A lightweight ambient air-cooling unit for use in hazardous environments.

Recent research demonstrated (a) the effectiveness of intermittent conditioned air cooling during rest breaks to significantly reduce cumulative heat storage and (b) that longer work sessions were possible for individuals wearing chemical defense ensembles. To further advance this concept, a strategy for implementing continuous air cooling was conceived; ambient air cooling was added during work cycles and conditioned air cooling was delivered during rest periods. A compact battery-powered beltpack cooling unit (3.9 kg) designed and made at the U.S. Air Force Armstrong Laboratory was used to deliver 5.7 L/sec filtered ambient air during work cycles: 4.7 L/sec to the body and 1 L/sec to the face. Five experimental cycles were conducted in a thermally controlled chamber under warm conditions (32 degrees C, 40% relative humidity) with (1) no cooling-intermittent work, (2) intermittent cooling, (3) continuous cooling during intermittent exercise, and (4) no cooling-continuous work and (5) ambient air cooling during continuous exercise. Intermittent, conditioned, and continuous air cooling resulted in significant reductions in rectal temperature, mean skin temperature, and heart rate as compared with the no-cooling trials. The continuous air-cooling trial significantly improved thermal comfort and sweat evaporation. Results suggest that ambient air delivered during work cycles by a lightweight portable unit (in conjunction with conditioned air delivered during rest periods), can definitely improve personal comfort, reduce skin temperature, and decrease the cumulative fatigue common to repeated work/rest cycles in selected military and industrial applications in which individuals work in chemical defense ensembles.

Continuous and intermittent personal microclimate cooling strategies.

A comparison was made between two personal auxiliary cooling approaches for the relief of thermal stress while wearing the standard USAF Chemical Defense Ensemble (CDE). Subjects exercised at approximately 40% VO2max in either warm (28/24/34 degrees C) or hot (38/26/43 degrees C) environmental conditions, (Tdb/Twb/Tbg degrees C, respectively). During each of three trials, four hours of intermittent work (four work/rest cycles) were attempted. Microclimate air cooling was applied in two different fashions and compared with a control trial during which no cooling was received (NC). In one trial, conditioned air cooling (Tin approximately 20 degrees Cdb) was delivered during rest periods only (intermittent cooling, IC), while during the second trial, ambient air cooling was also applied during the work period in addition to the conditioned air delivered during rest periods (continuous cooling, CC). During the warm condition, exposure cycle time was 45 min work and 15 min rest, while under the hot conditions, exposure cycle time was 30 min work and 30 min rest. Both CC and IC trials resulted in significantly extended work times, lower final rectal temperatures, heart rates, and sweat production (SP) than in the NC trial. Additionally, CC results in significantly lower SP, higher % sweat evaporation, and lower ratings of perceived exertion (RPE) and thermal comfort (TC) than IC at both warm and hot temperatures. Moreover, subjects were better able to maintain thermal equilibrium (i.e., cumulative heat balance) over time using CC compared to IC in the warm environment. The physiological significance of these findings, in some cases, was secondary to the improvement in subjective measures of TC and RPE.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermal convergence fails to predict heat tolerance limits.

Work under very hot, humid conditions may raise skin temperature (Tsk) to meet rectal temperature (Tre). This convergence has been said to produce imminent collapse and therefore to predict human tolerance limits for work in heat, especially for those wearing impermeable protective clothing. The purpose of this study was to examine the ability of subjects to continue work beyond the time when they experienced convergence. A total of 15 healthy adult volunteers participated in two protocols: A) Each of nine subjects performed four experiments wearing impermeable clothing and walking on an inclined treadmill at a metabolic rate averaging 450 W with dry bulb temperature (Tdb) 29 or 38 degrees C; B) Each of nine subjects performed eight experiments wearing heavy, semipermeable clothing under a range of conditions involving Tdb = 22-40 degrees C, relative humidity 15-88%, and work load = 200-500 W. Convergence occurred in 42 cases; in the majority (60%) the subject continued walking until Tre rose to the criterion temperature 39 degrees C, working for 10-45 min after convergence. No subject approached collapse, nor did convergence have any special effect on the rate of rise of temperature or heart rate. Thus, while convergence marks severe, time-limited heat stress, it does not accurately predict tolerance limits in highly motivated subjects. Termination of work at convergence would unnecessarily truncate heat stress exposures, depriving investigators of valuable data and industrial users of a large portion of their safe work time.

Lung and pleural "free-cell responses" to the intrapulmonary deposition of particles in the rat.

Deposition of a high lung burden of particulate carbon or latex in the mouse elicits a biphasic macrophagic response, with the early increase in the size of the population of the alveolar macrophages (AM) being mainly due to an influx of mononuclear phagocytes from the blood compartment and the later phase being due to the egression of interstitial macrophages (IM). In the present study, we investigated the lung's free-cell response in the rat to the intrapulmonary instillation of microspheres and determined the contributions of newly arrived blood monocytes to the macrophagic response over a 30-d period. As of 24 h after deposition, the lavageable population size increased approximately fivefold. Most of the increase in the free cell population was due to a recruitment of polymorphonucleated leukocytes (PMN), although the size of the AM population nearly doubled. Only about 13% of the AM on d 1 were positive for myeloperoxidase activity, suggesting that recruitment of mononuclear phagocytes from the blood compartment plays a limited role in the early expansion of the AM pool in the rat. As of 14 and 30 d after particle deposition, lavaged AM numbers continued to be elevated; the enlarged sizes of the AM populations at these times could be explained, in part, by a continuing influx of blood monocytes. In a parallel component of the study, we also investigated how the pleural cell population might be affected during the lung's free-cell response to the particulate burden. No acute influx of PMN into the pleural space (PS) accompanied the early free-cell response; the chemotactic factors initially involved in recruitment of the PMN into the lung apparently did not reach the PS in significant or biologically active concentrations, or they were inoperable in the pleural compartment. On the other hand, the numbers of macrophages in the PS were significantly elevated on d 1 and 14 after particle deposition in the lung. The macrophagic response in the PS subsided by d 30, but at this latter sacrifice time, pleural mast-cell and lymphocyte numbers were significantly increased and decreased, respectively. These results indicate that the deposition of particles into the lung can lead to numerical alterations in the cell types composing pleural cell populations.