A proximal enhancer regulates RORA expression during early human Th17 cell differentiation

BACKGROUND

Gene regulatory elements, such as enhancers, greatly influence cell identity by tuning the transcriptional activity of specific cell types. Dynamics of enhancer landscape during early human Th17 cell differentiation remains incompletely understood. Leveraging ATAC-seq-based profiling of chromatin accessibility and comprehensive analysis of key histone marks, we identified a repertoire of potential enhancers that potentially exert control over the fate specification of Th17 cells. We found 23 SNPs associated with autoimmune diseases within Th17-enhancers that precisely overlapped with the binding sites of transcription factors actively engaged in T-cell functions. Among the Th17-specific enhancers, we identified an enhancer in the intron of RORA and demonstrated that this enhancer positively regulates RORA transcription. Moreover, CRISPR-Cas9-mediated deletion of a transcription factor binding site-rich region within the identified RORA enhancer confirmed its role in regulating RORA transcription. These findings provide profound insights into the potential mechanism by which the RORA enhancer orchestrates Th17 differentiation.

PIM kinases regulate early human Th17 cell differentiation

The serine/threonine-specific Moloney murine leukemia virus (PIM) kinase family (i.e., PIM1, PIM2, and PIM3) has been extensively studied in tumorigenesis. PIM kinases are downstream of several cytokine signaling pathways that drive immune-mediated diseases. Uncontrolled T helper 17 (Th17) cell activation has been associated with the pathogenesis of autoimmunity. However, the detailed molecular function of PIMs in human Th17 cell regulation has yet to be studied. In the present study, we comprehensively investigated how the three PIMs simultaneously alter transcriptional gene regulation during early human Th17 cell differentiation. By combining PIM triple knockdown with bulk and scRNA-seq approaches, we found that PIM deficiency promotes the early expression of key Th17-related genes while suppressing Th1-lineage genes. Further, PIMs modulate Th cell signaling, potentially via STAT1 and STAT3. Overall, our study highlights the inhibitory role of PIMs in human Th17 cell differentiation, thereby suggesting their association with autoimmune phenotypes.

Cell-connectivity-guided trajectory inference from single-cell data

MOTIVATION

Single-cell RNA-sequencing enables cell-level investigation of cell differentiation, which can be modelled using trajectory inference methods. While tremendous effort has been put into designing these methods, inferring accurate trajectories automatically remains difficult. Therefore, the standard approach involves testing different trajectory inference methods and picking the trajectory giving the most biologically sensible model. As the default parameters are often suboptimal, their tuning requires methodological expertise.

RESULTS

We introduce Totem, an open-source, easy-to-use R package designed to facilitate inference of tree-shaped trajectories from single-cell data. Totem generates a large number of clustering results, estimates their topologies as minimum spanning trees, and uses them to measure the connectivity of the cells. Besides automatic selection of an appropriate trajectory, cell connectivity enables to visually pinpoint branching points and milestones relevant to the trajectory. Furthermore, testing different trajectories with Totem is fast, easy, and does not require in-depth methodological knowledge.

AVAILABILITY AND IMPLEMENTATION

Totem is available as an R package at https://github.com/elolab/Totem.

Benchmarking methods for detecting differential states between conditions from multi-subject single-cell RNA-seq data

Single-cell RNA-sequencing (scRNA-seq) enables researchers to quantify transcriptomes of thousands of cells simultaneously and study transcriptomic changes between cells. scRNA-seq datasets increasingly include multisubject, multicondition experiments to investigate cell-type-specific differential states (DS) between conditions. This can be performed by first identifying the cell types in all the subjects and then by performing a DS analysis between the conditions within each cell type. Naïve single-cell DS analysis methods that treat cells statistically independent are subject to false positives in the presence of variation between biological replicates, an issue known as the pseudoreplicate bias. While several methods have already been introduced to carry out the statistical testing in multisubject scRNA-seq analysis, comparisons that include all these methods are currently lacking. Here, we performed a comprehensive comparison of 18 methods for the identification of DS changes between conditions from multisubject scRNA-seq data. Our results suggest that the pseudobulk methods performed generally best. Both pseudobulks and mixed models that model the subjects as a random effect were superior compared with the naïve single-cell methods that do not model the subjects in any way. While the naïve models achieved higher sensitivity than the pseudobulk methods and the mixed models, they were subject to a high number of false positives. In addition, accounting for subjects through latent variable modeling did not improve the performance of the naïve methods.

scShaper: an ensemble method for fast and accurate linear trajectory inference from single-cell RNA-seq data

MOTIVATION

Computational models are needed to infer a representation of the cells, i.e. a trajectory, from single-cell RNA-sequencing data that model cell differentiation during a dynamic process. Although many trajectory inference methods exist, their performance varies greatly depending on the dataset and hence there is a need to establish more accurate, better generalizable methods.

RESULTS

We introduce scShaper, a new trajectory inference method that enables accurate linear trajectory inference. The ensemble approach of scShaper generates a continuous smooth pseudotime based on a set of discrete pseudotimes. We demonstrate that scShaper is able to infer accurate trajectories for a variety of trigonometric trajectories, including many for which the commonly used principal curves method fails. A comprehensive benchmarking with state-of-the-art methods revealed that scShaper achieved superior accuracy of the cell ordering and, in particular, the differentially expressed genes. Moreover, scShaper is a fast method with few hyperparameters, making it a promising alternative to the principal curves method for linear pseudotemporal ordering.

AVAILABILITY AND IMPLEMENTATION

scShaper is available as an R package at https://github.com/elolab/scshaper. The test data are available at https://doi.org/10.5281/zenodo.5734488.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

ILoReg: a tool for high-resolution cell population identification from single-cell RNA-seq data

MOTIVATION

Single-cell RNA-seq allows researchers to identify cell populations based on unsupervised clustering of the transcriptome. However, subpopulations can have only subtle transcriptomic differences and the high dimensionality of the data makes their identification challenging.

RESULTS

We introduce ILoReg, an R package implementing a new cell population identification method that improves identification of cell populations with subtle differences through a probabilistic feature extraction step that is applied before clustering and visualization. The feature extraction is performed using a novel machine learning algorithm, called iterative clustering projection (ICP), that uses logistic regression and clustering similarity comparison to iteratively cluster data. Remarkably, ICP also manages to integrate feature selection with the clustering through L1-regularization, enabling the identification of genes that are differentially expressed between cell populations. By combining solutions of multiple ICP runs into a single consensus solution, ILoReg creates a representation that enables investigating cell populations with a high resolution. In particular, we show that the visualization of ILoReg allows segregation of immune and pancreatic cell populations in a more pronounced manner compared with current state-of-the-art methods.

AVAILABILITY AND IMPLEMENTATION

ILoReg is available as an R package at https://bioconductor.org/packages/ILoReg.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Corrigendum: Adult-Onset Anti-Citrullinated Peptide Antibody-Negative Destructive Rheumatoid Arthritis Is Characterized by a Disease-Specific CD8+ T Lymphocyte Signature

[This corrects the article DOI: 10.3389/fimmu.2020.578848.].

Evaluation of tools for identifying large copy number variations from ultra-low-coverage whole-genome sequencing data

BACKGROUND

Detection of copy number variations (CNVs) from high-throughput next-generation whole-genome sequencing (WGS) data has become a widely used research method during the recent years. However, only a little is known about the applicability of the developed algorithms to ultra-low-coverage (0.0005-0.8×) data that is used in various research and clinical applications, such as digital karyotyping and single-cell CNV detection.

RESULT

Here, the performance of six popular read-depth based CNV detection algorithms (BIC-seq2, Canvas, CNVnator, FREEC, HMMcopy, and QDNAseq) was studied using ultra-low-coverage WGS data. Real-world array- and karyotyping kit-based validation were used as a benchmark in the evaluation. Additionally, ultra-low-coverage WGS data was simulated to investigate the ability of the algorithms to identify CNVs in the sex chromosomes and the theoretical minimum coverage at which these tools can accurately function. Our results suggest that while all the methods were able to detect large CNVs, many methods were susceptible to producing false positives when smaller CNVs (< 2 Mbp) were detected. There was also significant variability in their ability to identify CNVs in the sex chromosomes. Overall, BIC-seq2 was found to be the best method in terms of statistical performance. However, its significant drawback was by far the slowest runtime among the methods (> 3 h) compared with FREEC (~ 3 min), which we considered the second-best method.

CONCLUSIONS

Our comparative analysis demonstrates that CNV detection from ultra-low-coverage WGS data can be a highly accurate method for the detection of large copy number variations when their length is in millions of base pairs. These findings facilitate applications that utilize ultra-low-coverage CNV detection.

Adult-Onset Anti-Citrullinated Peptide Antibody-Negative Destructive Rheumatoid Arthritis Is Characterized by a Disease-Specific CD8+ T Lymphocyte Signature

Rheumatoid arthritis (RA) is a complex autoimmune disease targeting synovial joints. Traditionally, RA is divided into seropositive (SP) and seronegative (SN) disease forms, the latter consisting of an array of unrelated diseases with joint involvement. Recently, we described a severe form of SN-RA that associates with characteristic joint destruction. Here, we sought biological characteristics to differentiate this rare but aggressive anti-citrullinated peptide antibody-negative destructive RA (CND-RA) from early seropositive (SP-RA) and seronegative rheumatoid arthritis (SN-RA). We also aimed to study cytotoxic CD8+ lymphocytes in autoimmune arthritis. CND-RA, SP-RA and SN-RA were compared to healthy controls to reveal differences in T-cell receptor beta (TCRβ) repertoire, cytokine levels and autoantibody repertoires. Whole-exome sequencing (WES) followed by single-cell RNA-sequencing (sc-RNA-seq) was performed to study somatic mutations in a clonally expanded CD8+ lymphocyte population in an index patient. A unique TCRβ signature was detected in CND-RA patients. In addition, CND-RA patients expressed higher levels of the bone destruction-associated TNFSF14 cytokine. Blood IgG repertoire from CND-RA patients recognized fewer endogenous proteins than SP-RA patients’ repertoires. Using WES, we detected a stable mutation profile in the clonally expanded CD8+ T-cell population characterized by cytotoxic gene expression signature discovered by sc-RNA-sequencing. Our results identify CND-RA as an independent RA subset and reveal a CND-RA specific TCR signature in the CD8+ lymphocytes. Improved classification of seronegative RA patients underlines the heterogeneity of RA and also, facilitates development of improved therapeutic options for the treatment resistant patients.

Comparing biological information contained in mRNA and non-coding RNAs for classification of lung cancer patients

BACKGROUND

Deciphering the meaning of the human DNA is an outstanding goal which would revolutionize medicine and our way for treating diseases. In recent years, non-coding RNAs have attracted much attention and shown to be functional in part. Yet the importance of these RNAs especially for higher biological functions remains under investigation.

METHODS

In this paper, we analyze RNA-seq data, including non-coding and protein coding RNAs, from lung adenocarcinoma patients, a histologic subtype of non-small-cell lung cancer, with deep learning neural networks and other state-of-the-art classification methods. The purpose of our paper is three-fold. First, we compare the classification performance of different versions of deep belief networks with SVMs, decision trees and random forests. Second, we compare the classification capabilities of protein coding and non-coding RNAs. Third, we study the influence of feature selection on the classification performance.

RESULTS

As a result, we find that deep belief networks perform at least competitively to other state-of-the-art classifiers. Second, data from non-coding RNAs perform better than coding RNAs across a number of different classification methods. This demonstrates the equivalence of predictive information as captured by non-coding RNAs compared to protein coding RNAs, conventionally used in computational diagnostics tasks. Third, we find that feature selection has in general a negative effect on the classification performance which means that unfiltered data with all features give the best classification results.

CONCLUSIONS

Our study is the first to use ncRNAs beyond miRNAs for the computational classification of cancer and for performing a direct comparison of the classification capabilities of protein coding RNAs and non-coding RNAs.

Peripheral blood DNA methylation differences in twin pairs discordant for Alzheimer's disease

BACKGROUND

Alzheimer's disease results from a neurodegenerative process that starts well before the diagnosis can be made. New prognostic or diagnostic markers enabling early intervention into the disease process would be highly valuable. Environmental and lifestyle factors largely modulate the disease risk and may influence the pathogenesis through epigenetic mechanisms, such as DNA methylation. As environmental and lifestyle factors may affect multiple tissues of the body, we hypothesized that the disease-associated DNA methylation signatures are detectable in the peripheral blood of discordant twin pairs.

RESULTS

Comparison of 23 disease discordant Finnish twin pairs with reduced representation bisulfite sequencing revealed peripheral blood DNA methylation differences in 11 genomic regions with at least 15.0% median methylation difference and FDR adjusted p value ≤ 0.05. Several of the affected genes are primarily associated with neuronal functions and pathologies and do not display disease-associated differences in gene expression in blood. The DNA methylation mark in ADARB2 gene was found to be differentially methylated also in the anterior hippocampus, including entorhinal cortex, of non-twin cases and controls. Targeted bisulfite pyrosequencing of the DNA methylation mark in ADARB2 gene in 62 Finnish and Swedish twin pairs revealed that, in addition to the disease status, DNA methylation of this region is influenced by gender, age, zygosity, APOE genotype, and smoking. Further analysis of 120 Swedish twin pairs indicated that this specific DNA methylation mark is not predictive for Alzheimer's disease and becomes differentially methylated after disease onset.

CONCLUSIONS

DNA methylation differences can be detected in the peripheral blood of twin pairs discordant for Alzheimer's disease. These DNA methylation signatures may have value as disease markers and provide insights into the molecular mechanisms of pathogenesis. We found no evidence that the DNA methylation marks would be associated with gene expression in blood. Further studies are needed to elucidate the potential importance of the associated genes in neuronal functions and to validate the prognostic or diagnostic value of the individual marks or marker panels.

Comparing deep belief networks with support vector machines for classifying gene expression data from complex disorders

Genomics data provide great opportunities for translational research and the clinical practice, for example, for predicting disease stages. However, the classification of such data is a challenging task due to their high dimensionality, noise, and heterogeneity. In recent years, deep learning classifiers generated much interest, but due to their complexity, so far, little is known about the utility of this method for genomics. In this paper, we address this problem by studying a computational diagnostics task by classification of breast cancer and inflammatory bowel disease patients based on high‐dimensional gene expression data. We provide a comprehensive analysis of the classification performance of deep belief networks (DBNs) in dependence on its multiple model parameters and in comparison with support vector machines (SVMs). Furthermore, we investigate combined classifiers that integrate DBNs with SVMs. Such a classifier utilizes a DBN as representation learner forming the input for a SVM. Overall, our results provide guidelines for the complex usage of DBN for classifying gene expression data from complex diseases.

Effects of long-term whole-body cold exposures on plasma concentrations of ACTH, beta-endorphin, cortisol, catecholamines and cytokines in healthy females

OBJECTIVE

Cold therapy is used to relieve pain and inflammatory symptoms. The present study was designed to determine the influence of long-term regular exposure to acute cold temperature. Two types of exposure were studied: winter swimming in ice-cold water and whole-body cryotherapy. The outcome was investigated on humoral factors that may account for pain alleviation related to the exposures.

MATERIAL AND METHODS

During the course of 12 weeks, 3 times a week, a group of healthy females (n = 10) was exposed to winter swimming (water 0-2 degrees C) for 20 s and another group (n = 10) to whole-body cryotherapy (air -110 degrees C) for 2 min in a special chamber. Blood specimens were drawn in weeks 1, 2, 4, 8 and 12, on a day when no cold exposure occurred (control specimens) and on a day of cold exposures (cold specimens) before the exposures (0 min), and thereafter at 5 and 35 min.

RESULTS

Plasma ACTH and cortisol in weeks 4-12 on time-points 35 min were significantly lower than in week 1, probably due to habituation, suggesting that neither winter swimming nor whole-body cryotherapy stimulated the pituitary-adrenal cortex axis. Plasma epinephrine was unchanged during both experiments, but norepinephrine showed significant 2-fold to 3-fold increases each time for 12 weeks after both cold exposures. Plasma IL-1-beta, IL-6 or TNF alpha did not show any changes after cold exposure.

CONCLUSIONS

The main finding was the sustained cold-induced stimulation of norepinephrine, which was remarkably similar between exposures. The frequent increase in norepinephrine might have a role in pain alleviation in whole-body cryotherapy and winter swimming.

Lung function after acute and repeated exposures to extremely cold air (-110oC) during whole-body cryotherapy

Whole-body cryotherapy (WBC) is one mode of cold therapy, during which rheumatic patients are exposed to very cold air (-110 degrees C) in minimal clothing. It is also proposed to have a bronchodilatory effect. The aim was to examine the effects of WBC on lung function in healthy humans after acute and repeated exposures. Twenty-five healthy, non-smoking subjects participated in the study. They were exposed to WBC for 2 min three times per week for 12 weeks. The peak expiratory flow rate (PEF) and forced expiratory volume in 1 s (FEV1) were measured before and after (at 2 and 30 min) the first WBC, and then similarly at 4, 8 and 12 weeks. At all time points, after 30 min of the WBC the PEF values were slightly lower compared with values before the WBC, and the reductions reached statistical significance at 1 month (5.1 +/- 1.2%), and at 3 months (3.2 +/- 1.7%). After 30 min of the first WBC, the FEV1 was significantly reduced by 2.3 +/- 0.8%, but no other changes were observed during the study. In conclusion, the WBC induced minor bronchoconstriction in healthy humans instead of proposed bronchodilatation. The WBC seems not to be harmful for lung function, but should be used with caution in susceptible individuals.

Acute and long-term effects of winter swimming and whole-body cryotherapy on plasma antioxidative capacity in healthy women

The effects of severe cold stress on total peroxyl radical trapping antioxidant capacity of plasma (TRAP) were studied in two groups of healthy women: a whole-body cryotherapy group (WBC, n = 10) and a winter swimming group (WS, n = 10). The biovariability of TRAP values was also analysed. The WBC group was exposed to -110 degrees C for 2 min, whereas the exposure for the WS group lasted 20 s in ice-cold water. Sessions were organized three times per week for 12 weeks. Blood specimens were collected at 2, 4, 8 and 12 weeks at rest, 2 and 35 min after the cold exposures and at the corresponding times without cold exposure on a separate day. Conventional methods were used to determine TRAP values. The between-subject variation was 13.6% and the within-subject variation 6.4%. The index of individuality was 0.46, and the index of heterogeneity was 0.079. These results indicate a marked heterogeneity among subjects. During the first 4 weeks, the mean TRAP value significantly increased at 2 min after cold exposure in the WBC group, returning to baseline 35 min after the exposure. Similar changes were observed in the WS group. However, all changes due to cold were relatively mild (<5%). After 4 weeks no changes in TRAP values after the cold exposures were noticed and no long-term changes in basal TRAP values were observed. In the main, regular WBC and WS do not seem to be harmful as far as plasma antioxidative capacity is concerned.

Effect of cold exposure on older humans

Epidemiological studies have shown excess winter mortality particularly in older age groups. A question is how much these statistics are affected by age-related physiological changes in cold thermoregulation and how much due to other factors related to aging. In experimental studies concerning age and cold stress both whole-body and local exposures have been used mostly in resting subjects with minimal clothing. Older persons, particularly men over ca. 60 years, are less able to maintain core temperature during a given cold challenge compared to younger individuals. Older persons have a reduced cutaneous thermal sensitivity, and a reduced subjective thermal perception during cooling. Thus, older people may require a more intense stimulus to perform protective actions against cold stress. Older persons' skin vasoconstrictive response to cold is diminished compared to younger persons, which seems partly related to a reduced skin vasomotor sensitivity to sympathoneuronal stimuli. The cold-induced rise in metabolic rate is attenuated in older persons, but the mechanism is unknown. Both central and peripheral components seem to be involved in the age-related changes in regulatory effector functions. Enhanced aerobic fitness may not give added protection against core cooling during cold stress in the elderly, but seems to attenuate older subjects' heightened blood pressure response to cold. Bronchial responsiveness to face cooling may increase with age. Further studies are needed to examine the age-related changes in non-thermoregulatory responses to cold (e. g. hemodynamics, cardiac function, respiration, autonomic nervous function), and the modifying effects of acute exercise and physical training.

Work ability, physical activity, and cardiorespiratory fitness: 2-year results from Project Active

An adequate level of physical activity may maintain or promote work ability in aging workers. Project Active is a randomized trial comparing a Lifestyle physical activity program with a Structured exercise program in sedentary but healthy adults aged 35 to 60 years. Subjects in both groups received 6 months of intensive intervention followed by 18 months of active follow-up. The total number of subjects was 235, from which 80 subjects participated in the work ability assessment. Primary outcome measures were energy expenditure (kcal.kg-1.day-1), cardiorespiratory fitness (peak oxygen uptake in ml.min-1.kg-1), and the Work Ability Index. At 6 months, daily energy expenditure had increased significantly over baseline (mean +/- SD, from 33.0 +/- 0.9 to 34.4 +/- 1.8 kcal.kg-1.day-1) and was maintained over baseline at 24 months (34.0 +/- 2.5 kcal.kg-1.day-1). The significant increase in energy expenditure was observed particularly in moderate levels of activity. The average percentage of body fat was significantly higher at baseline compared with 6 months and 24 months. Peak oxygen uptake increased from baseline significantly during the first 6 months (from 29.6 +/- 5.7 to 30.6 +/- 6.3 ml.min-1.kg-1) and decreased to the baseline level (29.1 +/- 5.5 ml.min-1.kg-1) at 24 months. At baseline, the average Work Ability Index was 44.2 +/- 4.0, and it remained unchanged at 6 months (44.4 +/- 3.9) and at 24 months (44.2 +/- 3.1). In conclusion, a 2-year physical activity intervention increased daily energy expenditure, reduced body fat, and maintained peak oxygen uptake in healthy, middle-aged, sedentary subjects. The average Work Ability Index score at baseline was excellent and did not change during the 2-year physical activity interventions.

Cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise

In occupational work, continuous repetitive and isometric actions performed with the upper extremity primarily cause local muscle strain and musculoskeletal disorders. They may also have some adverse effects on the cardiorespiratory system, particularly, through the elevation of blood pressure. The aim of the present study was to compare peak cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise. The subjects were 21 untrained healthy men aged 24-45 years. The dynamic hand-grip exercise (DHGE) was performed using the left hand-grip muscles at the 57 (SD 4)% level of each individual's maximal voluntary contraction (MVC) with a frequency of 51 (SD 4) grips x min(-1). The isometric hand-grip exercise (IHGE) was done using the right hand at 46 (SD 3)% of the MVC. The endurance time, ventilatory gas exchange, heart rate (HR) and blood pressure were measured during both kinds of exercise. The mean endurance times for DHGE and IHGE were different, 170 (SD 62) and 99 (SD 27) s, respectively (P < 0.001). During DHGE the mean peak values of the breathing frequency [20 (SD 6) breaths x min(-1)] and tidal volume [0.89 (SD 0.34) l] differed significantly (P < 0.01) from peak values obtained during IHGE [15 (SD 5) breaths x min(-1) and 1.14 (SD 0.32) l, respectively]. The corresponding peak oxygen consumptions, pulmonary ventilations, HR and systolic blood pressures did not differ, and were 0.51 (SD 0.06) and 0.46 (SD 0.11) l x min(-1), 17.1 (SD 3.0) and 16.7 (SD 4.7) l x min(-1), 103 (SD 18) and 102 (SD 17) beats x min(-1), and 156 (SD 17) and 161 (SD 17) mmHg, respectively. The endurance times of both DHGE and IHGE were short (< 240 s). The results indicate that the peak responses for the ventilatory gas exchange, HR and blood pressure were similar during fatiguing DHGE and IHGE, whereas the breathing patterns differed significantly between the two types of exercise. The present findings emphasize the importance of following ergonomic design principles in occupational settings which aim to reduce the output of force, particularly in tasks requiring isometric and/or one-sided repetitive muscle actions.

Physical activity, fitness and body composition of Finnish police officers: a 15-year follow-up study

This study evaluated changes in the physical activity, fitness and body composition of 103 police officers during a 15-year follow-up. The absolute aerobic capacity was similar in 1981 and 1996, muscular performance had declined, and body weight had increased approximately 0.5 kg/year. More than half the subjects (53%) had increased their leisure-time physical activity in 1996. The correlation was significant between physical activity in 1981 and physical fitness in 1996, but weak between physical activity in 1996 and fitness in 1996. It was also significant between waist circumference and waist/hip ratio in 1996 and physical activity during the previous 5 and 15 years. No significant correlations were found between physical activity and work ability or perceived physical or mental job stress. The physical fitness of middle-aged police officers seems to be predicted strongly by physical activity in early adulthood. Therefore health and fitness promotion measures should start at that time. This, together with regular systematic training, should help to sustain work ability of middle-aged police officers.

Physiological strain during kitchen work in relation to maximal and task-specific peak values

Six female and three male subjects from a hospital kitchen volunteered for the study. The subjects were working on a conveyor belt collecting and sorting dirty plates, glasses and cutlery for cleaning. In the study, a medical examination, a maximal clinical exercise test with a 12-lead electrocardiogram (ECG) and a maximal arm cranking test were performed in the laboratory. Further, each subject was studied for 30 min during a normal work shift in the kitchen. Oxygen uptake (VO2) and heart rate (HR) were continuously registered. During the work period, a rating of perceived exertion (RPE) was asked at the 5th, 15th and 30th minute. Physiological responses were measured by a portable system (K4) both in the laboratory and in the field. VO2 and HR measured in the field were proportioned to corresponding maximal values during cycling and to peak values during arm-cranking. The mean VO2 for the male and the female subjects during kitchen work was 0.65 +/- 0.16 l min-1. This corresponded to 24% of VO2max and to 41% of VO2peak during arm-cranking. The difference was significant (p < 0.001). Owing to a magnetic field at the conveyor belt, reliable HR values were obtained only from the female subjects. The mean HR during work among the female subjects was 101 beats min-1. It corresponded to 55% of HRmax and 67% of HRpeak during arm-cranking (p < 0.05). The present study shows that the relative work intensity is markedly higher when it is expressed relative to the corresponding muscle group's VO2peak instead of the VO2max. Similar difference was also seen in the HR response. More task-specific testing of physical capacity may provide improved evaluation of physical strain in a job.

Heart rate and blood pressure responses to isometric exercise in young and older men

The aim of this study was to examine the isometric endurance response and the heart rate and blood pressure responses to isometric exercise in two muscle groups in ten young (age 23-29 years) and seven older (age 54-59 years) physically active men with similar estimated forearm and thigh muscle masses. Isometric contractions were held until fatigue using the finger flexor muscles (handgrip) and with the quadriceps muscle (one-legged knee extension) at 20%, 40%, and 60% of the maximal voluntary contraction (MVC). Heart rate and arterial pressure were related to the the individual's contraction times. The isometric endurance response was longer with handgrip than with one-legged knee extension, but no significant difference was observed between the age groups. The isometric endurance response averaged 542 (SEM 57), 153 (SEM 14), and 59 (SEM 5) s for the handgrip, and 276 (SEM 35), 94 (SEM 10) and 48 (SEM 5) s for the knee extension at the three MVC levels, respectively. Heart rate and blood pressure became higher during one-legged knee extension than during handgrip, and with increasing level of contraction. The older subjects had a lower heart rate and a higher blood pressure response than their younger counterparts, and the differences were more apparent at a higher force level. The results would indicate that increasing age is associated with an altered heart rate and blood pressure response to isometric exercise although it does not affect isometric endurance.

Prediction of acceptable physical work loads based on responses to prolonged arm and leg exercise

Nine healthy men (aged 54-59 years) performed arm crank and leg cycle exercises for 30 min at relative work loads of 50 and 75% of peak oxygen uptake (VO2) for the corresponding muscle group, and for 60 min at a relative work load of 30% of peak VO2 for the corresponding muscle group. In the tests, heart rate (HR), blood pressure, gas exchange variables, rating of perceived exertion (RPE) and blood lactate were measured. At the 75% target exercise level, four subjects interrupted the arm-cranking test, and one subject interrupted the leg-cycle test. Owing to differences in peak values during arm-cranking and leg-cycling, the work load and the VO2 were higher during leg-cycling than during arm-cranking. There was no difference in HR between the work modes, but the HR increased to a greater extent during arm-cranking compared to leg-cycling at the 30% (NS) and 50% (P < 0.05) exercise levels. Similarly, the RPE increased more during arm-cranking compared to leg-cycling at each exercise level. The blood lactate concentration was higher after arm-cranking than after leg-cycling; at the 50% exercise level the difference was statistically significant. The results indicate a higher physiological strain with time during arm exercise than during leg exercise at the same muscle group-specific relative work load. The acceptable physical work load, expressed as the percentage peak VO2 for the corresponding muscle group, should thus be lower during arm exercise than during leg exercise. The RPE and the relative HR, expressed as percentage of peak HR for the corresponding muscle group, however, seem to be comparable indicators for the physiological strain during arm and leg exercise.

Cardiorespiratory and subjective responses to prolonged arm and leg exercise in healthy young and older men

Ten young (aged 23-30 years) and nine older (aged 54-59 years) healthy men with a similar size of limb muscle mass performed arm crank and leg cycle exercise for 30 min at relative exercise intensities of 50% and 75% of maximal oxygen uptake for the corresponding muscle group. In the tests, heart rate, blood pressure, gas exchange variables, rating of perceived exertion and blood lactate concentration were measured. The limb muscle mass was determined by anthropometric measurements. At the 75% target exercise level, four of the older men and two of the young men could not complete the arm-cranking test, and one of the older men and two of the young men could not complete the leg-cycle test. During arm-cranking the absolute exercise intensity was similar for the young and older men because of similar maximal values during arm-cranking. But during leg-cycling the absolute exercise intensity was higher for the young men than for the older men due to the difference in corresponding maximal values. During arm-cranking there were no significant differences in the physiological responses between the age groups except that a higher ventilatory response was noted among the older compared to the young men. During leg-cycling the heart rate values were higher among the young compared to the older men. But, when the heart rate values were expressed as a percentage of maximal heart rate in the corresponding maximal tests, no significant differences between the age groups were found. The results indicated that 30-min of arm or leg exercise at the same relative submaximal exercise intensity produces a similar degree of physiological strain in healthy older compared to young men. During armcranking, the young and the older men exercised at the same external intensity, indicating a similar ability to perform prolonged excercise using smaller muscle groups expressed both in absolute and relative terms.

Physical work capacity in dynamic exercise with differing muscle masses in healthy young and older men

Ten young (aged 23-30 years) and nine older (aged 54-59 years) healthy men with similar estimated limb muscle volumes performed, in random order, three different types of ergometer exercise tests (one-arm cranking, two-arm cranking, and two-leg cycling) up to the maximal level. Values for work load (WL), peak oxygen consumption (V0(2)), peak heart rate (HR), peak ventilation (V(E)), respiratory gas exchange ratio (R), recovery blood lactate concentration [La-], and rating of perceived exertion (RPE) were compared between the age-groups in the given exercise modes. No significant age-related differences in WL, peak V0(2), peak HR, R, [La-], or RPE were found in one-arm or two-arm cranking. During one-arm cranking the mean peak V0(2) was 1.65 (SD 0.26)1*min(-1) among the young men and 1.63 (SD 0.10)l*min(-1) among the older men. Corresponding mean peak V0(2) during two-arm cranking was 2.19 (SD 0.32)1*min(-1) and 2.09 (SD 0.18)1*min(-1), respectively. During one-arm cranking peak V(E) was higher (P <0.05) among the older men compared to the young men. During two-leg cycling the young men showed higher values in WL (P <0.001), peak V0(2) (P <0.001), and peak HR (P <0.001). The mean peak V0(2) was 3.54 (SD 0.24)1*min(-1) among the young men and 3.02 (SD 0.20)1 . min(-1) among the older men. Corresponding mean peak HR was 182 (SD 5) beats*min(-1) and 170 (SD 8) beats*min(-1), respectively. During two-leg cycling, peak V(E), R, [La-], and RPE did not differ between the two age-groups. In summary, the older men with similar sizes of estimated arm and leg muscle volumes as the young men had a reduced physical work capacity in two-leg cycling. In one-arm or two-arm cranking, no significant difference in work capacity was found between the age-groups. These results indicate, that in healthy men, age, at least up to the 6th decade of life, is not necessarily associated with a decline in physical work capacity in exercises using relatively small muscle groups, in which the limiting factors are more peripheral than central.

Energy expenditure and clearing snow: a comparison of shovel and snow pusher

In order to assess the energy demands of manual clearing of snow, nine men did snow clearing work for 15 min with a shovel and a snow pusher. The depth of the snowcover was 400-600 mm representing a very heavy snowfall. Heart rate (HR), oxygen consumption (VO2), pulmonary ventilation (VE), respiratory exchange ratio (R), and rating of perceived exertion (RPE) were determined during the work tasks. HR, VE, R, and RPE were not significantly different between the shovel and snow pusher. HR averaged (+/- SD) 141 +/- 20 b min-1 with the shovel, and 142 +/- 19 beats.min-1 with the snow pusher. VO2 was 2.1 +/- 0.41.min-1 (63 +/- 12%VO2 max) in shovelling and 2.6 +/- 0.51.min-1 (75 +/- 14%VO2max) in snow pushing (p < 0.001). In conclusion manual clearing of snow in conditions representing heavy snowfalls was found to be strenuous physical work, not suitable for persons with cardiac risk factors, but which may serve as a mode of physical training in healthy adults.

Response to rest and exercise in the cold: effects of age and aerobic fitness

The aim of this study was to determine whether age-related differences in the response to cold exposure are due to aging per se or are caused by a reduced maximal oxygen uptake (VO2max) often observed with aging. Three groups of men, 8 young adults (YA), 8 well-trained seniors (TS), and 11 untrained seniors (US), were tested on a cycle ergometer in thermoneutral (22 degrees C) and cold (5 degrees C) conditions during rest and then during exercise (approximately 50 W). In the thermoneutral conditions, 10 min of rest were followed by 10 min of exercise. After 60 min of rest, subjects entered the cold where 30 min of rest were followed by 30 min exercise. The subjects of the three groups had similar body surface area and subcutaneous fat thickness. It was found that rectal temperature (Tre) decreased during rest in the cold and continued to decrease at a higher rate during exercise in TS and US but not in YA. The mean skin temperature was similar in all the groups, except for the thigh temperature, which was lower in YA than in TS and US. Oxygen uptake (VO2) increased during cold, significantly more so at rest than during exercise. YA displayed the highest VO2 during the first 10 min of rest in the cold, whereas TS displayed the highest VO2 during exercise in the cold. Neither aging nor VO2max appeared to affect thermal comfort or cold sensation.(ABSTRACT TRUNCATED AT 250 WORDS)

Capacity for vasodilatation in the forearms of manual and office workers

The aim of the present study was to investigate whether occupational physical work using the arms would have a local training effect on the capacity for vasodilatation in the forearm. The subjects were 13 installation workers, and 13 office workers, who were similar in age, height, and body mass. The installation workers were exposed to heavy manual tasks during most of their workshift, whereas the office workers did no heavy manual exercise. The index of forearm capacity for vasodilatation was the plethysmograph flow response after 10 min of arterial occlusion (240 mmHg, 32 kPa). Systolic and diastolic blood pressure, and skin red cell flux (laser-Doppler) were determined together with the blood flow. In both groups, the dominant arm had significantly higher circumference and volume compared to the nondominant arm, whereas handgrip strength was similar for both the arms. The manual workers had greater volumes in both arms in comparison to the office workers, but handgrip strength did not differ between groups. In both groups, the peak forearm vascular conductance was higher in the dominant arm compared to the nondominant arm. In both forearms, the manual workers exhibited significantly higher peak blood flow, and peak vascular conductance than the office workers. No significant difference in skin blood flow was seen between the groups or arms. In conclusion, the forearms of the manual workers had a greater capacity for vasodilatation compared to the office workers suggesting a local vascular training effect due to frequent exposure to heavy physical work using hands.

Responses to whole body and finger cooling before and after an Antarctic expedition

Eight subjects, who were indoor workers and not habitually exposed to cold, spent 53 days in Antarctica. They did mainly geological field work often requiring the use of bare hands. The effects of the expedition on responses to a whole body cold exposure test, a finger blood flow test and a cold pressor test were studied. After the expedition, during whole-body cooling the time for the onset of shivering was delayed by 36 min (P < 0.001) and forearm and thigh temperatures were 1.5 degrees C higher (P < 0.05) at the end of exposure. During local cooling of the finger with 10 degrees C perfusion, finger vascular resistance was 14.9 (SEM 6.6) mmHg.ml-1.min.100 ml (P < 0.05) lower and finger temperature 3.9 (SEM 0.8) degrees C higher (P < 0.01). However, the decrease in rectal temperature during whole-body cooling was unaltered and the response to a cold pressor test was unchanged. The data would indicate that partial acclimatization to cold had been developed. Changes in forearm temperature were correlated with the duration of cold exposure of the hands (P < 0.05) and finger vascular resistance and finger temperature were correlated with responses to cooling before the expedition (P < 0.001 and P < 0.01, respectively). Because the ambient temperature was not clearly lower in Antarctica in comparison to Finland, the reason for the changes developed seems to be the increased exposure to the outdoor climate in Antarctica.

Circadian variation in peripheral blood flow in relation to core temperature at rest

The aim of the present study was to examine the circadian variation in skin blood flow and its relationship to the rhythm of rectal temperature. Eight young men were confined to continuous bed rest for 24 h in a thermoneutral environment. Rectal temperature, oxygen consumption, and peripheral blood flow (laser-Doppler flowmetry and plethysmography) were measured at intervals of 2 h, except at 2400 hours and 0600 hours. According to the cosinor-method, the mean rectal temperature displayed a statistically significant circadian variation with a minimum at 0400 hours. A significant circadian rhythm was also observed in total finger blood flow, finger laser-Doppler flow, and forearm laser-Doppler flow, but not in total forearm blood flow and forehead laser-Doppler flow. The rhythms of rectal temperature and extremity skin blood flow were phased differently, i.e. the decrease in rectal temperature was preceded by an increase in extremity skin blood flow with an average of 4-h time difference. The results would support the idea that circadian rhythm of core temperature is, at least in part, regulated by variation in extremity skin blood flow.

Physiological responses of firefighting students during simulated smoke-diving in the heat

While wearing a self-contained breathing apparatus and fire-protective clothing, 35 healthy firefighting students aged 19-27 years performed smoke-diving (entry into a smoke-filled room) during a simulated shipboard fire. The mean (+/- SD) ambient temperature inside the simulator was 119 +/- 12 degrees C, and the task lasted 17 +/- 4 min. All subjects were fit according to their maximal oxygen consumption, which was 52.4 +/- 5.2 mL/min/kg (4.08 +/- 0.45 l/min). During the smoke-diving the average heart rate was 150 +/- 13 beats/min (79 +/- 6% of maximal heart rate attained in a cycle-ergometer test), and the peak heart rate was 180 +/- 13 beats/min (95 +/- 6% of maximal heart rate). The estimated oxygen consumption was 2.4 +/- 0.5 L/min (60 +/- 12% of maximal oxygen consumption). Neither ability to tolerate stress (as determined by the instructors) nor previous experience in smoke-diving tasks seemed to influence the heart rate or estimated oxygen consumption during experiment. Smoke-diving was physically very demanding even for the young and fit subjects, showing the importance of regular evaluation of the health and physical fitness of every firefighter who has to carry out smoke-diving tasks.

Quantification of heat balance during work in three types of asbestos-protective clothing

Three types of protective suits for asbestos removal work were tested in a climatic chamber at two ambient temperatures, 25 degrees and 36 degrees C. Four subjects performed 50 min of bicycle exercise at 90 W dressed in shorts, socks and sneakers (NoPS). The same test was carried out with three different types of asbestos-protective suits worn on top of NoPS. Suits were made of GoreTex (GT), polypropylene (PP) and Tyvek (TYV). At 25 degrees C, responses differed very little between suits and thermal strain was small. At 36 degrees C, strain was least with NoPS. TYV resulted in significantly higher physiological and thermal strain than did PP and GT. Evaporative heat loss was maintained at a similar level with less permeable ensembles, but at the expense of increased skin wetness and sweat rate. Measured values compared favourably with calculated values for skin wetness and sweat rate according to ISO 7933, when resultant, rather than standard, basic data for insulation and evaporative resistance of ensembles were used. Results indicate that differences between suits that may be of little importance at normal room temperature become significant at higher stress levels (increased activity and/or air temperature).

Thermoregulation during rest and exercise in the cold in pre- and early pubescent boys and in young men

Eight minimally dressed pre- and early pubescent boys (age 11-12 yr) and 11 young adult men (age 19-34 yr) rested for 20 min and exercised on a cycle ergometer for 40 min at approximately 30% of their maximum oxygen consumption (VO2max) at 5 degrees C. To quantify the added increase in metabolic rate because of cold, a separate test was carried out at 21 degrees C at rest and at equal work rates as in the cold. Both groups were similar in subcutaneous fat thickness and VO2max per kilogram body weight. Rectal temperature increased slightly during the exposure to the cold, but no significant difference was observed between the boys and men. In the cold, the boys had lower skin temperatures than the adults in their extremities but not in the trunk. The boys increased their metabolic rates in the cold more than did the men. As a result, the boys maintained their core temperature as effectively as the adults. Similar age-related differences in thermoregulatory responses to cold were observed when two boys and two men with equal body sizes were compared. Our results suggest that there may be maturation-related differences in thermoregulation in the cold between children and adults.

Effect of heat stress on muscle blood flow during dynamic handgrip exercise

During exercise in a hot environment, blood flow in the exercising muscles may be reduced in favour of the cutaneous circulation. The aim of our study was to examine whether an acute heat exposure (65-70 degrees C) in sauna conditions reduces the blood flow in forearm muscles during handgrip exercise in comparison to tests at thermoneutrality (25 degrees C). Nine healthy men performed dynamic handgrip exercise of the right hand by rhythmically squeezing a water-filled rubber tube at 13% (light), and at 34% (moderate) of maximal voluntary contraction. The left arm served as a control. The muscle blood flow was estimated as the difference in plethysmographic blood flow between the exercising and the control forearm. Skin blood flow was estimated by laser Doppler flowmetry in both forearms. Oesophageal temperature averaged 36.92 (SEM 0.08) degrees C at thermoneutrality, and 37.74 (SEM 0.07) degrees C (P less than 0.01) at the end of the heat stress. The corresponding values for heart rate were 58 (SEM 2) and 99 (SEM 5) beats.min-1 (P less than 0.01), respectively. At 25 degrees C, handgrip exercise increased blood flow in the exercising forearm above the control forearm by 6.0 (SEM 0.8) ml.100 ml-1.min-1 during light exercise, and by 17.9 (SEM 2.5) ml.100 ml-1.min-1 during moderate exercise. In the heat, the increases were significantly higher: 12.5 (SEM 2.2) ml.100 ml-1.min-1 at the light exercise level (P less than 0.01), and 32.2 (SEM 5.9) ml.100 ml-1.min-1 (P less than 0.05) at the moderate exercise level.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of work load on cutaneous vascular response to exercise

The purpose of the present study was to examine whether intensity of exercise affects skin blood flow response to exercise. For this purpose, six healthy men cycled, in a random order on different days, for 15 min at 50, 60, 70, 80, and 90% of their maximum oxygen consumption (VO2max) at a room temperature of 25 degrees C. At the end of exercise, esophageal temperature (Tes) averaged 37.4 +/- 0.2, 37.7 +/- 0.2, 37.9 +/- 0.2, 38.6 +/- 0.3, and 38.9 +/- 0.4 degrees C (SE) at the 50, 60, 70, 80, and 90% work loads, respectively. At the two highest work loads, no steady state was observed in Tes. Skin blood flow was estimated by measuring forearm blood flow (FBF) with strain-gauge plethysmography and by laser-Doppler flowmetry on the upper back. Both techniques showed that skin blood flow response to rising Tes was markedly reduced at the 90% work load compared with other work loads. At the end of exercise, FBF averaged 7.5 +/- 1.7, 10.7 +/- 3.1, 9.6 +/- 2.1, 11.3 +/- 2.6, and 5.4 +/- 1.3 (SE) ml.min-1.100 ml-1 (P less than 0.01) at the 50, 60, 70, 80, and 90% VO2max work loads, respectively. The corresponding values for Tes threshold for cutaneous vasodilation (FBF) were 37.42 +/- 0.16, 37.48 +/- 0.13, 37.59 +/- 0.13, 37.79 +/- 0.19, and 38.20 +/- 0.22 degrees C (P less than 0.05) at 50, 60, 70, 80, and 90% VO2max, respectively. In two subjects, no cutaneous vasodilation was observed at the 90% work load.(ABSTRACT TRUNCATED AT 250 WORDS)

Work load and physiological responses during asbestos removal with protective clothing

The removal of asbestos-containing building materials requires the use of dust-repelling protective clothing and a respirator. The present study was aimed at measuring physiological responses to asbestos removal in actual work situations. The subjects were eight asbestos workers. During the work, the men wore permeable or impermeable clothing along with a powered or non-powered filtering device including a full-face or half-face mask. Environmental parameters, work postures, heart rate (HR), the skin temperature at two sites and the rectal temperature were recorded every minute during work. Perceived exertion, thermal sensation, thermal comfort, and skin wetness were rated by the subjects. The ambient temperature at work sites ranged from 19 degrees to 37.5 degrees C and relative humidity, from 21% to 50%. The mean HR ranged from 101 to 141 beats min-1. The calculated (from HR measurements) average oxygen consumption (VO2) varied from 0.9 to 1.9 l min-1, which corresponded to 27%-60% of the maximal value. The peak rectal temperature and the highest mean of two measurements of skin temperature were 37.7 degrees +/- 0.3 degree C and 34.4 degrees +/- 0.9 degree C, respectively. The sweat rate varied from 162 to 583 g h-1. Poor work posture was common during asbestos removal. The arms were elevated over shoulder level for 35% of the work time. During the work the mean physiological strain was considered to be moderate, with some heavy peak loads being registered.(ABSTRACT TRUNCATED AT 250 WORDS)

Individual response to physical work in the heat in relation to sweating and skin blood flow

The aim of the present study was to examine heart rate and rectal temperature responses to dynamic exercise in a hot environment and their relationship to sweating and skin blood flow. Eight physically trained men were the study subjects. The experiments consisted of 60-min bicycle ergometer tests at intensities of 50 and 100 W in the heat (36 degrees C/30% relative humidity). During the tests, oxygen consumption, heart rate, rectal temperature, and skin temperatures on eight sites were measured. The whole-body sweat rate and evaporation rate and the rate of dripping sweat were measured by a continuous weighing technique. Skin blood flow was estimated from the changes in forearm blood flow. In all, 13 tests were done at 50 W and 10 tests were conducted at 100 W. At 50 W, a physiological steady state was attained in all tests, i.e. the rise in heart rate was less than 10 beats min-1. At 100 W, in all experiments the heart rate and rectal temperature increased continuously throughout the tests. At the end of exercise, the heart rate varied from 98 to 150 beats min-1. At 50 W work load, the heart rate and rectal temperature did not significantly correlate with any of the thermoregulatory parameters. At 100 W, the heart rate and rectal temperature correlated with the total sweat rate (r = -0.66 and -0.71, respectively; P less than 0.05), with the onset of dripping (r = 0.74 and 0.66, respectively, P less than 0.05), and with the ratio of forearm blood flow to dripping sweat rate (r = 0.83 and 0.85, respectively; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Sweating and skin blood flow during exercise: effects of age and maximal oxygen uptake

Individuals greater than or equal to 60 yr of age are more susceptible to hyperthermia than younger people. However, the mechanisms involved remain unclear. To gain further insight, we examined the heat loss responses of 7 young (24-30 yr) and 13 older (58-74 yr) men during 20 min of cycle exercise [67.5% maximal O2 uptake (VO2max)] in a warm environment (30 degrees C, 55% relative humidity). Forearm blood flow (FBF) and chest sweat rate (SR) were plotted as a function of the weighted average of mean skin and esophageal temperatures [Tes(w)] during exercise. The sensitivity and threshold for each response were defined as the slope and Tes(w) at the onset of the response, respectively. When the young sedentary men were compared with a subgroup (n = 7) of the older physically active men with similar VO2max, the SR and FBF responses of the two groups did not differ significantly. However, when the young men were compared with a subgroup of older sedentary men with a similar maximal O2 pulse, the SR and FBF sensitivities were significantly reduced by 62 and 40%, respectively. These findings suggest that during a short exercise bout either 1) there is no primary effect of aging on heat loss responses but, rather, changes are associated with the age-related decrease in VO2max or 2) the decline in heat loss responses due to aging may be masked by repeated exercise training.

An evaluation of heat stress indices (ISO 7243, ISO/DIS 7933) in the prediction of heat strain in unacclimated men

The ISO 7243 heat stress standard based on the wet bulb globe temperature (WBGT) heat stress index and the analytical standard proposal ISO/DIS 7933 were evaluated in eight physically trained and eight untrained, unacclimated men during prolonged light exercise carried out while wearing industrial work clothing. The exercise tests were done in a thermoneutral (20 degrees C/40%), a warm humid (30 degrees C/80% humidity), and a hot dry (40 degrees C/20% humidity) environment. Both of the standards were effective in predicting the excessive thermal strain observed in the dry and humid heat (WBGT, 28 degrees C). In dry heat, neither of the standards took into account the higher sweating capacities of the physically trained men. The large inter-individual variability in the physiological responses to heat stress questioned the calculations of definite allowable exposure times (ISO/DIS 7933).

The combined effect of the cold pressor test and isometric exercise on heart rate and blood pressure

The purpose of this study was to determine if the cold pressor test during isometric knee extension [15% of maximal voluntary contraction (MVC)] could have an additive effect on cardiovascular responses. Systolic and diastolic blood pressures, heart rate and pressure rate product were measured in eight healthy male subjects. The subjects performed the cold pressor tests and isometric leg extensions singly and in combination. The increases of systolic and diastolic blood pressure during isometric exercise were of almost the same magnitude as those during the cold pressor test. The responses of arterial blood pressure, and heart rate to a combination of the cold pressor test and isometric knee extension were greater than for each test separately. It is suggested that this additional effect of cold immersion of one hand during isometric exercise may have been due to vasoconstriction effects in the contralateral unstressed limb. In summary, the circulatory effects of the local application of cold during static exercise at 15% MVC were additive.

Responses of young and older men during prolonged exercise in dry and humid heat

Eight young, sedentary men (aged 34 years, SD 3) and six older moderately active, unacclimated men (aged 57 years, SD 2) walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [dry bulb temperature (Td) 21 degrees C, relative humidity (r.h.) 43%)], a warm humid (Tdb 30 degrees C, r.h. 80%) and a hot dry (Tdb 40 degrees C, r.h. 20%) environment while wearing ordinary working clothes (0.7 clo). Their oxygen consumption, heart rate (fc), rectal (Tre) and mean skin temperature (Tsk), sweat rate (SR), and evaporative rate (ER) were measured during the tests. The ratings of thermal sensation (TS) and perceived exertion (RPE) were assessed using standard scales. In the heat stress tests, the number of experiments discontinued did not significantly differ between the two groups. The mean levels and end-exercise values of Tre, Tsk, fc, TS and RPE were not significantly different between the young and older subjects in any of the environments. In the warm humid environment, however, the Tre and RPE of the older subjects increased continuously (P less than 0.05) during the test compared to the young subjects. No significant difference between the groups was observed in SR or in ER. In the hot dry environment, however, the ER of older men increased more slowly compared to the young men. In spite of some time-related differences observed in Tre, RPE, and ER, the older subjects did not exhibit higher fc during exercise in the heat, they were not more hyperthermic and their performance times were similar to the young subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulatory and thermal responses of men with different training status to prolonged physical work in dry and humid heat

Eight physically trained and eight untrained, unacclimated men walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [20 degrees C/40% relative humidity (RH)], a warm humid (30 degrees C/80% RH), and a hot dry (40 degrees C/20% RH) environment while wearing industrial work clothing. Their oxygen consumption, rectal and skin temperatures, sweating, cardiac output, heart rate, stroke volume, and peripheral blood pressure were measured during the tests. Thirteen of the 32 heat stress tests were prematurely stopped due to high rectal temperature, high heart rate, subjective fatigue, or heat syncope. The physiological strain, as indicated by the rectal temperature and heart rate, was not significantly different between the warm humid and hot dry environments (wet bulb globe temperature approximately 28 degrees C). The rectal temperature and heart rate responses of the physically trained and untrained subjects did not differ in any of the environments. In the heat, the heart rate was significantly higher than in the thermoneutral environment, but because of the markedly reduced stroke volume the average cardiac output was not different between the three environments. The impaired work performance in the heat seemed mainly to be related to the circulatory instability accompanying the increased cutaneous circulation.

Skin blood flow during incremental exercise in a thermoneutral and a hot dry environment

Eight physically fit men performed two incremental bicycle ergometer tests, one in an ambient temperature of 25 degrees C and the other at 40 degrees C. Oesophageal temperature (Tes) increased continuously throughout the tests up to 38.0 and 38.3 degrees C, respectively. In both environments, forearm blood flow (plethysmography) was linearly related to Tes above the Tes threshold for vasodilation, but at the heaviest work loads this relationship was clearly attenuated and therefore indicated skin vasoconstriction, which tended to be more pronounced at 25 degrees C. During recovery at 25 degrees C, in some subjects the forearm blood flow increased above the levels observed at the end of the graded exercise in spite of a decreasing Tes. Skin blood flow, measured by laser Doppler flow meter at the shoulder, was quantitatively different but, on average, seemed to reveal the same response pattern as the forearm blood flow. In spite of the higher level of skin blood flow in the heat, blood lactate accumulation did not differ between the two environments. The present results suggest that there is competition between skin vasoconstriction and vasodilation at heavy work rates, the former having precedence in a thermoneutral environment to increase muscle perfusion. During short-term graded exercise in a hot environment, skin vasoconstriction with other circulatory adjustments seems to be able to maintain adequate muscle perfusion at heavy work levels, but probably not during maximum exercise.

Aerobic and anaerobic responses to incremental exercise in a thermoneutral and a hot dry environment

In an investigation of the effect of acute heat exposure on aerobic and anaerobic metabolism, eight unacclimated men performed two incremental bicycle ergometer tests in random order, once under thermoneutral conditions (25 degrees C) and once in a hot dry (40 degrees C) environment. Oxygen consumption (VO2) and pulmonary ventilation were measured every minute. Fingertip blood samples were taken at each work level for blood lactate (LA) determination. Compared to the results at 25 degrees C, the mean VO2 was significantly (P less than 0.01) lower during exercise at 40 degrees C. In the hot dry environment the blood lactate threshold was slightly reduced in four subjects, but neither the average peak nor the post-exercise blood LA values differed from the findings at 25 degrees C. During the exercise-heat stress, the ventilatory threshold did not change significantly. The results indicated that, during relatively short-term incremental exercise in a hot environment, almost adequate muscle metabolism can be maintained.

Effects of industrial respirators on breathing pattern at different work levels

The effects of a filtering device and an air-line apparatus on breathing pattern were studied in healthy men with different physical characteristics and work capacity. The subjects comprised nine construction workers aged 35-44, and nine firemen aged 21-35. The construction workers' mean maximal oxygen consumption (VO2max) was 34.5 ml min-1 kg-1, the firemen's 66.9 ml min-1 kg-1. Breathing pattern was analyzed for its components, inspiratory time, expiratory time, breathing frequency, tidal volume, and pulmonary ventilation at rest, during two submaximal treadmill walks when the subjects' absolute work load was equal, and during recovery. Neither the filtering device nor the air-line apparatus had a significant effect on breathing pattern when compared with the control values measured twice with a low-resistance breathing valve. A significantly longer expiratory time, lower breathing frequency, and smaller pulmonary ventilation were found for the firemen with the breathing valve and the industrial respirators. The breathing pattern of the construction workers and the firemen differed, but the alterations were not induced by the use of the filtering device or the air-line apparatus when studied at aerobic work levels up to 60% VO2max.

Physiological strain in work with gas protective clothing at low ambient temperature

Wearing an impermeable gas protective suit (Dräger 500 or 600) and a self-contained breathing apparatus (Dräger PA 80; total weight 27 kg (59.5 lb], seven experienced firemen and one mechanic performed simulated repair and rescue tasks in a chemical plant. The subjects' mean (+/- SD) age, height, weight and estimated maximal oxygen consumption were: 36 +/- 4 years; 181 +/- 6 cm; 83 +/- 8 kg; and 42 +/- 5 mL/min/kg, respectively. The operations took place outdoors (ambient temperature 2.0 degrees C (35.6 degrees F), wind velocity 0-4 m/s). The total work time averaged 37 minutes. During tasks of search, handling vents, and sawing and replacing bolts, the mean (+/- SE) heart rates measured by a Depex recording device were 146 +/- 2, 148 +/- 2, and 147 +/- 5 beats/min, respectively. The mean rectal temperature increased 0.8 degrees C during the whole work period. Weight loss due to sweat averaged 300 g. In conclusion, typical tasks with gas protective clothing caused marked physiological strain among subjects in average physical condition even though the thermal strain was relatively low because the weather was cool. The results emphasized the need to evaluate physical fitness during the periodic check-ups of workers who may have to use gas protective clothing.