Abstract-We report a novel coaxial antenna for hepatic microwave ablation. This device uses a floating sleeve, that is, a metal conductor electrically isolated from the outer connector of the antenna coaxial body, to achieve a highly localized specific absorption rate pattern that is independent of insertion depth. This floating sleeve coaxial dipole antenna has low power reflection in the 2.4-GHz IMS band. Ex vivo experiments confirm our numerical simulation results.

The carotid body type I cell contains amines and has features, both morphological and cytochemical, which indicate that it may also produce a peptide. Many regulatory peptides are now known to be present in both central and peripheral tissues. In the periphery these neuropeptides occur in both classical endocrine (APUD) cells and the neurones of the autonomic nervous system. We have now investigated the possible presence of neuropeptides in the cat carotid body using both immunocytochemistry and radioimmunoassay. Met- and Leu-enkephalin-like material occurred in considerable quantities in carotid body extracts and enkephalin-like immunoreactivity was localised in type I cells. Both vasoactive intestinal polypeptide (VIP)- and substance P-like immunoreactivity was also present but was localised in nerve fibres distributed throughout the organ. These active neuropeptides are widely distributed in mammalian tissues, forming a diffuse regulatory system which now seems to include the carotid body.

Susceptibility to oxygen toxicity was studied in three inbred and two hybrid strains of mice. Because in vitro studies have shown that the cytochrome P-450 enzymes can produce oxygen radicals and H202, we tested the hypothesis that inducibility of these enzymes might play a role in oxygen toxicity. Mice responsive to hepatic microsomal enzyme induction by aromatic hydrocarbons [C3H/HeJ, C3H/HeN, C3H/HeJ x DBA/2J (designated C3D2F1/J), C3H/HeN x DBA/2J (designated C3D2F1/N)] were more sensitive to the toxic effects of 100% oxygen exposure than were genetically unresponsive mice (DBA/2J). DBA/2J mice survived significantly longer exposure periods with less lung damage. Lung and liver cytochrome P-450 levels increased 2-to 3-fold in C3H and F1 mice during 100% oxygen exposure (maximum levels at 72-96 hr) and subsequently fell prior to death. No increases were seen in cytochrome P-450 levels in DBA/2J mice. Meta-

Lipid X, the major biosynthetic precursor of lipid A, has recently been described. Although lipid X is a mitogen and coagulates the Limulus amebocyte lysate, we found that it is not lethal for mice, even when given in large doses (2 x 106 gig/kg). Furthermore, lipid X was found to give partial protection against a 100% lethal dose of endotoxin, even if the lipid X was given as late as 6 h after endotoxin challenge.

Electromuscular incapacitating devices (EMDs), such as Tasers, deliver high current, short duration pulses that cause muscular contractions and temporarily incapacitate the human subject. Some reports suggest that EMDs can kill. To help answer the question, "Can the EMD directly cause ventricular fibrillation (VF)?", ten tests were conducted to measure the dart-to-heart distance that causes VF in anesthetized pigs [mass = 64 kg +/- 6.67 standard deviation (SD)] for the most common X26 Taser. The dart-to-heart distance that caused VF was 17 mm +/- 6.48 (SD) for the first VF event and 13.7 mm +/- 6.79 (SD) for the average of the successive VF events. The result shows that when the stimulation dart is close enough to the heart, X26 Taser current will directly trigger VF in pigs. Echocardiography of erect humans shows skin-to-heart distances from 10 to 57 mm (dart-to-heart distances of 1-48 mm). These results suggest that the probability of a dart on the body landing in 1 cm2 over the ventricle and causing VF is 0.000172.

We used a four-terminal plunge probe to measure myocardial resistivity in two directions at three sites from the epicardial surface of eight open-chest pigs in-vivo at eight frequencies ranging from 1 Hz to 1 MHz. We calibrated the plunge probe to minimize the error due to stray capacitance between the measured subject and ground. We calibrated the probe in saline solutions contained in a metal cup situated near the heart that had an electrical connection to the pig's heart. The mean of the measured myocardial resistivity was 319 ohm x cm at 1 Hz down to 166 ohm x cm at 1 MHz. Statistical analysis showed the measured myocardial resistivity of two out of eight pigs was significantly different from that of other pigs. The myocardial resistivity measured with the resistivity probe oriented along and across the epicardial fiber direction was significantly different at only one out of the eight frequencies. There was no significant difference in the myocardial resistivity measured at different sites.

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The maximum distance between the heart and a model Taser stimulation dart, called the dart-to-heart distance, at which the Taser can directly cause ventricular fibrillation (VF), was measured in pigs. A 9-mm-long blunt probe was advanced snugly through the surrounding tissues toward the heart. Five animals [pig mass=61.2+/-6.23 standard deviation (SD) kg] for ten dart-to-heart distances where the Taser caused VF were tested. The dart-to-heart distances where the Taser caused VF of the first stimulation site ranged from 4 to 8 mm with average 6.2 mm+/-1.79 (SD) and of the second stimulation site ranged from 2 to 8 mm with average 5.4 mm+/-2.41 (SD). The results help inform the evolving discussion of risks associated with Tasers.