Estimation of %V˙O2 reserve from heart rate during arm exercise and running

The purpose of the present investigation was to examine the relationship between the percent heart rate reserve (%HRR) in arm exercise and the corresponding percent oxygen uptake (V˙O₂) reserve, and to compare this relationship to that occurring in running. Fourteen male physical education students took part in the study. Each subject performed a maximal running exercise test and a maximal arm cycling test. The subjects also performed three submaximal exercise bouts (in both exercise modes) at 30%, 60% and 80% of their HRR. The subjects were monitored for their heart rate (HR) at rest, maximal HR (HR_max), HR at submaximal work loads, maximal V˙O₂ (V˙O_2max), V˙O₂ at rest and V˙O₂ at submaximal loads. For each subject, load and exercise mode, %HRR and %V˙O₂ reserve were calculated (from HR_max and V˙O_2max as measured during running and arm cycling) and the relationship between the two was evaluated. The main finding of the present investigation is that the prediction of %V˙O₂ reserve in arm cycling from %HRR is grossly overestimated when calculated from HR_max and V˙O_2max measured during running. The prediction is better but still overestimated when calculated from HR_max and V˙O_2max measured during arm cycling. The findings indicate a better prediction of %V˙O₂ reserve from %HRR for running than for arm exercise. These findings should be taken into consideration when prescribing the target HR for arm training. Accepted: 24 July 2000     

Overshoot in <Emphasis Type="Italic">V̇</Emphasis>O<Subscript>2</Subscript> following the onset of moderate-intensity cycle exercise in trained cyclists

We have previously observed that following the onset of moderate intensity cycle ergometry, the pulmonary O₂ uptake (O₂) in trained cyclists often does not increase towards its steady-state value with the typical mono-exponential characteristics; rather, there is a transient overshoot. The purpose of this study was to systematically examine this phenomenon by comparing the O₂responses to two moderate-intensity work rates and one high-intensity work rate in trained and untrained subjects. Following a ramp exercise test to the limit of tolerance for the determination of the gas exchange threshold (GET) and O_2peak, seven trained cyclists [mean (SD); O_2peak 66.6 (2.5) ml·kg^–1·min^–1] and eight sedentary subjects [O_2peak 42.9 (5.1) ml·kg^–1·min^–1] completed six step transitions from baseline cycling to work rates requiring 60% and 80% GET and three step transitions from baseline cycling to a work rate requiring 50% of the difference between GET and O_2peak (50%). O₂ was measured breath-by-breath and modelled using standard techniques. The sedentary subjects did not overshoot the steady-state O₂ at any intensity. At 60% GET, six of the seven cyclists overshot the steady-state O₂ [by an integral volume of 164 (44) ml between ~45 and 125 s]. At 80% GET, four of the seven cyclists overshot the steady-state O₂ [by an integral volume of 185 (92) ml between ~55 and 140 s]. None of the cyclists showed an overshoot at 50%. These results indicate that trained cyclists evidence an overshoot in O₂ before steady-state is reached in the transition to moderate-intensity exercise. The mechanism(s) responsible for this effect remains to be elucidated, as does whether the overshoot confers any functional or performance benefit to the trained cyclist.     

Effect of sampling strategy on measures of<Emphasis Type="Italic"> V̇</Emphasis>O<Subscript>2peak</Subscript> obtained using commercial breath-by-breath systems

The purpose of this study was to determine the effect of sampling strategy (i.e., number of breaths) on measured peak rate of oxygen uptake (V̇O_2peak) elicited by a range of severe intensity exercise bouts. The hypothesis was that a smaller sample (i.e., fewer breaths) would produce a higher measure of V̇O_2peak and that this effect would be greater in shorter tests than in longer tests. Thirty-three university students performed constant-power cycle ergometer tests at intensities selected to elicit fatigue in ~3.0 min (short duration), ~5.5 min (medium duration), and ~8.0 min (long duration). Values for V̇O_2peak were the highest rates of oxygen uptake obtained using the following sampling methods: single breath, and 3-, 5-, 15- and 30-breath rolling averages. As hypothesized, measures of V̇O_2peak increased systematically with decreasing sample size. Contrary to the hypothesis, the effect of sample size was greater in medium duration and long duration tests than in the short duration tests. The interaction between test duration and sample size on measures of V̇O_2peak highlights the importance of standardizing the analysis protocol for exercise in the severe domain. If such standardization is not feasible, it should be recognized that specific analysis protocols may exert a substantial effect upon the reported V̇O_2peak.     

Effect of H<Subscript>1</Subscript>-antagonist Dithiaden<Superscript>®</Superscript> on human PMN-leukocyte aggregation and chemiluminescence is stimulus-dependent

OBJECTIVE AND DESIGN: Contradictory data published on histamine-PMN leukocyte interactions stimulated us to study to the role of histamine and H1-antagonist Dithiaden in generation of reactive oxygen species (ROS) and aggregation of human neutrophils. METHODS AND MATERIALS: Whole blood or isolated PMN-leukocytes were exposed in a dose-dependent way to histamine or H1-antagonist Dithiaden and subsequently stimulated. Whole blood was stimulated with opsonised zymosan (OZ). Isolated cells were stimulated with membrane stimuli (OZ, N-formyl-methionyl-leucyl-phenylalanine--fMLP), or membrane bypassing stimuli (Ca2+-ionophore A23187, phorbol-myristate-acetate--PMA). The luminol-enhanced chemiluminescence (CL) was measured separately (whole blood) in a luminometer or simultaneously with neutrophil aggregation in a whole blood lumiaggregometer. RESULTS: Depending on the concentration used, Dithiaden" was 1.5- to 25.0-times more effective in inhibiting activated CL of whole blood than histamine. In isolated neutrophils both histamine and Dithiaden inhibited OZ- and A23187-stimulated CL dose-dependently, with potentiation observed after stimulation with PMA and fMLP. Histamine did not alter aggregation with any of the stimuli tested. Dithiaden inhibited A23187-, OZ- and PMA-stimulated PMN-leukocytes but potentiated fMLP-induced aggregation of isolated neutrophils. Simultaneous application of Dithiaden and histamine abolished the effect of Dithiaden on fMLP-stimulated CL. CONCLUSIONS: Dithiaden, depending on the stimuli applied, inhibited human neutrophils, both isolated or in whole blood, more markedly than histamine. The inhibition of aggregation and CL was dose- and stimulus-dependent. Histamine administered simultaneously abolished the effect of Dithiaden on fMLP-stimulated PMN-leukocytes. It seems likely that the interaction of Dithiaden with neutrophils operated both at an extra- and intracellular level.     

Effect of an α<Subscript>1</Subscript>-adrenergic blocker on plasticity elicited by motor training

Recovery of motor function elicited by motor training after cortical lesions in rats is enhanced by norepinephrine (neurotransmitter mediating α₁-adrenergic function) and downregulated by α₁-adrenergic antagonists. In spite of this, α₁-adrenergic antagonists are used to treat elderly patients with hypertension and prostate hyperplasia in stroke settings. The purpose of this study was to determine the effects of a single oral dose of the α₁-adrenergic antagonist prazosin on training-dependent plasticity in intact humans, a function thought to contribute to recovery of motor function after cortical lesions. We report that prazosin decreased the ability of motor training to elicit training-dependent plasticity relative to a drug-free condition. These data suggest caution when using α₁-adrenergic blockers in rehabilitative clinical settings following brain lesions. Electronic Publication     

The Role of Integrin α<Subscript>4</Subscript>β<Subscript>7</Subscript> in HIV Pathogenesis and Treatment

Purpose of Review

Acute HIV infection is characterized by high-level viral replication throughout the body’s lymphoid system, particularly in gut-associated lymphoid tissues resulting in damage to structural components of gut tissue. This damage is irreversible and believed to contribute to the development of immune deficiencies. Antiretroviral therapy (ART) does not restore gut structure and function. Studies in macaques point to an alternative treatment strategy that may ameliorate gut damage. Integrin α₄β₇ mediates the homing of lymphocytes to gut tissues. Vedolizumab, a monoclonal antibody (mAb) antagonist of α₄β₇, has demonstrated efficacy and has been approved for the treatment of inflammatory bowel disease in humans. Here, we describe our current knowledge, and the gaps in our understanding, of the role of α₄β₇ in HIV pathogenesis and treatment.

Recent Findings

When administered to macaques prior to infection, a nonhuman primate analogue of vedolizumab prevents transmission of SIV. In combination with ART, this mAb facilitates durable virologic control following treatment interruption.

Summary

Targeting α₄β₇ represents a novel therapeutic approach to prevent and treat HIV infection.

     

Estimation of<Emphasis Type="Italic"> V̇</Emphasis>O<Subscript>2max</Subscript> from the ratio between HR<Subscript>max </Subscript>and HR<Subscript>rest</Subscript> – the Heart Rate Ratio Method

The effects of ̇raining and/or ageing upon maximal oxygen uptake (O_2max) and heart rate values at rest (HR_rest) and maximal exercise (HR_max), respectively, suggest a relationship between O_2max and the HR_max-to-HR_rest ratio which may be of use for indirect testing of O_2max. Fick principle calculations supplemented by literature data on maximum-to-rest ratios for stroke volume and the arterio-venous O₂ difference suggest that the conversion factor between mass-specific O_2max (ml·min^–1·kg^–1) and HR_max·HR_rest ^–1 is ~15. In the study we experimentally examined this relationship and evaluated its potential for prediction of O_2max. O_2max was measured in 46 well-trained men (age 21–51 years) during a treadmill protocol. A subgroup (n=10) demonstrated that the proportionality factor between HR_max·HR_rest ^–1 and mass-specific O_2max was 15.3 (0.7) ml·min^–1·kg^–1. Using this value, O_2max in the remaining 36 individuals could be estimated with an SEE of 0.21 l·min^–1 or 2.7 ml·min^–1·kg^–1 (~4.5%). This compares favourably with other common indirect tests. When replacing measured HR_max with an age-predicted one, SEE was 0.37 l·min^–1 and 4.7 ml·min^–1·kg^–1 (~7.8%), which is still comparable with other indirect tests. We conclude that the HR_max-to-HR_rest ratio may provide a tool for estimation of O_2max in well-trained men. The applicability of the test principle in relation to other groups will have to await direct validation. O_2max can be estimated indirectly from the measured HR_max-to-HR_rest ratio with an accuracy that compares favourably with that of other common indirect tests. The results also suggest that the test may be of use for O_2max estimation based on resting measurements alone.An erratum to this article can be found at     

The slow component of V̇O2 kinetics in very heavy and fatiguing square-wave exercise

We hypothesized that oxygen consumption (O₂) rises incrementally in very heavy and fatiguing exercise where the slow component gain increases with higher work rates. Eight trained males completed a graded exercise test and bouts of square-wave cycle ergometry at 40% and 60% of the difference between the estimated lactate threshold (LT) and O_2peak (designated 40%D and 60%D). Exhaled gases were collected and analyzed every breath using models that allowed for a linear slow component or a slow component with one or more exponential increments. All subjects were able to complete 30 min at 40%D but not at 60%D. The slow component was generally best fit with two increments at 40%D and two or three increments at 60%D. In further (<Emphasis Type=Italic>, our results question the reliability of determining parameters of multiple slow component increments when repeated bouts are averaged together. This study demonstrates that O₂ can continue to rise incrementally beyond the onset of the slow component in very heavy and fatiguing exercise. These results support the concept of a recurring mechanism underlying the slow component of O₂ kinetics during square-wave exercise and suggest that the dynamics (time of onset, rate of development, magnitude) of this mechanism may vary from day to day.     

The differential contribution of dopamine D<Subscript>1</Subscript> and D<Subscript>2</Subscript> receptors to μ-opioidergic immunomodulation

Activation of μ-opioid receptors (μ-OR) by the highly selective agonist DAGO (100 μg/kg) significantly increased the immune response in CBA mice. This effect of the μ agonist was prevented by prior blockade of dopamine D₂ receptors with haloperidol (2 mg/kg). In contrast, the selective D₁ receptor antagonist SCH 23390 (1 mg/kg) had no effect on the nature of the immune reaction in response to antigen (sheep erythrocytes, 5·10⁸ cells). However, blockade of both types of dopamine receptor led to the same effect-immunosuppression. These data lead to the suggestion that D₁ and D₂ receptors make different contributions to modulating immunogenesis on activation of μ-OR. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 92, No. 5, pp. 546–551, May, 2006.     

Effects of priming exercise intensity on the dynamic linearity of the pulmonary V̇O2 response during heavy exercise

Prior heavy-intensity exercise facilitates the pulmonary oxygen uptake (O₂) response during subsequent exercise, such that its kinetics returns towards first-order. To better understand this priming phenomenon, we investigated the effect of priming exercise, over a range of intensities, on the O₂ response to heavy-intensity cycle ergometry at a work rate of 50% [halfway between lactate threshold (LT) and O_2max]. Eight subjects performed two consecutive 6-min bouts separated by 6 min at 20 W. The first bout was each of: no warm-up control (CON), sub-lactate threshold (LT) at 80% of LT, and three supra-LT conditions (20%, 40%, and 60%). The O₂ response during the subsequent bout was evaluated using the effective time constant (), and the O₂ difference between minutes 3 and 6 (O_2(6–3)). The goodness-of-fit, indicative of first-order kinetics, was determined by the residual profile, and the mean square of errors (MSEr). The heart rate and blood lactate concentration ([La]r) just prior to the second bout were also measured. Compared with CON, and O_2(6–3) were significantly reduced following all supra-LT priming bouts, while the goodness-of-fit was significantly improved following 40% exercise. O_2(6–3) and [La]r were negatively correlated (P<0.05), unlike HR. In conclusion, prior exercise just above, but not below, LT facilitated the O₂ response in a threshold-like manner. Supra-LT priming exercise influenced the O₂ response allowing it to return to within as little as 12% from first-order (compared to ~50% in CON). The associated increases in circulating lactate and/or related factors seem to be centrally involved in this phenomenon.     

Role of Intracellular Calcium and Cyclic Nucleotides in Realization of Cardioprotective Effects of δ<Subscript>1</Subscript>- and κ<Subscript>1</Subscript>-Opioid Receptor Agonists

The role of cyclic nucleotides (cAMP, cGMP) and Ca²⁺-ATPase of the sarcoplasmic reticulum in the mechanism of cardioprotective effects of selective δ₁- and κ₁-opioid receptor agonists DPDPE and U-50488 was studied under conditions of global ischemia and reperfusion of isolated and perfused rat heart. Activation of both types of opioid receptors 2-fold reduced the reperfusion release of creatine phosphokinase. The cardioprotective effect of U-50488 was paralleled by a 2-fold decrease in cAMP content in the myocardium, while DPDPE did not modify the content of cAMP throughout the experiment. None of these substances changed the content of cGMP in the myocardium. The cardioprotective effect of DPDPE was not observed after inhibition of sarcoplasmic reticulum Ca²⁺-ATPase with cyclopiazonic acid. The cardioprotective effect of U-50488 was associated with reduction of cAMP level in the myocardium, while the cytoprotective effect of DPDPE was mediated by opioidergic modulation of Ca²⁺ transport at the level of the sarcoplasmic reticulum.     

Expression of Transforming Growth Factor-β<Subscript>2</Subscript> in Vitreous Body and Adjacent Tissues during Prenatal Development of Human Eye

Expression of transforming growth factor-β₂ was detected by PCR in the vitreous body, lens, retina, and ciliary-iris complex of human eye at early stages of fetal development. Immunochemical assay of the corresponding protein in eye tissues revealed a correlation between the localization of transforming growth factor-β₂ and the development of intraocular hyaloid vascular network, its regression, formation of the vitreous body, and development of definite retinal vessels.     

Effect of IFN-α on CC1<Subscript>4</Subscript>-Induced Fibrosis of the Liver and Immune Status in Mice of Different Age

In young, adult, and old mice fibrosis was induced by administration of CC1₄ and treated with IFN-α. Liver fibrosis was evaluated by morphometry of argyrophilic fibers, immune status by the splenocyte proliferative response. Minimum immunosuppression and maximum antifibrotic effect were observed in young mice, while adult mice exhibited pronounced immunotoxicity and weak response to interferon therapy.__________Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 139, No. 3, pp. 303–306, March, 2005     

Opioid Peptide Deltorphin II Simulates the Cardioprotective Effect of Ischemic Preconditioning: Role of δ<Subscript>2</Subscript>-Opioid Receptors,Protein Kinase C,and K<Subscript>ATP</Subscript> Channels

The cardioprotective properties of a δ₂-opioid receptor agonist deltorphin II were studied in rats with coronary occlusion and reperfusion. Opioid receptor ligands and inhibitors (glybenclamide, chelerythrine, and 5-hydroxydecanoate) were injected intravenously before ischemia and reperfusion. A δ₂-opioid receptor agonist deltorphin II signifi cantly decreased the infarction zone/risk zone index. This effect was abolished by naltrexone, naloxone methiodide, and δ₂-opioid receptor antagonist naltriben, but not by a δ₁-opioid receptor antagonist BNTX. The infarct-limiting effect of deltorphin II was not observed after inhibition of protein kinase C or blockade of mitochondrial K_ATP channels.     

Oxytocin and prostaglandins F<Subscript>2α</Subscript> and E<Subscript>2</Subscript> do not enhance HIV antigen production <Emphasis Type="Italic">in vitro</Emphasis>

Summary.  Oxytocin and prostaglandins (PGs) are hormones involved in labor and are used clinically for its induction. In this study the effect of oxytocin, PGF_2α, and PGE₂ on Humour immunodeficiency virus-1 production in acutely and persistently infected cells was measured. No significant effect on p24 antigen production was found with oxytocin or PGs, except for a transient decrease in persistently infected cells treated with 1 μM PGF_2α. These results showed that oxytocin and PGs could be used clinically for labor induction without any direct enhancement in viral production. Besides, the results with PGF_2α at the highest concentration studied may indicate a pharmacological effect. Received October 10, 2002; accepted October 28, 2002     

Circulatory “Efficacy” during progressive aerobic exercise in children: insights from the <Emphasis Type="Italic">Q</Emphasis>: <Emphasis Type="Italic">V</Emphasis>O<Subscript>2</Subscript> relationship

The relationship between circulatory flow (Q) and oxygen uptake ( ) may provide insights into performance of peripheral mechanisms which govern blood flow during exercise (circulatory efficacy). This study evaluated the response of Q relative to during progressive upright cycle exercise in a group of 39 preadolescent boys (mean age 12.2 ± SD 0.5 years). The Q– relationship was curvilinear, best described by the cubic equation Q = 3.60()³ + 5.24()² + 2.40() − 0.94. Circulatory efficacy, defined as the %ΔQ/%Δ × 100, fell from 70.4% between the first two workloads to 49.7% at peak exercise. This decline in circulatory efficacy is consistent with other published data suggesting a decline in skeletal muscle pump function at high intensity workloads. The pattern of change in relationship of Q and during progressive exercise in these children is similar to that observed in studies of adults. This implies that performance of peripheral determinants of circulatory responses to exercise is not affected by biological maturation.     

Interaction of Afobazole with σ<Subscript>1</Subscript>-Receptors

The capacity of living systems to perceive low-intensity stimuli sometimes inducing protective reactions is still little studied. Incubation of neurons under conditions increasing the content of cAMP and Ca²⁺ increases the amplitude of their responses to lidocaine (10⁻³ M). After cell preconditioning with low concentrations of lidocaine (10⁻¹⁵ M) under these conditions, the protective effects of “ineffective” concentrations were detected, because the response amplitude did not decrease. It was hypothesized that the basic amplitude responses retrieved by lidocaine in a concentration of 10⁻³ M are memory traces about the effects of this compound in subthreshold concentrations. Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 147, No. 1, pp. 43-46, January, 2009