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Biomedical subjects

K Myhre

Publications and source records attributed to K Myhre.

At least 37 records · Page 2Linked to original sources
PubMed1987

The light reflex in retinal vessels and its relation to age and systemic blood pressure.

The light streak characteristics on retinal vessels were studied by microdensitometry on fundus photographs. We compared the width and the intensity of the reflex in a young group (mean: 19.7-year-old; n = 40) and in an older group (mean: 45.3-years-old; n = 22) of normal subjects. By subgrouping according to age and blood pressure levels, we studied possible effects of these parameters on the light streak. We found higher intensity of reflection from both arteries and veins in the older group (P less than 0.01). This effect seemed mostly related to the age of the subjects. We also registered a relation between systolic blood pressure and intensity of reflection from veins in the young group (P less than 0.03). Optical changes in the vessel walls in the ageing process and intravascular pressure effects on the indices of refraction in the erythrocytes/plasma may account for these findings. The width of the reflex was not found to be related to either the age or the blood pressure level of the subjects.

Adolescent↗
PubMed1987

The central light reflex of retinal arteries and veins in insulin-dependent diabetic subjects.

The width (Wr/Wo) and the intensity (Ir) of the central light reflex were studied on retinal arteries and veins in insulin-dependent diabetic patients. A diabetic group (n = 45) was compared to normal subjects (n = 57), and the groups were matched according to age and blood pressure levels. A computerized scanning microdensitometer was applied across various sites on vessels in fundus photographs. The Ir of the reflected light was significantly reduced in diabetic arteries and veins compared to the vessels in the control group (P less than 0.001). This may implicate abnormalities in blood rheology of the retinal circulation in diabetes. The Wr/Wo was found narrower in veins in diabetic patients (P less than 0.001). This probably indicates differences in haemodynamics of venous flow in diabetic and normal subjects. The intensity was correlated to the duration of diabetes (P less than 0.05), while neither the width nor the intensity were found related to sex, metabolic control, intraocular pressure or retinopathy.

Adolescent↗
PubMed1986

Proteinuria in fighter pilots after high +Gz exposure.

Exposure to high gravitational forces acting along the body axis towards the feet (+Gz) causes considerable strain on several organ systems, including the kidneys. During +Gz tolerance studies without anti-G suits, significant amounts of protein and hyaline casts were found in 17 of 20 fighter pilots after centrifugation. The G load alternated between 3.5 and 5.5 G. Mean time in the centrifuge was 15 min. For comparison we examined another group of 19 fighter pilots after air combat maneuver training with anti-G suits. None showed proteinuria. The proteinuria most likely indicates a severely depressed renal blood flow during centrifugation.

Adult↗
PubMed1985

Isometric abdominal muscle training and G tolerance.

Methods to increase G tolerance of pilots flying high-performance aircraft are of vital importance. Straining maneuvers to increase G tolerance involve abdominal muscles, and high intra-abdominal pressures (IAP) are recorded during G exposure. This study was carried out to examine the effects of an 11-week abdominal muscle training program on maximal IAP, G tolerance and muscle strength/endurance in 10 fighter pilots. G tolerance was measured in a human centrifuge using simulated aerial combat maneuvers (ACM). The pilots had a higher maximal IAP before training than a control group. G tolerance, maximal IAP, and maximal peak torque of knee extensors were not changed by the training. In contrast, leg muscle endurance increased (p less than 0.01) and ratings of local perceived exertion decreased (p less than 0.01). Static endurance of the knee extensors was positively correlated (p less than 0.05) with G tolerance. It is concluded that the present abdominal training program, employed in experienced fighter pilots, is not sufficient to increase IAP or G tolerance.

Abdomen↗
PubMed1985

Analyses of maximum cardiopulmonary performance during exposure to acute hypoxia at simulated altitude--sea level to 5000 meters (760-404 mm Hg).

The maximum cardiopulmonary performance of seven healthy male subjects was studied repeatedly in graded hypoxia at ambient pressures ranging from 760 to 404 mm Hg (sea level to 5000 m of simulated altitude). Using this approach it has been possible to not only establish a reproducible value for VO2max, but to determine an equation which may be used to predict the VO2 at altitude for healthy, unacclimatized males exercising to exhaustion. Moreover, we have attempted to explain the limits to pulmonary ventilation at decreasing levels of PO2 by comparing a given VO2max (STPD) to the corresponding VEmax (BTPS), showing that any further increase in the latter is impossible when a certain level of altitude has been reached. Finally, our series of experiments indicates that the HRmax falls at altitude. Although statistically significant, this decrement is not conspicuous. Thus, when used with the VO2max to calculate the number of ml of O2 consumed per beat of the heart, the "oxygen pulse" turns out to be more sensitive to the fall in VO2max at altitude than to the corresponding decrease in the HRmax.

Adult↗
PubMed1982

Release of hypoxanthine and phosphate from exercising human legs with and without arterial insufficiency.

Release of hypoxanthine and phosphate from exercising legs was studied in eight subjects without known obstructive arterial disease and in 20 claudicants. Lower leg blood flow was measured with a thermodilution catheter in the popliteal/distal femoral vein. The catheter allowed blood sampling from the calf before, during and after exhaustive exercise on a bicycle ergometer at a stepwise increasing load. Resting plasma hypoxanthine levels were higher in claudicants than in normal subjects (p less than 0.05). Hypoxanthine concentrations increased 2-4-fold during exercise, amounting to values ten times higher than the resting levels 5 and 10 min post exercise, in the venous effluent of the normal legs. A similar rise was found in the claudicants despite half the exercise intensity at exhaustion. Popliteal venous concentrations of phosphate increased by approximately 25% during exercise without significant differences between the two groups. During exercise the release of hypoxanthine increased 38-fold and of phosphate 21-fold in the normal lower legs, while a ten-fold increase in both metabolites was recorded in the claudicating legs. The study demonstrated a high release of hypoxanthine and phosphate from the human lower leg during rhythmic, exhaustive exercise (with maximal vasodilation). The result is compatible with the assumption that metabolites from the catabolism of adenine nucleotides (adenosine) play a role in the autoregulation of blood flow in human skeletal muscle. Increased plasma hypoxanthine concentrations at rest may indicate peripheral arterial insufficiency.

Adult↗
PubMed1982

Physical activity and peripheral atherosclerosis.

This article describes changes in the muscular blood flow and metabolism in intermittent claudication (pain in the legs during physical work) and the effect of physical training on these factors. The disease (arteriosclerosis obliterans) is characterized by a reduction in the blood flow through muscles and in oxygen uptake, together with increased lactate excretion during work, usually in spite of a developed arterial collateral system. An increased ability to extract oxygen from the blood while the affected muscle metabolism is modified in the direction of greater aerobic capacity can partially compensate for the reduction in blood perfusion. Physical activity which involves large muscle groups and is continued beyond the boundary of pain leads to an increase in both claudication distance (the distance until pain appears during normal walking on the flat) and the walking distance (maximal distance the patient can walk). Since the blood flow is unchanged or reduced, the effect seems not to be due to improved vascular capacity. It has however been shown that training gives rise to further increase both in the ability to extract oxygen from the blood and in the metabolic activity of muscle tissue. It is concluded that, if indications for surgical treatment are not present, training by walking with regular controls constitutes good treatment favourable to health economics and able to improve the patient's quality of life.

Arteriosclerosis↗
PubMed1981

Relationship of high density lipoprotein cholesterol concentration to the duration and intensity of endurance training.

Eleven healthy, male students were studied over period of 8 months. Five were sedentary subjects, and six were competitive cross-country skiers engaged in endurance training of varying amount and intensity. Serum concentration of high density lipoprotein (HDL) cholesterol increased significantly during physical endurance training of low intensity and long duration. With fewer hours of training, but of greater intensity, HDL cholesterol concentration was lower but was still significantly higher than in the control group of sedentary individuals. In conclusion the study suggests that elevated HDL cholesterol concentrations associated with high levels of physical activity are related to both amounts and intensity of the training.

Adult↗
PubMed1981

Adipose tissue perfusion and fatty acid release in exercising rats.

Arterial concentrations of free fatty acids (FFA), glycerol and lactate were measured in male Wistar rats before, during and after 30 minutes exercise on a treadmill. The arterial concentration of glycerol increased 120% and lactate 340% during exercise, but fell immediately upon its termination. The arterial concentration of FFA increased only 20% during the exercise, but was followed by a sharp rise in the recovery period. Maximum FFA concentration was found after 6 minutes of recovery, reaching 70% above the preexercise level, whereafter plasma FFA fell. Using radioactivity labelled microspheres it was found that the fraction of cardiac output reaching adipose tissue after 10 min of exercise was reduced by 30-90% in relation to the resting value. After 3 min recovery, however, the fractional distribution to the same tissue was in average 300% above the value measured 3 min before termination of exercise. It is concluded that the increase in plasma FFA observed during the early recovery period is caused by increased FFA release from adipose tissue, as a consequence of increased adipose tissue perfusion in the recovery period.

Adipose Tissue↗
PubMed1978

Exercise-and post-exercise metabolism of the lower leg in patients with peripheral arterial insufficiency.

Exercise- and post-exercise metabolism were studied in the lower legs of six subjects without known arterial insufficiency and in sixteen claudicants. Lower leg blood flow was measured with a thermodilution catheter in the popliteal vein. The catheter allowed blood sampling from the calf before, during and after an exhaustive, stepwise increasing load exercise on a bicycle ergometer. A higher oxygen extraction and higher lactate release during exercise in claudicants than in normal subjects persisted in the post-exercise period (P less than 0.05). Leg arteriopoplitealvenous differences of free fatty acids (FFA) showed an inverse intergroup relationship to that of glucose. Being higher in claudicants than in normal subjects during exercise (P less than 0.05). However, net uptake of FFA was not significantly different in the groups of legs although it appeared increased relative to glucose in claudicants both during and after the exercise. Thus no statistically significant substrate preference was detected although the results suggests a preference for FFA relative to glucose in legs with arterial insufficiency. The study furthermore demonstrated the lag of exercise metabolism into the post-exercise period in such legs and a close relationship between this metabolic delay and the severity of the disease.

Adult↗
PubMed1978

Lower leg blood flow in intermittent claudication.

Lower leg blood flow was measured at rest and both during and after graduated bicycle exercise in five healthy men and in seventeen patients suffering from various degrees of obliterating arteriosclerosis of the lower limbs. A thermodilution technique was used for flow determinations. The subject exercised in the sitting position and the work load was increased stepwise from a starting load of 100 kpm/min (100 kpm/min load increment every second minute until exhaustion). Three flow phases were depicted during and after the exercise: the aerobic phase, the phase of relative ischaemia and a postexercise phase. During exercise, lower leg blood flow increased approximately twenty times in healthy subjects, while in the arteriosclerotic subjects there was a two-fold to ten-fold increase in flow. In patients with serious distal and proximal stenoses a proximal steal phenomenon was demonstrated during submaximal and maximal exercise. A close correlation was found between maximum individual work load capacity and maximum lower leg blood flow (r = 0.71, P less than 0.001). In the patient group lower leg blood flow at a certain work load was 45% (P less than 0.001) higher in the sitting than in the supine position.

Adult↗