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O Eiken

Publications and source records attributed to O Eiken.

At least 19 recordsLinked to original sources
PubMed2004

Hypoxia increases the cutaneous threshold for the sensation of cold.

Cutaneous temperature sensitivity was tested in 13 male subjects prior to, during and after they breathed either a hypocapnic hypoxic (HH), or a normocapnic hypoxic (NH) breathing mixture containing 10% oxygen in nitrogen. Normocapnia was maintained by adding carbon dioxide to the inspired gas mixture. Cutaneous thresholds for thermal sensation were determined by a thermosensitivity testing device positioned on the plantar side of the first two toes on one leg. Heart rate, haemoglobin saturation, skin temperature at four sites (arm, chest, thigh, calf) and adapting temperature of the skin (T(ad); degrees centigrade), i.e. the temperature of the toe skin preceding a thermosensitivity test, were measured at minute intervals. Tympanic temperature (T(ty); degrees centigrade) was measured prior to the initial normoxic thermosensitivity test, during the hypoxic exposure and after the completion of the final normoxic thermosensitivity test. End-tidal carbon dioxide fraction and minute inspiratory volume were measured continuously during the hypoxic exposure. Ambient temperature, T(ty), T(ad) and mean skin temperature remained similar in both experimental conditions. Cutaneous sensitivity to cold decreased during both HH (P<0.001) and NH conditions (P<0.001) as compared with the tests undertaken pre- and post-hypoxia. No similar effect was observed for cutaneous sensitivity to warmth. The results of the present study suggest that sensitivity to cold decreases during the hypoxic exposure due to the effects associated with hypoxia rather than hypocapnia. Such alteration in thermal perception may affect the individual's perception of thermal comfort and consequently attenuate thermoregulatory behaviour during cold exposure at altitude.

Adult↗
PubMed2004

Ischaemia in working muscles potentiates the exercise-induced sweating response in man.

AIM: The purpose was to examine whether graded ischaemia in the working muscles affects the rate of sweating and the control of exercise core temperature. METHODS: Eight subjects performed cycle ergometry exercise in the supine position with (ischaemic exercise) and without (control exercise) restriction of blood flow in the contracting muscles, accomplished by exposure of the legs to a supra-atmospheric pressure of 6.6 kPa. Each subject performed one exhaustive incremental work rate trial and one steady-state exercise trial (at 33% of control peak work rate), in both the control and ischaemia conditions. RESULTS: Ischaemia decreased work performance by 45% so that in this condition the steady-state work rate level corresponded to 63% of ischaemic peak work rate. Ischaemia did not affect the oesophageal temperature equilibrium in the steady-state trials, but potentiated the exercise sweating response. Exercise responses of mean arterial pressure, heart rate and pulmonary ventilation were potentiated by ischaemia. CONCLUSION: During ischaemic exercise sweat secretion was potentiated by non-thermal and/or local thermal stimuli.

Adult↗
PubMed2004

Comparison of vascular distensibility in the upper and lower extremity.

AIM: Because of the great differences in hydrostatic pressure acting along the blood vessels in the erect posture, leg vessels are exposed to greater transmural pressures than arm vessels. The in vivo pressure-distension relationship of arteries, arterioles and veins in the arm were compared with those of the leg. METHODS: Experiments were performed with the subject (n = 11) positioned in a pressure chamber with an arm or lower leg (test limb) extended at heart level through a hole in the chamber door. Intravascular pressure in the arm/lower leg was increased by stepwise increasing chamber pressure to +180 and +210 mmHg, respectively. Diameters of blood vessels and arterial flow were measured using ultrasonographic/Doppler techniques. Changes in forearm and lower leg volumes were assessed using an impedance technique. The subject rated perceived pain in the test limb. RESULTS: The brachial and radial arteries were found to be more distensible than the posterior tibial artery (P < 0.001). Likewise, the distension was more pronounced in the cephalic than in the great saphenous vein (P < 0.001). In the brachial artery, but not in the posterior tibial artery, flow increased markedly at the highest levels of distending pressure (P < 0.001). At the highest intravascular pressures, the rate of change in tissue impedance was greater in the forearm than the lower leg (P < 0.01). At any given level of markedly increased pressure, pain was rated higher in the arm than in the leg (P < 0.001). CONCLUSION: It seems that the wall stiffness of arteries, pre-capillary resistance vessels and veins adapts to meet the long-term demands imposed by the hydrostatic pressure acting locally on the vessel walls.

Adult↗
PubMed2003

Relation between the elastic properties and intima-media thickness of the common carotid artery.

The purpose of the study was to describe the relation between wall elasticity and intima-media thickness in the human carotid artery prior to the development of atherosclerotic plaques. Fifty-eight apparently healthy men, aged 42-65 years (mean 55 years), without symptoms of cardiovascular disease were studied. Thickness and elastic properties of the common carotid artery wall were assessed using ultrasonography and non-invasive arterial pressure measurements. The relation between the calculated intima-media area and the pressure strain elastic modulus was positive and statistically significant on the right but not on the left side. No statistically significant relations were found between the calculated intima-media area and the stiffness or between the intima-media thickness and the elastic modulus or stiffness on either side. Thus, the relations between the common carotid artery intima-media thickness/calculated intima-media area and the common carotid artery elastic modulus/stiffness are weak. In regions without atherosclerotic plaques, the elastic properties of the human carotid artery wall do not seem to be influenced by the wall thickness in an important way.

Adult↗
PubMed2003

The effect of straining maneuvers on G-protection during assisted pressure breathing.

INTRODUCTION: Pilots flying high-performance aircraft increase their acceleration tolerance by using straining maneuvers and anti-G suits. Recently, assisted positive pressure breathing has been added in some aircraft systems. This study assessed the effect of anti-G straining maneuvers on the G-protective properties of one such system, the AGE-39 anti-G ensemble used in the Swedish JAS 39 Gripen aircraft. METHODS: Ten subjects were studied in a centrifuge using each of the following: 1) the AGE-39 in combination with anti-G straining maneuvers (AGSM) throughout each high-G exposure (full maneuver; FM); 2) the AGE-39 in combination with AGSM only during the initial part of each high-G exposure (reduced maneuver; RM). G-tolerance was established during exposures to rapid onset rate (ROR) G profiles with plateau levels ranging from 6.5 to 9.0 G. RESULTS: Mean G-tolerance was > or = 8.8 G (range: 8.5 to > or = 9.0 G) in the RM condition and > or = 9.0 G in all subjects in the FM condition. Mean arterial pressure was 30-50 mm Hg higher (p < 0.001) in the FM than in the RM condition at any given ROR G-load. CONCLUSIONS: AGE-39 in combination with a brief period of straining provide efficient G-protection as illustrated by the finding that all subjects could tolerate 8.5 G while performing AGSM during the initial part of the high-G exposures. However, at 9.0 G, 40% of the subjects had to perform AGSM throughout the duration of the G-exposure. That arterial pressure was only 30-50 mm Hg higher in the FM than RM condition suggests that in the presence of straining maneuvers, pressure breathing makes only a minute contribution to the arterial-pressure response.

Adult↗
PubMed2002

A new hydrostatic anti-G suit vs. a pneumatic anti-G system: preliminary comparison.

HYPOTHESIS: A newly developed hydrostatic anti-G suit is now commercially available. The suit is said to offer a high level of protection against +Gz acceleration. However, past experience shows that it is difficult to produce a hydrostatic suit with effective high-G protection. Careful testing is, therefore, needed to verify its efficacy. METHODS: The G-protective properties of the hydrostatic anti-G suit (Libelle; L) were compared with those of a pneumatic anti-G ensemble (AGE-39) used in the Swedish JAS 39 Cripen aircraft. Three pilots were studied during vertical (+Gz) acceleration in a centrifuge using the following: 1) the L-suit with varied straining maneuvers; 2) the AGE-39 in combination with full anti-G straining maneuvers (AGSM) throughout each high-G exposure (full maneuver; FM); and 3) the AGE-39 in combination with AGSM during the initial part of each high-G exposure (reduced maneuver; RM). G-intensity tolerance was established during exposures to rapid onset rate (ROR) profiles with G-plateau levels ranging from +6.0 to +9.0 Gz. G-endurance was studied during simulated aerial combat maneuvers (SACM) consisting of 10 cycles of 5.5 to 7.5 G. RESULTS: All three pilots tolerated 9.0 G with the pneumatic system both in the RM and FM conditions; their tolerances averaged 6.3 G (range 6.0 to 7.0 G) for the L suit. Thus, during the ROR exposures only the 6.0 G profile was completed by all subjects in all three conditions. At this G-load both muscle straining (as indicated by electromyographic activity in thigh and abdomen) and heart rate were higher in the L than in the RM condition. Mean arterial pressure at eye level was higher in the FM than in the L and RM conditions. Only one subject was able to complete the SACM profile in the L condition. In the RM condition all subjects completed the SACM profile and in the FM condition two subjects completed the SACM. CONCLUSIONS: Whether the AGE-39 was used in combination with maximal AGSM throughout the duration of each high-G exposure or with AGSM only during the initial part of the high-G exposure, G-intensity tolerance was 9.0 G. While wearing the L-suit, G-tolerance was 6.3 G. Thus, under the conditions tested, the G-protection afforded by the L-suit is not adequate for use in a 9-G aircraft.

Acceleration↗
PubMed2001

Motion sickness potentiates core cooling during immersion in humans.

1. The present study tested the hypothesis that motion sickness affects thermoregulatory responses to cooling in humans. 2. Ten healthy male volunteers underwent three separate head-out immersions in 28 degrees C water after different preparatory procedures. In the 'control' procedure immersion was preceded by a rest period. In the 'motion sickness' procedure immersion was preceded by provocation of motion sickness in a human centrifuge. This comprised rapid and repeated alterations of the gravitational (G-) stress in the head-to-foot direction, plus a standardized regimen of head movements at increased G-stress. In the 'G-control' procedure, the subjects were exposed to similar G-stress, but without the motion sickness provocation. 3. During immersion mean skin temperature, rectal temperature, the difference in temperature between the forearm and 3rd digit of the right hand (DeltaT(forearm-fingertip)), oxygen uptake and heart rate were recorded. Subjects provided ratings of temperature perception, thermal comfort and level of motion sickness discomfort at regular intervals. 4. No differences were observed in any of the variables between control and G-control procedures. In the motion sickness procedure, the DeltaT(forearm-fingertip) response was significantly attenuated, indicating a blunted vasoconstrictor response, and rectal temperature decreased at a faster rate. No other differences were observed. 5. Motion sickness attenuates the vasoconstrictor response to skin and core cooling, thereby enhancing heat loss and the magnitude of the fall in deep body temperature. Motion sickness may predispose individuals to hypothermia, and have significant implications for survival time in maritime accidents.

Adult↗
PubMed2001

Effects of hypergravity and anti-G suit pressure on intraregional ventilation distribution during VC breaths.

The effects of increased gravity in the head-to-foot direction (+G(z)) and pressurization of an anti-G suit (AGS) on total and intraregional intra-acinar ventilation inhomogeneity were explored in 10 healthy male subjects. They performed vital capacity (VC) single-breath washin/washouts of SF(6) and He in +1, +2, or +3 G(z) in a human centrifuge, with an AGS pressurized to 0, 6, or 12 kPa. The phase III slopes for SF(6) and He over 25-75% of the expired VC were used as markers of total ventilation inhomogeneity, and the (SF(6) -- He) slopes were used as indicators of intraregional intra-acinar inhomogeneity. SF(6) and He phase III slopes increased proportionally with increasing gravity, but the (SF(6) -- He) slopes remained unchanged. AGS pressurization did not change SF(6) or He slopes significantly but resulted in increased (SF(6) -- He) slope differences at 12 kPa. In conclusion, hypergravity increases overall but not intraregional intra-acinar inhomogeneity during VC breaths. AGS pressurization provokes increased intraregional intra-acinar ventilation inhomogeneity, presumably reflecting the consequences of basilar pulmonary vessel engorgement in combination with compression of the basilar lung regions.

Adult↗
PubMed2001

Relationship between arm pain and distension of arteries and veins caused by elevation of transmural pressure in local vascular segments.

BACKGROUND: Exposure to high +Gz forces may induce arm pain, which has been hypothesized to be caused by pressure-induced overdistension of local blood vessels. The purpose of the present investigation was to study the pressure-distension relation of veins and arteries in the human arm and the relation between arm pain and distension of local vessels. METHODS: Increased distending pressures (DP) in the vasculature of the arm were accomplished by placing the subject (n = 8) in a pressure chamber with one arm positioned through a port in the chamber door, and increasing chamber pressure to +180 mm Hg in a stepwise manner. Diameters in the brachial artery and in the brachial, radial and cephalic veins were measured by ultrasonography. Changes in forearm volume were estimated from measurement of tissue impedance. Perceived pain was rated using a 10-point scale. RESULTS: Arm pain increased with pressure to a maximum rating of 8.5 (= median; range: 4-10). Increasing DP from 30 to 180 mm Hg resulted in a steady increase (p < 0.05) in venous diameter which varied from 12 +/- 8% (mean +/- SD) in the brachial vein to 23 +/- 14% in the radial vein. Inthe brachial vein diameter increases were most pronounced at the sites of the venous valves. Arterial diameter was unchanged up to a DP of about 200 mm Hg (calculated as diastolic arterial pressure + applied chamber pressure), but then increased by 32 +/- 9% (p < 0.001). Forearm impedance dropped with increasing pressure (delta = 23 +/- 5%; p < 0.01); the rate of change was non-linear with a faster change at the highest DP which may indicate pressure distension of precapillary resistance vessels. CONCLUSIONS: Elevation of pressure in arm vessels to levels that may occur in pilots flying high-performance aircraft results in distension not only of veins but also of arteries and probably of smaller precapillary vessels. Therefore, and because these changes coincide with the development of severe arm pain, local overdistension of blood vessels remains a plausible cause of G-induced arm pain.

Adult↗
PubMed2000

Hyperbaric oxygen therapy does not affect recovery from delayed onset muscle soreness.

PURPOSE: This study investigated whether hyperbaric oxygen therapy (HBOT) improves recovery after exercise-induced muscle injury. METHODS: Healthy male subjects (N = 24) were randomly assigned to either a placebo group or a HBOT group. Subjects were tested for maximal isometric strength (preexercise) of their right elbow flexors. Each subject then completed a high-force eccentric workout of the elbow flexor muscle group to induce delayed onset muscle soreness (DOMS). On the seven successive days after this workout, the subjects were exposed to a hyperbaric environment of 2.5 ATA for 60 min, inspiring either a normoxic mixture (P(I)O2 = 0.2 ATA; placebo group) or a hyperoxic gas mixture (P(I)O2 = 2.5 ATA; HBOT group). Before the eccentric workout and daily for the next 10 d, measurements were obtained regarding: maximal isometric muscle strength of the elbow flexor muscles, right upper arm circumferences, and rating of the perceived muscle soreness. RESULTS: Isometric strength decreased significantly from preexercise levels of 25.1 +/- 3.8 kp to postexercise levels of 12.0 +/- 4.6 kp, for the HBOT group, and from 24.6 +/- 3.4 kp to 12.5 +/- 3.7 kp, respectively, for the placebo group. Over the 10-d recovery period, there was no difference in the rate of recovery of muscle strength between the two groups. Perceived soreness peaked at about 48 h after exercise with no difference between groups. Also, the exercise-induced increases in arm circumference were similar in the two groups. CONCLUSIONS: These results indicate that HBOT is not an effective therapy for the treatment of DOMS.

Adult↗
PubMed1999

Muscle control in elite alpine skiing.

PURPOSE: The purpose of this study was to determine whether muscle control may be influenced by accelerative forces brought about by the downhill displacement of body mass in combination with the sharp turns during alpine skiing. METHODS: Sixteen elite skiers performed either super G (SG), giant slalom (GS), slalom (SL), or freestyle mogul (FM) skiing. Knee and hip joint angles and electromyographic (EMG) activity of the knee extensors were recorded. RESULTS: During the course of a turn, the minimum (deepest stance position) knee angle of the outside (main load-bearing) leg ranged from 60 degrees to 100 degrees, where the smallest angle was obtained in the FM event. Among the traditional alpine disciplines, smaller knee angles were obtained in the high-speed events (i.e., knee angle: SG<GS<SL). Knee angular velocity of the outside leg ranged from 15 degrees to 300 degrees x s(-1), with the slower movements in the high-speed disciplines (i.e., knee angular velocity: SG<GS<SL<FM). In all disciplines, EMG activity reached near-maximal levels during the course of a turn. In SG, GS, and SL, but not in FM skiing, a marked predominance of eccentric over concentric muscle actions was observed. The dominance of slow eccentric muscle actions has not been observed in other athletic activities. CONCLUSIONS: We believe these results have important implications for the design of specific training models.

Adult↗
PubMed1999

Pain in the arms induced by markedly increased intravascular pressure decreases after repeated exposures to moderately increased pressures.

It is well documented that exposure to high gravitational (G)-load in the head-to-foot direction may induce arm pain. Such G-induced arm pain is of vascular origin and caused by markedly increased pressure in the arm vessels. It has been hypothesized that the arm pain is due to pressure-induced overdistension of local blood vessels. Indeed, elevation of local intravascular pressure to levels that induce considerable arm pain results in distension of both veins and arteries. There appears to be a paucity of data regarding the effects of repeatedly increasing intravascular pressure in the arms. Accordingly, the purpose of the present study was to investigate the effect of iterative exposures to moderate pressure elevations in the arm vessels (here termed "pressure training") on the pressure distension relationships of the vessels and on pressure-induced arm pain. To experimentally induce increased transmural pressure over the vessel walls of the arms we used a modified version of a method described elsewhere; this method has also proven a useful tool for simulating G-induced arm pain.

Adaptation, Physiological↗
PubMed1996

Effect of nitrous oxide on human skeletal muscle function.

BACKGROUND: Nitrous oxide (N2O) is commonly administered in conjunction with parturition, which requires the performance of repeated high-force voluntary muscle actions. Therefore, we examined the effect of a subanesthetic dose of N2O on the force-velocity relationship of the quadriceps femoris muscle. METHODS: Nine healthy subjects performed maximal voluntary muscle actions once while breathing air and once while breathing a normoxic gas mixture containing 35% (N2O). Peak torque of the knee extensors was measured during concentric muscle contractions at different angular velocities (30, 60, 90, 150 and 210 degrees s-1), and eccentric (30, 60, 90, and 150 degrees s-1) and isometric (knee-joint angle approximately equal to 60 degrees) muscle actions. Maximal angular velocity was determined during unloaded knee extensions. RESULTS: N2O decreased peak torque at any given angular velocity. The overall decrease in peak averaged 4.8 +/- 2.2% (P < 0.0001). Likewise, N2O decreased maximal angular velocity by 5.7 +/- 4.3% (P < 0.01). Thus, the impairment in muscle function induced by a 35% N2O is only minute and hence most likely of little significance in clinical practice.

Adult↗
PubMed1995

Nitrogen narcosis attenuates shivering thermogenesis.

Thermoregulatory responses of eight healthy subjects (six men and two women) were compared when they were head-out immersed in 15 degrees C water at both 1 and 6 ATA. Both trials were conducted in a hyperbaric chamber. During the immersions, esophageal temperature (T(es)) and skin temperature at two sites (chest and calf) were recorded at minute intervals. Oxygen uptake was determined at 5-min intervals with the Douglas bag method. The order of the two trials was alternated. The rate of T(es) cooling was greater during the 6-ATA trial [2.1 +/- 0.5 degrees C/h (SE)] than during the 1-ATA trial (1.3 +/- 0.5 degrees C/h; P < 0.01). Despite the greater rate of core cooling, and presumably a greater thermal drive for shivering, the oxygen uptake response for a similar decrement in T(es) was lower during exposure to 6 than to 1 ATA (P < 0.05). Also, for similar displacement in T(es), the subjects perceived the immersions at 6 ATA to be less cold than those at 1 ATA (P < 0.05). It is concluded that the development of hypothermia in compressed-air divers may be due, in large part, to the attenuation of heat production and cold perception. Most likely, the observed effects on the autonomic responses and thermal perception are due to an inhibitory action of hyperbaric nitrogen on central neural structures involved in temperature regulation.

Adult↗
PubMed1995

Inhalation rewarming from hypothermia: an evaluation in -20 degrees C simulated field conditions.

The present study evaluates the efficacy of inhaling warm moist air as a method of rewarming from hypothermia in -20 degrees C field conditions. The method of inhalation rewarming is compared to two other methods of rewarming: a) passive rewarming; and b) passive rewarming, with a respiratory heat exchanger designed to minimize respiratory heat loss. Eight male subjects were rendered hypothermic by immersion in 15 degrees C water for 1 h. They were withdrawn from the tank earlier, in the event that their rectal temperature (Tre) decreased to 35 degrees C, or by 1.5 degrees C from the pre-immersion value. Upon completion of the immersion, they were placed in a well-insulated sleeping bag assembly and transferred to a cold room maintained at -20 degrees C for a 2 h rewarming period. They participated in 3 trials: Control-passive rewarming; Heat Treat-inhalation rewarming with the Heat Treat; HME-passive rewarming in conjunction with a respiratory heat and moisture exchanger (HME). During the rewarming period, inspired air temperature was -19.4 +/- 1.1 degrees C in the control trial. In the HME and Heat Treat trials subjects breathed via an oro-nasal mask. The inspired air temperature was +20.5 +/- 1.2 degrees C in the HME and +36.2 +/- 2.9 degrees C in the Heat Treat trial. The post-immersion drop in Tre was significant in all conditions. The reduction in the post-exposure drop in Tre observed with the Heat Treat may be attributed to the minimization of respiratory heat loss, since the magnitude of the reduction was similar to that observed with the HME.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Involvement of eccentric muscle actions in giant slalom racing.

Joint angular movements and muscle activation (EMG), were determined in male elite racers while performing the giant slalom. Movement cycles averaged 3.5 +/- 0.6 s (left plus right turn), and knee angle ranged 66-114 degrees (180 degrees = straight leg). Knee extensor muscle use was dominated (rectified EMG; P < 0.05) by the leg controlling the outside (downhill) ski during the turn. Time spent while decreasing knee angle (eccentric muscle action) of outside leg averaged 1.0 +/- 0.2 s. This phase was longer (P < 0.05) than the average push-off (concentric muscle action) phase of 0.5 +/- 0.1 s. Moreover, EMG activity of the outside leg during eccentric muscle actions exceeded (P < 0.05) that of concentric actions and was similar to that attained during maximum isometric knee extension in laboratory tests. Knee and hip angular movement ranged 20-50 degrees. Average joint velocities equalled 20-40 degrees.s(-1) during the turning phase. Thus, competitive giant slalom skiing is dominated by slow eccentric muscle actions performed at near maximum voluntary force. Because of their greater ability to generate force, eccentric muscle actions may be warranted or even required to resist the G-forces induced during the turn phase.

Adult↗
PubMed1994

Effects of blood-volume distribution on the characteristics of the carotid baroreflex in humans at rest and during exercise.

Seven supine subjects were studied at rest and during mild to moderate dynamic leg exercise with and without unloading of the cardiopulmonary baroreceptors accomplished by exposing the lower portion of the body to a subatmospheric pressure of 20 mmHg (Lower Body Negative Pressure, LBNP). The function of the cardiac branch of the carotid baroreflex was studied over its full operational range by measuring R-R intervals during application of pulse synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) induced increasing R-R intervals in all conditions. In conformity with previous results from our laboratories it was found that the maximal rate of change in relative R-R intervals and the corresponding transmural pressure were higher during exercise than at rest, indicating that exercise increased the carotid baroreflex sensitivity and shifted its optimal buffering range to higher arterial pressures. LBNP did not affect the characteristics of the reflex at rest nor during exercise. It is concluded that reduced central venous pressure with consequent selective cardiopulmonary receptor disengagement exerts no influence on the carotid baroreflex control of heart rate (HR), as tested over the entire arterial pressure-effector response relation, either at rest or during mild-moderate exercise.

Adult↗