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PubMed1994

Effect of supine exercise on platelet aggregation and fibrinolytic activity.

In 12 healthy young men, strenuous cycling exercise in the supine position, caused platelet aggregability to decrease and the ADP threshold to rise from 7.0 microM resting, to 9.5 exercising (P < 0.01). At the same time, fibrinolytic activity increased markedly: euglobulin clot lysis time shortened from 178 to 68 min, PAI-1 fell from 8.91 to 5.16 IU ml-1, and t-PA rose from 0.56 to 3.95 IU ml-1, all three values were significant to P < 0.01. When the erect posture was assumed after lying at ease for 1 h after exercise, it did not increase platelet activity as expected, but caused a modest increase of fibrinolytic activity. These results suggest that supine exercise will not affect the haemostatic system adversely.

Adult↗
PubMed1998

Sodium bicarbonate ingestion does not attenuate the VO2 slow component during constant-load exercise.

We examined the effects of sodium bicarbonate ingestion on the VO2 slow component during constant-load exercise. Twelve physically active males performed two 30-min cycling trials at an intensity above the lactate threshold. Subjects ingested either sodium bicarbonate (BIC) or placebo (PLC) in a randomized, counterbalanced order. Arterialized capillary blood samples were analyzed for pH, bicarbonate concentration ([HCO3-]), and lactate concentration ([La]). Expired gas samples were analyzed for oxygen consumption (VO2). The VO2 slow component was defined as the change in VO2 from Minutes 3 and 4 to Minutes 28 and 29. Values for pH and [HCO3-] were significantly higher for BIC compared to PLC. There was no significant difference in [La] between conditions. For both conditions there was a significant time effect for VO2 during exercise; however, no significant difference was observed between BIC and PLC. While extracellular acid-base measures were altered during the BIC trial, sodium bicarbonate ingestion did not attenuate the VO2 slow component during constant-load exercise.

Adult↗
PubMed1998

Bayesian analysis of twinning and ovulation rates using a multiple-trait threshold model and Gibbs sampling.

The Multiple-Trait Gibbs Sampler for Animal Models programs were extended to allow analysis of ordered categorical data using a Bayesian threshold model. The algorithm is based on data augmentation, where a value on the unobserved underlying normally distributed variable (liability) is generated in each round of iteration for each categorical observation. The programs allow analysis of several continuous and ordered categorical traits. Categorical traits can have any number of response levels. Models can be different for each trait. The programs were used to analyze twinning and ovulation rates from a herd of cattle selected for twinning rate at the U.S. Meat Animal Research Center. Data included number of calves born at each parturition for the lifetime of a cow and number of eggs ovulated for several estrous cycles before first breeding as heifers. A total of 6,411 calvings was recorded for 2,087 cows with 83.2% single and 16.8% multiple births. A total of 19,849 ovulations was recorded for 2,332 heifers with 85.2% single and 14.8% multiple ovulations. Mean posterior estimates of heritability and fraction of variance accounted for by permanent environmental effects (PE) were .128 and .103 for twinning rate and .168 and .079 for ovulation rate. Mean posterior estimate of genetic correlation was .808, and correlation of PE effects was .517. Use of a threshold model could allow for more rapid genetic improvement of the twinning herd through improved identification and selection of genetically superior animals because of higher heritability on the underlying scale.

Algorithms↗
PubMed1997

A new method for data presentation in incremental cardiorespiratory exercise testing.

In incremental cardiopulmonary exercise testing, the averaging of data is usually performed to provide group mean data for statistical purposes. They are usually presented as averaged maximum values, or as averaged data at different exercise levels. However, during incremental exercise testing the change in metabolic status may vary between subjects, thus averaging data may not classify the metabolic status accurately. We present an averaging method using a segmented ordinal scale based on individual maximal work performance and the anaerobic threshold (AT). Individual exercise data are grouped into ten classes ranging from unloaded exercise to maximal exercise. The classes are defined in relation to the AT, resulting in an ordinal scale of four classes for exercise data below the AT, one class at the AT and five classes beyond the AT. Resting and unloaded pedalling are treated as separate classes. For evaluation, this method of classification is compared to one based on an absolute scale of oxygen uptake (Cabs) and to another based on a relative scale in 10% steps of maximal oxygen uptake (Crel). Ten healthy male subjects (mean age 23.3 years) performed a ramp cycle ergometer test. When using the Cabs classification method for mean data averaging, mean values for performance at high-intensity exercise were calculated using data from only two of the ten subjects because of variations in individual work capacity. In addition, the AT data were distributed across four classes, thus anaerobic and aerobic exercise data were mixed. Using the Crel classification method enabled data for all ten subjects to be included in the calculation of every data point, but the AT values were still distributed across three classes, resulting in the mixing of anaerobic and aerobic exercise data. However, using the segmented ordinal scale method of classification enabled data from all ten subjects to be included in the calculation of all data points, and it permitted the grouping of the AT values into one class. Thus, this latter method more accurately represents the data of the whole group under study and it allows the metabolic status of the subjects to be taken into consideration.

Adult↗
PubMed2001

Neurovisual abnormalities preceding the retinopathy in patients with long-term type 1 diabetes mellitus.

BACKGROUND: Changes in the retina caused by diabetes may lead to visual impairment in dim light, even with good visual acuity and visual fields. To evaluate the visual abnormalities preceding the retinopathy in patients with type 1 diabetes mellitus (DM), we applied electrophysiological methods. METHODS: The visual evoked responses were recorded with sinusoidally modulated vertical gratings at 10 spatial frequencies presented sequentially on a high-resolution monitor in patients with type 1 DM and in normal volunteers. Similarly, the contrast visual evoked responses of 10 contrast levels were recorded at five spatial frequencies. Both amplitudes at the second harmonic were calculated by discrete Fourier transform. The visual acuity and contrast thresholds were determined objectively. RESULTS: There was dissociation between the Snellen and the estimated visual evoked response acuity measurements in patients with diabetes (r2=0.077, P=0.44). The saturation phenomena were observed at lower levels of contrast stimuli than in normal individuals at. 1.0, 2.0, 4.0 and 8.0 cycles per degree (P=0.0001). The contrast sensitivity function was deeply abnormal in all tested patients despite the metabolic control. The values of the area under the curve of the visual evoked response amplitude-contrast level function at five spatial frequencies were smaller in patients with DM than in the control group (P<0.05) at all spatial frequencies tested. CONCLUSIONS: Patients with type 1 DM without retinopathy showed significant lower amplitude of the visual evoked responses at all spatial frequencies tested, with the saturation phenomena observed at lower level of contrast stimuli. In addition, there was a dissociation between the sweep visual evoked responses and the Snellen acuity measurements. A significant and nonselective neuronal visual loss involving the visual pathway precedes the ophthalmoscopically detectable retinopathy in patients with type 1 DM.

Adult↗
PubMedDate not supplied

Personal monitoring instrument for the selective measurement of multiple organic vapors.

Development and laboratory testing of a small instrument capable of recognizing and quantifying multiple organic vapors at low- and sub-ppm concentrations is described. The instrument is slightly larger than a standard personal sampling pump and employs an array of three polymer-coated surface-acoustic-wave microsensors for vapor detection. Vapors are first trapped on a miniature adsorbent preconcentrator housed within the instrument and then thermally desorbed for analysis by the microsensor array. Each measurement cycle requires 5.5 min. The collective responses from the array are stored and then analyzed using pattern recognition methods to yield the identities and concentrations of collected vapors and vapor mixture components. Following initial optimization of instrument operating parameters, calibrations were performed with 16 organic solvent vapors and selected mixtures to establish a response library for each of two identical instruments. Limits of detection < or = 0.1 x threshold limit value were obtained for most vapors. In a series of 90 subsequent exposure tests, vapors were recognized with an error of < 6% (individual vapor challenges) and < 16% (binary mixture challenges) and quantified with an average error of < 10%. Monte Carlo simulations were coupled with pattern recognition analyses to predict the performance for many possible vapor mixtures and sensor combinations. Predicted recognition errors ranged from < 1 to 24%. Performance is shown to depend significantly on the interfacial polymer layers deposited on the sensors in the array and the nature and complexity of the vapor mixtures being analyzed. Results establish the capability of this technology to provide selective multivapor monitoring of personal exposures in workplace environments.

Adsorption↗
PubMed2001

Basal concentrations of oestradiol may predict the outcome of in-vitro maturation in regularly menstruating women.

Retrospectively it was examined whether the number of retrieved oocytes, the maturation rate and cleavage rate can be predicted in regularly menstruating women by the use of the following predictive variables on cycle day 3-4: the concentration of FSH, oestradiol, inhibin B and inhibin A in serum and and the number of ovarian follicles seen by vaginal ultrasound. The study included 132 consecutive aspirations in 100 women attending the clinic for in-vitro maturation due to male factor and/or tubal factor. Fifteen pregnancies were obtained after transfer in 83 cycles, giving a pregnancy rate of 15/132 (11%) per aspiration and 15/83 (18%) per transfer. The concentration of FSH and the number of follicles on day 3 predicted the number of oocytes retrieved, whereas these parameters did not predict the subsequent development of oocytes. No correlation was found between the inhibin B, inhibin A, oestradiol and the number of oocytes respectively. The group with a low concentration of oestradiol on cycle day 3 (threshold <200 pmol/l) (group 1, n = 106 cycles) had a significantly higher pregnancy rate compared to the group with a higher concentration (group 2, n = 26 cycles) (14 versus 0% per aspiration, P = 0.03). The group with a low concentration of oestradiol was subdivided according to the concentration of inhibin A. Group 1a: low inhibin A (threshold <10 pg/ml, n = 84 cycles) and group 1b: high inhibin A concentration (> or =10 pg/ml, n = 19). The pregnancy rate in group 1a (14/84, 17%) differed significantly from group 1b (0/19, 0%) (P = 0.03). It is concluded that a low basal concentration of oestradiol (<200 pmol/l) was shown to be a useful prognostic factor of pregnancy in IVM. The concentration of inhibin A (<10 pg/ml) was of added value.

Culture Techniques↗
PubMed1988

Cellular aspects of pre-ovulatory folliculogenesis in primate ovaries.

According to current concepts of pre-ovulatory folliculogenesis in primate ovaries, each growing follicle has a 'threshold' requirement for stimulation by FSH which must be met if it is to enter the oestrogen-secretory phase of pre-ovulatory development. Until recently, our understanding of the intra-follicular mechanisms underlying FSH action on granulosa cells was based largely on information from non-primate laboratory animals, mainly polyovulators such as rats. The present paper describes studies on FSH-regulated granulosa cell function in relation to pre-ovulatory development in vivo and in vitro using a laboratory primate, the common marmoset (Callithrix jacchus). Measurement of aromatase activity is used as an index of granulosa cell cytodifferentiation to verify three major tenets of the 'threshold' hypothesis: (i) that granulosa cells acquire increased responsiveness to FSH and LH during pre-ovulatory growth; (ii) that these developmentally related changes are directly induced by FSH; and (iii) that intrafollicular steroids modify FSH action and thereby contribute to the establishment of follicular FSH thresholds. The results obtained highlight the value of this experimental animal model for studies of cellular and molecular aspects of pre-ovulatory folliculogenesis which are relevant to human ovaries.

Animals↗
PubMed2001

VO(2) slow component: to model or not to model?

PURPOSE: The purpose of this study was to compare several techniques often used in the literature for measuring the amplitude of the slow component of oxygen uptake kinetics. METHODS: Eight healthy male volunteer cyclists performed two identical bouts of square wave cycle ergometry, from a VO(2) of 60% of the lactic acid threshold (LAT) to 30% of the difference between LAT and VO(2) peak. Predetermined intervals (3--6 and 3--10 min) were chosen to reflect those often used in the literature, namely 3-6 min and 3 min to the end of exercise. Several procedures were used to estimate the 3, 6, and 10-min VO(2) values (20-s averaging, 60-s averaging, and mono-exponential modeling). These were compared with the modeled slow component amplitude using a two-phase model with independent time delays: VO(2)(t) = B VO(2) + A(1)(1 -- e(-(t-TD1)/tau(1)) + A(2)(1 -- e(-(t-TD2)/tau(2)). CONCLUSIONS: The results showed a significant underestimation for all methods of slow component amplitude estimation (P < 0.05) when compared with the actual (modeled) amplitude. In so far as research on oxygen uptake kinetics is used to understand the underlying physiology, it is imperative that the components of the kinetics be determined accurately. The use of a predetermined time frame for estimation of the amplitude of the slow component is not supported by this study. Future investigations should consider these results and make every effort to model the underlying response.

Adult↗
PubMedDate not supplied

Influence of a novel platinum compound--cis-dichloro (dimethylsulphoxide) (1-beta-D-rybofuranosyl-1,2,4-triazolo-3-arboxyamide) platinum (II)--"Pt-rib-1"--on cell cycle and apoptosis in ClS91 and B16 mouse melanoma in vitro.

Cisplatin has a significant role in the treatment of selected human tumors including advanced melanoma, but new platinum compounds are still in focus of search for better properties. Modern drug design is often based on studies detecting the abilities of tested drug to induce apoptosis and disturb cell cycle. Aim of the study was to establish the influence of a platinum complex Pt-rib-1 on cell cycle and apoptosis occurrence in mouse melanoma B16 and ClS91 cells. Pt-rib-1 is a ribavirin derivative. previously characterized and described as cytotoxic to B16 and ClS91 mouse melanoma cells in vitro. The new platinum complex (Pt-rib-1); cis- dichloro (dimethylsulphoxide) (1- beta- D-ribofuranosyl- 1,2,4-triazolo -3- carboxyamide) platinum (II) was supplied. Cisdiaminodichloroplatinum (II), (cisplatin) was used in control groups. To detect apoptotic and necrotic cells, Annexin V- conjugated with fluorescein isothiocyanate (Annexin V-FITC, Immunotech) and propidium iodide (IP, Immunotech) were used. Apoptosis detection were done using fluorescence microscopy and flow cytometry. The total DNA content within the cell indicated phase of the cell cycle. DNA content was measured using flow cytometry. Values given represent the mean from three determinations. Results were presented as mean +/- standard deviation (SD). Statistical analysis was done using t-Student test. There were 70.4% of apoptotic cells in the ClS91 culture after 24 h incubation with Pt-rib-1 at a concentration of 2.04 x 10(-3) M (4 x IC50). In B16 group, 83.2 per cent of apoptotic cells was found after 24h incubation with Pt-rib-1 at high concentration (2.30 x 10(-3) M). A 24-h experiment shows a threshold at a concentration higher than 3 x IC50 responsible for apoptosis induction in B16 and ClS91 cells. After 48 h incubation with Pt-rib-1 the per cent of apoptotic cells increased gradually with rising concentrations of Pt-rib-1 up to a final concentration of 2.04 x 10(-3) M and 0.92 x 10(-3) M in ClS91 and B16 groups, respectively. Cell accumulation was observed in S phase after 48 h incubation with Pt-rib-1. The per cent of cells in S phase increased from 31 to 51.1% and 38.8 to 50.0% in ClS91 and B16 culture, respectively. There were no B16 and ClS91 cells in G2/M phase after incubation with higher concentrations of Pt-rib-1 (from 0.2 to 2.0 x 10(-5) M/dm3). Pt-rib-1 partially exhibits action of cisplatin. which has no specific influence on cell cycle and ribavirin. probably responsible for DNA synthesis delay.

Animals↗
PubMed2006

Longitudinal assessment of cardiovascular exercise performance after pediatric heart transplantation.

BACKGROUND: No existing longitudinal data document exercise performance after pediatric heart transplantation. We report the exercise performance findings from the longitudinal study of pediatric heart transplantation patients and the association of aerobic capacity with echocardiographic measures of graft function. METHODS: We performed a retrospective analysis of 28 children after heart transplantation who underwent 87 exercise tests and echocardiograms. Subjects exercised using graded cycle or treadmill protocols. Maximal oxygen consumption (VO2), physical working capacity, peak heart rate, and anaerobic threshold were evaluated. To measure systolic and diastolic function, shortening fraction and mitral valve pressure half-time (PHT) respectively, were obtained by echocardiography. RESULTS: The average age at transplantation was 10.9 +/- 5.6 years, at initial exercise test was 13.8 +/- 5.0 years, and at final exercise test was 15.8 +/- 5.2 years. Percent-predicted values at the initial exercise test were VO2, 59.3%; physical working capacity, 60.2%; and peak heart rate, 75.8%; these remained similarly decreased at the final exercise test. Shortening fraction and PHT were within normal limits, but PHT was significantly greater at final test (p < 0.05). The relationship of VO2% with time was statistically significant, described by a quadratic equation that included initial VO2% and time from heart transplantation. This relationship remained significant when the shortening fraction (p < .05) but not PHT was added as a covariate in the equation. CONCLUSIONS: Exercise performance after pediatric heart transplantation is impaired and, despite an initial improvement, declines over time. This can be explained by increasing diastolic dysfunction independent of donor graft age. If confirmed, these findings point the direction to further research aimed at limiting this aerobic capacity decline after heart transplantation.

Adult↗
PubMed2004

Diagnosis of pulmonary vascular limit to exercise by cardiopulmonary exercise testing.

BACKGROUND: Given the recent development of newer and less-invasive treatments for pulmonary hypertension, and the long wait for lung transplantation, early and correct diagnosis of this condition is increasingly important. The purpose of this study was to determine and improve the accuracy of a non-invasive, cardiopulmonary exercise-testing algorithm for detecting a pulmonary vascular limit to exercise. METHODS: We performed 130 consecutive, incremental cycling-exercise tests for exertional symptoms with pulmonary and radial artery catheters in place. Pulmonary vascular limit was defined as pulmonary vascular resistance at maximum exercise >120 dynes. sec/cm(5) and a peak-exercise systemic oxygen delivery <80% predicted, without a pulmonary mechanical limit or poor effort. We applied a previously reported non-invasive exercise-test-interpretation algorithm to each patient and sequentially manipulated branch point threshold values to maximize accuracy. RESULTS: The sensitivity of the original non-invasive algorithm for pulmonary vascular limit was 79%, specificity was 75%, and accuracy was 76%. Sensitivity did not change with systematic alteration of branch-point threshold values, but specificity and accuracy improved to 88% and 85%, respectively. Accuracy improved most by modifying the threshold values for percent predicted maximum oxygen uptake and carbon dioxide output ventilatory equivalents at lactate threshold. CONCLUSION: Non-invasive cardiopulmonary exercise testing is a useful tool for detecting and excluding a pulmonary vascular limit and for determining whether abnormal pulmonary hemodynamics limit aerobic capacity.

Adult↗
PubMed2000

Resistive index: an experimental study of the normal range in the pig.

OBJECTIVES: To study the normal range and distribution of the resistive index (RI) and the resistive index ratio (RIR) in the non-obstructed non-dilated porcine kidney, and to assess the reliability of the threshold values RI 0.70 and RIR 1.10 as prognosticators of true obstruction in the upper urinary tracts. METHODS AND MATERIALS: Twenty female pigs of Danish land race breed were studied under general anaesthesia. Blood pressure and urine output was monitored throughout the experiment. Doppler evaluations were obtained from an interlobar artery in the lower half of each kidney, and the RI was calculated as the average of 3 x 3 cycles for each side independently. Statistical analysis of the obtained results was performed. RESULTS: Forty renal units were studied. The RI values ranged from 0.48-0.85 (mean 0.63). Nine renal units (22.5%) had RI values > or = 0.70. RIR values ranged from 1.00-1.38 (mean 1.07). Three RIR values (15%) were above 1.10. There was no statistically significant relationship between RI and laterality (p = 0.25), and no overall significant relationship between RI and mean arterial blood pressure (r2 = 0.21) or urine output (r2 = 0.004). CONCLUSIONS: This study shows a wide distribution of the RI normal values in the pig model, and our results do not support the normal ranges for RI and RIR, or the cut-off values used in clinical practice.

Animals↗
PubMed1995

Prediction of fatigue screw loosening in anterior spinal fixation using dual energy x-ray absorptiometry.

STUDY DESIGN: A biomechanical study was performed to investigate a relation between the bone mineral density of the vertebral body and the number of loading cycles to induce fatigue loosening of an anterior vertebral screw. OBJECTIVES: The objective of this study was to investigate the potential usefulness of dual energy x-ray absorptiometry of measuring bone mineral density of the vertebral body in predicting the fatigue loosening of th anterior vertebral screw. SUMMARY OF BACKGROUND DATA: Loosening of the vertebral body screw is a well know failure in spinal instrumentation, and more commonly observed than pullout failure. The relation between bone mineral density and pullout strength of the screw has been investigated previously, but no studies are available on the fatigue loosening in anterior spinal fixation. METHODS: Bone mineral density was measured using dual energy x-ray absorptiometry and the screw loosening was produce by a cyclic loading in the cephalad-caudal direction. Screw loosening was defined as 1 mm displacement of the screw relative to bone, and the number of loading cycles to induce the screw loosening was obtained and statistically correlated with bone mineral density. RESULTS: There was a positive correlation between the number of loading cycles to induce screw loosening and bone mineral density (R = 0.8, P < 0.01). The average number of loading cycles to induce screw loosening was significantly less for specimens with bone mineral density < 0.45 g/cm2 compared to those with bone mineral density > or = g/cm2. CONCLUSIONS: These findings suggest that bone mineral density may be a good predictor of anterior vertebral screw loosening. Bone mineral density < 0.45 g/cm2 may be critical value of loosening of the anterior vertebral body screw. However, further biomechanical and clinical studies are required before using threshold value clinically.

Absorptiometry, Photon↗
PubMed1994

Dynamics of oxygen uptake for submaximal exercise and recovery in patients with chronic heart failure.

STUDY DESIGN AND OBJECTIVES: Attainment of a steady state for oxygen uptake (VO2) during constant work rate exercise has been reported to take longer for patients with chronic heart failure (CHF) compared with normal. The steady state is also delayed in normal subjects during high-intensity exercise compared with moderate exercise, however, and the delay correlates with the degree of associated lactic acidosis. To determine whether prolonged kinetics of VO2 are attributable solely to the reduction of exercise capacity in CHF, VO2 kinetics were compared for patients with CHF and normal subjects, both for exercise of matched absolute work rate and for matched relative work intensity. SUBJECTS: Eighteen men with CHF and 10 normal men. METHODS AND RESULTS: Subjects performed 6 min of constant work rate cycle ergometry with breath-by-breath measurement of VO2. Patients were studied using 25 W, and a work rate midway between the lactic acidosis threshold and maximal capacity (50 percent delta). Normal subjects were tested similarly, and also at a work rate matched to the patients' average 50 percent delta work rate. The VO2 kinetics were characterized by the mean response time (MRT) to attain the 6 min VO2 value. Rates of recovery of VO2 were analyzed for 2 min following exercise. For the same absolute work rate, VO2 MRTs were significantly longer for patients than controls (25 W, 67 +/- 26 vs 37 +/- 25 s; approximately 60 W, 87 +/- 20 vs 54 +/- 27 s), but there was no significant difference in VO2 MRT between the two groups at a matched intensity of 50 percent delta (87 +/- 20 vs 81 +/- 18 s). However, the decrease in VO2 during 2 min of recovery was slower for the patients on all comparisons, even for matched exercise intensity. CONCLUSION: The VO2 dynamics for submaximal exercise are slowed in CHF. The slower dynamics are not entirely accounted for by the relatively higher intensity of a given work rate, since delayed recovery is evident even at a matched relative work intensity. Exercise intolerance in CHF is characterized not only by decreased maximal exercise capacity, but also by slower adaptations to and from submaximal levels of exercise.

Anaerobic Threshold↗
PubMed1979

Processing of ampullary input in the brain: comparison of sensitivity and evoked responses among elasmobranch and siluriform fishes.

1. Averaged evoked potentials (AEP) in response to pulses and sine waves of electric current, either as a homogeneous field or a large dipole field around the fish, have been recorded from the brain in 5 genera of elasmobranchs and 10 genera of siluriform fishes. 2. In the elasmobranchs, AEP's and spike-hash bursts are described from medulla, cerebellum, mesencephalon and telencephalon. A complex sequence of early and late waves is found in each level. Two sets of factors influence the latency and amplitude of the component waves. One is stimulus parameters including intensity, stimulus orientation, sign of the change of current, position of dipole, serial number in the first few cycles of a train as well as interval or frequency of a regular series. Separate component peaks of the complex AEP appear to have different dependencies upon these factors. To sinusoidal stimuli the best response by a certain criterion is at 20--30 Hz in a shark (Carcharhinus), 10--15 Hz in a ray (Potamotrygon); these are much higher than the values based on behavior from previous authors. The lowest threshold, with moderate averaging, was 0.015 muV/cm (= 0.8 nA/cm2) in marine species, less than 50 muV/cm (= 0.7 nA/cm2) in the freshwater ray. 3. The other set of factors determining AEP is brain parameters, including the recording locus, the type of electrode and electrode advance and the state of the brain (anesthesia, etc.). There is evidence of topographic segregation of some stimulus parameters, but mapping was not undertaken. Responsive regions are described in the several brain levels. 4. The best loci for electric AEP are distinct from those for acoustic and photic AEPs. No interaction between these was found. 5. All of the siluriforms tested show electroreception by the criterion of high sensitivity AEP. No obvious specialization was noted among the diverse species, but most were represented by a single experiment. Taken together with the previously known species, the sample of nine families of this large order suggests that this is a general characteristic of the order. 6. The best responses were found in the region of the torus semicircularis and in the lateral lobe. The lowest threshold by the criterion used was less than 0.15 mV/cm (= 2 nA/cm2), but some were nearly 2 mV/cm. Compared to much lower values in Ictalurus, this suggests species differences although part of the difference may be due to failure to record from the optimal locus. The AEP may be useful as a method of suveying for other electroreceptive groups. It is also potentially useful to reveal discriminable parameters of importance, such as dipole position, orientation, polarity and frequency.

Animals↗
PubMed1992

The respiratory system as an exercise limiting factor in normal trained subjects.

Recently, we have shown that an untrained respiratory system does limit the endurance of submaximal exercise (64% peak oxygen consumption) in normal sedentary subjects. These subjects were able to increase breathing endurance by almost 300% and cycle endurance by 50% after isolated respiratory training. The aim of the present study was to find out if normal, endurance trained subjects would also benefit from respiratory training. Breathing and cycle endurance as well as maximal oxygen consumption (VO2max) and anaerobic threshold were measured in eight subjects. Subsequently, the subjects trained their respiratory muscles for 4 weeks by breathing 85-160 l.min-1 for 30 min daily. Otherwise they continued their habitual endurance training. After respiratory training, the performance tests made at the beginning of the study were repeated. Respiratory training increased breathing endurance from 6.1 (SD 1.8) min to about 40 min. Cycle endurance at the anaerobic threshold [77 (SD 6) %VO2max] was improved from 22.8 (SD 8.3) min to 31.5 (SD 12.6) min while VO2max and the anaerobic threshold remained essentially the same. Therefore, the endurance of respiratory muscles can be improved remarkably even in trained subjects. Respiratory muscle fatigue induced hyperventilation which limited cycle performance at the anaerobic threshold. After respiratory training, minute ventilation for a given exercise intensity was reduced and cycle performance at the anaerobic threshold was prolonged. These results would indicate the respiratory system to be an exercise limiting factor in normal, endurance trained subjects.

Adolescent↗
PubMed2002

Relationship of exercise test variables to cycling performance in an Ironman triathlon.

The purpose of this study was, firstly, to investigate the intensity of exercise performance of highly trained ultra-endurance triathletes during the cycling portion of an Ironman triathlon, and, secondly, to examine the anaerobic threshold and its relationship to this performance. Following a peak oxygen consumption (VO(2peak)) test on a cycle ergometer to determine the heart rate (HR(Th,vent)) and power output (PO(Th,vent)) at the ventilatory threshold (Th(vent)), 11 highly trained male triathletes [mean (SEM) age 35.8 (1.6) years, body fat 11.7 (1.2)%. VO(2peak) 67.5 (1.0) ml x kg(-1) x min(-1)] who were participating in an Ironman triathlon, in random order: (1) cycled at their PO(Th,vent) (Bi(Th,vent)) until they were exhausted, and (2) cycled for 5 h at a self-selected intensity (Bi(SSI)). Cycling power output (PO), oxygen uptake (VO(2)), heart rate (HR) and blood lactate concentration ([La(-)](b)) were recorded at regular intervals during these trials, while performance HR was recorded during the cycling phase of the Ironman triathlon. Significantly greater (P < 0.05) values were attained during Bi(Th,vent) than during Bi(SSI) for PO [274 (9) compared to 188 (9) W], VO(2) [3.61 (0.15) compared to 2.64 (0.09) l x min(-1)], and [La(-)](b) [6.7 (0.8) compared to 2.8 (0.4) mmol x l(-1)]. Moreover, mean HR during the Ironman triathlon cycle phase [146.3 (2.4) beats.min(-1); n=7] was significantly greater than mean HR during Bi(SSI) [130 (4) beats x min(-1)], and significantly less than mean HR during Bi(Th,vent) [159 (3) beats x min(-1); all P < 0.05]. However, HR during the cycle portion of the Ironman triathlon was highly related to (r = 0.873; P < 0.05) and not significantly different to HR(Th,vent) [150 (4) beats x min(-1)]. These data suggest that ultra-endurance triathletes cycle during the Ironman triathlon at a HR intensity that approximates to HR(Th,vent), but at a PO that is significantly below PO(Th,vent).

Adult↗