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Biomedical subjects

O Eiken

Publications and source records attributed to O Eiken.

At least 37 records · Page 2Linked to original sources
PubMed1994

Perception of thermal comfort during narcosis.

We examined the perception of thermal comfort in six male subjects immersed in water at 28 degrees C (study I) and 15 degrees C (study II), breathing either room air (AIR) or a normoxic mixture containing 30% N2O (N2O). Immersions were terminated if esophageal temperature (Tes) decreased by 2 degrees C from resting levels or to 35 degrees C. At regular intervals, subjects rated their perception of thermal comfort on a 21-point scale (thermal comfort vote, TCV; +10 = very, very hot, 0 = neutral, -10 = very, very cold). For similar decreases in Tes from resting preimmersion values (mean +/- SD = -0.90 degrees +/- 0.13 degrees C and -0.92 degrees +/- 0.15 degrees C during the AIR and N2O trials in study I, and -0.90 degree +/- 0.22 degree C and -0.89 degree +/- 0.27 degree C during the AIR and N2O trials in study II), subjects perceived the immersions as less cold during the N2O trials. The median TCVs for the AIR condition of -5 in study I and -7.75 in study II, were significantly lower than those reported by the subjects for the respective N2O conditions (1.75 in study I and -5.5 in study II). It is concluded that behavioral adjustments required for maintaining thermal balance may be diminished during narcosis due to the altered perception of thermal discomfort. Assuming that the effect of inert gas narcosis on thermoregulatory responses is similar to that of N2O, then combined with the significant attenuation of heat gain mechanisms by anesthetic gases, the attenuation of the perception of thermal comfort may represent a significant factor in the etiology of hypothermia observed in compressed air divers.

Body Temperature Regulation↗
PubMed1993

Autonomic nervous control of heart rate during blood-flow restricted exercise in man.

Power spectra of instantaneous heart rate (fc) allows the estimation of the contribution of sympathetic and parasympathetic control of fc during steady-state conditions. The present study was designed to examine autonomic control of fc as influenced by normal dynamic leg exercise and by ischemic leg exercise. Eight subjects performed supine cycle ergometry at 30% of their control peak work rate, with and without blood-flow restriction. Blood-flow restriction was induced by exposing the exercising legs to a supra-atmospheric pressure of 6.7 kPa (leg positive pressure; LPP). The exercise responses of arterial pressure and fc increased (P < 0.05) by LPP exposure. The exaggerated pressor response may be attributed to a chemoreflex drive originating in the ischemic muscles. Exposure to LPP during exercise also produced a significant decrease in parasympathetically mediated high frequency (HF; 0.15-1.00 Hz) fluctuation of fc, as indicated by a decrease (P < 0.05) in percent HF power compared to the control exercise level. During LPP exercise, the sympathetically mediated very low frequency (VLF; 0-0.05 Hz) fluctuation of fc increased, as indicated by an increase (P < 0.05) in percent VLF power above control exercise levels. Both LPP and control exercise conditions decreased (P < 0.05) power in all frequency ranges of interest compared to their respective resting conditions. The results suggest that the increase in fc associated with normal dynamic exercise was mediated predominantly by parasympathetic withdrawal, whereas the exaggerated fc response during ischemic exercise resulted from a combination of cardiac sympathetic drive and parasympathetic withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Effects of ischaemic training on local aerobic muscle performance in man.

The aim of the study was to compare the effects of ischaemic and non-ischaemic training on aerobic performance. In 10 subjects, peak oxygen uptake (peak VO2) and time to fatigue (TTF) for one-legged exercise were measured before and after 4 weeks (4 times week-1) of one-legged training. Each training session started with one leg training for 45 min with 20% blood-flow reduction induced by local application of a supra-atmospheric external pressure of 50 mmHg (ischaemic leg; I-leg). We have previously shown that this decreases leg blood flow by about 20%. The contralateral leg (non-restricted-flow leg; N-leg), serving as a control, then trained with an identical power-output profile for 45 min but without flow restriction. In the I-leg the average training-induced increments in TTF and peak VO2 were 27 and 24%, respectively. In the N-trained leg TTF and peak-VO2 increased 10 and 14%, respectively. Both increments were significantly greater (P < 0.05) in the I-trained leg. Moreover, the performance increase in the I-trained leg was exaggerated (P < 0.05) in the ischaemic test condition, i.e. there was a specificity in the training response. In conclusion, ischaemia acts as an additive stimulus to training leading to an exaggerated increase in endurance and peak-VO2 compared to identical training without blood-flow restriction. The main explanation is probably an enhanced local adaptation in the I-trained leg.

Adult↗
PubMed1993

Muscle fibre types and enzyme activities after training with local leg ischaemia in man.

Eight healthy men performed supine one-legged training on a bicycle ergometer 45 min per leg four times per week for 4 week. The ergometer and lower body were inside a pressure chamber, the opening of which was sealed at the level of the crotch. One leg trained with impeded leg blood flow (I-leg), induced by an increased (50 mmHg) chamber pressure, at the highest tolerable intensity. The contralateral leg trained at the same power under normal pressure (N-leg). Before and after training biopsies were taken from the vastus lateralis of both legs and maximal one-legged exercise tests were executed with both legs. Biopsies were repeated when the subjects had been back to their habitual physical activity for 3 months. Training increased exercise time to exhaustion, but more in the I-leg than in the N-leg. After training, the I-leg had higher activity of citrate synthase (CS), a marker of oxidative capacity, and lower activity of the M-subunit of lactate dehydrogenase isoenzymes. It also had a higher percentage of type-I fibres and a lower percentage of IIB fibres, larger areas of all fibre types and a greater number of capillaries per fibre. It is concluded that ischaemic training changes the muscle metabolic profile in a direction facilitating aerobic metabolism. An altered fibre-type composition may contribute, but is not enough prerequisite for the change.

Adult↗
PubMed1992

The effect of 30% nitrous oxide on thermoregulatory responses in humans during hypothermia.

Clinical studies have reported that body core temperature decreases during prolonged surgery and anesthesia. Although this finding has been attributed primarily to increased heat loss resulting from exposure of body cavities and infusion of cold solutions, it is generally recognized that anesthesia interferes with the thermoregulatory system. The present study examined the effects of mild narcosis induced by 30% N2O on shivering thermogenesis and cutaneous thermoregulatory vasoconstriction in humans, during exposure in a much more intense peripheral thermal stimulus than the ones often used in clinical studies. Nine male subjects were immersed in 15 degrees C water on two separate occasions. During one occasion subjects inspired air (control condition), and during the other occasion the inspired gas mixture contained 20% O2, 30% N2O, and 50% N2 (N2O condition). On both occasions, subjects were immersed to the neck for 60 min, or until their core temperature decreased by 2 degrees C from the preimmersion value. Following the cooling phase, subjects rewarmed via endogenous thermogenesis while lying in a well-insulated bed for 48 min. In the N2O condition, subjects continued to inspire the anesthetic gas mixture during the 48-min period of recovery. O2 uptake (VO2), esophageal temperature (Tes), mean skin temperature (Tsk), mean heat flux (Q) and forearm-fingertip temperature gradient (Tsk-gr) were recorded at 1-min intervals. Tsk and Q in both conditions stabilized within 10 and 25 min of immersion, respectively, and were not significantly different between the two conditions. The cooling rate of Tes was greater during the N2O than the control condition. VO2 increased during the immersion in both conditions and was greater in the control than in the N2O condition. In both conditions, VO2 increased linearly with decreasing Tes, but at any given Tes, VO2 was higher in the control than in the N2O condition. No significant difference was observed in cutaneous thermoregulatory vasoconstriction between the two experimental conditions, as indicated by the Tsk-gr values. The estimated Tes threshold for shivering (estimated from the O2 consumption vs. delta Tes regression) was reduced by 0.95 +/- 0.26 (SE) degrees C during the immersion phase and by 0.39 +/- 0.05 (SE) degrees C during the rewarming phase in the N2O condition compared to the control conditions. Although the thermosensitivity (gain) of shivering appeared preserved during the immersion phase, it was reduced during the N2O rewarming phase.(ABSTRACT TRUNCATED AT 400 WORDS)

Administration, Inhalation↗
PubMed1992

Characteristics of the carotid baroreflex in man during normal and flow-restricted exercise.

Eight subjects were studied in the supine position at rest, during normal dynamic leg exercise (control exercise) and with blood-flow restriction in the working legs (flow-restricted exercise). Graded muscle blood-flow restriction was accomplished by applying a supra-atmospheric pressure of 50 mmHg to the working legs. During incremental-load exercise, flow restriction reduced exercise performance and peak heart rate by 36% and 13%, respectively. The function of the cardiac branch of the carotid baroreflex was studied over its full operational range, at rest and during constant-load control and flow-restricted exercise, by measuring R-R intervals during application of pulse-synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Heart rate and arterial pressure were higher during flow-restricted than control exercise, indicating that the flow restriction activated the muscle chemoreflex. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) was accompanied by increasing R-R intervals in all conditions. The set point (point of baseline carotid transmural pressure and R-R interval) coincided with the midportion of the pressure-response curve at rest and with the threshold point of the curve during exercise. The maximal rate of change in relative R-R intervals and the corresponding carotid transmural pressure range were higher during control exercise than at rest and highest during flow-restricted exercise, indicating that exercise and especially flow-restricted exercise increased carotid baroflex sensitivity, and shifted the carotid baroreflex optimal buffering range to higher pressures. The results suggest that the carotid baroflex attenuates exercise heart rate increases mediated by the muscle chemoreflex and/or by central command.

Adult↗
PubMed1991

Effects of ischaemic training on force development and fibre-type composition in human skeletal muscle.

Force (peak torque) of m. quadriceps femoris was measured during 60 repeated, voluntary dynamic knee extensions in 10 men before and after a 4-week training regimen of one-legged cycle exercise. Biopsies for histochemical analysis were obtained from the lateral vastus muscle after the training period. One leg was trained with the blood flow to the leg muscles reduced by local supra-atmospheric external pressure of 50 mmHg ('Ischaemic leg, I-leg'). Employing the same work-load profile the other leg was trained at normal atmospheric pressure ('Non-restricted-flow leg, N-leg'). In response to I-training, Maximum Peak Torqued (MPT; the highest torque produced in any contraction) and Initial Peak Torque (IPT; the average peak torque of the initial 12 contractions) decreased by 8% (P less than 0.01) and 9% (P less than 0.001), respectively. Final Peak Torque (FPT; the average peak torque of the final 12 contractions) increased by 13% (P less than 0.05) after I-training. No changes in MPT, IPT or FPT occurred following N-training. After training the proportion of slow-twitch fibres was higher (P less than 0.05) and the mean slow-twitch fibre area was larger (P less than 0.05) in the I-than in the N-trained leg. The results indicate that blood flow-restricted training, in contrast to non-restricted-flow training, decreases maximum voluntary dynamic force, possibly by inducing an increase in the share of the muscle cross-sectional area consisting of slow-twitch fibres. That flow-restricted training improves maintenance of force during short-term local exercise may reflect ischaemically induced changes in the metabolic characteristics of skeletal muscle.

Adult↗
PubMed1990

Muscle oxidative capacity and work performance after training under local leg ischemia.

Healthy young men executed supine one-legged cycle training four times per week for 4 wk with legs and the cycle ergometer inside a pressure chamber, the opening of which was sealed by a rubber membrane at the level of the crotch. Each training session started by training one leg under ischemic conditions induced by increased chamber pressure (50 mmHg) at the highest intensity tolerable for 45 min. Then the other leg was trained with the same power profile but normal atmospheric chamber pressure. Before and after the training period, both legs executed one-legged exercise tests under both normal and increased chamber pressure and muscle biopsies were taken from the vastus lateralis. Ischemic training increased performance more than normal training, the difference being greater for exercise executed under ischemic conditions. The difference in performance increase between the legs was paralleled by a greater muscle citrate synthase activity in the ischemically than in the normally trained leg.

Adult↗
PubMed1989

Physiological effects of a mouth-borne heat exchanger during heavy exercise in a cold environment.

A mouth-borne heat and moisture exchanger (HME) was tested. Nine healthy subjects performed an incremental-load cycle ergometry test to exhaustion, breathing once through the HME and once through a similar device without heat-exchange function (control). HME substantially increased inspired gas temperatures and decreased expired gas temperatures measured at the mouth; at 260 W (pulmonary ventilation (VE) approximately 1001 min-1) these changes amounted to + 15 degrees C and -5 degrees C, respectively. The breathing resistance was increased by HME but remained well within tolerable levels even during severe exercise. This was reflected in the subjective assessments of breathing resistance and breathing discomfort which, at any given workload, were rated similarly in the HME and control conditions. Also, time to exhaustion as well as oxygen uptake and VE at a given workload were unaffected by HME. That even at high pulmonary ventilations HME provided a good heat-exchange function while keeping breathing resistance relatively low suggests HME to be a useful aid for individuals suffering from cold-induced bronchospasm.

Adult↗
PubMed1989

Effects of continuous positive- and negative-pressure breathing on the pattern of breathing in man during exercise.

Breathing pattern and static lung volumes were studied in 10 subjects at rest and during incremental-load cycle ergometry under three different conditions, viz. with normal pressure in the airways (control) and during continuous positive- and negative-pressure breathing (CPPB, CNPB) of +15 and -15 cmH2O. End-expiratory, end-inspiratory and mid-expiratory volumes were increased by CPPB and decreased by CNPB; these effects were especially pronounced at rest and during mild exercise. Both at rest and during exercise mean inspiratory flow (VT/TI) was exaggerated by CPPB and attenuated by CNPB. At rest these changes were due mainly to concomitant changes in tidal volume (VT) which was increased by CPPB and decreased by CNPB, while inspiratory time duration (TI) was relatively unaffected by pressure breathing. The transition from rest to loadless pedalling induced an increase in VT but no change in TI in the control condition, whereas in the CPPB and CNPB conditions TI decreased and VT remained unaltered. This CPPB- and CNPB-induced change in the volume-time threshold relationship at the onset of pedalling is attributed to increased stretch receptor activity in the extrathoracic portion of the trachea as a result of the increments in transmural pressure. During the course of exercise there was an inverse relationship between the slope of the VT-TI curve and the mid-expiratory volume in that the slope was greater in the control than in the CPPB condition and greatest during CNPB, suggesting that in exercise hyperpnoea the VT-TI relationship is also determined by pulmonary and/or thoracic wall stretch receptors capable of sensing the absolute lung volume.

Adult↗
PubMed1988

Effects of increased muscle perfusion pressure on responses to dynamic leg exercise in man.

Ventilatory, cardiovascular and metabolic functions and work performance were studied in men performing incremental-load dynamic leg exercise until exhaustion. Part I: Responses to supine exercise were investigated in 8 subjects during exposure of the lower body to subatmospheric pressure at -6.67 kPa (-50 mm Hg) (Lower Body Negative Pressure, LBNP). Due to curtailment of stroke volume, cardiac output was reduced by LBNP over a wide range of work intensities, including heavy loads: ventilation, oxygen uptake and blood lactate concentrations increased with work load, but at lower rates than in the control condition. Part II: In 9 subjects, work performance was compared in three conditions: supine exercise with and without LBNP, and upright exercise. Performance in supine exercise was enhanced by LBNP, and was further improved in upright exercise. In supine exercise, the LBNP-induced reduction in blood lactate and enhancement of work performance are attributed to a more efficient muscle blood flow resulting from increased local perfusion pressure. This strongly suggests that the primary limitation of work performance was set by the peripheral circulation in working muscles rather than by cardiac performance. A similar mechanism may, in part, explain why work performance in dynamic leg exercise was greater in the upright than in the supine posture. It is also concluded that supine leg exercise during LBNP is a useful model of upright exercise, with regard to the central circulation and the circulation in working muscles.

Adult↗
PubMed1987

The pattern of breathing during hypoxic exercise.

Breathing pattern was studied in six subjects in normoxia (FIO2 = 0.21) and hypoxia (FIO2 = 0.12) at rest and during incremental work-rate exercise. Ventilation (V) as well as mean inspiratory flow (VT/TI) increased with exercise intensity and were augmented in the hypoxic environment, whereas the ratio between inspiratory (TI) and total (Ttot) breath durations increased with exercise intensity but was unaffected by hypoxia. The relationship of tidal volume (VT) and inspiratory time duration (TI) showed linear, coinciding ranges for the normoxic and hypoxic conditions up to VT/TI values of about 2.5 1.s-1. At higher VT/TI values TI continued to decrease, whereas VT tended to level off, an effect which was more evident in the hypoxic condition. The results suggest that the hypoxic augmentation of exercise hyperpnea is primarily brought about by an enhancement of central inspiratory drive, the timing component being largely unaffected by the hypoxic environment, and that at low to moderate levels of exercise hyperpnea inspiratory off-switch mechanisms are essentially unaffected by moderate hypoxia.

Adult↗
PubMed1987

Effects of triglycyl-lysine-vasopressin on cardiovascular responses to orthostatic stress.

The influence of triglycyl-lysine-vasopressin (TGLVP) on cardiovascular responses to orthostatic stress was studied. Arterial pressures, heart rate (HR) and stroke volume (SV) were measured in eight healthy males subjected to 20 min 70 degrees head-up tilt. On different days they received either 0.01 mg/kg b.w. of TGLVP or a corresponding volume of 0.9% saline i.v. after 15 min supine rest. After the drug injection, in supine subjects, HR had decreased from 58 to 50 beats min-1, total peripheral resistance (TPR) was elevated by 29%, systolic (SAP) and diastolic pressure (DAP) had increased by 7 and 8 mmHg, respectively. During tilt, values for HR and SAP were similar with and without TGLVP whereas DAP and MAP were elevated 8 and 7 mmHg, respectively, by the drug. 4-8 min into the tilt, TGLVP caused an 8% sustained curtailment of SV. Both with and without the drug TPR increased by about 30% in response to head-up tilt. Thus, the marked peripheral arteriolar constriction after vasopressin in the supine position was not affected by head-up tilt. Tilting also abolished the drug-induced elevation in SAP, most likely explained by the reduction in SV. Although TPR was markedly increased by TGLVP during head-up tilt, reflected in the behaviour of DAP, the response of SV speaks against any beneficial effect of this drug on orthostatic tolerance in healthy subjects.

Adult↗
PubMed1987

Dynamic exercise in man as influenced by experimental restriction of blood flow in the working muscles.

The effects of reduced muscle perfusion pressure on dynamic exercise performance and cardiovascular and respiratory functions were investigated. Eight subjects were studied during supine cycle ergometry at stepwise increasing workloads until exhaustion with and without the legs exposed to a supra-atmospheric pressure of 50 mmHg (Leg Positive Pressure, LPP), a novel and convenient means of reducing the perfusion pressure in the working muscles. In the LPP condition exercise performance was reduced by 40% which, judging from assessments of perceived exertion, was due to premature muscle fatigue, indicating local or overall underperfusion of the working muscles. At any given work load, the arterial pressure response was considerably stronger during LPP than in the control condition. LPP also caused greater increases in blood lactate concentration and pulmonary ventilation, the differences from control increasing with the work load. Furthermore, the ventilatory equivalent for O2 at a given work load was markedly higher in the LPP than in the control condition, while exercise-induced decreases in end-tidal PCO2 were considerably exaggerated by LPP. The augmented pressor response during flow-restricted exercise, together with the strong ventilatory response which was out of proportion to overall O2 uptake, suggests increased activation of muscle chemoreflexes by accumulation of metabolic end products, the increased pressor response tending to reduce the local flow error in the working muscles.

Adult↗
PubMed1987

Human skeletal muscle function and metabolism during intense exercise at high O2 and N2 pressures.

The maximal contractile force (peak torque) of the quadriceps femoris was studied during 60 repeated unilateral dynamic knee extensions in nine subjects under three different conditions, viz., during air breathing at normal (1 ATA) and raised (6 ATA) ambient pressures and during O2 breathing at 1.3 ATA. In six subjects the electromyographic (EMG) activity of the working muscle was recorded. Muscle biopsies were obtained from the vastus lateralis before, immediately after, and 1 min after exercise. Tissue specimens were subsequently assayed for various muscle metabolites. Peak torque, as an average of the 60 knee extensions, was higher (P less than 0.05) at 1.3 ATA than at 6 or 1 ATA. Peak torque of the exercising muscle declined more rapidly at 1 ATA than at 1.3 ATA, differing in the final 24 contractions by 14%. At 6 ATA peak torque of the initial 12 contractions was 6% lower (P less than 0.05) than at 1 ATA but equaled 1-ATA values in the latter third of the exercise bout. Although the EMG activity at 1 ATA increased relative to that at 6 ATA as exercise proceeded, the rate of force decline was greater at 1 ATA. Despite greater total work produced at 1.3 ATA than at 1 ATA, the metabolic response to exercise was not substantially altered at increased O2 pressure. However, the restitution rate of energy-rich phosphagens and the elimination of lactate during recovery were greater (P less than 0.05) at 1.3 ATA. These results suggest that hyperoxia may enhance the rate of energy release, whereas high N2 pressure and/or high hydrostatic pressure seem to interfere with neuromuscular activity.

Adenosine Triphosphate↗