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Biomedical subjects

N Roewer

Publications and source records attributed to N Roewer.

At least 127 records · Page 7Linked to original sources
PubMed1991

Intravenous dantrolene does not exhibit calcium channel blocking effects on the cardiac conduction system in humans.

In malignant hyperthermia, dantrolene, a drug assumed to possess calcium channel blocking properties, effectively suppresses supraventricular and ventricular arrhythmias. To investigate antiarrhythmic properties of dantrolene, six patients (three women and three men, age 42 +/- 18 yr) with symptomatic atrioventricular (AV)-nodal reentry tachycardia were studied. Electrocardiographic measurements included sinus cycle length, PQ-interval, width of the QRS-complex, and QT- and rate-corrected QT-interval. During the electrophysiologic study, effective refractory periods of the right atrium, AV node, right ventricle, and AV-nodal conduction intervals were determined, and AV-nodal reentry tachycardia was induced in all patients. Dantrolene was administered intravenously over a period of 15 min at doses of 1.0, 1.5, or 3.0 mg/kg in two patients each. The dosage was not further increased because of side effects at the dose of 3.0 mg/kg. After the infusion of dantrolene, the electrocardiographic measurements and electrophysiologic study were repeated. The plasma concentrations of dantrolene ranged from 1.69 to 6.61 micrograms/ml at the time of the electrophysiologic study. After dantrolene administration, the sinus cycle length shortened from 686 +/- 80 to 622 +/- 55 ms (P less than 0.05). No significant changes of any other parameter could be demonstrated after intravenous dantrolene. AV-nodal reentry tachycardia remained inducible in all patients without change of the tachycardia cycle length and without change in coupling intervals of tachycardia-inducing extrastimuli. Antiarrhythmic properties of dantrolene could not be demonstrated in patients with AV-nodal reentry tachycardia at therapeutic doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Effects of caffeine, halothane, succinylcholine, phenylephrine and isoproterenol on myocardial force of contraction of malignant hyperthermia susceptible swine.

The effects of caffeine, halothane, succinylcholine, phenylephrine and isoproterenol on force of contraction were studied in electrically driven (0.2 Hz) trabeculae isolated from the right ventricles of the hearts of malignant hyperthermia susceptible (MHS) and healthy control (nMHS) swine. Caffeine (0.1-10 mmol/l) had positive inotropic effects, amounting to 275 +/- 35% of control in nMHS and 268 +/- 34% in MHS (n = 16). Halothane (0.25-4 vol%) decreased the force of contraction maximally to 52 +/- 4% in nMHS and 51 +/- 5% of control in MHS (n = 16). Propranolol did not change these effects. Succinylcholine (0.1-10000 mumol/l) had a small positive inotropic effect in both groups, which was blocked by propranolol. Phenylephrine (0.1-300 mumol/l) increased the force of contraction maximally to 188 +/- 24% of control in nMHS and to 193 +/- 23% in MHS (n = 16). The inotropic effect was blocked by prazosin but not by succinylcholine (1 mmol/l). Isoproterenol (0.01-10 mumol/l) had a positive inotropic effect of maximally 275 +/- 21% of control in nMHS and 396 +/- 31% in MHS (n = 17) (P less than 0.05). Succinylcholine potentiated this effect, and propranolol shifted the concentration-response curves to the right. We conclude that caffeine, halothane, succinylcholine and phenylephrine have similar inotropic effects in the hearts of nMHS and MHS, whereas isoproterenol has a significantly greater effect in MHS than in nMHS.

Animals↗
PubMed1990

Alterations in brain electrical activity may indicate the onset of malignant hyperthermia in swine.

The time course of changes in brain electrical activity during halothane anesthesia was examined in 12 malignant hyperthermia-susceptible (MHS) and 14 normal (nMHS) swine. Power densities in selected frequency bands were calculated from the electroen-cephalogram (EEG). EEG and systemic variables were determined over a period of 60 min after starting halothane (1% inspired). Malignant hyperthermia (MH) was triggered in all susceptible pigs. Initial changes in the EEG during development of MH consisted of a decrease in total power and a shift to lower frequencies (delta-theta activity) in all animals. These EEG alterations were noted when there was an increase in heart rate, but other systemic variables were still normal. EEG changes in all MHS animals started at an arterial oxygen tension (PaO2) greater than 90 mmHg and an arterial carbon dioxide tension (PaCO2) less than 50 mmHg. In 5 MHS animals EEG became isoelectric at a PaO2 of 61-82 mmHg and a PaCO2 of 53-68 mmHg. Mean arterial blood pressure at this time was 54-66 mmHg. To determine the effects of hypoxia on the EEG in 7 nMHS animals, oxygen was decreased over a period of 45-60 min to 7% inspired. In 7 other nMHS animals, hypercarbia was produced by admixture of carbon dioxide to the fresh gas supply to achieve incremental increases of PaCO2 to 110-120 mmHg. Significant EEG changes during hypoxia comparable to those seen at the onset of MH were noted at a PaO2 below 40 mmHg and during hypercarbia at a PaCO2 greater than 68 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMed1990

[The effects of incremental PEEP on atrial natriuretic peptide, right atrial pressure and the size of the right atrium in anesthetized patients].

8 ASA class II-III patients (50-67 years) undergoing traumatic-surgical procedures were studied. Since the release of atrial natriuretic peptide (ANP) is stimulated by volume loading and increased right atrial pressure (RAP), the effects of incremental positive end-expiratory pressure (PEEP) on ANP-concentration, RAP and right atrial dimensions were investigated. Anaesthesia was induced with intravenous etomidate and vecuronium and maintained after endotracheal intubation with 66% N2O in O2 and ethrane (0.4-0.6 Vol.-%). A catheter was inserted into the A. radialis for blood sampling and determination of mean arterial pressure (MAP). For determining endsystolic (RAESA) and end-diastolic (RAEDA) areas of the right atrium a 5 MHz transoesophageal echocardiographic (TEE)-probe was positioned at the level of the foramen ovale. Under TEE-control a catheter was placed into the right atrium for measurement of RAP. The method for ANP determination was based on a direct radioimmunoassay that is specific for human ANP (ANP-J125). PEEP was incrementally raised from 0 to 16 mbar in 4 mbar steps each for 5 min and thereafter reduced to 0 mbar. During the investigation no significant differences were detectable for MAP, heart rate, end-expiratory CO2 partial pressure and the arterial O2 saturation. However, 16 mbar PEEP ventilation increased plasma ANP concentrations (from 44.3 +/- 9.7 to 58.1 +/- 8.7 pg/ml) and RAP (from 4.4 +/- 0.9 to 10.7 +/- 0.9 mmHg) whereas the right atrial dimensions RAESA (from 9.4 +/- 1.0 to 4.6 +/- 0.6 cm2) and RAEDA (from 5.9 +/- 1.2 to 3.2 +/- 0.4 cm2) decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

[The effects of midazolam on the mechanical and electrical properties of the isolated ventricular myocardium].

The direct effects of midazolam on isometric force of contraction (Fc) and on transmembrane action potential (AP) in electrically driven right ventricular papillary muscles were investigated. The results were compared with the effects of thiopental. Midazolam (0.01-200 mumol/l) had a concentration-dependent maximal negative inotropic effect of 94 +/- 4% compared with the pre-drug value on the papillary muscles of animals pretreated with reserpine (RES) [7.5 mg/kg b.wt. i.p., 16-18 h prior to the study]. The IC25 and IC50 values were 2.9 mumol/l (2.0-4.5; n = 9) and 12.4 mumol/l (6.5-30; n = 9) respectively. However, on the papillary muscles of untreated animals (nRES) midazolam developed a concentration-dependent positive inotropic effect (maximal 20 +/- 7%). Midazolam at a clinically relevant concentration of 2.8 mumol/l (= 1 microgram/ml; equivalent with the maximum plasma level following a midazolam i.v. bolus injection of 0.15 mg/kg b. wt.) reduced Fc by 15 +/- 3% (p less than 0.05) compared with the pre-drug value on the RES papillary muscles (n = 6) and increased Fc by 3 +/- 0.3% (p less than 0.05) on nRES animals. The resting membrane potential (RMP), the AP amplitude (APA) and the AP duration at 20% (APD20) and 90% (APD90) repolarisation showed no significant differences with midazolam (2.8 mumol/l; n = 5). Thiopental (0.01-200 mumol/l) produced a concentration-dependent maximal negative inotropic effect of 86 +/- 2% compared with the pre-drug value on the papillary muscles of nRES animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1989

[Intraoperative detection of air embolism and corpuscular embolism using pulse oximetry and capnometry. Comparative studies with transesophageal echocardiography].

19 patients undergoing total hip replacement in general anesthesia because of transcervical femur fractures were continuously monitored throughout surgery to detect any embolic events. Aside from the standard monitoring with ECG and control of arterial pressure in regular short intervals, the pulse-oximetry and capnography were applied for a comparative examination of their sensitivity in detecting gas and corpuscular embolisms. Transesophageal echocardiography (TEE) which allows an extensive assessment regarding the extent and differentiation between gaseous and corpuscular embolisms was chosen as a reference method. The examination concentrated on the implantation of the acetabulum and femur prosthesis since this phase of the operation has been associated with a high incidence of embolisms. The TEE monitoring revealed corpuscular as well as gaseous emboli during surgery. In the 36 cases of echocardiographic detectable embolisms prospectively defined changes of the heart rate were observed in 17%, of the mean arterial pressure in 56%, of the end-expiratory CO2 partial pressure in 47% and of the arterial O2 saturation in 31% of the cases. The embolisms which had been categorized by means of TEE according to their severity reflected a decrease of the end-expiratory CO2 partial pressure in 25% of the cases with light, in 45% of the cases with moderate and in 69% of the cases with severe embolisms, whereas a decrease in arterial O2 saturation was detected in 8% with light, 27% with moderate and in 54% of the cases with severe embolisms. Corpuscular embolism had no stronger influence on the frequency of relevant changes of end-expiratory CO2 partial pressure and the arterial O2 saturation than did the gaseous emboli.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

Effects of beta- and alpha-adrenergic agonists, adenosine, and carbachol in heart muscle isolated from malignant hyperthermia susceptible swine.

During malignant hyperthermia crisis, cardiac arrhythmias and increased myocardial oxygen consumption are observed. It was the purpose of the present study to investigate whether or not a greater sensitivity to cardiac alpha- or beta-adrenoceptor stimulation or an impaired adenosine- or m-cholinoceptor-mediated inhibition of beta-adrenergic stimulation contributes to the cardiac symptoms of malignant hyperthermia. The effects of phenylephrine, isoproterenol, adenosine, [-]-N6-phenylisopropyladenosine (PIA), and carbachol on force of contraction were studied in electrically driven trabeculae isolated from the left ventricles of malignant hyperthermia susceptible (MHS) and healthy control pigs. The positive inotropic effects of phenylephrine and of isoproterenol were similar in MHS and control pigs. The EC50 values for the inotropic effect of phenylephrine were 4.1 (2.1-8.3) mumol.l-1 (n = 9) in MHS and 6.3 (3.4-12.9) mumol.l-1 (n = 9) in control swine. The maximal positive inotropic effects at 30 mumol.l-1 phenylephrine also did not differ in both groups (176.7 +/- 14.4% of pre-phenylephrine value in MHS swine, n = 9; 170.3 +/- 15.9% of pre-phenylephrine value in control swine, n = 9). The EC50 values for isoproterenol were 0.16 (0.06-0.39) mumol.l-1 (n = 9) and 0.19 (0.05-0.29) mumol.l-1 (n = 9) in MHS and control swine, respectively. The maximal positive inotropic effects at 1 mumol.l-1 isoproterenol were also similar (213.8 +/- 12.6% of the pre-isoproterenol value in MHS swine, n = 9; 216.4 +/- 36.0% of the pre-isoproterenol value in control swine, n = 9). Also, no difference could be detected in the antiadrenergic effects of adenosine, PIA, or carbachol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1988

[Effect of flumazenil on global cerebral blood flow and on intracranial pressure in the reperfusion phase following incomplete global cerebral ischemia].

Sedation with benzodiazepines in intensive care patients with head injuries has become part of a standard concept in controlling intracranial pressure (ICP) and metabolic demands of an injured brain. The specific benzodiazepine antagonist flumazenil, which is supposed to exert no direct effect on cerebral blood flow (CBF) in healthy volunteers, suggests that rapid reversal from midazolam sedation might be achieved without any deleterious side effects. It remains however ambiguous if the same holds true in subjects with head trauma. This study describes the effect of flumazenil on CBF, ICP and cerebral perfusion pressure (CPP) during the reperfusion period after incomplete global ischemia in 10 goats. After preparation progressively decreasing CBF in 7 goats was achieved by stepwise external occlusion of the a. max. interna. 90-120 min after reestablishment of CBF 15 mg midazolam i.v. were given followed by 0.5 mg flumazenil i.v. 5 min later. Within 60 sec after application of the antagonist an increase of CBF by 30-165% and of ICP by 25-310% was noted in 5 goats. Simultaneous changes in arterial pressure, CBF and ICP suggest a severe impact of the benzodiazepine antagonist after midazolam sedation on ICP and CBF during periods of impaired cerebral autoregulation. Until the cerebrovascular and cerebral metabolic effects of flumazenil have been elaborated in detail, it is recommended to titrate the effect of flumazenil over long intervals in head injured patients.

Animals↗
PubMed1988

[Intraoperative determination of heart time volume with transesophageal pulsed Doppler echocardiography].

Stroke volume and cardiac output (CO) can be determined noninvasively by means of the pulsed Doppler technique to measure blood flow velocities in specified regions of the heart or neighboring great vessels along with 2D-echocardiographic imaging to measure the diameter of vessels or valve orifices. Disadvantages of the transthoracic approach, such as precordial inaccessibility and instability of the probe position, have prevented the continuous application of pulsed Doppler echocardiography during surgery. Recently, we presented a new technique using the transesophageal approach with combined pulsed Doppler measurements and 2D-echocardiographic imaging. This study was designed to assess the feasibility of transesophageal pulsed Doppler echocardiography (TDE) for CO measurements during surgery and to test the method for accuracy against the thermodilution technique (TD) as well as evaluate its ability to track dynamic CO changes during general anesthesia. Transmitral and pulmonary artery flow analysis using TDE was performed in 35 adult patients undergoing a variety of surgical procedures under general anesthesia. For the transesophageal approach we used the prototype of a new 5-MHz phased array transducer with 64 elements fixed at the distal end of a 9 mm gastroscope. The mitral valve flow methods combined the velocity of transmitral flow at the mitral anulus with the cross-sectional area of the anulus calculated from its diameter at middiastole, while the pulmonary flow method combined the velocity of pulmonary artery flow with the cross-sectional area of the vessel calculated from its diameter during early systole. High-resolution 2D-echocardiograms of the mitral valve allowed accurate diameter measurements of the mitral valve orifice in all patients. A fixed esophageal transducer position behind the left atrium enabled continuous transmitral Doppler recordings of invariably high quality to be made. Regression analysis of TDE-CO vs. TD-CO for 50 measurements in 27 patients yielded a good correlation (r = 0.95, y = 0.95x + 0.42, SEE = 0.34 l/min). Use of halothane in 8 further patients resulted in a 21.0 +/- 5.9% and 37.3 +/- 11.7% decrease of TDE-CO at 1.0 MAC and 1.5 MAC, respectively. Transesophageal images adequate to determine the cross-sectional area of the pulmonary artery could be obtained in 16 of 27 (59.3%) patients. CO determined by the TDE pulmonary flow method (28 measurements in 16 patients) correlated with the TD-CO, with an r value of 0.91 and SEE 0.49 l/min.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1987

Continuous measurement of intracardiac and pulmonary blood flow velocities with transesophageal pulsed Doppler echocardiography: technique and initial clinical experience.

Pulsed Doppler techniques have become well established adjuncts to conventional echocardiography in the noninvasive diagnosis of various cardiac malfunctions. Disadvantages of the transthoracic approach, such as inaccessibility and instability of the probe position, limit the continuous application of pulsed Doppler echocardiography during surgery. This study presents a new technique using the transesophageal approach that combines pulsed Doppler measurements with two-dimensional echocardiographic imaging (TDE). The first intraoperative experience with this new enhancement to two-dimensional transesophageal echocardiography (TEE) showed that this relatively noninvasive technique is a safe method allowing constant monitoring of cardiac and pulmonary blood flow velocities. The simultaneous high-resolution two-dimensional imaging facilitates spatial orientation and placement of the sample volume, as well as continued control of the sampling location. The typical flow velocity patterns in standard TEE views are described. The mitral valve and pulmonary artery offer particularly favorable conditions for continuous high-quality TDE measurements. It is concluded that the new technique may further increase the value of TEE to clinicians in the perioperative period.

Adolescent↗
PubMed1987

Electrophysiological effects of intravenous dantrolene on canine heart.

The electrophysiological effects of an intravenous dantrolene infusion (10 mg kg-1) were evaluated in healthy, anaesthetized dogs by intracardiac electrophysiological study. Dantrolene administration resulted in a significant prolongation of the refractory periods of the right atrium and ventricle, while the functional refractory period of the AV node was not altered. A slight increase of AV nodal conduction, measured as atrial-His bundle interval, without any change in infranodal conduction, measured as His bundle-ventricular interval, was observed during sinus rhythm. Dantrolene had no significant effects on surface ECG parameters. We conclude that intravenously administered dantrolene, at the maximal recommended doses, has primary effects on electrophysiological parameters. These findings support the hypothesis that the beneficial effects of dantrolene on cardiac arrhythmias associated with malignant hyperthermia may be related to its intrinsic activity on the electrophysiological properties of the heart, but confirmation requires further investigations on induced arrhythmias in experimental models.

Animals↗
PubMed1986

[Electrophysiologic and intropic effects of dantrolene on isolated ventricular myocardium. Studies on guinea pig papillary muscle].

The effect of dantrolene (D) on transmembrane potential and contractile force was examined in electrically driven right ventricular papillary muscles of guinea-pigs. Independent of stimulation frequency D (100 mumol/l) caused a significant reduction of contractility by ca. 40% from control levels. Action potential duration measured at the 90% and 50% repolarisation level was significantly increased while plateau phase was slightly depressed by D. Resting membrane potential, action potential amplitude and maximum rate of depolarisation in phase 0 were unaffected. The effect of D on action potential duration was significantly dependent upon the frequency of stimulation. At faster rates action potential duration was increased relatively more than at slower rates. Slow response action potentials were unaffected by D. Unlike Ryanodine D did not flatten the force-frequency-relationship curve and did not influence the force-interval-relationship under extrastimulation. - It is concluded that the direct negative inotropic effect of D is not accompanied by a transsarcolemmal influence such as an inhibition of fast Na+- or slow Ca++-channels. The results are compatible with an intracellular site of action of D as postulated for skeletal muscle. D acts differently from ryanodine, another presumed inhibitor of sarcoplasmic reticulum.

Action Potentials↗
PubMed1985

[Detection of venous embolism during intraoperative monitoring by two-dimensional transesophageal echocardiography].

12 patients (mean age: 81 +/- 9 years) undergoing total hip replacement because of transcervical femoral fractures were studied intraoperatively by two-dimensional transoesophageal echocardiography (TEE). The purpose of this study was to evaluate the ability of this new technique for detection of embolic events in the right heart by intraoperative 2D-TEE monitoring during hip surgery. In all patients (pts) we observed a transient increase of contrast intensity in the right atrium immediately after insertion of the acetabulum prosthesis ("snow flurry"). Contrast was maximal 15-20 seconds after insertion and persisted for approximately 2 min. While contrast intensity decreased in the minutes thereafter, in 3 pts contrast became more heterogeneous:we detected structures like "flakes" passing the right heart, sometimes circulating for some seconds in the right atrium respectively the right ventricle. Detected embolism was followed by a transient decrease of arterial pO2 (greater than 10 mmHg) in 5 pts. However, haemodynamic responses occurred infrequently; 4 pts experienced no changes at this moment. During insertion of the femoral prosthesis the contrast events were even more pronounced and persistent. In all pts we observed the appearance of "flake"-like structures passing the right atrium and the right ventricle, some measuring up to 6 cm in length. This was accompanied in 10 pts with a decrease (greater than 10 mmHg) of arterial pO2 and in 8 pts with a decrease (greater than 5 mmHg) of endtidal CO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1985

[Prognosis of preclinical cardiopulmonary resuscitation].

480 preclinical cardiopulmonary resuscitations performed at the Emergency Center of the Federal Military Hospital in Hamburg were analysed. The late success was 7.9%, i.e., 38 patients were released after initially successful resuscitation and subsequent clinical treatment. Prognostic parameters indicating late success were deduced from the data. The age of the patients, call times, and organisational course do not influence the survival rate. For this reason resuscitation should be attempted in every patient, even in those with longer transport times, and if resuscitation proves unsuccessful, the measures should be discontinued at the site. Patients with multiple injuries or craniocerebral trauma, who require resuscitation, and patients with asystole, who are older than 70 years of age, do not survive. Even in young patients, the prognosis for asystole is extremely poor. Although the prognosis for patients with ventricular fibrillation is better, we are of the opinion that the success rate of preclinical cardiopulmonary resuscitations can be improved by systematic use of antiarrhythmics; metaproterenol sulfate should no longer be administered. The prognosis of resuscitated patients with contracted pupils and gasping breath and of patients with severe tachycardia is relatively good. Cardiac arrest after drowning carries best prognosis: 4 of 7 patients survived.

Adolescent↗
PubMed1985

[Long-term result and quality of life following preclinical cardiopulmonary resuscitation].

The value of successful cardiopulmonary resuscitation (CPR) must be considered in the light of late outcome of survivors, including the neurological situation as well as the subsequent quality of life. We followed up the fates of 168 patients (pts) primary successfully resuscitated by rescue helicopter and mobile intensive care unit of the rescue centre at the military hospital of Hamburg and admitted to emergency hospitals after heart action became stabilised. 130 pts died during hospitalisation and 38 pts (7.9% of 480 resuscitation attempts total) were discharged from hospital. 32 of them had no essential neurologic damage. Within the next 3 years after discharge from hospital 15 of the 38 survivors died (3-year-survival rate: 4.8% of all attempts of CPR or 60% of survivors). 4 of the 6 survivors with persistent cerebral damage died within 6 months after discharge from hospital. Interviews (n = 28) with survivors or their relatives provided information on social situation, physical and psychical condition after CPR as well as recollection of CPR. 29% (n = 8) became incapacitated for work after CPR. 68% considered meaning of life unchanged, 25% as limited and for 7% the incident had a positive effect concerning their outlook on life. 18% (n = 5) suffered from depressions after CPR. Reductions of physical efficiency (64%), of memory (68%) and of concentration capacity (61%) were realised. The majority of survivors did not remember anything, neither experiences of intubation nor of external cardiac massage. Only one patient thought he remembered the incident and reported about "blows on the chest". 89% considered resuscitation to be a sensible and important provision.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗