Decrease In VO2 Research Articles

Assessment of Oxygen Deficit in Collegiate Runner during Steady State Exercise

Oxygen deficit (OD) for the same absolute workload intensity decreases with aerobic training through improved aerobic metabolism and likewise increases with detraining. It is unclear if the amount of increase in OD with detraining is the same in middle distance (MD) and long distance (LD) runners and what training related OD changes occur in these groups with subsequent retraining. PURPOSE: To compare and contrast the changes in OD values of collegiate MD and LD runners which accompany a post-competitive season cessation of training and subsequent endurance retraining. METHODS: Fourteen members of the collegiate track team (7 MD and 7 LD) runners completed a steady-state treadmill test (SS) at their gender-specific mean 5k velocity (15.3 kph for females and 18.5 kph for males) at the conclusion of their track season followed by 3 additional SS tests at 2-week intervals. Participants did not train between SS1 and SS2 and performed identical prescribed training programs between SS2 and SS4. VO2 steady state was identified as the breakpoint of the second phase of the OD curve. OD area under the curve comparisons were made using a 2x4 repeated measures ANOVA. RESULTS: MD demonstrated a significant decrease in VO2 at SS pace over the 6-week study resulting in a reduction in their mean OD (6.4%) versus LD (-0.5%) (P<.01). Mean anaerobic contributions to reach SS were greater in LD than MD (36.9% vs. 32.2%) at the end of 4-weeks of retraining (P<.01). CONCLUSION: There are differences in OD patterns that accompany both detraining and endurance retraining in collegiate MD and LD runners. LD runners were more aerobically challenged than MD to maintain SS velocity after detraining and may require a greater volume of anaerobic training than MD runners during the early retraining phase in order to retain a faster training pace.

Impact of early mammalian development on the response of the O2 transport system to muscle contraction

A continuous supply of O2 to the cells in the body is necessary to maintain normal physiological function and the microcirculation is especially important in this matter as it is the site of O2 exchange. Under conditions of active/functional hyperemia following muscle contractions, the O2 transport system in older subjects does not appear to respond as rapidly and to the same degree as in younger subjects. With aging, elements of the O2 transport and regulatory systems are changed in such a way that matching O2 supply to O2 demand does not work as well in older as in younger subjects. An intravital microscopic approach is being used to show that developmental changes in the O2 transport system begin earlier than previously thought. Significant and rapid changes in the microvascular network of skeletal muscle have been observed during the first few weeks of postnatal development. Four different developmental groups of male Sprague‐Dawley rats (8, 16, 24, and 52 weeks) are used to investigate changes in the O2 demand component of the transport system by measuring oxygen consumption (VO2) and the PISFO2 dependence of VO2 under conditions of rest and contraction. VO2 was measured with a quasi‐continuous, flash‐synchronized, rapidly pressurizing airbag system to briefly arrest flow and determine the rate of change in oxygen tension (dPO2/dt). Changes in the O2 supply component are investigated by measuring capillary and interstitial fluid PO2 (PcapO2 and PISFO2 respectively, using phosphorescence quenching microscopy) and surface area available for O2 exchange (i.e., capillary density). Preliminary experiments were carried out on six animals that ranged from 8 w to 20 w in age with an average weight of 331 ± 35 g. Average baseline VO2 for the 8 w group was 307 ± 26 nL O2/cm3·s (n = 6), average baseline VO2 for the 16 w group was 287 ± 31 nL O2/cm3·s (n = 6), and average baseline VO2 for those in the 24 w group was 264 ± 12 nL O2/cm3·s (n = 6). Average baseline PISFO2 for the 8 w group was 68 ± 3 mmHg (n = 6), average baseline PISFO2 for the 16 w group was 74 ± 4 mmHg (n = 6), and average baseline PISFO2 for the 24 w group was 68 ± 3 mmHg (n = 6). The observed decreases in tissue VO2 are consistent with literature showing that whole body VO2 decreases from 499, 396, to 345 nL O2/cm3·s at 8 w, 16 w, and 24 w, respectively. However, it is still unclear how well matched O2 supply and demand are. As O2 demand increases by increasing muscle contraction, O2 supply should also increase to match it and PISFO2 is at least one element that links the two components of the transport system which requires further investigation.

Intermittent hypoxic training for 6 weeks in 3000 m hypobaric hypoxia conditions enhances exercise economy and aerobic exercise performance in moderately trained swimmers.

Athletic endurance performance at sea level can be improved via intermittent hypoxic training (IHT). However, the efficacy of IHT for enhancement of aerobic exercise performance at sea level is controversial because of methodological differences. Therefore, the aim of the study was to determine whether the IHT regimen ameliorates exercise economy and aerobic exercise performance in moderately trained swimmers. A total of 20 moderately trained swimmers were equally assigned to the control group (n=10) training in normoxic conditions and the IHT group (n=10) training at a simulated altitude of 3000 m. They were evaluated for metabolic parameters and skeletal muscle oxygenation during 30 min submaximal exercise on a bicycle, and aerobic exercise performance before and after 6 weeks of training composed of aerobic continuous exercise set at 80% maximal heart rate (HRmax) during 30 min and anaerobic interval exercise set at the exercise load with 90% HRmax measured in pre-test during 30 min (10 times 2 min exercise and 1 min rest). According to the results, the IHT group demonstrated greater improvement in exercise economy due to decreases in VO2 (p=.016) and HHb (p=.002) and increases in O2Hb (p<.001) and TOI (p=.006). VCO2 was decreased in the IHT group (p=.010) and blood lactate level was decreased in the control (p=.005) and IHT groups (p=.001). All aerobic exercise performance including VO2max (p=.001) and the 400 m time trial (p<.001) were increased in the IHT group. The present findings indicate that the 6 week IHT regime composed of high-intensity aerobic continuous exercise and anaerobic interval exercise can be considered an effective altitude/hypoxic training method for improvement of exercise economy and aerobic exercise performance in moderately trained swimmers.

Effects of annealing temperature and dopant concentration on the structure, optical, and magnetic properties of Cu-doped ZnO nanopowders

This study analyzed the effects of annealing temperature and dopant concentration on the structural, optical, and magnetic properties of Cu-doped ZnO nanopowders. Cu-doped ZnO nanopowders were prepared using a solid-state reaction method. The X-ray diffraction results demonstrated that the Cu ions successfully substituted the Zn ions in the hexagonal wurtzite structure of the ZnO nanoparticles. Ultraviolet–visible spectroscopy measurements revealed that the band gap decreased due to the incorporation of Cu. The photoluminescence results showed that the intensity of the emissions increased with doping and decreased as the annealing temperature (TA) increased, which can be attributed to the increase and decrease of the oxygen vacancies (VO), respectively. The magnetic properties of the ZnO nanopowders were also found to be affected by Cu doping and TA. The ferromagnetic behavior of the ZnO nanopowders decreased as both the doping concentration and TA increased. This behavior can be explained by the increase in the antiferromagnetic superexchange interaction along with Cu doping due to the decrease in the distance between the Cu ions and the decrease in VO, respectively. Thus, the results indicate oxygen stoichiometry and VO both play a dominate role in the room temperature ferromagnetic response of ZnO nanopowders.

Metabolic Cost and Fuel Utilization of Normal and Lower Body Positive Pressure Treadmill Running

Lower body positive pressure (LBPP) treadmill walking and running are being used more frequently in clinical and athletic settings. Accurate exercise intensity and knowledge of fuel utilization is a needed for proper exercise prescription especially for obese patients that may benefit from LBPP exercise. It is unclear if current ACSM metabolic equations are suitable for LBPP running. There are currently no accepted calculations to estimate caloric cost or exercise intensity for LBPP running. PURPOSE: To measure oxygen uptake and caloric expenditure of treadmill running at normal body weight and LBPP. METHODS: Thirteen physically active non-obese participants completed four bouts of running exercise in a counterbalanced manner: (a) running on a normal (100% body weight, BW) treadmill (TM) and (b) running on a LBPP treadmill at 40, 60, and 85% of BW for 4 min intervals. Oxygen consumption was measured using open flow indirect calorimetry (Medgraphics Ultima) and last minute averages were defined as steady state. RESULTS: Volunteers’ average (±SD) absolute VO2 at a treadmill speed of 3.13 m·s-1 was 1528.38±308.38,1762.00±341.57, 2037.07±337.47, and 2453.23±406.49 ml·min-1 for 40, 60, 85, and 100% body weight. Respiratory exchange ratio (RER) at a treadmill speed of 3.13 m·s-1 was 0.91±0.05, 0.93±0.08, 0.98±0.05, and 1.02±0.07 for all four weighted conditions (40, 60, 85, and 100% BW, respectively). Average caloric expenditure was 7.55±1.51, 8.74±1.74, 9.51±1.72, and 12.43±2.01 kcal·min-1 for 40, 60, 85, and 100% BW, respectively. CONCLUSION: As expected, treadmill running in LBPP resulted in significantly lower oxygen consumption and caloric expenditure at all three reduced weight conditions compared to 100% BW. One-way repeated measures ANOVAs indicated statistically significant differences in VO2 across all four BW conditions F(3,36) = 64.636, p < 0.05, partial η2 = 0.843, and in caloric expenditure F(3,36) = 81.460, p < 0.05, partial η2 = 0.872. The percent difference in VO2 from TM and LBPP conditions (85, 60, and 40% of BW) was only ~15, 30, and 40%. We conclude that metabolic cost of LBPP running is significantly less than normal treadmill running, yet the decrease in VO2 and caloric expenditure is not as great as predicted by the change in body mass.

Treadmill cycling trial in diagnostics Open Access endurance preparation of MTB cyclists before Olympic Games or World Championship

Background: The evaluation of endurance preparation of MTB cyclists in conditions corresponding to the specificity of routes of World Championship (WCh) and Olympic Games (OG) is very difficult. Treadmill cycling trials are used in order to make working conditions similar to the conditions of a race (Miller et al. 2014 J. Sci. Cycling 3(2) 85). The choice of an optimal tactics to be used on the whole distance is conditioned by information about the effectiveness of energetic sources in the course of an MTB cyclist’s interval effort of 90-135 min, in which aerobic metabolism is the dominant one. (Impellizzeri, Marcora 2007 J.Sport Med. 37(1): 59-71) Purpose: The aim of the research was to create a trial protocol run on a treadmill corresponding to the profile of a MTB route during OG or WCh as well as to evaluate the changes of a cyclist’s physiological indicators in the course of preparation to the most important sports event in the season. Methods: A female cyclists of the Polish National Team MTB XCO (28 years, 168 cm, 52 kg), a world champion who ranked second in Olympic games and an European champion, took part in the research. On the basis of the analysis of the race route in an pre-Olympic trial and the measurement of the profile of the route a trial protocol was created for treadmill Saturn (Cosmed, Germany). During effort VO2, O2/HR (K4b2, Cosmed Italy), heart rate (Polar Vantage, Finland) and blood lactate concentration (Biosen C-line, EKF Germany) were measured. The research was conducted in the preparatory and competition period. The participant made effort in time corresponding to a full MTB race, performing a round of the same profile four times. The trial constructed in this way enabled to analyze the changes of physiological changes depending on a training period and period of effort (a round). Results: Table 1 presents the description of values recorded in the preparatory and competition period during the trial. In the competition period a significant rise in the effectiveness of work was observed. Work of the same intensity were performed at a lower energetic cost. Whereas the average VO2 value was lowered during the first two rounds by 14-15%, in the third and fourth rounds this difference amounted to 20 and 28%. Such a description of changes in the second part of the route resulted from the stabilization of the average VO2 value at the level of 50-56 mlxkg-1xmin-1 in the whole distance in the competition period. In the preparatory period a significant increase in the value of this parameter in the third and fourth round of the trial (after effort of 50 min.) was observed. Heart rate was characterized by a decrease of value by udxmin-1 in the starting period. At the same time this is the parameter which has a stable value in the course of effort. A decrease in the value of O 2 /HR when there were stable differences between HR values resulted from the decrease of oxygen consumption, which in the third and fourth round caused the decrease of this parameter by almost 25% in comparison to values recorded in an earlier period. Blood lactate concentration (LA) measured after distances of the greatest steepness of slope (uphill) maintained the same stable differences (2-2.5 mmol/l) between the preparatory and competition period in rounds 1-3. The greatest difference in LA was measures in the fourth round – it amounted to 5 mmol/l. Disussion: The values and direction of changes in parameters indicated an increase in the cyclist’s endurance in the analyzed training period by increasing the effectiveness of aerobic and anaerobic effectiveness (a decrease of VO2 and LA while maintaining the intensity of work). The obtained training effect enabled to change the training loads parameter in the direction of increasing the effectiveness of work in individual route sections. Modelling training loads is at first limited to the selected round or sections. Then subsequent sections are connected with each other. Conclusion: It has been proven that the diagnostics of an MTB cyclist’s training on a treadmill in laboratory conditions and its usage programming an MTB training: Determining the scope of the intensity of training loads directed at developing aerobic and anaerobic endurance, Determining the volume of training loads which affect effectively various areas of a cyclist’s preparation, Determining the value of effort parameters (force, speed) which can be used in the course of a sports competition.

Effects of pre-exercise alkalosis on the decrease in VO2 at the end of all-out exercise.

This study determined the effects of pre-exercise sodium bicarbonate ingestion (ALK) on changes in oxygen uptake (VO2) at the end of a supramaximal exercise test (SXT). Eleven well-trained cyclists completed a 70-s all-out cycling effort, in double-blind trials, after oral ingestion of either 0.3 g kg(-1) of sodium bicarbonate (NaHCO3) or 0.2 g kg(-1) body mass of calcium carbonate (PLA). Blood samples were taken to assess changes in acid-base balance before the start of the supramaximal exercise, and 0, 5 and 8 min after the exercise; ventilatory parameters were also measured at rest and during the SXT. At the end of the PLA trial, which induced mild acidosis (blood pH = 7.20), subjects presented a significant decrease in VO2 (P < 0.05), which was related to the amplitude of the decrease in minute ventilation (VE) during the SXT (r = 0.70, P < 0.01, n = 11). Pre-exercise metabolic alkalosis significantly prevented the exercise-induced decrease in VO2 in eleven well-trained participants (PLA:12.5 ± 2.1 % and ALK: 4.9 ± 0.9 %, P < 0.05) and the decrease in mean power output was significantly less pronounced in ALK (P < 0.05). Changes in the VO2 decrease between PLA and ALK trials were positively related to changes in the VE decrease (r = 0.74, P < 0.001), but not to changes in power output (P > 0.05). Pre-exercise alkalosis counteracted the VO2 decrease related to mild acidosis, potentially as a result of changes in VE and in muscle acid-base status during the all-out supramaximal exercise.

Application of the Critical Heart Model to Treadmill Running.

The mathematical model used to estimate critical power has been applied to heart rate (HR) measurements during cycle ergometry to derive a fatigue threshold called the critical heart rate (CHR). This study had 2 purposes: (a) determine if the CHR model for cycle ergometry could be applied to treadmill running and (b) examine the times to exhaustion (Tlim) and the VO2 responses during constant HR runs at the CHR. Thirteen runners (mean ± SD; age = 23 ± 3 years) performed an incremental treadmill test to exhaustion. On separate days, 4 constant velocity runs to exhaustion were performed. The total number of heart beats (HBlim) for each velocity was calculated as the product of the average 5-second HR and Tlim. The CHR was the slope coefficient of the HBlim vs. Tlim relationship. The Tlim and VO2 responses were recorded during a constant HR run at the CHR. Polynomial regression analyses were used to examine the patterns of responses for VO2 and velocity. The HBlim vs. Tlim relationship (r = 0.995-1.000) was described by the linear equation: HBlim = a + CHR (Tlim). The CHR (176 ± 7 b·min, 91 ± 3% HRpeak) was maintained for 47.84 ± 11.04 minutes. There was no change in HR but quadratic decreases in velocity and VO2. These findings indicated that the CHR model for cycle ergometry was applicable to treadmill running and represented a sustainable (30-60 minutes) intensity but cannot be used to demarcate exercise intensity domains.

V˙O2max and Microgravity Exposure

Exposure to a microgravity environment decreases the maximal rate of O2 uptake (VO(2max)) in healthy individuals returning to a gravitational environment. The magnitude of this decrease in VO(2max) is, in part, dependent on the duration of microgravity exposure, such that long exposure may result in up to a 38% decrease in VO(2max). This review identifies the components within the O(2) transport pathway that determine the decrease in postmicrogravity VO(2max) and highlights the potential contributing physiological mechanisms. A retrospective analysis revealed that the decline in VO(2max) is initially mediated by a decrease in convective and diffusive O(2) transport that occurs as the duration of microgravity exposure is extended. Mechanistically, the attenuation of O(2) transport is the combined result of a deconditioning across multiple organ systems including decreases in total blood volume, red blood cell mass, cardiac function and mass, vascular function, skeletal muscle mass, and, potentially, capillary hemodynamics, which become evident during exercise upon re-exposure to the head-to-foot gravitational forces of upright posture on Earth. In summary, VO(2max) is determined by the integration of central and peripheral O(2) transport mechanisms, which, if not maintained during microgravity, will have a substantial long-term detrimental impact on space mission performance and astronaut health.

Factors Underlying the Perception of Effort during Constant Heart Rate Running

PURPOSE: This study examined the intensity (velocity), metabolic (VO2), respiratory (minute ventilation [VE] and breathing frequency [fb]), and neuromuscular (electromyographic amplitude [EMG AMP] and EMG mean power frequency [MPF]) factors that may underlie the perception of effort (rating of perceived exertion [RPE]) during constant heart rate (HR) running within the heavy exercise intensity domain. METHODS: Eight runners (mean ± SEM; age = 24 ± 1 years) completed an incremental test to exhaustion for the determination of the gas exchange threshold (GET), respiratory compensation point (RCP), heart rate peak (HRpeak), and peak oxygen consumption rate (VO2peak). The RPE, velocity, VO2, VE, fb, EMG AMP, and EMG MPF responses were recorded during a constant HR run (88.3 ± 1.1 %HRpeak; 78.9 ± 2.1 % VO2peak) within the heavy exercise intensity domain at 50% of the difference between the GET and RCP. The relationships for each variable versus time were examined using polynomial regression models (linear and quadratic) at an alpha level of p ≤ 0.05. RESULTS: During the constant heart rate run, the subjects reached the selected HR within 1.83 – 5.00 min and maintained the run for 57.17 ± 0.4 min. The mean percent changes from the time the HR was reached to the end of the run for RPE, velocity, VO2, VE, fb, EMG AMP, and EMG MPF were 9.0 ± 8.1%, -23.3 ± 1.4%, -12.1 ± 2.1%, -18.4 ± 2.1%, 15.8 ± 5.7%, -10.0 ± 4.9%, and 5.1 ± 3.5%, respectively. The polynomial regression analyses indicated there was no change in HR (r2 =0.20), but quadratic increases in RPE (R2 =0.88) and fb (R2 =0.87) as well as a linear increase in EMG MPF (R2 =0.65). In addition, there were quadratic decreases in velocity (R2 =0.90), VO2 (R2 =0.95), and VE (R2 =0.94) as well as a linear decrease in EMG AMP (r2 =0.74). CONCLUSION: These findings indicated that during constant HR running within the heavy exercise intensity domain, increases in RPE were associated with fb and EMG MPF, but dissociated from HR, velocity, VO2, VE, and muscle activation (EMG AMP), which remained constant or decreased. It is possible the RPE was influenced by afferent signals from the respiratory muscles associated with fb and/or sensory cues from increases in muscle/core temperature typical of prolonged (>20 min) exercise within the heavy domain. Supported by the 2013 NSCA Doctoral Research Grant.

Beetroot Juice Supplementation Does Not Improve Mitochondrial Efficiency or ADP Sensitivity in Humans

Ingestion of sodium nitrate (NaNO3) simultaneously reduces whole-body oxygen consumption (VO2) during sub-maximal exercise while improving mitochondrial efficiency, suggesting a causal link. Consumption of beetroot juice (BRJ) elicits similar decreases in VO2 but potential effects on the mitochondria remain unknown. Therefore we examined the effects of 6 day supplementation with BRJ (280 ml/d, ~26 mmol NO3-) in young active males (n=10) who had muscle biopsies taken Pre and Post supplementation for assessments of mitochondrial bioenergetics. Subjects performed 20 min of cycling (10 min at 50% and 70% VO2Max) 48 h prior to receiving biopsies, and on day 4 of supplementation. Mitochondrial respiration in permeabilized muscle fibres showed no change in oligomycin-leak respiration, maximal substrate-supported respiration, or ADP sensitivity (apparent Km). To compare the effects of BRJ to previous findings with NaNO3, 5 subjects had muscle taken for isolation of subsarcolemmal and intermyofibrillar mitochondria. Neither subpopulation showed an improvement in mitochondrial efficiency assessed by the oxygen consumed/ATP produced (P/O Ratio), or in mitochondrial coupling assessed by respiratory control ratio (RCR). Membrane potential determined fluorometrically using safranine-O during respiration was not different Post vs. Pre supplementation. In summary, in contrast to NaNO3, BRJ supplementation did not alter key parameters of mitochondrial function. This occurred despite a decrease in exercise VO2, suggesting that the ergogenic effects are not due to a change in mitochondrial coupling or efficiency. Supported by NSERC, Canada.

Torpor in Tenrecs, a Basal Protoendothermic Mammal

Thirty of the 33 described tenrec species are endemic to Madagascar. These basal mammals possess features such as a cloaca and variable body temperature (Tb). We measured the energetics of common tenrecs, Tenrec ecaudatus, during the hibernation season. Tenrecs are capable of variable arousal from torpor but do not perform the predictable interbout arousals characteristic of all other known small hibernators. At lower ambient temperatures, ventilation may be punctuated with periods of 30 min or more between breaths. We found discordant changes to oxygen consumption (VO2), heart rate (HR), and Tb e.g. a spontaneous 23% decrease in VO2 was accompanied by an 47% decrease in HR and no change in Tb. Marked changes in Tb could occur with little change to VO2. We hypothesize that hibernation in tenrecs may represent a plesiomorphic form that is manifested by poor coordination of key homeostatic processes.

Effects of hybrid cycling versus handcycling on wheelchair-specific fitness and physical activity in people with long-term spinal cord injury: a 16-week randomized controlled trial.

This is an open randomized controlled trial. The objective of this study was to investigate the effects of a 16-week hybrid cycle versus handcycle exercise program on fitness and physical activity in inactive people with long-term spinal cord injury (SCI). The study was conducted in two rehabilitation centers with a specialized SCI unit. Twenty individuals (SCI⩾8 years) were randomly assigned to a hybrid cycle (voluntary arm exercise combined with functional electrical stimulation (FES)-induced leg exercise) or a handcycle group. During 16 weeks, both groups trained twice a week for 30 min at 65-75% heart rate reserve. Outcome measures obtained before, during and after the program were fitness (peak power output, peak oxygen consumption), submaximal VO2 and heart rate (HR), resting HR, wheelchair skill performance time score) and physical activity (distance travelled in wheelchair and Physical Activity Scale for Individuals with Physical Disabilities (PASIPD) score). Changes were examined using a two-factor mixed-measures analysis of variance. For all fitness parameters, except for submaximal VO2, no interaction effects were found. The hybrid cycle group showed a decrease in VO2 over time in contrast to the handcycle group (P=0.045). An overall reduction in HRrest (5±2 b.p.m.; P=0.03) and overall increase in PASIPD score (6.5±2.1; P=0.002) were found after 16 weeks of training. No overall training effects were found for the other fitness and activity outcome measures. In the current study, hybrid cycling and handcycling showed similar effects on fitness and physical activity, indicating that there seem to be no additional benefits of the FES-induced leg exercise over handcycle training alone.

5-year serial follow-up of clinical condition and ventricular function in patients after repair of tetralogy of Fallot

ObjectiveTo study the changes over time in biventricular size and function, and clinical parameters in patients after repair of tetralogy of Fallot (TOF) without subsequent pulmonary valve replacement (PVR). MethodsWe prospectively included 78 non-PVR patients (age 20(6–60)years at baseline), who were studied twice with a 5-year interval. Patients underwent magnetic resonance imaging for assessment of biventricular size and function. Exercise testing and electrocardiography were performed to determine peak oxygen uptake (peak VO2) and QRS duration. N-terminal prohormone brain natriuretic peptide (NT-proBNP) was assessed additionally. ResultsPulmonary regurgitation (PR), right ventricular (RV) volumes and QRS duration increased during 5-year follow-up (RV end-diastolic volume (EDV) 130±30ml/m2 to 138±34ml/m2; QRS 132±27msec to 139±27msec); peak VO2 decreased (96±19% to 91±17%). RV ejection fraction, RV effective stroke volume (eff.SV), and NT-proBNP levels remained unchanged. The slope of RVEDV increase was 1.6±3.0ml/m2/year, and depended on RVeff.SV, not on RVEDV, at baseline. Increase in RVEDV correlated with increase in QRS duration over time (r=0.28, p=0.016), and with decrease in RV mass/EDV ratio over time (r=−0.42, p<0.001), not with decrease in peak VO2. In subgroup analysis, patients with larger RVs at baseline showed larger increase in PR during follow-up and larger decrease in NYHA class over time. ConclusionsIn TOF patients with moderate RV dilatation, RVEDV increased by 1.6±3.0ml/m2/year, irrespective of RV size at baseline, but depended on RVeff.SV at baseline. Despite limited progression in RV size, unfavourable changes occurred during 5years follow-up, which suggests there is a need for close follow-up.

Can 123 I-MIBG cardiac scintigraphy predict functional recovery in heart failure after cardiac resynchronization?

Background: Cardiac heart failure patients may benefit from cardiac resynchronization, but around 30% do not respond. Several parameters have been studied to evaluate possible positive predictive factors. Aim: To evaluate if baseline 123 I-MIBG cardiac scintigraphy parameters can predict functional capacity modification after cardiac resynchronization (CRT), assessed by cardiopulmonary testing, in patients (P) with chronic heart failure (CHF). Methods: We prospectively assessed 49 consecutive CHF P referred to CRT, mean age 68±14 (34-82 years old), 68% male, LVEF<35%; 28% ischemic cardiomyopathy P and 72% nonischemic cardiomyopathy P; 37% diabetic P; 43% P class III and 57%≤ class II (NYHA). All patients underwent, before CRT and 6 months post-CRT, echocardiogram for left ventricular ejection fraction (LVEF), cardiopulmonary testing, CPT, for peak oxygen consumption (VO2p), and 123 I-MIBG cardiac scintigraphy, for early heart-mediastinum rate (HMR), late HMR and washout (WO). Results: Our preliminary results showed, mean LVEF 27±8%; VO2p mean value 14.8±5.5 ml/kg/min. Regarding 123 I-MIBG scintigraphy parameters, we found early HMR mean value 1.5±0.17 (75% P with early HMR < 1.6); late HMR mean value 1.4+/0.16, (94% P with late HMR<1.6); washout (WO) mean value 41±27. VO2 change after CRT at 6 months was positive in 68% of the P (mean variation +4.3+/2.7 ml/kg/min), group A, and negative in 32% of the P (mean variation -3.4+/2.3), group B. There was a very significant difference between VO2 variation in group A and B (p 1.6 (100%) had a positive VO2 variation (group A); P with baseline early HMR <1.6, had negative VO2 variation in 60% (group B) and positive in 40% (group A).Considering early HMR<1.5, 88% P had negative VO2 variation (group B). No significant differences were found in the late HMR, WO and LVEF. Conclusion: In this heart failure patients group, ischemic and nonischemic, baseline MIBG early heart-mediastinum rate was predictive of functional capacity modification: early HMR superior to 1.6 was always associated to VO2 increase after CRT (100% P); contrarly, early HMR inferior to 1.5 was mostly associated to VO2 decrease (88% P).

Ventricular response to dobutamine stress relates to the change in peak oxygen uptake during the 5-year follow-up in young patients with repaired tetralogy of Fallot

To evaluate the additional value of dobutamine stress testing in patients with repaired tetralogy of Fallot (TOF) by relating stress imaging parameters at baseline to relevant parameters of clinical condition and right ventricular (RV) size during a serial follow-up. We prospectively included 27 patients (14 ± 4 years at baseline), who were studied twice with a 5-year interval. Patients underwent cardiovascular magnetic resonance imaging to assess RV systolic and diastolic function at rest and during dobutamine stress. Normal response to dobutamine was defined as a decrease in RV end-systolic volume, and a increase in RV ejection fraction (EF) during stress. Exercise testing and electrocardiography were performed to determine peak oxygen uptake (peak VO₂), QRS duration, and QT interval corrected for heart rate (QTc) interval. RV volumes, QRS duration, and QTc interval increased significantly from baseline to follow-up; peak VO₂ tended to decrease (95 ± 20-89 ± 14%, P = 0.086). Response to dobutamine was normal in 26 of 27 patients and remained stable during the follow-up [relative increase in RVEF during stress: +25 ± 9% (baseline) vs. +27 ± 10% (follow-up)]. A smaller relative increase in RVEF during stress at baseline related to a larger relative decrease in peak VO₂ during the follow-up (r = 0.59, P = 0.004). No significant associations were found with the relative increase in QRS duration, QTc interval, or RV end-diastolic volume during a 5-year follow-up. In a young TOF population, response to dobutamine stress was normal and remained stable during the 5-year follow-up. A smaller increase in RVEF during stress at baseline was predictive for a larger decrease in peak VO₂ during the 5-year follow-up.

Measurement of systemic oxygen consumption in patients during extracorporeal membrane oxygenation — description of a new method and the first clinical observations

Extracorporeal membrane oxygenation (ECMO) provides temporary life-saving support for patients with severe cardiac failure, but is associated with significant morbidity and mortality. While ECMO enables oxygen delivery (DO2), little is known about oxygen consumption (VO2), largely due to technical difficulties. We aimed to introduce the adaptation of respiratory mass spectrometry to measure VO2 in patients during ECMO and to use this unique model to determine the pathological dependency of VO2 on DO2 in humans. Respiratory mass spectrometry remains the 'state-of-the-art' method, allowing the highly sensitive and rapid measurement of VO2 in critically ill patients. The principle and design of the respiratory mass spectrometer are described, together with the setting up of this machine with the ECMO oxygenator and the native lungs of the patients. In two patients with severe dilated cardiomyopathy and little cardiac contraction, the decrease in pump flow and, hence, DO2 by 20% was associated with a decrease in VO2 by 5% and 8%, respectively, whereas the increase in pump flow was not associated with any significant change in VO2. The direct measurement of VO2 by respiratory mass spectrometry in ECMO patients provides a unique technique for clinical research on the metabolism and VO2-DO2 relationship in this special group of critically ill patients. Our pilot study is the first to demonstrate a pathological dependency of VO2 on DO2 in humans. Further studies are warranted with this technique to examine the changes and the factors affecting systemic oxygen transport in patients during ECMO.

Inferior Exercise Economy in Children: Perpetuating a Myth?

It is one of the most established, well-documented pieces of dogma in the pediatric exercise physiology literature: compared with adults, children exhibit a greater metabolic requirement to move body mass—an inferior exercise economy—during weight-bearing exercise (1,7). In a typical example provided by Unnithan and Eston, 9–10 year old boys had a 24% greater mass-relative oxygen demand while running on a treadmill at 9.6 km h-1 compared with 18–25 year old men (47 ml kg-1 min-1 versus 38 ml kg-1 min-1; 15). Cross-sectional studies indicate that this economy improves with increasing age. In an early study, Skinner et al. demonstrated a progressive decline in metabolic demand during uphill treadmill walking from 46 ml kg-1 min-1 in a group of 6–8 year old children to 41 ml kg-1 min-1 in a cohort of 12–16 year old youth (13). Longitudinal studies have verified this trend. In the Amsterdam Growth, Health, and Fitness Study, data from 192 subjects showed a mean decrease in VO2 per kg from 37.6 to 30.3 ml kg-1 min-1 between the ages of 13 and 27 years (16). Rowland et al. determined treadmill walking economy at 3.25 mph and 8% grade annually for five years in children beginning at age 9 years (9). Mass-relative oxygen uptake fell progressively over this time span from an initial mean value of 31.0 ml kg-1 min-1 to 26.5 ml kg-1 min-1. The findings have been remarkably consistent: metabolic cost per kg body mass at a given exercise load progressively decreases in a continuum through the growing years. VO2/kg at a given treadmill speed and grade setting can be predicted to decline by an average of approximately 1.0 ml kg-1 min-1 for each year of increasing age until midlate adolescence. From the perspective of developmental exercise physiology, this “wasteful gait” of children has been considered as a disadvantage in their capacity for endurance exercise compared with adults. “The high metabolic cost of walking and running,” it has been suggested, “makes the small child less of an ‘aerobic machine” (1). From a more pragmatic standpoint, the progressive change in exercise economy

Фазовые изменения энергетического метаболизма при периодической гипоксии

Male Wistar rats were exposed to periodic hypobaric hypoxia (PHH), by "lifting" in barochamber at "altitude" 5600 m for 1 h every 3 days (6 séances). The dynamics of changes in oxygen consumption (VO2), and body temperature (Tm), as well as in HIF-1alpha and HIF-3alpha gene expression, and mitochondrial respiration in the ventricles of the heart was studied. On the basis of the data we identified four phases of the physiological changes. The first phase, hypometabolic (1-3 séances), is characterized by decrease in VO2 and Tm, induction of HIF-1alpha and HIF-3alpha with delayed transient stimulation of metabolism in response to each séance of hypoxia. In heart mitochondria, V3 and V4 are increased, but V3/V4 and ADP/O are reduced. During the second phase, transitional (3-4 séances), there is reorganization of metabolism and decrease its hypoxic reactivity. The third phase, hypermetabolic (4-5 séances), is characterized by intensification of metabolism and compensation of hypoxic disorders. The fourth phase (after 5 séance) - is a state of metabolic adaptation with normalization of VO2 and Tm, expression of HIF-1alpha and HIF-3alpha, mitochondrial respiration, increased NAD-dependent oxidation of carbohydrate and lipid substrates. Thus, during PHH consequent rebuilding of processes of oxygen transport, tissue respiration and thermogenesis occurs, mediated by induction of the HIF subunits.

A Pre-season Comparison of Aerobic Fitness and Flexibility of Younger and Older Professional Soccer Players

Aerobic fitness and flexibility generally present age-related decreases, yet the influence of age on these variables in soccer players is still unknown. We obtained oxygen consumption (VO(2)) and heart rate (HR) at 12 km · h (- 1), anaerobic threshold and maximum intensities, and athletes' flexibility profiles using Flexitest (FLX). Pre-season data (2005-2011) from the 2 extreme age terciles (n=54) - YOUNGER (17-22 years old) and OLDER (27-36 years old) - of a group of 162 players from an elite Brazilian soccer club were compared. The effects of aging were also assessed by contrasting VO(2), HR and FLX linear regressions - slope and intercept - vs. age-predicted and reference values. The results were similar between the YOUNGER and OLDER terciles for VO(2max), at 62.7 ± 6.1 vs. 63.2 ± 6.2 mL · kg (- 1) · min (- 1), respectively (p=0.67), effect size (ES)=0.08, and for FLX, at 43 ± 5.9 vs. 41 ± 6.0, respectively (p=0.11, ES=0.34); the YOUNGER tercile exhibited higher values for HRmax than the OLDER tercile, at 194 ± 8.1 vs. 189 ± 8.8 b · min (- 1), (p<0.01, ES=0.59). Players in the OLDER tercile did not present an age-predicted decrease in VO(2max), whereas HRmax and FLX diminished with age as predicted. We conclude that, at least for these variables, younger and older players were effectively identical in their pre-season levels of conditioning.