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PubMed2000

Increase characteristics of the cumulated excess-CO2 and the lactate concentration during exercise.

The so-called excess-CO2 in physical exertion results stoichiometrically directly from the quantity of protons bound in bicarbonate buffering. This situation is used in determining the ventilatory threshold (VT). However, the extent to which the degree and increase characteristics of excess-CO2 can be used as an equivalent to blood lactate concentrations is uncertain. To investigate this relationship, 21 healthy men exercised on a cycle ergometer (starting at 50 watt, increases of 50 watt every 3 minutes) to subjective exhaustion. To evaluate the characteristics of this increase, a slope constant lambda was calculated in relation to performance for both the blood lactate concentration (lambda lactate) and the cumulated excess-CO2 (lambda CO2 excess). The start of the lactate increase (LT) and excess-CO2 (VT) showed good intercorrelation (VT=2.27+0.98 x LT; r=0.914; P<0.001). Mean lambda lactate and lambda CO2 excess were of similar dimensions in all subjects (69.3 +/- 39.8 watt vs. 80.11 +/- 15.7 watt), but a minority of the subjects (n=7) showed a considerably more gradual increase for the excess-CO2 to the maximum. Since in addition there was no significant correlation between the absolute values for maximum lactate concentrations and the cumulative excess-CO2, an interindividual prediction of lactate concentrations from the excess-CO2 would be difficult. It is an open question, however, whether perhaps additional performance-limiting factors, such as the ventilation or the buffering capacity, may be included when measuring the excess-CO2 so that this parameter could be more a measure for the formation rate of new lactate than the blood lactate concentration alone.

Adult↗
PubMed1985

Lactate, pyruvate, and lactate-to-pyruvate ratio during exercise and recovery.

The pattern of lactate increase and its relation to pyruvate and lactate-to-pyruvate (L/P) ratio were studied during exercise and early recovery in 10 normal subjects for incremental exercise on a cycle ergometer. Gas exchange was measured breath by breath. Lactate and pyruvate were measured by enzymatic techniques. Lactate and log lactate changed only slightly at low levels of O2 uptake (VO2) but both began to abruptly increase at approximately 40-55% of the maximal VO2. However, the point of abrupt increase in pyruvate occurred at higher work rates and the rate of increase was not as great as that for lactate. Thus L/P ratio increased at the same VO2 as the log lactate increase. Following the exercise, pyruvate continued to increase steeply for at least the first 5 recovery min, whereas at 2 min lactate increased only slightly or decreased. Thus arterial L/P ratio reversed its direction of change and decreased toward the resting value by 2 min of recovery. Lactate, as well as L/P ratios, decreased in all subjects by 5 min. This study demonstrates that lactate and pyruvate concentrations increase slightly at low levels of exercise without a change in L/P ratio until a threshold work rate at which lactate abruptly increases without pyruvate. The resulting increase in L/P ratio is progressive as work rate is incremented and abruptly reverses when exercise stops.

Adult↗
PubMed1997

Inheritance of hypoxic exercise tolerance in mice.

All mammals tested, when exposed acutely to a degree of hypoxia above some threshold, exhibit a reduced capacity to perform work. Chronic hypoxic exposure is usually associated with some degree of acclimation resulting in partial recovery of the preexposure work capacity. The present study reports that, among mice, interindividual variability in recovery of ability to tolerate a standardized hypoxic exercise [t(et); time elapsed in treadmill exercise in hypoxia until 4-s failure to avoid a grid configured to deliver a mild aversive current (0.15 mA)], after 8 weeks' exposure to half-atmospheric pressure, is influenced predominantly by two unlinked genes of major effect. Two approaches were taken toward genetic characterization. In one, a maximum-likelihood procedure was applied to 11 models of genetic determinacy in the t(et) distributions of BALB/cBy (C) and C57BL/6By (B6) parental inbred strains, their F1 hybrid, and the backcross (BC) generations. Breeding tests of the resulting candidate "best-fit" major locus inheritance models involved repeated cycles of selecting, as the progenitor of a new BC generation, the male with the highest value of the test variable in the previous BC generation, and breeding him to C females. Mice from each of four distinct phenotypes appearing in BC3 were bred to C mice, producing distributions expected from two-locus segregation. The second approach was based upon CXB/By RI strain distribution pattern and derivative breeding tests to reveal phenotypic distributions consistent with two-locus inheritance of tet. Melding these results with a positional cloning strategy may permit relating a behavioral difference to specific heritable elements and identifying their products as the (partial) physiological substrata of the behavior.

Animals↗
PubMed2000

Effects of caffeine on muscle glycogen utilization and the neuroendocrine axis during exercise.

To examine the effect of caffeine ingestion on muscle glycogen utilization and the neuroendocrine axis during exercise, we studied 20 muscle glycogen-loaded subjects who were given placebo or caffeine (6 mg/kg) in a double blinded fashion 90 min before cycling for 2 h at 65% of their maximal oxygen consumption. Exercise-induced glycogen depletion in the thigh muscle was noninvasively measured by means of 13C nuclear magnetic resonance spectroscopy (NMR) spectroscopy, and plasma concentrations of substrates and neuroendocrine hormones, including beta-endorphins, were also assessed. Muscle glycogen content was increased 140% above normal values on the caffeine trial day (P < 0.001). After cycling for 2 h, caffeine ingestion was associated with a greater increase in plasma lactate (caffeine: +1.0 +/- 0.2 mmol/L; placebo, +0.1 +/- 0.2 mmol/L; P < 0.005), epinephrine (caffeine, +223 +/- 82 pg/mL; placebo, +56 +/- 26 pg/mL; P < 0.05), and cortisol (caffeine, +12 +/- 3 mg/mL; placebo, +2 +/- 2 mg/mL; P < 0.001) levels. However, plasma free fatty acid concentrations increased (caffeine, +814 +/- 133 mmol/L; placebo, +785 +/- 85 mmol/L; P = NS), and muscle glycogen content decreased (caffeine, -57 +/- 6 mmol/L muscle; placebo, -53 +/- 5 mmol/L muscle; P = NS) to the same extent in both groups. At the same time, plasma beta-endorphin levels almost doubled (from 30 +/- 5 to 53 +/- 13 pg/mL; P < 0.05) in the caffeine-treated group, whereas no change occurred in the placebo group. We conclude that caffeine ingestion 90 min before prolonged exercise does not exert a muscle glycogen-sparing effect in athletes with high muscle glycogen content. However, these data suggest that caffeine lowers the threshold for exercise-induced beta-endorphin and cortisol release, which may contribute to the reported benefits of caffeine on exercise endurance.

Adult↗
PubMed1999

[Cardiovascular and metabolic response to dynamic stress echocardiography by patients with coronary heart disease and healthy probands].

25 patients with coronary heart disease (CHD, 62 +/- 9 years) and 18 subjects free from cardiovascular disease (28 +/- 9 years) were tested on a cycle ergometer using a graded incremental test protocol: a) in the common upright position, b) as dynamic stress echocardiography in a semi-supine position. Whereas no relevant differences could be detected between the two conditions for the healthy subjects concerning heart rate, blood pressure, and rate-pressure product (2 x 3 ANOVA, t-tests with alpha-adjustment), the CHD patients showed both significantly higher heart rates as well as a significantly higher rate-pressure product (50 W: 15,300 +/- 2973 mm Hg/min vs. 13,822 +/- 3042 mm Hg/min; 75 W: 18,028 +/- 3479 mm Hg/min vs. 16,337 +/- 2619 mm Hg/min) on equivalent stages during stress echocardiography if compared to the sitting position. There were no differences for systolic blood pressure in this group; the diastolic values were higher in the sitting position at rest and during 50 W. Lactate concentrations (determined only in the healthy subjects) were significantly higher on all stages during dynamic stress echocardiography. The workload at the individual anaerobic threshold (IAT) was significantly lower. In conclusion, we found a higher metabolic along with a similar cardiovascular strain at equivalent workloads in stress echocardiography compared to upright bicycle ergometry for healthy subjects. However, CHD patients have a higher cardiocirculatory load in the semi-supine position. When investigating these patients with stress echocardiography, higher heart rates of about 8 beats/min have to be expected for equivalent workloads if compared to the upright position.

Adult↗
PubMed2006

The intensity level of physical exercise and the bone metabolism response.

This study investigated the short-term effects of the intensity level of physical exercise on bone metabolism and related hormones. The responses of calciotropic hormones and bone biochemical markers were evaluated in seven male cyclists (mean age 24.4 years, range 20-39) during two 50-min cycling tests performed 15% below (-VT) and 15% above (+VT) the ventilatory threshold. In each test, venous blood samples were drawn at rest, at the 30th and 50th min of exercise, and after 15 min of recovery. For both intensity levels, no significant variation in calcium, 25-hydroxyvitamin D, 1.25-dihydroxyvitamin D, or cortisol level was observed. Intact parathyroid hormone (iPTH) level increased significantly after the last minute of the test (41%, p < 0.05) and peaked during the recovery (80%, p < 0.05) only in response to exercise performed at +VT. Serum phosphorus concentration rose during both tests, while albumin levels increased only at +VT. Concerning bone cell activity, osteocalcin, and type I-C telopeptide breakdown products transiently increased only in response to exercise performed at +VT (11% and 16.8%, respectively; p < 0.05). Bone alkaline phosphatase increased similarly for both intensity levels after 30 min (12%, p < 0.05) and 50 min (12% for -VT vs. 14% for +VT, p < 0.05). All markers of bone turnover returned to initial values during the recovery. In conclusion, a no-impact but intense and sustained exercise performed at +VT transiently stimulated bone turnover and iPTH secretion, suggesting the existence of a bone stimulation threshold. In addition to the well known effect of mechanical constraints, both the duration and intensity of exercise may induce changes in bone turnover.

Adult↗
PubMed1996

Influence of different exercise protocols on functional capacity and symptoms in patients with chronic heart failure.

This study compares hemodynamic, metabolic, and gas exchange responses, catecholamine levels, and symptoms in 35 male patients with chronic heart failure (CHF) ([mean +/- SD] age 53 +/- 11 yr; ejection fraction 24 +/- 11%) during three differently graded exercise test protocols. On three consecutive days patients performed cycle ergometry supine, with prolonged steps (prol BE) and right heart catheterization, ramplike cycle ergometry sitting (ramp BE), and ramplike treadmill walking (TMW). As in routine clinical practice, the prol BE was terminated when pathologic central hemodynamics and/or increased symptomology occurred, and ramp BE and TMW due to increased symptomology and/or physician's decision. During prol BE at ventilatory threshold (VT) the VO2 (8.6 +/- 1.8 ml.kg-1.min-1) was lower than during ramp BE (9.3 +/- 2.1 ml.kg-1.min-1) (P < 0.017) and TMW (11.8 +/- 2.3 ml.kg-1.min-1) (P < 0.0001). Prol BE, ramp BE, and TMW also differed significantly with respect to ventilation (22 +/- 7 l.min-1; 26 +/- 6 l/min-1; 29 +/- 7 l.min-1; P < 0.01) and heart rate (100 +/- 15 beats.min-1; 103 +/- 18 beats.min-1; 110 +/- 16 beats.min-1; P < 0.017). No differences were found in lactate levels, catecholamine levels, and ratings of leg fatigue and dyspnea. At test termination, the peak VO2 during prol BE (100.8 +/- 3.3 ml.kg-1.min-1) was lower than during ramp BE (13.3 +/- 4.1 ml.kg-1.min-1) (P < 0.0001) and TMW (14.7 +/- 3.4 ml.kg-1.min-1) (P < 0.0001). Peak norepinephrine value during ramp BE (4.531 +/- 2.788 nmol.l-1) was higher than during prol BE (3.707 +/- 2.262 nmol.l-1) (P < 0.001). Among the three tests, no significant differences were found for peak values of heart rate, lactate, and ratings of dyspnea. Although the VO2.kg-1 at VT was significantly higher during ramp BE and TMW compared to prol BE (P < 0.001), the values expressed as a percent of peak VO2.kg-1 were significantly lower (70 +/- 4%; 72 +/- 6%; 79 +/- 3%; P < 0.017). A systematic effect on aerobic capacity with reduced peak values during ramp BE and TMW was demonstrated when test termination was based primarily on pathological findings of central hemodynamics from prol BE.

Adolescent↗
PubMed1985

A Bekesy descending-only procedure: effects of attenuation rate and step size, and starting level.

Bekesy fixed-frequency thresholds for pulsed and continuous tones at 1 kc/s yielded by a descending-only technique were compared for suprathreshold starting levels of 38, 58, 78, and 98 db SPL, and attenuation rates of 1, 2, 4, and 8 db/sec with associated attenuation steps of 0.25, 0.5, 1, and 2 db, respectively, with 3 normal-hearing adults. For pulsed tones of 250 msec (duty cycle 50%), thresholds were not significantly affected by attenuation rate/step size or by starting level. However, for continuous tones, increasing attenuation rate/step size yielded better thresholds for a given starting level. Decreasing starting level yielded better thresholds for a given attenuation rate/step size. Thus, deteriorated thresholds were yielded by the slower attenuations/step sizes and by the higher starting levels. These data may be explained as a manifestation of normal adaptation. The similar relative effects found here of attenuation rate/step size and of starting level, as compared to the data of an earlier study (Harbert and Young, 1968) which used the traditional up-down Bekesy method of threshold tracing lend support to the possible future clinical use of a descending-only technique.

Audiometry↗
PubMed2003

Delayed afterdepolarization inhibitor: a potential pharmacologic intervention to improve defibrillation efficacy.

INTRODUCTION: Electrical and optical mapping studies of defibrillation have demonstrated that following shocks of strength near the defibrillation threshold (DFT), the first several postshock cycles always arise focally. No immediate postshock reentry was observed. Delayed afterdepolarizations (DADs) have been suggested as a possible cause of this rapid repetitive postshock activity. The aim of this study was to test the hypothesis that DFT is decreased by application of a DAD inhibitor. METHODS AND RESULTS: Six pigs (30-35 kg) were studied. First, control DFT was determined using a three-reversal up/down protocol. Each shock (RV-SVC, biphasic, 6/4 msec) was delivered after 10 seconds of ventricular fibrillation (VF). Then, flunarizine (a DAD inhibitor) was injected intravenously (2 mg/kg bolus and 4 mg/kg/hour maintenance) and the DFT was again determined. A third DFT was determined 50 minutes after drug infusion was terminated to allow the drug to wash out. DFT after flunarizine application (520 +/- 90 V, 14 +/- 3 J) was significantly lower than control DFT (663 +/- 133 V, 23 +/- 4 J). After the drug washed out, DFT (653 +/- 107 V, 22 +/- 4 J) returned to the control DFT value (P = 0.6). Flunarizine reduced the DFT approximately 22% by leading-edge voltage and approximately 40% by energy. CONCLUSION: Flunarizine, a DAD inhibitor, significantly improved defibrillation efficacy. This finding suggests that DADs could be the source of the rapid repetitive focal activation cycles arising after failed near-DFT shocks before degeneration back into VF. Future studies are needed to investigate the cause of the earliest postshock activation and to determine if the DADs are responsible.

Animals↗
PubMed1993

Trityl monitoring of automated DNA synthesizer operation by conductivity: a new method of real-time analysis.

AutoAnalysis is a new method for detecting and quantitating the trityl cation released each cycle on automated DNA synthesizers. The trityl (dimethoxytrityl) cation is removed from the growing oligonucleotide after each base addition and is a useful measure of synthesis efficiency. The traditional absorbance method of collecting each trityl effluent with a fraction collector, followed by dilution with an acid solution and careful quantitation by UV/VIS spectroscopy is costly, tedious and prone to error. The absorbance method for trityl cation analysis must usually wait until the synthesis is complete. Interruption of a failed operation, for a variety of reasons, such as an empty reagent reservoir, is thus not possible. Taking advantage of the conductive properties of the trityl cation, immediate and real-time quantitation is now possible by integrating the total conductance of the flowing stream during the detritylation step after each nucleoside addition in DNA synthesis. A conductivity cell is mounted downstream, past the synthesis column. The conductivity signal is processed and displayed as the current average stepwise yield and overall yield. If the yield drops below a pre-set threshold value because of a failure situation, the synthesizer will interrupt, preserving reagents. AutoAnalysis allows trityl monitoring with complete automation on the Applied Biosystems Models 392 and 394 DNA/RNA Synthesizers.

Base Sequence↗
PubMed1997

Feasibility and sensing thresholds of temporary single-lead VDD pacing in intensive care.

Long-term pacemaker treatment of patients with a high-degree atrioventricular (AV) block routinely uses AV synchronous pacing because of its hemodynamic advantages compared with VVI pacing. In cases of temporary pacing, however, the limitations inherent in attempting to reliably position a temporary atrial lead generally influences the use of VVI pacing. We therefore tested the use of temporary single-lead VDD pacing, making AV pacing possible with only 1 lead, in 22 patients requiring temporary pacing due to a high-degree AV block. AV synchronous stimulation was achieved in all patients using a quadripolar lead with an atrial dipole with the atrial rings spaced 30 mm apart. During follow-up (14.1 +/- 12.5 hours) intermittent undersensing was detected in 4 of the 22 patients. We initially evaluated the atrial sensing threshold by decreasing the pacemaker device sensitivity stepwise in all patients (1.54 +/- 1.08 mV; n = 22). In 15 patients an intra-atrial electrocardiogram was recorded. During the breathing cycle, the maximum P-wave amplitude was significantly different from the minimum P-wave amplitude (2.19 +/- 1.00 mV vs 1.25 +/- 0.65 mV, p < 0.005). The atrial signal detected by the single lead was further analyzed in 10 of 15 patients using various filters. A mean signal loss of 45% was observed, increasing the lower bandpass frequency from 0.1 to 40 Hz (1.73 +/- 0.71 mV vs 0.92 +/- 0.51 mV, p < 0.02). Lowering the upper filter range from 1,000 Hz down to 100 Hz did not significantly influence the atrial signal (1.73 +/- 0.71 mV vs 1.61 +/- 0.75 mV, NS). Single-lead VDD pacing, even on a temporary basis, is a reliable means of achieving AV synchronous pacing. Due to the floating atrial dipole, the system is characterized by a high degree of variability in the atrial signal with intermittent lower values. A significant signal loss must be expected when a lower bandpass frequency of 40 Hz is used.

Aged↗
PubMed1992

Single-fibre and whole-nerve responses to clicks as a function of sound intensity in the guinea pig.

This paper describes a study of the intensity dependence of click-evoked responses of auditory-nerve fibres in relation to the simultaneously recorded compound action potential (CAP). Condensation and rarefaction clicks were presented to normal hearing guinea pigs over an intensity range of 60 dB. The recorded poststimulus time histograms (PSTHs) were characterized by the latency (tp), amplitude (Ap) and synchronization (Sp) of their dominant peak, parameters that are particularly important for the understanding of the CAP. For all fibres tp decreased monotonically with increasing intensity, in a continuous way for fibres with high characteristic frequency (CF greater than 3 kHz), and in discrete steps of one CF-cycle for low-CF (CF less than or equal to 3 kHz) fibres. An additional analysis of PSTH envelopes revealed that average latency shifts with intensity are similar for all CFs above 2 kHz. For all fibres Ap increased monotonically with intensity; the increase was stronger and maximum values were larger for low-CF than for high-CF fibres. A schematic model PSTH was then formulated on the basis of the experimental data. A sum of these model PSTHs from a hypothesized fibre population was convolved with an elemental unit response (Versnel et al., 1992) in order to simulate the compound action potential. Synthesized CAPs agreed with experimental CAPs in their main aspects.

Acoustic Stimulation↗
PubMed2002

Ventilatory efficiency during exercise in healthy subjects.

When evaluating dyspnea in patients with heart or lung disease it is useful to measure the quantity of ventilation needed to eliminate metabolically produced CO2 (i.e., the ventilatory efficiency). Mathematically, the relationship between ventilation (VE) and CO2 output is determined by the arterial CO2 pressure and the physiologic dead space-tidal volume ratio. We decided to determine how age, sex, size, fitness, and the type of ergometer influenced ventilatory efficiency in normal subjects. Three methods were compared for expressing this relationship: (1) the VE versus CO2 output slope below the ventilatory compensation point, commonly used by cardiologists for estimating the severity of heart failure; (2) the VE/CO2 output ratio at the anaerobic threshold, commonly used by pulmonologists; and (3) the lowest VE/CO2 output ratio during exercise, the latter parameter not previously reported. We studied 474 healthy adults, between 17 and 78 years of age during incremental cycle and treadmill cardiopulmonary exercise tests at three test sites, correcting the total VE for the equipment dead space. The lowest VE/CO2 output ratio was insignificantly different from the ratio at the anaerobic threshold, less variable than that for the slope relationship, and unaffected by the site, ergometer, and gas exchange measurement systems. The regression equation for the lowest VE/CO2 output ratio was 27.94 + 0.108 x age + (0.97 = F, 0.0 = M) - 0.0376 x height, where age is in years and height is in centimeters. We conclude that the lowest VE/CO2 output ratio is the preferred noninvasive method to estimate ventilatory inefficiency.

Adult↗
PubMed2004

Effects of acute hypoxia on the determination of anaerobic threshold using the heart rate-work rate relationships during incremental exercise tests.

Anaerobic threshold which describes the onset of systematic increase in blood lactate concentration is a widely used concept in clinical and sports medicine. A deflection point between heart rate-work rate has been introduced to determine the anaerobic threshold non-invasively. However, some researchers have consistently reported a heart rate deflection at higher work rates, while others have not. The present study was designed to investigate whether the heart rate deflection point accurately predicts the anaerobic threshold under the condition of acute hypoxia. Eight untrained males performed two incremental exercise tests using an electromagnetically braked cycle ergometer: one breathing room air and one breathing 12 % O2. The anaerobic threshold was estimated using the V-slope method and determined from the increase in blood lactate and the decrease in standard bicarbonate concentration. This threshold was also estimated by in the heart rate-work rate relationship. Not all subjects exhibited a heart rate deflection. Only two subjects in the control and four subjects in the hypoxia groups showed a heart rate deflection. Additionally, the heart rate deflection point overestimated the anaerobic threshold. In conclusion, the heart rate deflection point was not an accurate predictor of anaerobic threshold and acute hypoxia did not systematically affect the heart rate-work rate relationships.

Acute Disease↗
PubMed1990

[Latent retrograde atrioventricular conduction in healthy persons].

45 patients (13 females and 32 males; mean age-37 years) without an organic heart disease underwent the study, on condition that effective transesophageal, ventricular stimulation was achieved. The transesophageal pacemaker SP-5 made by OBR TEMED ZABRZE was used. Ventricular stimulation threshold and a lock of evident retrograde conduction was estimated during ventricular stimulation with a constant cycle length of 500 ms. To assess concealed retrograde atrioventricular conduction, programmed ventricular stimulation of a 50 ms cycle length was applied between late diastole and left ventricular refraction. Concealed retrograde atrioventricular conduction was diagnosed of a sinus impulse reached later ventricles than that during sinus rhythm preceding an examination. There was no evident atrioventricular retrograde conduction in 15 patients (33%). In 9 of them (60%) programmed stimulation revealed concealed retrograde atrioventricular conduction reaching atrioventricular node. Obtained results indicate, that the transesophageal programmed ventricular stimulation enables to examine concealed a-v conduction phenomenon and can be helpful in approximate localization of retrograde atrioventricular block.

Adolescent↗
PubMed2000

Visual, long-latency auditory and brainstem auditory evoked potentials in migraine: relation to pattern size, stimulus intensity, sound and light discomfort thresholds and pre-attack state.

We aimed to estimate primary sensory evoked potential (EP) amplitude, amplitude-intensity functions and habituation in migraine patients compared with healthy control subjects and to investigate the possible relation to check size, sound and light discomfort thresholds, and the time to the next attack. Amplitudes of cortical visual evoked potentials (VEP, check size 8' and 33'), cortical long latency auditory evoked potential (AEP NIP1; 40, 55 and 70 dB SL tones) and brainstem auditory evoked potential (BAEP wave IV-V; 40, 55 and 65 dB SL clicks) were recorded and analysed in a blind and balanced design. The difference between the response to the first and the second half of the stimulus sequence was used as a measure of habituation. Twenty-one migraine patients (16 women and five men, mean age 39.3 years, six with aura, 15 without aura) and 22 sex- and age-matched healthy control subjects were studied (18 women and four men, mean age 39.5 years). Low sound discomfort threshold correlated significantly with low levels of BAEP wave IV-V amplitude habituation (r = -0.30, P = 0.05). VEP an AEP amplitudes, habituation, and amplitude-intensity function (ASF) slopes did not differ between groups when ANOVA main factors were considered. Control group VEP habituation was found for small check stimuli (P = 0.04), while potentiation was observed for medium sized checks (P = 0.02). The eight migraine patients who experienced headache within 24 h after the test tended to have increased BAEP wave IV-V ASF slopes (P = 0.08). This subgroup did also have a significant VEP habituation to small checks (P = 0.04). No correlation was found between different modalities. These results suggest that: (i) VEP habituation/potentiation state and brainstem activatio state may depend on the attack-interval cycle in migraine; (ii) VEP habituation/ potentiation may depend on spatial stimulus frequency; (iii) phonophobia (and possibly photophobia) may depend more on subcortical (brainstem) function than on cortical mechanisms; (iv) low cortical preactivation in migraine could not be confirmed; (v) EP habituation and ASF analysis may reflect sensory modality-specific, not generalized, central nervous system states in migraine and healthy control subjects.

Acoustic Stimulation↗
PubMed1982

Mechanisms of phytohaemagglutinin (PHA) stimulation of normal human lymphocytes: 'trigger' 'push' or both?

The growth in volume of human peripheral blood lymphocytes after stimulation with various concentrations of PHA was measured with an electronic particle counter. The percentage of growing cells and averaged values describing their growth rates during the elapsed period of culture were estimated by fitting to the observed data the volume distributions derived from a mathematical model. With sub-optimal doses, the percentage of cells stimulated , and their incremental growth rate, increased with increasing dose of PHA, but the time-course of recruitment into the G1-phase was similar with all PHA concentrations studied. The results provide strong support for the 'trigger' hypothesis that there is a distribution of stimulation thresholds within the lymphocyte population: consequently, increasing mitogen concentration will be expected to result in increased numbers of responding cells within the suboptimal concentration range.

Adult↗
PubMed1991

Effect of work load on cutaneous vascular response to exercise.

The purpose of the present study was to examine whether intensity of exercise affects skin blood flow response to exercise. For this purpose, six healthy men cycled, in a random order on different days, for 15 min at 50, 60, 70, 80, and 90% of their maximum oxygen consumption (VO2max) at a room temperature of 25 degrees C. At the end of exercise, esophageal temperature (Tes) averaged 37.4 +/- 0.2, 37.7 +/- 0.2, 37.9 +/- 0.2, 38.6 +/- 0.3, and 38.9 +/- 0.4 degrees C (SE) at the 50, 60, 70, 80, and 90% work loads, respectively. At the two highest work loads, no steady state was observed in Tes. Skin blood flow was estimated by measuring forearm blood flow (FBF) with strain-gauge plethysmography and by laser-Doppler flowmetry on the upper back. Both techniques showed that skin blood flow response to rising Tes was markedly reduced at the 90% work load compared with other work loads. At the end of exercise, FBF averaged 7.5 +/- 1.7, 10.7 +/- 3.1, 9.6 +/- 2.1, 11.3 +/- 2.6, and 5.4 +/- 1.3 (SE) ml.min-1.100 ml-1 (P less than 0.01) at the 50, 60, 70, 80, and 90% VO2max work loads, respectively. The corresponding values for Tes threshold for cutaneous vasodilation (FBF) were 37.42 +/- 0.16, 37.48 +/- 0.13, 37.59 +/- 0.13, 37.79 +/- 0.19, and 38.20 +/- 0.22 degrees C (P less than 0.05) at 50, 60, 70, 80, and 90% VO2max, respectively. In two subjects, no cutaneous vasodilation was observed at the 90% work load.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗