Evaluation of the IITC tail cuff blood pressure recorder in the rat against intraarterial pressure according to criteria for human devices.

National standards govern the manufacture and marketing of medical devices in the United States, including those for indirect blood pressure measurement in man. There are no comparable standards for devices for recording in laboratory animals. Noninvasive tail cuff blood pressure (BP) recording in the rat is widely accepted, but beset by methodologic difficulties. Intraarterial recording is regarded as the "gold standard" but is invasive and also susceptible to methodologic error. We compared the IITC Mark 12 photoelectric/oscillometric tail cuff system (IITC Life Sciences, Woodland Hills, CA) versus simultaneous femoral intraarterial recordings in spontaneously hypertensive rats, during anesthesia and 1 to 2 days after recover (150 recordings under each condition), according to the guidelines for human data collection and analysis suggested the American National Standard for automated sphygmomanometers. Within- and between-observer disagreements in estimates made by two observers from 40 anesthetized recordings were less for intraarterial measurements than for the tail cuff method. Within-observer differences (mean +/- SD of differences [SDD]) for systolic, diastolic, and mean pressure were 0 +/- 1, 0 +/- 1, and 0 +/- 1 mm Hg for intraarterial versus -1 +/- 3, 0 +/- 8, and 0 +/- 5 mm Hg for tail cuff. Between-observer differences were 0 +/- 2, 0 +/- 1, and 6 +/- 2 mm Hg versus 5 +/- 4, 13 +/- 7, and 0 +/- 5 mm Hg, respectively. Differences between tail cuff and intraarterial methods were 16 +/- 13, -5 +/- 11, and 2 +/- 8 mm Hg in anesthetized animals and 8 +/- 14, -5 +/- 9, and 0 +/- 9 mm Hg in conscious animals (39% to 82% of differences exceeded 5 mm Hg). The upper limits of clinically acceptable disagreement in the American National Standard are: mean of 5 mm Hg, SDD of 8 mm Hg. The disagreement between tail cuff and intraarterial recordings cannot be ascribed to either method with certainty. These findings do not support the manufacturer's guarantee of tail-cuff readings within "5 mm Hg of intraarterial." Inaccuracy and unreliability of devices intended for laboratory animal use have considerable scientific, fiscal, and ethical implications. Marketing of these devices should also be governed by rigorous standards.

Amino acid concentrations in hypothalamic and caudate nuclei during microwave-induced thermal stress: analysis by microdialysis.

Exposure to radiofrequency radiation (RFR) may produce thermal responses. Extracellular amino acid concentrations in the hypothalamus (Hyp) and caudate nucleus (CN) were measured by using in vivo microdialysis before and during exposure to RFR. Under urethane anesthetic, each rat was implanted stereotaxically with a nonmetallic microdialysis probe and temperature probe guides and then placed in the exposure chamber. The rat laid on its right side with its head and neck placed directly under the wave guide. Temperature probes were placed in the left brain, right brain, face (subcutaneously), left tympanum, and rectum. Each microdialysis sample was collected over a 20 min period. The microdialysis probe was perfused for 2 h before the rat was exposed to 5.02 GHz radiation (10 microseconds pulse width, 1000 pulses/s). The right and left sides of the brain were maintained at approximately 41.2 and 41.7 degrees C, respectively, throughout a 40 min exposure period. Initially when the brain was being heated to these temperatures, the time-averaged specific absorption rates (SARs) for the right and left sides of the brain were 29 and 40 W/kg, respectively. Concentrations of aspartic acid, glutamic acid, serine, glutamine, and glycine in dialysate were determined by using high-pressure liquid chromatography with electrochemical detection. In the Hyp and CN, the concentrations of aspartic acid, serine, and glycine increased significantly during RFR exposure (P < .05). These results indicate that RFR-induced thermal stress produces a general change in the amino acid concentrations that is not restricted to thermoregulatory centers. Changes in the concentrations of glutamic acid (Hyp, P = .16; CN, P = .34) and glutamine (Hyp, P = .13; CN, P = .10) were not statistically significant. Altered amino acid concentrations may reveal which brain regions are susceptible to damage in response to RFR-induced thermal stress.

Recovery characteristics of a rigid, nonmetallic microdialysis probe for use in an electromagnetic field.

It is well known that metal objects perturb electromagnetic fields. Therefore, a conventional metal microdialysis probe cannot be used to determine the bioeffects of electromagnetic radiation. Using fused-silica tubing, we developed an inexpensive nonmetallic, rigid microdialysis probe for use in electromagnetic radiation research or during magnetic resonance imaging. This probe has a concentric tube design, with the membrane length adjustable to the size of the area to be dialyzed. The probes tested had regenerated-cellulose membranes that were 3 mm in length. This report describes how to make this probe. Average relative recovery rates at flow rates of 2.0, 1.0, and 0.5 microliters/min were 21%, 27%, and 42%, respectively. These rates were slightly lower than the 30%, 42%, and 68% obtained with the commercially available metallic CMA10 microdialysis probe with a 3 mm membrane. This may be due to the fused-silica probe and CMA10 probe being made with different types of dialysis membranes.