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PubMed2000

Hemodynamic and thermal responses to a 30-minute constant-workload aerobic exercise in middle- or old-aged patients with cardiovascular diseases.

The aim of the present investigation was to compare the hemodynamic and thermal responses to a 30-min aerobic exercise between middle- or old-aged patients with normal left ventricular function and those with left ventricular dysfunction. Constant-load sitting ergometer exercise of approximately 90% of the subject's oxygen uptake (VO2) at the anaerobic threshold for 30 min was conducted in 21 patients with left ventricular dysfunction (61+/-10 years, left ventricular ejection fraction (LVEF) 35+/-7%) and 24 patients with normal left ventricular function (59+/-9 years, LVEF 71+/-7%). Heart rate (HR), blood pressure, deep temperatures in the forehead and thigh, and forearm skin blood flow (SkBF) were measured every minute, and cardiac output (CO) and stroke volume (SV) were determined every 10 min with the dye-dilution technique during the exercise. Patients of both groups exhibited a progressive elevation in each temperature and an increase in SkBF during the exercise. Although the VO2 and CO remained stable, almost the same magnitude of decrease in SV as increase in HR was seen after the 10th min of exercise in both groups. The magnitude of the decrease in SV was greater in old-aged than middle-aged patients with left ventricular dysfunction. Thus, the downward drift in SV during a 30-min constant-load aerobic exercise might not be influenced by left ventricular function, but intensified by aging in patients with left ventricular dysfunction.

Adult↗
PubMed2006

Automation reliability in unmanned aerial vehicle control: a reliance-compliance model of automation dependence in high workload.

OBJECTIVE: Two experiments were conducted in which participants navigated a simulated unmanned aerial vehicle (UAV) through a series of mission legs while searching for targets and monitoring system parameters. The goal of the study was to highlight the qualitatively different effects of automation false alarms and misses as they relate to operator compliance and reliance, respectively. BACKGROUND: Background data suggest that automation false alarms cause reduced compliance, whereas misses cause reduced reliance. METHOD: In two studies, 32 and 24 participants, including some licensed pilots, performed in-lab UAV simulations that presented the visual world and collected dependent measures. RESULTS: Results indicated that with the low-reliability aids, false alarms correlated with poorer performance in the system failure task, whereas misses correlated with poorer performance in the concurrent tasks. CONCLUSION: Compliance and reliance do appear to be affected by false alarms and misses, respectively, and are relatively independent of each other. APPLICATION: Practical implications are that automated aids must be fairly reliable to provide global benefits and that false alarms and misses have qualitatively different effects on performance.

Aircraft↗
PubMed1997

Visual accommodation and virtual images: do attentional factors mediate the interacting effects of perceived distance, mental workload, and stimulus presentation modality?

A study was conducted to examine the effect on the visual accommodation response of processing information presented either visually or aurally while viewing a real-world scene. A number of different conditions were tested in which a mental processing task, a virtual image overlaying the real world (as is the case with head-up displays), or both were present. These manipulations provided two factors that have previously been demonstrated to have some influence on the accommodation response: mental effort and perceived distance. They also allowed the investigation of the influence of the source modality of the information to be processed. The results suggested that these influences may have a cumulative effect on the visual accommodation response, possibly mediated by attentional factors.

Accommodation, Ocular↗
PubMed1992

Mathematical performance before, during, and following cycling at workloads of low and moderate intensity.

Mental arithmetic performance before, during, and following low (40% maximal heart-rate reserve; approximately 90 watts exercise for 15 min.) and moderate (60% maximal heart-rate reserve; approximately 150 watts exercise for 10 min.) intensity cycling by 20 male students (M age = 28.1 yr.) was studied. Subjects were grouped, by using a median-split on their total mathematical performance scores, into a group of 10 low in arithmetic skill and a group of 10 high in arithmetic skill. The numbers and percentages of right answers to 1-min. mathematical problem-sets of either group were not different in the various conditions, suggesting that 25 min. of progressive cycling exercise did not influence mathematical problem-solving efficacy.

Adult↗
PubMed1992

Increased breathing gas density enhances cardiac workload.

The effect of increased breathing gas density on the left ventricular pressure (LVP), cardiac contractility (dP/dt), heart rate (HR), intrapleural pressure (P(ip)) and respiratory frequency (RF) was evaluated in pentobarbital-anaesthetized rats (n = 8) and cats (n = 6). Catheters were placed in the left cardiac ventricle via the right carotid artery to measure the LVP, in the oesophagus for indirect measurements of P(ip) and RF, and into the aorta from the right femoral artery for arterial pressure measurements. The RF fell significantly within the first 30 s and had reached a stable value 2 min after gas shift in both rats and cats. Concomitant with the RF fall, the depth of inspiration and intrapleural pressure differences in both rats and cats increased. The acid-base balance remained at control levels in both animal groups. LVP and dP/dt started to increase during the first half-minute, and reached their maximum values 2-5 min after the introduction of normoxic sulphur hexafluoride. A linear relationship between the enhanced dP/dt and the P(ip) increase was found. The HR remained unchanged in both cats and rats. These findings indicate that the breathing gas density might influence the cardiac contractility found during hyperbaric exposure, and that a gas density of five times that of air at 1 bar does not influence the diffusion of O2 and CO2 in the lung. The O2 consumption of the heart in cats and rats was calculated to rise by 25% and 30% respectively in the dense breathing gas atmosphere.

Acid-Base Equilibrium↗
PubMed1993

Association of overweight, trauma and workload with coxarthrosis. A health survey of 7,217 persons.

In a population sample health survey, body mass, previous trauma and physical stress were studied for associations with coxarthrosis. A sample of 8,000 persons representative of the Finnish population aged 30 or over was invited for examination, and 90 percent participated. On the basis of a standardized clinical examination, a physician diagnosed coxarthrosis in 6 percent of the women and 4 percent of the men. The prevalence rose with age. In persons with a past traumatic lower-limb injury, the odds ratio of unilateral coxarthrosis was 2.1 and of bilateral coxarthrosis 1.5, as adjusted for sex, age and other determinants using logistic regression. The sum index reflecting self-reported features of physical stress in present or previous occupations was directly proportional to the prevalence of coxarthrosis. Body mass index (kg/m2) was closely associated with bilateral coxarthrosis; the adjusted odds ratio (95 percent confidence intervals) for indices > 35, compared to those < 25, was 2.8 (1.4-5.7). In terms of the population attributable fraction, prior trauma, physical stress and body mass were estimated to explain 59 percent of the prevalence of coxarthrosis. The potential for primary prevention may be great, but longitudinal population studies are necessary to elucidate causal significance of the risk factors.

Adult↗
PubMed1992

Metacognition in psychophysical judgment: an unfolding view of comparative judgments of mental workload.

An experiment is reported in which it was found that when subjects were required to indicate which of two visual extents was more difficult to categorize as "long" or "short," they executed these categorizations and then measured the distance of the representation of each stimulus from the long-short category boundary; the stimulus nearer the boundary was judged to be the more difficult. When they were requested to indicate which was easier to categorize, they selected the alternative that was farther. Coombs's theory of data (1952, 1964) and his unfolding theory of preferential choice (1950, 1964) provided the conceptualization of metacognition in this psychophysical task context. Strong support for the probabilistic version of unfolding theory was obtained from the observed selective effects of laterality on the levels of stochastic transitivity attained for various classes of triples and the reliably longer times for comparisons with bilateral pairs than with unilateral pairs. The semantic congruity effects obtained, together with the changes in the form of the relationship between probability and response time as a function of practice, can be best accounted for by an evidence accrual theory in which the distances from the active reference point are measured and compared with a criterion on each evidence accrual. No support is provided for the view that propositionally based semantic "ease"-"difficulty" codes serve as the basis for these metacognitive comparative judgments of ease and difficulty.

Adult↗
PubMed1990

A workload shared.

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Emergency Medical Services↗