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Biomedical subjects

W M Caldwell

Publications and source records attributed to W M Caldwell.

At least 19 recordsLinked to original sources
PubMed1992

Supercritical fluid extraction of chemical warfare agent simulants from soil.

Chemical warfare agent simulants are efficiently recovered from 2-ppm spikes in 1 g of Rocky Mountain Arsenal Standard Soil using methanol-carbon dioxide (5:95) at 300 atm for 2 min at 60 degrees C. Recoveries (n = 3) were 79 +/- 23% for dimethylmethylphosphonate, 93 +/- 14% for 2-chloroethylethyl sulfide, 92 +/- 13% for diisopropylfluorophosphate and 95 +/- 17% for diisopropylmethylphosphonate. Recoveries are higher than, but less precise than those achieved from a 5-min ultrasonic micro-scale extraction using methanol. Much less laboratory waste is generated than the current standard organic solvent extraction method (33 g of soil shaken with 100 ml of chloroform).

Chemical Warfare Agents↗
PubMed1990

Digital processing of equine exercise electrocardiograms.

We have developed and used a system for recording and analyzing the electrocardiogram (ECG) of the horse during exercise. The system consists of a commercial ECG transmitter telemetering a Z lead (base-apex) ECG from an exercising horse. The received data are then remodulated at an audio frequency and stored on a audio cassette recorder. Exercise protocols of up to 10 minutes are digitized using a Macintosh II computer. For rhythm analysis, a computer program to identify the various waves of the ECG uses a modification and refinement of the integrated-squared-derivative (ISD) technique. This technique consists of frequency selective digital filtering and differentiation followed by integration of the squared derivative. The waves of the ECG are identified using adaptive thresholding of the ISD and the derivative of the ECG. Thus far, we have been able to successfully identify the Q, R, and the end of T in ECGs severely contaminated by exercise artifact. The system can place the absolute time of occurrence of the Q, R, and end of T in a text file for export to other analysis programs such as spreadsheets and statistics packages.

Algorithms↗
PubMed1989

An automatic syringe for coronary occlusion in long-term collateralization studies.

A portable apparatus for performing repeated, brief coronary artery occlusions automatically in long-term chronic studies involving dogs and larger animals is described. The battery-operated, back-pack-carried device uses a motorized syringe driven by a digital-programmable timing circuit to inflate a coronary artery occluder for durations of 10 s to 3 min at intervals from 14 s to 16 h. A single battery charge produces 450 occlusions. The generated pressure is adjustable to 1,000 mmHg maximum. A separate fail-safe circuit monitors system operation to open a pressure-relief valve if occlusions exceed a preset duration.

Animals↗
PubMed1989

A miniaturized ultrasonic flowmeter and telemetry transmitter for chronic animal blood flow measurements.

An ultrasonic blood flowmeter telemetry system, using only two integrated circuits and one transistor, has been designed for chronic unanesthetized animal studies. Standard components and construction techniques are utilized. The CW Doppler system employs LZT piezoelectric 10 MHZ transmitting and receiving crystals held in a lightweight polystyrene arterial transducer. The audio frequency, FM Doppler signal modulates an FM oscillator-transmitter to produce an FM/FM radio frequency carrier which is transmitted to an FM receiver at a remote location. The transmitted Doppler audio flow signal is demodulated at the receiver by a zero crossing detector. Power consumption is 48 mw. The 12.4 cc package volume can be further reduced for animal implantation.

Animals↗
PubMed1977

DC proportional heater-cooler temperature controlled for physiological research.

A DC proportional temperature control circuit for driving resistive heaters and Peltier thermoelectric devices in physiological research is described. The instrument, supplying +/- 12.5 V DC at 8 A is designed for temperature control of anesthetized animals, generation of hot or cold thermal stimuli, and control of thermal environments.

Physiology↗
PubMedDate not supplied

Liquid chromatographic determination of total formaldehyde in drinking water.

Formaldehyde is readily quantitated at micrograms/L levels in drinking water. The analyte present in 1 L water samples is derivatized with 2,4-dinitrophenylhydrazine in a 2M acid medium and then extracted with chloroform. After the solvent is exchanged for methanol, the product is separated and quantitated using reverse-phase liquid chromatography with UV detection (365 nm). Reporting limits as low as 20 micrograms/L (corrected for laboratory blank) are routinely achieved. Formaldehyde recovery typically exceeds 90% at 20-200 micrograms/L. The method was applied to hot and cold water samples from thirty-four 1- and 2-story houses equipped with poly(acetal) plumbing elbows and tees. The drinking water samples were accompanied by sets of blanks and spikes specified by a quality assurance/quality control plan. Formaldehyde was observed above the reporting limit in 80% of hot and cold water samples from the 1-story dwellings, but in less than 50% of those from the 2-story dwellings. The results may depend on both the construction of the houses (1- vs 2-story) and the time of year the water is sampled (mid-summer).

Chromatography, Liquid↗