Biomedical subjects

John Popovich

Publications and source records attributed to John Popovich.

3 recordsLinked to original sources

PubMed2006

Multidetector computed tomography for acute pulmonary embolism.

BACKGROUND: The accuracy of multidetector computed tomographic angiography (CTA) for the diagnosis of acute pulmonary embolism has not been determined conclusively. METHODS: The Prospective Investigation of Pulmonary Embolism Diagnosis II trial was a prospective, multicenter investigation of the accuracy of multidetector CTA alone and combined with venous-phase imaging (CTA-CTV) for the diagnosis of acute pulmonary embolism. We used a composite reference test to confirm or rule out the diagnosis of pulmonary embolism. RESULTS: Among 824 patients with a reference diagnosis and a completed CT study, CTA was inconclusive in 51 because of poor image quality. Excluding such inconclusive studies, the sensitivity of CTA was 83 percent and the specificity was 96 percent. Positive predictive values were 96 percent with a concordantly high or low probability on clinical assessment, 92 percent with an intermediate probability on clinical assessment, and nondiagnostic if clinical probability was discordant. CTA-CTV was inconclusive in 87 of 824 patients because the image quality of either CTA or CTV was poor. The sensitivity of CTA-CTV for pulmonary embolism was 90 percent, and specificity was 95 percent. CTA-CTV was also nondiagnostic with a discordant clinical probability. CONCLUSIONS: In patients with suspected pulmonary embolism, multidetector CTA-CTV has a higher diagnostic sensitivity than does CTA alone, with similar specificity. The predictive value of either CTA or CTA-CTV is high with a concordant clinical assessment, but additional testing is necessary when the clinical probability is inconsistent with the imaging results.

Acute Disease↗

PubMed2006

Chirality in anesthesia I: minimum alveolar concentration of secondary alcohol enantiomers.

Most studies of chirality in inhaled anesthetic action have used the enantiomers of isoflurane. These enantiomers are expensive and scarce, which limits studies, such as the preliminary identification of molecular targets of anesthetic action, that can be performed with these isomers. We hypothesized that secondary alcohols (i.e., compounds having a -CH2-CHOH-CH3 group) that are experimental anesthetics would show enantioselectivity. To test this hypothesis, we determined the minimum alveolar anesthetic concentration (MAC) of the enantiomers of the homologous series of 2-alcohols from 2-butanol to 2-heptanol in rats. Because these alcohols are partially metabolized to 2-ketones during the course of study (i.e., having a -CH2-CO-CH3 group), we independently measured the MAC of the 2-ketones. Assuming additivity of MAC of the ketones with the alcohols, we corrected for the anesthetic effect of the ketones in rats to determine the MAC of the alcohols. We found that the 2-butanol and 2-pentanol isomers were enantioselective. S-(+)-2-butanol had a MAC that was 17% larger than for the R-(-)-enantiomer, whereas S-(+)-2-pentanol had a MAC that was 38% larger than the R-(-)- enantiomer. No stereoselectivity was observed for 2-hexanol and 2-heptanol. These findings may permit studies of chirality in anesthesia, particularly in in vitro systems where metabolism does not occur, using inexpensive volatile compounds.

Alcohols↗

PubMed2006

Contrasting roles of the N-methyl-D-aspartate receptor in the production of immobilization by conventional and aromatic anesthetics.

We hypothesized that N-methyl-d-aspartate (NMDA) receptors mediate some or all of the capacity of inhaled anesthetics to prevent movement in the face of noxious stimulation, and that this capacity to prevent movement correlates directly with the in vitro capacity of such anesthetics to block the NMDA receptor. To test this hypothesis, we measured the effect of IV infusion of the NMDA blockers dizocilpine (MK-801) and (R)-4-(3-phosphonopropyl) piperazine-2-carboxylic acid (CPP) to decrease the MAC (the minimum alveolar concentration of anesthetic that prevents movement in 50% of subjects given a noxious stimulation) of 8 conventional anesthetics (cyclopropane, desflurane, enflurane, halothane, isoflurane, nitrous oxide, sevoflurane, and xenon) and 8 aromatic compounds (benzene, fluorobenzene, o-difluorobenzene, p-difluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, pentafluorobenzene, and hexafluorobenzene) and, for comparison, etomidate. We postulated that MK-801 or CPP infusions would decrease MAC in inverse proportion to the in vitro capacity of these anesthetics to block the NMDA receptor. This notion proved correct for the aromatic inhaled anesthetics, but not for the conventional anesthetics. At the greatest infusion of MK-801 (32 microg x kg(-1) x min(-1)) the MACs of conventional anesthetics decreased by 59.4 +/- 3.4% (mean +/- sd) and at 8 microg x kg(-1) x min(-1) by 45.5 +/- 4.2%, a decrease not significantly different from a 51.4 +/- 19.0% decrease produced in the EC50 for etomidate, an anesthetic that acts solely by enhancing gamma-amino butyric acid (GABA) receptors. We conclude that some aromatic anesthetics may produce immobility in the face of noxious stimulation by blocking the action of glutamate on NMDA receptors but that conventional inhaled anesthetics do not.

Anesthetics, Inhalation↗