Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men

We analysed the importance of systemic and peripheral arteriovenous O₂ difference ( difference and a‐v_fO₂ difference, respectively) and O₂ extraction fraction for maximal oxygen uptake ( ). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with . Articles (n = 17) publishing individual data (n = 154) on , maximal cardiac output ( ; indicator‐dilution or the Fick method), difference (catheters or the Fick equation) and systemic O₂ extraction fraction were identified. For the peripheral responses, group‐mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a‐v_fO₂ difference and O₂ extraction fraction (arterial and femoral venous catheters) were obtained. and two‐LBF increased linearly by 4.9‐6.0 L · min^–1 per 1 L · min^–1 increase in (R² = .73 and R² = .67, respectively; both P < .001). The difference increased from 118‐168 mL · L^–1 from a of 2‐4.5 L · min^–1 followed by a reduction (second‐order polynomial: R² = .27). After accounting for a hypoxemia‐induced decrease in arterial O₂ content with increasing (R² = .17; P < .001), systemic O₂ extraction fraction increased up to ~90% ( : 4.5 L · min^–1) with no further change (exponential decay model: R² = .42). Likewise, leg O₂ extraction fraction increased with to approach a maximal value of ~90‐95% (R² = .83). Muscle O₂ diffusing capacity and the equilibration index Y increased linearly with (R² = .77 and R² = .31, respectively; both P < .01), reflecting decreasing O₂ diffusional limitations and accentuating O₂ delivery limitations. In conclusion, although O₂ delivery is the main limiting factor to , enhanced O₂ extraction fraction (≥90%) contributes to the remarkably high in endurance‐trained individuals.     

Human C5a and C5a analogs as probes of the neutrophil C5a receptor

Quantitative assessment of the human neutrophil chemotactic response and immunologic evidence demonstrate that human C5a and/or its physiological equivalent, C5a_{des Arg'} serves as the predominant chemotactic factor in complement activated serum. Both C5a and its des Arg74 derivative are capable of promoting directed cellular migration as well as lysosomal enzyme release. When neutrophil chemotaxis is assessed by an ‘under agarose methodology’, in the absence of extraneous human serum proteins. C5a is found to be some 10- to 30-fold more active than C5a_{des Arg} Quantitatively similar results are obtained when each factor is assessed for its ability to promote secretion of azurophilic granular enzymes from cytochalasin B-treated neutrophils. The C5a structural analog C5a-(1–69), lacking five residues of the C-terminal portion of the parent molecule, and a synthetic pentapeptide l-methionyl-l-glutaminyl-l-leucylglycyl-l-arginine, which mimics the C-terminal linear sequence of C5a (Chenoweth et al., 1979a), are found to be devoid of biological activity when examined either-alone or in combination. These findings imply that the C-terminal portions of C5a contribute importantly to modulating ligand-receptor interactions on neutrophils. Based on these observations, a conceptual model of the interaction of human C5a with the neutrophil C5a receptor is proposed. We hypothesize that C5a possesses an internal ‘recognition’ site in addition to the ‘activation’ site contained in the C-terminal region of the molecule.     

Serum factors other than albumin are needed for the maintenance of normal capillary permselectivity in rat hindlimb muscle

To investigate the effects of different perfusates on capillary permeability, we determined the capillary filtration coefficient (CFC), the capillary diffusion capacity (PS) for Cr-EDTA and clearance of albumin during isogravimetric conditions and maximal vasodilatation in the isolated, perfused rat hindquarter preparation. Experiments were conducted in 30 rats with different perfusates. We were able to confirm the classical ‘protein effect’. Absence of proteins, using pure dextran solution as perfusate, induced a 45% increase in CFC and a three-fold increase in albumin clearance. However, we also found evidence for a ‘serum effect’. Hence, the clearance of albumin was normal when the serum content exceeded 5% (v/v) in perfusates otherwise composed of albumin in Tyrode, but increased three-fold from 0.0305 to 0.0912 ml (min-100 g)^-1 when the rats were perfused with albumin in Tyrode with no serum present, without any change in CFC, PS for Cr-EDTA or vascular resistance to flow. Thus, certain non-dialysable serum factors, other than albumin, seem to be needed for the maintenance of normal capillary permselectivity in rat hindquarters. These factors are probably needed for the capillary membrane to maintain its character of a negatively charged barrier.     

Slow recovery of the maximal rate of rise (\dot V_{max} ) of the action potential in sheep cardiac Purkinje fibers

Measurements of the maximal rate of rise ( ) of the action potential in cardiac Purkinje fibers were made at different intervals following an action potential or a long-duration depolarization. Recovery of is fast after a short depolarization but is composed of a fast phase and a very slow phase (time constant order of 1 s) after a long-duration depolarization. The existence of a slow phase in the recovery explains the shift of the ( - E_m) relationship to negative potentials in fibers with reduced resting potential.     

Pulmonary function hysteresis during compression to,and decompression from 31.3 ATA

Tracheal gas density breathing heliox at 31.3 atmospheres absolute (O² at 0.42 ATA) is 6.287 g 1^-1, or approximately 5.5 times greater than air at 1 ATA. This constitutes a significant respiratory load, previously shown to induce respiratory adaptation. During a saturation dive to 31.3 ATA, five divers were exposed to this load for 16 days. This project aimed at investigating possible hysteresis in pulmonary function during dive compression, adaptation and decompression phases. Pulmonary function tests were performed at the surface in air, and at four pressure stops during compression and decompression, with divers breathing the helium-oxygen gas mixture. Significant hysteresis patterns were observed for pooled maximal voluntary ventilation, forced expired volume at 1 s, peak expiratory flow, and maximum expiratory flows (P < 0.05), with post-adaptation flows consistently exceeding those observed during compression. Two mechanisms may explain these observations. Differences may be attributable to positive effort-dependence in the forced expiratory flow; or it is possible the subjects adapted to the respiratory load by modifying neural input to airway smooth muscle, thereby modifying airway resistance.     

TOTAL BODY POTASSIUM FAT FREE WEIGHT AND MAXIMAL AEROBIC POWER IN CHILDREN WITH ANOREXIA NERVOSA

ABSTRACT. Body Composition and aerobic work performance have been studied in 5 boys and 10 girls suffering from anorexia nervosa. The average ages of the two groups of children were 15.4 (boys) and 15.2 (girls) years respectively. Measurements of body composition included height, weight ( W ), body potassium (⁴⁰K), skinfold thickness (SFT) at triceps and subscapularis, blood volume (BV) and femoral condylar and radioulnar breadths. From these measurements estimates of fat free weight (FFW), skeletal weight (S) and lean body mass (LBM) were made. Work performance was assessed by measurement of the maximal aerobic power (V_O2 max). The patients had lost on average 26 % of their former body weight. The boys had on average >7 % of their body weight as fat compared with >9 % in the girls. However, the loss of weight was not solely due to loss of body fat, but could also be ascribed to a decrease in soft fatfree tissue. LBM or FFW could be estimated as well from SFT as from ⁴⁰K. V_O2 max averaged 1.43 1/min (35.1 ml/kg/min) in the anorexic boys and 1.24 1/min (33.2 ml/kg/min) in the girls and was associated with FFW and LBM. However, Vo, max was lower in relation to LBM than in healthy children of the same age. Thus it was suggested that the emaciation in anorexia is directly attributable to loss of both fat and muscle and accounts in part for the reduction of aerobic power observed. However, an important factor may be the debilitating effect of starvation on the patient, particularly in its advanced and later stages, which reduces his/her level of habitual physical activity.     

Strength training improves 5‐min all‐out performance following 185 min of cycling

To investigate the effects of heavy strength training on the mean power output in a 5‐min all‐out trial following 185 min of submaximal cycling at 44% of maximal aerobic power output in well‐trained cyclists. Twenty well‐trained cyclists were assigned to either usual endurance training combined with heavy strength training [E+S; n=11 (♂=11)] or to usual endurance training only [E; n=9 (♂=7, ♀=2)]. The strength training performed by E+S consisted of four lower body exercises [3 × 4–10 repetition maximum (RM)], which were performed twice a week for 12 weeks. E+S increased 1 RM in half‐squat (P≤0.001), while no change occurred in E. E+S led to greater reductions than E in oxygen consumption, heart rate, blood lactate concentration, and rate of perceived exertion (P<0.05) during the last hour of the prolonged cycling. Further, E+S increased the mean power output during the 5‐min all‐out trial (from 371 ± 9 to 400 ± 13 W, P<0.05), while no change occurred in E. In conclusion, adding strength training to usual endurance training improves leg strength and 5‐min all‐out performance following 185 min of cycling in well‐trained cyclists.     

General strength and kinetics: fundamental to sprinting faster in cross country skiing?

To determine relationships between general strength, maximal skiing speed (V_max), pole and leg kinetics and kinematics, 16 male elite skiers underwent three V_max tests in double poling, diagonal stride and V2 on a treadmill. The analyzed skiing speeds and leg and arm kinetics were among the highest ever recorded. Relationships between general strength exercises and V_max were technique dependent. Power output in bench press and bench pull were related to V_max in DP and diagonal stride, whereas each 1 repetition maximum was related to V2. Isometric squats were not associated with V_max in all three techniques, whereas jump height and rate of force development during squat jump were. Analysis of kinetics and kinematics revealed that it was not exclusively the magnitude of applied forces during skiing, but the timing and proper instant of force application were major factors discriminating between faster and slower skiers. For all techniques, the faster skiers used different skiing strategies when approaching V_max when compared with the slower skiers. General strength and power per se seem not to be major determinants of performance in elite skiers, whereas coordination of these capacities within the different and complex skiing movements seems to be the discriminating factor.     

EFFECT OF FLUOXETINE ON MAXIMAL ELECTROSHOCK SEIZURES IN MICE: ACUTE VS CHRONIC ADMINISTRATION

There are no definite reports regarding the effects of chronic fluoxetine on animal models of epilepsy. Since chronically administered fluoxetine, in comparison to acutely administered fluoxetine has different effects on CNS, the present study was undertaken to investigate the effect of acute and chronic fluoxetine pretreatment, on a median anticonvulsant dose (ED50) of phenytoin in male ICR albino mice. Additionally, the effects of fluoxetine pretreatment on median convulsive current (CC50) in the presence and absence of phenytoin were investigated and results were compared. The maximal electroshock seizure (MES) test was used to estimate the ED50of phenytoin. The electroshock threshold test was used to estimate CC50. ED50and CC50values were calculated by probit analysis. The effects of the chronic and acute fluoxetine groups on the ED50of phenytoin were significantly different (P<0.05), and on CC50this difference was not statistically significant. Chronic fluoxetine insignificantly increased the ED50of phenytoin and decreased the CC50while acute fluoxetine decreased the ED50of phenytoin and increased the CC50. Our results indicate that chronic fluoxetine does not have an antiepileptic property and it may have dubious proconvulsant properties, contrary to acute fluoxetine.