Static and dynamic operating characteristics of a pericardial balloon.

Previously, we developed a balloon transducer to measure the constraint of the pericardium (i.e., pericardial pressure) on the surface of the heart. It was validated physiologically in that it was shown to measure a pressure equal to the difference between the left ventricular end-diastolic pressure measured before and after pericardiectomy at the same left ventricular volume. To define its static operating characteristics, we loaded the balloon nonuniformly with weights that covered fractions of the balloon surface and found that the balloon accurately recorded the average stress if the stress was applied over at least 23% of its surface. To test its performance when curved, we placed it in large and small cylinders (minimum diameter 31 mm) and found that the balloon accurately recorded the stress. To define its dynamic operating characteristics, we applied sinusoidal stresses and found that its frequency response was limited only by that of the connecting catheter. When better dynamic response is required, we introduce a micromanometer-tipped catheter to obtain a unity-gain frequency response that is flat to 200 Hz.

Preliminary experience with MR-guided thermal ablation of brain tumors.

PURPOSE: To evaluate the feasibility of a technique of MR-guided stereotactic radio frequency ablation, which was developed as a minimally invasive treatment for brain tumors, and to determine MR characteristics and sequential evolution of radio frequency lesions created to ablate brain tumors. METHODS: Fourteen lesions in 12 patients with primary and metastatic brain tumors were treated with this technique and followed for up to 10 months. The stereotactic coordinates of the tumor and the angle of the radio frequency probe were calculated on MR imaging. The radio frequency lesion was generated in the awake patient by increasing the temperature to 80 degrees C within the tumor for 1 minute. This was repeated until the entire tumor volume was destroyed. MR imaging was performed before, during, and immediately after the radio frequency procedure, and sequential MR was obtained during clinical follow-up. RESULTS: MR imaging clearly showed well-defined radio frequency lesions and provided feedback for treatment planning. The radio frequency lesion boundary was well identified as a dark signal rim on T2-weighted images and showed ring enhancement on contrast-enhanced T1-weighted images. The sequential MR imaging showed the radio frequency lesions decreased in volume in all cases, suggesting focal control. CONCLUSION: Stereotactic MR-guided radio frequency brain tumor ablation is a feasible and promising technique that can be an attractive brain tumor treatment alternative. MR provided not only accurate tumor location but also visualization of feedback of thermal tissue changes that reflected therapeutic effect.

Calculation of 131I-ortho-iodohippurate absorbed kidney dose: a literature review.

Extensive information has been made available relative to the physical aspects necessary for calculation of radiation absorbed dose from radiopharmaceuticals. A similar data base for the biological factors involved in these calculations has not been documented as thoroughly. The authors present an extensive literature review for the radiation absorbed dose of 131I-ortho-iodohippurate and discuss the rationale for adjusting previously accepted values with new biodistribution information.

Orthostatic hypotension and the role of changes in venous capacitance.

We suggest a mechanism by which blood volume changes might explain the hypotension that, after space flight, often accompanies the return to normal gravity. Upon entering microgravity, peripheral veins may collapse and, because of volume redistribution, raise the pressure in the central venous compartment. After some time in space, homeostatic mechanisms may cause volume excretion and reduce the pressure in the central venous compartment to normal values. Upon return to normal gravity, peripheral veins may re-expand and distribute a reduced blood volume into an enlarged space, thus lowering pressure in the central venous compartment. This would reduce cardiac preload, output, and arterial pressure. To prevent this sequence of events, leg cuffs might be inflated before the end of the space flight to allow homeostatic mechanisms to increase blood volume to normal levels.

A comparative study of radiation safety practices at selected hospitals in the UK and USA.

The radiation safety practices in a group of 25 UK and USA hospitals have recently been assessed. This took the form of detailed inspections of some 62 medical radiation departments, including Diagnostic X-ray, Radiotherapy, Nuclear Medicine and Pathology/Research (Radionuclide) Departments. Empirical expressions called "Radiation Safety Indices" were devised to evaluate the incidence of personal doses and radiological incidents occurring from 1977-82 and to characterise the safety facilities, procedures, supervision and educational techniques in each department. An outline is given of national legislative material and voluntary codes of conduct, together with the results of the departmental inspections. The computed indices are presented graphically and an analysis given of apparent national trends.

Ultrasound evaluation of the magnitude of pneumothorax: a new concept.

Pneumothorax is commonly seen in trauma patients; the diagnosis is confirmed by radiography. The use of ultrasound where radiographic capabilities are absent, is being investigated by the National Aeronautics and Space Administration. We investigated the ability of ultrasound to assess the magnitude of pneumothorax in a porcine model. Sonography was performed on anesthetized pigs in both ground-based laboratory (n = 5) and microgravity conditions (0 x g) aboard the KC-135 aircraft during parabolic flight (n = 4). Aliquots of air (50-100 cm3) were introduced into the chest to simulate pneumothorax. Results were videorecorded and digitized for later interpretation. Several distinct sonographic patterns of partial lung sliding were noted including the combination of a sliding zone with a still zone and a "segmented" sliding zone. These "partial lung sliding" patterns exclude massive pneumothorax manifested by a complete separation of the lung from the parietal pleura. In 0 x g, the sonographic picture is more diverse; one x g differences between posterior and anterior aspects are diminished. Modest pneumothorax can be inferred by the ultrasound sign of "partial lung sliding." This finding, which increases the negative predictive value of thoracic ultrasound, may be attributed to intermittent pleural contact, small air spaces, or alterations in pleural lubricant. Further studies of these phenomena are warranted.

Interventional computed tomography and MR imaging in the head and neck.

Many modern surgical techniques have been developed to provide exposure or visualization of the surgical field to perform definitive treatment. The actual therapeutic part of surgery is often a small fraction of the procedure. In obtaining exposure, however, morbidity can ensue. This has led to newer techniques that use minimally invasive treatments, thus substantially decreasing overall morbidity and patient costs. By providing physicians with visualization alternatives, MR imaging and computed tomography, when combined with a therapeutic procedure, can reduce the morbidity of surgery.

Abdominal compressions during CPR: hemodynamic effects of altering timing and force.

To determine the optimal method of applying abdominal compressions during cardiopulmonary resuscitation (CPR), 3 levels of pressure (25, 50, and 100 torr) were applied to the abdomen a) continuously and b) as 500 msec pulses at 10 different phases during the CPR cycle in 8 anesthetized dogs. Thoracic aortic (Ao) and right atrial (RA) pressures were measured and PAo-PRA was calculated as the coronary perfusion gradient. A pneumatic piston device provided external chest compression (60/min, 120 lbs, for 50% of the cycle) and ventilation (80% O2, 12/min, at 20cm, H2O). Another identical device provided abdominal compression (AC) via an air-filled bladder. High-pressure (100 torr) AC applied for 500 msec commencing 200 msec prior to chest compression demonstrated the best overall profile, raising mean aortic pressure 26 torr (P less than 0.001) and peak coronary perfusion gradient pressure 17 torr (P less than 0.02) from control values during standard CPR of 58 and 41 torr, respectively. We conclude that applying high-pressure, 500-msec pulses of AC 200 msec before chest compressions significantly improves CPR hemodynamics.

Where's the tube? Evaluation of hand-held ultrasound in confirming endotracheal tube placement.

INTRODUCTION: The diagnosis of endotracheal tube (ETT) mal-position may be delayed in extreme environments. Several methods are utilized to confirm proper ETT placement, but these methods can be unreliable or unavailable in certain settings. Thoracic sonography, previously utilized to detect pneumothoraces, has not been tested to assess ETT placement. HYPOTHESIS: Thoracic sonography could correlate with pulmonary ventilation, and thereby, help to confirm proper ETT placement. METHODS: Thirteen patients requiring elective intubation under general anesthesia, and data from two trauma patients were evaluated. Using a portable, hand-held, ultrasound (PHHU) machine, sonographic recordings of the chest wall visceral-parietal pleural interface (VPPI) were recorded bilaterally in each patient during all phases of airway management: (1) pre-oxygenation; (2) induction; (3) paralysis; (4) intubation; and (5) ventilation. RESULTS: The VPPI could be well-imaged for all of the patients. In the two trauma patients, right mainstem intubations were noted in which specific pleural signals were not seen in the left chest wall VPPI after tube placement. These signs returned after correct repositioning of the ETT tube. In all of the elective surgery patients, signs correlating with bilateral ventilation in each patient were imaged and correlated with confirmation of ETT placement by anesthesiology. CONCLUSIONS: This report raises the possibility that thoracic sonography may be another tool that could be used to confirm proper ETT placement. This technique may have merit in extreme environments, such as in remote, pre-hospital settings or during aerospace medical transports, in which auscultation is impossible due to noise, or capnography is not available, and thus, requires further scientific evaluation.

Risk-based evaluation of postmortem inspection procedures for pigs in Australia.

The results of traditional (incision) and risk-based (visual) postmortem inspection procedures were compared on groups of approximately 30,000 pigs. The performance characteristics used as a basis for comparison included the non-detection rates of grossly detectable abnormalities, the microbiological contamination rates of carcases and boned product, the association of reactive lymph nodes with carcase condemnation and the achievement of 'finished product standards' for 'wholesomeness'. It was estimated that 6 per cent of all cases of abscessation and 28 per cent of all cases of arthritis were undetected by the traditional method, and the comparable figures for the risk-based procedure were 19 per cent and 39 per cent. However, when the rates of contamination of undetected abnormalities with foodborne hazards and other carcase contamination parameters were taken into account, it was concluded that both inspection systems were likely to result in a very similar level of consumer protection. Any increase in potential exposure to foodborne hazards in the abnormalities undetected by risk-based inspection would be insignificant in comparison with the potential exposure to foodborne hazards resulting from contaminated 'normal' lymph nodes and carcase surfaces. There were no statistically significant differences between the two procedures in the contamination rates of pre-chill carcases or boned retail products with Salmonella and Yersinia species.

Percutaneous aspiration of fluid for management of peritonitis in space.

BACKGROUND: As a medical emergency that can affect even well-screened, healthy individuals, peritonitis developing during a long-duration space exploration mission may dictate deviation from traditional clinical practice due to the absence of otherwise indicated surgical capabilities. Medical management can treat many intra-abdominal processes, but treatment failures are inevitable. In these circumstances, percutaneous aspiration under sonographic guidance could provide a "rescue" strategy. HYPOTHESIS: Sonographically guided percutaneous aspiration of intra-peritoneal fluid can be performed in microgravity. METHODS: Investigations were conducted in the microgravity environment of NASA's KC-135 research aircraft (0 G). The subjects were anesthetized female Yorkshire pigs weighing 50 kg. The procedures were rehearsed in a terrestrial animal lab (1 G). Colored saline (500 mL) was introduced through an intra-peritoneal catheter during flight. A high-definition ultrasound system (HDI-5000, ATL, Bothell, WA) was used to guide a 16-gauge needle into the peritoneal cavity to aspirate fluid. RESULTS: Intra-peritoneal fluid collections were easily identified, distinct from surrounding viscera, and on occasion became more obvious during weightless conditions. Subjectively, with adequate restraint of the subject and operators, the procedure was no more demanding than during the 1-G rehearsals. CONCLUSIONS: Sonographically guided percutaneous aspiration of intra-peritoneal fluid collections is feasible in weightlessness. Treatment of intra-abdominal inflammatory conditions in spaceflight might rely on pharmacological options, backed by sonographically guided percutaneous aspiration for the "rescue" of treatment failures. While this risk mitigation strategy cannot guarantee success, it may be the most practical option given severe resource limitations.

How can i avoid lyme disease? What to say to the patient who asks.

No magic bullet for eliminating or medical breakthrough for preventing Lyme disease can be seen on the horizon. This fast-growing pandemic, second only to acquired immunodeficiency syndrome in public interest and concern, will probably continue to increase in range and incidence for the foreseeable future. Ticks are notoriously difficult to thwart, but intelligent application of control measures may be effective. More important, commonsense safety measures offer personal protection to the degree that they are assiduously practiced.

Lyme disease. The hidden pandemic.

Physicians will recognize Lyme disease faster if they maintain a high index of suspicion in a young patient with arthritis accompanied by negative rheumatoid factor and antinuclear antibody in combination with cardiac conduction problems or lymphocytic meningitis. The Lyme spirochete (Borrelia burgdorferi) has notable sensitivity to tetracycline, penicillin, and erythromycin; therefore, proper and complete treatment of the disease, once it is identified, can be easily achieved. Finkel observed that Lyme disease manifests itself as a "great imitator," as do many disorders caused by a spirochete. The total impact of Lyme disease on public health will be known only when the disease is fully recognized, consistently reported, and adequately managed.

Sori tumas: the decision not to treat.

I am convinced that one of the most important and difficult aspects of the work on a specialist surgeon in Papua New Guinea, is knowing when not to treat conditions that would be enthusiastically treated in other countries. Most of our patients would rather die at home than in hospital, and they appreciate and can accept an honest assessment of their prognosis.

Bone grafting the tibia using a posterolateral, or a posterior approach.

A posterolateral, or a posterior approach for bone grafting a non-union of a fractured tibia, or a tibial defect secondary to osteomyelitis, has advantages over the more obvious anteromedial approach. This article describes the technique, reports success in fifteen consecutive tibial bone grafts performed at Nonga Base Hospital, Rabaul over a five-year period, and reviews reports from other centres that have advocated this approach.

Mycetoma in PNG with special reference to a case of extradural mycetoma.

An account is given of 6 instances of mycetoma found in Papua New Guinea. One of these occurred in a 16 year old girl presenting with paraplegia due to a solitary extradural spinal myectoma, diagnosed only after laminectomy.

Oesophageal varices due to idiopathic portal vein thrombosis: a new surgical approach.

Life-threatening bleeding oesophageal varices due to idiopathic portal vein thrombosis occurred in a five-year-old male. Diagnosis was made by endoscopy and ultrasonography and decompression of the portal system performed by splenorenal shunt using the end renal vein to side splenic vein. This avoided the difficult mobilization of the splenic vein from the pancreatic bed in the conventional distal splenorenal shunt.