Phrenic Nerve Stimulation for Central Ventilatory Failure with Bipolar and Four-Pole Electrode Systems

A multi-channel phrenic nerve stimulator developed in Tampere has been implanted into seven patients with C2-tetraplegia and into three patients with central sleep apneas. Six bipolar cuff electrodes were implanted bilaterally into the neck. Two four-pole cuff and 14 four-pole noncuff electrodes were used in seven patients and to replace one bipolar electrode. Four-pole electrodes were implanted within the thorax. Seven patients achieved total independence from conventional ventilators within 4 months of implantation, and one for 18 hours each day. Two patients died 12 days and 3 months after implantation and two patients after having achieved independence from mechanical ventilators from causes unrelated to the stimulators. Reoperations were necessary because of dislocation of receivers, electrodes, electrode lesions, nerve injuries, and technical failures in seven patients. Most of the problems appeared in two patients with obesity and in three patients with very thin phrenic nerves. Single unit prototypes failed technically more frequently than units of prototype serial fabrication. New electrode design, progress in the manufacture of receivers, and improved implantation technique should help to diminish failures in future.     

Hemodynamic Responses to Rapid Pacing: A Model for Tachycardia Differentiation

The hemodynamic responses to rapid atrial and ventricular pacing were examined in 10 closed-chest anesthetized dogs in an attempt to distinguish hemodynamically stable from unstable tachycardias. Pressure monitoring catheters were placed in the femoral artery, right atrium, and right ventricle to measure mean arterial pressure, mean right atrial pressure, and mean right ventricular pressure at baseline heart rate and after rapid high right atrial and right ventricular apex pacing. Pressures recorded during rapid pacing (average of the pressures at 30 and 60 seconds of pacing) at pacing rates of 180, 250, and 280/minute were compared to those recorded initially at baseline heart rates. Rapid right ventricular apex pacing resulted in significant increases in mean right atrial pressure (from 6 ± 1 mmHg (mean ± standard error) to 12 ± 1 mmHg, a 100% increase, P < 0.001) and mean right ventricular pressure (from 11 ±1 mmHg to 16 ± 1 mmHg, a 45% increase, p < 0.02) with marked hemodynamic compromise (mean arterial pressure decreased from 85 ± 6 mmHg to 50 ± 6 mmHg, a 41% decrease, P < 0.01). These parameters remained stable (no statistically significant difference from baseline) during high right atrial pacing. In half of the dogs high right atrial pacing at rates 250 resulted in atrioventricular Wenckebach. Thus, it is concluded that mean right atrial pressure and mean right ventricular pressure may be useful in distinguishing hemodynamically significant tachycardias, and in the future design of antitachycardia devices.     

Elevation of gastric pH heals peptic oesophagitis - A role for omeprazole

The aim of this study was to investigate the hypothesis that the prolonged and substantial elevation of gastric pH which can be achieved with the antisecretory agent omeprazole will result in healing of peptic oesophagitis. Eight patients with erosive or ulcerative peptic oesophagitis were treated with omeprazole (30 mg daily) for 8 weeks. Complete healing occurred in seven patients after 8 weeks of omeprazole therapy. Only a small area of residual ulceration persisted in one unhealed patient. Heartburn resolved within the first 2 weeks of therapy in all but one patient. Specific food intolerances also were eliminated in most cases. Post-prandial oesophageal pH monitoring during omeprazole administration showed abolition of acid reflux episodes (pH < 4). This effect appeared to be due solely to the antisecretory effect of omeprazole, since motility measurements demonstrated a continued high frequency of reflux while concurrent gastric pH monitoring showed sustained elevation of gastric pH above 4. These results support the hypothesis that a prolonged and potent inhibition of gastric acid secretion renders refluxed gastric juice sufficiently innocuous to allow healing of severe peptic oesophagitis.     

USING MULTIPLE DECREMENT MODELS TO ESTIMATE RISK AND MORBIDITY FROM SPECIFIC AIDS ILLNESSES

A simple non-parametric approach is developed to simultaneously estimate net incidence and morbidity time from specific AIDS illnesses in populations at high risk for death from these illnesses and other causes. The disease–death process has four-stages that can be recast as two sandwiching three-state multiple decrement processes. Non-parametric estimation of net incidence and morbidity time with error bounds are achieved from these sandwiching models through modification of methods from Aalen and Greenwood, and bootstrapping. An application to immunosuppressed HIV-1 infected homosexual men reveals that cytomegalovirus disease, Kaposi's sarcoma and Pneumocystis pneumonia are likely to occur and cause significant morbidity time.     

MICROVASCULAR ANGIOPATHY IN ADVANCED PERIODONTAL DISEASE

Previous studies have shown a perivascular hyaline thickening affecting restricted regions of the microcirculation in gingivitis and moderate periodontitis and in the pulpal vessels in chronic pulpitis. In the present study of the lesion of advanced periodontitis, immunostaining for type IV collagen and laminin demonstrated widespread deposition of basement membrane material, with manifest involvement of the venous network. Some vessels were associated with an increased deposition of both basement membrane proteins, while others showed preferential deposition of either laminin or type IV collagen. Immunostaining also revealed an extensive trabecular network of type IV collagen throughout the affected gingival tissue that was not related to recognizable vessels but was co-extensive with less intense staining for laminin. This network was not associated with viable endothelial cells demonstrable by staining with the endothelial marker Ulex agglutinin (UEA-1). The results indicate extensive vascular pathology in advanced periodontitis that could explain the attenuation of the inflammatory reaction and the restricted ability to develop reparative granulation tissue in this disease.     

White Matter Changes in Depression and Alzheimer's Disease: A Review of Magnetic Resonance Imaging Studies

This article reviews magnetic resonance imaging (MRI) studies of white matter lesions in depression and Alzheimer's disease. Although conflicting reports exist, many studies show that white matter lesions are more prevalent in both conditions, with depression associated with deep white matter lesions (DWML) and Alzheimer's disease with periventricular lesions (PVL). In normal ageing and depression there is some evidence that such lesions may be associated with neuropsychological dysfunction, though the relationship is less clear for Alzheimer's disease. One difficulty in drawing firm conclusions from work so far is that confounding variables, such as cerebrovascular risk factors, have now always been taken into account. Most studies have been cross-sectional so there is little information regarding the progression, prognostic significance and pathogenesis of such lesions. These issues merit examination in longitudinal studies combining serial MRI with clinical assessments of subjects who have been fully assessed for vascular risk factors.