Biomedical subjects

R Heus

Publications and source records attributed to R Heus.

8 recordsLinked to original sources

PubMed2003

Positive pressure breathing during rest and exercise.

The requirements to maintain a positive pressure with respiratory protection during heavy exercise and the effects on ventilation and feelings of discomfort were investigated. Eight male subjects participated, using the respirator system during rest and exercise at about 80% of their individual maximum power. A blower was used at maximum and medium capacity and at two pressure levels (3 and 15 mbar). Additionally, the mouth pressure was used as a feedback for the blower. The blower decreased the fraction of the breathing cycle with negative pressures from 50% (SD 4%) to 15% (SD 10%) during exercise. Negative pressures occurred at all settings of the blower during exercise. Thus, the currently available commercial blower systems do not supply a sufficient airflow to maintain a positive pressure during heavy exercise. Positive pressure breathing did not affect the ventilation and the circulation. But the oxygen consumption was higher with the blower and respirator than without.

Adult↗

PubMed2002

Maximal oxygen uptake during cycling is reduced in moving environments; consequences for motion-induced fatigue.

In previous studies on physical fatigue during simulated ship movements, the apparent exhaustion of subjects after experimentation suggested that the traditional index of physical workload, oxygen consumption expressed as the percentage of peak oxygen consumption (VO2-peak) measured in a separate graded exercise test (GXT), underestimates workload in a moving environment. In these studies, the GXT was carried out in a stationary environment, as is standard practice. To explain the underestimation, it was hypothesized that VO2-peak might have been less if the GXT had been carried out in the moving environment. This paper reports on three experimental tests of this hypothesis, performed with a ship motion simulator and aboard a ship at sea. In all three experiments, VO2-peak was indeed significantly reduced when the GXT was carried out in the moving environment. Theoretical reasons for this phenomenon are discussed and investigated, but a clear explanation is still lacking.

Adult↗

PubMed1998

Human energy expenditure when walking on a moving platform.

The assumption that working on board ship is more strenuous than comparable work ashore was investigated in this study. Various physiological parameters (VO2, VCO2, VE and HR) have been measured to determine the energy expenditure of subjects walking slowly on a moving platform (ship motion simulator). Twelve subjects (eight men and four women) walked either freely on the floor or on a treadmill at a speed of 1 m x s(-1). Platform motion was either in a heave, pitch or roll mode. These three conditions were compared with a control condition in which the platform remained stationary. The results showed that during pitch and roll movements of the platform, the energy expenditure for the same walking task was about 30% higher than under the stationary control condition (3.6 J x kg[-1] x m[-1] vs 2.5 J x kg[-1] x m[-1], P < 0.05) for both walking on a treadmill and free walking. The heart rate data supported the higher energy expenditure results with an elevation of the heart rate (112 beats x min[-1] vs 103 beats x min[-1], P < 0.05). The heave condition did not differ significantly from the stationary control condition. Pitch and roll were not significantly different from each other. During all experimental conditions free walking resulted in a higher energy cost of walking than treadmill walking (3.5 J x kg[-1] x m[-1] vs 2.7 J x kg[-1] x m[-1], P < 0.05) at the same average speed. The results of this experiment were interpreted as indicating that the muscular effort, needed for maintaining balance when walking on a pitching or rolling platform, resulted in a significantly higher work load than similar walking on a stable or a heaving floor, independent of the mode of walking. These results explain in part the increased fatigue observed when a task is performed on a moving platform.

Adult↗

PubMed1995

Physiological criteria for functioning of hands in the cold: a review.

Hands are important instruments in daily life. Without hands man is hardly able to function independently. Proper functioning of the hands is determined by several physiological parameters. These physiological parameters in turn are influenced by environmental factors. In this view of the literature, physiological processes in manual dexterity are described and the influence of a cold environment on separate physiological processes is studied. In general, cold means loss of dexterity. For reasons of safety and performance, it is important to restrict the loss of manual dexterity. For this purpose, in this study minimum criteria are given for all separate physiological components. Most important minimum criteria are: a local skin temperature of 15 degrees C, a nerve temperature of 20 degrees C and a muscle temperature of 28 degrees C. Only during maximum dynamic work is a muscle temperature of 38 degrees C recommended. These temperatures are average values, and of course individual differences are evident.

Journal Article↗

PubMed1995

The hand in the cold, performance and risk.

When a person is exposed to cold and his metabolic rate is insufficient to maintain a positive or neutral heat balance, the body will cool down. For the extremities this will result in a drastic reduction of blood flow, resulting in a so called "physiological amputation" with extremity cooling towards ambient temperature. The dexterity decrease observed with cold extremities is most likely caused by cooling of muscles and joints, and not by effects on receptors, nerve conduction or central effects. It is shown, that dexterity decreases can be described in terms of wind chill equivalent temperature and exposure time for a certain clothing and work configuration. Further, the risk of skin freezing and reduced dexterity due to touching cold objects can be described using the contact coefficient of the respective material and the contact time. This risk is modulated by metabolic rate and hand protection (gloves). Gloves drastically reduce cooling speed and freezing risk, but they also cause increased risks due to reduced dexterity due to glove thickness. For a general description of performance and risk of hand cold exposure in relation to climate and exposure time more data are needed.

Cold Temperature↗

PubMed1992

Effects of temperature on electromyogram and muscle function.

The effects of 30 min of cooling (15 degrees C water) and warming (40 degrees C water) on arm muscle function were measured. A reference condition (24 degrees C air) was included. Of nine young male subjects the maximal grip force (Fmax), the time to reach 66% of Fmax (rate of force buildup) and the maximal rhythmic grip frequency were determined, together with surface electromyographic activity (EMG) of a forearm muscle (flexor digitorum superficialis). The results showed that in contrast to warming, cooling resulted in a significant decrease of 20% in the Fmax and a significant 50% decrease in force build-up time and the maximal rhythmic grip frequency. The relationship between the root mean square value (rms) of the EMG and the static grip force did not change due to temperature changes. The median power frequency (MPF) in the power spectrum of the EMG signal decreased by 50% due to cooling but remained unchanged with heating. During a sustained contraction at 15% of Fmax (Fmax depending on the temperature) the increase in the rms value with contraction time was 90% larger in the warm condition and 80% smaller in the cold condition compared to the increase in the reference condition. The MPF value remained constant during the warm and reference conditions but in the cold it started at a 50% lower value and increased with contraction time.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1992

Physiological strain due to load carrying in heavy footwear.

To determine the effects of wearing heavy footwear on physiological responses five male and five female subjects were measured while walking on a treadmill (4, 5.25, and 6.5 km.h-1) with different external loads (barefooted, combat boots, and waist pack). While walking without an external load the oxygen uptake, as a percentage of maximal oxygen uptake (%VO2max) of the men increased from 25% VO2max at 4 km.h-1 to 31% VO2max at 5.25 km.h-1 and to 42% VO2max at 6.5 km.h-1. The women had a significantly higher oxygen uptake of 30%, 40%, and 55% VO2max, respectively. In the most strenuous condition, walking at 6.5 km.h-1 with combat boots and waist pack (12 kg), the oxygen uptake for the men and women amounted to 53% and 75% VO2max, respectively. The heart rate showed a similar response to the oxygen uptake, the women having a heart rate which was 15-40 beats.min-1 higher than that of the men, depending on the experimental condition. The perceived exertion was shown to be greatly dependent on the oxygen uptake. From the results a regression formula was calculated predicting the oxygen uptake depending on the mass of the footwear, walking speed and body mass. It was concluded that the mass of footwear resulted in an increase in the energy expenditure which was a factor 1.9-4.7 times greater than that of a kilogram of body mass, depending on sex and walking speed.

Body Mass Index↗

PubMed1992

Pain, thermal sensation and cooling rates of hands while touching cold materials.

Hand cooling and resulting comfort and pain were studied in 12 subjects, while touching six different materials (polyurethane foam, wood, nylon, rustproof steel, aluminium, and temperature-controlled metal) which were initially at ambient temperature. This was done for three ambient temperatures (-10 degrees, 0 degree and 10 degrees C), after pre-exposure exercise or rest, with bare hands or while wearing gloves. The observed cooling curves were analysed as Newtonian cooling curves. The observed time constants appeared to be significantly related to the materials' contact coefficients, the presence of hand protection, the preceding activity, and the interaction between contact coefficient and the presence of hand protection. These parameters also allowed a good description of the time constant (r2 = 0.8) of the related cooling curves. Thermal and pain sensation could be described in terms of the local skin temperature, ambient temperature and hand protection. Equal pain and thermal levels were associated with lower temperatures of the back of the hand than of the contact side. The slightly painful condition was associated with a skin temperature of 16 degrees C for the back and 19 degrees C for the palm of the hand. The pain level appeared to be inversely related to cooling speed. Skin freezing occurred at higher skin temperatures when touching cold objects than when exposed to cold air as a result of reduced supercooling. The regression equations determined allowed calculations to be made of safety limits for hand cooling while in contact with a wide range of materials.

Adolescent↗