Physiological consequences of a high work of breathing during heavy exercise in humans

The healthy respiratory system has a remarkable capacity for meeting the metabolic demands placed upon it during strenuous exercise. For example, in order to regulate alveolar partial pressure of oxygen and carbon dioxide during heavy workloads, a 20-fold increase in alveolar ventilation can occur. The high metabolic costs and subsequent increased work of breathing associated with this ventilatory increase can result in a number of limitations to the healthy respiratory system. Two examples of respiratory system limitations that are associated with a high work of breathing are expiratory flow limitation and exercise-induced diaphragmatic fatigue. Expiratory flow limitation can lead to an inability to increase alveolar ventilation () in the face of increasing metabolic demands, resulting in gas exchange impairment and diminished endurance exercise performance. Furthermore, the high ventilatory requirements of endurance athletes and the inherent anatomical differences in females could make these groups more susceptible to expiratory flow limitation. Fatigue of the diaphragm has also been documented after strenuous exercise and may be related to a mechanism which increases sympathetic vasoconstrictor outflow and reduces limb blood flow during prolonged exercise. This competition between the muscles of respiration and locomotion for a limited cardiac output may have dramatic consequences for exercise performance. This brief review summarizes the literature as it pertains to the work of breathing, expiratory flow limitation, and exercise-induced diaphragmatic fatigue in healthy humans.     

特需医疗服务机构中护士工作满意度的调查分析

目的：了解目前从事特需医疗服务工作的护士对自身工作的满意程度及其影响因素，探讨提高护士工作积极性及护理管理效率的途径和方法，为护理人力资源的有效管理提供依据，方法：采用自行设计的问卷对61名相关的临床护士进行问卷调查。结果：被调查护士的工作满意度为中等水平，影响满意度的原因由强到弱依次为个人发展机会少、福利待遇低、工作负荷过重、专业交流机会少等。此外，针对特需医疗服务的特点，对如何提高该领域护士工作满意度提出了建议。     

呼和浩特地区2018-2020年噪声作业人员听力检查情况分析

目的 了解近年呼和浩特地区噪声作业工人职业健康检查听力检查情况,按行业、经济类型、企业规模、性别、年龄、工龄等维度进行统计分析,提出补充对策,为行政部门监管及用人单位日常管理提供科学依据。方法 采用2018-2020年呼和浩特地区噪声岗中职业健康检查结果,用SPSS19.0统计学软件对结果进行卡方检验。结果 呼和浩特地区噪声作业工人听力损害在不同行业、经济类型、企业规模、性别、年龄、工龄等方面存在显著性差异。结论 呼和浩特地区近年职业健康岗中检查噪声异常检出率较高,噪声对工人的危害不容忽视,应引起企业及行政管理部门的足够重视。     

疾控人员职业倦怠潜在剖面分析及与工作特征的关系

目的 通过对疾控(CDC)人员职业倦怠进行潜在剖面分析识别不同的职业倦怠类别,探讨工作特征各维度与职业倦怠类别间的独立效应。 方法 采用中文版职业倦怠量表(MBI-GS)、工作特征量表和自编一般资料调查表对943名疾控人员进行调查。使用潜在剖面分析方法识别疾控人员职业倦怠潜在类别,多分类Logistic回归分析探讨工作特征各维度与不同职业倦怠类别间的独立效应。 结果 疾控人员职业倦怠存在3种类别:低倦怠型(Ⅰ,54.7%)、高倦怠型(Ⅱ,24.1%)和成就感低落型(Ⅲ,21.2%)。高工作反馈、高工作意义是个体进入高倦怠型组的独立保护因素(OR=0.561;OR=0.612),高工作负荷、高工作对个体控制及情绪表达的要求是个体进入高倦怠型组的独立风险因素(OR=1.693;OR=1.770);高工作自主性是个体进入成就感低落型组的独立风险因素(OR=1.810),高工作对个体控制及情绪表达的要求是个体进入成就感低落型组的独立保护因素(OR=0.582)。 结论 疾控人员可区分出3种潜在职业倦怠类别,工作特征不同维度与潜在职业倦怠类别间存在独立效应。     

Isokinematic muscle mechanics in four groups of women of increasing age

Summary The purpose of this study was to evaluate the effects of age on dynamic muscle attributes of the knee extensors and flexors in postmenopausal women. Young healthy women (3rd decade,n = 15; 4th decade,n = 5) and older healthy women (6th decade,n = 9; 7th decade,n = 6) were tested at six angular velocities from 60° · s^–1 to 400° · s^–1. The 3rd and 4th decade groups produced greater extensor and flexor values for strength related variables at all angular velocities (peak torque, angle specific torque, work, power) than both the 6th and 7th decade groups (P<0.05). However, relative changes in these variables, with increments in angular velocity, were equivalent among the groups. Analysis of the flexor: extensor ratios for these variables demonstrated a differential loss in flexor function with increased age, perhaps indicative of type II motor unit loss or muscle fibre atrophy. It is suggested that such changes may be present even within 4th decade subjects.     

External load can alter the energy cost of prolonged exercise

Summary The present study was undertaken to examine the energy cost of prolonged walking while carrying a backpack load. Six trained subjects were tested while walking for 120 min on a treadmill at a speed of 1.25 m · s^–1 and 5% elevation with a well fitted backpack load of 25 and 40 kg alternately. Carrying 40 kg elicited a significantly higher (p<0.01) enery cost than 25 kg. Furthermore, whereas carrying 25 kg resulted in a constant energy cost, 40 kg yielded a highly significant (p<0.05) increase in energy cost over time. The study implies that increase in load causes physical fatigue, once work intensity is higher than 50% maximal work capacity. This is probably due to altered locomotion biomechanics which in turn lead to the increase in energy cost. Finally, the prediction model which estimates energy cost while carrying loads should be used with some caution when applied to heavy loads and long duration of exercise, since it might underestimate the acutal enery cost.     

Body composition,work capacity,and work efficiency of active and inactive young men

On 46 healthy young men, of whom 18 took part in strenuous sport at least once a week, height, weight, total body fat (as % of body mass) and lean body mass (LBM) were determined. The subjects performed submaximal exercise on a bicycle ergometer and climbing on an upwardly inclined treadmill at work loads of 60, 110, and 140 watts. Oxygen consumption ( ), respiratory quotient (RQ), energy expenditure (), and heart rate (f _H) were measured at rest and at each work load, and maximum oxygen intake ( max) and physical work capacity (PWC₁₅₀, PWC₁₇₀) were calculated.Anthropometric parameters did not differ significantly between sportsmen and sedentary subjects. max, PWC₁₅₀, and PWC₁₇₀ had higher correlations with LBM than with the other anthropometric parameters. max expressed in terms of LBM (ml/kg LBM/min) was the parameter which showed the clearest distinction between sportsmen and sedentary individuals. The sportsmen had higher max on the treadmill test than on the bicycle ergometer. PWC₁₅₀ and PWC₁₇₀ were higher on the bicycle than on the treadmill and had high correlations with max. Work efficiency was of the same order in both groups and showed negative correlation with the degree of obesity on the bicycle ergometer and positive correlation on the treadmill.     

Predicting Home and Work Blood Pressure Measurements from Resting Baselines and Laboratory Reactivity in Black and White Americans

The relationship between blood pressure in the laboratory (both at rest and in response to laboratory tasks) and ambulatory blood pressure at home and at work was evaluated. One hundred nineteen normotensive and unmedicated mild-moderate hypertensive black and white females and males participated in laboratory blood pressure monitoring at rest and during four challenging tasks (structured interview, video game, bicycle exercise, and cold pressor test) as well as ambulatory blood pressure monitoring while at home and at work. Baseline blood pressure taken while subjects were at rest was the strongest predictor of ambulatory systolic blood pressure (r = .64) and diastolic blood pressure (r = .77) at work. Among reactivity tasks the strongest predictors of ambulatory blood pressure in the total population were the structured interview and the video game (both psychological tasks) followed by the cold pressor test. Racial comparisons, however, determined that the cold pressor test predicted diastolic blood pressure significantly better for blacks (r = .73) than for whites (r = .40), suggesting a possible difference in blood pressure regulation.     

Endogenous adenosine improves work rate to oxygen consumption ratio in catecholamine stimulated isovolumic rat heart

This study examines the possibility that endogenous adenosine modulates efficiency in isovolumic perfused rat hearts stimulated with isoproterenol or norepinephrine. Efficiency in these hearts is calculated as the rate of pressure work divided by the myocardial oxygen consumption. Within 2 min of infusion of isoproterenol (50 nM), heart rate increased by 35%, the rate pressure product by 290%, oxygen consumption by 142%, and efficiency by 67%. Infusion of adenosine deaminase (2–4 IU/ml), or 8-phenyltheophylline (5 M), into stimulated hearts augmented the increase in heart rate by 40–45%, rate-pressure product by 18–20%, and oxygen consumption by 50–55%. Efficiency was reduced by 30–35%. Adenosine release into the coronary venous effluent increased from 195±20 pmol/min/g to 2400±180 pmol/min/g after 5 min. A similar pattern of results was observed when norepinephrine (0.1 mM) was used. The results indicate that extracellular adenosine, released by catecholamine treatment, inhibits the effects of the catecholamines on rate and contractility. Consequently, adenosine reduces cardiac work (rate-pressure product), but in so doing, improves efficiency.