Biomedical subjects

K Myhre

Publications and source records attributed to K Myhre.

At least 19 recordsLinked to original sources

PubMed1992

Physiological effects of altitude training on elite male cross-country skiers.

Seven elite male cross-country skiers trained for 3 weeks at an altitude of 1900 m. Haemoglobin concentration ([Hb]), haematocrit (Hct) (obtained from venous blood), maximal oxygen uptake (VO2 max) and energy expenditure during a standard submaximal workload were measured before and after training at altitude, and 1 year later while training at sea level (control). Both [Hb] and Hct increased significantly, and the skiers with the lowest initial [Hb] and Hct experienced the largest increases during training at altitude. The increase in blood lactate (BLa) concentration (using haemolysed capillary blood) during a standard submaximal exercise test was significantly lower after training at altitude than before it or 1 year later (control). A significant correlation was found between the magnitude of increase in [Hb] and Hct and the difference in the lactate response to the standard submaximal workload pre- and post-altitude training. Although VO2 max remained unchanged, lower BLa concentration during the submaximal test probably reflects an improved ability to exercise at higher submaximal workloads shortly after training at altitude compared with pre-altitude training. It is suggested that subjects with low initial [Hb] and Hct improve their aerobic performance capacity most during altitude training.

Altitude↗

PubMed1991

Increased plasma hypoxanthine values in humans during exposure to simulated altitude of 7,620 meters (25,000 feet).

In this study we have determined the effect of severe and moderate hypoxemia on plasma hypoxanthine and lactate values. Hypoxemia was induced in healthy humans in a low pressure chamber. The test subjects breathed atmospheric air at barometric pressures of 279 mm Hg and 385 mm Hg, representing a simulated altitude of about 7,620 and 5,334 m (25,000 and 17,500 ft), respectively. Exposure to 279 mm Hg represents a severe hypoxemia and all subjects exposed to this simulated altitude for 2 min showed symptoms related to hypoxia. After this exposure, plasma hypoxanthine increased by an average of 2.4 times compared to preexposure values. Exposure to 385 mm Hg represents a moderate hypoxemia and the persons tested at this simulated altitude for 45 min showed no or minor symptoms related to hypoxia and there was no change in plasma hypoxanthine values. In contrast to the unchanged plasma hypoxanthine values there was a 50% increase in plasma lactate values after 30 min exposure. We conclude that plasma hypoxanthine is a reliable marker for severe cellular hypoxia in humans and that enhanced plasma hypoxanthine levels are a rapid response to cellular hypoxia.

Adolescent↗

PubMed1991

Prolonged photostress macular recovery after reduced blood pressure.

In order to investigate an association between systemic blood pressure and restitution of normal visual function in dim illumination after photostress, macular recovery time and blood pressure were measured in two groups: 1) 90 young and healthy military pilots and applicants for military pilot training; and 2) 10 hypertensive patients before and after 12 weeks of antihypertensive treatment. Young normotensive subjects (20/20 vision) with low diastolic blood pressure performed less well (longer macular recovery time) than those with higher pressure (r = -0.42, p less than or equal to 0.05). Among the hypertensive patients three were given doxazosin, three, prazosin, and four, placebo. The treatment period produced significant fall in blood pressures, a small reduction in intraocular pressure (p less than or equal to 0.03) and a lengthening of initial monocular recovery period (p = 0.04) in addition to reduced monocular (p = 0.015) and binocular (p = 0.022) macular recovery in the remaining part of the 2-min test period. This observation may be important for antihypertensive treated patients whose occupation requires fast visual adjustment to changing stimuli in dim light.

Adaptation, Physiological↗

PubMed1990

[Iron and sports].

We review normal iron metabolism and iron deficiency in athletes with and without anemia, and possible causal relationships. Hard physical training, such as medium and long distance running, appears to promote negative iron balance, with and without fall in hemoglobin concentration. A normally varied diet is suggested as adequate to meet the iron requirements in male athletes. Iron supplementation is not recommended unless blood/serum concentration of hemoglobin, ferritin, iron and transferrin are measured and the results indicate a state of iron deficiency. However, female athletes should consider iron supplementation, since loss of iron is higher in women than in men.

Adult↗

PubMed1990

Hypoxia and deposition of iron in liver and spleen of mice given iron supplement.

Iron-related changes in peripheral blood and variations in liver and spleen iron concentrations during alternating periods of hypoxia and normoxia have been investigated in iron-supplemented mice by chemical and histological methods. During hypoxia, packed cell volume increased from 40 to 70%. The iron content of the liver increased during the first hypoxic and the following normoxic period, while an increase in spleen iron started after the first hypoxic period. Transferrin saturation fell from about 60 to about 20% during hypoxia and normalized during normoxia. Hypoxia together with iron supplementation led to increased erythropoiesis and parenchymal iron deposition in liver. The reduction in transferrin saturation may be attributed to the effective uptake of iron by hepatocytes simultaneously with the erythropoiesis. The spleen seemed to participate in the production of red cells during hypoxia. The increase in spleen iron during normoxia can be explained by the role of the spleen in the catabolism of excess erythrocytes.

Animals↗

PubMed1990

The response of the light reflex of retinal vessels to reduced blood pressure in hypertensive patients.

The response of retinal arteries and veins to 3 months of antihypertensive medication was studied in 10 patients (39-56 years old) with essential hypertension. We used computerized microdensitometry on fundus photographs, a technique allowing for objective and simultaneous measures of the caliber of blood columns and the width and intensity of their central 'light reflex'. A moderate lowering of diastolic and systolic blood pressures (P less than 0.001) resulted in a significant reduction in the intensity of reflection from retinal arteries (38.6%; P less than 0.005). An increase in the width of the blood column (2.8%; n.s.) and the reflex (8.6%; n.s.) was indicated. Traditionally, changes in light reflectivity has been associated with arteriosclerosis of the vessel wall. The study shows, however, that the vascular reflex is most sensitive to changes in the systemic blood pressure. This signals a need for critical reviewal of interpretation and usefulness of classical grading systems of ophthalmoscopic signs of hypertensive retinopathy.

Adult↗

PubMed1990

Impairment of rat polymorphonuclear neutrophilic granulocyte phagocytosis following repeated hypobaric hypoxia.

Exposure of rats to repeated hypobaric hypoxia (17 h at 0.5 atm for 0-7 d) induced significant reduction of the phagocytic capacity of peripheral blood polymorphonuclear neutrophilic granulocytes (PMNL). In addition, the hypoxia induced a significant increase of the hematocrit, hemoglobin, thrombocyte, and total leukocyte concentrations. Differential counting of peripheral blood revealed significant granulocytosis. An increase of the concentration of corticosterone was demonstrated following 2 d of hypobaric hypoxia, whereas 5 d later the corticosterone concentrations were similar to that of the controls. The reduced PMNL phagocytic capacity observed following repeated hypobaric hypoxia may have consequences for host defence in situations of hypoxia exposure.

Aerospace Medicine↗

PubMed1990

Vascular response of retinal arteries and veins to acute hypoxia of 8,000, 10,000, 12,500, and 15,000 feet of simulated altitude.

Computerized scanning microdensitometry of fundus photographs was used to study the effect of acute hypoxia on vessel diameters of 238 retinal arteries and 227 veins in 40 men aged 18-23 years. Fundus photography was performed at sea level and at simulated altitudes in a low-pressure chamber, randomly selecting 10 men to each of four altitudes--8,000, 10,000, 12,500, and 15,000 ft (2,400, 3,000, 3,800, and 4,500 m). After 15 min of hypoxic exposure, the caliber of small arteries (less than 75 microns) increased 4% (p less than 0.01) and that of large arteries (greater than or equal to 75 microns) 7% (p less than 0.05), already at 8,000 ft (2,400 m). The caliber of large veins did not change until an increase of 6% (p less than 0.01) was observed at 15,000 ft (4,500 m). Although large arteries increased 7% (p less than 0.05) and 8% (p less than 0.01) in diameter at 10,000 ft (3,000 m) and 15,000 ft and small veins 9% (p less than 0.05) and 12% (p less than 0.01) at the same altitudes, respectively, no change was observed at 12,500 ft (3,800 m). Thus, the dilating effect of hypobaric hypoxia was nonlinear from sea level to 15,000 ft of simulated altitude. As an overall response to the four simulated altitudes the vasodilation was negatively correlated to the vessel diameter at sea level (r = -0.20) in both arteries and veins (p less than 0.01). The variability of hypoxic vascular response was as great within different parts of individual retinas as between different retinas.

Adolescent↗

PubMed1990

The form of selenium determines the response to supplementation in a selenium replete population.

In an ongoing study of selenium bioavailability, effects of supplementation with organic and inorganic forms of selenium were investigated in healthy, Norwegian women, aged 23-50 years. In phase I of the study, 58 women received 200 micrograms selenium per day either as selenite or selenium-rich pea flour for 3 months. The selenium tablets were taken together with placebo or ascorbic acid in a double blind design. Initial blood and serum selenium concentrations were 153 +/- 15 micrograms/l and 117 +/- 12 micrograms/l, respectively. These are average values for Norwegians. Indications of increased blood levels were seen in all groups, but the rise reached significance only for the subgroup receiving selenite and ascorbic acid, 14 micrograms/l, P less than 0.05. On the other hand, selenium analysis of 72-h urine samples confirmed that at an average 50 per cent of the selenium supplements had been absorbed. In phase II of the study, 28 of the participants continued for another 5 weeks, still on 200 micrograms Se per day, but this time consuming commercially available preparations. Of four preparations that were tested, two consisted of yeast Se. Only one of these produced a significant rise in blood and serum selenium levels, 60 and 55 micrograms/l respectively. Blood glutathione peroxidase values were not affected by any supplementation. The study demonstrates that different forms of organic selenium elicit widely different responses when administered to a relatively selenium-replete population, and that the explanation for this must be sought at the metabolic level.

Adult↗

PubMed1989

Retinal vessel responses to exercise and hypoxia before and after high altitude acclimatisation.

Computerised microdensitometry was used to study diameter changes in 93 arterial and 91 venous vessel sites in the retinas of four mountain climbers before and after spending seven weeks in the Himalaya mountains. The vascular response to short-term strenuous exercise was measured at sea level, to acute hypoxia of simulated altitude of 15,000 ft (4,572 m) at rest, and to strenuous exercise while acutely exposed to the same hypoxic condition. Before the mountain exposure, retinal vessels constricted during exercise -1.9% (arteries); -3.3% (veins) and dilated in acute hypoxia 9.4% (arteries); 8.1% (veins). Superimposed exercise on hypoxic dilated arteries reduced the vasodilation (9.4% to 6%). After acclimatisation, the same physical work load at sea level constricted the arteries more (-5.4% vs -1.9%) but did not constrict the veins (0.2% vs -3.3%). Superimposed exercise on hypoxic dilated vessels, excessively dilated both arteries (8.4% vs 6.0%) and veins (13.7% vs 8.4%), compared to changes seen before the mountain sojourn. This study shows that physical conditioning and long adaptation to hypoxia, significantly change the vascular response of the retina to physical activity both in normal atmospheric conditions and during hypoxic stress. High altitude retinal hemorrhages (HARH) were present in one climber, and the study may indicate why HARH is seen often in young and physical well-trained subjects.

Acclimatization↗

PubMed1989

Arterial PCO2 and pH in man during 3 days' exposure to 2.8 kPa CO2 in the inspired gas.

It has not been firmly established how respiration adapts to long-term CO2 exposure in man. We have therefore exposed five healthy human subjects to 2.8 kPa CO2 in the inspired gas for about 70 h in a chamber with controlled atmospheric conditions at ambient pressure PCO2 and pH were determined in arterial or arterialized venous blood drawn before, during and after the exposure. One subject was studied twice. We found that PaCO2 increased acutely and then increased further within the 5- to 24-h period of exposure to 2.8 kPa CO2. No consistent change was observed during the following 2 days. At the end of exposure the PaCO2 was 0.5 kPa above the pre-exposure level. When the breathing gas was switched back to room air, PaCO2 promptly returned to pre-exposure values. The secondary rise in PaCO2 within the first day would correspond to a decrease in alveolar ventilation of about 10% assuming constant production and elimination of CO2. Arterial pH remained slightly below the pre-exposure level during the entire exposure period. A slight renal compensation resulting in an increase in base excess of about 1 mmol l-1 may have occurred in the middle part of the exposure period. We conclude that a significant, but moderate, respiratory adaptation takes place during the first day of exposure to an increased inspired load of CO2.

Acid-Base Equilibrium↗

PubMed1989

Correlation of plasma erythropoiesis stimulating factor(s) and immunoreactive erythropoietin levels during rapid growth in the mouse.

During the early neonatal period of rapid growth in the mouse, increased plasma levels of erythropoiesis stimulating factor(s) (ESF) have been found when measured by an in-vitro bioassay technique. It is unclear whether these increased ESF levels represent increased levels of circulating erythropoietin (Ep) alone or Ep in combination with other less-defined erythropoietic stimulatory factors. To examine this issue, plasma from neonatal mice of varying post-natal ages and from normoxic and hypoxic adult mice was studied. We found that plasma Ep levels measured by radioimmunoassay (RIA) correlated significantly with in-vitro bioassayed ESF levels (r = 0.84, P less than 0.0001, n = 21). Although an in-vivo bioassay for plasma Ep proved too insensitive for rigorous correlation with data from the RIA and in-vitro bioassay, the in-vivo data were in qualitative agreement with the other two, more sensitive, assays. In all three assays the highest plasma levels were observed in the 20-day-old mice and in adult mice which had been subjected to hypobaric hypoxia for 8 h. Based on the strong agreement of the results obtained with the RIA and the in-vitro bioassay in both neonatal and adult mouse plasma, we conclude that the high plasma ESF levels of 20-day-old mice measured with the in-vitro bioassay are largely immunochemically identifiable Ep. However, the data also suggest the presence of non-Ep factors in neonatal plasma which stimulate the in-vitro bioassay.

Age Factors↗

PubMed1989

Psychophysical and electrophysiological testing of retinal function. Macular recovery time and oscillatory potentials in normal subjects.

We evaluated different aspects of 1) psychophysical and 2) electrophysiological testing procedures of retinal function, represented by macular recovery time (nyctometry) and oscillatory potentials (electroretinography), respectively. Ninety healthy males, aged 18-28 years, were used in the study. We registered two different phases of macular recovery time, IRT: initial recovery time (less than 40 sec) and AUC: area under the curve (less than 120 sec) and both individual and summed nodes of oscillatory potentials (OPs). A significant effect of training was observed in monocular registration of IRT and AUC (P less than 0.01), and the superiority of binocular recovery was numerically compared to monocular recovery (P less than 0.01). The inter-variability (coefficient of variation) of IRT was high (40%) in both monocular and binocular registrations, while AUC had a smaller variability binocularily than monocularily (33% vs 21%). The inter-variability of OPs was low (16%). Intra-variability, between first and second eye tested, showed highly correlated values in IRT, AUC and OPs (r = 0.51-0.82; P less than 0.004), while IRT/AUC was not correlated to amplitudes of OPs. The results emphasize that selecting one eye, mean of two eyes or both eyes are critical for accuracy and validity in psychophysical testing of visual performance.

Adolescent↗

PubMed1989

The effect of hypoxia on the central light reflex of retinal arteries and veins.

Computerized scanning microdensitometry was used on fundus photographs of 40 men (aged 18-23 years) and effects of hypoxia on intensity profiles of the 'light reflex' in 140 arteries and 138 veins were analysed. Changes from sea level to four levels of acute hypoxia of simulated altitude were studied: 8000 feet (ft) (2438 meters) (m), 10,000 ft (3048 m), 12,500 ft (3810 m), and 15,000 ft (4572 m) using a low-pressure chamber. The intensity of the reflex increased at 12,500 ft and 15,000 ft by 24% (P less than 0.05) and 39% (P less than 0.01) in arteries and 50% and 33% in veins (P less than 0.05), respectively. As an overall response from sea level to all four altitudes, the width of the reflex was reduced. The reduction in width was negatively correlated to the diameter of the arteries (P less than 0.0001) and veins (P less than 0.001) at sea level, and the variability of changes was larger in veins (P less than 0.01). Funduscopic light reflected from intravascular blood columns of retinal vessels is thus influenced by hypoxic stress, and 12,500 ft of simulated altitude represents a threshold value of circulatory interest.

Adolescent↗

PubMed1989

Reduced systolic blood pressure elevations during maximum exercise at simulated altitudes.

Ten healthy female subjects performed maximum exercise on a bicycle in an altitude chamber during normoxia and hypobaric hypoxia simulating altitudes of 2,450, 3,700 and 4,600 m. The increases in systolic blood pressure responses were reduced with the degree of hypobaric hypoxia, whereas heart rate and diastolic pressure responses were unchanged. The increases in blood levels of aldosterone, plasma renin activity, adrenaline, noradrenaline, neuropeptide-Y and vasoactive intestinal peptide were similar at the different simulated altitudes. Angiotensin-converting enzyme and vasoactive intestinal peptide levels were not affected by hypoxia or maximum exercise. The present results suggest that the decreases in systolic blood pressure responses during hypobaric hypoxia could not be explained by altered responses of the measured vasoactive substances from the renin-angiotensin, gastrointestinal, and autonomic nervous systems.

Adult↗

PubMed1989

The effect of hypoxia upon macular recovery time in normal humans.

Bright light illumination (photostress) of the macula produces a negative after-image in the form of a central scotoma. The time needed for restoring normal visual acuity function, "macular recovery time," may be measured using a nyctometer. We have measured the recovery in 30 normal men, aged 18 to 23 years, at sea level and at 8,000 ft (n = 10), 15,000 ft (n = 10), and 18,000 ft (n = 10) of simulated altitudes in a low pressure chamber. The degree of initial recovery (the first 30-40 s) was unaffected by hypoxia equivalent to 8,000, 15,000, and 18,000 ft. The recovery at 2 min was impaired by hypoxia at an altitude of 18,000 ft (p = 0.009) but not at 8,000 ft or 15,000 ft. The initial phase of recovery may represent the neural phase of macular function and appears to be more resistant to hypoxia than the recovery at 2 min, the latter probably being dominated by photochemical recovery. The study establishes a critical level of hypoxia where complete recovery of macular sensitivity is not achieved.

Adolescent↗

PubMed1989

Blood pressure, intraocular pressure, and retinal vessels after high altitude mountain exposure.

Identical test protocols were used before and after 2 to 7 weeks of high altitude exposure in 23 climbers participating in 3 separate mountain expeditions in the Himalayas. The three groups reached altitudes of 4,000 m, 5,200, and 5,850 m, respectively. High altitude retinal hemorrhages (HARH) were found in three subjects (13%). Two weeks after the mountain exposure, reduced mean values of systolic (p less than 0.005) and diastolic (p less than 0.05) blood pressure and intraocular pressure (p less than 0.005) were found. Retinal veins were dilated 2.6% (p less than 0.001), and in both arteries (p less than 0.001) and veins (p less than 0.005) we observed a tendency for small vessels to dilate and large vessels to constrict. The intensity of reflection of light ("the central light reflex") from arteries was reduced (p = 0.003), indicating hemorrheology changes in the vessels. This study shows that significant changes in blood pressure, intraocular pressure and retinal vascularity follow hypoxic and physical strain of high altitude. The vascular conditioning of altitude acclimatization can be demonstrated in the retinal circulation 2 weeks after the exposure.

Adult↗

PubMed1987

Erythropoietic factors in plasma from neonatal mice. In vivo studies by the exhypoxic polycythaemic mice assay for erythropoietin.

The erythropoiesis stimulating factor(s) (ESF) in plasma from 20-day-old WLO-mice have previously been studied by a cell culture assay, and also by means of gel filtration chromatography and affinity chromatography. It was concluded that the high levels of ESF found in the neonatal mouse plasma probably consisted of erythropoietin (Ep) alone. The objective of the present investigation was to obtain further information of whether this high ESF found in vitro is Ep alone, or Ep in combination with other factors. To accomplish this plasma from 20-day-old WLO mice and a standard Ep were studied in vivo by the exhypoxic polycythaemic mice assay for Ep, with and without preincubation with rabbit anti-Ep serum (AS). Aliquots of some samples were also studied in vitro by the exhypoxic polycythaemic mice assay for Ep, with and without pre- in both assays (P less than 0.001). However, incubation with AS significantly reduced (P less than 0.001) but did not totally block either the in vivo or the in vitro activity of the plasma (P less than 0.005). This also was the case regarding the in vivo activity of the standard Ep (P less than 0.001), while the in vitro activity of this Ep preparation was totally blocked by incubation with AS (P greater than 0.3). These results indicate that a considerable part of the high erythropoietic stimulatory activity found in plasma from 20-day-old mice, with both assays, is Ep. This supports the previous in vitro studies. However, the present results also support the conclusion that part of the activity is due to non-Ep stimulatory factors.

Age Factors↗