Patient Dose Comparison for Intraoperative Imaging Devices Used in Orthopaedic Lumbar Spinal Surgery.

BACKGROUND: The aim of this study was to determine the amount of radiation exposure from intraoperative imaging during two-level and four-level lumbar fusions. METHODS: Five imaging systems were studied: multidetector CT (MDCT) scanner (CT A); two mobile CT units (CT B and CT C); a C-arm (D); and fluoroscopy (E). Metal oxide semiconductor field effect transistor dosimeters measured doses at 25 organ locations using an anthropomorphic phantom. A fat-equivalent phantom was used to simulate an obese body mass index (BMI). RESULTS: The effective dose (ED) for C-arm D was estimated using commercial software. The ED for others was computed from the measured mean organ doses. EDs for a normal BMI patient, receiving a four-level fusion, are as follows: CT A (12.00 ± 0.30 mSv), CT B (5.90 ± 0.25 mSv), CT C (2.35 ± 0.44 mSv), C-arm D (0.44 mSv), and fluoroscopy E (0.30 ± 0.3 mSv). The rankings are consistent across all three BMI values except CT C and fluoroscopy E, which peaked in the overweight size because of system limitations. The other machines' ED trended with patient BMI. CONCLUSION: The dose reduction protocols were confirmed according to the manufacturer's specifications. The results of this study emphasize the need for the appropriate selection of the imaging system, especially because the type of device could have a substantial effect on patient radiation risk.

Subscores of the FAB differentiate frontotemporal lobar degeneration from AD.

OBJECTIVE: To determine the clinical utility of the Frontal Assessment Battery (FAB), a short test of frontal lobe functions, in differentiating frontotemporal lobar degeneration (FTLD) from Alzheimer disease (AD). METHODS: FAB total scores and subscores for 23 subjects with FTLD and 31 subjects with AD were compared for sensitivity, specificity, and positive predictive value. Concurrent validity of the FAB with the Mini-Mental State Examination (MMSE) and other scales was also assessed. RESULTS: The FAB did not have positive predictive value for FTLD. Total FAB scores did not differ between the FTLD and AD groups. However, three subtests of the FAB (mental flexibility, motor programming, and environmental autonomy) demonstrated significant differences between the two groups. Total FAB scores correlated with scores on the MMSE, a more general test of cognition. CONCLUSION: The Frontal Assessment Battery did not discriminate subjects with frontotemporal lobar degeneration from those with Alzheimer disease, though certain subtests may be helpful in differential diagnosis.

Extinction, working memory, and line bisection in spatial neglect.

The authors studied four patients with spatial neglect, using a task in which lines contain an off-centered bisection mark and a task in which the right and left segments of these bisected lines are presented independently and sequentially. In the prebisected line task, subjects reported the position of the bisection. In the segments task, subjects compared the length of the segments. Accuracy was greater with the sequential presentation of line segments, suggesting that an extinction-like phenomenon plays a role in line bisection bias.

Do phosphatidylinositides modulate vertebrate phototransduction?

Mammalian rod cyclic nucleotide gated (CNG) channels (i.e., alpha plus beta subunits) are strongly inhibited by phosphatidylinositol 4, 5-bisphosphate (PIP(2)) when they are expressed in Xenopus oocytes and studied in giant membrane patches. Cytoplasmic Mg-ATP inhibits CNG currents similarly, and monoclonal antibodies to PIP(2) reverse the effect and hyperactivate currents. When alpha subunits are expressed alone, PIP(2) inhibition is less strong; olfactory CNG channels are not inhibited. In giant patches from rod outer segments, inhibition by PIP(2) is intermediate. Other anionic lipids (e.g., phosphatidyl serine and phosphatidic acid), a phosphatidylinositol-specific phospholipase C, and full-length diacylglycerol have stimulatory effects. Although ATP also potently inhibits cGMP-activated currents in rod patches, the following findings indicate that ATP is used to transphosphorylate GMP, generated from cGMP, to GTP. First, a phosphodiesterase (PDE) inhibitor, Zaprinast, blocks inhibition by ATP. Second, inhibition can be rapidly reversed by exogenous regulator of G-protein signaling 9, suggesting G-protein activation by ATP. Third, the reversal of ATP effects is greatly slowed when cyclic inosine 5'-monophosphate is used to activate currents, as expected for slow inosine 5' triphosphate hydrolysis by G-proteins. Still, other results remain suggestive of regulatory roles for PIP(2). First, the cGMP concentration producing half-maximal CNG channel activity (K(1/2)) is decreased by PIP(2) antibody in the presence of PDE inhibitors. Second, the activation of PDE activity by several nucleotides, monitored electrophysiologically and biochemically, is reversed by PIP(2) antibody. Third, exogenous PIP(2) can enhance PDE activation by nucleotides.

Oxygen free radicals and contrast nephropathy.

Ionic, high-osmolality contrast medium causes nephrotoxicity associated with increased intrarenal adenosine production. To test the hypothesis that oxygen free radicals (produced during intrarenal adenosine catabolism to xanthine) should be implicated in the pathogenesis of ionic, high-osmolality contrast medium nephrotoxicity in humans and to determine whether magnesium protects the kidney from oxygen free radical injury following contrast, 39 patients with mild renal dysfunction were divided into low (LoMg++) and normal (NlMg++) magnesium states and randomized to precoronary angiography oral allopurinol (a xanthine oxidase inhibitor) or placebo. Creatinine clearance and urinary xanthine excretion were measured before and after angiography. Forty-eight hours after contrast medium exposure, placebo-treated LoMg++ and NlMg++ patients had 61%+/-5% and 67%+/-6% increases in urinary xanthine excretion, respectively; however, placebo-treated LoMg++ patients had a greater (79%+/-9% v 35%+/-6%; P < 0.01) decrease in creatinine clearance than placebo-treated NlMg++ patients. Allopurinol-treated LoMg++ and NlMg++ patients had no significant change in urinary xanthine excretion, but did have 40%+/-7% and 33%+/-5% decreases, respectively, in creatinine clearance 48 hours after contrast medium exposure. There was no difference in renal dysfunctional response among placebo-treated NlMg++ patients or allopurinol-treated LoMg++ or NlMg++ patients. These data suggest (1) that oxygen free radicals contribute to ionic, high-osmolality contrast medium nephrotoxicity in hypomagnesemic patients with mild renal disease and (2) that magnesium attenuates the nephrotoxicity mediated by oxygen free radicals.

Nephrotoxicity from contrast media: attenuation with theophylline.

PURPOSE: To determine if depression of creatinine clearance after administration of contrast medium may be prevented with theophylline. MATERIALS AND METHODS: A nonionic, low-osmolality contrast medium (iopamidol) or an ionic, high-osmolality contrast medium (sodium diatrizoate) was administered to 93 patients. Before the examination, these patients were given theophylline or a placebo orally. There were also 30 patients who received an adenosine-uptake inhibitor (dipyridamole). Creatinine clearance and urinary adenosine levels were measured before and after angiography. RESULTS: Creatinine clearance decreased 18% +/- 4 in the placebo-iopamidol group but did not decrease in the theophylline group; urinary adenosine increased 67% +/- 7. Creatinine clearance decreased 42% +/- 5 in the placebo-sodium diatrizoate group and decreased 24% +/- 3 in the theophylline group; urinary adenosine increased 119% +/- 8. In the dipyridamole group in which iopamidol was given, urinary adenosine increased 96% +/- 7 and creatinine clearance decreased 37% +/- 5. CONCLUSION: Intrarenal adenosine can be implicated in the pathogenesis of hypertonic contrast medium nephrotoxicity.

Nephrotoxicity of nonionic low-osmolality versus ionic high-osmolality contrast media: a prospective double-blind randomized comparison in human beings.

To test whether a nonionic, low-osmolality contrast medium (iopamidol) administered for coronary angiography was less harmful to renal function than ionic, high-osmolality medium (sodium diatrizoate), a prospective, double-blind randomized study of 70 patients with normal or mildly depressed renal function (serum creatinine < or = 2.0 mg/dL (175 mumol/L) was performed. Creatinine clearance was determined before coronary angiography and 24 and 48 hours after. There were no significant differences between the low- and high-osmolality groups with regard to age, baseline creatinine clearance, or dose of contrast medium given. In patients receiving low-osmolality medium (n = 35), creatinine clearance decreased by 19% +/- 13 (1 standard deviation) at 24 hours and recovered by 48 hours. In patients receiving high-osmolality medium (n = 35), creatinine clearance decreased by 40% +/- 16 at 24 hours and remained depressed by 47% +/- 14 at 48 hours. In patients with normal or mildly depressed renal function, use of a non-ionic, low-osmolality contrast medium minimized nephrotoxicity as measured by reductions in creatinine clearance after coronary angiography.

Increased incidence of silent ischemia after acute myocardial infarction.

OBJECTIVE: To determine the incidence of angina pectoris during induced myocardial ischemia in patients who have had thrombolytic therapy for acute myocardial infarction in comparison with patients with angina pectoris. DESIGN: During percutaneous transluminal coronary angioplasty, both study groups had coronary artery occlusion by the balloon dilatation catheter for 5 minutes. SETTING: A tertiary, cardiology referral center. PATIENTS: Twenty-five patients with angina pectoris who were undergoing angioplasty were compared with 30 patients having angioplasty 2 days after thrombolytic therapy for acute myocardial infarction. OUTCOMES: Development of angina pectoris during balloon occlusion of the coronary artery was the primary end point; the ischemic response and muscle viability were assessed using both surface and intracoronary electrocardiograms and pulmonary artery wedge pressure. RESULTS: During balloon occlusion 16 (64%) of 25 patients in the angina pectoris group developed angina. In contrast, nine (30%) of 30 patients in the thrombolysis group had angina pectoris during balloon occlusion of the infarct artery (P less than .01). The electrocardiographic response to ischemia and changes in pulmonary wedge pressure were similar in the two study groups. CONCLUSION: After thrombolytic therapy for myocardial infarction, silent ischemia may be the rule rather than the exception.

Motorcycle helmet use in Texas.

Helmets worn by motorcyclists decrease head injuries and the likelihood of being killed in a crash by about 30 percent. From 1968 to 1977, Texas had a comprehensive motorcycle helmet use law, which was estimated to have saved 650 lives. But the law was amended in 1977 to apply only to motorcycle operators and passengers under age 18. In September 1989, a new law was passed that required helmets for all motorcycle operators and passengers. Observations of helmet use were conducted before and after the law took effect in 18 Texas cities using a survey design providing a cross-section of urban and suburban traffic across the State. The surveys indicated that helmet use increased from less than 50 percent just before the law to 90 percent immediately after, and it increased further to more than 95 percent 2 months later. These results confirm the unique effectiveness of comprehensive helmet use laws in applying the proven public health benefits of helmets to the reduction of motorcycle injuries and deaths.