VO2 Response Research Articles

Signal-morphology impedance cardiography is a non-invasive tool to predict responses to exercise based cardiac rehabilitation in chronic heart failure patients

Abstract Background All the studies and meta-analyses showed beneficial effects of the exercise based cardiac rehabilitation (ExBCR) on peak value of oxygen uptake (VO2peak) in patient with chronic heart failure (CHF). It is widely recognized that changes in VO2peak induced by training (ΔVO2peak) have a prognostic value. A 5.0% increase in ΔVO2peak has been associated with a significant clinical improvement1. However, 20 to 30 % of CHF are non-responders to ExBCR. The Signal-Morphology Impedance Cardiography (SM-ICGTM) technology has allowed previous researchers to show the role of cardiac output (CO) on DVO2peak2. CO responses may be partly attributed to the peak ejection flow velocity that can explain the impaired response to ExBCR. Purpose The study aimed to establish whether SM-ICGTM is an appropriate technology to predict responses to ExBCR in CHF patients. Methods A retrospective study was conducted on 65 CHF patients (LVEF: 29.0±8.3%). All patients performed a cardiopulmonary exercise test (CPET) on bicycle to determine ventilation (VE) and VO2peak before and after 20 ExBCR sessions. In addition, stroke volume (SV), heart rate (HR), and CO were continuously monitored by SM-ICGTM (PhysioFlow® Lab1). The value of peak ejection flow velocity, so called CTi by the manufacturer, was calculated as the peak of the first mathematical derivative over the time of the impedance waveform during the systole and measured by PhysioFlow® throughout the test. For the analysis of training response patients were divided in two groups: the normal CTi profile which was characterized by an initial increase followed by a plateau until CPET exhaustion, and the abnormal CTi response if CTi decreased at the onset of CPET or increased then decreased before exhaustion. Statistical analyses were performed with JASP. The significant level was set at p value < 0.05 for 95% confidence interval. Results Our study population consisted in 32 patients who presented a normal CTi profile and 33 with an abnormal CTi profile. As shown in Table 1, no significant difference was found at baseline between both groups. ExBCR induced significant changes in VO2peak even if 29 % patients were non-responders. Patients with normal CTi profile presented a greater DVO2peak compared to patients with abnormal CTi profile (28 ± 30 vs. 14 ± 19 %, p<0.01). 78% of patients with normal CTi profile versus only 64% of patients with abnormal CTi profile were ExBCR responders. The logistic regression showed that patient with normal CTi profile were 3.3 time more likely to present a ΔVO2peak ≥ 5%. Conclusion Exercise CTi profiles determined by SM-ICGTM prove to be an interesting tool to help predicting ExBCR responses in CHF patients and maybe highlighting the hemodynamic determinants of VO2 responses to exercise training.

Evaluating tissue hypoxia and the response to fluid administration in septic shock patients: a metabolic cluster analysis

BackgroundThe selection of adequate indicators of tissue hypoxia for guiding the resuscitation process of septic patients is a highly relevant issue. Current guidelines advocate for the use of lactate as sole metabolic marker, which may be markedly limited, and the integration of different variables seems more adequate. In this study, we explored the metabolic profile and its implications in the response to the administration of a fluid challenge in early septic shock patients.MethodsObservational study including septic shock patients within 24 h of ICU admission, monitored with a cardiac output estimation system, with ongoing resuscitation. Hemodynamic and metabolic variables were measured before and after a fluid challenge (FC). A two-step cluster analysis was used to define the baseline metabolic profile, including lactate, central venous oxygen saturation (ScvO2), central venous-to-arterial carbon dioxide difference (PcvaCO2), and PcvaCO2 corrected by the difference in arterial-to-venous oxygen content (PcvaCO2/CavO2).ResultsSeventy-seven fluid challenges were analyzed. Cluster analysis revealed two distinct metabolic profiles at baseline. Cluster A exhibited lower ScvO2, higher PcvaCO2, and lower PcvaCO2/CavO2. Increases in cardiac output (CO) were associated with increases in VO2 exclusively in cluster A. Baseline isolated metabolic variables did not correlate with VO2 response, and changes in ScvO2 and PcvaCO2 were associated to VO2 increase only in cluster A.ConclusionsIn a population of early septic shock patients, two distinct metabolic profiles were identified, suggesting tissue hypoxia or dysoxia. Integrating metabolic variables enhances the ability to detect those patients whose VO2 might increase as results of fluid administration.

The Cardiac and Cerebrovascular Response to Lower Body Negative Pressure in Patients with Postural Orthostatic Tachycardia Syndrome

Introduction: Postural orthostatic tachycardia syndrome (POTS) is characterized by excessive heart rate response upon standing and symptoms that drastically reduce quality of life. Symptoms are often cerebral in nature (e.g., dizziness, headache), however the relationship between the underlying physiology and the symptoms is unknown. We tested the hypothesis that, compared to healthy controls (HC) individuals with POTS would have greater decreases in cardiac, and cerebral hemodynamic function during a simulated orthostatic challenge (lower-body negative pressure; LBNP) measured using magnetic resonance (MR) imaging. Methods: Eleven patients with POTS (17±1yrs; 1 male) and 10 HC (18±2yrs; 1 male) were studied at rest (supine in MRI) and during 20-minutes of -25mmHg LBNP. Symptoms were measured by Vanderbilt Orthostatic Symptom Score (VOSS). Heart rate and blood pressure (BP) were measured using an automated cuff and finger pulse oximeter, respectively. Left and right ventricular volumes, ejection fraction, stroke volume (SV), and cardiac output (Qc) were determined by cardiac MR. Cerebral oxygen utilization (VO2) was calculated as cerebral blood flow (CBF) multiplied by venous oxygen saturation (SVO2), measured by MR phase contrast and susceptomtery-based oximetry in the superior sagittal sinus. Results: At rest, there were no differences between groups for any cardiac hemodynamic measure (p>0.05 for all), however cerebral SvO2 and VO2 were lower in the POTS group (p=0.02 for both). In response to LBNP, patients with POTS had greater VOSS (25±21 vs 5±12; p=0.02). Heart rate increased in response to LBNP (p<0.001), but the increase was not different between groups (HC: +9±8bpm; POTS: +13±11bpm; p=0.35). SV and Qc decreased during LBNP (both, p<0.01), despite no change in mean arterial BP (p=0.13) which did not differ between groups (HC: +9±8mmHg; POTS: 3±6mmHg; p=0.377). Additionally, both left and right ventricular volumes as well as ejection fraction decreased during LBNP (p<0.01 for all). The decreased Qc during LBNP coincided with lower CBF in the superior sagittal sinus (p=0.01) although the response was not different between groups (HC: -17±13ml/min; POTS: -25±32ml/min; p=0.51). Cerebral SvO2 also decreased during LBNP (p=0.03) indicating increased oxygen extraction, resulting in no change in cerebral VO2 during LBNP (p=0.28) and no difference between groups in the VO2 response (HC: -0.2±3.7ml/min; POTS: +1.1±2.0ml/min; p=0.33). Conclusion: In response to a simulated orthostatic challenge (-25mmHg LBNP), patients with POTS do not have impaired cardiac function or cerebral oxygenation despite having a higher symptom score; however, a stronger stimulus may have been necessary to expose differences. Further investigations are needed to elucidate mechanisms of autonomic dysfunction in this population. Women and Children's Health Research Institute. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sleep Duration Irregularity is Associated with Elevated Blood Pressure During Submaximal Exercise in Young Adults.

Irregularity in nightly sleep duration is reported to associate with elevated blood pressure (BP), but it is unclear whether this association can be observed with BP measured during exercise after controlling for factors known to influence the exercise pressor reflex. Twenty-nine young adults (22±4y; 19 men, 10 women) performed cycling exercise until volitional fatigue to assess peak oxygen uptake (VO2). Actigraphy was used to monitor sleep duration and daily physical activity for seven consecutive days after which participants completed two bouts of moderate-intensity cycling while BP and VO2 were measured using a Tango+ device and indirect calorimetry, respectively. Systolic BP was averaged from the two bouts of exercise and expressed as a change from seated rest (∆SBP). Sleep duration regularity was calculated as standard deviation (SD) and coefficient of variation (CV). Systolic BP at seated rest, during exercise, and ∆SBP was 113±13, 152±21, and 38±13 mmHg, respectively. Sleep duration SD (range 10-146 min) and sleep duration CV (range 2-54%) when excluding weekend nights were significantly correlated with ∆SBP (r = 0.58 and r = 0.62, respectively; both p<0.01) after adjusting for age, sex, body mass index, peak VO2, physical activity, resting systolic BP, chronotype, and the VO2 response to exercise. Sleep duration regularity analyzed with weekend nights included (across all seven days) was also significantly correlated with ∆SBP (p≤0.01), but had weaker correlation coefficients. These results indicate that sleep regularity, especially when excluding weekend nights, is associated with the rise in systolic BP during moderate-intensity exercise in young adults. Sleep duration regularity may be a useful tool to capture the impact of intermittent nights of insufficient sleep on BP dysregulation.

Functional electrical stimulation combined with voluntary cycling accentuates VO2 response in people with severe multiple sclerosis: A pilot study

BackgroundLower limb muscle weakness and reduced balance due to disease progression in multiple sclerosis (MS) may make robust aerobic exercise difficult. Functional electrical stimulation (FES) cycling combined with voluntary cycling may allow people with severe MS to enhance the intensity of aerobic exercise. The aim of this study was to investigate the cardiorespiratory, power, and participant-reported perceptions during acute bouts of FES cycling, voluntary cycling, and FES cycling combined with voluntary cycling (FES assist cycling). MethodsParticipants with severe MS (Expanded Disability Status Scale [EDSS] ≥ 6.0) undertook three exercise trials on a leg cycle ergometer. Trial 1 involved 30 min of FES cycling; Trial 2 involved two 10-minute bouts of voluntary cycling separated by 10 min rest; and Trial 3 was a combination of trials 1 and 2 (FES assist cycling). Outcome measures included VO2 (volume of oxygen consumption), cycle power output, heart rate, RPE, and post-exercise perceptions of pain and fatigue. ResultsTen people with severe MS participated (9 female; age 52.4 ± 9.98 y; EDSS 7.1 ± 0.6). The average VO2 during the 30-minute trials was significantly higher for FES assist cycling compared to voluntary cycling (429.7 ± 111.0 vs 388.5 ± 101.0 mL/min, 95% CI 23.4 to 113.0 mL/min, p = 0.01), with a large effect size (Hedges' g = 1.04). Participants reported similar rates of perceived exertion at the end of FES cycling (13 ± 2), voluntary cycling (14 ± 2), and FES assist cycling (15 ± 1); p = 0.14. Self-reported pain was higher during both FES cycling (5.4 vs 0.3; 95% CI 3.4 to 6.7, p = 0.01, Hedges’ g = 2.07) and FES assist cycling (4.2 vs. 0.3; 95% CI 2.3 to 5.5, p = 0.01, Hedges’ g = 1.71) than voluntary cycling, both with large effect sizes. There was no difference in self-reported fatigue at the end of each trial (p = 0.21). ConclusionThis study found FES assist cycling produced significantly higher VO2 values than voluntary cycling, although the clinical significance of these differences is unknown. Participants performed FES assist cycling at a self-reported RPE consistent with moderate to vigorous intensity, however it was considered light-intensity exercise when expressed by METS. FES assist cycling was no more fatiguing post-exercise than the other modes.

Validation of Air Storage System for Hypoxia Exposure During Exercise.

Norberto, Matheus S., João Victor G. Torini, Matheus S. Firmino, and Marcelo Papoti. Validation of air storage system for hypoxia exposure during exercise. High Alt Med Biol. 00:000-000, 2024.-Considering the importance of optimizing normobaric hypoxia exposure (i.e., higher delivery capacity), the current study aims to validate a hypoxic air storage system. The study has a cross-over, one-blind randomized design. The air storage is composed of a piping system that directs hypoxic air from a hypoxia generator into nylon bags. Sixteen men (age, 25.4 ± 4.8 years; height, 174.9 ± 9.4 cm; weight, 77.1 ± 17.2 kg) performed three incremental treadmill tests until exhaustion on different days. For test-retest, the subjects repeated two tests in similar hypoxia conditions (H1 and H2; fraction of inspired O2 [FIO2] = ∼0.13; reliability analysis), and one time in normoxia (FIO2 = ∼0.20; condition comparison). Subjects' performance, blood lactate concentration ([La-]), arterial oxygen saturation (SpO2), oxygen consumption (VO2), heart rate (HR), and several respiratory-derived variables were evaluated. A comparison was made between the rest, moderate intensity, and exhaustion stages. All variables were compared using the Friedman test with Durbin-Conover post hoc (p < 0.05). The hypoxia test-retest showed no statistical differences for any variable. Time analysis showed similar behavior for SpO2, HR, and cardiorespiratory variables (p < 0.01) for both conditions. The mean FIO2 at rest and during the incremental treadmill test was higher for normoxia (20.6 ± 0.2%) than for H1 (13.8 ± 0.8%) and H2 (13.7 ± 0.3%) (p < 0.001). The VO2 response was higher in normoxia than during hypoxia exposure at moderate intensity (Normoxia = 43.1 ± 8.1; H1 = 38.7 ± 5.7; H2 = 35.8 ± 8.8 ml.kg-1.min-1) and at the exhaustion stage (Normoxia = 52.7 ± 12.5; H1 = 41.9 ± 8.8; H2 = 40.5 ± 8.9 ml.kg-1.min-1) (p < 0.01). SpO2 and HR showed excellent intraclass correlation coefficient (ICC) during all moments, whereas VO2, SpO2, ratio between ventilation and CO2 production (VE/VCO2), ratio between oxygen consumption and ventilation (VE/VO2), and HR showed moderate or good ICC and coefficient of variation <9% during hypoxia test-retest exercises. Thus, the air storage system showed validity for its application and reliability in the measurements associated.

Physiological and haemodynamic differences between peak exercise blood pressure and blood pressure-power output slope in healthy women

Abstract Background A hypertensive response to exercise (HRE) is considered indicative of increased arterial stiffness (1). However, HRE is common in individuals with high cardiorespiratory fitness (CRF) (2), which we hypothesize is due to increased stroke volume (SV) and cardiac output (Qc). Purpose This study compared differences in CRF and peak-exercise SV (SVpeak) and Qc (Qcpeak) according to absolute and workload-indexed definitions of exercise hypertension in women. Methods Women free of overt CVD (n=142; 52±8years, BMI: 26.3±4.5kg/m2) underwent exercise cardiac magnetic resonance to quantify SVpeak and Qcpeak, and cardiopulmonary exercise testing to quantify peak VO2, power output (PO) and systolic blood pressure (SBP) responses. SBP-PO slope was determined using linear regression of SBP and PO values obtained every 2-minutes throughout exercise. HRE was defined as peak SBP ≥190mmHg (3), and elevated SBP-PO slope was defined as a slope &amp;gt;90th percentile for sex and age based on previously published values (4). Results 51% and 23% of the cohort met criteria for HRE and elevated SBP-PO slope, respectively, with 16% meeting both criteria. HRE was associated with higher VO2peak (2.03±0.53 vs 1.83±0.44 L/min, P=0.015), peak PO (191±66 vs 167±51 Watts, P=0.014), SVpeak (109±27 vs 98±19 mLs, P=0.008), and Qcpeak (15.1±3.3 vs 13.9±2.8 L/min, P=0.023). In contrast, elevated SBP-PO slope was associated with lower VO2peak (1.57±0.36 vs 2.04±0.48 L/min), peak PO (135±34 vs 192±60Watts) SVpeak (88±13 vs 108±24 mLs) and Qcpeak (12.5±1.8 vs 15.1±3.1 L/min; P&amp;lt;0.001 for all). Overall, the group with HRE and elevated SBP-PO slope had the lowest physical capacity, VO2peak and haemodynamic response to exercise (Figure 1A-D), whilst the opposite trend was seen for those with a HRE and a normal SBP-PO slope. All results remained significant (P&amp;lt;0.05) after adjustment for age, BMI, resting SBP and menopausal status (pre vs peri/post-menopausal). Conclusion Contextualising exercise SBP responses against measures of PO better accounts for confounding from increased Qcpeak, and may improve identification of women with increased arterial stiffness.Figure 1A-D

Differential response to interleukin-1 blockade with anakinra on cardiorespiratory fitness in patients with heart failure with preserved ejection fraction stratified according to ejection fraction

Abstract Background Patients with heart failure with preserved ejection fraction (HFpEF) are a heterogeneous clinical population and might respond differently to pharmacologic therapies based on their baseline left ventricular EF (LVEF) (50-59% vs. ≥60%). Interleukin-1 (IL-1) is a key pro-inflammatory cytokine being explored as a therapeutic target in HFpEF for its effects on numerous outcomes including cardiorespiratory fitness (CRF). Purpose Our aim was to examine changes in CRF and C-reactive protein (CRP), a surrogate for IL-1 activity, in patients with HFpEF treated with the IL-1 recombinant human receptor antagonist anakinra, stratified according to resting LVEF. Methods We analyzed data from 32 patients (median age 55 [51-64] years, 24 (75%) female) with HFpEF, defined as a presence of HF symptoms, LVEF≥50%, and evidence of left ventricular diastolic dysfunction or elevated filling pressures. All patients were treated with anakinra 100 mg subcutaneously daily for 12 [2-12] weeks. Patients were stratified into two groups: LVEF 50-59% and LVEF ≥60%. At baseline and during treatment, patients underwent cardiopulmonary exercise testing and venipuncture to measure changes in peak oxygen consumption (peak VO2) and CRP. Categorical and continuous variables are expressed as N (%) and median (interquartile range) and were compared with the chi-square and Mann-Whitney test, respectively. The within-group paired differences were compared using the Wilcoxon signed-rank test. Results The cohort included 15 patients with LVEF 50-59% and 17 with LVEF ≥60%, without significant differences in age and sex between groups. In patients with LVEF 50-59% and ≥60%, baseline peak VO2 was 14.1 [13.1–17.3] and 13.8 [11.8-18.6] mLO2·kg-1·min-1, respectively (p = 0.82), and CRP was 6.2 [3.4-15.9] and 6.1 [3.7-17.6] mg/L, respectively (p = 0.74). A significant increase in peak VO2 (from 13.8 [11.8-18.6] to 15.8 [12.7-19.9] mLO2·kg-1·min-1, p = 0.033) and decrease in CRP (from 6.2 [3.4-15.9] mg/L to 3.4 [1.0-6.7] mg/L, p = 0.003) was seen in patients with LVEF ≥60%; whereas in those with LVEF 50-59% there were no significant changes in peak VO2 (from 14.1 [13.1–17.3] to 14.1 [11.0–17.3] mLO2·kg-1·min-1, p = 0.25) despite a significant reduction in CRP (from 6.1 [3.7-17.6] mg/L to 1.4 [0.8-11.4] mg/L, p = 0.016). We found a difference in the interval changes in peak VO2 (0 [from -1.1 to +0.3] vs +1.7 [from -0.7 to +2.3] mLO2·kg-1·min-1 in patients with LVEF 50-59% and ≥60%, respectively, p = 0.01), without differences in the interval change in CRP levels (–3.5 [from -6 to -2.1] vs –3.0 [from -11.4 to -2.1] mg/L, respectively, p = 0.91). Figure 1. Conclusions Patients with HFpEF demonstrate differential peak VO2 response to anakinra treatment based on resting LVEF, with those with a LVEF ≥60% showing greater improvement in CRF. Further randomized control trials are needed to validate these data and explore the potential underlying mechanisms.

Cardiorespiratory Responses to an Acute Bout of High Intensity Interval Training and Moderate Intensity Continuous Training on a Recumbent Handcycle in People With Spinal Cord Injury: A Within-Subject Design.

To compare acute cardiorespiratory responses during high intensity interval training (HIIT) and moderate intensity continuous training (MICT) on a recumbent handcycle in persons with spinal cord injury (PwSCI). Eleven males and nine females with chronic SCI (T3 - L5), aged 23 (9) years, participated in this within-subject design. Based off peak power outputs from an incremental test to exhaustion, participants engaged in a HIIT and MICT session at matched workloads on a recumbent handcycle. Workloads (Joules), time, oxygen uptake (VO2), metabolic equivalent of task (MET), heart rate (HR), and energy expenditure (kcal) were recorded during HIIT and MICT. Total workload was similar across HIIT (87820 ± 24021 Joules) and MICT sessions (89044 ± 23696 Joules; p > .05). HIIT (20.00 [.03] minutes) was shorter in duration than MICT (23.20 [2.56]; p < .01). Average VO2 (20.96 ± 4.84 vs. 129.38 ± 19.13 mL/kg/min O2), MET (7.54 ± 2.00 vs. 6.21 ± 1.25), and HR (146.26 ± 13.80 vs. 129.38 ± 19.13 beats per minute) responses were significantly greater during HIIT than MICT (p < .01). Participants burned significantly more kilocalories during HIIT (128.08 ± 35.65) than MICT (118.93 ± 29.58; p < .01) and at a faster rate (6.40 ± 1.78 [HIIT] vs. 5.09 ± 1.14 [MICT] kcal/min; p < .01). HIIT elicits greater increases in oxygen uptake and HR than MICT in PwSCI. In significantly less time, HIIT also burned more calories than MICT.

Use of Near-InfraRed Spectroscopy (NIRS) during Vascular Occlusion Test (VOT) for predicting an increase in oxygen consumption after fluid challenge in circulatory shock patients

Background: The goal of fluid challenge (FC) is to increase cardiac output (CO) and oxygen delivery (DO2) (known as fluid responders) to correct tissue hypoxia. To optimize fluid administration, fluid challenge (FC) during dependence of oxygen consumption on oxygen delivery (VO2/DO2 dependency) would correct tissue hypoxia confirmed by an increase of oxygen consumption (VO2) and oxygen delivery (DO2) after FC (known as VO2 responders) and get more benefit from a reduction in tissue hypoxia. Markers of anaerobic metabolisms, such as blood lactate concentration or the ratio of venous-arterial CO2 tension difference (P(cv-a)CO2) over arterial-to-venous oxygen content difference (C(a-cv)O2), can predict VO2 responders but still have several limitations. Therefore, near-infrared spectroscopy (NIRS) has been developed to evaluate tissue perfusion, presented as tissue oxygen saturation (StO2), at the bedside. Combining StO2 with the vascular occlusive test (VOT) and introducing a short period of forearm ischemia is a non-invasive technique to examine microvascular alterations at the bedside. However, a study validating the ability of these variables to predict VO2 response has not been conducted. Methods: We plan to conduct a single-center prospective study on circulatory failure patients. The cardiac index (CI), oxygen delivery (DO2), oxygen consumption (VO2), arterial lactate, central venous oxygen saturation (ScvO2), ratio of venous-arterial carbon dioxide tension to arterial-to-central venous oxygen content difference (P(cv-a)CO2/ C(a-cv)O2), and tissue oxygen saturation measured by near-infrared spectroscopy (NIRS) probe during vascular occlusion test variables (NIRS-VOT variables) will be collected before and after the fluid challenge. Hypothesis: We hypothesize that markers of reactive hyperemia by NIRs will predict an increase in VO2 after FC in patients with circulatory shock. Ethics: The study protocol has been approved by the ethics committee of the faculty of medicine, Ramathibodi Hospital, Mahidol University (COA. MURA2022/80).

Dynamics of PO2 and VO2 in resting and contracting rat spinotrapezius muscle.

This study examined changes in interstitial PO2, which allowed calculation of VO2 during periods of rest, muscle contraction and recovery using an in situ rat spinotrapezius muscle preparation. The PO2 was measured using phosphorescence quenching microscopy and the muscle VO2 was calculated as the rate of O2 disappearance during brief periods of muscle compression to stop blood flow with a supra-systolic pressure. The PO2 and VO2 measurements were made during "5s compression and 15s recovery" (CR) cycles. With all three stimulation frequencies, 1, 2 and 4Hz, the fall in interstitial PO2 and rise in VO2 from resting values occurred within the first 20s of contraction. The PO2 during contraction became lower as stimulation frequency increased from 1 to 4Hz. VO2 was higher at 2Hz than at 1Hz contraction. With cessation of stimulation, PO2 began increasing exponentially towards baseline values. After 1 and 2Hz contraction, the fall in muscle VO2 was delayed by one CR cycle and then exponentially decreased towards resting values. After 4Hz stimulation, VO2 increased for 2 cycles and then decreased. The post-contraction transients of PO2 and VO2 were not synchronous and had different time constants. With further analysis two distinct functional responses were identified across all stimulation frequencies having PO2 during contraction above or below 30mmHg. The corresponding VO2 responses were different - for "high" PO2, muscle VO2 reached high levels, while for the "low" PO2 data set muscle VO2 remained low. Recovery patterns were similar to those described above. In summary, local microscopic PO2 and VO2 were measured in resting and contracting muscle in situ and the post-contraction transients of PO2 and VO2 were all much slower than the onset transients.

Cardiovascular responses of exercises performed within the extreme exercise domain.

Stroke volume (SV), heart rate (HR) and arterio-venous O2 difference (a-vO2diff) responses to heavy and severe-intensity exercise have been well documented; however, there is a lack of information on the SV, HR and a v-O2diff responses of work rates within extreme exercise domain. The aim of this study was, therefore, to focus on central and peripheral components of VO2 responses to exercises performed within the heavy, severe and extreme exercise domain. Eight well-trained male cyclists participated in this study. Maximal O2 consumption (VO2max) and corresponding work rate (P@VO2max) were determined by multisession constant work rate exercises. Cardiovascular responses to exercises were evaluated by nitrous-oxide rebreathing method with work rates from 40 % to 160 % of P@VO2max, VO2max corresponded to 324+/-39.4 W; however, maximal SV responses occurred at 205+/-54.3 W (p<0.01). Maximal cardiac output (Q), HR, and a vO2diff responses were revealed by the P@VO2max. VO2 response to exercise significantly decreased from severe-intense exercises to the first work rate of extreme exercise domain due to significant decreases in Q, SV, and HR responses (p<0.05), except a v-O2diff (p>0.05). Moreover, non-significant decreases in Q, SV, and a v-O2diff were evaluated as response to increase in work rate belonging to extreme work rates (p>0.05), except the HR (p<0.05). Work rates within the lower district of the extreme exercise domain have an important potential to improve peripheral component of VO2, while the P@VO2max seems the most appropriate intensity for aerobic endurance development as it maximizes the central component of VO2max.

Oxygen Uptake Kinetics and Time Limit at Maximal Aerobic Workload in Tethered Swimming.

This study aimed to apply an incremental tethered swimming test (ITT) with workloads (WL) based on individual rates of front crawl mean tethered force (Fmean) for the identification of the upper boundary of heavy exercise (by means of respiratory compensation point, RCP), and therefore to describe oxygen uptake kinetics (VO2k) and time limit (tLim) responses to WL corresponding to peak oxygen uptake (WLVO2peak). Sixteen swimmers of both sexes (17.6 ± 3.8 years old, 175.8 ± 9.2 cm, and 68.5 ± 10.6 kg) performed the ITT until exhaustion, attached to a weight-bearing pulley-rope system for the measurements of gas exchange threshold (GET), RCP, and VO2peak. The WL was increased by 5% from 30 to 70% of Fmean at every minute, with Fmean being measured by a load cell attached to the swimmers during an all-out 30 s front crawl bout. The pulmonary gas exchange was sampled breath by breath, and the mathematical description of VO2k used a first-order exponential with time delay (TD) on the average of two rest-to-work transitions at WLVO2peak. The mean VO2peak approached 50.2 ± 6.2 mL·kg-1·min-1 and GET and RCP attained (respectively) 67.4 ± 7.3% and 87.4 ± 3.4% VO2peak. The average tLim was 329.5 ± 63.6 s for both sexes, and all swimmers attained VO2peak (100.4 ± 3.8%) when considering the primary response of VO2 (A1' = 91.8 ± 6.7%VO2peak) associated with the VO2 slow component (SC) of 10.7 ± 6.7% of end-exercise VO2, with time constants of 24.4 ± 9.8 s for A1' and 149.3 ± 29.1 s for SC. Negative correlations were observed for tLim to VO2peak, WLVO2peak, GET, RCP, and EEVO2 (r = -0.55, -0.59, -0.58, -0.53, and -0.50). Thus, the VO2k during tethered swimming at WLVO2peak reproduced the physiological responses corresponding to a severe domain. The findings also demonstrated that tLim was inversely related to aerobic conditioning indexes and to the ability to adjust oxidative metabolism to match target VO2 demand during exercise.

Assembly of CQDs/mesoporous SiO2/VO2 composites with wide optical response and abnormal phase transition temperature

The rapid reversible metal-insulator transition (MIT) of vanadium dioxide (VO2) between the monoclinic and rutile phase brings about an abrupt change in optical properties. Until now, most researches focused on regulating near-infrared spectra and lowering phase transition temperature (Tc) while the optical response in the region of UV–vis and high Tc for VO2 are ignored. Herein, carbon quantum dots (CQDs) were introduced into mesoporous SiO2 microspheres and then CQDs/mesoporous SiO2/VO2 composites were synthesized in situ to expand the optical response and Tc range of VO2. Water bath time and annealing temperature have important influences on the morphologies and properties of as-prepared composites. The prolongation of hydrothermal time could promote the formation of VO2 nanoparticles. After annealing, the Tc for as-prepared CQDs/mesoporous SiO2/VO2 composites was in the range of 80.5–93.6 °C. The CQDs/mesoporous SiO2/VO2 composites exhibited broad and strong UV–vis absorption in the range of 200–1200 nm, and the sample prepared under the conditions of a water bath time of 3 h and annealing temperature of 550 °C had the maximum luminous transmittance (Tlum = 64.665 %) as well as the highest solar modulating ability (ΔTsol = 2.42 %). Therefore, the wide range of optical response and abnormal Tc besides typical phase transition behaviors for CQDs/mesoporous SiO2/VO2 composites have a potential application in the field of optical devices related to UV–vis region and high temperature environments.

Effect of the obese phenotype on expression of hepatic T4–5’ deiodinase activity, T3 generation and thyroidal mediated actions in congenic LA/Ntul//–cprats

Parameters of thyroidal responses to diet and environment have long been shown to be impaired in the obese phenotype of the LA/Ntul//–cp rat. To characterize the effect of expression of the obese phenotype on activity of maximum T4–5’ deiodinase (T4–DI) activity on adiposity and aspects of metabolism, groups of lean and obese littermates were subjected to measures of resting metabolic rate (RMR, VO2) at thermal neutrality (30°C) after a brief fast, followed by dose response Norepinephrine (NE) stimulation. Hepatic T4–DI activity represents a major source of hormonally active T3 in plasma and is readily delivered to peripheral tissues. At 16 weeks of age animals were sacrificed by cervical dislocation, blood was collected, and liver tissue was dissected for measures of serum levels of T3 and T4, and measures of maximal tissue dithiolthreitol (DTT)–stimulated T4–DI activity determined. The retroperitoneal and dorsal white adipose (WAT) depots were also dissected to estimate the magnitude of adiposity present upon sacrifice in each phenotype. Measures of RMR and the VO2 response to NE were greater in lean than obese phenotype, and indicators of BW and adiposity were much greater in obese than lean (p=&lt;0.01). Measures of serum T3 were greater in lean than obese, but T4 was similar in both phenotypes. Measures of the rate of hepatic T4 DI activity were greater in lean than obese (p=&lt;0.05), and the T1/2 for T4 disappearance were also prolonged in the obese phenotype. These results are consistent with other studies of impaired nonshivering thermogenesis in this strain, and suggest that decreased activity of hepatic T4–5’ deiodinase activity may be a contributing factor in the impaired capacity for nonshivering thermogenesis and excess fat accretion in the obese phenotype of this strain.

Physiological and biomechanical responses to exercise on two different types of rowing ergometers in NCAA Division I oarswomen.

Stationary (SE) and dynamic (DE) rowing ergometers, that are utilized for indoor training and physical assessment of competitive rowers, may elicit different physiological and biomechanical responses. The present study used SE and DE ergometers to examine submaximal and peak physiological and biomechanical responses during an incremental rowing test. Twelve National Collegiate Athletic Association (NCAA) Division I oarswomen performed seven-stage rowing tests with the last stage performed with maximal effort. Heart rate (HR), lactate (LA), oxygen uptake (VO2), ventilation (VE), stroke rate (SR), gross efficiency (GE), and rating of perceived exertion (RPE) were obtained; while trunk, hip, knee, shoulder, and elbow ranges of motion (ROM) were measured. SR was higher at maximal stage DE (29.3 vs. 34.8 strokes/min, p = 0.018, d = 1.213). No difference occurred in responses of maximal stage HR, RPE, VO2, VE, LA, or GE between the two ergometers. Submaximal LA and SR were greater on the DE for all submaximal stages. Submaximal VE was greater on the DE for all submaximal stages except Stage 3 (p = 0.160, d = 0.655). VO2 was higher on the DE Stages 2-5. GE was higher on the SE for Stages 2-5. Athletes showed increased trunk (p = 0.025, [Formula: see text] = 0.488) and knee (p = 0.004, [Formula: see text] = 0.668) ROM on SE. Rowing on the DE appears to elicit a greater stroke rate and more optimal joint angles especially at high intensities. Hence, the DE is worthy of consideration as a preferred ergometer for women rowers.

Can caffeine activate your brown fat? Effects of caffeine, ephedrine, and norepinephrine on nonshivering thermogenesis in congenic lean and obese LA/Ntul//-cp rats

To determine the effects of norepinephrine (NE) or of caffeine (CAF) alone or in combination with ephedrine (EPH) were determined in groups of lean and obese LA/Ntul//-cp Rats, Body weights of obese were &gt;&gt; lean littermates (p=&lt;0.01) and measures of RMR of lean &gt; Obese (p=&lt;0.05). The effects of caffeine, ephedrine, a caffeine+ephedrine combo, and the β- agonist epinephrine was examined. Caffeine (CAF) resulted in a 33% increase in VO2, ‘nonephedrine’ (EPH) a 48% increase, the combination CAF+EPH a 53% increase, and the NE a 33% increase in VO2. In obese rats, the increases in VO2 were of a similar percentage (21 vs 48 vs 47 % vs 31% for CAF, EPH, CAF+EPH and NE respectively although the peak responses attained in the obese tended to be of a significantly lesser absolute magnitude than were observed in the lean phenotype. The time to peak thermogenic response was similar in lean and obese phenotypes for each of the 4 treatment regimens, but the duration of the peak responses to each treatment differed between lean and obese phenotypes (Obese &gt; lean) for CAF, EPH and the CAF+EPH combination but duration of the VO2 response was similar in both phenotypes for the NE treatment. Thus, these observations are consistent with a significant CAF-stimulated thermogenic response that was qualitatively similar to that of NE in both lean and obese phenotypes of the congenic LA/Ntul//-cp rat and which thermogenic responses were further augmented with EPH alone or in combination with CAF. Although the mechanisms of action of the pharmacologic and physiologic mechanisms elicited may differ among the three agents studied the results indicate that they are complimentary in nature in bringing about increases in parameters of nonshivering thermogenesis and thus increasing metabolic energy expenditure in both lean and obese rats. In conclusion, while caffeine as monotherapy may bring about limited weight loss, the combination of caffeine plus ephedrine was more effective in the lean and obese phenotypes of the congenic, non-diabetic LA/Ntul//-cp (Corpulent) rat.

Oxygen Consumption and Heart Rate Responses in Different Vinyasa Yoga Sequences.

Yoga is widely practiced for its numerous health benefits, and it can also increase energy expenditure. Vinyasa yoga, a system of hatha yoga, meets criteria for moderate-intensity physical activity. It is unclear whether the individual sequences produce different oxygen consumption (VO2) and heart rate responses. The purpose of the present study was therefore to evaluate potential differences in VO2 and heart rate responses across sequences of a 60-minute vinyasa session. Participants included 40 healthy male (n = 20) and female (n = 20) adults (age 30.9 ± 8.8 y) with self-reported yoga experience. The sequence implemented was based on Baron Baptiste's Journey into Power sequence. This vinyasa yoga practice included several sequences: integration, sun salutation, crescent lunges, balancing, standing, back bending, and restorative. VO2 (mL/kg/min) was measured by portable indirect calorimetry and expressed as metabolic equivalents (MET). Heart rate was measured using a Polar HR monitor and presented as a percentage of age-predicted maximal heart rate (APMHR). METs and APMHR differed significantly across sequences (each p < 0.001). METs for the integration, sun-salutation, crescent-lunges, balancing, standing, back-bending, and restorative sequences were significantly different from one another (p < 0.001); balancing and back-bending sequences, however, were similar. During the integration and restorative sequences, APMHR was similar (p = 1.00) and significantly lower compared to sun-salutation, crescent-lunge, balancing, standing, and back-bending sequences (each p < 0.001). METs and APMHR differed significantly across sequences of a vinyasa yoga practice. These data could inform an individualized yoga series based on current fitness levels to maintain or improve cardiorespiratory fitness.

Functional threshold power is not a valid marker of the maximal metabolic steady state

ABSTRACT Functional Threshold Power (FTP) has been considered a valid alternative to other performance markers that represent the upper boundary of the heavy intensity domain. However, such a claim has not been empirically examined from a physiological perspective.This study examined the blood lactate and VO2 response when exercising at and 15 W above the FTP (FTP+15W). Thirteen cyclists participated in the study. The VO2 was recorded continuously throughout FTP and FTP+15W, with blood lactate measured before the test, every 10 minutes and at task failure. Data were subsequently analysed using two-way ANOVA. The time to task failure at FTP and FTP+15W were 33.7 ± 7.6 and 22.0 ± 5.7 minutes (p < 0.001), respectively. The VO2peak was not attained when exercising at FTP+15W (VO2peak: 3.61 ± 0.81 vs FTP+15W 3.33 ± 0.68 L·min−1, p < 0.001). The VO2 stabilised during both intensities. However, the end test blood lactate corresponding to FTP and FTP+15W was significantly different (6.7 ± 2.1 mM vs 9.2 ± 2.9 mM; p < 0.05). The VO2 response corresponding to FTP and FTP+15W suggests that FTP should not be considered a threshold marker between heavy and severe intensity.

Respiratory Threshold as A New Threshold Determination Method based on Respiratory Responses and It’s Success to Indicate Critical Power

Yeni bir solunumsal eşik türü olarak ortaya atılan respirasyon eşiği (RE) kademeli bir rampa testinde dakika ventilasyonu bölü ekspirasyon sonu CO2 kısmi basıncı (VE/PETCO2) değerindeki zamana bağlı değişimlerin analizine dayanır. Ancak RE tekniğinin yaygın olarak kullanılan önemli bir eşik belirleme yöntemi olan kritik gücü (KG) hangi düzeyde işaret edebildiğine odaklanan bir araştırma bulgusu rapor edilmemiştir. Bu çalışmanın amacı, RE tekniği kullanılarak elde edilen egzersiz şiddetinin, KG’yi hangi düzeyde karşılayabildiğini araştırmaktır. Çalışmaya iyi antrene on erkek bisiklet sporcusu katılmıştır. Sporcuların gaz değişim eşiği (GDE), solunumsal kompanzasyon noktası (SKN) ve RE düzeyleri kademeli rampa testleriyle belirlenmiştir. Bu testlerde GDE ve SKN düzeyleri, Innocor sistemi yoluyla VCO2-VO2 ve VE-VCO2 ilişkilerinde saptanan kırılmalar tespit edilerek değerlendirilmiştir. RE düzeyi SegReg paket programı kullanılarak VE/PETCO2-zaman ilişkisindeki en güçlü kırılma noktası tespit edilerek bulunmuştur. Sonrasında KG’yi hesaplamak için farklı günlerde sabit iş oranlarında testler uygulanmıştır. Tüm eşik göstergelerinin birbirleriyle ilişkilerinin sınanması için geçerlik analizleri yapılmıştır. Bulgular, RE (328±35,5 W; 4,23±0,39 L·dk−1) ile SKN (324±34,3 W; 4,21±0,45 L·dk−1) güç çıktıları ve her birine ait VO2 yanıtları arasında yüksek bir ilişki ve uyum olduğunu göstermiştir (p&amp;gt;0,05; t= 1,19; r&amp;gt;0,96; % tahmini standart hata &amp;lt;5). Ancak hem RE hem de SKN güç çıktıları KG'den (298±32 W) yaklaşık %10 daha yüksek bulunmuştur (p&amp;lt;0,001). Çalışmamız, iyi antrene bisikletçilerde VE/PETCO2-zaman ilişkisinde oluşan en güçlü kırılmanın çok büyük bir başarı ile SKN’yi gösterdiğini, fakat KG’yi doğrudan belirlemede başarısız olduğunu ortaya koymuştur.