Improved Accuracy of Cardiac Tissue-Level Simulations by Considering Membrane Resistance as a Cellular-Level Optimization Objective

Cardiac cellular models are utilized as the building blocks for tissue simulation. One of the imprecisions of conventional cellular modeling, especially when the models are used in tissue-level modeling, stems from the mere consideration of cellular properties (e.g., action potential shape) in parameter tuning of the model. In our previous work, we put forward an accurate framework in which membrane resistance (R_m) reflecting inter-cellular characteristics, i.e., electrotonic effects, was considered alongside cellular features in cellular model fitting. This paper, for the first time, examines the hypothesis that considering R_m as an additional optimization objective improves the accuracy of tissue-level modeling. To study this hypothesis, after cellular-level optimization of a well-known model, source-sink mismatch configurations in a 2-dimensional model are investigated. The results demonstrate that including R_m in the optimization protocol yields a substantial improvement in the relative error of the critical transition border which is defined as the minimum window size between source and sink that wave propagates. Model developers can utilize the proposed concept during parameter tuning to increase the accuracy of models.

A Novel Bi-Level Framework for Fitting the Parameters in Cardiac Cellular Models

Cardiac models constructed from sets of differential equations provide invaluable information about heart mechanism and disorder of both human and animals. As tuning the parameters is a profoundly important step of modeling, this paper presents a novel parametrization technique based on a bilevel framework that benefits from two solution approaches, namely mixed integer genetic algorithm (MIGA) and linear least squares (LLS). In the upper-level optimization step, the action potential (AP) of the model is fitted to the reference AP using MIGA. In the lower-level optimization step, the mismatch between the total current of the model and reference is minimized via a clamp concept-based linearization and LLS solution approach. Notably, the clamp concept can diminish the nonlinearity of the parameter fitting problem. The issue of dependency on initial parameters in the lower-level problem, as well as the sensitivity of model parameters to linearization, are circumvented by MIGA in the upper-level optimization. For evaluation of MIGA-LLS performance, two complex human ventricular models are employed. The results demonstrate that in comparison to the genetic algorithm (GA)-based approach, the proposed framework significantly reduces the average and variation of normalized root-mean-squared error (NRMSE) in terms of the AP and total current in different trials. Variability in the resulting parameter values is considerably decreased as well.

Altered response in renal blood flow and oxygen tension to contrast media in diabetic rats

Purpose: To investigate the effect of the contrast medium (CM) iopromide on renal microcirculation and oxygen tension in non-diabetic control and streptozotocin-diabetic Wistar Furth rats.

Materials and Methods: Oxygen tension was measured with Clark-type microelectrodes and blood flow with laser-Doppler flow probes. In order to differentiate between an acutely increased blood glucose concentration and a long-term diabetic state, some of the non-diabetic control rats were intravenously infused with glucose.

Results: CM decreased the medullary oxygen tension in control (non-diabetic normoglycemic) rats (∼35%) but not in diabetic rats. Medullary blood flow in control rats increased after CM administration and remained elevated, while it was unchanged in the diabetic rats. In response to CM, glucose-infused control rats responded similarly to control animals in medullary oxygen tension, but similarly to diabetic rats in medullary blood flow. Contrary to in control rats, medullary oxygen tension was unchanged in diabetic animals after CM administration.

Conclusion: Streptozotocin-diabetic rats have an altered response to intravenous injection of the CM iopromide compared to non-diabetic rats. The unaltered medullary oxygen tension, seen in the diabetic group after injection of CM, suggests that non-hemodynamic mechanisms are responsible for the increased frequency of renal failure commonly seen among diabetic patients.

Effects of High- and Low-Osmolar Contrast Media on Renal Plasma Flow and Glomerular Filtration Rate in Euvolaemic and Dehydrated Rats

The effects of a slow intravenous injection of contrast media (CM) on renal function and haemodynamics were investigated in euvolaemic and dehydrated rats. Iodine-equivalent doses (1600 mg I/kg body weight) of ioxithalamate, ioxaglate, iopamidol and iohexol were used. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were assessed with clearance techniques. In euvolaemic rats no statistically significant decrease in GFR or RPF was found after CM injections. In the dehydrated rats the changes in GFR were more pronounced and this was significantly decreased in the ioxithalamate and iopamidol groups while RPF was still not decreased. This study indicates that dehydration potentiates adverse effects of CM on GFR and that there may be differences between the effects of low-osmolar and high-osmolar CM on GFR and also between different low-osmolar CM.

ET-A receptor antagonist BQ123 prevents radiocontrast media-induced renal medullary hypoxia

Purpose: Renal vasoconstriction with resultant tissue hypoxia, especially in the renal medulla, has been suggested to play a role in contrast media (CM)-induced nephropathy. Endothelin (ET) is released into the blood stream following CM injection and has been proposed as a potential mediator through its vasoconstrictive properties.

Material and Methods: To investigate the possible protective influence of ET-receptor antagonists against CM-induced reduction in renal function, we studied the effects of injection of iopromide with and without pretreatment with BQ123 (ET-A antagonist) or BQ788 (ET-B antagonist) on renal superficial cortical flow (CBF), outer medullary blood flow (OMBF) and outer medullary oxygen tension (pO2) in normal rats.

Results: Administration of CM (1600 mg I/kg b.w.) did not affect CBF in any of the groups. However, a transient decrease in OMBF occurred, which was unaffected by both BQ123 and BQ788. Also a transient decrease in outer medullary pO2 was induced by CM administration. The pO2 reduction was significantly smaller after pretreatment with BQ123, than after injection of CM alone or together with BQ788, and pO2 returned more rapidly to the control level. Neither receptor antagonist had an effect on CM-mediated increases in electrolyte excretion.

Conclusion: In the normal rat, activation of ET-A receptors is partly involved in the depression of outer medullary pO2 caused by injection of iopromide. However, the decrease in OMBF after iopromide injection is not mediated by ET receptors. The beneficial effects of the ET-A receptor antagonist on CM-induced changes in outer medullary pO2 seem therefore not primarily mediated on the hemodynamic level but may rather involve tubular transport mechanisms.

Effect of Intravenous Contrast Media on Proximal and Distal Tubular Hydrostatic Pressure in the Rat Kidney

The effect of i.v. injection of contrast media (CM, 1 600 mg I/kg b.w.) on proximal and distal tubular hydrostatic pressure (PTHP, DTHP) in the rat was investigated using a micropuncture technique. The PTHP and DTHP after injection of diatrizoate, iohexol, ioxaglate, or mannitol returned to control values within approximately 20 min. However, following iotrolan injection PTHP was still elevated above control levels after 35 min while DTHP remained elevated throughout the experiment (50 min). Iotrolan has a lower osmotic potential than the other CM when given in equivalent iodine doses. The concentration of iotrolan may thus increase more along the tubules than the other CM and consequently lead to a higher viscosity of urine, resulting in increases in PTHP and DTHP. The high intratubular pressure induced by iotrolan may explain our previous findings of reduced single nephron glomerular filtration rate caused by this CM.

Pressure-dependent changes in haematocrit and plasma volume during anaesthesia, a randomised clinical trial

BACKGROUND

Induction of general anaesthesia has been shown to cause haemodilution and an increase in plasma volume. The aim of this study was to evaluate whether prevention of hypotension during anaesthesia induction could avoid haemodilution.

METHODS

Twenty-four cardiac surgery patients, 66 ± 10 years, were randomised to receive either norepinephrine in a dose needed to maintain mean arterial blood pressure (MAP) at pre-anaesthesia levels after induction or to a control group that received vasopressor if MAP decreased below 60 mmHg. No fluids were infused. Changes in plasma volume were calculated with standard formula: 100 × (Hct(pre)/Hct(post) - 1)/(1 - Hct(pre)). Arterial blood gas was analysed every 10 minutes and non-invasive continuous haemoglobin (SpHb) was continuously measured.

RESULTS

Pre-anaesthesia MAP was 98 ± 7 mmHg. Ten minutes after anaesthesia induction, the haematocrit decreased by 5.0 ± 2.5% in the control group compared with 1.2 ± 1.4% in the intervention group, which corresponds to increases in plasma volume by 310 ml and 85 ml respectively. MAP decreased to 69 ± 15 mmHg compared to 92 ± 10 mmHg in the intervention group. The difference maintained throughout the 70 min intervention period. The change in haemoglobin level measured by blood gas analysis could not be detected by SpHb measurement. The mean bias between the SpHb and blood gas haemoglobin was 15 g/l.

CONCLUSION

During anaesthesia induction, haematocrit decreases and plasma volume increases early and parallel to a decrease in blood pressure. This autotransfusion is blunted when blood pressure is maintained at pre-induction levels with norepinephrine.

Cardiac fiber rotation distorts surface measurements of anisotropic propagation

Anisotropy is often determined experimentally from epicardial propagation measurements. We hypothesize that the direction of wave propagation on the epicardial surface is not aligned with the epicardial fiber orientation, due to intramural fiber rotation. In this paper, we modeled the effect of cardiac tissue fiber rotation on wave propagation. We used a three dimensional computer model of varying thickness with a 120 degree fiber rotation through the thickness. The angle difference between the direction of propagation and fiber orientation was most pronounced for thin tissue, and decreased with increasing tissue thickness. This angle also increased with the time elapsed since stimulation. Finally, we demonstrated that the fiber rotation from epicardium to endocardium results in inaccurate measurements of conduction velocities at the epicardium, particularly in thin tissues.

Application of scale-space descriptors for the reliable detection of keypoints for image registration in optical mapping studies in whole heart preparations

Data acquired using Optical Mapping (OM) studies are affected by motion artifacts due to the inherent contraction of the heart. Those artifacts can be reduced by registering the images obtained by the OM system or by the combination of approaches like physical restraint of the heart or ratiometry with image registration. Due to the lack of high contrast features most registration methods are not suitable for this application. This paper is focused on the utilization of scale space theory and local descriptors to enhance the detection of local features in OM images and to describe the movement of keypoints. This information can be used to determine a suitable set of transformations to perform the registration process.

Norepinephrine causes a pressure-dependent plasma volume decrease in clinical vasodilatory shock

BACKGROUND

Recent experimental studies have shown that a norepinephrine-induced increase in blood pressure induces a loss of plasma volume, particularly under increased microvascular permeability. We studied the effects of norepinephrine-induced variations in the mean arterial pressure (MAP) on plasma volume changes and systemic haemodynamics in patients with vasodilatory shock.

METHODS

Twenty-one mechanically ventilated patients who required norepinephrine to maintain MAP > or =70 mmHg because of septic/postcardiotomy vasodilatory shock were included. The norepinephrine dose was randomly titrated to target MAPs of 60, 75 and 90 mmHg. At each target MAP, data on systemic haemodynamics, haematocrit, arterial and mixed venous oxygen content and urine flow urine were measured. Changes in the plasma volume were calculated as 100 x (Hct(pre)/Hct(post)-1)/ (1-Hct(pre)), where Hct(pre) and Hct(post) are haematocrits before and after intervention.

RESULTS

Norepinephrine doses to obtain target MAPs of 60, 75 and 90 mmHg were 0.20+/-0.18, 0.29+/-0.18 and 0.42+/-0.31 microg/kg/min, respectively. From 60 to 90 mmHg, increases in the cardiac index (15%), systemic oxygen delivery index (25%), central venous pressure (CVP) (20%) and pulmonary artery occlusion pressure (33%) were seen, while the intrapulmonary shunt fraction was unaffected by norepinehrine. Plasma volume decreased by 6.5% and 9.4% (P<0.0001) when blood pressure was increased from 60 to 75 and 90 mmHg, respectively. MAP (P<0.02) independently predicted the decrease in plasma volume with norepinephrine but not CVP (P=0.19), cardiac index (P=0.73), norepinephrine dose (P=0.58) or urine flow (P=0.64).

CONCLUSIONS

Norepinephrine causes a pressure-dependent decrease in the plasma volume in patients with vasodilatory shock most likely caused by transcapillary fluid extravasation.

Low-dose vasopressin increases glomerular filtration rate, but impairs renal oxygenation in post-cardiac surgery patients

BACKGROUND

The beneficial effects of vasopressin on diuresis and creatinine clearance have been demonstrated when used as an additional/alternative therapy in catecholamine-dependent vasodilatory shock. A detailed analysis of the effects of vasopressin on renal perfusion, glomerular filtration, excretory function and oxygenation in man is, however, lacking. The objective of this pharmacodynamic study was to evaluate the effects of low to moderate doses of vasopressin on renal blood flow (RBF), glomerular filtration rate (GFR), renal oxygen consumption (RVO2) and renal oxygen extraction (RO2Ex) in post-cardiac surgery patients.

METHODS

Twelve patients were studied during sedation and mechanical ventilation after cardiac surgery. Vasopressin was sequentially infused at 1.2, 2.4 and 4.8 U/h. At each infusion rate, systemic haemodynamics were evaluated by a pulmonary artery catheter, and RBF and GFR were measured by the renal vein thermodilution technique and by renal extraction of 51chromium-ethylenediaminetetraacetic acid, respectively. RVO2 and RO2Ex were calculated by arterial and renal vein blood samples.

RESULTS

The mean arterial pressure was not affected by vasopressin while cardiac output and heart rate decreased. RBF decreased and GFR, filtration fraction, sodium reabsorption, RVO2, RO2Ex and renal vascular resistance increased dose-dependently with vasopressin. Vasopressin exerted direct antidiuretic and antinatriuretic effects.

CONCLUSIONS

Short-term infusion of low to moderate, non-hypertensive doses of vasopressin induced a post-glomerular renal vasoconstriction with a decrease in RBF and an increase in GFR in post-cardiac surgery patients. This was accompanied by an increase in RVO2, as a consequence of the increases in the filtered tubular load of sodium. Finally, vasopressin impaired the renal oxygen demand/supply relationship.

Reduced conduction reserve of the propagating cardiac impulse in the diabetic rat heart: a model study

Conduction velocity is dependent on two main factors: intercellular electrical coupling and cellular electrical excitability. There is significant redundancy, 'conduction reserve', in these parameters such that significant reduction in the conduction velocity of the action potential requires either a severe change in one of these parameters or a combined change in both parameters. Studies in diabetic rat hearts have shown a significant reduction in the conduction reserve and it was hypothesized that this is mainly due to the lateralization of the gap junction protein connexin 43 (Cx43). To gain a better understanding of the effect of reduced intercellular coupling, a rat ventricle myocyte model was used to simulate propagation along a strand of cells. Simulations were performed to assess the effect of reduction of intercellular conductance on the conduction velocity. As the conductance of the gap junction decreased a significant reduction in the conduction velocity was observed. The relationship between conduction velocity and intercellular coupling became steeper with decreasing coupling, such that conduction velocity became increasingly sensitive to further uncoupling. This is consistent with experimental results, in which application of the gap junction uncoupler heptanol caused a larger conduction slowing in diabetic hearts than in controls.

Vasopressin decreases intestinal mucosal perfusion: a clinical study on cardiac surgery patients in vasodilatory shock

BACKGROUND

Low to moderate doses of vasopressin have been used in the treatment of cathecholamine-dependent vasodilatory shock in sepsis or after cardiac surgery. We evaluated the effects of vasopressin on jejunal mucosal perfusion, gastric-arterial pCO2 gradient and the global splanchnic oxygen demand/supply relationship in patients with vasodilatory shock after cardiac surgery.

METHODS

Eight mechanically ventilated patients, dependent on norepinephrine to maintain mean arterial pressure (MAP) > or = 60 mmHg because of septic/post-cardiotomy vasodilatory shock and multiple organ failure after cardiac surgery, were included. Vasopressin was sequentially infused at 1.2, 2.4 and 4.8 U/h for 30-min periods. Norepinephrine was simultaneously decreased to maintain MAP at 75 mmHg. At each infusion rate of vasopressin, data on systemic hemodynamics, jejunal mucosal perfusion, jejunal mucosal hematocrit and red blood cell velocity (laser Doppler flowmetry) as well as gastric-arterial pCO2 gradient (gastric tonometry) and splanchnic oxygen and lactate extraction (hepatic vein catheter) were obtained.

RESULTS

The cardiac index, stroke volume index and systemic oxygen delivery decreased and systemic vascular resistance and systemic oxygen extraction increased significantly, while the heart rate or global oxygen consumption did not change with increasing vasopressin dose. Jejunal mucosal perfusion decreased and the arterial-gastric-mucosal pCO2 gradient increased, while splanchnic oxygen or lactate extraction or mixed venous-hepatic venous oxygen saturation gradient were not affected by increasing infusion rates of vasopressin.

CONCLUSIONS

Infusion of low to moderate doses of vasopressin in patients with norepinephrine-dependent vasodilatory shock after cardiac surgery induces an intestinal and gastric mucosal vasoconstriction.

Insulin secretion in alcoholics in a withdrawal state

Insulin secretion was studied after stimulation with oral glucose and intravenous glucagon in 23 chronic alcoholics in a withdrawal state. Each subject was studied twice at one week's interval between the examinations. The insulin and C-peptide responses to glucagon were lower in the early withdrawal state. Moreover, the insulin and C-peptide increments were, when related to the magnitude of the glycemic stimulus, lower in the early than in the late withdrawal state. The fasting values of blood glucose, insulin and C-peptide and the blood glucose and C-peptide levels after oral glucose were higher in the early withdrawal state. These findings indicate that glucose metabolism in alcoholics in a withdrawal state can be disturbed by impaired insulin secretion and insulin resistance.

Immunoreactive insulin in portal and hepatic venous blood in patients with insuloma

The insulin level has been determined simultaneously in portal and hepatic venous blood in four patients with insuloma before and after administration of glucose and tolbutamide. Three patients displayed a higher insulin level in hepatic than in portal blood, although no hepatic metastases could be detected by radiologic examination. In contrast, portal insulin concentrations always exceeded hepatic in four control patients investigated in a similar way. The implications of these results are discussed.

Four cases of long-standing diarrhoea and colic pains cured by fructose-free diet--a pathogenetic discussion

Four patients with a long history of abdominal swelling, colic pains and diarrhoea were cured by a fructose-free diet. They were all given an oral load of (14C) fructose and their expiratory excretion of 14CO2 was found to be significantly lower than that of control patients with similar symptoms. It is concluded taht the patients cured by a fructose-free diet might have a partial fructose malabsorption.

Is glucose intolerance after pancreatitis related to pancreatic tissue damage?

Endoscopic retrograde pancreatography (ERP) was performed in 48 patients who had been hospitalized for pancreatitis. The findings were related to results of oral glucose tolerance tests. Patients with gross changes at ERP tended to have latent or manifest diabetes. In patients with latent or manifest diabetes, the increase in C-peptide after oral glucose was lower than in healthy subjects, while insulin sensitivity, estimated with euglycemic insulin clamp technique, was within the same range as in healthy subjects. It is concluded that gross changes of the pancreatic ducts after pancreatitis are often accompanied by widespread tissue damage leading to deficient B-cell function and decreased glucose tolerance.

Isolated thyrotropin deficiency in a man with narcoleptic attacks

A patient with narcoleptic attacks and isolated thyrotropin deficiency is presented. Substitution with l-thyroxine did not relieve his narcoleptic attacks. Deficiency, in the central nervous system, of the ergotropic substance thyrotropin-releasing hormone (TRH) might have caused the thyrotropin deficiency and contributed to the narcoleptic attacks. However, prolonged oral medication with TRH, in doses of 120 or 240 g daily, failed to attain any significant relief. Although this does Not exclude TRH unresponsiveness due to absent or defective TRH receptors, the true cause of the disease remains to be elucidated.

Insulin in portal, hepatic and peripheral venous blood after glucose, tolbutamide and glipizide stimulation. Indication of insulin release from peripheral tissues

Insulin in portal, hepatic and/or peripheral venous blood was determined in 16 patients admitted to a surgical ward for various diseases. Portal venous blood was obtained via a catheter introduced into the portal vein either through the umbilical vein remnant or transhepatically. Four subjects were given a peroral load of glucose, followed after 60 min by i.v. tolbutamide. In simultaneous blood samples, two of these subjects showed higher insulin concentrations in peripheral venous blood than in portal venous blood. Twelve subjects were given i.v. glipizide. In one subject blood samples were drawn from the portal vein, a hepatic vein and a peripheral vein and in six subjects from the portal vein and a hepatic vein. Two subjects showed higher insulin concentrations in peripheral venous blood than in portal venous blood. The mean peripheral insulin response (six subjects) was of the same magnitude as the mean hepatic insulin response (six subjects). It is suggested that these findings reflect a release of previously bound insulin from peripheral tissues.

Does a disturbed insulin release promote hypoglycemia in alcoholics?

Peroral glucose tolerance tests, i.v. tolbutamide tests and postfasting alcohol tests were performed in three alcoholics, who had been admitted to hospital with hypoglycemic symptoms. In one one case the findings indicated extreme insulin sensitivity and in two cases there was evidence of a distrubed insulin release. These two factors might have a bearing on the occurrence of hypoglycemic symptoms in alcoholics.

Relative cardiac expression of growth hormone receptor and insulin-like growth factor-I mRNA in congenital heart disease

GH may exert direct growth-promoting and metabolic actions on target tissues, but most of its effects are mediated by circulating (endocrine) or local (auto-/paracrine) IGF-I. The GH/IGF-I system has an important role in cardiac development and in maintaining the structure and function of the heart. A subgroup of children with pronounced heart defects will eventually need transplants, owing to congestive heart failure. Since the symptoms are often severe and may progress while waiting for surgery, it is necessary to develop supportive medical treatment. GH has been proposed as a therapeutic agent in adults with heart failure, but to date studies are lacking on children and more information is necessary. We have examined the expression of IGF-I mRNA and GH-receptor (GH-R) mRNA in children undergoing surgery for congenital heart disease. Eighteen children scheduled for open-heart surgery were included in the study. Right auricular biopsies were taken at the time of venous catheterization preceding cardiac bypass. The specimens were analysed using realtime PCR. We were able to show expression of both IGF-I mRNA and GH-R mRNA in the pediatric heart. The relative expressions were intercorrelated (r=0.75, p<0.001). GH-R mRNA correlated positively to standardized weight (r=0.65, p=0.004), body mass index (BMI) (r=0.59, p=0.01), and standardized BMI (r=0.59, p=0.01). IGF-I mRNA only correlated to BMI (r=0.50, p=0.04). This is the first study displaying cardiac expression of IGF-I mRNA and GH-R mRNA in children with congenital heart disease, although further studies are needed to define a role for GH in the treatment of these patients.

Propagation of the cardiac impulse in the diabetic rat heart: reduced conduction reserve

Diabetes mellitus is a growing epidemic with severe cardiovascular complications. Although much is known about mechanical and electrical cardiac dysfunction in diabetes, few studies have investigated propagation of the electrical signal in the diabetic heart and the associated changes in intercellular gap junctions. This study was designed to investigate these issues, using hearts from control and diabetic rats. Diabetic conditions were induced by streptozotocin (STZ), given i.v. 7-14 days before experiments. Optical mapping with the voltage-sensitive dye di-4-ANEPPS, using hearts perfused on a Langendorff apparatus, showed little change in baseline conduction velocity in diabetic hearts, reflecting the large reserve of function. However, both the gap junction uncoupler heptanol (0.5-1 mM) and elevated potassium (9 mM, to reduce cell excitability) produced a significantly greater slowing of impulse propagation in diabetic hearts than in controls. The maximal action potential upstroke velocity (an index of the sodium current) and resting potential was similar in single ventricular myocytes from control and diabetic rats, suggesting similar electrical excitability. Immunoblotting of connexin 43 (Cx43), a major gap junction component, showed no change in total expression. However, immunofluorescence labelling of Cx43 showed a significant redistribution, apparent as enhanced Cx43 lateralization. This was quantified and found to be significantly larger than in control myocytes. Labelling of two other gap junction proteins, N-cadherin and beta-catenin, showed a (partial) loss of co-localization with Cx43, indicating that enhancement of lateralized Cx43 is associated with non-functional gap junctions. In conclusion, conduction reserve is smaller in the diabetic heart, priming it for impaired conduction upon further challenges. This can desynchronize contraction and contribute to arrhythmogenesis.

Optical mapping system for recording action potential durations in adult mouse left and right atrium

The increasing availability of murine models of the cardiovascular system has created a need for instrumentation and methods for assessing murine cardiovascular function. We have adapted an existing optical mapping system based on voltage-sensitive dyes to record from an isolated mouse atrial preparation. Initial results indicate that our approach is capable of recording action potentials from isolated mouse atria with sufficient signal quality to determine action potential duration (APD). Preliminary observations suggest that gradients in APD exist in the mouse atria and are similar to those observed in the atria of larger mammals. Future work with this technique will provide important information about mouse atrial electrophysiology and how it relates to that of larger mammals.

Actions of emigrated neutrophils on Na+ and K+ currents in rat ventricular myocytes

Interactions between neutrophils and the ventricular myocardium can contribute to tissue injury, contractile dysfunction and generation of arrhythmias in acute cardiac inflammation. Many of the molecular events responsible for neutrophil adhesion to ventricular myocytes are well defined; in contrast, the resulting electrophysiological effects and changes in excitation-contraction coupling have not been studied in detail. In the present experiments, rat ventricular myocytes were superfused with either circulating or emigrated neutrophils and whole-cell currents and action potential waveforms were recorded using the nystatin-perforated patch method. Almost immediately after adhering to ventricular myocytes, emigrated neutrophils caused a depolarization of the resting membrane potential and a marked prolongation of myocyte action potential. Voltage clamp experiments demonstrated that following neutrophil adhesion, there was (i) a slowing of the inactivation of a TTX-sensitive Na(+) current, and (ii) a decrease in an inwardly rectifying K(+) current. One cytotoxic effect of neutrophils appears to be initiated by enhanced Na(+) entry into the myocytes. Thus, manoeuvres that precluded activation of Na(+) channels, for example holding the membrane potential at -80 mV, significantly increased the time to cell death or prevented contracture entirely. A mathematical model for the action potential of rat ventricular myocytes has been modified and then utilized to integrate these findings. These simulations demonstrate the marked effects of (50-fold) slowing of the inactivation of 2-4% of the available Na(+) channels on action potential duration and the corresponding intracellular Ca(2+) transient. In ongoing studies using this combination of approaches, are providing significant new insights into some of the fundamental processes that modulate myocyte damage in acute inflammation.

Cardiopulmonary bypass in humans--jejunal mucosal perfusion increases in parallel with well-maintained microvascular hematocrit

BACKGROUND

An imbalance between splanchnic oxygen supply and demand occurs during cardiopulmonary bypass (CPB) in man, which might disrupt the intestinal mucosal barrier function. The aim of the present study was to evaluate the effects of mild hypothermic CPB on intestinal mucosal perfusion in man undergoing cardiac surgery. Additionally we aimed to identify variables, which independently could predict changes of intestinal mucosal microcirculatory variables during CPB.

METHODS

Jejunal mucosal perfusion (JMP), jejunal mucosal hematocrit (JMHt), red blood cell (RBC) velocity and arteriolar vasomotion using endoluminal jejunal laser Doppler flow metry were studied in eight cardiac surgical patients before and during CPB at a temperature of 34 degrees C.

RESULTS

Cardiopulmonary bypass and the accompanied hemodilution (25-30%) induced a 44% increase in JMP (P < 0.05) and a 42% increase in RBC velocity (P < 0.01), with no change in JMHt. The oscillation amplitude of JMP, at a fundamental frequency of 2.8 cycles min(-1), increased with 175% (P < 0.05) during CPB. Splanchnic oxygen extraction increased by 64% during CPB (P < 0.05). Stepwise multiple regression analysis identified systemic hematocrit, arterial O2 and CO2 tension and splanchnic oxygen extraction as independent predictors of RBC velocity during CPB (R2=0.63, P < 0.001). The oscillation amplitude of JMP was predicted by RBC velocity and splanchnic oxygen extraction (R2= 0.68, P <0.0001).

CONCLUSIONS

The increase in RBC velocity and enhanced arteriolar vasomotion, as well as maintained jejunal mucosal hematocrit, are microcirculatory, compensatory mechanisms for the splanchic oxygen supply/demand mismatch seen during cardiopulmonary bypass in humans.

Two-minute rapid eye movement (REM) density fluctuations in human REM sleep

Rapid eye movement (REM) density fluctuations during REM sleep were studied in five healthy young adults (23-26 years of age). Appropriate electro-oculographic (EOG) montage and automated EOG analysis enabled the detection of horizontal, vertical, and oblique REMs. REM density time series based on these REMs were formed for all the REM periods of the subjects. Autoregressive (AR) spectral analysis of the REM density time series estimated periodicities in the range of 1.7-2.4 min for 14 of the 16 REM periods analyzed, regardless of duration or number of REMs. Four subjects had such periodicities in each of their REM periods and the fifth subject had such periodicities in half the REM periods. This REM density fluctuation at a periodicity of about 2 min may relate to an important 'rhythmic' component of the REM generating mechanism(s).

Altered response in renal blood flow and oxygen tension to contrast media in diabetic rats

PURPOSE

To investigate the effect of the contrast medium (CM) iopromide on renal microcirculation and oxygen tension in non-diabetic control and streptozotocin-diabetic Wistar Furth rats.

MATERIALS AND METHODS

Oxygen tension was measured with Clark-type microelectrodes and blood flow with laser-Doppler flow probes. In order to differentiate between an acutely increased blood glucose concentration and a long-term diabetic state, some of the non-diabetic control rats were intravenously infused with glucose.

RESULTS

CM decreased the medullary oxygen tension in control (non-diabetic normoglycemic) rats ( approximately 35%) but not in diabetic rats. Medullary blood flow in control rats increased after CM administration and remained elevated, while it was unchanged in the diabetic rats. In response to CM, glucose-infused control rats responded similarly to control animals in medullary oxygen tension, but similarly to diabetic rats in medullary blood flow. Contrary to in control rats, medullary oxygen tension was unchanged in diabetic animals after CM administration.

CONCLUSION

Streptozotocin-diabetic rats have an altered response to intravenous injection of the CM iopromide compared to non-diabetic rats. The unaltered medullary oxygen tension, seen in the diabetic group after injection of CM, suggests that non-hemodynamic mechanisms are responsible for the increased frequency of renal failure commonly seen among diabetic patients.

Voltage-sensitive dye mapping in Langendorff-perfused rat hearts

An imaging system suitable for recordings from Langendorff-perfused rat hearts using the voltage-sensitive dye 4-[beta-[2-(di-n-butylamino)-6-naphthyl]vinyl]pyridinium (di-4-ANEPPS) has been developed. Conduction velocity was measured under hyper- and hypokalemic conditions, as well as at physiological and reduced temperature. Elevation of extracellular [K(+)] to 9 mM from 5.9 mM caused a slowing of conduction velocity from 0.66 +/- 0.08 to 0.43 +/- 0.07 mm/ms (35%), and reduction of the temperature to 32 degrees C from 37 degrees C caused a slowing from 0.64 +/- 0.07 to 0.46 +/- 0.05 mm/ms (28%). Ventricular activation patterns in sinus rhythm showed areas of early activation (breakthrough) in both the right and left ventricle, with breakthrough at a site near the apex of the right ventricle usually occurring first. The effects of mechanically immobilizing the preparation to reduce motion artifact were also characterized. Activation patterns in epicardially paced rhythm were insensitive to this procedure over the range of applied force tested. In sinus rhythm, however, a relatively large immobilizing force caused prolonged PQ intervals as well as altered ventricular activation patterns. The time-dependent effects of the dye on the rat heart were characterized and include 1) a transient vasodilation at the onset of dye perfusion and 2) a long-lasting prolongation of the PQ interval of the electrocardiogram, frequently resulting in brief episodes of atrioventricular block.

Et-A receptor antagonist BQ123 prevents radiocontrast media-induced renal medullary hypoxia

PURPOSE

Renal vasoconstriction with resultant tissue hypoxia, especially in the renal medulla, has been suggested to play a role in contrast media (CM)-induced nephropathy. Endothelin (ET) is released into the blood stream following CM injection and has been proposed as a potential mediator through its vasoconstrictive properties.

MATERIAL AND METHODS

To investigate the possible protective influence of ET-receptor antagonists against CM-induced reduction in renal function, we studied the effects of injection of iopromide with and without pretreatment with BQ123 (ET-A antagonist) or BQ788 (ET-B antagonist) on renal superficial cortical flow (CBF), outer medullary blood flow (OMBF) and outer medullary oxygen tension (pO2) in normal rats.

RESULTS

Administration of CM (1600 mg I/kg b.w.) did not affect CBF in any of the groups. However, a transient decrease in OMBF occurred, which was unaffected by both BQ123 and BQ788. Also a transient decrease in outer medullary pO2 was induced by CM administration. The pO2 reduction was significantly smaller after pretreatment with BQ123, than after injection of CM alone or together with BQ788, and pO2 returned more rapidly to the control level. Neither receptor antagonist had an effect on CM-mediated increases in electrolyte excretion.

CONCLUSION

In the normal rat, activation of ET-A receptors is partly involved in the depression of outer medullary pO2 caused by injection of iopromide. However, the decrease in OMBF after iopromide injection is not mediated by ET receptors. The beneficial effects of the ET-A receptor antagonist on CM-induced changes in outer medullary pO2 seem therefore not primarily mediated on the hemodynamic level but may rather involve tubular transport mechanisms.

The association between exposure to a rear-end collision and future health complaints

Different symptoms, together with neck pain, have been attributed to persons with persistent complaints after a previous motor vehicle crash (MVC) and are sometimes referred to as the "late whiplash syndrome." A cohort study was conducted to determine whether exposure to a rear-end collision, with or without whiplash injury, is associated with future health complaints. The results regarding future neck or shoulder pain have previously been described, and the objective of the present report was to focus on outcomes other than neck pain. Included in the study were persons 18 to 65 years of age and covered by traffic insurance at one of the largest insurance companies in Sweden. Claim reports were collected from the period November 1987 to April 1988. Drivers exposed to a rear-end collision were divided into two subgroups: those with reported whiplash injury (n = 232) and those without reported whiplash injury (n = 204). For comparison, 3688 subjects who were unexposed to MVCs were selected, with consideration taken to the age and gender distribution in the exposed subgroups. The prevalence of different health complaints among the study subjects was estimated according to a mailed questionnaire at follow-up in 1994, 7 years after the rear-end collision. When exposed subjects with whiplash injury were compared to unexposed subjects, increased relative risks in the range of 1.6-3.7 were seen for headache, thoracic and low back pain, as well as for fatigue, sleep disturbances and ill health. No corresponding increased risks were found among the exposed subjects without reported whiplash injury. We conclude that rear-end collisions resulting in reported whiplash injuries seem to have a substantial impact on health complaints, even a long time after the collision. There is a need to identify factors that predict a non-favorable outcome in order to improve clinical management.

Myocardial Doppler tissue velocity improves following myocardial gene therapy with VEGF-A165 plasmid in patients with inoperable angina pectoris

BACKGROUND

Myocardial tissue velocity and perfusion were studied in patients with severe angina pectoris following gene therapy by intramyocardial injection of phVEGF-A165 via thoracotomy. Plasma concentrations of VEGF-A increased postoperatively. Two months after treatment anginal status and myocardial tissue velocity improved and perfusion showed a tendency to improve. Tissue velocity imaging appears to be a sensitive, objective method for detecting changes in myocardial function following gene therapy.

OBJECTIVE

To study effects on myocardial tissue velocity and perfusion in patients with angina pectoris following intramyocardial injection of phVEGF-A165 via thoracotomy.

DESIGN

Open label, phase I/II.

METHODS

Six patients with Canadian Cardiovascular Society (CCS) angina pectoris functional class III - IV and with major defects at adenosine stress single-photon emission computerized tomography (SPECT) were studied. In addition to SPECT, coronary angiography and dobutamine stress echocardiography with tissue Doppler velocity imaging were performed before and two months after gene transfer.

RESULTS

Plasma concentrations of VEGF-A increased 2 to 3 times (P < 0.04) over baseline from 2 to 14 days after injection with normalization after 4 weeks. The CCS class improved about 40%, from 3.3 +/- 0.2 to 2.0 +/- 0.3 (P < 0.02) and nitroglycerine consumption decreased 30 - 40%, from 44 +/- 17 to 15 +/- 5 tablets per week (P < 0.05). The maximal systolic myocardial tissue velocity increased in all patients about 25% (P < 0.02) but did not reach the reference range. Myocardial perfusion at SPECT improved in four of the six patients.

CONCLUSIONS

Anginal status, myocardial tissue velocity and perfusion can be improved by phVEGF-A165 intramyocardial injection. Tissue velocity imaging appears to be a sensitive, objective method for detecting changes in myocardial function following gene therapy.