. With regard to myocardial parameters, pH-stat impaired myocardial function compared with both alpha-stat and alkalinity. At nearly identical mean aortic pressures and cardiac outputs, myocardial oxygen consumption reached the highest level in pH-stat (7.65 ml oxygen/100 gm/min; alpha-stat, 6.76 ml oxygen/100 gm/min; p < or = 0.05). Myocardial efficiency thus decreased from 21% (alpha-stat) to 17% (pH-stat). No evident changes in hemodynamic and metabolic values were found for alkalinity vs alpha-stat. The best response to continuously infused epinephrine, however, was found with alkalinity. According to our data there was an impairment of myocardial function without any evident further reduction in body metabolism with pH-stat vs alpha-stat. There were, however, no marked metabolic or hemodynamic differences between alkalinity and alpha-stat, with the exception of a better preservation of sensitivity to adrenergic stimuli with alkalinity.

Calculation of body transport function

A new model for simulation of recirculation has been developed which describes the measured concentration-time course of a drug in the aorta. It is based on repetitive convolution of the injected input dilution curve with a body transport function plus the input dilution curve. If the basic shape of a body transport function, i.e. such as log-normal distribution, is known, it is possible to calculate the parameters of this function with a non-linear least-squares procedure from measured tracer dilution data. In the present investigation this algorithm is used to estimate the body transport function for experimental data, obtained in two experiments with sheep. Once the body transport function is known, the formula can be used to describe the dispersion of a drug. Intravascular concentration time curves at different places in the body can also be predicted or the blood volume can be estimated.

Efficiency of the left ventricle assist device Hemopump in cardiac fibrillation

We have examined in sheep the efficiency of the Hemopump during ventricular fibrillation. Circulatory arrest was induced by electrical stimulation and maintained for 30 min. Haemodynamic measurements were recorded continuously and blood samples were taken before, during and after fibrillation to determine total body and myocardial metabolic activity. All hearts were defibrillated successfully after 30 min of fibrillation. During fibrillation, the Hemopump sustained a mean arterial pressure of about 60 mm Hg with a blood flow rate of about 2.3 litre min-1. These perfusion conditions were sufficient for maintenance of aerobic myocardial metabolism, but with a borderline circulatory supply to the total organism.

[The percutaneous implantable heart-lung machine in the coronary angioplasty of high-risk and emergency patients]

Using a recently developed, percutaneously introduced cardiopulmonary support system (PCPS) seven high-risk patients (four men, three women; mean age 61 [41-77] years) underwent percutaneous transluminal coronary angioplasty. In one patient, with unstable angina and in incipient cardiogenic shock, perfusion with PCPS was begun immediately before coronary angioplasty. In six patients it was undertaken with the PCPS on stand-by, but eventually not needed. Coronary angioplasty was successful in six patients, partially successful in one. Angina was considerably improved long-term in all patients, but one of them died 2.5 months afterwards at home. In two other patients (men, aged 41 and 71 years) with acute myocardial infarction, the PCPS was employed under circumstances of emergency resuscitation. In both cases recanalization of the occluded coronary artery was achieved mechanically during perfusion with PCPS; one patient survived. Availability of PCPS, also in an emergency, makes it possible to extend the indications for coronary angioplasty to include even high-risk patients.

Protective effects of the Hemopump left ventricular assist device in experimental cardiogenic shock

The efficacy of the new cable-driven rotating left ventricular assist device Hemopump in cardiogenic shock was examined in experiments with adult sheep (n = 14; body weight 50-71 kg). Shock was induced by high frequency ventricular pacing. Aortic, pulmonary, central venous and left ventricular pressures as well as electromagnetic measurements of coronary blood flow were recorded continuously; cardiac output was measured by thermodilution technique. Blood samples for determination of oxygen content, electrolytes and lactate were taken under control conditions, in shock, and during pump intervention at different levels of pump speed. Vascular resistance, total body and myocardial oxygen consumption as well as myocardial uptake and release of lactate were calculated. High frequency pacing led to a significant decrease in cardiac output (from 3.8 +/- 0.8 to 2.2 +/- 1.6 l/min), mean aortic pressure (89.1 +/- 14.4 to 47.6 +/- 7.2 mmHg), and total body oxygen consumption (2.6 +/- 0.3 to 1.4 +/- 0.7 ml/min per kg), as well as myocardial release of lactate (arterial coronary-venous difference of lactate: 0.27 +/- 0.26 to -0.32 +/- 0.72 mmol/l). Hemopump assist in this condition resulted in a significant increase in cardiac output (to 2.8 +/- 0.6 l/min), mean aortic pressure (to 65.6 +/- 13.9 mmHg), and myocardial perfusion pressure (from 25.5 +/- 11.0 to 59.0 +/- 14.7), and led to nearly normal total body oxygen consumption (2.5 +/- 0.7 ml/min per kg), a decrease in myocardial oxygen consumption (from 6.1 +/- 2.1 in shock, to 4.8 +/- 1.7 ml/min per 100 g), and to normal arterial coronary-venous difference of lactate (0.24 +/- 0.26 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial support and protection during regional myocardial ischemia using the Hemopump assist device

A study was designed to quantify the influence of the Hemopump on myocardial metabolism in regional myocardial ischemias induced by repetitive balloon-occlusions (3.5 minutes) of the LAD in 12 sheep (b.w. 49-61 kg). In order to make immediate comparisons and obtain paired-couples, ischemias were carried out with and without the Hemopump in operation. An energetic unloading of the left ventricle was achieved by the Hemopump already under preocclusion conditions, reducing myocardial O2-consumption from 7.52 to 5.98 ml/min/100 g LV (= 20%) as well as lowering the LVEDP from 13.3 to 9.8 mmHg (p less than or equal to 0.01). During ischemia a clear increase of LVEDP (13.3 to 21.0 mmHg) occurs, which was prevented in the group with Hemopump-assist (9.8 to 12.1 mmHg). Combined with a sustained higher diastolic aortic pressure, a better myocardial perfusion pressure resulted. Energetic unloading and improvement of perfusion conditions might be the cause of the significantly lowered release of lactate and potassium. Due to theses fibrillation (n = 3) only occurred during occlusions without Hemopump-support. In summary, a significant reduction of the ischemic burden on the myocardium was found. Thus the Hemopump could be of benefit to patients who fail to be weaned from CPB or who are suffering from instable cardiovascular performance.

[The energetics and economics of the cardiac pump function]

In anesthesiology and intensive care medicine it is often necessary to treat disorders involving cardiac failure or low-output syndrome. However, in patients who are endangered by ischemic heart disease, any pharmacologic therapy with positive inotropic agents should improve cardiac output without increasing myocardial oxygen demand significantly: the heart should perform its task as efficiently as possible. In the present study a mathematical model of myocardial efficiency was developed. The implications of this theoretical concept of myocardial efficiency were evaluated in animal experiments. THEORETICAL MODEL. Cardiac efficiency is predominantly dependent on preload, afterload, and inotropic state. Quantitatively, it can be calculated from end-diastolic volume, left ventricular systolic pressure (Psyst), stroke volume (SV), and ejection time. The implications of the theoretical analysis are: (1) the inotropic state, which leads to optimal myocardial efficiency, is specifically determined by preload and afterload: for each preload and afterload one matched inotropic state is necessary to achieve optimal efficiency; (2) an increase in blood pressure leads to a decrease in myocardial efficiency even if the inotropic state is optimally matched to preload and afterload; and (3) an increase in end-diastolic volume improves the efficiency of myocardial pump work. ANIMAL EXPERIMENTS. The validity of the theoretical model was studied in animal experiments with emphasis on the following items: (1) is theoretically optimal efficiency of myocardial pump work achieved by physiologic regulation of myocardial performance? (2) how does sympathetic stimulation influence myocardial efficiency? and (3) how do cardiodepressive agents such as beta-blockers or volatile anesthetics influence myocardial efficiency? METHODS. Experiments were performed on nine mongrel dogs after induction of piritramide--nitrous oxide anesthesia. Standard hemodynamics: heart rate, Psyst, maximum left ventricular pressure rise (dP/dtmax), and SV (thermodilution) as well as coronary blood flow (pressure difference catheter) and myocardial oxygen consumption (Fick principle) were measured. In order to create a broad range of different hemodynamic settings, blood withdrawal and retransfusion of blood and/or colloid osmotic solutions were used to modify intravascular volume. Additionally, the inotropic state was varied by infusion of catecholamines (isoproterenol 0.4-0.8 microgram.kg-1.min-1 or norepinephrine 1-2 micrograms.kg-1.min-1). Experimental myocardial failure was induced by adding halothane (0.8-1.5 MAC) to the basic anesthesia, beta-blockade with propranolol (125-250 micrograms.kg-1), and combination of beta-blockade with a pressure load imposed on the myocardium (propranolol 125-250 micrograms.kg-1 + norepinephrine 1-2 micrograms.kg-1.min-1). RESULTS. During variation of the intravascular blood volume by normo-, hypo-, and hypervolemia, the myocardial efficiency very closely matched the theoretically predicted values of optimal efficiency: the average observed efficiency was 98.8% of predicted optimal efficiency. Increasing afterload with norepinephrine did not alter this close relationship, although absolute values of efficiency decreased as predicted by the theoretical model. Application of isoproterenol resulted in SVs that exceeded optimal values by 41.5%. In contrast, during experimental myocardial failure SVs were too small to achieve the necessary values for optimal pump work; observed myocardial efficiency was therefore significantly lower than optimal efficiency. CONCLUSIONS. For pharmacological interventions, it can be concluded that maximal efficiency of cardiac pump work requires maximal end-diastolic filling in combination with minimal afterload. (ABSTRACT TRUNCATED AT 400 WORDS)

Application of a CCD linear array camera in the quantification of tissue staining: NBT detection in ischaemic myocardium

A method was developed to quantify the intensity of tissue staining using a CCD (charge-coupled device) camera. Reflection spectra of NBT-stained (nitro-blue tetrazolium-stained) and unstained myocardium were recorded via fibre optics coupled to a CCD camera, connected to a microcomputer. The calculation of the intensity of staining was based on evaluation of the NBT-related changes of the reflectance spectrum. In each of six anaesthetized sheep, global ischaemia was induced by cross-clamping of the aorta. The hearts were removed and incubated at 35 degrees C. At predetermined times two sections of ventricular myocardium were taken, one of which was then stained with NBT, the other being left unstained. Evaluation of the reflectance spectra from stained sections during the first phase of ischaemia showed a slight loss of NBT colour intensity followed by a more rapid loss of staining until the values of the unstained sections were reached. In contrast to the conventional visual evaluation, the method provides quantitative data on the intensity of staining, and allows use of the NBT technique for statistical evaluation of what happens over time, and the regional distribution of ischaemic injury of tissue. This method may also be applied to other staining techniques.

Transport of inert gases in mammalian myocardium: comparison with a convection-diffusion model

Because tracer techniques are gaining an increasing importance for imaging flow (and metabolism) in the heart, experimental evidence is needed on the role of convection and diffusion in the transcoronary transport of solutes. In the present work, the transport of four different inert gases through the coronary system is studied in five closed-chest dog experiments and is compared with a digital multicapillary convection-diffusion model. Transport may be defined as flow dependent, as judged by the gross similarity of shape of the time-normalized dilution curves. However, the results show that the transcoronary transport of helium and xenon is more dispersed than that of argon and krypton, probably because of differences in diffusibility and solubility. A comparison of the animal and model experiments emphasizes the importance of diffusive transport of the gases. It is suggested that there is a diffusion shunt that is mainly located within the capillary network itself rather than between conduit vessels. Only for helium (which has the highest diffusivity) was a small arteriovenous shunt fraction seen that is thought to bypass the capillary exchange region. The conclusion is that although there is evidence of diffusional shunting at a capillary level, the inert gas kinetics in the heart are compatible with a basically flow-limited transport.

Transfemoral placement of the left ventricular assist device "Hemopump" during mechanical resuscitation

The Hemopump is a new left-ventricular assist device (21 F diameter), which provides up to 3.5 L/min output after placement in the left ventricle via the femoral artery. We describe the first case in which the device was inserted during resuscitation. The patient developed untreatable sustained ventricular tachycardias/fibrillation 40 hours after coronary artery bypass grafting. After prolonged mechanical resuscitation (about 3 hours) as a last resort the Hemopump was inserted and rhythm and hemodynamics stabilized. In the following hours a decrease in aortic pressure pulsatility indicated, effective left ventricular support when the Hemopump was running. For short periods the patient had nonpulsatile aortic pressure wave forms, implying complete pump dependence. In this situation cardiac output was about 3.0 L/min, mean aortic pressure reached nearly 50 mmHg using high dosage of catecholamines. The patient remained pump-dependent and died due to untreatable ventricular fibrillation. There was no significant hemolysis during the 20 hours the Hemopump was running. Autopsy revealed no signs of thrombembolism, but intimal lesions of the A. iliaca and of the abdominal aorta with subsequent thrombus formation were demonstrated. In view of the experimentally proven benefit in cardiogenic shock and problems and risks caused by the insertion, future indications for clinical use of this new device are discussed.

Heterogeneity of myocardial blood flow under normal conditions and its dependence on arterial PO2

We studied the heterogeneity of myocardial blood flow in nine anesthetized closed-chest dogs using an indicator-dilution technique that allows the stochastic description of transport characteristics for three inert gases (helium, argon, and xenon) from the coronary inflow to outflow. The results show that under normal conditions the transcoronary transport of the tracers is spatially heterogeneous. Heterogeneity is strongly dependent on the arterial oxygen tension over a range of 40-200 Torr. This could be similarly observed with each tracer gas despite different physicochemical properties and was largely independent from the magnitude of coronary blood flow. The results are interpreted to mean that the arteriolar or intratissue PO2 influences myocardial blood flow over a broad range and possibly acts as an important integrating factor in the local regulation of coronary blood flow and flow reserve.

Validity of the lagged normal density function as a model for pulmonary indicator dispersion

The aim of this study was to investigate whether the lagged normal density function is a useful model for the dispersion of intravascular and diffusible indicators in the lungs. In 18 mongrel dogs anesthetized with N2O-piritramide, 221 sets of thermal-indocyanine green dye kinetics were recorded in the pulmonary artery and in the aorta after central venous indicator injection. A model-free deconvolution technique was used to compute the pulmonary transport functions for dye and heart from the measured indicator kinetics (reference method). The lagged normal density function was used to model pulmonary indicator transport. Its parameters were computed by a nonlinear least-squares procedure by iterative convolution. After baseline measurements in nine dogs, pulmonary edema was induced by central venous application of oleic acid. In nine other dogs, measurements were performed before and after postural changes from the horizontal to the vertical position. The mean transit times derived from the lagged normal density function were in good agreement with those obtained after model-free deconvolution. Although the shape (relative dispersion, skewness) of the transport function is less well described by the model, the authors conclude that the lagged normal density function is useful to determine indicator volumes of distribution that require only the correct mean transit times.

Characteristics of the pulmonary transport functions for heat and dye in pulmonary edema and orthostasis

The aim of this study was to investigate whether changes in the distribution of pulmonary blood flow and disturbances of the pulmonary microcirculation can be detected by use of inflow-outflow indicator-dilution measurements. In 18 anesthetized (N2O-piritramide) mongrel dogs 221 thermal-indocyanine green dye indicator dilution kinetics were recorded in the pulmonary artery and aorta after central venous indicator injection. The lagged normal density function was used as a model for the pulmonary transport functions for heat and dye. The parameters of the lagged normal density function were computed by a non-linear least squares procedure by iterative convolution. After baseline measurements, in nine dogs, pulmonary edema was induced by central venous application of oleic acid. In nine other dogs, measurements were performed before and after postural changes. Our data show that both the microvascular injury caused by oleic acid edema and the perfusion heterogeneity caused by orthostasis can be detected by the indicator dilution technique since the both relative dispersion and skewness of the transport functions for heat and dye were significantly increased after these interventions.

Evaluation of methods for indirect calorimetry with a ventilated lung model

A combined lung and ventilator model was built, validated and used to test commercial systems for indirect calorimetry. It simulates O2 uptake and CO2 excretion under ventilator treatment conditions. In the model inspiratory gases are diluted with N2 and CO2 to give the desired expiratory concentrations. Minute volume, FIO2, ventilatory pressure, VO2, VCO2 and consequently RQ can be altered to simulate the adult clinical situation. A selected respiratory pattern is maintained by the lung model. Equipment for indirect calorimetry can then be connected to it and the results compared. Reference values are derived from measurements with a mass spectrometer and a Godart spirometer. Three commercially available instruments (Beckman MMC, Horizon MMC and Engström MC) were evaluated with this system. The limits of agreement with the reference values under different conditions (FIO2 0.4-0.7, ventilatory pressure 0-50 cmH2O) were determined. Differences as high as 15% from the true values of VO2 and V CO2 were observed. The pattern of mechanical ventilation and the intrinsic properties of the analyzers in the equipment used for indirect calorimetry influence measurements to a significant extent.

No pulmonary edema or congestion after central venous injection of conventional and newer contrast media in dogs

Our aim was to determine whether large central venous doses of ionic diatrizoate, nonionic iopromide, or nonionic iotrolane produce pulmonary edema or pulmonary congestion in dogs. Eighteen dogs (six per group) anesthetized with piritramide and N2O received three sequential doses (1.5 mL/kg body weight) of one contrast medium in less than 20 seconds. Before the first injection, and again 1, 5, 10, 20, and 30 minutes after each contrast injection, extravascular lung water, pulmonary blood volume, and cardiac output were determined by thermal-dye dilution. Neither extravascular lung water nor pulmonary blood volume increased after any contrast medium. Pulmonary blood volume and cardiac output decreased slightly but not significantly after all contrast media during the course of the study. We conclude that diatrizoate, iopromide, or iotrolane do not produce pulmonary edema or congestion in dogs.

Interference with the prostaglandin system as a therapeutical concept to protect the myocardium during ischemic stress: experimental studies with inhibition of thromboxane synthesis

The characterization of thromboxane A2 as vasoconstrictor and potent stimulus of platelet aggregation has led to attempts to overcome these effects obviously unfavourable in ischemia. As an attractive approach, we examined potentially protective results of thromboxane synthetase inhibition on canine myocardium stressed by transient ischemia, using as inhibitor the imidazole derivative UK 38.485. On anaesthetized open-chest mongrel-dogs (n = 5) repeated ischemia (3 min) was produced by proximal, intermittent occlusion of the LAD artery. In each experiment 3-4 control occlusions were compared to 3-4 occlusions under therapy. The efficiency of the drug (5 mg/kg body weight, i.v., 30 min before therapy occlusion) was examined (a) by quantification of the energy deficit occurring as the difference between oxygen demand and uptake during occlusion, (b) by the amounts of potassium, inorganic phosphate, and lactate released in the postischemic reperfusion and (c) by changes of the regional myocardial wall function in the central- and peripheral ischemic zone. Compared to control, premedication with UK 38.485 led to a reduced energy deficit (-39.1%; p less than 0.01) combined with a significant decrease in the release of potassium (-15.7%; p less than 0.001), inorganic phosphate (-20.2%; p less than 0.002), and lactate (-20.7%; p less than 0.01). Regional myocardial wall function was improved in the central and peripheral ischemic region as demonstrated by a significantly reduced systolic bulging. The protective effects seem to be mainly due to enhanced flow to ischemic areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effects of right atrial, right ventricular apex and atrioventricular sequential pacing on myocardial oxygen consumption and cardiac efficiency: a laboratory investigation

As the impact of cardiac pacing on myocardial energetics has not yet been established, this laboratory investigation was undertaken to evaluate the effects of right atrial (AP), right ventricular apex (VP) and atrioventricular sequential pacing (AVP) on cardiac energetics in a closed-chest model. Ninety-two pacing interventions were performed in ten anesthetized mongrel dogs with normal loading conditions and contractile states. The energetic effects of pacing were assessed in terms of myocardial oxygen consumption (MVO2), its hemodynamic determinants and cardiac efficiency. Efficiency was calculated as the ratio of O2-equivalent of external cardiac work to MVO2, using standard definitions. In the first series of experiments 36 intra-individual comparisons were made between AP and VP at identical rates (95-210 beats/min). In the second series AVP was compared to VP in 10 intra-individual comparisons at identical rates (109-190 beats/min). MVO2 was lower (p less than 0.001) during AP (8.30 +/- 2.14 ml O2/min.100 g) compared to VP (10.16 +/- 3.15 ml O2/min.100 g) at the same rate (158 +/- 32 beats/min). Efficiency (p less than 0.001) was considerably higher during AP (21.6 +/- 5.7%) compared to VP (12.8 +/- 5.9%). During AVP, MVO2 (10.85 +/- 1.76 ml O2/min.100 g) was not significantly different from VP (10.57 +/- 1.34 ml O2/min.100 g) at the same rate (146 +/- 25 beats/min). Hemodynamics were superior with AVP compared to VP. Efficiency was significantly higher (p less than 0.01) with sequential (15.4 +/- 3.9%) as compared to ventricular pacing (12.0 +/- 3.2%). In conclusion, this study indicated that VP exerts disadvantageous effects on MVO2 and cardiac efficiency. AP has beneficial effects on cardiac energetics because it improves the relationship between mechanical performance of the heart and its energy requirements. AVP results in a higher efficiency than VP due to superior hemodynamics, despite MVO2 levels comparable to those of VP. The mechanism of energy waste with right ventricular apex pacing is probably related to an asynchronous contraction in the ventricular myocardium due to a nonphysiological spread of excitation.

Thermal recovery after passage of the pulmonary circulation assessed by deconvolution

For indicator-dilution studies, complete thermal recovery after passage of heat through the pulmonary circulation would be desirable. However, the results in the literature obtained by extrapolation techniques are inconsistent. To overcome problems of the extrapolation approach, transport functions of the pulmonary circulation (including the left heart) were computed by deconvolution of pulmonary arterial and aortic pairs of thermodilution curves after central venous indicator injection (10 ml of an ice-cold blood indocyanine green dye mixture). Thermal recovery was determined as the finite integral of the transport function. Thirteen mongrel dogs under piritramid-N2O anesthesia were examined under base-line conditions, in orthostasis to alter the distribution of pulmonary blood flow (9 dogs), and in oleic acid edema (8 dogs). Using the deconvolution approach, thermal recovery was 0.97 +/- 0.04 under base-line conditions, 0.96 +/- 0.03 in orthostasis, and 0.96 +/- 0.05 in pulmonary edema. Thermal recovery determined from extrapolated dilution curves was greater than 100% in all groups, a physically impossible finding. It is concluded that thermal recovery is incomplete but insensitive with respect to the distribution of blood flow and to the size of the extravascular compartment. Monoexponential extrapolation is unsuited for the determination of thermal recovery.