Occupational asthma and allergy in snow crab processing in Newfoundland and Labrador.

BACKGROUND: Risk factors and prevalence of occupational asthma (OA) and occupational allergy (OAl) in the snow crab-processing industry have been poorly studied. OBJECTIVE: To estimate the prevalence of OA and OAl in snow crab-processing workers and determine their relationship with exposure to snow crab allergens and other potential risk factors. METHODS: A total of 215 workers (120 female/95 male) were recruited from four plants in Newfoundland and Labrador, Canada in 2001-2002. Results from questionnaires, skin-prick tests to snow crab meat and cooking water, specific IgEs against the latter, spirometry and peak flow monitoring were used to develop a diagnostic algorithm. An index based on work history and exposure measurements of snow crab aeroallergens was developed to estimate the cumulative exposure for each worker. RESULTS: The prevalences of almost certain or highly probable OA and OAl were 15.8% and 14.9%, respectively. A high cumulative exposure to crab allergens, in jobs mostly held by women, was associated with OA (odds ratio (OR) = 14.0, 95% CI 3.0 to 65.8) (highest vs lowest Cumulative Exposure Index) and with OAl (OR = 7.1, 95% CI 1.9 to 29.0); job held when symptoms started (cleaning, packing, freezing) also predicted OA (OR = 3.9, 95% CI 1.6 to 8.7) and OAl (OR = 3.2, 95% CI 1.4 to 7.5). Atopy (OR = 2.8, 95% CI 1.2 to 6.8), female gender (OR = 10.7, 95% CI 3.6 to 32.1) and smoking were significant determinants for OA (OR = 3.1, 95% CI 1.3 to 7.4). CONCLUSIONS: The prevalences of OA and OAl are high in snow crab-processing workers of Canada's East Coast. Cumulative exposure to snow crab allergens was related to the prevalences of OA and OAl in a dose-response manner taking into account atopy, gender and smoking.

Regional access to acute ischemic stroke intervention.

BACKGROUND AND PURPOSE: Benefit-risk ratios from recombinant tissue plasminogen activator (rtPA) therapy for acute ischemic stroke demonstrate lack of efficacy if intravenous administration is commenced beyond 3 hours of symptom onset. We undertook to enhance therapeutic effectiveness by ensuring equitable access to rtPA for patients affected by acute ischemic stroke within a 20 000 km(2) population referral base served by a tertiary facility. METHODS: Representatives of all provider groups involved in emergency medical services developed a Regional Acute Stroke Protocol (RASP), a coordinated regional system response by dispatch personnel, paramedics, physicians, community service providers, emergency and inpatient staff in community hospitals, and the tertiary facility acute stroke team. RESULTS: As of July 26, 1999, all ambulance services in Southeastern Ontario began bypassing the closest hospital to deliver patients meeting the criteria for the RASP to the Kingston General Hospital. At 12 months, approximately 403 ischemic strokes have occurred in the region, the RASP has been activated 191 times, and 42 patients have received rtPA. CONCLUSIONS: We conclude that (1) acute stroke patients in Southeastern Ontario have improved access to interventions for stroke care; (2) geography of the region is not a barrier to access to interventions for patients with acute stroke; and (3) acute ischemic stroke patients treated with rtPA account for 5% of all acute strokes and 10% of all ischemic strokes in this region.

In-patient treatment of chronic daily headache using dihydroergotamine: a long-term follow-up study.

BACKGROUND: The treatment of chronic daily headache (CDH) due to medication overuse remains a common and difficult problem. For selected patients refractory to outpatient management we have used a treatment protocol using dihydroergotamine (DHE) as introduced by Raskin, during a brief (typically 48 hours) in-patient stay. While many studies have documented the short-term efficacy of the DHE protocol, there are limited data on its long-term effects. The purpose of this study was to evaluate quality of life, at three months post treatment and the present time. METHODS: A retrospective chart review of all patients admitted for the DHE protocol from 1991 to 1996 revealed 174 cases. Of these, 132 patients were interviewed by phone. RESULTS: The DHE protocol was shown to decrease headache frequency, severity, headache medication use, and absences from work both at three months and the time of interview. CONCLUSION: This study has the largest patient base and the longest follow-up period for the use of DHE for CDH. The results confirm that the DHE protocol is helpful in breaking the cycle of CDH, although the long-term outcomes of this study are more conservative than other studies have reported.

Performance of QPET, a high-resolution 3D PET imaging system for small volumes.

QPET is a positron imaging system developed at Queen's University for high-resolution, 3D imaging of small volumes; it includes a pair of planar gamma-ray detectors 25.4 cm square, which rotate about a central axis with a quasi-cylindrical geometry. The authors describe the performance of this system. Basic characteristics of the detectors are evaluated: a spatial sampling of 1 mm, a quantum efficiency of 9.3% (for 511 keV gamma rays with normal incidence), and a time resolution of 88 ns. Models are developed to characterize the system deadtime and the sensitivity in terms of the noise-equivalent counting rate. With an 8 cm diameter spherical source, the noise-equivalent counting rate reaches a maximum at just over 3 kcps for an activity concentration of 2 muCi/cc; the random coincidence events and the deadtime losses both contribute significantly and the scatter contribution is small. Spatial resolution and uniformity over the field of view are evaluated by imaging short and long line sources; a spatial resolution of 2.7 mm in the transverse directions and 2.0 mm in the axial direction is achieved, with excellent uniformity throughout the field of view. The detector response is amplitude invariant across a 20 cm transverse diameter and a 9 cm axial length with the acceptance angle limited to +/-25 degrees in the axial direction. As an example of the imaging capabilities of QPET, the authors show 3D images of (18)F uptake in the bones of a rat, showing the excellent spatial resolution. This system is best suited to limited-volume applications where high counting rates are not necessary, but where high spatial resolution and uniform detector response are priorities.

Reversible parkinsonism induced by hypercalcemia and primary hyperparathyroidism.

We describe a patient who had the recent onset of both primary hyperparathyroidism and parkinsonism. Surgical removal of a parathyroid adenoma was followed by spontaneous resolution of the parkinsonism. Hypoparathyroidism and other disorders of calcium metabolism are recognized causes of secondary parkinsonism, while hyperparathyroidism is not. We review the relevant literature, which supports the hypothesis that hypercalcemia may have induced cytotoxic changes in the basal ganglia of this patient.

Removing the interference error between attenuation correction and scatter subtraction in 3D PET imaging.

A method to remove the interference between attenuation correction and scatter subtraction has been developed for the QPET 3D imaging system at Queen's University. Because the detector system has more than 10(10) lines of response, we reconstruct the image by first backprojecting, then filtering. We correct for attenuation at backprojection by weighting each event by the inverse of the attenuation factor calculated by reprojection through an attenuation image. Since the scatter background has not been corrected at backprojection time, this has the side effect that a fraction of the detected scattered events get incorrectly weighted. When a scatter subtraction is subsequently applied, the correction is inaccurate because the scatter distribution has been modified by the attenuation correction procedure. The residual interference error in the reconstructed image is a distorted image of the attenuator. An approximation to this error is obtained by reprojecting through the attenuation image, backprojecting with appropriate weights, then reconstructing. This image is then scaled and multiplied by the calculated scatter distribution to obtain an estimate of the interference error. Both simulations and measurements indicate that for our system, this method provides a reasonable approximation of the interference error in the image.

A deconvolution scatter correction for a 3-D PET system.

A method to remove the scattered background from a reconstructed image by deconvolution with a point response function which includes the scatter contribution is presented. The amplitude of the scattered response function is obtained by constraining a region of the corrected image to zero average amplitude. This method assumes that the shape of scatter distribution is shift invariant and independent of the shape of the scattering object and the distribution of the positron activity. The validity of these approximations for the QPET geometry was tested using simulations. An average scatter response function for the system was obtained from these simulations and compared with results from measurements. The method was tested using experimental data from an irregularly shaped acrylic phantom. It was simple to implement and resulted in a satisfactory correction of the scattered background for a small-volume system.

Accurate attenuation correction for a 3D PET system.

An accurate attenuation correction has been developed for a small-volume three-dimensional positron emission tomography (PET) system. Transmission data were measured as twenty-four 2D slices which were reconstructed and combined to form a 3D attenuation image. Emission data were reconstructed using a backproject-then-filter technique, and each event was corrected for attenuation at backprojection time by a reprojection through the attenuation image. This correction restores the spatial invariance of the point response function, thus allowing a valid deconvolution and producing an undistorted emission image. Scattering corrections were not applied to either the transmission or the emission data but simulation studies indicated that scattering made only a small contribution to the attenuation measurement. Results are presented for two phantoms, in which transmission scans of 57,500 and 18,700 events/slice were used to correct emission images of 5.2 and 2.8 million events. Although the attenuation images had poor statistical accuracy and a resolution of 13 mm, the method resulted in accurate attenuation-corrected images with no degradation in image resolution (which was 3 mm for the first emission image), and with little effect on image noise.

Radiation absorbed dose estimates for oxygen-15 radiopharmaceuticals (H2(15)O, C15O, O15O) in newborn infants.

In preparation for measurement of regional cerebral oxygen metabolism by positron emission tomography, radiation absorbed dose estimates for 19 internal organs, blood, and total body were calculated for newborn infants following bolus intravenous administration of H2(15)O and brief inhalation of C15O and O15O. Cumulated activity for each radiopharmaceutical was calculated from a compartmental model based on the known biologic behavior of the compound. Values for mean absorbed dose/unit cumulated activity (S) for internal organs and total body were based on a newborn phantom. S was separately calculated for blood. Total radiopharmaceutical absorbed dose estimates necessary to measure cerebral oxygen metabolism in a 3.51-kg infant based on 0.7 mCi/kg H2(15)O and 1 mCi/kg C15O and O15O were determined to be 1.6 rad to the lung (maximum organ dose), 0.28 rad to the marrow, 0.46 rad to the gonads, and 0.22 rad to total body. These values are similar to those for current clinical nuclear medicine procedures employing 99mTc in newborn infants.

Compton scattering in a large-aperture positron imaging system.

Compton scattering of gamma rays within the image volume has been assessed for a large-aperture positron-emission-tomography imaging system. The Compton scattered attenuation and the Compton scattered background were both modeled and measured for point sources centered in scattering spheres up to 10 cm in diameter. Good agreement was obtained between simulations and measurements. The attenuation problem is independent of the detector system, but its correction is more difficult in a large-aperture system. The scattered coincidence background is large in this system (43% for a 10-cm-diameter scattering sphere), but the background overlap is reduced with 3D imaging.

The anticoagulant effects of the hookworm, ancylostoma ceylanicum: observations on human and dog blood in vitro and infected dogs in vivo.

Extracts of adult Ancylostoma ceylanicum prolonged the prothrombin time (PT) and partial thromboplastin time with kaolin ( PPTK ) of both human and dog plasmas in vitro. Excretory/secretory (E/S) products of these worms had similar effects while larval extract prolonged the PTTK only. Thus, the anticoagulant activities of this parasite are dependent upon the stage of the worm's life cycle. Collagen- and ADP-induced platelet aggregation were inhibited by adult and larval extracts. When the peripheral blood and bleeding times of dogs with varying worm burdens were examined, the only abnormality was shortening of the PTTK in the most heavily infected animals. Homogenates of dog small bowel subjacent to adult hookworms prolonged the PT of dog plasma and electron microscopical examination of this tissue revealed aggregation of platelets in blood venules without fibrin deposition. Thus, this study provides evidence that the anticoagulant properties of hookworms may have biological significance in infected animals.

Purification of an anticoagulant from the body fluid of Ascaris suum.

An anticoagulant has been purified from the body fluid of Ascaris suum by sequential passage through Sephadex G-50, CM-cellulose and Sephadex G-25 columns then treated with 2 M NaCl, passaged through a Sephadex G-25 column, separated from the phosphate buffer by precipitation of the latter with the CaCl2, then passaged through a Sephadex G-10 column in water. In the body fluid of the worm, the anticoagulant is ionically-bound to a carrier substance. The complex can be split by treatment with 2 M NaCl. The molecular weight of the anticoagulant is slightly less than 1400.

Inhibition of human blood clotting by extracts of Ascaris suum.

The effects of soluble extracts of Ascaris suum on human blood coagulation were investigated. Whole worm supernatant solution prolonged the whole blood clotting time and the kaolin-activated, partial thromboplastin time but it did not alter the prothrombin time. These data indicate impairment of the intrinsic pathway of blood coagulation. Whole worm supernate inhibited platelet aggregation induced by ADP and ristocetin. This supernate did not affect fibrinolysis. The maximal concentration of anticoagulant activity was found in the pseudocoelomic fluid of the worm. Activity was also noted in the cuticle and secretory/excretory products. Perhaps inhibition of blood clotting by helminths may facilitate their passage through the blood stream.

Computerized cranial tomography in Wilson disease.

Hepatolenticular degeneration (Wilson disease) is suspected by the clinical picture and confirmed by characteristic laboratory demonstration of impaired copper metabolism. Three patients with Wilson disease involving the basal ganglia were shown to have abnormalities on computerized tomography (CT) scan, whereas four other patients without signs of cerebral involvement had normal brain scans. Wilson disease may be added to the long list of diseases to which the EMI scan may make a useful diagnostic contribution.

Metabolic responses to status epilepticus in the rat, cat, and mouse.

Prolonged sustained seizure activity (status epilepticus) was created in rats and cats using paralysis and ventilation to prevent muscular contraction and its secondary systemic effects. Under physiologic control, seizure activity was maintained for 30, 60, and 120 min. At this time the brains were frozen using the in situ technique and the cortical tissue was analyzed for energy-related metabolites. The alteration of metabolites found at these times was similar to that previously described in the first 10 min of seizure activity. No evidence was found of any significant or progressive derangement of oxidative metabolism. A progressive lactic acidemia developed in spite of adequate arterial oxygen tensions. In contrast, when mice received a similar dose of the convulsant and were allowed to convulse freely in an oxygen-enriched environment, major derangements of energy metabolism were found which were progressive and persisted following recovery for at least 18 h.