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P K Pedersen

Publications and source records attributed to P K Pedersen.

36 records · Page 2Linked to original sources
PubMed1987

Muscle and blood ammonia and lactate responses to prolonged exercise with hyperoxia.

Investigations using nonsteady-state and fatiguing exercise protocols have demonstrated a strong relationship between ammonia and lactate metabolism and have suggested a cause and effect relationship between these two variables. We investigated the lactate-ammonia response using prolonged exercise and inspiration of hyperoxic gas (60% O2-40% N2). The exercise consisted of either 70-75% maximal O2 uptake (VO2 max) for 40 min (series 1, n = 6) or 75-80% VO2max for 30 min (series 2, n = 6) with the subjects inspiring room air on one occasion and hyperoxia in the other test. In both series blood ammonia rose continuously throughout the exercise regardless of the inspired gas treatment; in contrast blood lactate did not increase after 10 min with room air, and with hyperoxia blood lactate was reduced. Muscle lactate and ammonia (series 2; vastus lateralis) had responses similar to the blood data. The data demonstrated no apparent lactate-ammonia relationship with prolonged exercise or in response to hyperoxia, suggesting that ammonia production can be independent of lactate metabolism. The data also suggest that type I fibers can be a major source of ammonia in humans.

Adult↗
PubMed1986

Role of hemoglobin and capillarization for oxygen delivery and extraction in muscular exercise.

Through the years the role of the various links in the transport of oxygen in the human body has been discussed extensively, and especially whether one of these links could be singled out as limiting oxygen uptake during exercise. In his thesis work Lars Hermansen dealt with several of these variables related to oxygen transport and uptake. Two of these were the hemoglobin concentration of the blood (Hb) and skeletal muscle capillarization. These are the focus of this article. It can be demonstrated that variation in arterial oxygen content due to different Hb concentrations is fully compensated for at the level of the muscle, i.e. the amount of oxygen delivered to contracting muscles is adjusted by a variation in the blood flow so that it is the same regardless of Hb concentration in the range of 118-172 g X l-1. At the systemic level, with a large fraction of the muscle exercising, this causes an increase in submaximal heart rate and a lowering in maximal oxygen uptake in people with low as compared to normal or high Hb concentration. The primary significance of an enlarged capillary network in the muscle does not appear to be for accommodating a larger flow, but rather to allow for a long enough mean transit time and large enough surface area for optimal exchange of gases, substrates and metabolites.

Capillaries↗
PubMed1984

Sex differences in endurance capacity and metabolic response to prolonged, heavy exercise.

In order to test for possible sex differences in endurance capacity, groups of young, physically active women (n = 6) and men (n = 7) performed bicycle ergometer exercise at 80% and 90% of their maximal oxygen uptakes (VO2 max). The groups were matched for age and physical activity habits. At 80% VO2 max the women performed significantly longer (P less than 0.05), 53.8 +/- 12.7 min vs 36.8 +/- 12.2 min, respectively (means +/- SD). Mid-exercise and terminal respiratory exchange ratio (R) values were significantly lower in women, suggesting a later occurrence of muscle glycogen depletion as a factor in their enhanced endurance. At 90% VO2 max the endurance times were similar for men and women, 21.2 +/- 10.3 min and 22.0 +/- 5.0 min, respectively. The blood lactate levels reached in these experiments were only marginally lower (mean differences 1.5 to 2 mmol X l-1) than those obtained at VO2 max, suggesting high lactate levels as a factor in exhaustion. The changes in body weight during the 80% experiments and the degree of hemoconcentration were not significantly different between men and women.

Adult↗
PubMed1984

Absolute or relative work load in exercise testing--significance of individual differences in working capacity.

A commun multistage bicycle ergometer test (50 W increases every third minute until exhaustion) was analysed for significance of individual differences in working capacity in six young borderline hypertensive and six young normotensive males. From measurements of O2 uptake (VO2) during each of the prescribed work rates, up to and including maximal effort, relationships with relative work load (% VO2 max) could be established for each of the variables observed in the study. An alternative procedure was tested in which the relative work load was established on the basis of the individual's maximal mechanical power output (Wmax). In heavy exercise the variation coefficients for some variables were nearly halved when observed at a given relative (% VO2 max or % Wmax) rather than absolute (number of watts) exercise level. In light exercise the effect of this normalization was negligible. The two expressions of relative work load were closely correlated. Relative work load in % VO2 max could be predicted from the relative work load in % Wmax with an average standard error of estimate of 2.8%. Exercise heart rate and rate of perceived exertion (Borg scale) were also significantly correlated with relative work load. However, these latter variables were less precise as indicators of relative work load, the standard error of estimates being 3 and 5 times larger than that of % Wmax, respectively. The procedure of establishing relative work load on the basis of Wmax may be of value if a precise setting is desirable when measurements of VO2 are impracticable. The method may also be of use if an individual's HR-work load relationship is abnormal, for example because of medication.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1981

Measurement of metabolic rate in hyperoxia.

The conventional Douglas bag calculation for estimating O2 uptake (VO2) during exercise in normoxia and hyperoxia, VO2 = VE . (FIO2 . FEN2/FIN2 - FEO2), was tested against two other valid calculations: the Fick equation, VO2 = VI . FIO2 - VE . FEO2, and the equation VO2 = VI - VE - VCO2 (VE and VI are expired and inspired ventilation, respectively; FEO2 and FIO2 are expired and inspired O2 contents, respectively; FEN2 and FIN2 are expired and inspired N2 contents, respectively; and VCO2 is CO2 production.). These calculations are based on different assumptions, in part, and are affected to a varying degree of errors in volume or gas fraction measurements. With the conventional Douglas bag technique, we found evidence of an overestimate of VO2 during hyperoxia. After the introduction of a mixing chamber for sampling expired air, the means of the three methods were not significantly different. The variability among the methods was least with the conventional calculation but increased with higher O2 fractions. The average VO2 for submaximal exercise in hyperoxia was not significantly different from that of normoxia. VO2 max was significantly higher in hyperoxia. The increased variability of the Douglas bag method in hyperoxia may lead to overestimates of VO2 max unless special precautions are taken.

Humans↗
PubMed1978

Maximal oxygen uptake in young women with training, inactivity, and retraining.

Six young, healthy, sedentary females performed intense endurance training at a constant training stimulus (HR = 170 beats x min-1) twice a week in two 7-week periods separated by seven weeks of inactivity. Inactivity was defined as a period without scheduled exercise but with necessary daily activities. An increase in Vo2max (10-14%) and in training intensity at target heart rate (24%) were observed in both periods (p less than 0.001). Considering the intensity and duration of the program these gains are similar to those reported previously in women and men. The training response was the same in the two periods. Thus, there was no indication of beneficial effects during retraining from the previously performed activity. After the inactivity period Vo2max, as well as the work intensity at target heart rate, did not differ significantly from the pretraining observations. Thus seven weeks with no training was sufficient to neutralize the effect of a conditioning program of similar duration.

Adult↗
PubMedDate not supplied

Determination of potassium/sodium ratio in heart tissue. Evaluation of its use as an index of myocardial ischaemic damage. Comparison with the nitro-BT test.

The succinate dehydrogenase method of staining and the determination of the K+/Na+ ratio of heart tissue have been applied to forensic material as a tool for demonstrating early signs of myocardial infarctions. Both methods are controlled by a series of forensic cases dying from causes other than arteriosclerosis of the coronary arteries. Based on an analysis of normal material some factors influencing the K+/Na+ ratio are defined. It is concluded that the determination of the K+/na+ ratio shows more infarcts than the formazan method; however, the evaluation of the K+/Na+ ratio is difficult. The K+/Na+ determination is not recommended for routine use. A possible indication for the use of the K+/Na+ determination together with the formazan test could be cases of instantaneous death by accidents suspected to have been provoked by a fatal heart attack.

Adolescent↗
PubMedDate not supplied

Poor results in attempting to demonstrate the cause of death by examination of the conduction system of the heart in cases of sudden death.

A microscopic examination of the proximal part of the conduction system in the heart was undertaken in seven cases of sudden death due to coronary arteriosclerosis; the same technique was applied to 31 control cases. A few infiltrations of mononuclear cells were demonstrated in relation to the conduction system in cases of sudden death as well as in controls. In one case severe narrowing of the sinus node artery was found without particular arteriosclerosis of the coronary arteries.

Adult↗