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Biomedical subjects

U Boutellier

Publications and source records attributed to U Boutellier.

42 records · Page 3Linked to original sources
PubMed1983

Oxygen deficit and stores at onset of muscular exercise in humans.

Single-breath O2 consumption (VO2) at the mouth and heart rate were determined in five healthy male subjects at rest, during 8 min of cycloergometric exercise (50, 100, 125, and 150 W), and in the recovery period following two experimental conditions: air breathing throughout (AA); hypoxic breathing (FIO2 = 0.11) for 6 min of preexercise rest followed by air breathing from the onset of exercise (HA). The O2 deficits and debts as well as the t 1/2 values of the VO2 on- and off-responses were determined and blood lactate concentrations measured at rest and in the recovery after 4 and 8 min of exercise. At all work loads: 1) O2 deficits were on the average 0.39 liter smaller in HA than in AA; 2) VO2 on-responses were faster in HA (t 1/2 approximately equal to 7 s) than in AA (t 1/2 = 20-30 s); and 3) O2 debts and VO2 off-responses were the same in the two conditions. Since the VO2 and heart rate levels at steady state as well as the blood lactate concentrations after 4 and 8 min of exercise were the same in AA and HA, the observed differences of O2 deficit cannot be attributed to changes of energy metabolism in the two conditions; they therefore depend on the reduction of body O2 stores at rest in HA. This, independently measured, was found to be 0.46 liters, not far from the observed O2 deficit difference (0.39 liters). Thus a decrease of O2 stores before exercise is accompanied by a reduction of the O2 deficit and faster VO2 kinetics at the onset of exercise.

Adult↗
PubMed1983

Human muscle adaptations to chronic hypoxia.

Maximal aerobic power (V02max) decreases with increasing altitude, the drop being about the same in acute and chronic hypoxia. To elucidate this well established but still rather inexplicable finding, experiments were carried out on a group of participants before and immediately after return from a mountaineering expedition to Mount Lhotse Shar (8398 m). The results of a typical subject exposed over a period of 5 weeks to an altitude of at least 5200 m indicate that: A) In the vastus lateralis muscle the number of capillaries to the number of fibers ratio was unchanged, the mean fiber diameter was reduced from 77.3 to 67.9 mu while the mitochondrial to fiber volume ratio increased from 6.7 to 7.9%; in addition, muscle protein concentration diminished by 37% and succinate dehydrogenase activity (SDH) was 48% less than in control conditions; B) Cardiac output and muscular (vastus lateralis) blood flow at submaximal work loads were reduced by 21% and 53%, respectively; C) The V02 on-response kinetics at the mouth upon rectangular submaximal work loads was delayed (t 1/2 = 37.5 vs. 27.0 s). From the above results it is concluded that the apparent lack of beneficial effects of acclimatization on maximal aerobic power is likely the consequence of the interaction of a number of positive (increased hematocrit, rightward shift of the 02 dissociation curve) and negative (reduced thoracic and peripheral blood flow, decreased muscle mass and oxidative enzymes activity) changes induced by hypoxia.

Adaptation, Physiological↗
PubMed1981

Propranolol and the respiratory, circulatory, and ECG responses to high altitude.

The role of the sympatho-adrenal system in the acute respiratory and cardiovascular responses to high altitude was studies in 20 volunteers during ascent to 6,000 m in a low pressure chamber, once without (control) and once with beta-adrenergic blockade. Special attention was paid to the hypoxia-induced ECG changes. Propranolol lowered the level of hypoxia-induced cardiovascular reactions, whereas it had no effect on hypoxic hyperventilation and alveolar gases. At altitude, ECG changes during myocardial depolarization occurred in both the propranolol and the control groups, probably due to the direct effects of hypoxia. During the repolarization phase, propranolol led to an almost complete abolition of S-T depression and to significant reduction of T wave flattening. The minor but still significant flattening of the T wave as well as the relative (to the heart rate) lengthening of Q-T is probably due to the direct effects of hypoxia. Propranolol abolishes or diminishes the signs of cardiac hypoxia by antagonizing the effects of catecholamine release and/or by reducing myocardial oxygen consumption, thus probable increasing the ability to withstand oxygen-want at altitude.

Adult↗
PubMed1981

Comparison of hypoxanthine, lactate, and ECG signs as indicators of hypoxia.

High altitude-induced hypoxemia in 26 young adults was used to compared hypoxia parameters such as blood lactate, hypoxia-induced electrocardiogram signs, and the recently proposed plasma hypoxanthine concentration. At a PaO2 of 30 mm Hg, no elevation in hypoxanthine and small increase in lactate was observed. Minimal leg exercise was added to further increase hypoxic during hypoxemia. A significant increase in lactate and considerable ST-T depression in electrocardiogram indicated hypoxia, but no change in plasma hypoxanthine was found. Work-dependent hyperventilation as a main cause of lactate elevation was excluded. Blockade of hypoxanthine breakdown by allopurinol in vivo increased plasma hypoxanthine levels, but hypoxemia with or without leg exercise failed to consistently increase this level further. Elevations of blood lactate above the normal range were found at a PaO2 of 30 mm Hg and below.

Adult↗