Readdressing personal cooling with ice.

An ice-based system of personal, non-restrictive cooling of workers exposed to high temperature work environments in nuclear power plants was evaluated. The garments were designed to be worn under the protective clothing donned for penetration into radiation areas. The cooling system consisted of direct body contact with small packets of frozen water enclosed in the pockets of a shirt in high ambient temperatures (55 degrees C) and moderate metabolic heat production (200-300 kcal/hr). Mean exposure time without cooling (control) was 52 min for workloads demanding 200 kcal/hr energy expenditure. A long garment with 7.2 kg of frozen water (LFWG) increased mean exposure time over the control by 242% (163% for the same garment with 6.2 kg of frozen water). A short version garment with 3.8 kg of frozen water (SFWG) increased the stay time by 115%. In field observations, the LFWG with 6.2 kg of frozen water improved stay time by 125%. The leveling off of the body temperatures and heart rates during the work both in the laboratory and in the field confirmed a reduction of heat strain associated with the use of these garments. Calculated heat balance equations of heat uptake by the ice predicted these results very closely. It was concluded that direct body contact with frozen water provided predictable adequate body cooling for the work and ambient conditions investigated in this study.

Hot air breathing: effects of elevated wet bulb temperatures on tissue temperatures of the mouth.

Six healthy young men breathed room air or one of nine hot humid air conditions on separate days for one hour while walking on a treadmill (40% VO2 max). Inspired wet bulb temperatures ranged from 18.9 (room air) to 49.3 degrees C. Tissue temperatures in the mouth were measured by means of thermocouples placed on the tongue and hard palate. Analysis of variance on repeated measures showed significant increases in both tongue and hard palate tissue temperatures (p less than 0.001) as a result of increasing wet bulb temperatures; however, core temperature and heart rate were not affected (p greater than 0.05). Ratings of subjective discomfort increased proportionally with increases in wet bulb temperature of the inspired air. It was concluded that wet bulb temperature of inspired air is a valuable measure to uses in studying temperature responses of mouth tissues when inhaling hot humid air, particularly when investigating human tolerance levels in order to recommend federal standards for the design of breathing apparatus.

Multichannel data acquisition system for recording the acoustic brainstem response.

A system has been developed to sample and average multi-channel ABR data. All channels are sampled simultaneously. The simple design incorporates one sample-and-hold amplifier and one analog-to-digital converter in each channel. For sampling of 13 channels or less, sampling interval must exceed 36 microseconds for full 10-bit resolution. For sampling more than 13 channels, data transfer to the host computer limits minimum sampling interval to 20 + (1.2 X N) microsecond, where N is the number of channels sampled.

Single breath cardiac output--enhanced sampling and analysis techniques.

The single breath method for measuring cardiac output (Q) was enhanced using new computer sampling and analysis techniques. The carbon dioxide (CO2) elimination rate was measured breath by breath using computer integration of expired flow rate and CO2 concentration. The concentration of CO2 in the arterial blood was determined from the CO2 partial pressure at the end of a normal breath. The concentration of CO2 in mixed venous blood was determined with a modification of the single breath method. The variability and relative accuracy of measurement of cardiac output were evaluated using four healthy men who exercised at three work rates from 0.5 L X min-1 (rest) to 2 L X min-1 oxygen consumption (VO2). Repeatability of measurements was assessed by making repeated measurements on one subject at a steady state exercise work rate. The coefficients of variation for repeated measurements made at 0.5 L X min-1 (rest), 1.0 L X min-1 VO2, and 2.0 L X min VO2 were 18.2, 10.5% and 8.8%, respectively. Regression lines relating cardiac output and oxygen consumption from three separate studies, employing the direct Fick method, and the described method were all similar. The probability of a successful breathing maneuver was increased to nearly 100%. Success was defined as a linear regression correlation coefficient (r2), relating instantaneous exchange ratio and CO2 during the breathing maneuver, of greater than 0.9.

Calculator/computer-assisted calibration and use of the IL-182 CO-Oximeter.

Of the many techniques and methods available for measuring carbon monoxide in blood, one of the easiest involves the use of the IL-182 CO-Oximeter, a specialized triple-wavelength spectrophotometer. Although easy to use, the calibration procedure can be lengthy and impractical if performed routinely to ensure accuracy. A method is described for an equivalent calibration by using a programmable calculator or minicomputer. The new method allows rapid and easy calibration as well as the analysis of unknown blood samples. Three anticoagulated blood samples, each containing as little as 2 ml, are required to calibrate. One sample is chemically reduced, one is tonometered in pure oxygen, and the third is tonometered in pure carbon monoxide. The optical densities of these three known calibration samples, determined at each of the three specific wavelengths used by the IL-182, allow one to derive the constants used in the equations needed to solve for an unknown sample.

Physiological responses to resistance breathing during short and prolonged exercise.

Respirators which impose a resistance to breathing may cause a limitation in maximum exercise intensity. This limitation is of particular concern when respirators are used in emergency situations requiring high levels of exercise intensity. Many studies have defined the limitations of exercise intensity imposed by breathing resistance as the point where the subject feels "uncomfortable". Perhaps of greater importance is the true physiological limit. Using motivated subjects, the physiological limits of exercise intensity and related respiratory responses resistances of 11, 16, 25, 40, and 57 cm H2O pressure at a flow rate of 120 L.min-1 exercise limits were 72, 72, 79, 60, and 54 percent of maximum aerobic capacity (% VO2 max) for the short term and 58, 60, 49, 43, and 35% VO2max for the prolonged exercise (1 hour). The presence of significant external resistance to breathing was found to influence the traditional relationship between exercise intensity and duration.

A dryer for rapid response on-line expired gas measurements.

A dryer is described for use in on-line breath-by-breath gas analysis systems. The dryer continuously removes water vapor by condensation and controls the sample gas at 2 degrees C dew-point temperature or 5 Torr water vapor partial pressure. It is designed to operate at gas sampling flow rates from 0.5 to 1 1.min-1. The step-response time for the described system including a Beckman LB-2 CO2 analyzer, sampling tubing, and dryer is 120 ms at 1 l.min-1. The time required for gas samples to transport through the dryer is 105 ms at a gas sampling-flow rate of 1 l.min=1.

Respiratory flow integrator with improved stability.

A circuit was designed for integrating respiratory flow signals over time to produce volume signals. The circuit involves a simple integrator and three compensation subcircuits which control integrator drift caused by ambient temperature changes, flow signal base-line errors, and random signal errors. A functional unit built according to the circuit design requires initial adjustment, but no further adjustment before or during sustained use. Integration errors are typically less than 1%. The only flow signal requirements are that they be bidirectional and within the human physiological frequency range.