Effectiveness of a field-type liquid cooling vest for reducing heat strain while wearing protective clothing.

This study examined the effectiveness of a field-type liquid cooling vest (LCV) worn underneath an impermeable protective suit on heat strain during walking. Eight men walked for 60 min at a moderate speed (3.0 km/h) wearing the suit in a warm environment (33°C, 60% relative humidity) without (control, CON) or with the LCV. A smaller increase in rectal temperature was recorded in participants in the LCV than in the CON condition (37.6 ± 0.1°C vs. 37.9 ± 0.1°C, p<0.05). Walking while wearing the LCV reduced the level of physiological heat strain, as measured by the mean skin temperature (35.5 ± 0.1°C vs. 36.3 ± 0.1°C), chest sweat rate (13.5 ± 3.0 mg/cm2/h vs. 16.6 ± 3.8 mg/cm2/h), chest cutaneous vascular conductance (349 ± 88% vs. 463 ± 122%), body weight loss (0.72 ± 0.05% vs. 0.93 ± 0.06%), and heart rate (101 ± 6 beats/min vs. 111 ± 7 beats/min) (p<0.05, for all comparisons). These changes were accompanied by a decrease in thermal sensation and discomfort. These results suggest that a field-type LCV attenuates exertional heat strain while wearing impermeable protective clothing.

Heat Strain and Hydration of Japanese Construction Workers during Work in Summer.

Objectives: The aim was to ascertain hydration and heat strain of construction workers in Japan during the summer who are at the highest risk of heat-related disorders. Methods: The subjects were 23 construction workers, whose average age was 41, average weight was 69 kg, and average height was 170 cm. We measured thermal working conditions with a wet bulb globe temperature (WBGT) measurement instrument affixed to the helmet of each worker, at fixed points outdoors in the sun and indoors. Heat strain was evaluated for water intake, urine specific gravity (Usg), urine temperature (UT), heart rate (HR), and body weight during work. Results: The average WBGT measured on the worker helmets over 3 consecutive days was 28.0 ± 0.7, 27.6 ± 0.8, and 27.6 ± 1.1°C. The average water intake was 2.6 l during a work shift. The average Usg, UT, and % HR reserve were the highest in the first half of afternoon work. Seventy-eight percent of the subjects exceeded at least one of the ACGIH TLV physiological guidelines for heat strain in terms of HR and weight loss or a clinically dehydrated level of Usg. Conclusions: Heat strain was the highest in the first half of afternoon work. The number of dehydrated workers increased during this shift because of insufficient water intake. Adequate hydration is required to decrease the risk of heat-related disorders among construction workers in the summer.

Effects of partial sleep restriction and subsequent daytime napping on prolonged exertional heat strain.

OBJECTIVES: It is considered that sleep restriction is one of the risk factors for the development of exertional heat stroke and illness. However, how sleep restriction affects exertional heat strain and the nature of the coping strategy involved in this phenomenon remain unclear. METHODS: Fourteen healthy subjects were studied on four occasions: after a night of normal sleep (NS, 7-8 h) and after a night of partial sleep restriction (PSR, 4 h), each with or without taking a daytime nap during the subsequent experimental day. The laboratory test consisted of two 40 min periods of moderate walking in a hot room in the morning and the afternoon. RESULTS: The increase in rectal temperature during walking was significantly greater in PSR than in NS in the afternoon. The rating scores for physical and psychological fatigue and sleepiness were significantly greater in PSR than in NS, both in the morning and in the afternoon. The reaction times and lapses in the psychomotor vigilance task (PVT) after walking were significantly worse in PSR than in NS in the morning and after lunch. The nap intervention attenuated significantly the scores for fatigue and sleepiness in PSR. Furthermore, the decreased PVT response in PSR was significantly reversed by the nap. CONCLUSIONS: These results suggest that PSR augments physiological and psychological strain and reduces vigilance in the heat. Taking a nap seemed to be effective in reducing psychological strain and inhibiting the decrease in vigilance.

Fan-precooling effect on heat strain while wearing protective clothing.

This study compared heat strain during walking while wearing impermeable protective suits between fan-precooling and nonprecooling conditions. Six males engaged in 60 min of walking at a moderate speed (∼2.5 km/h) in a hot environment (37 °C, 40% relative humidity). Fanning using a fan (4.5 m/s) and spraying water over the body before wearing the suits produced significantly lower rectal temperature before the walking (37.3 ± 0.1 °C vs. 37.0 ± 0.1 °C, P < 0.05). In addition, whilst walking, rectal temperature was significantly lower in the precooling condition (maximum difference: 0.4 °C at 15 min of walking; 38.0 ± 0.1 °C vs. 37.8 ± 0.1 °C at the end of walking, P < 0.05). Although skin temperature decreased during fanning, no difference was observed during walking. Heart rate was lower in the precooling condition during the early stages of walking. Thermal and fatigue perceptions whilst walking did not differ between the conditions. Body weight loss was significantly lower in the precooling condition. These results may indicate that fan precooling attenuates exertional heat strain while wearing impermeable protective clothing. The fan-cooling method is practical, convenient, and yields lower heat strain during prolonged moderate exertion.

Weekend sleep intervention for workers with habitually short sleep periods.

OBJECTIVES: This study was conducted to determine whether extended sleep time during the weekend improves alertness and performance during the subsequent week for workers who are habitually short on sleep time. METHODS: Daytime employees in the manufacturing industry [38.3, standard deviation (SD) 8.1 years old, mean weekday sleep ≤6 hours] participated in a study that lasted 3 successive weeks. Participants were instructed to stay in bed for ≥8 hours between 22:00-09:00 hours on weekends during the first week as a sleep intervention condition and keep their habitual sleep-wake patterns as a habitual weekend sleep condition beginning the weekend of the second week through Thursday of the third week. Half the participants underwent the conditions in one order and the other half in the reverse. Sleep was monitored by an actigraph. A psychomotor vigilance task, subjective fatigue, and blood pressure were measured on Monday and Thursday during the afternoon each week. RESULTS: Sleep duration on weekends was approximately 2 hours longer per day during the intervention. However, sleep duration during weekdays following the intervention returned to shorter periods. Significantly shorter reaction times and a smaller number of lapses on the psychomotor vigilance task were found on Mondays after the intervention than after the habitual weekend sleep. The opposite results, however, were observed on Thursdays. CONCLUSIONS: Sleep extension on weekends may be effective in improving alertness and performance during the first days in subsequent weeks among workers with short sleep times. These benefits might be maintained if sufficient sleep duration continues.

Zinc bioavailability is improved by the micronised dispersion of zinc oxide with the addition of L-histidine in zinc-deficient rats.

Zinc fortification of milk or soft drinks is usually used to combat zinc deficiencies in developing countries. Water-soluble zinc compounds, such as zinc sulfate or zinc citrate, are better absorbed but have an unacceptable taste. A micronised, dispersible zinc oxide (MDZnO), which does not have such a problem concerning taste, had higher solubility compared to ZnO (zinc oxide) in an artificial gastric solution. MDZnO was tested for its bioavailability using zinc-deficient Wistar rats. Prior to the experiment, rats were fed zinc-deficient diet for 3 wk and were orally administered control (distilled water) or zinc solutions (ZnO, ZnO+L-histidine (His), MDZnO, MDZnO+His, 1 mg zinc/kg or 3.2 mg His/kg body weight). Compared to ZnO, MDZnO showed a lag in peak time and a lengthy period of continued high plasma zinc concentration after the single oral administration of zinc compounds. Addition of His to MDZnO elevated serum zinc concentration. Serum zinc concentration (area under the curve) in rats administered MDZnO with His was significantly higher than in rats administered distilled water (p<0.05). Liver zinc level was significantly higher in rats administered MDZnO with His compared with control rats (p<0.05), although the level was not affected by the administration with ZnO alone, ZnO+His, or MDZnO alone. In conclusion, the solubility of ZnO was elevated by the micronised dispersion tecnique and an in vivo study using zinc-deficient rats confirmed that its bioavailability was significantly improved compared to ZnO and the coadministration of His additively enhanced the bioavailability of MDZnO.

The effects of initial hemostatic period on the mechanical strength and transformation of apatite cement.

It is well known that apatite cement causes inflammatory response if it is exposed to blood before setting. In this respect, the hemostatic procedure is very important. However, it has not been clarified how initial hemostasis affects the other basic properties of apatite cement. In the present study, the effect of initial hemostasis on the setting reaction was simulated by allowing the apatite cement paste to be hardened in an incubator for 1 to 30 minutes and then immersed in saline up to 7 days. We found faster transformation of apatite cement to apatitic mineral and higher mechanical strength of the set mass when the cement paste underwent a longer pre-hardening period. We also found that earlier exposure of apatite cement to saline resulted in a set mass with larger porosity. It is thought that the larger porosity of the cement is caused by the penetration of liquid into the cement paste, thus leading to lower mechanical strength and slower transformation of the apatite cement to apatitic mineral. We concluded, therefore, that hemostatic procedure is important not only to prevent inflammatory response but also to obtain a set mass with higher mechanical strength and faster transformation to apatitic mineral.

Comparison of the prevalence of ventricular and supraventricular premature beats with 24-hour Holter electrocardiography between hypertensive and normotensive shift workers in a manufacturing company.

We conducted 24-hour Holter electrocardiography (ECG) among shift workers to assess whether there were differences in the prevalence of ventricular apd supraventricular premature beats between hypertensive (HT) and normotensive (NT) workers. Among the selected 24 male shift workers, 20 were fitted with 24-hour Holter ECG monitors. Nine workers were in the HT group and 11 the NT group. The prevalence of isolated supraventricular premature beats (SVPBs) and SVPB runs were higher in the HT group than in the NT group, but without statistical significance. The prevalence of ventricular premature beats (VPBs) was similar between groups. One worker in each group experienced > or = 720 VPBs per 24 hours, while the worker in the HT group was detected as having a short run of VPBs. The results suggested the necessity of a larger scale study to clarify an association between hypertension and arrhythmias using 24-hour Holter electrocardiography.