Quantitative analyse der selbstassoziation von hämoglobinmolekülen anhand der konzentrationsabhängigkeit der spektren

The dependence of the spectrum of oxygenated hemoglobin (Hb) on the Hb concentration was measured and it was found that Hb solutions do not obey Lambert-Beer's law. The absorption coefficient depends clearly on the Hb concentration. As all external parameters were kept constant except Hb concentration, the only way to explain our result is to assume that Hb molecules undergo self association and that this self association is reflected in the behaviour of the absorption coefficient. To get parameters which are suited to describe the self association of Hb molecules, two models were used. The first model is based on the idea that Hb associates according to the following equation: Hb + Hb ? (Hb)₂. Hb represents a single Hb molecule (consisting of two α-and two β-chains) and (Hb)₂ a complex of two Hb molecules. The second, more complicated model, takes into account higher associates of Hb molecules (like (Hb)₃, (Hb)₄, . . .). By using a least square fitting, it was possible to match experimental data and theoretical curves. Furthermore it became evident that at Hb concentrations, which are of physiological relevance, about 90% of the Hb molecules are involved in self association. The second model revealed that at those Hb concentrations there is a considerable portion of complexes which are composed of 10 or more Hb molecules.     

Biodistribution of synthetic thymosin β4 in the serum,urine, and major organs of mice

Thymosin β₄ (Tβ₄) is a peptide of 43 amino acids that was first isolated from the thymus gland and subsequently found to be ubiquitous in nature. Tβ₄ functions mainly as an actin-sequestering molecule in non-muscle cells, where its primary role is to maintain the large pool of unpolymerized G-actin in the cell. Studies on the pharmacokinetics of Tβ₄ in human and other mammals have not been reported so far. In the present study, we have measured Tβ₄ concentrations in serum, urine, and 10 major organs of female Swiss-Webster mice following intraperitoneal administration of 400 μg synthetic Tβ₄. Using a modified enzymatic immu-noassay, our data show a significant increase of Tβ₄ in serum starting 2 min after injection and lasting for 40 min (average: 2.34±0.54μg/ml). High concentrations were found in urine (59.3 ± 7.54μg/ml) at three different time points after injection (20 min, 40 min, and 2 h). Of the 400 μg Tβ₄ administered to mice 83 % was recovered at the end of the study, 44.6% of which corresponded to urine, 1.4% to serum, and 37.5% to the organs. In 50% of the tested organs, the wet weight concentrations of Tβ₄ increased significantly from the first 40 min to 2 h after injection in comparison to their baseline wet weight concentrations. These organs were: the brain (72 μg/g vs 42 μg/g), heart (80 μg/g vs 37 μg/g), liver (15 μg/g vs 9 μg/g), kidneys (65 μg/g vs 28 μg/g), and peritoneal fat (47 μg/g vs 13 μg/g). Wet weight concentrations increased in the thymus (196 μg/g vs 147 μg/g) and muscle (45 μg/g vs 0 μg/g) after 6 h of injection. The spleen showed an increase in wet weight concentrations at the 2 min timepoint (267 μg/g vs 161 μg/g). Ovaries had a biphasic increase at 40 min(72 μg/g vs 62 μg/g) and 24 h (92 μg/g vs 62 μg/g) after Tβ₄ administration. In lungs, the highest wet weight increase after injection (149 μg/g at timepoint 6h) was not higher than its basal wet weight concentration (153 μg/g). These phar-macokinetic studies of Tβ₄ in mice have established that high levels of Tβ₄ are found in the blood following I.P. administration and the kidney rapidly removes the peptide from the circulation. The kinetics of this response should help define the proper scheduling of administration of Tβ₄ during clinical trials in disorders, such as the acute respiratory distress syndrome (ARDS), associated with actin toxicity.     

Effect of triiodothyronine on renal growth and renal sodium reabsorption in hypothyroid rats

Experiments were carried out to compare temporal changes in the paraaminohippuric acid clearance (C _PAH), renal sodium reabsorption ( \(R_{Na^ + } \) ), ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) content in hypothyroid rats after a single injection of triiodothyronine (T₃) (50 μg/100 g body wt).C _PAH and \(R_{Na^ + } \) showed no changes at 24 and 48 h. At 72 h, however, significant increases of 41% and 42% (per g kidney wet wt) were observed inC _PAH and \(R_{Na^ + } \) , respectively. The cortex in T₃-treated hypothyroid rats showed a significant increase in the protein/DNA and RNA/DNA ratios at 24 h and progressive increases to a level of 24%, and 37%, respectively, at 48 h. No changes in DNA content were observed at either time-points. The results show that the increases in RNA/DNA and protein/DNA ratios upon T₃ treatment preceded the increases inC _PAH and \(R_{Na^ + } \) , suggesting a direct effect of T₃ on renal cortical growth, rather than a secondary response to a primary increase in renal functions.     

“Live High–Train High” increases hemoglobin mass in Olympic swimmers

Purpose

This study tested whether 3–4 weeks of classical “Live High–Train High” (LHTH) altitude training increases swim-specific VO_2max through increased hemoglobin mass (Hb_mass).

Methods

Ten swimmers lived and trained for more than 3 weeks between 2,130 and 3,094 m of altitude, and a control group of ten swimmers followed the same training at sea-level (SL). Body composition was examined using dual X-ray absorptiometry. Hb_mass was determined by carbon monoxide rebreathing. Swimming VO_2peak was determined and swimming trials of 4 × 50, 200 and 3,000 m were performed before and after the intervention.

Results

Hb_mass (n = 10) was increased (P < 0.05)after altitude training by 6.2 ± 3.9 % in the LHTH group, whereas no changes were apparent in the SL group (n = 10). Swimming VO_2peak was similar before and after training camps in both groups (LHTH: n = 7, SL: n = 6). Performance of 4 × 50 m at race pace was improved to a similar degree in both groups (LHTH: n = 10, SL: n = 10). Maximal speed reached in an incremental swimming step test (P = 0.051), and time to complete 3,000 m tended (P = 0.09) to be more improved after LHTH (n = 10) than SL training (n = 10).

Conclusion

In conclusion, 3–4 weeks of classical LHTH is sufficient to increase Hb_mass but exerts no effect on swimming-specific VO_2peak. LHTH may improve performance more than SL training.     

Contribution of junctional conductance to the cellular voltage-divider ratio in frog skins

It has been suggested that distribution of lateral interspace resistance in association with a highly conductive junction can significantly affect the measurement of outer membrane(o)/epithelial(t) voltage divider ratios (F _o=δV _o/δV _t), thereby leading to erroneous inferences regarding the outer membrane fractional resistance [fR _o=R _o/R _c=R _o/(R _o+R _i)], whereR _o andR _i are the outer and inner cell membrane resistance respectively andR _c is the total cell membrane resistance. We present here experimental evidence for this point of view. During seasons when frog skins were highly permeable to Cl, transepithelial conductanceg _t often exceeded 2 mS/cm². High concentrations of external amiloride rapidly blocked cellular transport, butg _t initially remained high andF _o remained appreciably less than 1.0. These values ofF _o were found here to result from low junctional resistanceR _j: increase ofR _j, either gradually following the administration of amiloride, or abruptly with external replacement of Cl by other anions, was associated with increase ofF _o to near unity, without effect on the membrane potential or significant change in the short-circuit current. Experimental results following amiloride validated a simple equivalent circuit model predicting near-linear increase inF _o with progressive decrease ing _t and led to plausible values ofR _j and lateral space resistanceR _l. The possible influence of the paracellular resistance pattern on the evaluation of cell membrane resistances from voltage divider ratios is discussed.     

Physiological effects of variations in spontaneously chosen crank rate during incremental upper-body exercise

The aims of the present study were: first, to assess the interindividual variations of a spontaneously chosen crank rate (SCCR) in relation to the power developed during an incremental upper body exercise on an arm ergometer set at a constant power regime, and second, to compare heart rate (HR) responses, expired minute ventilation (V˙ _E) and oxygen consumption (V˙O₂) when the pedal rates were chosen spontaneously (T_SCCR) or set at ±10% of the freely chosen rates (T_+10% and T_?10%, respectively). The mean pedal rate values were linearly related (P?r?=?0.96), although large variations of pedalling rate strategies were observed between subjects. Maximal power (MP) and time to exhaustion values were significantly higher (P?SCCR than during T_+10% and T_?10%. Peak V˙O₂ values were significantly higher (P?+10% than in T_SCCR and T_?10%. The increase in HR, V˙ _E, and V˙O₂ mean values, in relation to the increase in the power developed, was significantly higher (P?±10%) than in the two other conditions. The findings of the present study suggest that the use of an electromagnetically braked ergometer, which automatically adjusts the resistance component to maintain a constant work rate, should be used in order to achieve the highest MP values during an incremental upper body exercise. A 10% increase of the SCCR should be used in order to provide the highest peak V˙O₂ value.     

Changes in the brain and core temperatures in relation to the various arousal states in rats in the light and dark periods of the day

In rats, brain temperature (T _br) and core temperature (T _c) were recorded in parallel with the sleep-wake activity throughout the 24-h diurnal cycle, consisting of a 12-h light (L) and a 12-h dark (D) period. In order to characterize the temperature changes associated with the arousal states in the L and the D separately, (i) the average temperatures in wakefulness (W), non-rapid eye movement sleep (NREMS) and REM sleep (REMS), and at the transitions between the arousal states were calculated; (ii) the courses of temperatures before and after the transitions (falling asleep, awakening from NREMS or REMS, transition from NREMS to REMS) were determined; (iii) the rates of changes inT _br andT _c were calculated for each state; and (iv) the correlations between the temperatures and the overall length of each arousal state, and betweenT _br andT _c were studied.In both the L and D periods,T _br andT _c decreased at the beginning of NREMS, then levelled off, and increased slightly before awakening. Apart from short arousals which did not affect temperature,T _br andT _c increased in W, peaked 15–20 min after awakening, and declined significantly before the falling asleep. In REMS,T _br increased at a high rate, while a slight increase inT _c was evident in the L only. Correlations between the temperatures and the arousal states were found in both the L and the D. The courses ofT _br andT _c were also correlated.The results support the existence of characteristic changes in body temperature related to the arousal states in the rat.     

The contribution of haemoglobin mass to increases in cycling performance induced by simulated LHTL

We sought to determine whether improved cycling performance following ‘Live High-Train Low’ (LHTL) occurs if increases in haemoglobin mass (Hb_mass) are prevented via periodic phlebotomy during hypoxic exposure. Eleven, highly trained, female cyclists completed 26 nights of simulated LHTL (16 h day⁻¹, 3000 m). Hb_mass was determined in quadruplicate before LHTL and in duplicate weekly thereafter. After 14 nights, cyclists were pair-matched, based on their Hb_mass response (ΔHb_mass) from baseline, to form a response group (Response, n = 5) in which Hb_mass was free to adapt, and a Clamp group (Clamp, n = 6) in which ΔHb_mass was negated via weekly phlebotomy. All cyclists were blinded to the blood volume removed. Cycling performance was assessed in duplicate before and after LHTL using a maximal 4-min effort (MMP_4min) followed by a ride time to exhaustion test at peak power output (T _lim). VO_2peak was established during the MMP_4min. Following LHTL, Hb_mass increased in Response (mean ± SD, 5.5 ± 2.9%). Due to repeated phlebotomy, there was no ΔHb_mass in Clamp (−0.4 ± 0.6%). VO_2peak increased in Response (3.5 ± 2.3%) but not in Clamp (0.3 ± 2.6%). MMP_4min improved in both the groups (Response 4.5 ± 1.1%, Clamp 3.6 ± 1.4%) and was not different between groups (p = 0.58). T _lim increased only in Response, with Clamp substantially worse than Response (−37.6%; 90% CL −58.9 to −5.0, p = 0.07). Our novel findings, showing an ~4% increase in MMP_4min despite blocking an ~5% increase in Hb_mass, suggest that accelerated erythropoiesis is not the sole mechanism by which LHTL improves performance. However, increases in Hb_mass appear to influence the aerobic contribution to high-intensity exercise which may be important for subsequent high-intensity efforts.     

Diffusion coefficients of oxygen and hemoglobin as obtained simultaneously from photometric determination of the oxygenation of layers of hemoglobin solutions

The oxygenation of layers of deoxygenated hemoglobin solutions after a sudden exposure to a gas containing oxygen at a partial pressureP ₁ has been studied by a photometric method. Layer thicknesses varied between 50 and 250 μm, hemoglobin concentrations between 0.1 and 0.34kg/l, and oxygen partial pressures between 4.65 and 93.1 kPa (35 and 700 mm Hg). The diffusion chamber containing the layer of hemoglobin solution permitted a step change in gas atmosphere without changing the optical apparatus constant. The following results were obtained:

1. The oxygen saturation increase is independent of the layer thickness when expressed as a function of time divided by layer thickness squared (normalized oxygenation time). This justifies the assumption of chemical equilibrium between oxygen and hemoglobin in the range considered.
2. The oxygen saturation increases proportionally to the square root of time over a wide range of oxygenation as expected. This range reaches to almost 100% oxygenation atP ₁=93.1 kPa (700 mm Hg) but less far asP ₁ is lower. Thus at highP ₁ values there is a sharp boundary between the oxygenated and deoxygenated part of the layer allowing the application of the advancing front concept.
3. Fitting the theoretical equations derived in a preceding paper to the experimental results provides simultaneous values of the oxygen permeability (or, knowing oxygen solubility, of the oxygen diffusion coefficient) and of the hemoglobin diffusion coefficient. These values agree fairly well with values obtained by other authors from experiments yielding the diffusion coefficients of oxygen or hemoglobin separately.

     

The CO single breath transfer factor of the lung

The CO single breath method for determining the transfer factor of the lung,T, and its component factors,Dm andVc, never gained wide application. The lack of generally accepted normal values has contributed to this. In this paper, based on the results of measurements in 28 normal subjects, it is shown that generally acceptable normal values can be obtained by: 1. determiningT at lung volumes above 80% TLC, and 2. expressingT, Dm andVc per unit of alveolar gas volume during breath-holding:T _v ,Dm _v andVc _v .     

Human intervertebral disc stiffness correlates better with the Otsu threshold computed from axial T2 map of its posterior annulus fibrosus than with clinical classifications

Degeneration of the intervertebral disc, sometimes associated with low back pain and abnormal spinal motions, represents a major health issue with high costs. A non-invasive degeneration assessment via qualitative or quantitative MRI (magnetic resonance imaging) is possible, yet, no relation between mechanical properties and T₂ maps of the intervertebral disc (IVD) has been considered, albeit T₂ relaxation time values quantify the degree of degeneration. Therefore, MRI scans and mechanical tests were performed on 14 human lumbar intervertebral segments freed from posterior elements and all soft tissues excluding the IVD. Degeneration was evaluated in each specimen using morphological criteria, qualitative T₂ weighted images and quantitative axial T₂ map data and stiffness was calculated from the load-deflection curves of in vitro compression, torsion, lateral bending and flexion/extension tests. In addition to mean T₂, the OTSU threshold of T₂ (T_OTSU), a robust and automatic histogram-based method that computes the optimal threshold maximizing the distinction of two classes of values, was calculated for anterior, posterior, left and right regions of each annulus fibrosus (AF). While mean T₂ and degeneration schemes were not related to the IVDs’ mechanical properties, T_OTSU computed in the posterior AF correlated significantly with those classifications as well as with all stiffness values. T_OTSU should therefore be included in future degeneration grading schemes.     

The effect of aging on the hepatic metabolism of sulfobromophthalein in BN/Bi female and WAG/Rij male and female rats

The effect of aging on sulfobromophthalein (BSP) metabolism was studied in three groups of rats—BN/Bi female and WAG/Rij male and female rats—of different ages ranging from 3 to 30 months. Under Nembutal anesthesia, BSP biliary transport maximum (T_m) and relative storage capacity (S) were determined by a single infusion rate method by directly determining T_m from bile samples collected through a common bile duct cannula. T_m values expressed as μg of BSP per min per g of liver were highest in the youngest rats (3-month-old) as compared with the older rats (12-, 24-, 30-month-old) for all three rat groups. T_m gradually decreased as age increased and at the age of 24 or 30 months reached a value of 66–70% of the highest values for 3-month-old rats. The percentage of conjugated BSP in the bile measured during the T_m period remained essentially unchanged with age in all three rat groups. S values, expressed as mg of BSP stored per mg of BSP per ml of plasma per g of liver, remained unchanged (BN/Bi female) or even increased (WAG/Rij male and female) with age. As a consequence, S values expressed per rat were higher in older age groups than in the youngest one for all three rat groups. In contrast with previous reports by other authors on man and rats, the BSP T_m appears to decraese with age regardless of rat strain and sex, while S does not show such a decrease.     

Regulation of local sweating in sleep-deprived exercising humans

Summary Thermoregulatory sweating [total body (m _sw,b), chest (m _sw,c) and thigh (m _sw,t) sweating], body temperatures [oesophageal (T _oes) and mean skin temperature (T _sk)] and heart rate were investigated in five sleep-deprived subjects (kept awake for 27 h) while exercising on a cycle (45 min at approximately 50% maximal oxygen consumption) in moderate heat (T _air andT _wall at 35° C. Them _sw,c andm _sw,t were measured under local thermal clamp (T _sk,1), set at 35.5° C. After sleep deprivation, neither the levels of body temperatures (T _oes,T _sk) nor the levels ofm _{sw, b},m _{sw, c} orm _{sw, t} differed from control at rest or during exercise steady state. During the transient phase of exercise (whenT _sk andT _sk,1 were unvarying), them _{sw, c} andm _{sw, t} changes were positively correlated with those ofT _oes. The slopes of them _{sw, c} versusT _oes, orm _{sw, t} versusT _oes relationships remained unchanged between control and sleep-loss experiments. Thus the slopes of the local sweating versusT _oes, relationships (m _{sw, c} andm _{sw, t} sweating data pooled which reached 1.05 (SEM 0.14) mg·cm^–2·min^–1°C^–1 and 1.14 (SEM 0.18) mg·cm^–2·min^–1·°C^–1 before and after sleep deprivation) respectively did not differ. However, in our experiment, sleep deprivation significantly increased theT _oes threshold for the onset of bothm _{sw, c} andm _{sw, t} (+0.3° C,P<0.001). From our investigations it would seem that the delayed core temperature for sweating onset in sleep-deprived humans, while exercising moderately in the heat, is likely to have been due to alterations occurring at the central level.     

Exogenous thymidine and reversal of the inhibitory effect of sulfamethoxazole-trimethoprim on streptococci

The practice of using sulfamethoxazole-trimethoprim (SXT) for the selective isolation ofStreptococcus pyogenes and as a taxonomic character in the presumptive identification of streptococci was applied to 17 strains of different groups of streptococci to determine their characteristic behaviour in the presence of exogenous thymidine.Streptococcus pyogenes,Streptococcus agalactiae and group D enterococci utilized thymidine, the first two species obtaining a maximum reversal of the inhibitory effect of SXT at thymidine concentrations of 1.2 μg/ml and 0.6 μg/ml or higher, respectively. For group D enterococci, the degree of reversal of the inhibitory effect was proportional to the thymidine concentration. In contrast, the four viridans species studied (Streptococcus sanguis I, Streptococcus salivarius,Streptococcus mitis andStreptococcus sanguis II) andStreptococcus pneumoniae were unable to utilize thymidine from an exogenous source and thus growth remained inhibited even at the highest concentrations of thymidine tested. For selective isolation and identification of streptococci only stable media with batch-to-batch consistency are recommended together with a known quantity of thymidine.     

Exercise-induced changes in blood levels of alpha-tocopherol

Levels of α-tocopherol (αT) in plasma and red blood cells (RBC) are assumed to be modulated by exercise. The mechanisms involved remain to be established. We examined the influence of different running bouts on the content of αT in RBC (αT_RBC), the concentration in plasma (αT_plasma), and their relationship with lipolysis, as indicated by changes (Δ) in plasma glycerol concentration ([glycerol]). Eleven healthy runners [mean (SD) age 35 (9) years, height 177.3 (7.6) cm, body mass 69.6 (9.4) kg, and peak oxygen consumption, , 57.8 (4.8) ml^.kg^–1.min^–1] performed an incremental treadmill test [duration 17 (2) min, peak velocity, v _peak 4.8 (0.4) m^.s^–1], a training run [173 (12) min, 57 (4)% v _peak] and a marathon [197 (24) min, 75 (5)% v _peak]. Before (pre) and after (post) each run, haematological and lipid parameters, αT_RBC and αT_Plasma were determined. Haemoconcentration was observed after each run. Δ[glycerol] was +0.10 (0.10) mmol^.l^–1, +0.40 (0.14) mmol^.l^–1 and +0.51 (0.15) mmol^.l^–1 in the treadmill test, training run and marathon, respectively. When corrected for haemoconcentration, values of αT_plasma decreased [–5.4 (7.5)%, P<0.05] in the treadmill test, were unchanged [+0.7 (8.7)%] in the training run and increased [+7.8 (8.3)%, P<0.05] in the marathon. αT_RBC decreased [pre vs post: 22.7 (3.2) nmol^.g haemoglobin^–1 (nmol^.g Hb^–1) vs 18.9 (3.8) nmol^.g Hb^–1, P<0.05] in the treadmill test and was not significantly changed in either the training run [20.8 (1.9) nmol^.g Hb^–1 vs 19.1 (3.0) nmol^.g Hb^–1] or the marathon [21.6 (2.9) nmol^.g Hb^–1 vs 23.4 (2.7) nmol^.g Hb^–1]. ΔαT_RBC and ΔαT_plasma were positively related to Δ[glycerol]. The reduction in αT_RBC and αT_plasma after short-lasting heavy exercise indicates the consumption of αT, whereas the association between ΔαT and Δ[glycerol] suggests mobilisation of αT, especially in long-lasting exercises. However, although αT appears to be influenced by exercise, the results suggest a well-balanced regulation of αT during exercise resulting in small, and only in part, significant ΔαT in blood. Electronic Publication     

Skin and core temperatures as determinants of heat production and heat loss in the goat

In 82 experiments on 10 goats body core temperature (T _core) was altered between 35° and 42°C by external heat exchangers acting on blood temperature while skin temperature (T_skin) was maintained constant, by a circulating shower bath, at different levels between 32° and 44°C. At all skin temperatures at least fourfold increases of heat production (M) and respiratory evaporative heat loss (REHL) occurred whenT _core was lowered or raised, respectively. The lower T_skin was, the higher were the thresholds ofT _core, at which M or REHL exceeded resting levels. The lower T_skin was, the higher were the slopes, at which M or REHL changed per unit ofT _core. At a given T_skin, the slopes decreased with increasing M or REHL, and were dependent on the range ofT _core. The higher the range ofT _core, the steeper changed M and REHL with changingT _core, if all other variables were held constant. The results support the concept that an exponential relationship betweenT _core and the rate of core temperature signals is the primary cause of the effects exerted by T_skin on the slopes, at which M or REHL change per unit ofT _core.     

The effect of ambient temperature and exercise intensity on post-exercise thermal homeostasis

We have previously demonstrated a prolonged (65?min or longer) elevated plateau of esophageal temperature (T _es ) (0.5–0.6°C above pre-exercise values) in humans following heavy dynamic exercise (70% maximal oxygen consumption, V˙O_2max) at a thermoneutral temperature (T _a) of 29°C. The elevated T _es value was equal to the threshold T _es at which active skin vasodilation was initiated during exercise (Th_dil). A subsequent observation, i.e., that successive exercise/recovery cycles (performed at progressively increasing pre-exercise T _es levels) produced parallel increases of Th_dil and the post-exercise T _es, further supports a physiological relationship between these two variables. However, since all of these tests have been conducted at the same T _a (29°C) and exercise intensity (70% V˙O_2max) it is possible that the relationship is limited to a narrow range of T _a/exercise intensity conditions. Therefore, five male subjects completed 18?min of treadmill exercise followed by 20?min of recovery in the following T _a/exercise intensity conditions: (1) cool with light exercise, T _a?=?20°C, 45% V˙O_2max (CL); (2) temperature with heavy exercise, T _a?=?24°C, 75% O_{2 max} (TH); (3) warm with heavy exercise, T _a?=?29°C, 75% V˙O_2max (WH); and (4) hot with light exercise, T _a?=?40°C, 45% V˙O_2max (HL). An abrupt decrease in the forearm-to-finger temperature gradient (T _fa??T _fi) was used to identify the Th_dil during exercise. Mean pre-exercise T _es values were 36.80, 36.60, 36.72, and 37.20°C for CL, TH, WH, and HL conditions respectively. T _es increased during exercise, and end post-exercise fell to stable values of 37.13, 37.19, 37.29, and 37.55°C for CL, TH, WH, and HL trials respectively. Each plateau value was significantly higher than pre-exercise values (P?dil values (i.e., 37.20, 37.23, 37.37, and 37.48°C for CL, TH, WH, and HL) were comparable to the post-exercise T _es values for each condition. The relationship between Th_dil and post-exercise T _es remained intact in all T _a/exercise intensity conditions, providing further evidence that the relationship between these two variables is physiological and not coincidental.     

Fast quantitative three‐dimensional ultrashort echo time (UTE) Cones magnetic resonance imaging of major tissues in the knee joint using extended sprial sampling

The purpose of this study is to investigate the effect of extending the spiral sampling window on quantitative 3D ultrashort echo time (UTE) Cones imaging of major knee joint tissues including articular cartilage, menisci, tendons and ligaments at 3 T. Nine cadaveric human whole knee specimens were imaged on a 3 T clinical MRI scanner. A series of quantitative 3D UTE Cones imaging biomarkers including T₂*, T₁, adiabatic T_1ρ, magnetization transfer ratio (MTR) and macromolecular fraction (MMF) were estimated using spiral sampling trajectories with various durations. Errors in UTE MRI biomarkers as a function of sampling time were evaluated using a nonstretched spiral trajectory as a reference standard. No significant differences were observed by increasing the spiral sampling window from 1116 to 2232 μs in the calculated T₂*, T₁, adiabatic T_1ρ, MTR and MMF, as all P‐values were over .05 as assessed by ANOVA with two‐sided Dunnett's test. Although extending the sampling window results in signal loss for short T₂ components, there was limited effect on the calculated quantitative biomarkers, with error percentages typically smaller than 5% in all the evaluated tissues. The total scan time can be reduced by up to 54% with quantification errors of less than 5% in any evaluated major tissue in the knee joint, suggesting that 3D UTE Cones MRI techniques can be greatly accelerated by using a longer spiral sampling window without causing additional quantitative bias.     

Relationship in humans between spontaneously chosen crank rate and power output during upper body exercise at different levels of intensity

The aim of this study was to assess the relationship between spontaneously chosen crank rate (SCCR) and power output during two upper body exercise tests: firstly, an incremental maximal aerobic power test (T₁), with an initial intensity of 50?W followed by 15-W increases at each subsequent 90-s stage and secondly, a test (T₂) with consecutive exercise periods set at 50%, 60%, 70%, 80%, 110% and 120% of maximal power (P _max) separated by passive recovery periods. Eight nationally and internationally ranked kayakers, aged 20 (SD 2) years, performed the tests. During both T₁ and T₂, mean SCCR values were correlated (r?=?1) and increased significantly (P?1 suggests that it may be used to predict the crank rate which will be chosen in upper body exercise, whatever the intensity. Finally, the results of testing at 110% and 120% of P _max would suggest that a high crank rate (>90?rpm) should be used during the test procedure using supramaximal exercises where accumulated oxygen deficit is calculated, and more particularly when exercise is performed using the upper body.