Metabolic transient studies by NMR

The time course of phosphocreatine (PC) hydrolysis in humans was measured by 31P-NMR spectroscopy (31P-NMRS) with a time resolution of 10.8 s in the gastrocnemius muscle and a relationship between muscle O2 consumption (VO2) and [PC] was derived from a bioenergetic model. This allowed a direct estimate of the half-time of the intracellular VO2 kinetics (t1/2 VO2) of the contracting human gastrocnemius in aerobic conditions. t1/2 VO2 was found to be approximately 16 s and independent of the work load. This value corresponds to the shortest t1/2 VO2 determined at the mouth of the subject in the absence of lactate accumulation in the rest to work transient. t1/2 VO2 may now be assessed in man at low muscle temperatures. To this aim a procedure was developed allowing corrections of the 31P-NMR spectra based on the muscle temperature profiles obtained by a simultaneously acquired proton image.

Cold and muscle performance

The effects of muscle temperature on the development of muscular power are discussed. Temperature influences power (both metabolic and mechanical) by means of its effects on the rate of ATP hydrolysis and/or resynthesis. One would therefore expect reduced power outputs at cold muscle temperatures in humans. However, this is not the case during submaximal aerobic exercise. In fact, no changes in metabolic power output at any given submaximal work load were found at cold muscle temperatures, despite the reduced rate of ATP resynthesis and/or splitting. To explain this, it has been postulated that the fraction of active muscle mass at any given time instant could increase in the cold, thus compensating for the reduced ATP splitting rate. This means that the aerobic ATP resynthesis in the cold may be carried out at a slower rate by a greater activated muscle mass. This compensation cannot be operational when maximal power is attained, for in this case the instantaneously activated muscle mass is constant and limited. In fact the maximal aerobic power and the maximal instantaneous anaerobic power decrease with decreasing muscle temperature, as indicated by an average Q10 of 1.4 in the physiological muscle temperature range. The reduction in maximal aerobic power in the cold may be the consequence particularly of a decrease in O2 supply associated with reduced maximal cardiac output and muscle blood flow. On the other hand, the Q10 of the maximal anaerobic power should strictly depend on the reduced rate of ATP hydrolysis. The Q10 of the latter, however, according to Arrhenius law, should be 2 to 3 instead of 1.4.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphocreatine hydrolysis by 31P-NMR at the onset of constant-load exercise in humans

The kinetics of phosphocreatine (PC) breakdown in human plantar flexors at the onset of constant-load aerobic exercise was determined by high-resolution 31P-nuclear magnetic resonance spectroscopy (NMRS). The half time of the process (t1/2PC) was obtained by fitting curves (n = 13) from five subjects at various aerobic work loads for which muscle pH was not different from that at rest. Steady-state PC concentration ([PC]) was not < 70% of the resting value and was linearly related to the work load (w) ([PC] = -3.01 +/- 0.08 w + 1 (r = 0.48, 2P < 0.1)). The average t1/2PC was 16.2 s and was independent of work load. Because the half time of the muscle PC kinetics reflects the half time of the O2 uptake (MO2) kinetics (t1/2MO2), the latter is equal to that found earlier in the isolated perfused dog gastrocnemius. Whereas in the dog the above t1/2MO2 compares well with the homologous half time of the O2 uptake at the alveolar level, in humans such equivalence is found only at extremely low work loads, when the transient contribution by anaerobic glycolysis is negligible.

Regulation of perfusive O2 transport during exercise in humans: effects of changes in haemoglobin concentration

1. Recently it was suggested that submaximal cardiac output (Q) could vary in response to changes in arterial O2 concentration (Ca,O2), so that arterial O2 delivery (Qa,O2 = Q x Ca,O2, in ml min-1) is kept constant. 2. This hypothesis was tested on eight healthy male subjects, at rest and during exercise (50, 100 and 150 W) in three conditions: normaemia (N), after 6 weeks of endurance training (T), and 2 days after subsequent autologous blood reinfusion (P). 3. Measured variables were oxygen consumption (VO2), by open circuit method, Q, by a CO2 rebreathing method, and haemoglobin concentration ([Hb]), by a photometric method. Ca,O2 was calculated as the product of [Hb], arterial O2 saturation (0.97), and the O2 binding coefficient. 4. [Hb] and thus Ca,O2 increased by 2.6% (T vs. N) and subsequently by further 5.8% (P vs. T). VO2 and Qa,O2 were linear functions of power (w), both relationships being unaffected by changes in Ca,O2. As a consequence, the linear Q vs. VO2 relationships were shifted downward as Ca,O2 increased. 5. The VO2 vs. w and the Qa,O2 vs. w relationships had the same slope. Therefore, the difference between Qa,O2 (w) and VO2 (w), equal to O2 flow in mixed venous blood (Qv,O2), was constant. 6. In conclusion, the tested hypothesis was supported by the present results. The observed constancy of Qv,O2 suggested that Qv,O2 may play a key role in regulating the cardiovascular response to exercise.

Effects of muscle temperature on the VO2 kinetics at the onset of exercise in man

The kinetics (i.e. the rate of readjustment) of O2 uptake (VO2) at the mouth of muscle blood flow in the vastus lateralis muscle (Qm), and the net accumulation of lactate in the rest-to-exercise transient (early lactate) were assessed in 6 untrained men (age 31 +/- 8 (SD) yrs) during constant-load 5-min duration exercises on the cyclo ergometer of 75 and 125 W, performed at muscle temperatures (Tm) of 35.5 +/- 0.9 degrees C (N) and of 28.0 +/- 1.65 degrees C (C). VO2 was measured breath-by-breath; Qm was assessed from 133Xe clearance; early lactate was calculated as the difference between the venous lactate concentrations observed after and before exercise. At both work loads, steady-state VO2 was slightly higher in N than in C (P less than 0.05 at 75 W; NS at 125 W). The half-times of VO2 kinetics were: in N, 36.2 +/- 6.7 s at 75 W and 41.6 +/- 8.6 s at 125 W; in C, 41.4 +/- 10.0 at 75 W and 43.8 +/- 14.0 at 125 W (NS). Mean steady state Qm was 8.5 ml.min-1.100 g-1 in C, and 13.4 in N at 75 W (NS); at 125 W, Qm was 18.3 ml.min-1.100 g-1 in C vs. 25.0 in N (NS). The half-times of the Qm kinetics tended to be slower in C than in N (NS). At both work loads, early lactate was slightly greater in C than in N (NS). It is concluded that, at submaximal exercise, (a) steady state VO2 and the VO2 kinetics are not affected by Tm, and (b) at the onset of exercise Qm does not affect VO2 kinetics.

Gas exchange kinetics in heart transplant recipients

Submaximal and/or peak levels of oxygen consumption (VO2), pulmonary ventilation (VE), heart rate (HR), stroke volume of heart (SV), cardiac output (Q), muscle blood flow (qm), as well as the kinetics of readjustment of gas exchange, Q and qm (t1/2 VO2on-, t1/2 Qon-, t1/2 qmon-) were determined in 44 heart transplant recipients (HTRs) and in a group of age-, sex-, and physical activity-matched control subjects (CTL) when carrying out rectangular loads (25 to 125 W) on a bicycle ergometer. The increase of SV occurring at work onset appears to compensate in HTRs for the sluggish readjustment of HR so that the rate of readjustment of Q is kept within normal limits. As a consequence, qm, t1/2 q mon-, and t1/2 VO2on- appear to be similar or only moderately delayed in HTRs compared with CTLs. It is concluded that in HTRs, because of constrained maximum HR, only work loads up to 60% of the VO2max of CTLs may be attained; also, owing to the fast readjustment of Q, up to work loads of 75 to 100 W, the rest to work transition phase is not impaired.

Somnofluoroscopy, computed tomography, and cephalometry in the assessment of the airway in obstructive sleep apnoea

BACKGROUND

Assessments of the upper airways in patients with the obstructive sleep apnoea syndrome are usually carried out on awake patients who are upright. The dynamics of the airway in a patient who is asleep and lying down may be different.

METHODS

Somnofluoroscopy, computed tomography of the upper airway, and cephalometry were carried out in 11 patients with the obstructive sleep apnoea syndrome (10 male; mean (SD) age 53 (10) years) to examine the airway while they were awake and asleep.

RESULTS

At somnofluoroscopy 10 patients were in stage 2 sleep and only one in REM sleep. At least five obstructive events were visualised by lateral fluoroscopy in each patient. Imaging allowed observation of the dynamics of airway collapse, which began in the oropharynx in all cases, progressing to the hypopharynx in 10 cases and to the laryngopharynx in five. At fluoroscopy the soft palate was seen to hook up during airway occlusion in 10 patients, thereby increasing its cross sectional area. It was then sucked down into the hypopharynx. Somnofluoroscopic and cephalometric findings agreed, eight of the 10 patients with hypopharyngeal collapse shown by somnofluoroscopy having an inferiorly placed hyoid bone according to cephalometry (distance from the mandibular plane to the hyoid bone (MP-H distance) increased); the one patient with no hypopharyngeal collapse had a normal MP-H. By contrast, six of the 11 patients had a normal or supranormal hypopharyngeal cross sectional area of the airway on the computed tomogram.

CONCLUSIONS

Somnofluoroscopy allows examination of the dynamics of airway closure in this disorder and shows the important role of the soft palate in acting as a plug in the oropharynx. Dynamic studies are required to determine the pattern of pharyngeal obstruction in obstructive sleep apnoea.

[Pleural fibrosis in asbestosis and ventilatory function: a study of 50 cases]

The importance of non-malignant pleural fibrosis in asbestosis in relation to respiratory function is still open to debate because of the differing results obtained in studies of different population groups. In the present study we selected 50 subjects with occupational exposure to asbestos presenting mono- or bilateral pleural fibrosis at X-ray but without lung impairment. Each subject underwent bronchial lavage and ventilatory function tests. The subjects were divided into 4 groups on the basis of the degree of pleural alterations according to the ILO Classification of Pneumoconioses. The results revealed that the mean values of CV and FEV1 in each group were within physiological limits. Moreover, analysis of the type of lung function showed a normal situation in 64% and restricted function in 28% of the cases. The prevalence of the latter finding was not correlated to the severity of pleural fibrosis in the various groups. Also, comparison between severity of pleural fibrosis and number of asbestos bodies/ml of BAL liquid on the one hand and frequency of alveolitis on the other did not reveal any relationship. Therefore, the onset of pleural fibrosis appears to be independent of the quantity of inhaled asbestos fibres and due to different mechanisms from those leading to lung fibrosis. In practice, a correct interpretation of the presence of pleural fibrosis from a clinical and prognostic viewpoint also requires other investigations such as BAL and a complete respiratory function study.

Interaction of a phosphatidylcholine derivative of 1,6-diphenyl-1,3,5-hexatriene (DPH-PC) with lymphocytes

In this study we have demonstrated a transfer of a phosphatidylcholine derivative of 1,6-diphenyl-1,3,5-hexatriene (DPH-PC) from self-quenched lipid vesicles to intact lymphocytes. Membrane labeling was followed measuring the time dependent reexpression of fluorescence. The results of fluorescence quenching by 2,4,6-trinitrobenzene sulfonate and the decrease of fluorescence polarization values during incubation at 37 degrees C, suggest that the probe could remain localized at level of the plasma membrane until 20-30 minutes. DPH-PC is identical to the natural phospholipid with respect to head group structure and polarity therefore we suggest that under appropriate experimental conditions, it could represent an useful tool to study the physico-chemical properties of specific phospholipid domains in the plasma membrane of intact cells.

Effects of temperature on the maximal instantaneous muscle power of humans

The maximal instantaneous muscle power (wi,max) probably reflects the maximal rate of adenosine 5'-triphosphate (ATP) hydrolysis (ATPmax), a temperature-dependent variable, which gives rise to the hypothesis that temperature, by affecting ATPmax, may also influence wi,max. This hypothesis was tested on six subjects, whose vastus lateralis muscle temperature (Tmuscle) was monitored by a thermocouple inserted approximately 3 cm below the skin surface. The Wi,max was determined during a series of high jumps off both feet on a force platform before and after immersion up to the abdomen for 90 min in a temperature controlled (T = 20 +/- 0.1 degrees C) water bath. Control Tmuscle was 35.8 +/- 0.7 degrees C, with control Wi,max being 51.6 (SD 8.7) W.kg-1. After cold exposure, Tmuscle decreased by about 8 degrees C, whereas wi,max 27% lower. The temperature dependence of Wi,max was found to be less (Q10 less than 1.5, where Q10 is the temperature coefficient as calculated in other studies) than reported in the literature for ATPmax. Such a low Q10 may reflect an increase in the mechanical equivalent of ATP splitting, as a consequence of the reduced velocity of muscle contraction occurring at low Tmuscle.

Plasma lipid changes in psoriatic children

Plasma lipid, lipoprotein and apoprotein concentrations were determined in psoriatic children and in healthy controls. The plasma total cholesterol (TC) was higher than in controls (p = 0.03). The higher cholesterol levels were explained by an almost significant increase in cholesterol associated with high-density lipoproteins and by the tendency towards higher values of cholesterol associated with low-density lipoproteins and very-low-density lipoproteins. No significant changes of plasma triglycerides were observed. Levels of apoproteins (apo) AI and apo B were not significantly different in psoriatic children; however, the levels of apo B were correlated differently with plasma TC in psoriatic children, and the ratio TC/apo B was significantly increased in patients with respect to the controls, suggesting some differences of plasma lipoprotein lipid/apoprotein relationship in psoriasis.

The energy cost of walking or running on sand

Oxygen uptake (VO2) at steady state, heart rate and perceived exertion were determined on nine subjects (six men and three women) while walking (3-7 km.h-1) or running (7-14 km.h-1) on sand or on a firm surface. The women performed the walking tests only. The energy cost of locomotion per unit of distance (C) was then calculated from the ratio of VO2 to speed and expressed in J.kg-1.m-1 assuming an energy equivalent of 20.9 J.ml O2-1. At the highest speeds C was adjusted for the measured lactate contribution (which ranged from approximately 2% to approximately 11% of the total). It was found that, when walking on sand, C increased linearly with speed from 3.1 J.kg-1.m-1 at 3 km.h-1 to 5.5 J.kg-1.m-1 at 7 km.h-1, whereas on a firm surface C attained a minimum of 2.3 J.kg-1.m-1 at 4.5 km.h-1 being greater at lower or higher speeds. On average, when walking at speeds greater than 3 km.h-1, C was about 1.8 times greater on sand than on compact terrain. When running on sand C was approximately independent of the speed, amounting to 5.3 J.kg-1.m-1, i.e. about 1.2 times greater than on compact terrain. These findings could be attributed to a reduced recovery of potential and kinetic energy at each stride when walking on sand (approximately 45% to be compared to approximately 65% on a firm surface) and to a reduced recovery of elastic energy when running on sand.

Heart rate overshoot at the beginning of muscle exercise

A characteristic notch in the heart rate (fc) on-response at the beginning of square-wave exercise is described in 7 very fit marathon runners and 12 sedentary young men, during cycle tests at 30% and 60% of maximal oxygen consumption (VO2max). The fc notch revealed a fc overshoot with respect to the fc values predicted from exponential beat-by-beat fitted models. While at 30% of VO2max all subjects showed a fc overshoot, at 60% of VO2max it occurred in the marathon runners but not in the sedentary subjects. The mean time of occurrence of the fc overshoot from the onset of the exercise was 16.7 (SD 4.7) s and 12.2 (SD 3.2) s at 30% of VO2max in the runners and the sedentary subjects respectively, and 23.8 (SD 8.8) s at 60% of VO2max in the runners. The amplitude of the overshoot, with respect to rest, was 41 (SD 12) beats.min-1 and 31 (SD 4) beats.min-1 at 30% of VO2max in the runners and the sedentary subjects respectively, and 46 (SD 19) beats.min-1 at 60% of VO2max in the runners. The existence and the amplitude of the fc overshoot may have been related to central command and muscle heart reflex mechanisms and thus may have been indicators of changes in the balance between sympathetic and parasympathetic activity occurring in fit and unfit subjects.

Evaluation of L-thyroxine replacement therapy in children with congenital hypothyroidism

The outcome of L-thyroxine (L-T4) replacement therapy in children with congenital hypothyroidism (CH) remains to be completely evaluated. In this paper the overall pattern of response to L-T4 replacement therapy was studied in a group of 19 children with CH diagnosed by neonatal screening (10 with hypoplastic/aplastic thyroid disease, group H/A; 9 with gland ectopy, group E) who were followed-up for 60 +/- 27 months (mean +/- SD). With 1 exception serum T4 at diagnosis was greater than 2 micrograms/dl in children of group E and less than 2 micrograms/dl in those of group H/A. The initial dose of L-T4 (8-10 micrograms/kg BW/day) was modified in relation to age and weight in order to maintain serum TSH less than or equal to 5 microU/ml and FT3 in the normal range. A general inverse correlation between serum TSH and FT4 or FT3 concentrations was found, and the mean levels of serum FT4 and FT3 were significantly higher according to the following order of TSH results: low TSH (0-0.5 microU/ml) greater than normal (greater than 0.5-5 microU/ml) greater than elevated TSH (greater than 5 microU/ml). TSH levels less than or equal to 5 microU/ml were associated with FT4 values in the upper half of the normal range (54% of observations) or even higher (46%). Elevation of serum FT4 alone with FT3 values in the normal range did not result in clinical thyrotoxicosis, alteration of growth or premature craniosynostosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet release products modulate some aspects of polymorphonuclear leukocyte activation

The aim of this research was to evaluate in vitro interactions between platelets and polymorphonuclear leukocytes. The effects of supernatant from thrombin-activated platelets and two platelet release products (adenosine triphosphate and beta-thromboglobulin) were tested on the following features of polymorphonuclear leukocytes activation: opsonized zymosan and phorbol myristate acetate stimulated chemiluminescence, release of membrane bound calcium, NADPH-oxidase activity, and membrane fluidity (fluorescent polarization). The results showed that the addition of platelet supernatant to polymorphonuclear leukocytes induces a significant activation of cells. On the other hand, after three hours of preincubation of polymorphonuclear leukocytes with platelet supernatant, a decreased response of polymorphonuclear leukocytes to stimulation with phorbol myristate acetate, a significant decrease in NADPH-oxidase activity, and a lowered membrane fluidity were observed. Adenosine triphosphate modulated only opsonized zymosan stimulated chemiluminescence, with and without preincubation with polymorphonuclear leukocytes. Beta-thromboglobulin caused a decrease of the chemiluminescent response of polymorphonuclear leukocytes, using both agonists, with and without preincubation with polymorphonuclear leukocytes. Moreover beta-thromboglobulin only caused a decrease of the polymorphonuclear leukocytes membrane fluidity without preincubation with the cells. These results support the thesis that platelets have a "time-related" modulating activity on polymorphonuclear leukocytes.

[Role and limits of x-ray computed tomography and magnetic resonance imaging in acquired diseases of the aorta]

The introduction of computed tomography (CT) and the more recent magnetic resonance imaging (MRI) has radically changed the means of investigating acquired aortic disease by association the visualisation of the blood flow, previously available with angiography, with that of the aortic wall and the surrounding structures of this vessel. The popularity of CT scanning, being nearly non-invasive though dependent on ionising radiation and requiring the injection of contrast, and its diagnostic performance have raised it to the status of a primary investigation for diagnosing aortic aneurysm, especially abdominal, of aortic dissection, its acute complications and postoperative follow-up. However, CT scanning remains unsatisfactory for the examination of collateral and bypass vessels issuing from the aorta and for detailed analysis of aortic trauma and aortitis. MRI, though providing significant diagnostic advantages by the 3 dimensional visualisation of the aorta, the presence of spontaneous contrast between the lumen and vessel wall and cine MRI, is still relatively little used because of the small number of installations dealing with this indication in France. Despite the limitation, this totally non-invasive and non-irradiating investigation is progressively extending its use for the diagnosis of certain subacute or chronic aortic diseases. MRI is the best non-invasive investigation for the diagnosis of thoracic aortic aneurysms, chronic or subacute aortic dissection and for repeated postoperative follow-up after thoracic aortic surgery. Technological advances of this new imaging method and the multiplication of the number of installations suggest that the field of application of MRI for disease of the aorta will steadily increase in the future.

Erythrocyte membrane fluidity and changes in plasma lipid composition: a possible relationship in childhood obesity

We have studied plasma lipid patterns and erythrocyte membrane fluidity in 60 obese children and 20 normal children. Plasma levels of total cholesterol and associated low-density lipoproteins were significantly increased in 20 obese patients with respect to controls. A significant decrease in membrane fluidity, measured as an increase in the fluorescence polarization value of the probe 1,6-diphenyl-1,3,5-hexatriene, associated with an increase in the cholesterol/protein ratio has been shown in obese patients. The study of the correlation between erythrocyte membrane fluidity and plasma cholesterol has indicated that significant changes in fluidity and membrane lipid composition also occur in erythrocytes of obese patients with normal plasma lipid levels. These findings confirm that the erythrocyte membrane responds very early to modifications of plasma lipoproteins and suggest that in childhood obesity a modified transfer of cholesterol from plasma to erythrocyte membrane may take place.

Beta-thromboglobulin and polymorphonuclear leukocytes activation. (Effects on chemiluminescence, release of membrane bound calcium, NADPH-oxidase activity and membrane fluidity)

The aim of this paper was to evaluate the "in vitro" interaction between beta-thromboglobulin, one specific platelet release product and polymorphonuclear leukocytes. The effects of beta-thromboglobulin were tested on the following features of polymorphonuclear leukocytes activation: opsonized zymosan and phorbol myristate acetate stimulated chemiluminescence, release of membrane bound calcium, NADPH-oxidase activity, and membrane fluidity. Beta-thromboglobulin caused a decrease of the chemiluminescent response of polymorphonuclear leukocytes, using both agonists, with and without preincubation with polymorphonuclear leukocytes. We observed that beta-thromboglobulin caused a decrease also in the activity of NADPH-oxidase but not in the release of membrane bound calcium. Moreover beta-thromboglobulin caused a decrease of the polymorphonuclear leukocytes membrane fluidity. Our results suggest that the beta-thromboglobulin could play a role in the reciprocal interactions between platelets and polymorphonuclear leukocytes.

Electrocardiogram during deep breath-hold dives by elite divers

A portable ECG recorder was used during breath-hold dives at sea by 3 elite divers to 65 and 45 m. ECG was also recorded during nonimmersed maximal breath holds in the divers and 8 control subjects. Heart rate in the dives decreased rapidly to 20-24 beats.min(-1). During the surface experiments in the divers, bradycardia was much slower in onset, reaching 28-36 beats.min(-1) at the end of the breath holds. The divers showed a more consistent bradycardial response than the controls. The difference in temporal pattern of bradycardia, in the dives and in the breath holds by the divers, may have been due to face immersion in cold water, chest compression, and/or redistribution of blood into the chest with concomitant stimulation of cardiac and other mechanoreceptors. Arrhythmias, mostly supraventricular and ventricular premature complexes, were observed coincidently with the lowest heart rates, presumably reflecting a high vagal tone. In addition, cardiac distention at depth might have made the heart more prone to arrhythmias, while in the surface breath holds hypoxia might have accounted for a similar effect.

Alveolar gas composition and exchange during deep breath-hold diving and dry breath holds in elite divers

End tidal O2 and CO2 (PETCO2) pressures, expired volume, blood lactate concentration ([Lab]), and arterial blood O2 saturation [dry breath holds (BHs) only] were assessed in three elite breath-hold divers (ED) before and after deep dives and BH and in nine control subjects (C; BH only). After the dives (depth 40-70 m, duration 88-151 s), end-tidal O2 pressure decreased from approximately 140 Torr to a minimum of 30.6 Torr, PETCO2 increased from approximately 25 Torr to a maximum of 47.0 Torr, and expired volume (BTPS) ranged from 1.32 to 2.86 liters. Pulmonary O2 exchange was 455-1,006 ml. CO2 output approached zero. [Lab] increased from approximately 1.2 mM to at most 6.46 mM. Estimated power output during dives was 513-929 ml O2/min, i.e. approximately 20-30% of maximal O2 consumption. During BH, alveolar PO2 decreased from approximately 130 to less than 30 Torr in ED and from 125 to 45 Torr in C. PETCO2 increased from approximately 30 to approximately 50 Torr in both ED and C. Contrary to C, pulmonary O2 exchange in ED was less than resting O2 consumption, whereas CO2 output approached zero in both groups. [Lab] was unchanged. Arterial blood O2 saturation decreased more in ED than in C. ED are characterized by increased anaerobic metabolism likely due to the existence of a diving reflex.

Energetics of locomotion in African pygmies

The energy cost of walking (Cw) and running (Cr), and the maximal O2 consumption (VO2max) were determined in a field study on 17 Pygmies (age 24 years, SD 6; height 160 cm, SD 5; body mass 57.2 kg, SD 4.8) living in the region of Bipindi, Cameroon. The Cw varied from 112 ml.kg-1.km-1, SD 25 [velocity (v), 4 km.h-1] to 143 ml.kg-1.km-1, SD 16 (v, 7 km.h-1). Optimal walking v was 5 km.h-1. The Cr was 156 ml.kg-1.km-1, SD 14 (v, 10 km.h-1) and was constant in the 8-11 km.h-1 speed range. The VO2max was 33.7 ml.kg-1.min-1, i.e. lower than in other African populations of the same age. The Cr and Cw were lower than in taller Caucasian endurance runners. These findings, which challenge the theory of physical similarity as applied to animal locomotion, may depend either on the mechanics of locomotion which in Pygmies may be different from that observed in Caucasians, or on a greater mechanical efficiency in Pygmies than in Caucasians. The low Cr values observed enable Pygmies to reach higher running speeds than would be expected on the basis of their VO2max.

On maximal oxygen consumption in hypoxic humans

The present paper discusses the factors affecting maximal O2 consumption (VO2max) in hypoxia (4300 m above sea level) along the following lines: 1) In acute hypoxia, the fractional limitation to VO2max imposed by circulatory O2 transport (FQ') is 50%, instead of 70% as in normoxia. This is due to the increase in the blood O2 transport coefficient (beta b) as PO2 decreases, as a consequence of the sigmoidal shape of the O2 dissociation curve of hemoglobin. The remaining 50% is assumed to be equally partitioned between tissue O2 transfer (Ft') and mitochondria O2 utilization (Fm'). 2) In chronic hypoxia, FQ' = 0.45, Ft' = 0.20 and Fm' = 0.35, as a consequence of reduced muscle fiber size and muscle mitochondrial density following acclimatization. 3) The relationship between VO2max and PIO2 in both acute and chronic hypoxia reflects the O2 dissociation curve. 4) Acclimatization to chronic hypoxia does not have the function of preserving VO2max.

Energetics of resting anaerobic frog gastrocnemius at different temperatures by 31P-NMR

The net rate of phosphocreatine hydrolysis [PCr] [symbol; see text], and tissue pH were determined in anaerobic resting frog (Rana Ridibunda Ridibunda) gastrocnemii by 31-P-NMR in the temperature (T) range from 5 to 30 degrees C. Absolute [PCr] [symbol; see text] values from 0.36 to 10.07 mM/h were estimated assuming a resting [PCr] of 26 mM at 20 degrees C. The corresponding Q10 values ranged from 2.1 (30 degrees C) to 17.5 (5 degrees C). Muscle pH was found to be T-dependent with a 10 degrees C drop in T resulting in an increase of 0.1 pH units. At any given T, pH was found to be constant over a period of at least one hour (30 degrees C) from the onset of anaerobiosis. Based on simultaneous [PCr] [symbol; see text] and pH estimates, the contribution of anaerobic glycolysis ([ATPLA]) to the overall rate of ATP resynthesis ([ATPTot]) was estimated assuming a approximately P/La ratio of 1.2. [ATPTot] was then calculated for each investigated T value as the sum of [PCr] and [ATPLa]. [ATPTot] was found to vary between 5 and 30 degrees C from 0.79 mM/h to 22.15 mM/h. The present study, besides proposing a methodology for the assessment of high energy phosphates hydrolysis by 31P-NMR spectroscopy at changing T, provides a comprehensive analysis of the T-dependence of anaerobic metabolism of the resting anaerobic frog gastrocnemius which may be extrapolated to other tissues.

Effects of intramembrane particle aggregation on erythrocyte membrane fluidity: an electron spin resonance study in normal and in dystrophic subjects

Mobilization and aggregation of intramembrane particles (IMPs) are physiological events observed in various cells. In erythrocyte membranes, aggregation of IMPs can be induced by the exposure of partially desprectrinized erythrocyte membranes to acidic pH. We investigated the association between IMPs aggregation, protein mobility, and membrane fluidity in erythrocyte membranes of healthy controls and Duchenne muscular dystrophy (DMD) patients by using electron spin resonance and specific spin labels for membrane proteins and lipids. In erythrocyte membranes of control subjects, the partial spectrin removal induced a decreased segmental motion of protein spin label indicating an increase of protein-protein interactions. Stearic acid spin labels 5- and 16-(N-oxyl-4,4'-dimethyloxazolidine) showed that the treatment induces an increase of membrane fluidity. In DMD patients, both treated and untreated erythrocyte membranes showed changes of membrane fluidity when compared to those of the controls. Our results suggest that defects in the interactions between skeletal proteins and/or between membrane and skeleton components may contribute to the alterations of erythrocyte membranes in DMD.