Microwave applicator design for cardiac tissue ablations.

A variety of microwave applicators were designed, fabricated and tested for catheter applications: I-radiators, U-radiators, O-radiators, forward helical coil radiator, reverse helical coil, double coil radiator, loaded monopole radiator, leaky coaxial radiator and tee radiators. The comparative and relative radiation characteristics of these applicators were tested in a saline bath and tissues. Most radiators designed produced larger lesions than have been described previously.

Differential response of the permeability of the rat liver canalicular membrane to sucrose and mannitol following in vivo acute single and multiple exposures to microwave radiation (2.45 GHz) and radiant-energy thermal stress.

Both acute and chronic exposures to microwave radiation altered the function of the rat canalicular membrane. A single acute exposure to microwave radiation [80 mW/cm2, 2.45 GHz, continuous wave, 30 min exposure (SAR approximately equal to 72 W/kg)] or a matched radiant-energy thermal load, both designed to raise core body temperature approximately 3 degrees C, decreased the permeability of the canalicular membrane of male Sprague-Dawley rats to sucrose. The change in canalicular membrane permeability was demonstrated by a significant increase in the percentage of [3H]sucrose recovered in bile following its administration by a segmented retrograde intrabiliary injection. Similar acute exposures to microwave and radiant-energy thermal sources produced no significant alterations in canalicular membrane permeability to [14C]mannitol. In both acute exposure protocols, a rapidly reversible increase in bile flow rate was observed. Four exposures (30 min/day x 4 days) to either microwave radiation (80 mW/cm2) or a matched radiant-energy thermal load resulted in a significant depression in bile flow rate at normothermic temperatures. Animals receiving multiple exposures to microwave radiation had significant decreases in canalicular membrane permeability to both [3H]sucrose and [14C]mannitol, while similar exposure to radiant-energy thermal load alone altered canalicular membrane permeability to [3H]sucrose. An examination of the hepatic clearance of sucrose and mannitol following acute microwave exposure demonstrated no significant differences. Thus acute single exposure to microwave and radiant-energy thermal loads produced similar alterations in canalicular membrane permeability. Conversely, multiple exposures produced nonreversible changes in bile flow rate and canalicular membrane permeability, with microwave exposure producing greater alterations in the function of the canalicular membrane than an equivalent radiant-energy thermal load.

Microwave facilitation of domperidone antagonism of apomorphine-induced stereotypic climbing in mice.

The dopaminergic agonist apomorphine produced dose-dependent stereotypic climbing behavior in mice housed in cages with vertical bars. This drug effect was competitively inhibited by systemic pretreatment with the centrally acting dopaminergic antagonist haloperidol but not by microwave irradiation (2.45 GHz, 20 mW/cm2, CW, 10 min) nor by systemic pretreatment with domperidone, a dopaminergic antagonist that only poorly penetrates the blood-brain barrier (BBB). Yet when mice were systemically pretreated with domperidone and then subjected to microwave irradiation (as above), the apomorphine effect was significantly reduced. Microwave irradiation also facilitated antagonism of the apomorphine effect by low and otherwise ineffective systemic pretreatment doses of haloperidol. Apomorphine-induced stereotypic climbing behavior was also reduced by domperidone administered intracerebrally, which bypassed the BBB. Exposure of intracerebral domperidone-pretreated animals to microwave irradiation failed to increase the degree of antagonism. These findings indicate that microwave irradiation can facilitate central effects of domperidone, a drug which acts mainly in the periphery. One possible explanation for these findings is that microwave irradiation alters the permeability of the BBB and increases the entry of domperidone to central sites of action.

Microwave facilitation of methylatropine antagonism of central cholinomimetic drug effects.

Pilocarpine-induced hypothermia and oxotremorine-induced tremors in mice are central cholinomimetic drug effects that are readily blocked by the muscarinic antagonist atropine. However, the quaternary ammonium derivative of atropine, methylatropine, is unable to block these cholinomimetic drug effects by virture of its inability to penetrate the blood-brain barrier (BBB) and blood-cerebral spinal fluid barrier (B-CSFB). Dose-response curves for pilocarpine and oxotremorine effects are not appreciably affected either by pretreatment with methylatropine (1.0 mg/kg) or by exposure to moderate-level microwave irradiation (2.45 GHz, 23.7 W/kg, CW, 10-min exposure). However, in mice receiving both the methylatropine pretreatment and microwave irradiation, the dose-response curves for both pilocarpine and oxotremorine effects were significantly shifted to the right, signifying a central anticholinergic action by methylatropine. These data indicate that a single acute exposure to a thermogenic level of microwave irradiation facilitates methylatropine antagonism of centrally mediated cholinomimetic drug effects. One possible explanation for this observation is that microwave radiation may enhance passage of quaternary ammonium compounds like methylatropine across the BBB and B-CSFB.

Microwave oven for improved biological solids determination.

This paper describes the evaluation of the use of microwave power to evaporate the water from biological solids in the suspended solids analysis for wastewater treatment plants. when microwave power was applied to the sample at a level of 1.8 watts per gram of water a constant weight was achieved in twelve minutes. This compares with sixty minutes drying time in the conventional test where thermal ovens are utilized. Solids results from microwaves oven drying were more precise than the results from drying with a thermal oven.