Larry G. Berglund

Skin Friction and Fabric Sensations in Neutral and Warm Environments

The influence of skin friction on the perception of fabric texture and pleasantness (acceptability) was studied by exposing eight men to a sequence of environmental conditions: neutral (comfortable), hot-dry, hot-humid, and return to neutral. The air and dew point temperatutes (T a:T dp) of these conditions were 23:15°C, 35:15°C, 35 :29°C, and 23:15°C, respectively; air velocity was 0.05 m/s. During each condition, which lasted 20 minutes, six different fabrics (worsted wool, brushed cotton, cotton, silk, linen, and burlap) were slowly pulled across the subjects forearm. Frictional force of fabric pull across the forearm and the subjects ratings of texture and pleasantness (hedonic) were recorded. Arm skin temperature and skin wettedness were recorded continually. The frictional force required to pull each fabric over the skin correlated positively (P < 0.05) with skin wettedness. As force and skin wettedness increased, the subjects rated all fabrics as feeling more textured (rougher) and less pleasant (P < 0.05). Increased perception of fabric texture significantly decreased fabric ac ceptability. On return to the neutral condition, the parameters returned to their initial values. The conclusion is that moisture on the skin surface increases skin friction, which enhances perception of roughness and decreases the acceptability of clothing worn in hot environments.

Ventilation requirements in buildings—I. Control of occupancy odor and tobacco smoke odor

Abstract Psychophysical measurements of odor, supplemented with certain physical measurements, were taken to examine ventilation requirements during smoking and nonsmoking occupancy in an environmental chamber. The facility provided the means to compare impressions of visitors (persons who inhaled air from the chamber only briefly) with impressions of occupants. For nonsmoking occupancy, 47 combinations of temperature, humidity, ventilation rate and occupancy density were examined. Odor level depended entirely on ventilation rate per person irrespective of the number of persons in the chamber. The ventilation necessary to satisfy 75 % of visitors equalled only about 4 l s −1 per person. Occupants, however, were satisfied with far less. In an array of 38 conditions of smoking occupancy, the ventilation deemed necessary to satisfy 75 % of visitors under customary conditions of occupancy equalled 17.5 l s −1 per person. For both smoking and nonsmoking conditions, a combination of high temperature (25.5°C) and humidity (r.h. > 70 %) exacerbated the odor problem. During smoking, carbon monoxide rarely reached dangerous levels, but suspended particulate matter often reached levels considered unacceptable outdoors. The results highlight the energy penalty incurred in ventilation for smoking occupancy.

On the thermoregulatory consequences of NMR imaging

A simple model of physiological thermoregulation has been adapted to predict the thermoregulatory consequences of exposure to the nuclear magnetic resonance (NMR) imaging environment. Based on our knowledge of thermoregulatory processes and how heat is exchanged between a person and the environment, the model can predict physiological heat loss responses in real time as a function of selected ambient temperature (Ta), air movement (v), and rate of whole-body radiofrequency (RF) energy deposition (SAR). Assuming a criterion elevation in deep body temperature (delta Tco) of 0.6 degree C, Ta = 20 degrees C and v = 0.8 m/sec, a 70 kg patient could undergo an NMR exposure of infinite duration at SAR less than or equal to 5 W/kg. Lowering Ta or increasing v permits a rise in permissible SAR for a given delta Tco. More restrictive delta Tco criteria result in lower permissible SARs and shorter exposure durations. The limiting response under all conditions tested was found to be the rate of peripheral blood flow, although sweating played a significant role in preventing excessive delta Tco. Some guidance for the clinical application of the predictions is offered.

Acute Exposure to Low-Level Methyl Tertiary-Butyl Ether (MTBE): Human Reactions and Pharmacokinetic Response

AbstractThis two-part investigation assessed the effects of 1-h exposures to methyl tertiary-butyl ether (MTBE) at an ambient concentration of 1.7 ppm on healthy adults. In one part, four subjects participated in a pharmacokinetic study of blood levels of MTBE. Concentration in blood rose 20-fold from baseline to 17 μg/L by the end of exposure and declined to one-half that level at 40 min after exposure. In another part, 43 subjects participated in a double-blind study of reactions to exposures to MTBE (1.7 ppm), to a mixture of 17 volatile organic compounds (VOCs) (7.1 ppm), and to air. Subjects rated symptoms (e.g., irritation, headache, mental fatigue), their mood, and various environmental attributes (e.g., odor, air quality, temperature), and also took computerized performance tests during exposures. Measures of eye irritation (e.g., tear-film breakup, eye redness) and nasal inflammation (i.e., measurement of polymorphonuclear neutrophilic leukocytes, PMNs) were taken before and after exposure as obj...

Thermoregulatory consequences of cardiovascular impairment during NMR imaging in warm/humid environments

A simple model of physiological thermoregulation, previously adapted to predict the thermoregulatory consequences of exposure to the nuclear magnetic resonance (NMR) imaging environment, has been further adapted to simulate impaired cardiovascular function. Restrictions on the rate of skin blood flow (SkBF), ranging from 0 to 89% of normal, were studied. Predictions of physiological heat loss responses in real time were generated as a function of ambient temperature (Ta), relative humidity (RH) and rate of whole-body radiofrequency (RF) energy deposition (SAR). Under conditions that are desirable in the clinic (Ta = 20 degrees C, 50% RH, still air), moderate restrictions (up to 67%) of SkBF yield tolerable increases in core temperature (delta Tco less than or equal to 1 degree C) during NMR exposures (SAR less than or equal to 4 W/kg) of 40 min or less. Increased Ta and RH exacerbate the thermal stress imposed by absorbed RF energy; severely impaired SkBF encourages short NMR exposures (e.g., 20 min or less) at SARs less than or equal to 3 W/kg. In warm/humid environments, sweating is predicted to be profuse and evaporative cooling curtailed, yielding a state of extreme thermal discomfort. Added insulation (e.g., a blanket) is discouraged. Some guidelines, incorporating SkBF restrictions, Ta, RH, and insulation, are offered for the prediction of tolerable NMR exposure conditions.

Ventilation requirements in buildings—II. particulate matter and carbon monoxide from cigarette smoking

Abstract Current efforts to reduce ventilation rates in buildings may conserve energy, but may also possibly empair human health and welfare through increased levels of indoor contaminants. Combustion of tobacco is one important source of indoor pollution. We measured both steady state levels and decays of total suspended Particulate mass between 0.01 and 10μm (TSP) and carbon monoxide (CO) generated during various rates of cigarette smoking and at various rates of ventilation. The measurements took place in an aluminum-lined environmental test chamber. Ninety-eight per cent of the particulate mass fell between 0.05 and 1.0 μm, with a volume median diameter of 0.225 μm. For many combinations of smoking rate and ventilation rate, including ventilation rates above normal, TSP exceeded levels considered acceptable outdoors. This rarely occurred, however, with CO. Although ventilation above governed the removal of CO from the chamber, adsorption on surfaces (e.g. ductwork, walls) provided an additional mechanism for the removal of TSP. Even with the additional clearance offered by adsorption, however, particulate levels will exceed commonly accepted background levels unless ventilation during smoking equals the high value of about 35cfm (17.5/−1) per occupant. An electrostatic precipitator, on the other hand, will drive TSP levels down to very low values in very short periods of time.

The Effect of Temperature and Humidity Levels in a Protective Mask on User Acceptability During Exercise

Subjective and physiological responses were obtained from six subjects wearing a ventilated face mask while exercising (3.8 met) for 15 min on a bicycle ergometer. Different combinations of ambient air temperatures (7 degrees, 16 degrees, 25 degrees C) and mask air temperatures (22 degrees, 27 degrees, 33 degrees C) were studied together with two different air humidities inside the mask (61% and 86% RH). Control experiments were performed without the mask at the same ambient temperatures. Skin temperatures, heart rates and skin wettedness were monitored during exercise. The subjects acceptance of the mask and thermal environment, thermal sensation, sensations of discomfort, sweating and skin wettedness, and their judgment of the work of breathing were assessed at the end of the 15 min exercise period. The acceptance of both the ambient thermal environment and of the thermal microclimate in the mask primarily was determined by the ambient air temperature, but it was influenced by the air temperature and humidity inside the mask. At ambient temperatures of 7 degrees C and 25 degrees C, the acceptance of the thermal work conditions decreased. In the warm environment a mask air temperature less than or equal to 27 degrees C was 100% acceptable and increased the acceptance of thermal environment. In the cool environment, a mask air temperature greater than or equal to 27 degrees C was 100% acceptable. The humidity content of the mask air was only important when the mask air was warm. Warm humid air significantly decreased acceptance of the mask conditions.

Methods of Evaluating Protective Clothing Relative to Heat and Cold Stress: Thermal Manikin, Biomedical Modeling, and Human Testing

Personal protective equipment (PPE) refers to clothing and equipment designed to protect individuals from chemical, biological, radiological, nuclear, and explosive hazards. The materials used to provide this protection may exacerbate thermal strain by limiting heat and water vapor transfer. Any new PPE must therefore be evaluated to ensure that it poses no greater thermal strain than the current standard for the same level of hazard protection. This review describes how such evaluations are typically conducted. Comprehensive evaluation of PPE begins with a biophysical assessment of materials using a guarded hot plate to determine the thermal characteristics (thermal resistance and water vapor permeability). These characteristics are then evaluated on a thermal manikin wearing the PPE, since thermal properties may change once the materials have been constructed into a garment. These data may be used in biomedical models to predict thermal strain under a variety of environmental and work conditions. When the biophysical data indicate that the evaporative resistance (ratio of permeability to insulation) is significantly better than the current standard, the PPE is evaluated through human testing in controlled laboratory conditions appropriate for the conditions under which the PPE would be used if fielded. Data from each phase of PPE evaluation are used in predictive models to determine user guidelines, such as maximal work time, work/rest cycles, and fluid intake requirements. By considering thermal stress early in the development process, health hazards related to temperature extremes can be mitigated while maintaining or improving the effectiveness of the PPE for protection from external hazards.

Predicted Thermophysiological Responses of Humans to MRI Fields

A relatively simple two-node model of human thermoregulation was developed to predict response changes during MRI procedures. Subsequent modifications of the model simulated impairments in cardiovascular function in terms of altered skin blood flow. In the present work, the model was programmed to predict the consequences of certain procedures used in the clinic, namely, precooling of the patient to the prevailing environment and covering the patient with a light blanket. Some of the fundamental predictions of the model during 20-min MRI scans at a low SAR were tested on two male subjects in the clinical setting. The following conclusions may be drawn: (1) Precooling of the patient for 20 min to the prevailing ambient conditions, whether inadvertent or deliberate, has little value in terms of preventing a rise in body temperatures. At the conclusion of a subsequent 20-min MRI scan, even at SARs as low as 2 W/kg, the modest effects of precooling are all but eliminated. Thus, inadvertent precooling should be no cause for concern; deliberate precooling carries little advantage for the patient and wastes valuable time. (2) Use of a blanket during an MRI scan should be discouraged in the normal clinical setting except when the SAR is 2 W/kg or less. At higher SARs, this added insulation impedes convective and radiative heat loss through evaporation of sweat. The result is an increase of heat storage in the body and a greater rise in core temperature than would occur otherwise. (3) Clinical tests on two normal male subjects have provided limited confirmation of the predictions of the two-node model. During 20-min MRI scans at a whole-body SAR of 1.2 W/kg, core and skin temperatures, sweat rate, and judgments of thermal sensation and discomfort were very similar to predicted values. Unexpected findings of an incremental increase in core temperature with successive scans and a sweating rebound following each scan may be important for future investigation. (4) Although pleased with the limited confirmation of our predictions, we are constantly aware of the limitations of the two-node model to accurately predict thermoregulatory responses of patients undergoing clinical MRI of various body parts. It is essential to keep in mind that the simulations are based on RF exposure of the whole body; thus, the predicted increase in core temperature will be proportionately higher than would be the case if only a portion of the body were exposed within the MRI device.(ABSTRACT TRUNCATED AT 400 WORDS)

THERMOREGULATION IN HUMANS OF DIFFERENT AGES DURING THERMAL TRANSIENTS

Publisher Summary This chapter discusses thermoregulation in humans of different ages during thermal transients. A description of appropriate thermoregulatory changes as a function of deviations from normal body temperature has helped clarify the contribution of afferent input from the skin and internal thermal receptors on heat loss and heat production responses. Some studies using thermal transients, whereby air temperature is changed toward the heat or toward the cold, have pointed out differential responses in the way a thermal load is handled among males and females. Both the range of increases or decreases in internal body temperature has been found to be wider in men than in females. Within a group, although thermoregulatory control is similar, the ease in handling a thermal load as a function of changes in deep body temperature can have dramatic effects on how an individual responds to the environment.