Sudden cardiac arrest due to recurrent coronary spasm in a young woman: a case report

Background

Coronary artery spasm (CAS) is a pathological condition resulting from transient functional narrowing of the coronary arteries leading to myocardial ischaemia and in some rare cases even to sudden cardiac arrest (SCA). The most important preventable risk factor is use of tobacco, whereas possible precipitating factors include some medications and psychological stress.

Case summary

A 32-year-old woman was hospitalized with burning chest pain. The immediate investigations revealed the diagnosis of non-ST-segment elevation myocardial infarction, because of ST elevations in one single lead and increased high-sensitivity troponin. Due to ongoing chest pain and a severe impaired left ventricular ejection fraction (LVEF) of 30% with apical akinesia, a prompt coronary angiography (CAG) was scheduled. After aspirin administration, she developed anaphylaxis with pulseless electrical activity (PEA). She could be resuscitated successfully. CAG revealed multi-vessel CAS for which she received calcium channel blockers. Five days after, she suffered from a second SCA due to ventricular fibrillation and was resuscitated again. Repeated CAG showed no critical coronary artery occlusion. LVEF improved progressively during hospitalization. Drug therapy was increased, and a subcutaneous implantable cardioverter defibrillator (ICD) was implanted for secondary prevention.

Discussion

CAS may in some instances lead to SCA, especially in case of multi-vessel involvement. Allergic and anaphylactic events can trigger CAS, which are frequently underestimated. Regardless of the cause, cornerstone of CAS prophylaxes remains optimal medical therapy as in the avoidance of predisposing risk factors. In case of life-threatening arrhythmia, the implantation of an ICD should be considered.

Development and Initial in Vivo Testing of a New Hydraulic Drive System (Paedipump) for Circulatory Support in Infants

The main limitation in the use of circulatory support in children is the lack of an adequate system with regard to size and pumping capacity Recently, two pneumatically driven ventricular support systems with low volume chambers for use in a pediatric population became available. We have developed a hydraulic drive system with an advantageous exact control of the stroke volume. The system enables two different modes of operation: the full-empty and the filled-empty modes. In both cases the ventricle is empty at the end of systole.

This new system was tested in experimental animals (6 pigs, body weight 9.5–14.0 kg) with normal and reduced left ventricular function (MAP<45 mmHg). A 25 ml ventricle (HIA-Medos) was implanted. The full-empty and the filled-empty mode used led to a significant load reduction, both in animals with normal and impaired cardiac function. Plasma lactate levels, pH-values and total body 0 2 consumption were in the normal range during circulatory support indicating adequate organ perfusion.

Results showed that sufficient ventricular support was achieved during all pumping modes due to the possibility of controlling and modifying the stroke volume of the hydraulically driven support system employed according to necessity. This is a promising feature for its future application in infants with congenital or acquired heart diseases.

Incidence and predictors of atrioventricular conduction impairment after transcatheter aortic valve implantation

Atrioventricular (AV) conduction impairment is well described after surgical aortic valve replacement, but little is known in patients undergoing transcatheter aortic valve implantation (TAVI). We assessed AV conduction and need for a permanent pacemaker in patients undergoing TAVI with the Medtronic CoreValve Revalving System (MCRS) or the Edwards Sapien Valve (ESV). Sixty-seven patients without pre-existing permanent pacemaker were included in the study. Forty-one patients (61%) and 26 patients (39%) underwent successful TAVI with the MCRS and ESV, respectively. Complete AV block occurred in 15 patients (22%), second-degree AV block in 4 (6%), and new left bundle branch block in 15 (22%), respectively. A permanent pacemaker was implanted in 23 patients (34%). Overall PR interval and QRS width increased significantly after the procedure (p <0.001 for the 2 comparisons). Implantation of the MCRS compared to the ESV resulted in a trend toward a higher rate of new left bundle branch block and complete AV block (29% vs 12%, p = 0.09 for the 2 comparisons). During follow-up, complete AV block resolved in 64% of patients. In multivariable regression analysis pre-existing right bundle branch block was the only independent predictor of complete AV block after TAVI (relative risk 7.3, 95% confidence interval 2.4 to 22.2). In conclusion, TAVI is associated with impairment of AV conduction in a considerable portion of patients, patients with pre-existing right bundle branch block are at increased risk of complete AV block, and complete AV block resolves over time in most patients.

Transapical implantation of a novel self-expanding sutureless aortic valve prosthesis

BACKGROUND AND AIM OF THE STUDY

To date, transapical aortic valve implantation has required a balloon-expandable stented valve prosthesis. More recently, a novel self-expanding sutureless stented bovine pericardial prosthesis has been developed which allows rapid aortic valve replacement via an open transaortic approach in humans. The aim of this animal study was to develop a reliable protocol to facilitate the transapical implantation of this self-expanding valve in a porcine model.

METHODS

Off-pump transapical aortic valve implantation was performed through a left mini-thoracotomy using a bovine pericardial valve mounted on a self-expandable nitinol stent of size 21 mm and 23 mm in 11 pigs (average weight 60 kg). The crimped valve was introduced through the left ventricular apex using a flexible and steerable delivery sheath, using a three-step technique. Biplane fluoroscopy and transesophageal echocardiography were simultaneously used for guidance. Successful adjustment of alignment along three axes prior to deployment of the valve was accomplished in each animal. Deployments were performed during a period of rapid pacing.

RESULTS

All valves were successfully deployed and functioned normally following transapical removal of the delivery system. Paravalvular leak was documented in one case (9.1%) due to prosthetic misalignment. There was no evidence of valve migration. Correct anatomic seating was confirmed during post-procedure necropsy.

CONCLUSION

Successful transapical implantation of a novel self-expandable bovine pericardial valve was accomplished in 11 animals, without cardiopulmonary bypass. A flexible, steerable delivery system with a three-step release mechanism allowed precise positioning of the valve with a low rate of paravalvular leakage, and excellent device stability.

Transcatheter aortic valve implantation: predictors of procedural success--the Siegburg-Bern experience

AIMS

The purpose of the present analysis was to identify predictors of procedural success of percutaneous transcatheter aortic valve implantation (TAVI).

METHODS AND RESULTS

We prospectively assessed in-hospital outcome of patients undergoing TAVI at two institutions. We analysed clinical, morphological, and procedural parameters using univariate and multivariate regression models. Between 2005 and 2008, a total of 168 consecutive patients with symptomatic aortic valve stenosis underwent TAVI using the self-expanding CoreValve Revalving prosthesis. Patients (93%) were highly symptomatic with a New York Heart Association grade III/IV and a mean aortic valve area of 0.66 +/- 0.21 cm(2). Acute and in-hospital procedural success rates were 90.5 and 83.9%, respectively, with an in-hospital mortality, myocardial infarction, and stroke rate of 11.9, 1.8, and 3.6%, respectively. Predictors of in-hospital procedural success were type of access (OR 0.33, 95% CI 0.13-0.82, P = 0.017), prior coronary intervention (OR 5.3, 95% CI 1.20-23.41, P = 0.028) and pre-procedural Karnofsky index using univariate regression. Pre-procedural Karnofsky index emerged as the only independent predictor (OR 1.04, 95% CI 1.00-1.08, P = 0.032) in the multivariate analysis.

CONCLUSION

Pre-procedural functional performance status predicts the in-hospital outcome after TAVI. Patients with a good functional status are likely to benefit more from TAVI than previously reported high-risk patients.

Incidence and correlates of drug-eluting stent thrombosis in routine clinical practice. 4-year results from a large 2-institutional cohort study

OBJECTIVES

We sought to determine the risk of late stent thrombosis (ST) during long-term follow-up beyond 3 years, searched for predictors, and assessed the impact of ST on overall mortality.

BACKGROUND

Late ST was reported to occur at an annual rate of 0.6% up to 3 years after drug-eluting stent (DES) implantation.

METHODS

A total of 8,146 patients underwent percutaneous coronary intervention with a sirolimus-eluting stent (SES) (n=3,823) or paclitaxel-eluting stent (PES) (n=4,323) and were followed up to 4 years after stent implantation. Dual antiplatelet treatment was prescribed for 6 to 12 months.

RESULTS

Definite ST occurred in 192 of 8,146 patients with an incidence density of 1.0/100 patient-years and a cumulative incidence of 3.3% at 4 years. The hazard of ST continued at a steady rate of 0.53% (95% confidence interval [CI]: 0.44 to 0.64) between 30 days and 4 years. Diabetes was an independent predictor of early ST (hazard ratio [HR]: 1.96; 95% CI: 1.18 to 3.28), and acute coronary syndrome (HR: 2.21; 95% CI: 1.39 to 3.51), younger age (HR: 0.97; 95% CI: 0.95 to 0.99), and use of PES (HR: 1.67; 95% CI: 1.08 to 2.56) were independent predictors of late ST. Rates of death and myocardial infarction at 4 years were 10.6% and 4.6%, respectively.

CONCLUSIONS

Late ST occurs steadily at an annual rate of 0.4% to 0.6% for up to 4 years. Diabetes is an independent predictor of early ST, whereas acute coronary syndrome, younger age, and PES implantation are associated with late ST.

Regional filling characteristics of the lungs in mechanically ventilated patients with acute lung injury

OBJECTIVES

The objective of the study was to determine regional pulmonary filling characteristics in 20 mechanically ventilated patients with acute lung injury.

METHODS

Regional filling characteristics were calculated from tracings of regional tidal volumes vs. global tidal volumes measured by electrical impedance tomography (EIT). These plots were fitted to a polynomial function of the second degree. Regional polynomial coefficients of the second degree characterized the curve linearity of the plots. Near-zero values of the polynomial coefficient indicated a homogeneous increase in regional tidal volumes during the whole inspiration. Positive values hinted at initial low regional tidal volume change suggesting lung volume recruitment. Negative values indicated late low regional tidal volume change implying hyperinflation of this lung region.

RESULTS

We found a broad heterogeneity of regional lung filling characteristics. The minimal regional polynomial coefficients varied from -2.80 to -0.56 (median -1.16), while the maximal regional polynomial coefficients varied from 0.58 to 3.65 (median 1.41).

CONCLUSIONS

Measurements of regional filling characteristics by EIT may be a helpful tool to adjust the respiratory settings during mechanical ventilation to optimize lung recruitment and to avoid overdistension. It applies a non-pressure-related assessment to the mechanics of lung inflation and gives a view of the real problems underlying ventilatory strategies dependent on global characteristics.

Early and late coronary stent thrombosis of sirolimus-eluting and paclitaxel-eluting stents in routine clinical practice: data from a large two-institutional cohort study

BACKGROUND

Stent thrombosis is a safety concern associated with use of drug-eluting stents. Little is known about occurrence of stent thrombosis more than 1 year after implantation of such stents.

METHODS

Between April, 2002, and Dec, 2005, 8146 patients underwent percutaneous coronary intervention with sirolimus-eluting stents (SES; n=3823) or paclitaxel-eluting stents (PES; n=4323) at two academic hospitals. We assessed data from this group to ascertain the incidence, time course, and correlates of stent thrombosis, and the differences between early (0-30 days) and late (>30 days) stent thrombosis and between SES and PES.

FINDINGS

Angiographically documented stent thrombosis occurred in 152 patients (incidence density 1.3 per 100 person-years; cumulative incidence at 3 years 2.9%). Early stent thrombosis was noted in 91 (60%) patients, and late stent thrombosis in 61 (40%) patients. Late stent thrombosis occurred steadily at a constant rate of 0.6% per year up to 3 years after stent implantation. Incidence of early stent thrombosis was similar for SES (1.1%) and PES (1.3%), but late stent thrombosis was more frequent with PES (1.8%) than with SES (1.4%; p=0.031). At the time of stent thrombosis, dual antiplatelet therapy was being taken by 87% (early) and 23% (late) of patients (p<0.0001). Independent predictors of overall stent thrombosis were acute coronary syndrome at presentation (hazard ratio 2.28, 95% CI 1.29-4.03) and diabetes (2.03, 1.07-3.83).

INTERPRETATION

Late stent thrombosis was encountered steadily with no evidence of diminution up to 3 years of follow-up. Early and late stent thrombosis were observed with SES and with PES. Acute coronary syndrome at presentation and diabetes were independent predictors of stent thrombosis.

Imaging pathologic pulmonary air and fluid accumulation by functional and absolute EIT

The increasing use of EIT in clinical research on severely ill lung patients requires a clarification of the influence of pathologic impedance distributions on the validity of the resulting tomograms. Significant accumulation of low-conducting air (e.g. pneumothorax or emphysema) or well-conducting liquid (e.g. haematothorax or atelectases) may conflict with treating the imaging problem as purely linear. First, we investigated the influence of stepwise inflation and deflation by up to 300 ml of air and 300 ml of Ringer solution into the pleural space of five pigs on the resulting tomograms during ventilation at constant tidal volume. Series of EIT images representing relative impedance changes were generated on the basis of a modified Sheffield back projection algorithm and ventilation distribution was displayed as functional (f-EIT) tomograms. In addition, a modified simultaneous iterative reconstruction technique (SIRT) was applied to quantify the resistivity distribution on an absolute level scaled in Omega m (a-EIT). Second, we applied these two EIT techniques on four intensive care patients with inhomogeneous air and fluid distribution and compared the EIT results to computed tomography (CT) and to a reference set of intrathoracic resistivity data of 20 healthy volunteers calculated by SIRT. The results of the animal model show that f-EIT based on back projection is not disturbed by the artificial pneumo- or haematothorax. Application of SIRT allows reliable discrimination and detection of the location and amplitude of pneumo- or haematothorax. These results were supported by the good agreement between the electrical impedance tomograms and CT scans on patients and by the significant differences of regional resistivity data between patients and healthy volunteers.

Regional pulmonary pressure volume curves in mechanically ventilated patients with acute respiratory failure measured by electrical impedance tomography

BACKGROUND

We hypothesized, that in mechanically ventilated patients with acute respiratory failure, regional pressure volume curves differ markedly from conventional global pressure volume curves of the whole lung.

METHODS

In nine mechanically ventilated patients with acute respiratory failure during an inspiratory low-flow manoeuvre, conventional global pressure volume curves were registered by spirometry and regional pressure volume curves in up to 912 regions were assessed simultaneously using electrical impedance tomography. We compared the lower (LIP) and upper (UIP) inflection points obtained from the conventional global pressure volume curve and regional pressure volume curves.

RESULTS

We identified from the conventional global pressure volume curves LIP [3-11 (8) cmH2O] in eight patients and UIP [31-39 (33) cmH2O] in three patients. Using electrical impedance tomography (EIT), LIP [3-18 (8) cmH2O] in 54-264 (180) regions and UIP [23-42 (36) cmH2O] in 149-324 (193) regions (range and median) were identified. Lung mechanics measured by conventional global pressure volume curves are similar to the median of regional pressure volume curves obtained by EIT within the tomographic plane. However, single regional pressure volume curves differ markedly with a broad heterogeneity of lower and upper inflection points.

CONCLUSION

Lower and upper inflection points obtained from conventional global pressure volume curves are not representative of all regions of the lungs.

Safety and exercise tolerance of acute high altitude exposure (3454 m) among patients with coronary artery disease

OBJECTIVES

To assess the safety and cardiopulmonary adaptation to high altitude exposure among patients with coronary artery disease.

METHODS

22 patients (20 men and 2 women), mean age 57 (SD 7) years, underwent a maximal, symptom limited exercise stress test in Bern, Switzerland (540 m) and after a rapid ascent to the Jungfraujoch (3454 m). The study population comprised 15 patients after ST elevation myocardial infarction and 7 after a non-ST elevation myocardial infarction 12 (SD 4) months after the acute event. All patients were revascularised either by percutaneous coronary angioplasty (n = 15) or by coronary artery bypass surgery (n = 7). Ejection fraction was 60 (SD 8)%. beta blocking agents were withheld for five days before exercise testing.

RESULTS

At 3454 m, peak oxygen uptake decreased by 19% (p < 0.001), maximum work capacity by 15% (p < 0.001) and exercise time by 16% (p < 0.001); heart rate, ventilation and lactate were significantly higher at every level of exercise, except at maximum exertion. No ECG signs of myocardial ischaemia or significant arrhythmias were noted.

CONCLUSIONS

Although oxygen demand and lactate concentrations are higher during exercise at high altitude, a rapid ascent and submaximal exercise can be considered safe at an altitude of 3454 m for low risk patients six months after revascularisation for an acute coronary event and a normal exercise stress test at low altitude.

Effect of positive end-expiratory-pressure on regional ventilation in patients with acute lung injury evaluated by electrical impedance tomography

BACKGROUND AND OBJECTIVE

For the treatment of patients with adult respiratory distress syndrome and acute lung injury bedside measurements of regional lung ventilation should be considered for optimizing ventilatory settings. The aim was to investigate the effect of positive end-expiratory pressure (PEEP) on regional ventilation in mechanically ventilated patients at the bedside by electrical impedance tomography.

METHODS

Eight mechanically ventilated patients were included in the study. PEEP levels were increased from 0 to 5, 10, 15 mbar and back to 0 mbar. Regional ventilation in 912 regions of the thorax was investigated at each PEEP by electrical impedance tomography. The obtained regions were divided in four groups: none (none and poorly ventilated regions including chest wall and mediastinum), bad, moderate and well-ventilated regions.

RESULTS

Increasing the PEEP stepwise from 0 to 15 mbar decreased the non-ventilated regions (none: 540 regions at PEEP 0 and 406 regions at PEEP 15). In contrast, the other regions increased (bad: 316 regions at PEEP 0 and 380 regions at PEEP 15; moderate: 40 regions at PEEP 0 and 100 regions at PEEP 15; well: 0 region at PEEP 0 and 34 regions at PEEP 15 (median values)) indicating an improvement of regional ventilation.

CONCLUSIONS

Increasing PEEP in mechanically ventilated patients reduces none ventilated regions (atelectasis). Furthermore, it leads to a shift from none and bad ventilated regions to moderately and well-ventilated regions. Electrical impedance tomography is a bedside technique and might be an alternative to computed tomography scan to assess aerated lung regions.

Ketamine enantiomers differentially relax isolated coronary artery rings

BACKGROUND AND OBJECTIVE

It has been shown that racemic ketamine increases coronary blood flow and that this effect is at least in part due to a direct vasorelaxing effect of this substance. This study was designed to determine whether ketamine might stereoselectively relax isolated porcine coronary arteries.

METHODS

Using the model of isolated vessels we studied the effects of S(+) ketamine, R(-) ketamine, and racemic ketamine (5-500 microg mL(-1)) on artery strips pre-contracted by either potassium chloride (KCl) or prostaglandin F2alpha (PGF2alpha). To elucidate possible mechanisms of action these experiments were repeated in the presence of one of the following compounds: N(omega)-nitro-L-arginine (L-NNA), indomethacin, glibenclamide, and tetraethylammonium (TEA) chloride, an inhibitor of the BK(Ca) K+ channel.

RESULTS

Both isoforms and racemic ketamine relaxed isolated coronary arteries in a concentration-dependent manner in concentrations beyond those used in clinical practice. S(+) ketamine exerted the strongest vasorelaxing effect, followed by racemic ketamine and R(-) ketamine. Pretreatment with L-NNA, indomethacin, or glibenclamide did not alter the vasodilating properties of ketamine, whereas TEA chloride significantly attenuated the vasorelaxing effects of all the three forms of ketamine.

CONCLUSIONS

Ketamine dilates coronary arteries in vitro when administered in high concentrations. There is a stereoselective difference with a stronger vasorelaxing effect of S(+) ketamine compared to racemic and R(-) ketamine. The impact of TEA chloride suggests that the activation of the BK(Ca) channel may contribute to the vasodilating effect of ketamine.

Mechanisms involved in the relaxing effect of midazolam on coronary arteries

BACKGROUND AND OBJECTIVE

Hypotension, especially in elderly and hypovolaemic patients, is frequently associated with intravenous midazolam administration. The mechanisms are not completely understood. This study was designed to investigate the mechanisms involved in the relaxing effect of midazolam on coronary arteries.

METHODS

The substance was studied in isolated porcine coronary artery rings precontracted by either potassium chloride or prostaglandin F2alpha.

RESULTS

Midazolam caused vasodilatation in a concentration-dependent manner. Relaxation was more pronounced in prostaglandin F2alpha precontracted segments than in those treated with potassium chloride (P < 0.001). Vasodilatation was unaffected by Nomega-nitro-L-arginine, indomethacin and glibenclamide. Tetraethylammonium chloride, an inhibitor of the BK(Ca) K+ channel (a high conductance Ca(2+)-sensitive K+ channel), dose dependently attenuated the vasodilating effect of midazolam (P < 0.01).

CONCLUSIONS

Hyperpolarization of the smooth muscle cell in the vessel wall, elicited by the activation the BK(Ca) K+ channel, may contribute to the vasorelaxing effect of midazolam.

Transarterial aortic valve replacement with a self expanding stent in pigs

OBJECTIVES

To evaluate the feasibility of percutaneous aortic valve replacement without cardiac arrest in animal experiments.

METHODS

A self expanding nitinol stent, containing pulmonary valves from pigs in its proximal part, was implanted in six pigs (94-118 kg) by means of a 25 French catheter through the left subclavian artery under guidance of fluoroscopy and transoesophageal echocardiography. During stent deployment the original aortic valve was pushed against the aortic wall by the self expanding force of the stent while the new valve was expanded.

RESULTS

It was possible to replace the aortic valve in the beating heart in four pigs (67%) with no complication or relevant drop in blood pressure. The procedure failed in two pigs (33%) due to dysfunction of the catheter device in one case and to problems with correct positioning in the left ventricular outflow tract in the other. After successful stent valve implantation, dopamine was infused in doses of 5 microg/kg/min, 10 microg/kg/min, and 15 microg/kg/min. Cardiac output increased from 4.4 to 8.8 l/min and the mean arterial pressure rose from 79 to 105 mm Hg. The maximum peak to peak pressure gradient across the valve carrying stent reached a maximum of 8 mm Hg under dopamine infusion. All pigs were killed six hours after transvascular aortic valve replacement. The chest was opened, and the left ventricle and the ascending aorta were carefully inspected. There were no signs of malfunction of the implant, of damage of the aortic vessel wall, or of obstruction of the coronary ostia.

CONCLUSIONS

Percutaneous aortic valve replacement with a self expanding nitinol stent in the beating heart is possible. The device was safe under pharmacological stress test. After successful chronic animal experiments, this concept may become a feasible option for treating patients with relevant aortic valve disease but where open heart surgery would be risky.

Activation of the K+ channel BK(Ca) is involved in the relaxing effect of propofol on coronary arteries

BACKGROUND AND OBJECTIVE

Propofol may cause undesirable hypotension due to vasodilation. The underlying mechanisms are not completely understood. We investigated the mechanisms by which propofol relaxes vascular segments.

METHODS

We studied the effect of propofol on isolated porcine coronary artery rings precontracted with potassium chloride or prostaglandin F2alpha.

RESULTS

Propofol, in a concentration-dependent manner, relaxed all segments at concentrations of 5 microg mL(-1) and above. This relaxation was unaltered in the presence of N(omega)-nitro-L-arginine, indomethacin, diltiazem and glibenclamide. Tetraethylammonium chloride, an inhibitor of the BK(Ca) K+ channel (a high conductance Ca2+-sensitive K+ channel), dose-dependently attenuated the vasodilating effect of propofol (P < 0.001).

CONCLUSIONS

Our results suggests that the activation of the BK(Ca) channel may contribute to the vasodilating effect of propofol, hereby causing hyperpolarization of the smooth muscle membrane and reduction of smooth muscle tone.

[Ketamine attenuates the contractile response to vasoconstrictors in isolated coronary artery rings]

OBJECTIVE

Ketamine was shown to increase coronary blood flow. It was the aim of this study to answer the question whether ketamine directly dilates coronary arteries.

METHODS

Using the model of isolated vessel rings we studied the effects of ketamine (2.5, 25, and 250 microg ml(-1)) on the contractile response to three vasoconstrictors, acetylcholine, histamine, and serotonin in porcine coronary artery segments. Other rings were contracted with KCl or PGF (2a) and then treated with ketamine (5 up to 500 microg ml(-1) added cumulatively).

RESULTS

Ketamine dose-dependently dilated coronary arteries in concentrations beyond those used in clinical practice. In intact rings ketamine racemate (250 microg ml(-1)) attenuated contractions mediated by acetylcholine by 38.8 +/- 2.8%, histamine by 33.0 +/- 4.4% and serotonin by 42.1 +/- 3.7% (p < 0.05). There were no differences between intact and denuded rings (acetylcholine 38.5 +/- 2.8%, histamine 26.6 +/- 4.7%, serotonin 30.0 +/- 3.2%). With low concentrations of ketamine (2.5 microg ml(-1)) a slight tendency towards a contraction was recorded (n. s.). In rings precontracted with either KCl or PGF (2a) ketamine caused a small enhancement of contraction (KCl: 101.4 +/- 0.4%, PGF (2a): 101.3 +/- 1.4%) when administered in low concentration (5 microg ml(-1)), but almost complete relaxation (KCl: 0.4 +/- 1.3%, PGF (2a): 0.0 +/- 5.4%) in high concentration (500 microg ml(-1)).

CONCLUSIONS

It is concluded that ketamine dose-dependently dilates porcine coronary arteries in concentrations beyond those used in clinical practice and that this effect is independent of endothelial function.

High-dose midazolam and the attenuation of the contractile response to vasoconstrictors in coronary artery segments

BACKGROUND AND OBJECTIVE

Benzodiazepines may cause hypotension and are reported to interfere with smooth vascular muscle activity. The aim was to elucidate the influence of three different benzodiazepines on the vascular reactivity of coronary arteries.

METHODS

Using the model of isolated vessels, we studied the impact of midazolam (0.15, 1.5, 15 microg mL(-1)), diazepam (0.1, 1.0, 10 microg mL(-1)) and flunitrazepam (0.01, 0.1, 1.0 microg mL(-1)) on the contractile responses to histamine (2 x 10(-5) mol L(-1)) and serotonin (3 x 10(-5) mol L(-1)) in isolated intact and denuded coronary arteries.

RESULTS

Midazolam significantly attenuated the contractile response when administered in high concentrations (15 microg mL(-1)). This effect was more pronounced in intact than in denuded preparations (histamine: -22.7 versus -7.3%, P = 0.0079; serotonin: -47.1 versus -15.9%, P < 0.0001). Diazepam and flunitrazepam exerted no significant effects on the vascular tone of coronary arteries.

CONCLUSIONS

Midazolam, but not diazepam or flunitrazepam, attenuates the contractile responses to vasoconstrictors in concentrations beyond those used in clinical practice. This effect is in part mediated by endothelial factors.

End-expiratory lung impedance change enables bedside monitoring of end-expiratory lung volume change

OBJECTIVE

The aim of the study was to investigate the effect of lung volume changes on end-expiratory lung impedance change (ELIC) in mechanically ventilated patients, since we hypothesized that ELIC may be a suitable parameter to monitor lung volume change at the bedside.

DESIGN

Clinical trial on patients requiring mechanical ventilation.

SETTINGS

Intensive care units of a university hospital.

PATIENTS

Ten mechanically ventilated patients were included in the study.

INTERVENTION

Patients were ventilated in volume-controlled mode with constant flow and respiratory rate. In order to induce changes in the end-expiratory lung volume (EELV), PEEP levels were increased from 0 mbar to 5 mbar, 10 mbar, and 15 mbar. At each PEEP level EELV was measured by an open-circuit nitrogen washout manoeuvre and ELIC was measured simultaneously using Electrical Impedance Tomography (EIT) with sixteen electrodes placed on the circumference of the thorax and connected with an EIT device. Cross-sectional electro-tomographic measurements of the thorax were performed at each PEEP level, and a modified Sheffield back-projection was used to reconstruct images of the lung impedance. ELIC was calculated as the average of the end-expiratory lung impedance change. RESULTS. Increasing PEEP stepwise from 0 mbar to 15 mbar resulted in an linear increase of EELV and ELIC according to the equation: y =0.98 x -0.68, r(2)=0.95.

CONCLUSION

EIT is a simple bedside technique which enables monitor lung volume changes during ventilatory manoeuvres such as PEEP changes.

Effects of epinephrine on the myocardial performance and haemodynamics of the isolated rat heart during moderate hypothermia--importance of calcium homeostasis

Controversies exist concerning myocardial performance in hypothermia. We have studied the effects of epinephrine on myocardial function at various calcium concentrations in moderate hypothermia (28 degrees C) and normothermia (37 degrees C) using an isolated antegrade perfused rat heart. The maximum pressure velocity (dP/dt(max)) developed was significantly higher in normothermia compared with hypothermia and was improved by the addition of calcium in both circumstances. Peak negative pressure velocity (dP/dt(min)) was significantly higher at 37 degrees C compared with 28 degrees C, and was increased by the addition of calcium in normothermia; in contrast to hypothermia, in which no change of dP/dt(min) was observed. A reduction in cardiac output and stroke volume by hypercalcaemia was observed in hypothermia. The addition of epinephrine improved dP/dt(max) and dP/dt(min), but had a depressive effect on stroke volume and cardiac output at normal and elevated calcium concentrations. Myocardial efficiency was significantly higher during hypothermia compared with normothermia, but was impaired by epinephrine during hypothermia. The variable or even paradoxical effects of epinephrine suggest the need for careful haemodynamic monitoring and determination of calcium levels in hypothermia. The impairment of myocardial performance may be explained by impaired diastolic relaxation and calcium overload.

Non-invasive radiation-free monitoring of regional lung ventilation in critically ill infants

OBJECTIVE

Established techniques used to examine lung function in critically ill infants cannot continuously follow regional aspects of lung ventilation although this information would be beneficial for proper therapy planning. We have studied the applicability and clinical relevance of a relatively new non-invasive radiation-free imaging method, electrical impedance tomography (EIT), in monitoring regional lung function in paediatric intensive care patients.

DESIGN

Prospective study.

SETTING

Neonatal and paediatric intensive care unit (ICU) at a university hospital.

PATIENTS

Eight infants (1 day-7 years old) suffering from miscellaneous diseases requiring intensive care therapy.

INTERVENTIONS

Adjustment of ventilator settings, surfactant administration, and postural changes.

MEASUREMENTS AND RESULTS

Repeated EIT measurements were performed with the intention to monitor regional lung ventilation in mechanically ventilated and spontaneously breathing infants. The follow-up time ranged between 1 and 11 days. During individual EIT measurements of 100-s duration electrical voltages resulting from repetitive injection of small electrical currents were continuously measured on the thoracic circumference using conventional surface electrodes. Acquired data were used to generate functional cross-sectional thoracic images of regional lung ventilation. A total of 638 EIT measurements were performed. The redistribution of lung ventilation and changes in regional ventilation magnitude resulting from adjusted positive end-expiratory pressure, peak inspiratory pressure, inspiration-expiration ratio, surfactant instillation, and prone or supine positioning were identified.

CONCLUSIONS

Provided that EIT hardware and software are further developed to guarantee stable and undisturbed measurements in the ICU and that practical handling is improved, this non-invasive method may become a useful bedside monitoring tool of regional lung ventilation in critically ill infants.

Gravity effects on regional lung ventilation determined by functional EIT during parabolic flights

Gravity-dependent changes of regional lung function were studied during normogravity, hypergravity, and microgravity induced by parabolic flights. Seven healthy subjects were followed in the right lateral and supine postures during tidal breathing, forced vital capacity, and slow expiratory vital capacity maneuvers. Regional 1) lung ventilation, 2) lung volumes, and 3) lung emptying behavior were studied in a transverse thoracic plane by functional electrical impedance tomography (EIT). The results showed gravity-dependent changes of regional lung ventilation parameters. A significant effect of gravity on regional functional residual capacity with a rapid lung volume redistribution during the gravity transition phases was established. The most homogeneous functional residual capacity distribution was found at microgravity. During vital capacity and forced vital capacity in the right lateral posture, the decrease in lung volume on expiration was larger in the right lung region at all gravity phases. During tidal breathing, the differences in ventilation magnitudes between the right and left lung regions were not significant in either posture or gravity phase. A significant nonlinearity of lung emptying was determined at normogravity and hypergravity. The pattern of lung emptying was homogeneous during microgravity.

Quantitative evaluation of the performance of different electrical tomography devices

Two widely used electrical tomography systems, the Sheffield Mark I and the DAS-01P, were quantitatively evaluated and compared to the newly developed Goe-MF system. The performance was quantified using a hardware phantom which closely matches the real input and transfer impedances of the human thorax and allows measurements equivalent to different states of lung inflation. Our results demonstrate that adequate averaging is necessary for noise reduction for the Mark I and especially for the DAS-01P system to get meaningful results even in visualizing maximal respiratory manoeuvres. The Goe-MF system showed a notably improved signal-to-noise ratio which allows also dynamic measurements at low levels of lung volume changes, e.g., in intensive care lung injury patients.

Impedance analyser module for EIT and spectroscopy using undersampling

In this paper we present the concept, the design and the test procedure for a DSP-based high-precision and high-performance wide-band (up to 10 MHz) bioimpedance analyser module for application in EIT or bioimpedance spectroscopy. The module implements a digital concept with appropriate signal conditioning hardware for voltage and current measurement, early signal digitization and subsequent digital signal processing in order to calculate the components of impedance (or admittance). At low frequencies, the module utilizes the conventional direct conversion method, whereas at high frequencies the undersampling technique is used. The advantages of the described system are the following: (a) the frequency range is extended to higher frequencies, (b) the number of data sampled per time interval is significantly reduced, and (c) the current consumption and the costs of the ADCs can be significantly reduced. The validation procedure is performed by comparing the measured and theoretical values of the magnitude and the phase of the impedance for a commonly used tissue model. The module offers an accuracy of better than 0.012% for the magnitude of impedance and better than 0.02 degrees for the phase.

Influence of opioids on the vascular tone of isolated porcine coronary artery segments

BACKGROUND

It was the aim of this study to elucidate the influence of opioids on coronary vascular tone using the model of isolated porcine coronary artery segments.

METHODS

We studied the effects of fentanyl (0.01, 0.1, 1.0 microg ml(-1)), alfentanil (0.1, 1.0, 10 microg ml(-1)), and sufentanil (0.01, 0.1, 1.0 microg ml(-1)) on the contractile response to three vasoconstrictors, acetylcholine, histamine and serotonin.

RESULTS

Fentanyl (0.1, 1.0 microg x ml(-1)) dose-dependently attenuated the contractile response to acetylcholine, but not to histamine and serotonin. There were no differences in fentanyl's vasorelaxing potency between rings with intact and denuded endothelium. Alfentanil and sufentanil did not exert any significant influence on any of the vasoconstrictors tested.

CONCLUSION

It is concluded that, in isolated porcine coronary artery rings, fentanyl at high concentrations has an attenuating effect on acetylcholine-induced contractions, which is independent of endothelial function, whereas alfentanil and sufentanil do not influence coronary vascular tone.

Do muscle relaxants influence vascular tone in isolated coronary artery segments?

The aim of this study was to elucidate the influence of four neuromuscular blocking substances on coronary vascular tone using the model of isolated porcine coronary artery segments. We studied the effects of four muscle relaxants, atracurium, pancuronium, rocuronium, and vecuronium (0.1, 1, and 10 microg mL-1 each), on the contractile response to three vasoconstrictors: acetylcholine, histamine, and serotonin. None of the neuromuscular blocking agents under investigation exerted a significant influence on the vasoconstricting effects of these mediators except for pancuronium, which dose-dependently attenuated acetylcholine-mediated contractions (-10.8% attenuation for 10 microg mL-1 pancuronium, P < 0.05). There was no difference between vessels with intact endothelium and denuded preparations. It is concluded that high-dose pancuronium exerts an antimuscarinic effect in vascular smooth muscle. The other neuromuscular agents studied do not alter vascular reactivity of isolated porcine coronary arteries.

Propofol and thiopental attenuate the contractile response to vasoconstrictors in human and porcine coronary artery segments

The effects of propofol and thiopental on three vasoconstrictors, acetylcholine, histamine, and serotonin were studied in isolated porcine and human coronary artery rings. Propofol and thiopental attenuated the contractile response to all mediators in a dose-dependent manner. This dilating effect was fairly weak using low concentrations (propofol 1 microg mL-1 and 10 microg mL-1, thiopental 5 microg mL-1 and 10 microg mL-1). In the presence of high concentrations (propofol 100 microg mL-1, thiopental 50 microg mL-1) marked relaxation was observed (propofol -32% up to -49%, P < 0,05; thiopental -23% up to -67%, P < 0.05). These dilating effects were seen both in intact and denuded rings, the differences were not significant. Human coronary artery segments were relaxed by thiopental (-22% to -76%) and propofol (-11% to -67%) to a similar extent. Our data indicate that propofol and thiopental relax isolated coronary segments in a dose-dependent manner, and that there is no evidence that these effects are dependent of endothelial factors.

A simple method to check the dynamic performance of electrical impedance tomography systems

The test concept as well as the design of a simple resistor phantom suitable for the evaluation of the properties of electrical impedance tomographic (EIT) systems is presented. Input and transfer impedance of the phantom are matched with those of the human thorax. Amplitude of the local impedance variations similar to in vivo conditions (ventilation) can be intentionally set to perform measurements on different states. The theoretical potential differences between the electrodes are calculated. The evaluation procedure is performed in terms of the local amplitude of the relative impedance change as well as the local distribution of noise. The whole procedure can be applied either to compare quantitatively the performance of different EIT data acquisition systems or to determine the amount of measurement disturbance caused by the external electrical environment in clinical settings.

Mapping of capillary flow, cellular redox state, and resting membrane potential in hypoperfused rat myocardium

The influence on myocyte viability of ischemia-induced changes in capillary perfusion was studied in the hearts of anesthetized rats subjected to partial occlusion of the left coronary artery for 45 min. Timed plasma labeling was applied to determine perfusion patterns. Changes in the fluorescence of preloaded potential-sensitive dyes [tetramethylrhodamine methyl ester (TMRM) and bis-oxonol], of trypan blue, and of endogeneous NADH were utilized in characterizing myocyte viability in histological sections of the heart. Within the hypoperfused zone, localized areas appeared vascularly nonlabeled for periods of at least 10 min. Within these areas a reduction in TMRM fluorescence occurred in 82. 5% of the tissue, signaling a reduced resting membrane potential. In the same areas 37.7% of the myocytes revealed an NADH fluorescence lower than that regularly found in anoxic tissues. This correlated with an especially low level of TMRM, with increased fluorescence bis-oxonol and with an accumulation of trypan blue. In conclusion, in localized hypoperfusion-induced zones lacking capillary flow, an inhomogeneous pattern of reductions in myocyte viability develops, which appears to be relevant in ischemia-induced arrhythmias.

Optimizing deconvolution techniques by the application of the Münchhausen meta algorithm

A deconvolution applied to disturbed data often gives poor results, due to fundamental difficulties associated with ill-posed problems. Many numerical and theoretical methods have been invented to circumvent this phenomenon. Their performance varies, depending on the given problem and data. The main aim of this paper is to provide a decision rule for choosing a method for deconvolution and application of this method to the same data. We have called this meta-algorithm Münchhausen. In this paper we introduce and describe for the first time the basic principle of artificial disturbance of the data in the set-up of deconvolution. We demonstrate some interesting features of the random procedure Münchhausen, such as the non parametric set-up, robustness to disturbance of the data and last but not least good performance.

Thoracic electrical impedance tomographic measurements during volume controlled ventilation-effects of tidal volume and positive end-expiratory pressure

The aim of the study was to analyze thoracic electrical impedance tomographic (EIT) measurements accomplished under conditions comparable with clinical situations during artificial ventilation. Multiple EIT measurements were performed in pigs in three transverse thoracic planes during the volume controlled mode of mechanical ventilation at various tidal volumes (V(T)) and positive end-expiratory pressures (PEEP). The protocol comprised following ventilatory patterns: 1) V(T)(400, 500, 600, 700 ml) was varied in a random order at various constant PEEP levels and 2) PEEP (2, 5, 8, 11, 14 cm H2O) was randomly modified during ventilation with a constant V(T). The EIT technique was used to generate cross-sectional images of 1) regional lung ventilation and 2) regional shifts in lung volume with PEEP. The quantitative analysis was performed in terms of the tidal amplitude of the impedance change, reflecting the volume of delivered gas at various preset V(T) and the end-expiratory impedance change, revealing the variation of the lung volume at various PEEP levels. The results showed: 1) an increase in the tidal amplitude of the impedance change, proportional to the delivered V(T) at all constant PEEP levels, 2) a rising end-expiratory impedance change, with PEEP reflecting an increase in gas volume, and 3) a PEEP-dependent redistribution of the ventilated gas between the planes. The generated images and the quantitative results indicate the ability of EIT to identify regional changes in V(T) and lung volume during mechanical ventilation.

Simulation of the initial concentration-time course after intravenous application of the drug

In this paper we present a widely applicable computational method for the description of the initial concentration-time-course after intravenous injection of a substance. The intravascular concentration-time course, r, is described as r = c0 + g x r, where the asterisk denotes the convolution operation, c0 is the concentration-time course during the first passage of the substance and g is the transport function of the body. If the body transport function is known, then the concentration-time course of a substance can be predicted. 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.

Monitoring regional lung ventilation by functional electrical impedance tomography during assisted ventilation

A new approach in discriminating the regional air volume changes in the lungs associated with either spontaneous or mechanical ventilation during assisted ventilation is presented. Impedance data are obtained by conventional electrical impedance tomography (EIT). The data are filtered in the range of either the spontaneous or the ventilator rate and processed by the functional EIT (f-EIT) evaluation technique, whereby the variation of the respective EIT data with time is determined and imaged. EIT measurements performed in an infant during synchronized intermittent mandatory ventilation were evaluated with this method and indicated that the specific local lung volume swings related to spontaneous and mechanical inhalations can be separated and imaged as tomograms. This noninvasive approach may become useful in optimizing the ventilatory pattern during advanced forms of artificial ventilation and may help the clinician in the therapy management of individual patients.

Errors of the backextrapolation method in determination of the blood volume

Backextrapolation is an empirical method to calculate the central volume of distribution (for example the blood volume). It is based on the compartment model, which says that after an injection the substance is distributed instantaneously in the central volume with no time delay. The occurrence of recirculation is not taken into account. The change of concentration with time of indocyanine green (ICG) was observed in an in vitro model, in which the volume was recirculating in 60 s and the clearance of the ICG could be varied. It was found that the higher the elimination of ICG, the higher was the error of the backextrapolation method. The theoretical consideration of Schröder et al (Biomed. Tech. 42 (1997) 7-11) was proved. If the injected substance is eliminated somewhere in the body (i.e. not by radioactive decay), the backextrapolation method produces large errors.

Electrical impedance tomography in monitoring experimental lung injury

OBJECTIVE

To apply electrical impedance tomography (EIT) and the new evaluation approach (the functional EIT) in monitoring the development of artificial lung injury.

DESIGN

Acute experimental trial.

SETTING

Operating room for animal experimental studies at a university hospital.

SUBJECTS

Five pigs (41.3 +/- 4.1 kg, mean body weight +/- SD).

INTERVENTIONS

The animals were anaesthetised and mechanically ventilated. Sixteen electrodes were attached on the thoracic circumference and used for electrical current injection and surface voltage measurement. Oleic acid was applied sequentially (total dose 0.05 ml/kg body weight) into the left pulmonary artery to produce selective unilateral lung injury.

MEASUREMENTS AND RESULTS

The presence of lung injury was documented by significant changes of PaCO2 (40.1 mmHg vs control 37.1 mmHg), PaO2 (112.3 mmHg vs 187.5 mmHg), pH (7.35 vs 7.42), mean pulmonary arterial pressure (29.2 mmHg vs 20.8 mmHg) and chest radiography. EIT detected 1) a regional decrease in mean impedance variation over the affected left lung (-41.4% vs control) and an increase over the intact right lung (+ 20.4% vs control) indicating reduced ventilation of the affected, and a compensatory augmented ventilation of the unaffected lung and 2) a pronounced fall in local baseline electrical impedance over the injured lung (-20.6% vs control) with a moderate fall over the intact lung (-10.0% vs control) indicating the development of lung oedema in the injured lung with a probable atelectasis formation in the contralateral one.

CONCLUSION

The development of the local impairment of pulmonary ventilation and the formation of lung oedema could be followed by EIT in an experimental model of lung injury. This technique may become a useful tool for monitoring local pulmonary ventilation in intensive care patients suffering from pulmonary disorders associated with regionally reduced ventilation, fluid accumulation and/or cell membrane changes.

Development and initial in vivo testing of a new hydraulic drive system (Paedipump) for circulatory support in infants

The main limitation in the use of circulatory support in children is the lack of an adequate system with regard to size and pumping capacity. Recently, two pneumatically driven ventricular support systems with low volume chambers for use in a pediatric population became available. We have developed a hydraulic drive system with an advantageous exact control of the stroke volume. The system enables two different modes of operation: the full-empty and the filled-empty modes. In both cases the ventricle is empty at the end of systole. This new system was tested in experimental animals (6 pigs, body weight 9.5-14.0 kg) with normal and reduced left ventricular function (MAP<45 mmHg). A 25 ml ventricle (HIA-Medos) was implanted. The full-empty and the filled-empty mode used led to a significant load reduction, both in animals with normal and impaired cardiac function. Plasma lactate levels, pH-values and total body O2-consumption were in the normal range during circulatory support indicating adequate organ perfusion. Results showed that sufficient ventricular support was achieved during all pumping modes due to the possibility of controlling and modifying the stroke volume of the hydraulically driven support system employed according to necessity. This is a promising feature for its future application in infants with congenital or acquired heart diseases.

Monitoring perioperative changes in distribution of pulmonary ventilation by functional electrical impedance tomography

BACKGROUND

Electrical impedance tomography (EIT) is a noninvasive technique providing cross-sectional images of the thorax. We have tested an extended evaluation procedure, the functional EIT (f-EIT), to identify the local shifts of ventilation known to occur during the transition between spontaneous, controlled and assisted ventilation modes.

METHODS

Ten patients scheduled for elective laparotomy were studied in the surgical ward, operating theatre and ICU during spontaneous and different modes of mechanical ventilation. Sixteen ECG electrodes were placed on the circumference of the thorax and connected with an EIT device (APT System Mark I, IBEES, Sheffield, UK). Measurements lasting 180 s were performed and f-EIT images of regional ventilation computed. The geometrical centre of ventilation was determined to quantify the regional distribution of lung ventilation during individual modes of ventilation.

RESULTS

F-EIT confirmed the differences in the distribution of ventilation associated with various modes of artificial ventilation. Accentuated ventilation of the dependent lung regions was observed during spontaneous breathing, whereas a shift of the centre of ventilation to the nondependent regions was found during controlled ventilation. In the course of assisted ventilation a continuous displacement of the centre of ventilation back towards the dependent lung regions, consistent with an increased proportion of spontaneous breathing, was detected. Unassisted spontaneous breathing after weaning from mechanical ventilation resulted in a similar ventilation distribution as during tidal breathing prior to surgery.

CONCLUSION

F-EIT determined the redistribution of lung ventilation during different modes of mechanical ventilation. We expect that f-EIT will become a useful noninvasive bedside monitoring technique for imaging regional ventilation in pulmonary diseased patients during mechanical ventilation.