Biomedical subjects

D W Hill

Publications and source records attributed to D W Hill.

At least 19 recordsLinked to original sources

PubMed1999

A physiological description of critical velocity.

Although critical velocity (CV) provides a valid index of aerobic function, the physiological significance of CV is not known. Twelve individuals performed exhaustive runs at 95% to 110% of the velocity at which VO2max was attained in an incremental test. VO2max was elicited in each run. Using the time to exhaustion at each velocity, CV was calculated for each participant. Using the time to achieve VO2max at each velocity, which was shorter at higher velocities, a parameter we have designated as CV' was calculated for each participant. During exercise at or below CV', VO2max cannot be elicited. CV (238+/-24 m x min(-1)) and CV' (239+/-25 m x min(-1)) were equal (t = 0.60, p = 0.56) and correlated (r = 0.97, p < 0.01). These results demonstrate that CV is the threshold intensity above which exercise of sufficient duration will lead to attainment of VO2max.

Adult↗

PubMed1999

Determination of critical power by pulmonary gas exchange.

Although the physiological underpinnings of critical power (CP) have yet to be fully elucidated, it has been proposed that CP demarcates the heavy and severe exercise intensity domains and that each domain is associated with a different pattern of metabolic response and mechanism of fatigue. Severe intensity has been defined such that, during exercise at intensities above CP, the slow component of the VO2 response will drive VO2 to VO2max at the point of fatigue. In this study, two parameters were derived for each of 8 participants: (a) CP, the asymptote of the relationship between power and time to exhaustion, and (b) a related parameter; CP', the asymptote of the relationship between power and time to VO2max. CP' theoretically represents the threshold intensity above which VO2max will be elicited during exercise of sufficient duration. Participants performed two exhaustive tests at CP. There were three important findings: First, there was a practice effect on time to exhaustion at CP, and times increase 27% in the second test. Second, both CP and CP' could be obtained with good precision. Third, and most important, CP was equal to CP', thereby providing a physiological description of the mathematically derived CP parameter. It was concluded that VO2max cannot be elicited at intensities equal to or less than CP.

Adult↗

PubMed1998

Simultaneous variation of temperature and gradient steepness for reversed-phase high-performance liquid chromatography method development. I. Application to 14 different samples using computer simulation.

The optimized reversed-phase HPLC separation of 14 different samples is reported, based on simultaneous changes in temperature and gradient steepness. Four experimental runs are required for each sample, following which preferred conditions can be predicted using computer simulation software (DryLab). The overall accuracy and effectiveness of this method development approach is discussed, with particular attention to the use of resolution maps provided by the software. These maps are useful for maximizing resolution for the total sample, for optimizing the separation of a smaller number of selected sample compounds, and as an initial step in the separation of more demanding samples.

Adrenal Cortex Hormones↗

PubMed1998

An alternative method to determine maximal accumulated O2 deficit in runners.

An accepted measure of anaerobic capacity is the maximal O2 deficit. But it is not feasible to use O2 deficit if > or =10 submaximal runs are needed to extrapolate the O2 demand of high velocity running (Medbø et al. 1988). Recently, an alternative method to determine O2 deficit was proposed (Hill 1996) using only results of supramaximal cycle ergometer tests. The purpose of this study was to evaluate this alternative method with data from treadmill tests. Twenty-six runners ran at 95%, 100%, 105%, and 110% of their velocity at VO2max. Times to exhaustion, velocity, and accumulated oxygen uptake (VO2) from each individual's four tests were fit to the following equation using iterative nonlinear regression: accumulated VO2 = (O2 demand x velocity x time)-O2 deficit. The mean value s derived for O2 demand and O2 deficit were 0.198+/-0.031 ml x kg(-1) x m(-1) and 42+/-22 ml x kg(-1). SEE for the parameters were 0.007+/-0.007 ml x kg(-1) x m(-1) and 8+/-10 ml x kg(-1), respectively. Mean R2 was 0.998+/-0.003. It was concluded that O2 deficit can be determined from all-out treadmill tests without the need to perform submaximal tests.

Adult↗

PubMed1998

Immediate response of retinal vessels to isometric muscle contraction.

Isometric muscle contraction results in a rise in systemic blood pressure (BP) and constriction of retinal arterioles. The responses in the anaesthetised cat have been studied to provide further insight into the results of human studies. Constriction (median 3.43% of control values) and dilatation (median 4.17% of control values) were observed; the onset of constriction was delayed by 4 s compared with dilatation. There was spatial and temporal variation in the observed calibre changes, and inter-experimental variation in the calibre change/BP ratio. It is concluded that the response of retinal arterioles of measurable size is not unified, and that the two modes of response differ in mechanism.

Animals↗

PubMed1998

Temporal specificity in adaptations to high-intensity exercise training.

OBJECTIVE: The purpose was to test the hypothesis that time to exhaustion and oxygen deficit in high-intensity exercise at a particular time of day would be influenced by training regularly at that time of day. METHODS: Over a 5-wk period, 12 college-age women performed 20 high-intensity exercise training sessions. On Mondays, they performed four 2-min bouts of cycling at 2.5 W x kg(-1) with 4-min recoveries; on Tuesdays and Thursdays, eight 1-min bouts at 3.0 W x kg(-1) with 2-min recoveries; and on Wednesdays, three 3-min bouts at 2.2 W x kg(-1) with 2-min recoveries. Six participants (a.m.-trained group) were randomly assigned to train in the morning (a.m.) and six others (p.m.-trained group) trained in the afternoon (p.m.). Upon completion of training, all participants were tested in both the a.m. and p.m. (random order) at the same times as training sessions had been scheduled. Tests involved exhaustive efforts at 2.6 W x kg(-1). RESULTS: Results of a repeated measures ANOVA revealed a significant time of day of training x time of day of testing interaction effect on time to exhaustion (F1,10=8.29, P=0.02). This suggested that the time of day of training affected the a.m.-p.m. pattern in time to exhaustion. Time to exhaustion for the a.m.-trained group was 398+/-258 s in the a.m. test and 351+/-216 s in the p.m. test (P=0.07). The p.m.-trained group had significantly higher values in the p.m. test compared with the a.m. test (422+/-252 s vs 373+/-222 s; P=0.03). There was also a significant interaction effect on oxygen deficit (F1,10=8.03, P=0.02). This suggested that the time of day of training affected the a.m.-p.m. pattern in anaerobic capacity. Oxygen deficit for the a.m.-trained group was 64+/-24 mL x kg(-1) in the a.m. test and 50+/-11 mL x kg(-1) in the p.m. test (P=0.10). The p.m.-trained group had significantly higher values in the p.m. tests (64+/-24 mL x kg(-1) vs 50+/-11 mL x kg(-1); P=0.01) compared to the a.m. tests. CONCLUSIONS: These results demonstrate that there is temporal specificity in training to increase work capacity in high-intensity exercise. Greater improvements can be expected to occur at the time of day at which high-intensity training is regularly performed.

Adaptation, Physiological↗

PubMed1998

The anticarcinogenic conjugated fatty acid, 9c, 11t-18:2, in human milk: confirmation of its presence.

The concentration of the anticarcinogenic fatty acid, 9c, 11t-18:2, in human milk was determined by gas-liquid chromatography (GLC). The mean concentration of 20 samples from 5 women taken at 1, 7, 14, and 21 days was: 0.18% +/- 0.02; range, 0.14-0.28%. Identity was confirmed by GLC-mass spectrometry (MS). Conjugated isomers other than 9c, 11t-18:2 were not detected. The amounts were not changed by supplementation of the maternal diet with fish oil beginning on day 1 after the milk sample was taken.

Anticarcinogenic Agents↗

PubMed1998

Influence of time of day on anaerobic capacity.

12 volunteers performed exhaustive exercise tests in the morning and afternoon. Paired-means t tests indicated that anaerobic capacity, as reflected by maximal accumulated oxygen deficit, was 26% higher (p < .01) in the afternoon than in the morning. VO2max appeared higher and VO2 kinetics seemed faster in the afternoon, but differences did not attain statistical significance. Thus, the time of day affects anaerobic capacity and may influence other responses to exercise.

Adult↗

PubMed1998

Isolation, purification, and structural characterization of flunixin glucuronide in the urine of greyhound dogs.

A urinary metabolite of flunixin in greyhound dogs was isolated and purified by a gradient-elution solid-phase extraction technique. The purified metabolite was shown to be hydrolyzed to free flunixin by strong base and by beta-glucuronidase, suggesting the presence of a C1-beta-glucuronide ester of flunixin. The metabolite was further characterized by positive-ion, tandem MS with electrospray ionization. Mass spectral data showed the presence of a protonated molecular ion (M+1) at m/z 473, which was consistent with the molecular weight of protonated flunixin glucuronide, and a product ion at m/z 297, which was consistent with the molecular weight of protonated flunixin. Collisionally induced dissociation of the m/z 297 product ion showed a fragmentation pattern consistent with that of standard flunixin. These data support the contention that this metabolite of flunixin in greyhound urine is the C1-beta-glucuronide of flunixin. Acyl glucuronide metabolites of some organic acid drugs have been shown to bind covalently to tissue proteins in vitro, in vivo, and ex vivo. The presence of this metabolite may, therefore, have pharmacokinetic and pharmacodynamic implications for flunixin in greyhound dogs, as well as in other animal species in which the acyl glucuronide of flunixin is a metabolite.

Analgesics↗

PubMed1998

Improved GC/MS analysis of opiates with use of oxime-TMS derivatives.

An improved gas chromatographic/mass spectrometric (GC/MS) assay is described for the quantitation of codeine and morphine as trimethylsyl (TMS) derivatives. The TMS derivatization of ketone-containing opiates results in the formation of multiple derivatives. Some of these products have retention times close to those of codeine-TMS and morphine-TMS. When the keto-opiates are present in samples assayed for codeine and morphine in urine, they can interfere with the quantitation of these commonly targeted opiates. The assay was improved with the addition of a pre-BSTFA derivatization step, whereby hydroxylamine was used to convert the keto-opiates into the corresponding oxime derivative. These derivatives were then reacted with BSTFA to form the TMS ethers and TMS oxime derivatives. The oxime step enabled production of single derivatives for hydrocodone and hydromorphone. In addition, the retention times for the oxime-TMS derivatives were increased so that they no longer elute near the targeted drugs of codeine and morphine. The addition of the oxime step does not affect the sylation of codeine and morphine, and the accuracy and precision of this assay were unaffected.

Codeine↗

PubMed1997

Responses to exercise at 92% and 100% of the velocity associated with VO2max.

The purpose of this study was to evaluate the rationale for using the velocity associated with VO2max (vVO2max) and the time that vVO2max can be sustained (tMAX) in exercise prescription. Six male runners performed a 0%-slope incremental treadmill test to determine their VO2max (61.6 +/- 9.1 ml x kg(-1) x min(-1)) and the velocity at which it was elicited (vVO2max; 271 +/- 18 m x min(-1)). Then, they performed exhaustive tests at vVO2max and at 92% of vO2max. VO2max in these tests (4.56 +/- 0.55 and 4.57 +/- 0.50 l x min(-1)) were not different from the incremental value (4.31 +/- 0.83 l x min(-1)). At vVO2max, VO2max was attained after 299 +/- 74 s and sustained for 32 +/- 41 s. At 92% of vVO2max, it took longer to attain VO2max (491 +/- 156 s), but it was sustained longer (130 +/- 66 s). Since no athlete reached VO2max in the first 60% of the runs, the results did not provide a rationale to support the recommendation that athletes train at vVO2max for a fixed percentage of tMAX when the goal in the training session is to maintain VO2max.

Adult↗

PubMed1997

The analysis of thebaine in urine for the detection of poppy seed consumption.

The consumption of poppy seeds in various foods may lead to a positive opiate result in urine subjected to testing for drugs of abuse. As a natural constituent of poppy seeds, thebaine was investigated as a possible marker for poppy seed consumption. Poppy seeds were examined for opiate content by gas chromatography-ion trap mass spectrometry (GC-MS) after extraction with methanol. Urine samples spiked with thebaine and urine from subjects given 11 g of poppy seeds were tested for the presence of thebaine, codeine, and morphine. Street heroin, one morphine and one codeine tablet, and urine from individuals who had used heroin were also examined for thebaine. Urine specimens were screened by enzyme immunoassay (EMIT) and confirmed for thebaine by GC-MS using a solid-phase extraction method. The GC-MS assay showed a linear response over a range of 1-100 ng/mL and a limit of detection of 0.5 ng/mL. Thebaine was detectable in the urine of poppy seed eaters in concentrations ranging from 2 to 81 ng/mL. Because thebaine was absent in powdered drugs and the urine of true opiate drug users, thebaine is proposed as a direct marker for poppy seed use.

Codeine↗

PubMed1997

Responses to exercise at the velocity associated with VO2max.

The purpose of this study was to assess the significance of the velocity at which an individual achieves VO2max in an incremental treadmill test (Vmax) and the time that this velocity can be sustained (Tmax) to evaluate the rationale for using Vmax and Tmax in the prescription of endurance exercise training. Mean (+/- SD) values for VO2max, and Vmax in 13 female track athletes were 52.1 +/- 5.1 ml.kg.min-1 and 271 +/- 18 m.min-1, respectively. Then each athlete performed an exhaustive run at her Vmax. In these runs, VO2max was achieved after 234 +/- 49 s and was maintained for 56 +/- 48 s (range, 10-155 s) which was the last 18 +/- 13% (range, 4-47%) of the total exercise bout. Only one of the 13 subjects reached VO2max in the first 60% of the constant velocity test. Thus, while VO2max was attained during exhaustive exercise at Vmax, the amount of time that it was sustained was quite small (less than 60 s) and highly variable. It was concluded that Vmax is a suitable intensity to elicit VO2max in training. But 60% (or less) of Tmax is not an appropriate duration for training at this intensity because it is too short a time to allow most athletes to reach VO2max.

Adult↗

PubMed1996

Combined use of temperature and solvent strength in reversed-phase gradient elution. I. Predicting separation as a function of temperature and gradient conditions.

It has been shown previously that computer simulation based on two initial experiments can predict separation in reversed-phase gradient elution as a function of gradient conditions (gradient steepness, gradient range and gradient shape) and column conditions (column length, flow-rate and particle size). The present study extends this capability for changes in temperature. Four initial experiments (two different gradient times, two different temperatures) provide input data that allow predictions of separation as a function of temperature as well as gradient and column conditions. A semi-empirical relationship, tR = a + bT, is able to relate gradient retention time tR to column temperature T (other conditions constant). The accuracy of this approach has been evaluated for 102 solutes and a variety of experimental conditions, including the use of five different HPLC instruments (four different models).

Chromatography, High Pressure Liquid↗

PubMed1996

Significance of time to exhaustion during exercise at the velocity associated with VO2max.

In theory, time to exhaustion at the velocity associated with VO2max (tLIM at vVO2max) together with the anaerobic threshold (AT) should provide information about the anaerobic capacity of an individual. The primary purpose of this study was to test that hypothesis, using oxygen deficit as a criterion for anaerobic capacity. A second purpose was to identify factors that might explain the large inter-individual variability reported in tLIM at vVO2max. Subjects were 13 female track athletes who performed incremental treadmill tests to determine VO2max and AT and constant velocity tests at vVO2max to determine tLIM and oxygen deficit. Correlations between oxygen deficit and tLIM at vVO2max and [(tLIM at vVO2max).(VO2max-AT)], a compound variable derived based on the critical power concept, were 0.51 (p < 0.05, one-tailed) and 0.67 (p < 0.01). To identify factors related to the inter-individual variability in tLIM at vVO2max, correlations between tLIM and AT, oxygen deficit, and [oxygen deficit/(VO2max-AT)] were calculated. Intra-individual differences in AT explained 44% of the variability in tLIM at vVO2max, oxygen deficit explained 26% of the variance, and the compound variable explained only 36%. It was concluded that (a) alone, or in combination with AT, tLIM at vVO2max cannot be used to estimate anaerobic capacity and (b) factors other than anaerobic capacity and AT contribute to the relatively large intra-individual variability in tLIM at vVO2max (CV = 21%). Determinants of tLIM at vVO2max must be elucidated if this measure is to be of use to sport scientists.

Adult↗

PubMed1996

Trauma life support education: a didactic and caprine laboratory course for Nigerian physicians.

The purpose of this study was to introduce the principles of initial hospital assessment and treatment of injured patients, tailored to the facilities and resources available in Nigeria. A 3-day didactic and laboratory course was presented by four trauma surgeons. The didactic session stressed the initial assessment and treatment of injured patients. The caprine laboratory taught the performance of common resuscitation manoeuvres: cricothyroidotomy, tube thoracostomy, i.v. cut-down, diagnostic peritoneal lavage, etc. The mean pre-course test score was 49.3 per cent and the mean post-course test score was 69.5 per cent; 93.5 per cent of the 124 participants increased their test scores. This represents a significant increase in knowledge in Nigerian physicians. Academic medical centres are encouraged to make such courses available in developing countries.

Animals↗

PubMed1996

Effect of protocol on determination of velocity at VO2 max and on its time to exhaustion.

The velocity associated with the achievement of VO2 max during an incremental treadmill test (v VO2 max) has been reported to be an indicator of performance in middle distance running events. Previous study has shown the reproducibility of the time to exhaustion (time limit: tlim) at v VO2 max performed by well-trained males in the same condition at one week of interval (Billat et al., 1994b). It is essential in studies involving tlim at v VO2 max that the v VO2 max be precisely determined, or else the measured tlim will be meaningless. The purpose of this study was to examine the influence of the stage duration and velocity incrementation on the velocity at VO2 max and, consequently, on the two times to exhaustion (tlim) associated with the two v VO2 max generated by the two protocols. v VO2 max was determined in 15 trained male endurance athletes as the lowest speed at which VO2 max was attained in speed-incremented 0%-slope treadmill tests. For one test, increments were 1.0 km.h-1 and stages were 2 min in duration; for the other test, increments were 0.5 km.h-1 and stages were 1 min in duration. Results of paired means t-tests revealed no difference in v VO2 max obtained using the two protocols. v VO2 max was 20.7 +/- 1.0 km.h-1 with the 1.0 km.h-1 x 2 min protocol and 20.8 +/- 0.9 km.h-1 with the 0.5 km.h-1 x 1 min protocol. In addition, VO2, VCO2, VE, VE/VO2 and respiratory exchange ratio at the submaximal intensities that were common to both protocols (e.g., 17.0 km.h-1, 18.0 km.h-1, 19.0 km.h-1, 20.0 km.h-1) did not differ. Times to exhaustion at the two v VO2 max demonstrated a high degree of inter-individual variability (coefficients of variation were 35% and 45%) but did not differ (345 +/- 120 s versus 373 +/- 169 s). These results demonstrated that small changes in protocol have no significant impact on the value of v VO2 max and in consequence on tlim v VO2 max.

Adult↗

PubMed1996

Influence of locus of control on mood state disturbance after short-term sleep deprivation.

Twenty-eight healthy university students were classified as having either an internal (n = 14) or external (n = 14) locus of control. Before and after 26-30 hours of sleep deprivation, their mood state was evaluated using the Profile of Mood States questionnaire. There was a significant sleep status x locus of control interaction effect on mood state disturbance (p = 0.049). In the individuals with an external locus of control, there was an increase (p < 0.001) in total mood disturbance from (mean +/- standard deviation) 115 +/- 23 during baseline testing to 148 +/- 22 after sleep loss (effect size = 1.4). Sleep loss did not significantly affect total mood disturbance in the subjects with an internal locus of control (115 +/- 26 vs. 128 +/- 34). These results suggest that locus of control is a factor that influences the degree of mood state disturbance caused by short-term sleep deprivation.

Adult↗