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R Ritz

Publications and source records attributed to R Ritz.

At least 55 records · Page 3Linked to original sources
PubMed1995

Cardiorespiratory effects of volume- and pressure-controlled ventilation at various I/E ratios in an acute lung injury model.

Numerous approaches to the provision of mechanical ventilation during acute lung injury are currently available. Of these, pressure control inverse ratio ventilation has been considered superior to volume control ventilation with PEEP with respect to improving gas exchange and minimizing cardiovascular compromise. However, no study systematically compares volume-controlled (VC) and pressure-controlled (PC) ventilation while maintaining mean airway pressure (MAP) constant at varying I/E ratios. We studied the effect of VC and PC with PEEP at normal (1:2) and inverse I/E ratios (2:1 and 4:1) on gas exchange, lung mechanics, and hemodynamics in a sheep lung injury model. Severe lung injury was induced in 12 sheep with bilateral lung lavages using normal saline; prelavage PO2 230 +/- 50 mm Hg, PEEP 5 cm H2O and postlavage, pretreatment PO2 70 +/- 20 mm Hg, PEEP 10 cm H2O, both at FIO2 0.50. MAP was kept constant throughout the study at 25 +/- 2 cm H2O while ventilating all animals with a VT of 10 ml/kg and a rate of 20/min by randomized application of VC and PC with I/E ratios of 1:2, 2:1, and 4:1. Despite liberal fluid administration, all ventilatory modes depressed cardiac output compared with preinjury values. However, gas exchange and hemodynamics did not differ among ventilation modes or I/E ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

[Acute pulmonary embolism].

Pulmonary embolism is a frequent event, even today the diagnostic comes often too late or not at all. Symptoms, clinical results and additional examinations like ECG, echocardiography, scintigraphy and angiography permit the differentiation between small peripheral and massive central pulmonary embolism [PE], important for the therapeutic procedure. Patients with peripheral PE have to be heparinized, sometimes they can be treated at home. The acute massive PE represents an emergency situation, the patient must be hospitalized immediately. The goals of therapy in massive PE consist in a rapid reduction of the threatening load on the right ventricule by the embolism. If the patient is in cardiogenic shock, surgical embolectomy is indicated, without shock the immediate start of thrombolytic therapy must be considered.

Acute Disease↗
PubMed1994

A biologically motivated and analytically soluble model of collective oscillations in the cortex. II. Application to binding and pattern segmentation.

Feature linking and pattern separation are shown to be performed as simultaneous processes by a highly connected auto-associative network of spiking neurons (spike response model). In principle, many (e.g., with nine) patterns can be separated, but with a biological set of parameters the number is limited to four. The patterns have been learned by an asymmetric hebbian rule that can handle a low activity which may vary from pattern to pattern (in a range between 4% and 7%). Spikes are generated by a threshold process and--with some delay--transmitted to postsynaptic neurons. There they evoke an excitatory or inhibitory postsynaptic potential (EPSP or IPSP). Spike emission is followed by an absolute refractory period (1 ms) and activates an inhibitory delay loop that prevents continuous firing. Three different network topologies are discussed, i.e., a structureless fully connected system, a network composed of two 'hemispheres', and finally a hierarchical network with four subsystems that represent different 'functions' and interact via feedforward and feedback connections. Functional feedback turns out to be essential for context-sensitive binding. The coherence between the two hemispheres is dependent on the interhemispheric delays. If these are on average too large, the two hemispheres oscillate coherently by themselves but phase-shifted by half a period with respect to each other.

Animals↗
PubMed1994

N-acetylcysteine enhances recovery from acute lung injury in man. A randomized, double-blind, placebo-controlled clinical study.

OBJECTIVE: To determine the effects of intravenous N-acetylcysteine (NAC) on the development of severe adult respiratory distress syndrome (ARDS) and mortality rate in patients with mild-to-moderate acute lung injury and to analyze the duration of ventilatory support and FIO2 required as well as the evolution of the lung injury score. SETTING: Three university hospital ICUs and one regional ICU in Switzerland. PATIENTS: Sixty-one adult patients presenting with mild-to-moderate acute lung injury and various predisposing factors for ARDS received either NAC, 40 mg/kg/d, or placebo intravenously for 3 days. MEASUREMENTS: Respiratory dysfunction was assessed daily according to the need for mechanical ventilation and FIO2, the evolution of the lung injury score, and the PaO2/FIO2 ratio. The cardiovascular state, liver function, and kidney function were also monitored. Data were collected at admission (day 0), during the first 3 days, and on the day of discharge from the ICU. RESULTS: The NAC and placebo groups (32 and 29 patients, respectively) were comparable at ICU admission for severity of illness assessed by the simplified acute physiology score (SAPS) (10.8 +/- 4.6 vs 10.9 +/- 4.8) and lung injury score (LIS) (1.39 +/- 0.95 vs 1.11 +/- 1.08) (mean +/- SD). Three patients in each group developed ARDS. The 1-month mortality rate was 22 percent for the NAC group and 35 percent for the placebo group (difference not statistically significant). At admission, 22 of 32 patients (69 percent) in the NAC group were mechanically ventilated compared with 22 of 29 (76 percent) in the placebo group. At the end of the treatment period (day 3), 5 of 29 (17 percent) in the NAC group and 12 of 25 (48 percent) in the placebo group were still receiving ventilatory support (p = 0.01), The FIO2 was 0.37 less than admission value (day 0) in the NAC group, and 0.20 less in the placebo group (p < 0.04); the oxygenation index (PaO2/FIO2) improved significantly (p < 0.05) from day 0 to day 3 only in the NAC-treated group. The LIS showed a significant regression (p = 0.003) in the NAC-treated group during the first 10 days of treatment: no change was observed in the placebo group. No adverse effects were observed during the treatment with NAC. CONCLUSIONS: Intravenous NAC treatment during 72 h improved systemic oxygenation and reduced the need for ventilatory support in patients presenting with mild-to-moderate acute lung injury subsequent to a variety of underlying diseases. Development of ARDS and mortality were not reduced significantly by this therapy.

Acetylcysteine↗
PubMed1993

[Factor VII and protein-C markers are no prognostic indicators in acute coronary heart disease].

Fibrinogen and factor VII have been identified as independent risk factors in cardiovascular morbidity. A relationship between factor VII coagulant activity (VII:C) and prognostically different manifestations of acute coronary heart disease (aCHD) has recently been suggested. In order to validate and to extend these observations, we prospectively studied patients admitted for aCHD (n = 76) and a control group without aCHD (CG, n = 27). According to their clinical evolution, the aCHD cases were subdivided into unstable angina (UA, n = 26), myocardial infarction without (M-I, n = 23) and with heart failure (M-II, n = 27). Before treatment blood was collected for the following assays: fibrinogen, factor VII procoagulant activity (VII:C), amidolytic test (VII:am), immunological (VII:Ag), protein C functional (PCf) and immunological (PC:Ag). We found no statistically significant difference between control and aCHD cases and between their subgroups for any assay of fibrinogen, factor VII and protein C. The VII:C/VII:Ag ratio was higher for UA, M-I, M-II and the entire aCHD group compared with the CG. However, it was not possible to separate the prognostically different aCHD subgroups from each other by ratios of measured values. Therefore, determinations of factor VII, protein C and fibrinogen in aCHD have no prognostic relevance.

Acute Disease↗
PubMed1993

A biologically motivated and analytically soluble model of collective oscillations in the cortex. I. Theory of weak locking.

A model of an associative network of spiking neurons with stationary states, globally locked oscillations, and weakly locked oscillatory states is presented and analyzed. The network is close to biology in the following sense. First, the neurons spike and our model includes an absolute refractory period after each spike. Second, we consider a distribution of axonal delay times. Finally, we describe synaptic signal transmission by excitatory and inhibitory potentials (EPSP and IPSP) with a realistic shape, that is, through a response kernel. During retrieval of a pattern, all active neurons exhibit periodic spike bursts which may or may not be synchronized ('locked') into a coherent oscillation. We derive an analytical condition of locking and calculate the period of collective activity during oscillatory retrieval. In a stationary retrieval state, the overlap assumes a constant value proportional to the mean firing rate of the neurons. It is argued that in a biological network an intermediate scenario of 'weak locking' is most likely.

Animals↗
PubMed1993

Determinants of survival after rodent cardiac arrest: implications for therapy with adrenergic agents.

Coronary perfusion pressure and its relation with the expired carbon dioxide concentration (end-tidal CO2) was examined in a rodent model of sustained ventricular fibrillation and subsequent cardiopulmonary resuscitation. Equipressor dosages of the pure alpha 1-agonist methoxamine, the mixed alpha/beta-agonists epinephrine and norepinephrine were randomly compared with 0.9% NaCl. Thirty two Sprague-Dawley rats were anesthetized and catheters were advanced into the aorta, right ventricle, right atrium and inferior vena cava. After 4 min of untreated ventricular fibrillation external chest compression was initiated and defibrillation was attempted after 8 min. Drugs were infused for 3 min during cardiopulmonary resuscitation into the inferior vena cava. A 60-min survival period followed methoxamine administration in 7 of 8 (P < 0.019 vs. NaCl), after epinephrine in 4 of 8, after norepinephrine in 5 of 8, and after NaCl in only 2 of 8 animals. Resuscitation success was determined by coronary perfusion and mean aortic pressures generated during cardiopulmonary resuscitation but not by arterial or venous blood gases. Adrenergic agents increased coronary perfusion and mean aortic pressures but decreased end-tidal CO2 which failed to correlate with these pressures. Accordingly, alpha-adrenergic agents mitigated the accuracy of end-tidal CO2 as a non-invasive hemodynamic monitor and predictor of survival after rodent cardiopulmonary resuscitation.

Acid-Base Equilibrium↗
PubMed1993

Gender and response to antilymphocyte globulin (ALG) for severe aplastic anaemia.

We have evaluated the speed of haematological recovery in 103 severe aplastic anaemia (SAA) patients treated with antilymphocyte globulin (ALG) and followed at our institution for 3-15 years. We found that haemopoietic recovery was significantly delayed in six girls under the age of 10 years. This slow recovery in girls might be explained by their relative inability to release haemopoietic growth factors, granulocyte colony stimulating activity and burst promoting activity, compared to all other sex and age groups. This defect is not explained by disease severity at presentation and thus indicates a functional abnormality of monocytes/macrophages and T-lymphocytes in addition to the deficiency of haemopoietic stem cells. In a multivariate analysis, low factor production and low pretreatment reticulocyte counts turned out to be strong predictors of slow haemopoietic recovery. We conclude that young girls have a particular form of SAA characterized by low haemopoietic factor production and delayed recovery after ALG. They are preferential candidates for early bone marrow transplantation or, if they are not eligible, for treatment with recombinant human haemopoietic growth factors.

Adolescent↗
PubMed1993

Evaluation of conventional chest tube therapy for iatrogenic pneumothorax.

STUDY OBJECTIVE: To assess conventional, large chest tube therapy in iatrogenic pneumothorax and to determine the optimal moment when to use more invasive procedures. DESIGN: Retrospective chart review. SETTING: Medical intensive care unit of a university hospital. PATIENTS: Forty-seven patients with needle-induced iatrogenic pneumothorax. Twenty-four patients had an underlying pleural or pulmonary disorder. INTERVENTIONS: After insertion of a 20- to 24-French plastic chest tube connected to an underwater seal, suction was maintained until gas egress stopped or up to 10 days in patients with a persisting gas leak. RESULTS: In 96 percent, a definite occlusion of the pneumothorax was achieved. In all patients without an underlying lung disorder, gas egress stopped definitely after 72 h. In the presence of an underlying lung disorder, 92 percent of the pneumothoraces were healed after 10 days of continuous suction therapy. At 72 h, only 71 percent of the latter group were healed (p < 0.05 vs patients without lung disease). No major complication of chest tube therapy occurred. CONCLUSION: Conventional chest tube therapy is a safe and effective treatment for iatrogenic pneumothorax. In patients with an underlying lung disease, gas egress may last for up to 10 days. In these patients, the earlier use of a more invasive approach may be justified if the air leak persists.

Adult↗
PubMed1993

Why spikes? Hebbian learning and retrieval of time-resolved excitation patterns.

Hebbian learning allows a network of spiking neurons to store and retrieve spatio-temporal patterns with a time resolution of 1 ms, despite the long postsynaptic and dendritic integration times. To show this, we introduce and analyze a model of spiking neurons, the spike response model, with a realistic distribution of axonal delays and with realistic postsynaptic potentials. Learning is performed by a local Hebbian rule which is based on the synchronism of presynaptic neurotransmitter release and some short-acting postsynaptic process. The time window of this synchronism determines the temporal resolution of pattern retrieval, which can be initiated by applying a short external stimulus pattern. Furthermore, a rate quantization is found in dependence upon the threshold value of the neurons, i.e., in a given time a pattern runs n times as often as learned, when n is a positive integer (n > or = 0). We show that all information about the spike pattern is lost if only mean firing rates (temporal average) or ensemble activities (spatial average) are considered. An average over several retrieval runs in order to generate a post-stimulus time histogram may also deteriorate the signal. The full information on a pattern is contained in the spike raster of a single run. Our results stress the importance, and advantage, of coding by spatio-temporal spike patterns instead of firing rates and average ensemble activity. The implications regarding modelling and experimental data analysis are discussed.

Animals↗
PubMed1992

[Cocaine poisoning from transport of the drug in the gastrointestinal tract (the body-packer syndrome)].

Three days after arriving in Switzerland from Bolivia a 35-year-old man presented at a casualty department. He was anxious, agitated and hallucinating, and he expressed delusional ideas of being poisoned. As a general physical examination was without abnormal findings he was thought to suffer from a psychiatric disorder. It was only when he had evacuated in stool a long oval foreign body, packed in plastic sheeting and filled with a dark paste, that cocaine poisoning due to cocaine transport in the gastrointestinal tract (body packer syndrome) was suspected. Plain X-ray of the abdomen revealed numerous regular structures of poor X-ray contrast and the urine contained cocaine metabolites, confirming the tentative diagnosis. As the patient's state of consciousness deteriorated and he had a grand mal seizure, an emergency laparotomy was performed. 78 packages (two of them had opened) were removed by gastro- and caecotomy. Total cocaine weight was 650 g. He was discharged from hospital after 11 days, free of symptoms.

Adult↗
PubMed1992

[Anti-arrhythmia treatment using L-carnitine in acute myocardial infarct].

Carnitine, a quaternary amine (3-hydroxy-4-N-trimethylaminobutyric acid), plays an important physiologic role in fatty acid transport and metabolism as well as in energy production of the myocardial cell. L-carnitine in high doses has been postulated to have an antiarrhythmic effect and this has also been clinically proven. We studied 20 patients with acute myocardial infarction (AMI), 4-12 hours after onset of pain. The patients were randomized and treated double-blind with 5 g L-carnitine (n = 12) or placebo (n = 8) at hours 0, 12, 24, 36, and with 2 x 3 g on days 3 to 7 by intravenous infusion over 2 hours. The two groups were similar for age, sex, infarct site, maximum CPK and conventional antiarrhythmic therapy. 24-hour Holter-ECG was performed on days 1, 2 and 7 and showed no significant difference between the two groups with respect to incidence of ventricular premature beats (VPB) per hour. On the second day following AMI, however, only 4 of 12 carnitine-treated patients showed high-grade VPB (Lown IVa and IVb), in comparison with 7 of 8 patients in the placebo group. The difference is significant: p = 0.028 (Fisher's Exact Test). Carnitine was well tolerated and the efficacy demonstrated on the second day following AMI must be interpreted with caution.

Aged↗
PubMed1992

[Acute left heart insufficiency: possible leading symptom of a pheochromocytoma].

A 42-year-old patient with acute left-ventricular failure is described in whom pheochromocytoma was diagnosed only after prolonged and fruitless efforts. Pheochromocytoma may present without the typical features of paroxysmal or sustained hypertension, headache, increased sweating, and palpitations. Therefore, in cases of acute left-sided cardiac failure of primarily undetermined origin, pheochromocytoma should be considered in differential diagnosis.

Acute Disease↗
PubMed1992

Possible risk for cardiac arrhythmia related to intravenous erythromycin.

OBJECTIVE: To evaluate the incidence of prolongation of the rate-corrected electrocardiographic QT interval (QTc) and of ventricular arrhythmia associated with intravenous administration of erythromycin lactobionate. DESIGN: A consecutive series of 7 critically ill patients treated with intravenous erythromycin for severe pneumonia. SETTING: A medical intensive care unit of a university hospital. MEASUREMENTS AND RESULTS: Registration of QTc duration before and after intravenous administration of erythromycin as a short infusion. Blood chemistry, hemodynamic variables, arrhythmias, and co-medications were recorded. Evaluation of at least 10 ECG intervals by 2 experienced investigators who were blinded as to the time of drug administration. If several measurements were performed in the same patient, only the mean value was used for further analysis. During 12 of 13 drug administrations studied in 7 patients QTc prolongation was observed. The extent of QTc prolongation was significantly correlated with the infusion rate (mg/min, r = 0.765, p = 0.05). In 3 patients ventricular arrhythmia occurred in close temporal relation to the erythromycin infusion; two of them developed ventricular fibrillation shortly after the first and second dose of erythromycin, respectively, and died within 3 h. CONCLUSION: In critically ill patients erythromycin-induced QTc prolongation is a frequent pharmacologic effect correlated with erythromycin infusion rate. To avoid changes in electrocardiographic intervals and thereby possibly potentially life-threatening ventricular arrhythmia administration with the lowest possible infusion rate and close cardiac rhythm monitoring are advisable in these patients.

Aged↗
PubMed1992

Absence of nitroglycerin-induced heparin resistance in healthy volunteers.

A previously described nitroglycerin-induced heparin resistance could not be verified by in-vitro experiments or in a randomized, double-blind, crossover trial in healthy volunteers. A clinically relevant attenuation of the anticoagulant effect of a heparin bolus (40 U.kg-1) by a concomitant infusion of nitroglycerin (100 micrograms.min-1) was absent. Activated partial thromboplastin time was not significantly different under nitroglycerin infusion as compared to placebo after heparin injection. Concentrations and activities of antithrombin III and heparin cofactor II remained unchanged during nitroglycerin infusion. An interaction of these two frequently combined drugs in patients with active thromboembolic disease or after a prolonged concomitant intravenous administration cannot be ruled out. Since this is of clinical importance, further studies must clarify a possible nitroglycerin-induced heparin resistance.

Adult↗
PubMed1992

Rapid reversal of heart failure in a patient with phaeochromocytoma and catecholamine-induced cardiomyopathy who was treated with captopril.

A patient with a phaeochromocytoma and severe left ventricular heart failure caused by a catecholamine-induced cardiomyopathy is described. The clinical signs of congestive heart failure resolved rapidly on treatment with captopril and myocardial performance became normal within two weeks of medical treatment with captopril for one week and with captopril in combination with phenoxybenzamine for another week.

Acute Disease↗