James A. Will

A floating sleeve antenna yields localized hepatic microwave ablation

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.

Oxygen transport in the llama (LAma glama)

Abstract Three male llamas 5–14 months old and born at sea level were studied first at 260 m altitude, and again after 5 and 10 weeks at 3420 m. Observations were made with the animals awake, standing and unsedated, at rest breathing air, acute hypoxia, acute hyperoxia and during treadmill exercise. O 2 tension, O 2 content, O 2 saturation and pH were measured on arterial and mixed venous blood. These data were adjusted to pH 7.40 and 37.0 °C to permit the construction of Hb-O 2 dissociation curves. Cardiac output () was measured by dye dilution. Llama Hb has a high affinity for O 2 : P 50 of 22.7 mm Hg at sea level, and 23.7 mm Hg at altitude, indicating no decrease in the affinity of Hb for O 2 at altitude. Exposure to 3420 m resulted in a decrease in Pao-from 87 to 51–53 mm Hg, but SaO 2 remained above 92%. With an increase in Hb concentration from 10.6 to 11.8 g per 100 ml, there was no decrease in CaO 2 . Furthermore, there was no change in , (CaO 2 -CVO 2 ), or systemic O 2 transport ( × CaO 2 ). Under all conditions, PVO 2 was lower than in most other mammals, but always exceeded 20 mm Hg, reflecting the efficient mechanisms of O 2 extraction in the llama.

Effects of leukotrienes on isolated guinea-pig pulmonary arteries

Leukotrienes C4 (LTC) and D4 (LTD) produced contractions of the isolated guinea-pig pulmonary arteries, but were much less potent in these segments than in the isolated trachea and parenchymal strip from the same species. Among the arterial segments, the leukotrienes were more effective in contracting the distal end of the main pulmonary artery than the arterial branches. FPL55712 was an effective competitive antagonist of LTC, but not LTD, in the arterial segments. The data suggest that the pulmonary arteries may possess leukotriene receptors which differ from those of airway smooth muscle.

Noncontact radio-frequency ablation for obtaining deeper lesions

Radio-frequency (RF) cardiac catheter ablation has been very successful for treating some cardiac arrhythmias, however, the success rate for ventricular tachycardias is still not satisfactory. Some existing methods for developing deeper lesions include active cooling of the electrode and modifying the electrode shape. We propose a method of noncontact ablation, to solve this problem. We apply 120 W of power through an 8-mm electrode for a 120-s duration, with distances from 0 to 3 mm between electrode and myocardium, to create lesions in myocardium. We apply flow rates of 1, 3, and 5 L/min to determine their effect. Results show that with an optimal distance from 0.5 to 1.5 mm between electrode and myocardium, we increase lesion depth from 7.5 mm for contact ablation to 9.5 mm for noncontact ablation. For different flow rates, the optimal distance various. The effect of flow rate is not obvious. Higher flow rate does not lead to a deeper lesion.

Localization of somatostatin-, bombesin-, and serotonin-like immunoreactivity in the lung of the fetal Rhesus monkey

SummaryImmunoreactivity of regulatory peptides has been demonstrated in the fetal lung of Macaca mulatta by the peroxidase anti-peroxidase method. Serotonin-immunoreactive neuroepithelial bodies are distributed in the airways from the bronchi to the alveolar ducts. Many neuroepithelial bodies also show bombesin-like immunoreactivity; a very few are immunoreactive to somatostatin antiserum. Four populations of neuroepithelial bodies were identified which contain immunoreactivity for 1) serotonin alone, 2) serotonin and bombesin, 3) serotonin and somatostatin, and 4) serotonin, bombesin, and somatostatin. Since bombesin and somatostatin have been demonstrated to have opposite effects on the release of other peptide hormones, it seems likely that the presence of these same peptides in neuroepithelial bodies may have a similar regulatory role in the lung.

The effect of furosemide on the pulmonary transvascular fluid filtration rate.

Considerable controversy exists over the use of furosemide for the prevention or treatment of posttraumatic respiratory insufficiency. The conflict revolves around the use of a diuretic in a patient with this condition. There is some evidence that a nondiuretic effect of furosemide may be responsible for the reported improvement in lung function. We studied the response to furosemide of the pulmonary microvascular fluid filtration rate reflected in lung lymph flow (Qlym) in the normal lung. Using the unanesthetized sheep lung lymph preparation of Staub, we found a 30% decrease in Qlym after 80 mg furosemide. However, the majority of the decrease occurred within 15 min after injection when diuresis was just beginning. This response appeared to be due to a large decrease in pulmonary venous resistance, decreasing hydrostatic pressure. Protein flow (Qlym X lymph protein content) remained constant. Pulmonary artery pressure remained constant with left atrial pressure decreasing slightly. We have demonstrated that in the normal lung, furosemide significantly decreases the fluid filtration rate by a nondiuretic effect. Further studies of this response should help resolve the controversy over the indications for diuresis and center more attention on the actual mechanism of action of furosemide.

In-vivo measurement of swine myocardial resistivity

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 pigs heart. The mean of the measured myocardial resistivity was 319 /spl Omega//spl middot/cm at 1 Hz down to 166 /spl Omega//spl middot/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.

Taser Blunt Probe Dart-To-Heart Distance Causing Ventricular Fibrillation in Pigs

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 = 61.2plusmn6.23 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 mmplusmn1.79 (SD) and of the second stimulation site ranged from 2 to 8 mm with average 5.4 mmplusmn2.41 (SD). The results help inform the evolving discussion of risks associated with Tasers.

A new catheter design using needle electrode for subendocardial RF ablation of ventricular muscles: finite element analysis and in vitro experiments

Radio-frequency (RF) cardiac ablation has been very successful for treating arrhythmias related with atrioventricular junction and accessory pathways with successful cure rates of more than 90%. Even though ventricular tachycardia (VT) is a more serious problem, it is known to be rather difficult to cure VT using RF ablation. In order to apply RF ablation to VT, we usually need to create a deeper and wider lesion. Conventional RF ablation electrodes often fail to produce such a lesion. We propose a catheter-electrode design including one or more needle electrodes with a diameter of 0.5-1.0 mm and length of 2.0-10 mm to create a lesion large enough to treat VT. One temperature sensor could be placed at the middle of the needle electrode for temperature-controlled RF ablation. From finite element analyses and in vitro experiments, we found that the depth of a lesion is 1-2 mm deeper than the insertion depth of the needle and the width increases as we increase the diameter of the needle and the time duration. We showed that a single needle electrode can produce a lesion with about 10-mm width and any required depth. If a wider lesion is required, more than one needle with suggested structures can be used. Or, repeated RF ablations around a certain area using one needle could produce a cluster of lesions. In some cases, a catheter with both conventional electrode and needle electrode at its tip may be beneficial to take advantage of both types of electrode.

Potentiation of the hypoxic contraction of guinea-pig isolated pulmonary arteries by two inhibitors of superoxide dismutase

1. Isolated proximal and distal extralobar branches of the pulmonary artery of the guinea-pig develop slow and well-sustained contractions in response to hypoxia (PO2 11-15 mm Hg) without prior stimulation with an agonist. These contractions are readily reversible by readministration of oxygen. 2. Incubation of these preparations with diethyldithiocarbamic acid (DETCA, 5 mM for 30 min), an inhibitor of superoxide dismutase, significantly increased the hypoxic contractions whether DETCA was added before the challenge with hypoxia or after the hypoxic contraction had reached a plateau. This treatment also reduced the oxygen-induced relaxation. 3. Similarly, incubation with triethylenetetramine (TETA, 5 mM for 30 min), another inhibitor of superoxide dismutase, produced larger potentiation of the hypoxic contraction in the two preparations and reduced the oxygen-induced relaxation. 4. Furthermore, addition of H2O2 (10(-5) M-3 x 10(-4) M) caused concentration-dependent relaxation of the hypoxic contraction while larger concentrations (10(-3) M and 3 x 10(-3) M) caused contraction that did not respond to readministration of oxygen. 5. These observations suggest that during hypoxic stress, the accumulation of superoxide anions may participate in the hypoxia-induced contraction and that the metabolism of these radicals into H2O2 by superoxide dismutase maintains the relaxed state during normoxia.