Variability of inspiratory conductance quantifies flow limitation

In the present study, our aim was to investigate whether the variability of conductance over the course of inspiration reflects flow limitation. Pressure/flow conditions in the upper airway were modelled by a collapsible tube within a rigid chamber and a pump simulating respiration. Instantaneous conductance was estimated every 20 ms as flow/resistive pressure, and its variability during inspiration expressed as the 90th/50th percentile ratio. Accuracy of this ratio to quantify flow limitation was evaluated by observing whether it changed predictably with adjustments of model parameters. To illustrate the potential of this ratio to quantify flow limitation in a clinical setting, we recorded pneumotachographic airflow and oesophageal pressure in 11 patients with obstructive sleep apnoea during nasal continuous positive airway pressure (CPAP) ventilation, and observed changes in the 90th/50th percentile ratio of inspiratory lung conductance induced by mask pressure titration. Rising pressure surrounding the collapsible tube from subatmospheric to positive values induced progressive inspiratory collapse and increased 90th/50th percentile ratios of inspiratory conductance as predicted. Changes in flow limitation induced by other model modifications were also correctly tracked by the 90th/50th conductance percentile ratio. Increasing mask pressure during CPAP ventilation in sleep apnoea patients from subtherapeutic to therapeutic pressure levels was associated with the expected decrease in the 90th/50th percentile ratio of inspiratory lung conductance from a mean of 6.5+/-3.1 to 1.6+/-0.3 ( P <0.001). We conclude that variability of inspiratory conductance quantified by the 90th/50th percentile ratio may serve as a measure of flow limitation that is independent of the absolute value of conductance.     

Modern long-term oxygen therapy--practical aspects

Modern and accurately performed long term oxygen therapy improves quality of life and life expectancy in patients with chronic obstructive lung disease suffering from hypoxemia. This type of therapy often fails since the patient is bothered by the nasal prongs and fears to dwell outside his home. As a consequence, the major goal of this form of therapy, namely enhanced patients mobility is not attained. Oxygen can be delivered at a high efficiency by a transtracheal catheter. This mode of application may considerably improve the patients comfort and hence his compliance and mobility.     

Acute experimental cerebral ischemia: MR enhancement using Gd-DTPA

The effects of a paramagnetic contrast agent, gadolinium-DTPA (Gd-DTPA), on magnetic resonance (MR) imaging of acute cerebral ischemia was investigated in a feline model of middle cerebral artery occlusion. Imaging was performed both before and after administration of an intravenous dose of 0.2 mmol/kg of Gd-DTPA. The animals were then sacrificed for pathologic correlation. No changes in intensity or relaxation times were noted before or after Gd-DTPA administration in two animals with 2 hours of occlusion. Infarcts were noted before and after contrast enhancement in all six cats with ischemia of greater than 16-hours duration. Gd-DTPA caused significant increase in intensity of infarct but not in that of normal cerebral tissue. Rapid enhancement was visible in infarcts of 16-24 hours, but such enhancement was slower in infarcts of 72-168 hours, presumably owing to slowed inflow caused by increased vasogenic edema in the latter group. Contrast enhancement of acute cerebral ischemic lesions with Gd-DTPA offers no improvement in sensitivity of MR imaging, although the conspicuity of the lesion may be improved. Additionally, contrast media may provide potential temporal and pathophysiological data for better characterization of cerebral ischemia.     

Confirmation of high blood flow rates through 150 μ filter/high-flow tubing

Many new products designed to assist in rapid blood infusion are appearing. Some highly touted and routinely used devices for intravenous (IV) infusion have recently been shown to be, at least in part, defective. A tubing with an in-line 150 μ filter (150 μ High-Flow Blood Filter; Saftifllter^® Blood Administration Sets; Cutter Biological, Berkeley, CA 94710) has recently been introduced to facilitate rapid blood transfusion. It is claimed that at least 8.5 units of blood can be rapidly run through each set before replacement is necessary. To test this under simulated clinical conditions, four sets of ten random units of outdated erythrocytes at 4 to 9°C were each admixed with 250 mL 70°C 0.9 NaCl and infused through the system under a constant 300 mmHg pressure. Two sets infused through unmodified tubing flowed at an average of 25 mL/sec (1500 mL/min) before there was an appreciable slowing of the flow rate. Two sets with 8 Fr catheters attached infused at an average of 22 mL/sec (1320 mL/min) before there was an appreciable slowing of the flow rate. Even after the flow slowed, the 9th and 10th units infused at an average greater than 10 mL/sec (600 ml/min). The tubing/filter exceeded the manufacturer's published claims. This tubing/filter appears to be one element that could be an effective component of a high-flow infusion system.     

Side effects of mandibular advancement devices for sleep apnea treatment.

Our purpose was to investigate side effects of sleep apnea treatment by removable oral appliances (OA) that advance the mandible. In 22 patients suffering from obstructive sleep apnea (OSA), questionnaire evaluations, polysomnographies, cephalographies, and dental plaster casts were obtained before initiation of treatment with OA that fully covered both dental arches. Patients were reevaluated after 3 to 12 mo (questionnaires, polysomnographies) and 12 to 30 mo (questionnaires, cephalographies, plaster casts) during continuous treatment. Polysomnographies confirmed improved breathing by OA. All patients experienced persistent alleviation of symptoms after 12 to 30 mo and wished to continue treatment. Side effects were common but only mildly disturbing: mucosal dryness (86% of patients), tooth discomfort (59%), and hypersalivation (55%). Cephalographies revealed a decrease in the mean (+/- SE) upper incisors to maxillary plane angle from 102 +/- 2 degrees at baseline, to 101 +/- 2 degrees after 12 to 30 mo (p < 0.05). Overbite and overjet were also slightly (mean reduction < 1 mm) but significantly reduced. None of these side effects required discontinuation of treatment. OA are an effective therapy of obstructive sleep apnea. Mild side effects are common but rarely require intervention. Nevertheless, close follow-up during long-term therapy by OA is advisable in order to timely detect potentially relevant orthodontic changes.     

Effect of whole brain radiation on local cerebral glucose utilization in the rat

We assessed, by means of the [14C]-2-deoxy-D-glucose autoradiography method, the effect of whole-brain x-radiation on local cerebral glucose utilization in the rat brain. Animals were exposed to conventional fractionation (200 +/- 4 cGy/day, 5 days/week; total dose, 4000 cGy). Metabolic experiments were made 2 to 3 weeks after completion of the radiation exposure. In comparison with control and sham-irradiated animals, cerebral metabolic activity was diffusely decreased after irradiation. Statistically significant decreases in metabolic activity were observed in 13 of 27 brain regions studied. In general, the brain areas with the highest basal metabolic rates showed the greatest percentage of decrease in glucose utilization. The concept that radiation suppresses glucose utilization before any morphological change takes place in the cell structures was the basis of this study. Metabolic alterations after irradiation may explain the syndrome of early delayed deterioration observed in humans after whole-brain radiotherapy. These studies have applications to observations made with the [18F]-fluorodeoxyglucose method in conjunction with positron emission tomographic scans in patients receiving radiation therapy for intracranial malignancies. The data reported here also have potential clinical implications for the evaluation of a risk/benefit ratio for radiotherapy in patients with benign neurosurgical diseases or children undergoing prophylactic treatment of the central nervous system.     

alpha1-Antitrypsin deficiency and lung disease: risk modification by occupational and environmental inhalants.

Chronic obstructive pulmonary disease (COPD) is a prevalent and preventable disease associated with high morbidity and mortality. Severe and intermediate alpha1-antitrypsin (AAT) deficiency (serum levels <11 and 11-20 micromol.L(-1), respectively) increase the risk of COPD in active smokers. However, little is known about the interaction of severe and intermediate AAT deficiency with modifiable COPD risk factors other than active smoking. In this study, a MEDLINE search was carried out for studies investigating the combined effect of environmental inhalants (occupation and passive smoking) and AAT deficiency in the lung. A total of 18 studies using established methods for the assessment of AAT deficiency were included in this review. Occupational exposures and passive smoking affected lung function decline or prevalence of respiratory symptoms in four out of five studies investigating subjects with severe AAT deficiency, and in eight out of 13 studies with a focus on intermediate AAT deficiency. While study designs mostly prohibited formal assessment of effect modification, an interaction between intermediate AAT deficiency and passive smoking was identified in two studies with children. Additional study limitations included small sample size, poor adjustment for confounding and misclassification of environmental exposure as well as AAT activity. In conclusion, population-based epidemiological studies with associated biobanks are needed to identify gene-environment interactions and population subgroups susceptible to alpha1-antitrypsin deficiency.     

Transient synovitis of the hip in children: role of US

Transient synovitis of the hip remains a common diagnostic problem for the clinician. The physical signs are not pathognomonic of the condition, and the classic technical examinations are of little help. Therefore, the authors retrospectively studied the value of hip arthrosonography in 46 children with clinical symptoms suggesting pathologic hip conditions. In 20 of the 21 patients with a final diagnosis of transient synovitis, articular effusion was detected on ultrasound (US). Conventional radiography showed an increased medial joint space in only eight of these patients. Increased echogenicity of the articular fluid was found in both transient synovitis and septic arthritis. The high sensitivity of US in detecting intraarticular fluid was demonstrated by cadaver studies.