Search

Type Ia supernovae arise from the thermonuclear explosion of white-dwarf stars that have cores of carbon and oxygen. The uniformity of their light curves makes these supernovae powerful cosmological distance indicators, but there have long been debates about exactly how their explosion is triggered and what kind of companion stars are involved. For example, the recent detection of the early ultraviolet pulse of a peculiar, subluminous type Ia supernova has been claimed as evidence for an interaction between a red-giant or a main-sequence companion and ejecta from a white-dwarf explosion. Here we report observations of a prominent but red optical flash that appears about half a day after the explosion of a type Ia supernova. This supernova shows hybrid features of different supernova subclasses, namely a light curve that is typical of normal-brightness supernovae, but with strong titanium absorption, which is commonly seen in the spectra of subluminous ones. We argue that this early flash does not occur through previously suggested mechanisms such as the companion-ejecta interaction. Instead, our simulations show that it could occur through detonation of a thin helium shell either on a near-Chandrasekhar-mass white dwarf, or on a sub-Chandrasekhar-mass white dwarf merging with a less-massive white dwarf. Our finding provides evidence that one branch of previously proposed explosion models-the helium-ignition branch-does exist in nature, and that such a model may account for the explosions of white dwarfs in a mass range wider than previously supposed. [ABSTRACT FROM AUTHOR]

Object. To evaluate the prophylactic effect of repeated intrathecal administration of nicardipine associated with hypertensive hypervolemic hemodilution therapy (triple H) and sodium correction, we analyzed a consecutive series of 177 patients with subarachnoid hemorrhage. Methods. All patients received aneurysmal clipping and placement of cisternal drainage within 48 hours of the onset. Intrathecal administration of 4 mg of nicardipine was performed every 12 h. Nicardipine concentrations in the cerebrospinal fluid (CSF) and blood before and after its administration were analyzed. Angiographic vasospasm (aVS), symptomatic VS (sVS), and clinical outcome 6 months after onset were also evaluated. Results. Nicardipine concentration in CSF on day 9 was 231.44±51.51 ng/ml (mean±SD), and that of blood was 21.05±15.57 ng/ml. Twenty patients (11.3%) showed aVS, and ten of those (5.7%) showed sVS (six were transient and four were permanent). Those with good outcome (assessed as good recovery and moderately disabled) 6 months after onset were 89.2% of the total. The number of patients requiring a shunt operation was 33 of 177 (18.6%), and 11 patients presented intracranial infection. Conclusions. These results suggest that our strategy may well prevent VS. However, hydrocephalus and infection may be serious disadvantages that should be resolved. [ABSTRACT FROM AUTHOR]

Abstract. The aim of this study was to investigate the prognostic utility of post-treatment technetium-99m ethyl cysteinate dimer ([sup 99m]Tc-ECD) single-photon emission tomography (SPET) for predicting ischemic tissue outcome in cases involving embolic middle cerebral artery occlusion treated with local intra-arterial thrombolysis. We examined twenty-five patients with a moderately ischemic area determined using pretreatment technetium-99m hexamethylpropylene amine oxime ([sup 99m]TC-HMPAO) SPET, and with complete recanalization within 6 h. Post-treatment [sup 99m]Tc-ECD SPET studies, consisting of scanning for 0.5-6.5 min (early scan) and 15-21 min (delayed scan) after tracer injection, were performed immediately after thrombolysis. The extent of the affected area outlined on pretreatment [sup 99m]Tc-HMPAO SPET was used for the post-treatment early and delayed [sup 99m]Tc-ECD SPET images, and the AR/CE ratio (ratio of affected regional activity to cerebellar activity) was calculated. The washout index of [sup 99m]Tc-ECD in the affected area was also calculated by dividing the difference between the AR/CE ratio in the early and delayed images by the AR/CE ratio in the early image. Twelve patients without infarction or with small subcortical/basal ganglial infarction, ten with medium or large cortical infarction, and three with hemorrhage were identified by follow-up computed tomography. Although the AR/CE ratio in post-treatment early [sup 99m]Tc-ECD SPET images was sig-... [ABSTRACT FROM AUTHOR]

The role of nitric oxide (NO) in the mechanism of delayed cerebral vasospasm (VS) after subarachnoid hemorrhage (SAH) was investigated by analyzing the stable metabolites of NO, nitrite and nitrate, by the Griess method in the cerebrospinal fluid (CSF) and venous blood of 29 patients with SAH, the CSF of 22 control patients, and venous blood from eight normal subjects. VS was defined as diffuse and severe angiographical vasospasm detected by angiography performed around days 7–9 after the onset. Six of the 29 patients had VS. The nitrite/nitrate levels in the blood of patients with SAH were almost within the range of those in normal subjects, but the levels in the CSF of patients with SAH were significantly higher than those of the control group. Patients with VS after SAH had significantly lower levels in the CSF than patients without VS on days 7–9, when VS is most likely to occur. These observations suggest that NO production in the CSF environment occurs following SAH, but possibly may not provoke VS. [ABSTRACT FROM AUTHOR]