A simple method for detecting breakthroughs in used chemical cartridges.

This study was intended to develop a simple method using a gas detector tube to detect the end of the service lives of chemical cartridges for organic solvent vapors. The practical usefulness of this method was confirmed by two series of experimental observations of cartridge service lives: (1) The breakthrough times for six organic solvents were determined by passing a test airflow through a cartridge, and the concentration at each breakthrough was measured with a gas chromatograph (GC). These GC-obtained concentrations were compared with the migrated vapor concentrations through each broken cartridge measured with a gas detector tube. (2) CS2 breakthrough of the cartridges used on 32 viscose rayon workers were measured with detector tubes, after which the residual service life of each cartridge was determined. In laboratory experiments the released concentrations detected by the gas detector tube were approximately equal to the final leak concentrations measured by GC. In a field survey the used cartridges exhibiting a stain of CS2 from detector tubes for concentrations greater than 4 ppm were found not to have enough residual adsorption capacity for CS2. Migrated concentrations of CS2 measured with detector tubes were found to be a reasonable predictor of remaining service life.

Lung lesions induced by intratracheal instillation of vanadium pentoxide powder in rats.

To clarify acute toxicity and histopathological changes in the lung after exposure to V2O5 powder, rats (SD, male, n=66) were observed for 4 weeks after an intratracheal administration of V2O5 powder (geometric mean diameter 0.31 microm, geomertic standard deviation sigmag=2.19) at three doses (0.88, 3.0, 13.0 mg/kg body weight). The histopathological lung lesions were developed dose-dependently, and characterized by exudative inflammation, injury of alveolar macrophages, and swelling and mucous degeneration in the broncho-bronchiolar epithelia. Growth rate of the V2O5 powder-instilled rat was also retarded dose-dependently. The V2O5 powder used was composed of not coagulated but well dispersed particles consisting of vanadium pentoxide of more than 99.8% (w/w) with vanadium tetraoxide of less than 0.2%. The V2O5 powder was found to be 8 times more soluble in an artificial biological fluid "Gamble's solution" than in a pure water. From the present findings as well as those from the related literature, it was inferred that the histopathological lesions induced by the intratracheally instilled V2O5 powder are caused not only by the V2O5 particles per se but also by vanadium ions dissolved from the particles into the lung fluid.

Job stress, social support at work, and insomnia in Japanese shift workers.

A cross-sectional study was conducted to clarify the contribution of psychological job stress to insomnia in shift workers. A self-administered questionnaire concerning job stress, sleep, depressive symptoms and lifestyle factors was submitted to a sample of 530 rotating shift workers of age 18-59 years (mean age 27) in an electric equipment manufacturing company. Perceived job stress, i.e., job demands, job control and social support at work, was assessed using the Japanese version of the Job Content Questionnaire. Insomnia was regarded as prevalent if the workers had at least one of the following symptoms in the last year; less than 30 minutes to fall asleep, difficulty in maintaining sleep, or early morning awakening almost everyday. Overall prevalence was 37.8%. Logistic regression analyses while adjusting relevant factors showed that lower social support at work was significantly associated with a greater risk of insomnia than the higher social support (adjusted OR 2.5). Higher job strain with lower social support at work increased the risk, compared to lower strain with higher support at work (crude OR 1.8; adjusted OR 1.5). Our findings suggest the low social support at work independently associated with insomnia in shift workers.

Maintenance of alertness and performance by a brief nap after lunch under prior sleep deficit.

We examined the effects of a 15-min nap after lunch on subsequent alertness, performance, and autonomic function following a short sleep the preceding night. Subjects were 12 healthy students who had slept for only 4 hours the night before being tested. They experienced both nap and no-nap conditions in a counterbalanced order, at least a week apart. The nap condition included a 15-min nap opportunity (12:30-12:45) in bed with polygraphic monitoring. We measured the P300 event-related potential, subjective sleepiness (Visual Analog Scale), and electrocardiogram (ECG) at 10:00, 13:15, and 16:15, and task performance (logical reasoning and digit span) at 10:00, 11:30, 13:15, 14:45, 16:15, and 17:45. Mean home sleep measured by actigraphy was 3.5 hours under both conditions. At 13:15, the P300 latency after the nap was significantly shorter than after no nap, but its amplitude was not affected by napping. Subjective sleepiness at 13:15 and 14:45 was significantly lower, and accuracy of logical reasoning at 13:15 was significantly higher after the nap than after no nap. No other performance measures or the ECG R-R interval variability parameters differed significantly between the nap and no-nap conditions. Mean total sleep time during the nap was 10.2 min, and no stage 3 and 4 sleep was observed. The above results suggest that under prior sleep deficit, a 15-min nap during post-lunch rest maintains subsequent alertness and performance, particularly in the mid-afternoon.

Construction of an exposure chamber for animals and its use for inhalation exposure to welding fumes and gases.

An inhalation exposure system, consisting of an inhalation chamber and an generating and feeding device for welding fumes and gases with a welding robot, was constructed and examined for its application to experimental toxicology for ventilatory responses of conscious rats to welding fumes and gases. The exposure system allowed an inhalation of fresh welding fumes and gases, and could supply airflow containing stable concentrations of fumes and ozone even the levels exceeding those corresponding occupational exposure limit values were supplied into the exposure chamber. The air temperature in the chamber was kept constant under rat's physiological conditions. Rats were exposed to fresh welding fumes and gases and examined for their ventilatory responses with a body plethysmograph in the chamber. A transient increase in breathing frequency with a concomitant decrease in the tidal volume was observed within several minutes immediately after the start of welding operation. The rapid, shallow breathing response disappears after repeated exposures, indicating rapid adaptation of this ventilatory response to inhalation of welding fumes and gases.

Laboratory measurement of hazardous fumes and gases at a point corresponding to breathing zone of welder during a CO2 arc welding.

Concentrations of fumes, ozone (O3), carbon monoxide (CO), nitric oxide (NO), manganese (Mn) and total and hexavalent chromium (Cr) as well as size distribution of fumes were measured at a point corresponding to the welder's breathing zone during CO2-arc welding, using a welding robot and three kinds of wires. Concentrations of fumes, O3, CO, Mn and total-Cr were found to exceed their corresponding occupational exposure limit (OEL) values, while the concentrations of NO and Cr(VI) were below those OEL levels. Airborne concentration of Mn exceeded its OEL value, and the Mn content was 8 times higher in welding fumes than in the wire. Using an additive equation of OEL and exposure concentration of each hazardous component, health risk in welders with combined exposure to welding fumes and gases was assessed as 18.6 to 46.0 times of OEL, which exceeded the unity. This finding suggests that effective protection of welders from the exposure can be attained by use of the supplied-air respirator or combined use of a dust respirator and a local exhaust system.

Nurses' workload associated with 16-h night shifts. II: Effects of a nap taken during the shifts.

This study aimed at examining the effects on the subjective symptoms in nurses of both timing and length of a 2-h nap during a 16-h night shift. Compared to pre-nap levels, sleepiness, fatigue, and dullness increased immediately after napping. Afterwards, sleepiness decreased significantly, and the other symptoms returned to the pre-nap values. The nurses' subjective symptoms after napping were not associated with the timing of the nap and post-nap fatigue lasted longer as the nap time increased (> 1.5 h). These results suggest that for effective napping during long night shifts, the nap length should be determined carefully to avoid persistent sleep inertia.

Shift work-related problems in 16-h night shift nurses (1): Development of an automated data processing system for questionnaires, heart rate, physical activity and posture.

To assess the shift work-related problems associated with a 16-h night shift in a two-shift system, we took the following important factors into consideration; the interaction between circadian rhythms and the longer night shift, the type of morningness and eveningness experienced, the subjective sleep feeling, the subjects' daily behavior, the effectiveness of taking a nap during the long night shift, and finally the effectiveness of using several different kinds of measuring devices. Included among the measuring devices used were a standard questionnaire, repetitive self-assessment of subjective symptoms and daily behavior at short intervals, and a continuous recording of such objective indices as physical activity and heart rate. A potential problem lies in the fact that field studies that use such measures tend to produce a mass of data, and are thus faced with the accompanying technical problem of analyzing such a large amount of data (time, effort and cost). To solve the data analysis problem, we developed an automated data processing system. Through the use of an image scanner with a paper feeder, standard paper, an optical character recognition function and common application software, we were able to analyze a mass of data continuously and automatically within a short time. Our system should prove useful for field studies that produce a large amount of data collected with several different kinds of measuring devices.

Shift work-related problems in 16-h night shift nurses (2): Effects on subjective symptoms, physical activity, heart rate, and sleep.

We compared the shift work-related problems between 16-h night shift and 8-h evening/night shifts among nurses in a university hospital with respect to subjective symptoms, physical activity, heart rate (HR), and sleep. The nurses of one group (n = 20) worked a 16-h night shift under a rotating two-shift system, while those of the other group (n = 20) worked an 8-h evening or night shift under a rotating three-shift system. The 16-h night shift was staffed by three or four nurses who alternately took a 2-h nap during the shift, and had at least one day off after each shift. Subjective symptoms and daily behavior were measured every 30 min by the nurses before, during, after each shift as well as during days off using a time-budget method. Also, physical activity, heart rate (HR), and posture were recorded during shifts. The results showed similar or lower levels of sleepiness, difficulty in concentration, fatigue, physical activity, and HR during the 16-h shift compared to the 8-h shifts. No differences in subjective symptoms between the two shift schedules were observed before or after the shifts or during days off. The main sleep was longer after the shifts and during days off in the 16-h shift group than in the 8-h shift group. Our results suggest that the work-related problems in 16-h night shift nurses may not be excessively greater than those in 8-h evening/night shift nurses, as long as appropriate countermeasures are taken during and after the extended shift.

Hexavalent chromium responsible for lung lesions induced by intratracheal instillation of chromium fumes in rats.

Lung toxicity of chromium fumes (Cr fumes) was examined by a single intratracheal instillation into rats of 10.6 mg and 21.3 mg Cr fumes/kg body weight and by repeated (3 times) instillations of 10.8 mg and 21.7 mg Cr fumes/kg. The pathological changes were compared with those induced by single administrations of 3.2 mg and 19.2 mg Na2CO3 solution-insoluble fraction of Cr fumes (Cr-Fr)/kg and 20.8 mg commercially available chromium (III) oxide powder (Cr (III) oxide)/kg. Single and repeated administrations of Cr fumes suppressed growth rate in a dose-dependent manner, but administrations of Cr-Fr and Cr (III) oxide did not. A single administration of Cr fumes produced granulomas in the entire airways and alveoli with progressive fibrotic changes, as well as severe mobilization and destruction of macrophages and foamy cells. Those histopathological changes were aggravated by the repeated administration of Cr fumes. On the other hand, single administrations of Cr-Fr and Cr (III) oxide produced no remarkable histopathological changes. Cr fumes were found to be composed of 73.5% chromium (III) oxide and 26.5% chromium (VI) oxide. The primary particles of Cr fumes and Cr-Fr were similar, 0.02 micron in size (sigma g: 1.25), and Cr (III) oxide particles were 0.30 micron in size (sigma g: 1.53), measured by analytical electron microscopy (ATEM). Diffuse clusters of the primary particles in Cr fumes were identified as Cr (VI) oxide. The present results suggested that the lung toxicity of Cr fumes was mainly caused by these Cr (VI) oxide (CrO3) particles in Cr fumes.

A new model rat with acute bronchiolitis and its application to research on the toxicology of inhaled particulate matter.

The aim of the present study was to establish a useful animal model that simulates humans sensitive to inhaled particulate matter (PM). We have developed a new rat model of acute bronchiolitis (Br) by exposing animals to NiCl2 (Ni) aerosols for five days. Three days following the Ni exposure, the animals developed signs of tachypnea, mucous hypersecretion, and bronchiolar inflammation which seemed to progress quickly during the fourth to fifth day. They recovered from lesions after four weeks in clean air. To assess the sensitivity of the Br rats to inhaled particles, two kinds of PM of respirable size were tested with doses similar to or a little higher to the recommended threshold limit values (TLVs) for the working environment in Japan. Titanium dioxide (TiO2 = Ti) was chosen as an inert and insoluble particles and vanadium pentoxide (V2O5 = V), as a representative soluble and toxic airborne material. The Br rats exposed to either Ti or V were compared the pathological changes in the lungs and the clearance of particles to those in normal control or Br rats kept in clean air. The following significant differences were observed in Br rats: 1. delayed recovery from pre-existing lesions or exacerbated inflammation, 2. reductions in deposition and clearance rate of inhaled particles with the progress of lesions. The present results suggest that Br rats are more susceptible to inhaled particles than control rats. Therefore, concentrations of particulate matter lower than the TLVs for Japan, which have no harmful effects on normal lungs, may not always be safe in the case of pre-existing lung inflammation.

Sleep inertia and autonomic effects on post-nap P300 event-related potential.

The objective of this study was to examine the relationship between post-nap measures of alertness and performance and non-rapid eye movement (NREM) sleep and parasympathetic activity during brief naps. Thirty healthy subjects were randomly assigned to no-nap, 15-min, and 45-min nap conditions after normal home sleep at prior night. Each nap was taken after lunch and monitored by electroencephalogram (EEG), electromyogram, electrooculogram, and electrocardiogram (ECG). Deep NREM sleep was quantified by EEG delta power density and the parasympathetic activity was quantified by the ECG high-frequency (HF) component of R-R interval variability during the 15- and 45-min naps. The P300 event-related potential, subjective sleepiness, and performance on a 90-min English transcription task were measured 30 min and 3 hr after the naps and tested for their association with the EEG and ECG measures. A positive correlation was obtained between EEG delta power density during the naps and P300 latency 30 min after the naps (r = 0.476, p < 0.05). The HF component during the naps was negatively correlated with the P300 latency 3 hr after the naps (r = -0.519, p < 0.05). These results suggest that the sleep inertia prolongs the P300 latency immediately after the naps, and that the parasympathetic predominance during the naps may improve subsequent alertness as assessed by the shortened P300 latency 3 hr after the naps.

Brief naps during post-lunch rest: effects on alertness, performance, and autonomic balance.

This study was designed to examine the effects of brief naps taken after lunch on alertness, performance, and autonomic balance. Three groups each comprising ten healthy subjects, who had slept normally at home the previous night, were randomly assigned to groups taking one of three 'lengths of nap (0, 15, and 45 min) after lunch. The P300, an event-related potential which is a neurophysiological correlate of cognitive function, subjective sleepiness (visual analogue scale), and electrocardiogram were measured before, 30 min after, and 3 h after the naps. Each measurement was followed by an English transcription task lasting 90 min. The P300 latency was significantly shorter after the 15-min than after the 45-min nap, or after no nap had been taken, while its amplitude was not affected by the length of nap. Subjective sleepiness was lower after both naps than after no nap. The task performance was significantly better during the second half of the last task session after the 15-min nap than after no nap. The high-frequency component of the R-R interval spectrum increased significantly during the 45-min nap, showing a temporary shift to a predominance of the parasympathetic nervous system. Mean total sleep times during the 15- and 45-min naps were 7.3 and 30.1 min, respectively. These results would indicate that the 15-min nap may serve to shorten the stimulus evaluation time, reducing subjective sleepiness, and slightly improving task performance. Our data demonstrated that in our subjects a brief nap after lunch was effective for enhancing subsequent alertness and performance after normal sleep the previous night.

Adaptation of extrapulmonary responses to ozone exposure in conscious rats.

The adaptation of cardiovascular and thermoregulatory responses to ozone (O3) was examined by repeated exposure of electrocardiographic (ECG) electrode- and thermistor sensor-implanted rats to O3 for 4 consecutive days (8 hrs/day). Circadian rhythms of heart rate (HR) and abdominal core temperature (Tco) were disrupted on the first and second O3 exposure days in a concentration dependent manner. The 8-hr and 12-hr averaged values of HR and Tco during the exposure period and the dark post-exposure period, respectively, decreased significantly on the first and second exposure days. The decreased HR and Tco recovered to respective control values after small but significant rebound increases on the third and fourth days of O3 exposure. The adaptation of the extrapulmonary responses to O3 exposure was discussed in light of the previously reported time periods required to abolish the spontaneous breathing, biochemical, cellular, and morphological responses to O3.

Age-related changes in ventilatory and heart rate responses to acute ozone exposure in the conscious rat.

To evaluate the effect of age on toxicant-induced pulmonary and extrapulmonary changes, we examined the effect of inhalation exposure to oxone (O3) on the ventilatory and heart rate (HR) responses in 4-6 and 20-22-month-old male rats. The rats, chronically implanted with an electrocardiographic (ECG) electrodes, were placed in a head-out plethysmograph for continuous ventilatory measurements of tidal volume and breathing frequency. Simultaneous measurements of HR were also obtained. A 6-hr exposure of each rat to filtered air was followed 2 days later by a 5-hr exposure to 0.1 ppm O3, 5 days later by a 5-hr exposure to 0.3 ppm O3 and 10 days later by a 5-hr exposure to 0.5 ppm O3. Each of the O3 exposures was preceded by a 1-hr exposure to filtered air. Transient rapid shallow breathing with slightly increased HR appeared 1-2 min after the start of O3 exposure. It was suggested on the basis of the electroencephalographic (EEG) activity of the olfactory bulb that this transient response was mediated through olfactory sensation. Persistent rapid shallow breathing with a progressive decrease in HR occurred with a latent period of 1-2 hr. The last 90-min averaged values for relative minute ventilation tended to decrease with the increase in the level of exposure to O3 and these values for young rats were significantly lower than those for old rats. An exposure of young rats to 0.1 ppm O3 for shorter than 5 hr significantly decreased the tidal volume and HR and increased breathing frequency, but no significant changes were observed in old rats. There were no differences between young and old rats in non-observable-adverse-effect-levels (NOAELs) for the O3-induced persistent ventilatory and HR responses, when the NOAELs were determined by exposure to 0.3 and 0.5 ppm O3. The present results, as well as the reported decrease in body temperature and blood pressure, suggested that the age-related changes in patterns and magnitude of the persistent rapid shallow breathing with a progressive decrease in HR are mediated through some age-related defense mechanism acting against O3 inhalation. The validity of the occupational exposure limit for O3 in workplaces was discussed in the light of the present findings.

Effects of a single cognitive task on power spectra of R-R interval and arterial blood pressure.

The present study was designed to examine the effects of a single cognitively demanding task on the R-R interval and systolic blood pressure (BP) power spectra. Ten healthy volunteers were asked to perform an English transcription task for 90 minutes using a word processor, and to read books as a non-task control. The influences of both posture and respiration were controlled in assessing the task effects. Performance of the single cognitive task significantly increased the normalized low-frequency component (% LF) of the BP spectrum following the task, as compared to the non-task control in the sitting position. However, the supine position did not produce the post-task increase in % LF of the BP spectrum. The spectral components of the R-R interval spectrum remained unchanged after the task. These results suggest that the post-task increase in sympathetic activity may be reflected by the BP spectrum under sympathetic predominance in the sitting position.

Effects of single and repeated cognitive tasks on autonomic balance as observed by an analysis of R-R intervals.

The effects on sympathic-parasympathetic nervous system balance of single exposure and repeated exposures to a cognitively demanding task were examined by power spectrum analysis of cardiac R-R intervals. In the single task experiment, 32 healthy subjects engaged in a 90-min English language transcription task and in 90-min reading as a nontask control. In the repeated task experiment, 14 subjects experienced either intermittent exposure to the transcription task until late at night, or daytime exposure to the transcription task followed by relax wakefulness until sleep onset. The single task exposure significantly increased the normalized low frequency component (%LF; 0.05-0.15 Hz) of the R-R interval spectrum compared with the nontask control, but there was no significant task difference in the normalized high frequency component (0.15-0.50 Hz). The increased %LF values immediately returned to control levels after cessation of the task. Repeated exposure to the cognitive task until late at night produced a significantly greater %LF during the first nonrapid eye movement sleep period when compared to relaxed wakefulness. These results would suggest that a single exposure to a cognitive task may produce a shift to sympathetic nervous system dominance only during the period of the task, whereas repeated exposures to a cognitive task until late at night may produce a shift to sympathetic nervous system dominance which lasts into the subsequent sleep period.

Suppression of electroencephalogram delta power density during non-rapid eye movement sleep as a result of a prolonged cognitive task prior to sleep onset.

The effects of a prolonged cognitive task prior to sleep onset on subsequent sleep patterns were examined in 14 healthy subjects who were randomly assigned to two conditions. Those assigned to a working condition were asked to engage in a prolonged cognitive task until close to bedtime (0200 hours), whereas those assigned to a relaxing condition were instructed to perform the same task during the daytime and then to stay awake in a relaxed state until the same bedtime as the work group. Visual scoring of sleep stages showed no significant differences in the amounts of stage 4 and slow wave sleep (stage 3+4) between the two conditions. Power spectrum analysis of sleep electroencephalogram (EEG) revealed that the EEG delta (0.5-4.0 Hz) power density in the first non-rapid eye movement (REM)-REM sleep cycle was significantly lower following the prolonged cognitive task prior to sleep onset than following the relaxed wakefulness and that the decreased EEG delta power density in the first sleep cycle was not compensated for during the later part of the sleep. These findings would indicate that the prolonged cognitive task prior to sleep onset may suppress EEG delta power density during subsequent sleep, suggesting that such a task may interfere with the development of deep non-REM sleep.

Effect of subchronic inhalation exposure to low-level trichloroethylene on heart rate and wakefulness-sleep in freely moving rats.

Electroencephalographic (EEG) and heart rate (HR) responses to repeated 8-h exposure for 6 weeks to trichloroethylene (TRI) vapor of 50, 100 and 300 ppm were examined in freely moving rats with chronically implanted electrodes for polygraphic recordings. Exposure to all the TRI levels significantly decreased amount of time spent in wakefulness (W) during the exposure period. Exposure to 100 ppm and higher levels significantly decreased the time-averaged HR during the post-exposure period. The HRs during the stages of slow-wave sleep (SWS) and paradoxical sleep (PS) were significantly lowered after cessation of exposure to 50 ppm. When compared with the previously reported responses to short-term exposure to TRI (Arito H, et al. Arch Toxicol 1993; 67: 193-199), significant changes in wakefulness-sleep and HR elicited by the long-term exposure appeared at lower exposure levels. The EEG and HR effects of long-term exposure to TRI of 50 ppm or higher levels are discussed for their causative factors on the basis of the reported findings and for validity of the ongoing biological exposure limit value of TRI with reference to documentations enlisted for ACGIH's TLV of 50 ppm (ACGIH. Documentation of the threshold limit values and biological exposure indices, 5th ed. 1986: 595-597).

Age-related changes in electrocardiographic responses to trichloroethylene inhalation in conscious rats.

Age-related effects of trichloroethylene (TRI) inhalation on heart rate (HR), its circadian rhythm, the incidence of spontaneous bradyarrhythmias (BA) and ventricular premature contractions (VPC) were examined in conscious rats, as was the dependence of arrhythmias on sleep-wakefulness. Indwelling electrodes were used for simultaneous electrocardiographic (ECG), electroencephalographic (EEG) and electromyographic (EMG) measurements in 2, 13, 20 and 26-month old rats. The rats were exposed for 8 hours to 300 ppm TRI followed by exposure to clean air for 7 days, after which they were exposed to 1,000 ppm for 8 hours. The polygraphic recordings were made during 8-hr exposures and for 28 hours thereafter. Control values for all physiological parameters were measured during 36-hr exposure to clean air. The exposure to TRI exacerbated an age-dependent decrease in HR and its circadian amplitude. Although the spontaneous BA incidence decreased with advancing age, the ratio of the number of BA episodes during the post-exposure period after TRI exposure to those during the corresponding period of clean-air exposure increased more pronouncedly for 20 and 26-month old rats than for 2 and 13-month old rats. The number of spontaneous VPC episodes increased for 20 and 26-month old rats but was not affected by the exposure to TRI. Gas chromatographic analysis of TRI and free trichloroethanol (TRI-OH) in the brain and blood of the TRI-exposed rats revealed the prolonged half-life of TRI and the delayed clearance of free TRI-OH from the tissues with advancing age. The age-related exacerbation of those ECG responses to TRI inhalation appears to be brought about in part by the age-related change in the pharmacokinetics of TRI and TRI-OH.