Classical and molecular cytogenetics of <Emphasis Type="Italic">Khawia sinensis</Emphasis> (Cestoda: Caryophyllidea), invasive parasite of carp, <Emphasis Type="Italic">Cyprinus carpio</Emphasis>

Chromosomes of the invasive tapeworm Khawia sinensis (Caryophyllidea), the specific parasite of common carp, were analyzed by means of conventional Giemsa staining and using fluorescent DAPI and YOYO-1 dyes, silver staining, and fluorescent in situ hybridization (FISH) with 18S rDNA probe. The karyotype is composed of eight pairs of metacentric and telocentric chromosomes (2n = 16, n = 3m + 5t, TCL = 42.54 μm). Constitutive heterochromatin was located at pericentromeric regions of all pairs, except for the largest metacentric pair (no. 1), which possessed no DAPI-positive band. FISH with rDNA probe revealed that both homologues of chromosome pair no. 6 carry a cluster of ribosomal arrays, which were located interstitially close to the centromere. Present results are compared with previous cytogenetic data on Khawia spp., and comments are made on the karyotypes with respect to their phylogenetic links.     

Karyotype analysis of Helianthus annuus using Giemsa banding and fluorescence in situ hybridization

The karyotype of H. annuus was analysed by computer-aided image processing with respect to the chromosome length, arm ratio, occurrence and chromosomal position of intercalary heterochromatin and the location of 18S/25S and 5S ribosomal RNA genes. The karyotype was subdivided into a group of four acrocentric chromosome pairs, of which two were distinguishable by HKG (HCl, KOH, Giemsa) banding and a group of 13 meta- to submetacentric pairs. The latter could be subdivided into seven pairs with one and six pairs with two HKG bands. Three pairs of submetacentric satellite chromosomes revealed 18S/25S rDNA loci after fluorescence in situ hybridization (FISH) and silver staining . A fourth, smaller and possibly inactive, locus occurred in the terminal position on a metacentric pair. One submetacentric satellite chromosome pair revealed a 5S rRNA gene locus in the pericentromeric position; a second locus marked a submetacentric pair with one HKG band. The C-banding technique marks exclusively centromeric heterochromatin. Measurements of chromosomes in combination with Giemsa banding and FISH enabled the discrimination of most chromosome pairs of the sunflower.This revised version was published online in November 2005 with corrections to the Cover Date.     

Multi-chromosomal location of ribosomal RNA genes and heterochromatin association in brown trout

The ribosomal rRNA genes have been mapped by fluorescentin situ hybridization (FISH) to brown trout chromosomes. One major NOR chromosome pair and 8 novel minor NOR chromosome pairs have been found. Both major and minor NORs were closely related to polymorphic heterochromatin, as revealed by FISH and C-banding. These results are discussed with respect to NOR expression, the relationship between rDNA and heterochromatin, and evolutionary aspects.     

The effects of simulated obstructive apnea and hypopnea on arrhythmic potential in healthy subjects

Preliminary evidence supports an association between OSA and cardiac dysrhythmias. Negative intrathoracic pressure, as occurring during OSA, may provoke cardiac dysrhythmias. Thus, we aimed to study the acute effects of simulated apnea and hypopnea on arrhythmic potential and measures of cardiac repolarization [QT_C and T _peak to T _end intervals ( $ T_{\text{p}} T_{{{\text{e}}_{\text{c}} }} $ )] in humans. In 41 healthy volunteers, ECG was continuously recorded prior, during and after simulated obstructive hypopnea (inspiration through a threshold load), simulated apnea (Mueller maneuver), end-expiratory central apnea and normal breathing in randomized order. The number of subjects with premature beats was significantly higher during inspiration through a threshold load (n = 7), and the Mueller maneuver (n = 7) compared to normal breathing (n = 0) (p = 0.008 for all comparisons), but not during end-expiratory central apnea (n = 3, p = 0.125). Inspiration through a threshold load was associated with a non-significant mean (SD) increase of the QT_C interval [+5.4 (22.4) ms, 95 %CI ?1.7 to +12.4 ms, p = 0.168] and a significant increase of the $ T_{\text{p}} T_{{{\text{e}}_{\text{c}} }} $ interval [+3.7 (8.9) ms, 95 %CI +0.9 to +6.6 ms, p = 0.010]. The Mueller maneuver induced a significant increase of the QT_C interval [+8.3 (23.4) ms, 95 %CI 0.9 to +15.6 ms, p = 0.035] and the $ T_{\text{p}} T_{{{\text{e}}_{\text{c}} }} $ interval (+4.2 (8.2) ms, 95 %CI +1.6 to +6.8 ms, p = 0.002). There were no significant changes of the QT_C and $ T_{\text{p}} T_{{{\text{e}}_{\text{c}} }} $ intervals during central end-expiratory apnea. These data indicate that simulated obstructive apnea and hypopnea are associated with an increase of premature beats and prolongation of QT_C and $ T_{\text{p}} T_{{{\text{e}}_{\text{c}} }} $ intervals. Therefore, negative intrathoracic pressure changes may be a contributory mechanism for the association between OSA and cardiac dysrhythmias.     

The determinants of performance in master swimmers: an analysis of master world records

Human performances in sports decline with age in all competitions/disciplines. Since the effects of age are often compounded by disuse, the study of master athletes provides the opportunity to investigate the effects of age per se on the metabolic/biomechanical determinants of performance. For all master age groups, swimming styles and distances, we calculated the metabolic power required to cover the distance (d) in the best performance time as: $ E _{\text{maxR}}^{\prime } = C \times d/{\text{BTP}} = C \times v_{\max } , $ where C is the energy cost of swimming in young elite swimmers, v _max?=?d/BTP is the record speed over the distance d, and BTP was obtained form “cross-sectional data” (http://www.fina.org). To establish a record performance, $ E_{\text{maxR}}^{\prime } $ must be equal to the maximal available metabolic power $ (E_{\text{maxA}}^{\prime } ) $ . This was calculated assuming a decrease of 1% per year at 40–70?years, 2% at 70–80?years and 3% at 80–90?years (as indicated in the literature) and compared to the $ E_{\text{maxR}}^{\prime } $ values, whereas up to about 55?years of age $ E_{\text{maxR}}^{\prime } = E_{\text{maxA}}^{\prime } ,$ for older subjects $ E_{\text{maxA}}^{\prime } > E_{\text{maxR}}^{\prime } ,$ the difference increasing linearly by about 0.30% (backstroke), 1.93% (butterfly), 0.92% (front crawl) and 0.37% (breaststroke) per year (average over the 50, 100 and 200?m distances). These data suggest that the energy cost of swimming increases with age. Hence, the decrease in performance in master swimmers is due to both decrease in the metabolic power available $ (E_{\text{maxA}}^{\prime } ) $ and to an increase in C.     

Prediction of peak oxygen uptake from differentiated ratings of perceived exertion during wheelchair propulsion in trained wheelchair sportspersons

Purpose

To assess the validity of predicting peak oxygen uptake ( $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ ) from differentiated ratings of perceived exertion (RPE) obtained during submaximal wheelchair propulsion.

Methods

Three subgroups of elite male wheelchair athletes [nine tetraplegics (TETRA), nine paraplegics (PARA), eight athletes without spinal cord injury (NON-SCI)] performed an incremental speed exercise test followed by graded exercise to exhaustion ( $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ test). Oxygen uptake ( $ {\dot{\text{V}}}{\text{O}}_2$ ), heart rate (HR) and differentiated RPE (Central RPE_C, Peripheral RPE_P and Overall RPE_O) were obtained for each stage. The regression lines for the perceptual ranges 9–15 on the Borg 6–20 scale ratings were performed to predict $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ .

Results

There were no significant within-group mean differences between measured $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ (mean 1.50 ± 0.39, 2.74 ± 0.48, 3.75 ± 0.33 L min^?1 for TETRA, PARA and NON-SCI, respectively) and predicted $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ determined using HR or differentiated RPEs for any group (P > 0.05). However, the coefficients of variation (CV %) between measured and predicted $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ using HR showed high variability for all groups (14.3, 15.9 and 9.7 %, respectively). The typical error ranged from 0.14 to 0.68 L min^?1 and the CV % between measured and predicted $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ using differentiated RPE was ≤11.1 % for TETRA, ≤7.5 % for PARA and ≤20.2 % for NON-SCI.

Conclusions

Results suggest that differentiated RPE may be used cautiously for TETRA and PARA athletes when predicting $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ across the perceptual range of 9–15. However, predicting $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ is not recommended for the NON-SCI athletes due to the large CV %s (16.8, 20.2 and 18.0 %; RPE_C, RPE_P and RPE_O, respectively).     

Faster \dot{V}{\text{O}}_{ 2} kinetics after eccentric contractions is explained by better matching of O2 delivery to O2 utilization

Purpose

This study examined the impact of eccentric exercise-induced muscle damage on the rate of adjustment in muscle deoxygenation and pulmonary O₂ uptake ( \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ) kinetics during moderate exercise.

Methods

Fourteen males (25 ± 3 year; mean ± SD) completed three step transitions to 90 % θ_L before (Pre), 24 h (Post24) and 48 h after (Post48) eccentric exercise (100 eccentric leg-press repetitions with a load corresponding to 110 % of the participant’s concentric 1RM). Participants were separated into two groups: phase II \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) time constant (τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ) ≤ 25 s (fast group; n = 7) or τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\)  > 25 s (slow group; n = 7). \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) and [HHb] responses were modeled as a mono-exponential.

Results

In both groups, isometric peak torque (0°/s) at Post24 was decreased compared to Pre (p < 0.05) and remained depressed at Post48 (p < 0.05). τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) was designed to be different (p < 0.05) at Pre between the Fast (τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ; 19 ± 4 s) and Slow (32 ± 6 s) groups. There were no differences among time points (τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) : Pre, 19 ± 4 s; Post24, 22 ± 3 s; Post48, 20 ± 4 s) in the Fast group. In Slow, there was a speeding (p < 0.05) from the Pre (32 ± 6 s) to the Post24 (25 ± 6) but not Post48 (31 ± 6), resulting in no difference (p > 0.05) between groups at Post24. This reduction of τ \(\dot{V}{\text{O}}_{{2{\text{p}}}} \,\) was concomitant with the abolishment (p < 0.05) of an overshoot in the [HHb]/ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ratio.

Conclusion

We propose that the sped \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) kinetics observed in the Slow group coupled with an improved [HHb]/ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ratio suggest a better matching of local muscle O₂ delivery to O₂ utilization following eccentric contractions.     

The effects of breathing a helium–oxygen gas mixture on maximal pulmonary ventilation and maximal oxygen consumption during exercise in acute moderate hypobaric hypoxia

To test the hypothesis that maximal exercise pulmonary ventilation ( $ \dot{V}{\text{E}}_{ \max } $ ) is a limiting factor affecting maximal oxygen uptake ( $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ ) in moderate hypobaric hypoxia (H), we examined the effect of breathing a helium–oxygen gas mixture (He–O₂; 20.9% O₂), which would reduce air density and would be expected to increase $ \dot{V}{\text{E}}_{ \max } $ . Fourteen healthy young male subjects performed incremental treadmill running tests to exhaustion in normobaric normoxia (N; sea level) and in H (atmospheric pressure equivalent to 2,500 m above sea level). These exercise tests were carried out under three conditions [H with He–O₂, H with normal air and N] in random order. $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ and arterial oxy-hemoglobin saturation (SaO₂) were, respectively, 15.2, 7.5 and 4.0% higher (all p < 0.05) with He–O₂ than with normal air ( $ \dot{V}{\text{E}}_{ \max } $ _, 171.9 ± 16.1 vs. 150.1 ± 16.9 L/min; $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ , 52.50 ± 9.13 vs. 48.72 ± 5.35 mL/kg/min; arterial oxyhemoglobin saturation (SaO₂), 79 ± 3 vs. 76 ± 3%). There was a linear relationship between the increment in $ \dot{V}{\text{E}}_{ \max } $ and the increment in $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ in H (r = 0.77; p < 0.05). When subjects were divided into two groups based on their $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ , both groups showed increased $ \dot{V}{\text{E}}_{ \max } $ and SaO₂ in H with He–O₂, but $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ was increased only in the high $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ group. These findings suggest that in acute moderate hypobaric hypoxia, air-flow resistance can be a limiting factor affecting $ \dot{V}{\text{E}}_{ \max } $ ; consequently, $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ is limited in part by $ \dot{V}{\text{E}}_{ \max } $ , especially in subjects with high $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ .     

Pulmonary O2 uptake kinetics during moderate-intensity exercise transitions initiated from low versus elevated metabolic rates: insights from manipulations in cadence

Introduction

The rate of adjustment (τ) of phase II pulmonary O₂ uptake ( \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ) is slower when exercise transitions are initiated from an elevated baseline work rate (WR) and metabolic rate (MR). In this study, combinations of cycling cadence (40 vs. 90 rpm) and external WR were used to examine the effect of prior MR on τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) .

Methods

Eleven young men completed transitions from 20 W (BSL) to 90 % lactate threshold, with transitions performed as two steps of equal ?WR (LS, lower step; US, upper step), while maintaining a cadence of (1) 40 rpm, (2) 90 rpm, and (3) 40 rpm but with the WRs elevated to match the higher \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) associated with 90 rpm cycling (40_MATCH); transitions lasted 6 min. \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) was measured breath-by-breath using mass spectrometry and turbinometry; vastus lateralis muscle deoxygenation [HHb] was measured using near-infrared spectroscopy. \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) and HHb responses were modeled using nonlinear least squares regression analysis.

Results

\(\dot{V}{\text{O}}_{{2{\text{p}}}}\) at BSL, LS and US was similar for 90 rpm and 40_MATCH, but greater than in 40 rpm. Compared to 90 rpm, τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) at 40 rpm was shorter (p < 0.05) in LS (18 ± 5 vs. 28 ± 8 s) but not in US (26 ± 8 vs. 33 ± 9 s), and at 40_MATCH, τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) was lower (p < 0.05) (19 ± 6 s) in LS but not in US (34 ± 13 s) despite differing external WR and ?WR.

Conclusions

A similar overall adjustment of [HHb] and \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) in LS and US across conditions suggested dynamic matching between microvascular blood flow and O₂ utilization. Prior MR (rather than external WR per se) plays a role in the dynamic adjustment of pulmonary (and muscle) \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) .     

Relationship of pulmonary diffusing capacity (D L ) and cardiac output (\dot Q_c ) in exercise

The present study was designed to investigate the interrelationships of pulmonary diffusing capacity for CO ( \(D_{L_{{\text{CO}}} } \) ), pulmonary capillary blood flow ( \(\dot Q_c \) ), oxygen uptake ( \(\dot V_{{\text{O}}_{\text{2}} } \) ), and related functions in exercise. Six young adult men were tested on a bicycle ergometer on 9–20 occasions at various intensities of exercise up to the maximal level that could be sustained for 5 min. Measurements at each exercise level included work load (kgm/min), heart rate (HR), minute ventilation (V _I ), \(\dot Q_c \) , \(D_{L_{{\text{CO}}} } \) , and \(\dot V_{{\text{O}}_{\text{2}} } \) . Using regression analysis, it was established that \(\dot Q_c \) and D _{L CO} increased linearly with \(\dot V_{{\text{O}}_{\text{2}} } \) throughout the work range in each subject and no tendency toward a plateau was observed. While the maximal value varied from subject to subject, there was no difference between individuals in the coefffcient describing the relationship of D _L and \(\dot Q_c \) to \(\dot V_{{\text{O}}_{\text{2}} } \) . Combining all subjects, D _L was found to increase linearly with \(\dot Q_c \) the regression equation being: $$D_L = 26.4 + 1.03{\text{ }}\dot Q_c ,{\text{ }}r = .79$$ These results suggest that high-intensity short-duration exercise (5 min) is probably not limited by either of these functions in normals.     

The effect of raised pH on pacemaker activity and ionic currents in cardiac purkinje fibers

1. Cardiac Purkinje fibers exposed to alkaline solutions (pH 8 to 9.5) show an increase in rate of diastolic depolarization, eventually resulting in induction of spontaneous activity or an increase of the spontaneous firing rate.
2. The voltage-clamp analysis of the transmembrane currents in pH 9–9.5 shows: i) a shift in the depolarizing direction of the activation (s∞) and time constants (τ _s ) curve of the \(i_{{\text{K}}_{\text{2}} }\) current, ii) a small increase in the maximal value of the fully activated \(i_{{\text{K}}_{\text{2}} }\) current, iii) no significant change of background current in the pacemaker region of membrane potentials.
3. The effect of NH₄Cl was studied as a means to vary intracellular pH. In the presence of Tris buffer the addition of 5 mM NH₄Cl resulted in i) a shift in the depolarizing direction and a decrease in slope of the activation curve of the \(i_{{\text{K}}_{\text{2}} }\) current, ii) a shift in the depolarizing direction of the time-constants curve together with an increase in the maximum value of τ _s , iii) an increase in the maximum value of the fully activated \(i_{{\text{K}}_{\text{2}} }\) current and a depolarizing shift of the reversal potential, similar to the effect of addition of K_c. In the presence of CO₂?HCO₃ buffer the addition of NH₄Cl had no significant effect on the kinetics of the \(i_{{\text{K}}_{\text{2}} }\) current. Since intracellular pH is only affected by NH₄Cl in the presence of Tris buffer, the results suggest that intracellular alkalinization is responsible for the change in \(i_{{\text{K}}_{\text{2}} }\) kinetics.
4. Based on the findings with NH₄Cl it is suggested that perfusion with Tris buffered alkaline solutions not only affects net negative surface charges on the outside but also and to a larger extent increases negative surface charges on the inside of the cell membrane.

     

Chromosomal study of a lamprey (<Emphasis Type="Italic">Lampetra zanandreai</Emphasis> Vladykov, 1955) (Petromyzonida: Petromyzontiformes): conventional and FISH analysis

Karyotype and other chromosomal characteristics in the Adriatic brook lamprey Lampetra zanandreai, representative of one of the most ancestral group of vertebrates, were examined using conventional (Ag-staining, C-banding as well as CMA₃ and DAPI fluorescence) and molecular (FISH with 18/28S rDNA and EcoRI satDNA as probes) protocols with metaphase chromosomes derived from whole blood cultures. The chromosome complement had a modal diploid chromosome number of 2n = 164, as in other petromyzontid lamprey species. Ag-staining and CMA₃ fluorescence, as well as FISH with 18/28S rDNA probes, detected nucleolar organizer regions (NORs) close to the centromeres of the biarmed chromosomes of pairs 1 and 2, the largest chromosome pairs of the complement. In addition to NORs, CMA₃ fluorescence revealed positive signals in approximately 40 other chromosomes. DAPI stained mostly centromeric regions of many chromosomes as well as conspicuously massive blocks overlapping NOR sites. C-banding evidenced a large amount of constitutive heterochromatin in somatic chromosomes, with approximately 40 C-positive acrocentric elements completely heterochromatic, corresponding with the 40 CMA₃+ chromosomes and positive heterochromatic blocks in pericentromeric regions of chromosome pairs 1 and 2. Polymerase chain reaction (PCR)-based cloning of satellite DNA with primers derived from Petromyzon marinus centromeric sequences was successful for L. zanandreai genomic DNA. The sequence was AT-rich (59%) and characterized by short consensus motifs similar to other centromeric satellite motifs. FISH using satDNA clones as a probe produced a fluorescent signal on a single pair of small chromosomes. This sequence was PCR-amplified also in L. planeri and P. marinus genomic DNA, and the evolution of this repetitive element in the above species was analysed.     

The validity of the Moxus Modular metabolic system during incremental exercise tests: impacts on detection of small changes in oxygen consumption

Purpose

We investigated the accuracy of the Moxus Modular Metabolic System (MOXUS) against the Douglas Bag Method (DBM) during high-intensity exercise, and whether the two methods agreed when detecting small changes in $\dot{V}{\text{O}}_{2}$ between two consecutive workloads ( $\Delta {\dot{{V}}\text{O}}_{ 2}$ ).

Methods

Twelve trained male runners performed two maximal incremental running tests while gas exchange was analyzed simultaneously by the two systems using a serial setup for four consecutive intervals of 30 s on each test. Comparisons between methods were performed for $\dot{V}{\text{O}}_{2}$ , ${\dot{{V}}}_{\text{E}}$ , fractions of expired O₂ (FeO₂) and CO₂ (FeCO₂) and $\Delta {\dot{{V}}\text{O}}_{ 2}$ .

Results

The MOXUS produced significant higher (mean ± SD, n = 54) readings for $\dot{V}{\text{O}}_{2}$ (80 ± 200 mL min^?1, p = 0.005) and ${\dot{{V}}}_{\text{E}}$ (2.9 ± 4.2 L min^?1, p < 0.0001), but not FeO₂ (?0.01 ± 0.09). Log-transformed 95 % limits of agreement for readings between methods were 94–110 % for $\dot{V}{\text{O}}_{2}$ , 97–108 % for $\dot{V}_{\text{E}}$ and 99–101 % for FeO₂. $\Delta \dot{V}{\text{O}}_{2}$ for two consecutive measurements was not different between systems (120 ± 110 vs. 90 ± 190 mL min^?1 for MOXUS and DBM, respectively, p = 0.26), but agreement between methods was very low (r = 0.25, p = 0.12).

Discussion

Although it was tested during high-intensity exercise and short sampling intervals, the MOXUS performed within the acceptable range of accuracy reported for automated analyzers. Most of the differences between equipments were due to differences in $\dot{V}_{\text{E}}$ . Detecting small changes in $\dot{V}{\text{O}}_{2}$ during an incremental test with small changes in workload, however, might be beyond the equipment’s accuracy.     

Influence of exercise intensity on respiratory muscle fatigue and brachial artery blood flow during cycling exercise

Purpose

During high intensity exercise, both respiratory muscle fatigue and cardiovascular reflexes occur; however, it is not known how inactive limb blood flow is influenced. The purpose of this study was to determine the influence of moderate and high exercise intensity on respiratory muscle fatigue and inactive limb muscle and cutaneous blood flow during exercise.

Methods

Twelve men cycled at 70 and 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) for 20 min. Subjects also performed a second 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) test after ingesting 1,800 mg of N-acetylcysteine (NAC), which has been shown to reduce respiratory muscle fatigue (RMF). Maximum inspiratory pressures (P _Imax), brachial artery blood flow (BABF), cutaneous vascular conductance (CVC), and mean arterial pressure were measured at rest and during exercise.

Results

Significant RMF occurred with 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) (P _Imax, ?12.8 ± 9.8 %), but not with 70 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) (P _Imax, ?5.0 ± 5.9 %). BABF and BA vascular conductance were significantly lower at end exercise of the 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) test compared to the 70 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) test. CVC during exercise was not different (p > 0.05) between trials. With NAC, RMF was reduced (p < 0.05) and BABF was significantly higher (~30 %) compared to 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) (p < 0.05).

Conclusions

These data suggest that heavy whole-body exercise at 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) leads to RMF, decreases in inactive arm blood flow, and vascular conductance, but not cutaneous blood flow.     

Energy cost of arm stroke,leg kick,and the whole stroke in competitive swimming styles

In male elite swimmers \(\dot V_{{\text{O}}_{\text{2}} } \) at a given velocity in freestyle and backstroke was on average 1 to 2 l x min^?1 lower as compared with breaststroke and butterfly. Except for breaststroke, swimming with arm strokes only demanded a lower \(\dot V_{{\text{O}}_{\text{2}} } \) at a given submaximal velocity than the whole stroke. In freestyle and backstroke the submaximal \(\dot V_{{\text{O}}_{\text{2}} } \) of leg kick at a given velocity was clearly higher than the whole stroke. The highest velocity during maximal swimming was always attained with the whole stroke, and the lowest with the leg kick, except for breast stroke, where the leg kick was most powerful. At a given submaximal \(\dot V_{{\text{O}}_{\text{2}} } \) , heart rate and \(\dot V_{\text{E}} :\dot V_{{\text{O}}_{\text{2}} } \) tended to be higher during swimming with arm strokes only as compared with the whole stroke. Highest values for \(\dot V_{{\text{O}}_{\text{2}} } \) , heart rate and blood lactate during maximal exercise were almost always attained when swimming the whole stroke, and lowest when swimming with arm strokes only. At higher velocities body drag was 0.5 to 0.9 kp lower when arms or legs were supported by a cork plate as compared with body drag without support.     

The verification phase and reliability of physiological parameters in peak testing of elite wheelchair athletes

The purpose of this study was (1) to examine the value of a verification phase (VER) in a peak testing protocol and (2) to assess the reliability of peak physiological variables in wheelchair athletes. On two separate days, eight tetraplegic (TETRA), eight paraplegic (PARA) and eight non-spinal cord-injured (NON-SCI) athletes performed treadmill ergometry, consisting of a graded exercise test to exhaustion (GXT) followed by a VER. Peak oxygen uptake $ \left( {\dot{V}{\text{O}}_{{ 2 {\text{peak}}}} } \right) $ was compared (1) between GXT and VER and (2) between test days. $ \dot{V}{\text{O}}_{{2{\text{peak}}}} $ did not differ between GXT and VER (P = 0.27), and coefficients of variation between GXT and VER were in the range of 2.9 and 6.4 % for all subgroups. Coefficients of variation of $ \dot{V}{\text{O}}_{{2{\text{peak}}}} $ between test days were 9.3 % (TETRA), 4.5 % (PARA) and 3.3 % (NON-SCI). It is therefore concluded that whilst a VER can be used for a more robust determination of $ \dot{V}{\text{O}}_{{2{\text{peak}}}} $ , a deviation of up to ~6 % between GXT and VER should be considered as acceptable. For between-day analyses, relatively large changes in $ \dot{V}{\text{O}}_{{2{\text{peak}}}} $ are required to confirm “true” differences, especially in TETRA athletes. This may be due to their lower aerobic capacity, which results in a larger relative variation compared with the other subgroups.     

Central leptin replacement enhances chemorespiratory responses in leptin-deficient mice independent of changes in body weight

Previous studies showed that leptin-deficient (ob/ob) mice develop obesity and impaired ventilatory responses to CO₂ $ \left( {{{\dot{V}}_{{{\text{E}}\,}}}{ - }\,{\text{C}}{{\text{O}}_{{2}}}} \right) $ . In this study, we examined if leptin replacement improves chemorespiratory responses to hypercapnia (7?% CO₂) in ob/ob mice and if these effects were due to changes in body weight or to the direct effects of leptin in the central nervous system (CNS). $ {\dot{V}_{{{\text{E}}\,}}}{\text{ - C}}{{\text{O}}_{{2}}} $ was measured via plethysmography in obese leptin-deficient- (ob/ob) and wild-type- (WT) mice before and after leptin (10???g/2???l?day) or vehicle (phosphate buffer solution) were microinjected into the fourth ventricle for four consecutive days. Although baseline $ {\dot{V}_{\text{E}}} $ was similar between groups, obese ob/ob mice exhibited attenuated $ {\dot{V}_{{{\text{E}}\,}}}{ - }\,{\text{C}}{{\text{O}}_{{2}}} $ compared to WT mice (134?±?9 versus 196?±?10?ml?min^?1). Fourth ventricle leptin treatment in obese ob/ob mice significantly improved $ {\dot{V}_{{{\text{E}}\,}}}{ - }\,{\text{C}}{{\text{O}}_{{2}}} $ (from 131 ± 15 to 197 ± 10?ml?min^?1) by increasing tidal volume (from 0.38?±?0.03 to 0.55?±?0.02?ml, vehicle and leptin, respectively). Subcutaneous leptin administration at the same dose administered centrally did not change $ {\dot{V}_{{{\text{E}}\,}}}{ - }\,{\text{C}}{{\text{O}}_{{2}}} $ in ob/ob mice. Central leptin treatment in WT had no effect on $ {\dot{V}_{{{\text{E}}\,}}}{ - }\,{\text{C}}{{\text{O}}_{{2}}} $ . Since the fourth ventricle leptin treatment decreased body weight in ob/ob mice, we also examined $ {\dot{V}_{{{\text{E}}\,}}}{ - }\,{\text{C}}{{\text{O}}_{{2}}} $ in lean pair-weighted ob/ob mice and found it to be impaired compared to WT mice. Thus, leptin deficiency, rather than obesity, is the main cause of impaired $ {\dot{V}_{{{\text{E}}\,}}}{ - }\,{\text{C}}{{\text{O}}_{{2}}} $ in ob/ob mice and leptin appears to play an important role in regulating chemorespiratory response by its direct actions on the CNS.     

A Numerical Study of Heat and Water Vapor Transfer in MDCT-Based Human Airway Models

A three-dimensional (3D) thermo-fluid model is developed to study regional distributions of temperature and water vapor in three multi-detector row computed-tomography-based human airways with minute ventilations of 6, 15 and 30 L/min. A one-dimensional (1D) model is also solved to provide necessary initial and boundary conditions for the 3D model. Both 3D and 1D predicted temperature distributions agree well with available in vivo measurement data. On inspiration, the 3D cold high-speed air stream is split at the bifurcation to form secondary flows, with its cold regions biased toward the inner wall. The cold air flowing along the wall is warmed up more rapidly than the air in the lumen center. The repeated splitting pattern of air streams caused by bifurcations acts as an effective mechanism for rapid heat and mass transfer in 3D. This provides a key difference from the 1D model, where heating relies largely on diffusion in the radial direction, thus significantly affecting gradient-dependent variables, such as energy flux and water loss rate. We then propose the correlations for respective heat and mass transfer in the airways of up to 6 generations: \(Nu = 3.504\left( {Re\frac{{D_{\text{a}} }}{{D_{\text{t}} }}} \right)^{0.277} , \quad R = 0.841\) and \(Sh = 3.652\left( {Re\frac{{D_{\text{a}} }}{{D_{\text{t}} }}} \right)^{0.268} , \quad R = 0.825\) , where Nu is the Nusselt number, Sh is the Sherwood number, Re is the branch Reynolds number, D _a is the airway equivalent diameter, and \(D_{\text{t}}\) is the tracheal equivalent diameter.     

Cycling time to failure is better maintained by cold than contrast or thermoneutral lower-body water immersion in normothermia

Purpose

To examine the effects of four commonly used recovery treatments applied between two bouts of intense endurance cycling on the performance of the second bout in normothermia (~21 °C).

Methods

Nine trained men completed two submaximal exhaustive cycling bouts (Ex1 and Ex2: 5 min at ~50 % ${\dot{\text{V}}\text{O}}_{2}$ peak, followed by 5 min at ~60 % ${\dot{\text{V}}\text{O}}_{2}$ peak and then ~80 % ${\dot{\text{V}}\text{O}}_{2}$ peak to failure) separated by 30 min of (a) cold water immersion at 15 °C (C15), (b) contrast water therapy alternating 2.5 min at 8 °C and 2.5 min at 40 °C (CT), (c) thermoneutral water immersion at 34 °C (T34) and (d) cycling at ~40 % ${\dot{\text{V}}\text{O}}_{2}$ peak (AR).

Results

Exercise performance, cardiovascular and metabolic responses during Ex1 were similar among all trials. However, time to failure (~80 % ${\dot{\text{V}}\text{O}}_{2}$ peak bout) during Ex2 was significantly (P < 0.05) longer in C15 (18.0 ± 1.6) than in CT (14.5 ± 1.5), T34 (12.4 ± 1.4) and AR (10.6 ± 1.0); and it was also longer (P < 0.05) in CT than AR. Core temperature and heart rate were significantly (P < 0.05) lower during the initial ~15 min of Ex2 during C15 compared with all other conditions but they reached similar levels at the end of Ex2.

Conclusions

A 30 min period of C15 was more beneficial in maintaining intense submaximal cycling performance than CT, T34 and AR; and CT was also more beneficial than T34 and AR. These effects were not mediated by the effect of water immersion per se, but by the continuous (C15) or intermittent (CT) temperature stimulus (cold) applied throughout the recovery.     

Changes in arterial blood pressure elicited by severe passive heating at rest is associated with hyperthermia-induced hyperventilation in humans

The arterial blood pressure and ventilatory responses to severe passive heating at rest varies greatly among individuals. We tested the hypothesis that the increase in ventilation seen during severe passive heating of resting humans is associated with a decrease in arterial blood pressure. Passive heating was performed on 18 healthy males using hot water immersion to the level of the iliac crest and a water-perfused suit. We then divided the subjects into two groups: MAP_NOTINC (n = 8), whose mean arterial blood pressure (MAP) at the end of heating had increased by ≤3 mmHg, and MAP_INC (n = 10), whose MAP increased by >3 mmHg. Increases in esophageal temperature (T _es) elicited by the heating were similar in the two groups (+2.3 ± 0.3 vs. +2.4 ± 0.4 °C). Early during heating (increase in T _es was <1.5 °C), MAP, minute ventilation ( $ \dot{V}_{\text{E}} $ ), and end-tidal CO₂ pressure ( $ P_{{{\text{ET}}_{\text{CO2}} }} $ ) were similar between the groups. However, during the latter part of heating (increase in T _es was ≥1.5 °C), the increase in $ \dot{V}_{\text{E}} $ and decrease in $ P_{{{\text{ET}}_{\text{CO2}} }} $ were significantly greater or tended to be greater, while the increase in MAP was significantly smaller in MAP_NOTINC than MAP_INC. Among all subjects, heating-induced changes in $ \dot{V}_{\text{E}} $ significantly and negatively correlated with heating-induced changes in MAP during the latter part of heating (r = ?0.52 to ?0.74, P < 0.05). These results suggest that, in resting humans, 25?50 % of the variation in the magnitude of the arterial blood pressure response to severe passive heating can be explained by the magnitude of hyperthermia-induced hyperventilation.