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Biomedical subjects

B Ekblom

Publications and source records attributed to B Ekblom.

At least 73 records · Page 4Linked to original sources
PubMed1988

Aerobic power during maximal exercise in untrained and well-trained persons with quadriplegia and paraplegia.

The aerobic power during maximal exercise was studied in 58 males with traumatic spinal cord lesions from C4 to L4 (25 well-trained "world-class athletes" and 33 untrained). For comparison we tested five well arm-trained and five arm-untrained able-bodied subjects. During maximal wheelchair exercise the aerobic power (VO2 peak), pulmonary ventilation and blood lactate concentration was higher in subjects with lower levels of spinal cord injury. At each injury level above C6-C7, nearly all trained subjects reached higher VO2 peaks than untrained subjects with the corresponding level of lesion. The mean values for trained paraplegic persons were 2.16 +/- 0.38 l x min-1, corresponding to 33.6 +/- 6.7 ml x kg-1 x min-1. The peak heart rate was lower in the quadriplegic than in the paraplegic group with no or only small difference between trained and untrained subjects at the same level of spinal cord injury. Spinal cord lesions with pareses reduce the total active skeletal muscle mass. This can cause physical inactivity, medical complications and social isolation. As a consequence, cardiovascular disorders as cause of death is higher in this group compared to the general population. Therefore, one aim of rehabilitation is to increase the individual's performance in daily life activities. It has been shown that the normal daily life activities of quadri- and paraplegic individuals with no additional physical training are not intense enough to maintain a satisfactory level of physical fitness.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Pharmacokinetics of haloperidol in psychotic patients.

Nine psychotic patients under continuous oral treatment with haloperidol were randomly given a test dose of 1.5-5 mg haloperidol orally and/or intravenously. Serum levels of haloperidol were determined by high performance liquid chromatography and serum concentration data obtained were submitted to pharmacokinetic analysis. The steady state concentration ratio between blood and plasma was determined and found to be 0.79 +/- 0.03. The blood clearance was then calculated to be 550 +/- 133 ml/min. The mean hepatic extraction ratio was intermediate (0.37). Consequently, for a drug mainly eliminated by hepatic metabolism like haloperidol, the total blood clearance and the extent of oral bioavailability can be affected by changes in hepatic blood flow, hepatic enzyme activities and drug binding. During continuous oral treatment with haloperidol, however, it can be shown that changes in the total metabolic capacity of the liver due to hepatic enzyme induction or inhibition should be important for the therapeutic effects of haloperidol. The volume of distribution at steady state (Vdss) was large (7.9 +/- 2.5 l/kg). The terminal half-life was 18.8 h after intravenous and 18.1 h after oral administration. The oral bioavailability (0.60 +/- 0.18) were in accordance with previous results in healthy subjects. A mean lag time after oral dose was 1.3 +/- 1.1 h and a longer absorption half-life (1.9 +/- 1.4 h) was found in the patients compared with healthy volunteers.

Administration, Oral↗
PubMed1987

Effects of anaemia and stepwise-induced polycythaemia on maximal aerobic power in individuals with high and low haemoglobin concentrations.

Increasing the haemoglobin concentration ([Hb]) improves the oxygen transport capacity but it also increases the viscosity of the blood. The influence of changes in [Hb] and viscosity on submaximal exercise capacity and maximal aerobic power was investigated in eight healthy males in varying states of training and with a normal resting [Hb] ([Hb]r), ranging from 123 to 178 g l-1. The subjects were venesected five times (450 ml per unit) and exercise tests were performed in the anaemic state. After 5-7 weeks, when [Hb] had returned to the 'normal' value, a stepwise re-transfusion of three to five units of blood was performed with exercise tests after each transfusion. The [Hb]r was 137 +/- 15 g l-1 in the anaemic state (A) and 170 +/- 16 g l-1 after the last re-transfusion (LT). The VO2max rose from 3.94 +/- 0.35 in A to 4.68 +/- 0.30 l min-1 after LT. Individual regression lines for [Hb] and VO2max revealed a mean increase in VO2max of 19 +/- 6 ml min-1 per g l-1 change in [Hb]. This value did not differ between individuals with high and low normal [Hb]. Furthermore, in intra-individual comparisons the relationship between [Hb] and VO2max in high and low individual [Hb] ranges was not found to be statistically different despite a 40% increase in the in vitro viscosity from the anaemic to the polycythaemic state.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Endurance, what is it? Muscle morphology after an extremely long distance run.

Biopsies of m. vastus lateralis of a well-trained 46-year-old man were analysed before and after an extremely long distance run (3529 km in 7 weeks). After the period of running, both a decrease of fibre size and a neuromuscular pathology were found. Muscle fibre degeneration and regeneration, especially of type 2 (fast-twitch) fibres, was seen as well as signs of damage to the peripheral nerves. The relative amount of type 1 (slow-twitch) fibres was higher after the run. The relationships between light and electron microscopical characteristics normally present could not be found in the specimens of this man. The changes in fibre size as well as the other microscopical characteristics may express an adaptation through more or less complete fibre transformation. However, we could not rule out that a selective elimination of fibres also contributed to the observed changes. In that case, the underlying pathophysiology might have been a peripheral arterial insufficiency which was related to the extreme functional demands. These disturbances may have affected type 2 fibres more than type 1 fibres. Endurance may, on this basis, express an adaptation of the muscle through elimination of weak fibres, that is, fibres related to limited functional capacities.

Biopsy↗
PubMed1986

Receptor binding of N-(methyl-11C) clozapine in the brain of rhesus monkey studied by positron emission tomography (PET).

By means of positron emission tomography the uptake and kinetics of N-(methyl-11C)clozapine in different brain regions have been studied in Rhesus monkeys. 11C-clozapine rapidly entered the brain and maximum radioactive uptake was seen 5-12 min after administration. Highest uptake was measured in the striatum. Other regions with an uptake higher than in the cerebellum were thalamus and mesencephalon. The radioactivity from different brain regions decreased with an elimination half-life of about 5 h and parallelled the plasma kinetics of unlabelled clozapine. The striatum/cerebellum ratio of 11C-clozapine-derived radioactivity remained constant during the period studied and did not change after pretreatment with atropine. In contrast, the striatum/cerebellum ratio was somewhat lower after pretreatment with N-methylspiperone (NMSP), indicating competition for the same binding sites in the striatum. After pretreatment with increasing doses of clozapine, a dose-dependent protection of binding sites in the striatum for 11C-NMSP was seen. It is concluded that clozapine is more loosely bound to dopamine receptors in the striatum than N-methylspiperone and that the kinetics of clozapine in the brain parallel that in the plasma. The binding properties of clozapine within the brain may explain some of the clinical properties of the drug.

Animals↗
PubMed1986

Anemia causes a relative decrease in blood lactate concentration during exercise.

The purpose of the present study was to examine to what degree a reduction in systemic oxygen transport capacity influences the absolute and relative levels (% of maximal oxygen uptake) of submaximal blood lactate accumulation. Anemia was induced by repeated venesections in eight healthy males. After 9-10 weeks of anemia, hemoglobin concentration [Hb] was restored by retransfusion of packed erythrocytes. The [Hb] values obtained were, before venesections, in control (C) = 145 +/- 10, in the anemic state (A) = 110 +/- 8, and after retransfusion (R) = 143 +/- 8 g X l-1 respectively. In all states, muscle biopsies were taken and measurements made of VO2max and VO2 at a running velocity corresponding to a blood lactate concentration of 4 mM (upsilon Hla 4.0). In the A condition Vo2max decreased by 19% as compared to C (P less than 0.01). upsilon Hla 4.0 was 14% lower in A as compared to C and R (p less than 0.01). VO2 at upsilon Hla 4.0 was 13% lower in A as compared to C (P less than 0.01). However, VO2 at upsilon Hla 4.0 expressed as a percentage of VO2max was increased (P less than 0.01) in the anemic state, the values obtained being C = 83.3%, A = 89.8% and R = 84.8%. Ventilation at upsilon Hla 4.0 was higher in A as compared to C and R (P less than 0.05). R and C values were not significantly different for any of the values presented above. The maximal activity of citrate synthase in muscle did not differ between the three different conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Evaluation of a modified acetylene rebreathing method for the determination of cardiac output.

In order to evaluate a computerized modified acetylene rebreathing method for the determination of cardiac output, 15 healthy subjects were studied at different levels of their maximal oxygen uptake (VO2max). Submaximal exercise was performed on a cycle ergometer and maximal exercise on a treadmill. Oxygen uptake, heart rate, and cardiac output (acetylene method) were determined in all test situations. In seven subjects simultaneous determinations of cardiac output were made by a modified acetylene rebreathing method (QA) and a dye dilution method (QD). Furthermore, a new resting rebreathing technique was used. The methodological error for QA (means of double samples) was 0.37 litre min-1 (2.8%) in the same individual at 150 W. The corresponding values between individuals were 0.71 (rest), 0.41 (50 W), 0.69 (150 W), and 0.40 litre min-1 (VO2max). Thus the methodological error of the modified acetylene method was very low. There was a significant difference (P less than 0.01), however, between the acetylene method and the dye dilution method, which showed a lower value for QA at all levels. This was probably due to the long response time of the mass spectrometer combined with anatomical and physiological arteriovenous shunt effects in the lungs during exercise. When these factors were considered the correcting formula was: QAc = QA + 0.005 X Q2A. There was no significant difference between the corrected cardiac output values (QAc), and the corresponding QD values. In conclusion, this modified acetylene rebreathing method is a very useful non-invasive method for measuring cardiac output at rest as well as during heavy exercise.

Acetylene↗
PubMed1986

Altered cardiovascular responsiveness to adrenaline in endurance-trained subjects.

The influence of physical training on responses to i.v. adrenaline infusions and to exercise were investigated in 10 endurance-trained men (mean age: 35 y; VO2max: 61.9 ml kg-1 min-1) and 10 age-matched and sedentary controls (36 y, 37.5 ml kg-1 min-1). The untrained subjects were reinvestigated after a 4 month training period which increased their VO2max by 18%. Resting heart rate and diastolic blood pressure were significantly lower in the trained state. The venous plasma adrenaline concentrations attained during infusions (4 dose levels, 8 min each) were lower in the well-trained than in the untrained subjects (2.15 vs. 3.59 nmol l-1 at the highest dose level, P less than 0.01). The adrenaline-induced increases in heart rate and in plasma cAMP and decreases in pre-ejection period (PEP) and PEP/LVET ratio were not dependent on the training state. The adrenaline-induced decrease in diastolic blood pressure was more pronounced (P less than 0.05) in the well-trained than in the untrained group and tended (0.05 less than P less than 0.1) to be enhanced by training in the latter group. The increases in systolic blood pressure were greater in the well-trained subjects (P less than 0.01) but training did not alter this response in the untrained subjects. The plasma noradrenaline response to maximal cycle ergometer exercise (VO2max test) was significantly greater in the well-trained than in the untrained subjects, while no difference was seen for adrenaline. The submaximal exercise systolic blood pressure was similar in all training conditions when related to the absolute rate of work. In summary, the present results indicate that both the vasodilator and systolic pressor responses to adrenaline are enhanced in endurance-trained subjects. The cardiac chronotropic and inotropic effects of adrenaline seem, however, to be independent of the training state.

Adult↗
PubMed1986

Temperature-induced changes in metabolic and hormonal responses to intensive dynamic exercise.

Seven male subjects performed intensive cycle exercise to exhaustion at subnormal muscle temperature (Tm, 29 +/- 2.8 degrees C). Exercise at exactly the same rate of exercise and duration (370 +/- 34 W, 1.5 +/- 0.15 min) was then repeated with normal Tm (35 +/- 0.9 degrees C). During exercise both the arterial (a) and femoral venous (fv) contents of oxygen were significantly higher at subnormal than at normal Tm, because of the higher haemoglobin concentration, but the a-fv oxygen difference was the same in the two situations. The rate of increase in lactate concentration in both arterial and venous blood during exercise was the same in two situations. During exercise the plasma concentrations of adrenaline and noradrenaline in arterial and venous blood were significantly higher at subnormal than at normal Tm. At rest and after exercise the calf blood flow was significantly reduced at subnormal Tm. At the end of exercise the concentrations of glucose-6-phosphate and lactate in the muscle were significantly higher at subnormal Tm than in the muscle of normal temperature. These findings suggest that there was a greater increase in glycolysis in the muscle of subnormal temperature during exercise, possibly as a result of impaired work efficiency and/or reduced blood flow in the cold muscle.

Adult↗
PubMed1986

Maximum activities of key glycolytic and oxidative enzymes in human muscle from differently trained individuals.

1. The maximum activities of hexokinase, 6-phosphofructokinase and oxoglutarate dehydrogenase, together with capillary density and fibre composition, have been measured in muscle from male and female untrained, medium-trained and well trained individuals. 2. The activity of hexokinase was almost identical in muscle from the three groups, whereas that of 6-phosphofructokinase decreased and that of oxoglutarate dehydrogenase increased with increased training. Values of maximum rate of O2 uptake (VO2, max) were also measured and were 21% higher in medium-trained and 49% higher in well trained compared to untrained individuals, whereas oxoglutarate dehydrogenase activities were 39% and 90% higher respectively. 3. There was a good positive correlation between the activity of oxoglutarate dehydrogenase and the percentage of type I fibres but the correlation between VO2, max and oxoglutarate dehydrogenase activity was less good. Changes in the values of VO2, max represent the effects on the circulatory and respiratory system whereas those in oxoglutarate dehydrogenase represent local effects of endurance training.

Adenosine Triphosphate↗
PubMed1986

Effect of long-term anemia and retransfusion on central circulation during exercise.

The purpose of this study was to evaluate the effect of long-term anemia and subsequent retransfusion of erythrocytes on various circulatory parameters. Anemia was induced in nine healthy male subjects by repeated venesections. The stored blood was retransfused after 9 wk (range 8-11 wk). Exercise tests were performed before venesection in the control state (C), in the anemic state (A), and 48 h after retransfusion (R). Hemoglobin concentration levels were 146 +/- 10 g/l in C, 110 +/- 7 g/l in A, and 145 +/- 9 g/l in R. Maximal O2 uptake was 4.55 +/- 0.6, 3.74 +/- 0.7, and 4.45 +/- 0.6 l/min in C, A, and R, respectively. A decrease in heart rate of 7 beats/min (P less than 0.01) and in cardiac output of 2 l/min (P less than 0.05) at maximal exercise occurred in the anemic state compared with control values. These decreases were not reversed but, rather, were further accentuated after retransfusion. The adaptive response to submaximal exercise (cycling at 150-175 W) in anemia was mediated to the amount of 50% by an increase in cardiac output (mainly an increase in heart rate) and 50% was due to increased O2 extraction in the peripheral tissue. In conclusion, long-term anemia was found to decrease the heart rate and cardiac output at maximal exercise. Furthermore the close correlation between hemoglobin concentration and maximal O2 uptake in humans is confirmed.

Anemia↗
PubMed1986

Factors determining maximal aerobic power.

Maximal aerobic power is the highest peak oxygen uptake that an individual can obtain during dynamic exercise using large muscle groups during a few minutes performed under normal conditions at sea level. In most subjects maximal aerobic power is limited by the central circulation. It is obvious that stroke volume is one very important factor. Another important one is the oxygen content of the arterial blood. If the oxygen content of the arterial blood is increased the maximal aerobic power and physical performance is increased. If it is decreased--except when there is an acute volume expansion--or if the heart rate is depressed the circulation can not compensate for it and the maximal aerobic power is decreased. Certain mainly external factors like drugs or induced hypothermia influences on circulation, thus reducing maximal aerobic power and physical performance. Despite all these possible ways of influencing circulation during maximal exercise, it is interesting to note that repeated measurements of maximal aerobic power show a fairly low variation from day to day.

Aerobiosis↗
PubMed1986

Effects of iron deficiency on endurance and muscle enzyme activity in man.

The purpose of the present study was to evaluate the effects of iron deficiency on enzyme activities and endurance. Iron deficiency was induced in 9 healthy male subjects by repeated venesections. After a period of 9 wk (range, 8-11 wk) when the subjects had become iron deficient as defined by laboratory parameters, blood was retransfused to reestablish the control hemoglobin concentration. In this state it was possible to evaluate the effect of iron deficiency isolated from anemia. In samples secured by muscle biopsies, glycolytic, oxidative, and iron depending enzymes were analyzed in the control (C) and anemic (A) states and after retransfusion (R). There were no significant changes in the maximal activities of any of the enzymes studied. The capillary/fiber ratio remained unchanged between C (1.92) and R (1.94). Times to exhaustion on treadmill tests were 49 min, 11 s in C, 26 min, 33 s in A, and 52 min, 3 s in R. Vo2max was 4.55 1 X min-1 in C, 3.74 1 X min-1 in A, and 4.45 1 X min-1 in R. An artificially induced iron deficiency defined by conventional laboratory parameters did not affect endurance when transfusion of red blood cells was performed in order to exclude the influence of a low hemoglobin concentration. A 4-wk period of severely depleted or absent tissue iron stores did not affect the maximal activities of various enzymes in human skeletal muscle.

Adult↗
PubMed1985

Co-release of neuropeptide Y and catecholamines during physical exercise in man.

Venous plasma levels of neuropeptide Y-like immunoreactivity (with chromatographic properties of synthetic neuropeptide Y) increased in parallel with catecholamines, heart rate and blood pressure during graded physical exercise in man. The plasma levels of neuropeptide Y correlated better with the levels of noradrenaline than adrenaline, suggesting release of a neural origin. Taken together with previous results, this suggests that neuropeptide Y is released together with noradrenaline upon sympathetic activation during physiological conditions in man. Determinations of plasma neuropeptide Y may therefore be valuable in the assessment of sympathetic nerve activity.

Adult↗
PubMed1985

Implementation of periodic acid-thiosemicarbazide-silver proteinate staining for ultrastructural assessment of muscle glycogen utilization during exercise.

Distribution of glycogen particles in semithin and ultrathin sections of biopsy samples from human muscles subjected to either short- or long-term running were investigated using PAS and Periodic Acid-ThioSemiCarbazide-Silver Proteinate (PA-TSC-SP) staining methods. Glycogen particles were predominantly found immediately under the sarcolemma or aligned along the myofibrillar I-band. After long-term exhaustive exercise type-1 fibers with a few or no glycogen particles in the core of the fibers were frequently observed. The subsarcolemmal glycogen stores of these "depleted" type-1 fibers were about three times as large as after exhaustive short-time exercise. Another indication of utilization of subsarcolemmal glycogen stores during anaerobic exercise was that many particles displayed a pale, rudimentary shape. This observation suggests fragmental metabolization of glycogen. Thus, depending on type of exercise and type of fiber differential and sequential glycogen utilization patterns can be observed.

Adolescent↗
PubMed1985

Comparative response of 2-week and 6-month old rat myocardium to hypoxia.

The effect of hypoxia on contractile performance of left ventricular papillary muscles from 2-week old and 6-month old rats was studied. Left ventricular glycogen concentration was not significantly different between 2-week and 6-month old hearts; however, the lactate dehydrogenase isoenzyme pattern of the left ventricular myocardium from the 2-week old rats demonstrated a shift toward M-type (anaerobic) distribution relative to 6-month-old animals. Papillary muscle performance was studied at 28 degrees C while contracting 12 times/min at the peak of the active tension curve in oxygenated (95% oxygen, 5% carbon dioxide) Krebs-Henseleit solution containing glucose concentrations from 5.5 to 22 mM. In a bath containing 5.5 mM glucose, the decline in developed tension during hypoxia (95% nitrogen, 5% carbon dioxide) of preparations from the 2-week old rats was significantly less (P less than 0.05) than the 6-month old group only at 15 min. Raising the glucose concentrations of the bath to 11 and 16.5 mM resulted in improved performance throughout 60 min of hypoxia in preparations from 2-week compared with 6-month old animals. Practolol (5 X 10(-5)M) did not prevent the increased tolerance to hypoxia observed in preparations from 2-week animals. Thus, increasing anaerobic substrate has differential effects on the performance of 2-week and 6-month myocardium during hypoxia. The data suggests that in contrast to 6-month old heart muscle, myocardium from 2-week old rats is capable of modulating its active mechanical activity during hypoxia in accordance with the availability of glycolyptic substrate.

Adrenergic beta-Antagonists↗