RPE drift during cycling in 18 degrees C vs 30 degrees C wet bulb globe temperature.

AIM: The potential influence of a hotter vs cooler environment on ratings of perceived exertion (RPE) estimations during longer duration exercise is not well-understood. This study compared overall and differentiated RPEs during cycling in 18 degrees C vs 30 degrees C wet bulb globe temperature (WBGT). METHODS: Male volunteers (n=16) completed a maximal cycling trial (60 rev . min(-1), 25 Watts . min(-1)) to determine VO(2) max and ventilatory threshold (VT) before completing 2 (counterbalanced) longer duration cycling trials. At 30 degrees C WBGT (30C) and 18 degrees C WBGT (18C), subjects cycled 60 min (60 rev . min(-1), 90% individualized VT). Heart rate (HR, b . min(-1)) and rectal temperature (Tre, degrees C) were recorded every 5 min with corresponding RPE-overall (RPE-O), RPE-legs (RPE-L) and RPE-chest (RPE-C) estimations. RESULTS: HR was not significantly different at 5 min but was greater (P<0.05) for 30C at all other time points. During 30C, Tre was significantly greater (25, 30, 35, 40, 45, 50, 55 and 60 min), RPE-O was significantly greater (5, 40, 45, 50, 55 and 60 min), RPE-L was significantly greater (55 and 60 min) and RPE-C was significantly greater (35, 40, 45, 50, 55 and 60 min). CONCLUSIONS: Greater cardiovascular (HR) and thermal (Tre) strain partially explain greater perceptual ratings during 30C. Discernible RPE differences resulted mid-way through 60 min cycling with minimal differences initially. Results suggest RPEs are magnified in a 30 degrees C (vs 18 degrees C) environment beyond 30 min duration. Additionally, a 30 degrees C environment resulted in a less pronounced impact on RPE-L (vs RPE-C and RPE-O).

Influence of aerobic fitness on ratings of perceived exertion during graded and extended duration cycling.

AIM: Ratings of perceived exertion (RPE) have been shown similar across subjects of varying fitness when estimations are made at relative physiological criteria. Because few studies have investigated the influence of fitness during longer duration bouts, the current investigation compared overall exertion (RPE-O), leg exertion (RPE-L) and breathing/chest exertion (RPE-C) between aerobically fit and unfit subjects. METHODS: Aerobically fit (61.6+/-2.5 mL . kg . min(-1)) (n=7) and unfit (41.8+/-6.3 mL . kg . min(-1)) (n=6) males completed a maximal bike test and then cycled for 60 min at approximately 90% of individualized ventilatory threshold (VT) (V(E)/VO(2) vs V(E)/VCO(2)). Heart rate (HR, b . min(-1)), rectal temperature (Tre, degrees C) and RPE estimations were collected during graded testing every 2 min and every 10 min during 60 min bouts. RESULTS: During graded testing, RPE estimations at VT were not significantly different between groups. During 60 min cycling, HR and Tre were not significantly different between groups. Also, there were no significant differences for HR increase (HR 60 min HR 5 min) or Tre increase (Tre 60 min Tre 5 min). Interactions between groups were; RPE-O (P=0.09), RPE-L (P=0.06) and RPE-C (P=0.19). Analyses suggest groups experienced similar relative cardiovascular (HR) and thermal (Tre) strain. CONCLUSIONS: Although RPE responses between groups were similar at 10, 20 and 30 min, RPE drift was magnified in aerobically unfit subjects (vs aerobically fit subjects) beyond the 30 min point. Contrary to previous studies suggesting aerobic fitness does not influence RPE, current results show lower aerobic fitness magnifies RPE at individualized relative intensities when cycling extends beyond 30 min.

RPE-lactate dissociation during extended cycling.

This study examined the association of blood lactate concentration [La] and heart rate (HR) with ratings of perceived exertion (RPE) during 60 min of steady workload cycling. Physically active college-aged subjects (n = 14) completed an exhaustive cycling test to determine VO(2) (peak) and lactate threshold (2.5 mmol l(-1)). Subjects then cycled for 60 min at the power output associated with 2.5 mmol l(-1) [LA]. HR, [LA], RPE-overall, RPE-legs and RPE-chest were recorded at 5, 10, 20, 30, 40, 50 and 60 min. The 60-min trials were below maximal lactate steady state, with peak lactate concentration occurring at 20 min after which [LA] declined. The 20-min point was therefore considered pivotal, and data at other points were compared to this time point. Repeated measures ANOVA with simple contrasts (alpha = 0.05) showed (a) [LA] at 40, 50 and 60 min was significantly lower than at 20 min, (b) RPE-O and RPE-L were significantly greater at 30, 40, 50 and 60 min than at 20 min, (c) RPE-C was significantly greater at 40, 50 and 60 min than at 20 min, and (d) HR was significantly greater at 30, 40, 50 and 60 min than at 20 min. Significant (P < 0.05) positive correlations were found between HR and RPE-O (r = 0.43), RPE-L (r = 0.48) and RPE-C (r = 0.41) while correlations for [LA]-HR (r = 0.13) and [LA]-RPE (RPE-O: r = -0.11, RPE-L: r = 0.01, RPE-C: r = -0.06) were weak and non-significant. There is a dissociation of RPE and [LA] owing to RPE drift and lactate kinetics in longer duration sub-maximal exercise. Apparently, [LA] is not a strong RPE mediator during extended cycling.

Sweat lactate response during cycling at 30 degrees C and 18 degrees C WBGT.

Sweat lactate reflects eccrine gland metabolism. However, the metabolic tendencies of eccrine glands in a hot versus thermoneutral environment are not well understood. Sixteen male volunteers completed a maximal cycling trial and two 60-min cycling trials [30 degrees C = 30 +/- 1 degrees C and 18 degrees C = 18 +/- 1 degrees C wet bulb globe temperature (WBGT)]. The participants were requested to maintain a cadence of 60 rev min(-1) with the intensity individualized at approximately 90% of the ventilatory threshold. Sweat samples at 10, 20, 30, 40, 50 and 60 min were analysed for lactate concentration. Sweat rate at 30 degrees C (1380 +/- 325 ml x h(-1)) was significantly greater (P < 0.05) than at 18 degrees C (632 +/- 311 ml x h(-1)). Sweat lactate concentration was significantly greater (P < 0.05) at each time point during the 18 degrees C trial, with values between trials tending to converge across time. During the 30 degrees C trial, both heart rate (20, 30, 40, 50 and 60 min) and rectal temperature (30, 40, 50 and 60 min) were significantly higher than in the 18 degrees C trial. Higher sweat lactate concentrations coupled with lower sweat rates may indicate a greater relative contribution of oxygen-independent metabolism within eccrine glands during exercise at 18 degrees C. Decreases in sweat lactate concentration across time suggest either greater dilution due to greater sweat volume or increased reliance on aerobic metabolism within eccrine glands. The convergence of lactate concentrations between trials may indicate that time-dependent modifications in sweat gland metabolism occur at different rates contingent partially on environmental conditions.

Sweat lactate response between males with high and low aerobic fitness.

Sweat lactate indirectly reflects eccrine gland metabolism. However the potential influence of aerobic fitness on sweat lactate is not well-understood. Six males with high aerobic fitness [peak oxygen consumption ( VO(2)peak): 61.6 (2.5) ml.kg(-1).min(-1)] and seven males with low aerobic fitness [ VO(2)peak: 41.8 (6.4) ml.kg(-1).min(-1)] completed a maximal exertion cycling trial followed on a different day by 60 min of cycling (60 rev.min(-1)) in a 30 degrees C wet bulb globe temperature environment. Intensity was individualized at 90% of the ventilatory threshold ( V(E)/ VO(2) increase with no concurrent V(E)/ VCO(2) increase). Sweat samples were collected from the lumbar region every 10 min and analyzed for lactate concentration. Sweat rate (SR) was significantly greater ( p<0.05) for subjects with a high [1445 (254) ml.h(-1)] versus a low [1056 (261) ml.h(-1)] fitness level. Also, estimated total lactate excretion (SRxmean sweat lactate concentration) was marginally greater ( p=0.2) in highly fit males. However, repeated measures ANOVA showed no significant differences ( p>0.05) between groups for sweat lactate concentration at any time point. Current results show highly fit (vs. low fitness level) males have a greater sweat rate which is consistent with previous literature. However aerobic fitness and subsequent variations in SR do not appear to influence sweat lactate concentrations in males.

Overall and differentiated ratings of perceived exertion at the respiratory compensation threshold: effects of gender and mode.

Research on gender differences in ratings of perceived exertion (RPE) has been equivocal with few studies comparing exercise modes and differentiated RPE. The current study examined gender differences in overall and differentiated RPE at the respiratory compensation threshold (RCT) during cycling and treadmill exercise. Each minute during a maximal treadmill and maximal cycling test, men (n=18) and women (n=16) estimated RPE corresponding to overall (RPE-O), legs (RPE-L), and breathing/chest (RPE-C) exertion. A 2 (gender) x 2 (mode) x 3 (RPE-O, RPE-L, RPE-C) repeated measures MANOVA revealed no significant mode x gender or RPE x gender interactions. The exercise mode x RPE interaction approached significance (P=0.055) when cycling [mean (SD) 14.8 (2.9)] and treadmill exercise [12.8 (2.9)] were compared. No main effects for gender [men: 13.7 (2.6), women: 13.4 (2.6)] were detected. Main effects for mode showed RPE to be significantly greater during cycling [14.4 (2.8)] versus treadmill exercise [12.7 (2.9)]. Main effects for differentiated RPE showed RPE-L [13.8 (2.6)] to be significantly greater than RPE-O [13.5 (2.6)] and RPE-C [13.3 (2.6)]. Results suggest that overall and differentiated RPE at the RCT are not significantly different between genders during cycling or treadmill exercise. While RPE-L was statistically greater than RPE-O and RPE-C, the magnitude of the differences makes this result of little practical significance. The marginal interaction suggests greater RPE-L values might be expected at the RCT during cycling versus treadmill exercise. However, results suggest that minimal RPE differences exist between men and women during cycling and treadmill exercise.

Physiological responses at 0% and 10% treadmill incline using the RPE estimation-production paradigm.

BACKGROUND: This study examined physiological responses during 0% and 10% inclined treadmill exercise at prescribed ratings of perceived exertion (RPE) using the perceptual estimation-production paradigm. METHODS: RPE's were estimated during a Bruce treadmill test to volitional exhaustion. Subjects then produced individually prescribed RPE's (associated with 50% and 70% VO2max) during level (0% grade) and inclined (10% grade) treadmill exercise. Heart rate response (HR) and oxygen consumption (VO2) were compared between estimation (EST), level production (LPR), and incline production (IPR) trials using one-way repeated measures ANOVA. Results were considered significant at < or = 0.05. RESULTS: At 50% VO2max, HR and VO2 were not significantly different between EST (134 +/- 13 b x min-1, 27.1 +/- 5.6 ml x kg x min-1) and IPR (139 +/- 18 b x min-1, 30.6 +/- 11.2 ml x kg x min-1). However, HR and VO2 during LPR (123 +/- 20 b x min-1, 24.3 +/- 8.8 ml x kg x min-1) were significantly lower than IPR. For 70% VO2max, HR and VO2 were not significantly different between EST (168 +/- 9 b x min-1, 42.1 +/- 9.4 ml x kg x min-1) and IPR (169 +/- 14 b x min-1, 41.1 +/- 10.2 ml x kg x min-1). However HR and VO2 during LPR (155 +/- 17 b x min-1, 35.1 +/- 8.1 ml x kg x min-1) were significantly lower than during EST and IPR. CONCLUSIONS: Results suggest physiological responses during RPE estimation-production trials correspond better when estimation and production trials were performed at a similar treadmill incline. For exercise prescription purposes, RPE estimations made during inclined treadmill exercise may require adjustments to achieve appropriate intensities during level treadmill exercise.

Serotonergic modulation of the P13 midlatency auditory evoked potential in the rat.

The vertex-recorded, sleep state-dependent P13 midlatency auditory evoked potential in the rat may be generated, in part, by pedunculopontine nucleus (PPN) projections. Injections into the PPN of the 5-HT(1A) serotonin receptor agonist, 8-hydroxy-2-di-n-propylaminotetralin hydrobromide (DPAT), were found to reduce the amplitude of the P13 potential in a dose- and time-dependent manner. The suppressive effect of DPAT was blocked or reduced by pretreatment with the 5-HT(1A) serotonin receptor antagonist, Pindobind. These results show that the P13 potential can be modulated by known inhibitory serotonergic inputs to the PPN.

Antigenic domains of the open reading frame 2-encoded protein of hepatitis E virus.

The antigenic composition of the hepatitis E virus (HEV) protein encoded by open reading frame 2 (ORF2) was determined by using synthetic peptides. Three sets of overlapping 18-, 25-, and 30-mer peptides, with each set spanning the entire ORF2 protein of the HEV Burma strain, were synthesized. All synthetic peptides were tested by enzyme immunoassay against a panel of 32 anti-HEV-positive serum specimens obtained from acutely HEV-infected persons. Six antigenic domains within the ORF2 protein were identified. Domains 1 and 6 located at the N and C termini of the ORF2 protein, respectively, contain strong immunoglobulin G (IgG) and IgM antigenic epitopes that can be efficiently modeled with peptides of different sizes. In contrast, antigenic epitopes identified within the two central domains (3 and 4) were modeled more efficiently with 30-mer peptides than with either 18- or 25-mers. Domain 2 located at amino acids (aa) 143 to 222 was modeled best with 25-mer peptides. A few 30-mer synthetic peptides derived from domain 5 identified at aa 490 to 579 demonstrated strong IgM antigenic reactivity. Several 30-mer synthetic peptides derived from domains 1, 4, and 6 immunoreacted with IgG or IgM with more than 70% of anti-HEV-positive serum specimens. Thus, the results of this study demonstrate the existence of six diagnostically relevant antigenic domains within the HEV ORF2 protein.

Biochemical analysis of the secreted and virion glycoproteins of Ebola virus.

The glycoproteins expressed by a Zaire species of Ebola virus were analyzed for cleavage, oligomerization, and other structural properties to better define their functions. The 50- to 70-kDa secreted and 150-kDa virion/structural glycoproteins (SGP and GP, respectively), which share the 295 N-terminal residues, are cleaved near the N terminus by signalase. A second cleavage event, occurring in GP at a multibasic site (RRTRR downward arrow) that is likely mediated by furin, results in two glycoproteins (GP1 and GP2) linked by disulfide bonding. This furin cleavage site is present in the same position in the GPs of all Ebola viruses (R[R/K]X[R/K]R downward arrow), and one is predicted for Marburg viruses (R[R/K]KR downward arrow), although in a different location. Based on the results of cross-linking studies, we were able to determine that Ebola virion peplomers are composed of trimers of GP1-GP2 heterodimers and that aspects of their structure are similar to those of retroviruses, paramyxoviruses, and influenza viruses. We also determined that SGP is secreted from infected cells almost exclusively in the form of a homodimer that is joined by disulfide bonding.

An electron-capture dienophile derivatization agent for increasing sensitivity: determination of a vitamin D analog (Ro 24-2090) in plasma samples with liquid chromatography/mass spectrometry.

A practical analytical method has been developed for the determination of an analog of vitamin D3 (Ro 24-2090) in plasma samples. The method employs liquid-liquid extraction, precolumn derivatization, HPLC separation using an automated column-switching system, and particle-beam negative ionization MS determination. An electron-capture derivatization reagent, 4-pentafluorobenzyl-1,2,4-triazoline-3,5-dione, is utilized to attain high sensitivity through a unique ionization mechanism. The method achieved a lower limit of quantitation of 25 pg (63 fmol) of Ro 24-2090 in plasma aliquots ranging from 0.125 to 1.0 ml. Method validation data were obtained for the quantitation of Ro 24-2090 in plasma from humans and seven animal species. Intraassay precision [mean percent relative standard deviation (%RSD)] ranged from 1.49 to 7.12% among the various species. Interassay precision (mean %RSD) ranged from 4.28 to 17.5%. Mean overall recovery ranged from 71 to 89%. The method has been successfully used to analyze plasma samples from several pharmacokinetic studies. The potential use of this method for determination of vitamin D2, vitamin D3, 1 alpha, 25-dihydroxyvitamin D3, and other drugs containing a diene structural moiety is discussed.

Simultaneous modeling of the pharmacokinetics and pharmacodynamics of midazolam and diazepam.

The pharmacokinetics and pharmacodynamics of midazolam and diazepam were compared after intravenous infusions of 0.03 and 0.07 mg/kg midazolam and 0.1 and 0.2 mg/kg diazepam on four separate occasions in 12 healthy male subjects in a randomized four-way crossover design. The Digit Symbol Substitution Test (DSST) was used as a measure of drug effect. Subjects performed three practice tests before dosing to account for any effects caused by familiarization ("learning curve") with the testing procedure. Pharmacokinetic and pharmacodynamic data were simultaneously fitted to a semiparametric model. In this model, a pharmacokinetic model related dose to plasma concentrations, a link model related plasma concentrations to the concentration at the effect site, and a pharmacodynamic model related the effect site concentration to the observed effect. The plasma-effect site equilibrium half-life was approximately 2 1/2 times longer for midazolam than for diazepam, which is in good agreement with previously published data. Based on the estimated effect site concentration at which half of the maximal effect was reached, midazolam had approximately a sixfold greater intrinsic potency than diazepam. This difference in potency was also observed in a previous study that used transformed electroencephalographic (EEG) data to assess pharmacodynamic activity. The findings reported here with a clinically relevant pharmacodynamic marker (DSST) confirm the utility of surrogate drug effect measures such as EEG. This work also shows the feasibility of conducting pharmacokinetic pharmacodynamic analysis during the drug development process.

Determination of Ro 19-6327 (Lazabemide) in human plasma and urine by gas chromatography-negative chemical ionization mass spectrometry.

A sensitive and specific analytical method was developed for determination of Ro 19-6327 (Lazabemide) in human plasma and urine samples to provide pharmacokinetic data from clinical trials. The new method employs a simple liquid-liquid extraction to isolate the drug from biological samples. The extract is reacted to form the trifluoroacetyl derivative of Ro 19-6327 and then analyzed by gas chromatography-negative chemical ionization mass spectrometry (GC-NCIMS). The lower limit of quantitation of the assay is 0.05 ng/ml for plasma and 5.0 ng/ml for urine, based on 1-ml aliquots. No interferences from anticoagulants, collection devices, or endogenous constituents of plasma and urine were observed. Recovery (64.3%), inter-assay precision (< 8% R.S.D.), and accuracy (> 85%) of the method were considered acceptable. The assay proved reliable enough to be automated for unattended sample analysis of approximately 50 samples daily. In an additional series of tests, Ro 19-6327 was shown to be stable under conditions that might be encountered during the analysis of samples from clinical trials.

The pharmacokinetic-pharmacodynamic (Digit Symbol Substitution Test) relationship of flumazenil in a midazolam steady-state model in healthy volunteers.

To characterize the plasma concentration-effect relationship of flumazenil in the presence of a predefined midazolam level, a double-blind, placebo-controlled, randomized two-way crossover study was conducted in nine healthy male subjects. After reaching a criterion level of midazolam-induced depression of the Digit Symbol Substitution Test (DSST), volunteers received a dose of flumazenil (1.0 mg) or placebo over 1 minute, with the infusion of midazolam continued. Blood samples were collected, simultaneously with the DSST assessment, at predetermined intervals and were assayed for flumazenil and/or midazolam plasma concentrations. Pharmacokinetic-pharmacodynamic modeling techniques were used to estimate the equilibration rate constant (keo) between plasma concentration and effect for flumazenil; a sigmoidal maximum-effect model was used to relate the DSST score to the flumazenil plasma concentration. Flumazenil exhibited a rapid onset (the half-life of equilibration between drug concentration in the blood and drug effect was 3.3 minutes) and short duration of action (the flumazenil plasma concentration causing half-maximal effect was 7.4 ng/ml, which was reached about 1 hour after dosing). The results of this study also show the competitive nature of flumazenil as a midazolam antagonist.

Using adapted short MASTs for assessing parental alcoholism: reliability and validity.

In previous research adapted versions of the Short Michigan Alcoholism Screening Test (SMAST) have been employed to assess an individual's father's (F-SMAST) and mother's alcohol abuse (M-SMAST). However, to date psychometric information on these forms has been limited. In order to more broadly assess the psychometric properties of these forms, several critical issues in five related studies were addressed. The samples for the five studies were drawn from a college population at a large midwestern university. Overall, the reliability and validity of the adapted SMASTs appears to be quite good. The F-SMAST demonstrated high reliability (from the standpoint of internal consistency, temporal stability, and reliability across siblings) as well as validity (both in respect to convergence with an interview measure and with father's own report on a parallel instrument). Furthermore, shortening both of these instruments to nine-item versions appears to improve their reliability and validity. For researchers and clinicians interested in assessing parental history of alcoholism, the F-SMAST and M-SMAST would appear to be a reliable and valid paper-and-pencil measure.

Quantitative determination of naltiazem in human plasma by gas chromatography/mass spectrometry.

A gas chromatographic/mass spectrometric procedure has been developed for the quantification of a diltiazem analog, naltiazem, in human plasma. The assay utilizes an extraction at neutral pH with hexane:ethylene dichloride:methyl-t-butyl ether (70:20:10), selective ion monitoring, methane or ammonia positive chemical ionization mass spectrometry and stable isotope dilution. The method has been used to analyze plasma concentrations of naltiazem in clinical samples over a range of 2-200 ng ml-1, using 1 ml of plasma.