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At least 253 records · Page 14Linked to original sources
PubMed1997

Comparison of a blocking vs. a flare-up protocol in poor responders with a normal and abnormal clomiphene citrate challenge test.

This study aimed to standardize the clomiphene citrate test (CC-t) in our laboratory while comparing two different protocols of controlled ovarian stimulation in poor responders. One hundred and forty-four patients scheduled for assisted reproductive techniques were submitted to the CC-t within 3 months before starting stimulation; 133 underwent controlled ovarian stimulation with a blocking protocol. Poor responders in the first cycle (n = 30) were subsequently treated with a flare-up protocol. Although it was not statistically significant, more patients reached oocyte retrieval with the flare-up protocol. In the completed cycles, more gonadotropin ampules (55 +/- 15 vs. 34 +/- 13; p < 0.001) and more stimulation days (12.6 +/- 1 vs. 11.6 +/- 1.2; p < 0.005) were needed in the blocking than in the flare-up protocol. No difference was observed in peak 17 beta-estradiol levels, preovulatory follicles, oocytes retrieved or pregnancy rate between the two protocols. According to the threshold values, established on CC-t of patients who obtained a clinical pregnancy (n = 44), the incidence of abnormal results was 10%. All but one patient with abnormal CC-t were poor responders during the first stimulation cycle. The flare-up protocol did not improve the ovarian response in these patients.

Adult↗
PubMed1991

Evaluation of Threshold: an independent living program for homeless adolescents.

The Threshold Project, a residential treatment program, was designed to work with homeless and alienated young women who were approaching 18 years of age but lacked the skills, values, and attitudes necessary to care for themselves and assume the responsibilities of adulthood. Project services were designed to prepare these young women for independent living and to break the intergenerational cycle of abuse and neglect experienced by this population. Threshold offered a series of progressively more independent living experiences to young homeless women ages 16-18 years, who had been sexually/physically/emotionally abused or neglected, and who had been involved in or at high risk for prostitution. A majority of the clients responded well to the requirements of the program, including the expectation that they maintain employment and participate in educational programs during the semi-independent living phase of the project. A follow-up assessment undertaken after clients left the project found that 42% of the young women met all "success" criteria, that is, they lived independently (or in stable situations), attended school and/or were employed, had not engaged in prostitution or other offense behavior, and did not abuse alcohol or other substances.

Activities of Daily Living↗
PubMed2001

Is GnRH self-priming an obligatory feature of the reproductive cycle?

Insufficient suppression of LH (premature elevation) and FSH (prolonged release) give rise to blood concentrations which may cause damaging effects on oocyte viability and too many follicles respectively. During the surge, LH rises from low to high threshold values to initiate processes from initiation of the resumption of oocyte meiosis to the induction of ovulation. In general, it is thought that a dramatic increase in LH concentration is required to attain the high threshold for ovulation. A self-priming mechanism, by which gonadotrophin-releasing hormone (GnRH) enhances the LH (and FSH) responses to its own action, was thought to be responsible. However, normal LH surges in rats consist of <2-7% of the maximal pituitary releasing capacity. The physiological roles of LH and FSH favour a control mechanism that restrains their blood concentrations during most of the cycle. Ovarian proteins, e.g. inhibin and putative gonadotrophin-surge-inhibiting factor/attenuating factor (GnSIF/AF), are involved in this process. We argue that the increased pituitary LH responsiveness during the mid-cycle surge is not the result of a self-priming process that 'dramatically' increases the LH releasing capacity of the pituitary gland. This is probably due to elimination by GnRH of the inhibitory action of the putative ovarian proteins GnSIF/AF.

Animals↗
PubMed1997

The plasma lactate response to exercise and endurance performance: relationships in elite triathletes.

The lactate response to exercise has been studied thoroughly during the last decades and it has been described using a variety of terms and definitions. Numerous investigations observed close relationships between the lactate response and endurance performance. The main question in this study was which of the various lactate responses during incremental exercise described in the literature was the best indicator of endurance performance. The plasma lactate response (PLR) was assessed during an incremental exercise test on 13 male elite triathletes (age 25.5+/-5.8 yrs; HT 179.7+/-5.4 cm; WT 71.3+/-4.7 kg) on a bicycle ergometer. The load was started at 2.5 W/kg and increased by 40 W every 4 min. We evaluated the following PLR-parameters: the workloads at the fixed lactate levels of 2, 3, 4, 5, 6, 7, and 8 mmol/l which were assessed by extrapolation from a workload-lactate-heart rate curve (P2, P3, P4, P5, P6, P7, P8 respectively), the lactate threshold which was defined as the workload at the point at which a non-linear increase of blood lactate occurred (Plt), and the workload at the lactate level that was 1 mmol/l above the baseline (P + 1). Four to seven weeks after the laboratory test, heart rate and lactate levels were assessed during a 40-km long time trial on a bicycle. Two parameters were considered as indicative of athletic performance: the road racing time (Tt), and the workload extrapolated from the workload-lactate-heart rate curve at the heart rate and lactate levels observed during the time trial (Pt). Only P2 showed a significant correlation with Tt (r=-0.65; p < 0.05; se = 72.5 s). Multiple regression analysis with the anthropometric parameters height and weight as additional independent parameters did not change the predictive value. We concluded that for predicting the cycling performance of similarly well-trained subjects the predictive value of PLR is negligible.

Adult↗
PubMed2000

Acute head-down tilt decreases the postexercise resting threshold for forearm cutaneous vasodilation.

The purpose of this study was to evaluate the role of baroreceptor control on the postexercise threshold for forearm cutaneous vasodilation. On four separate days, six subjects (1 woman) were randomly exposed to 65 degrees head-up tilt and to 15 degrees head-down tilt during a No-Exercise and Exercise treatment protocol. Under each condition, a whole body water-perfused suit was used to regulate mean skin temperature (T(sk)) in the following sequence: 1) cooling until the threshold for vasoconstriction was evident; 2) heating ( approximately 7.0 degrees C/h) until vasodilation occurred; and 3) cooling until esophageal temperature (T(es)) and (T(sk)) returned to baseline values. The Exercise treatment consisted of 15 min of cycling exercise at 70% maximal O(2) uptake, followed by 15 min of recovery in the head-up tilt position. The No-Exercise treatment consisted of 30 min resting in the head-up tilt position. After the treatment protocols, subjects were returned to their pretreatment condition, then cooled and warmed again consecutively. The calculated T(es) threshold for cutaneous vasodilation increased 0.24 degrees C postexercise during head-up tilt (P < 0.05), whereas no difference was measured during head-down tilt. In contrast, sequential measurements without exercise demonstrate a time-dependent decrease for head-up tilt (0.17 degrees C) and no difference for head-down tilt. Pretreatment thresholds were significantly lower during head-down tilt compared with head-up tilt. We have shown that manipulating postexercise venous pooling by means of head-down tilt, in an effort to reverse its impact on baroreceptor unloading, resulted in a relative lowering of the resting postexercise elevation in the T(es) for forearm cutaneous vasodilation.

Adult↗
PubMed1992

Discriminative performance of the domestic hen in a visual acuity task.

The performance of 6 domestic hens on a visual acuity task was studied using a spatial discrete-trial conditional discrimination procedure. Gray stimuli and vertical square-wave gratings, ranging in spatial frequency from 1 to 10 cycles per millimeter, were presented in a descending and ascending series of probes. On each trial, either a grating or gray stimulus was presented. Only one spatial frequency of grating was presented during each session. Between probe sessions, training continued at the coarsest grating value. Stimulus discriminability, measured as values of log d, changed with changes in grating spatial frequency for both probe series. Fitted lines described the linear portion of the psychometric functions. Thresholds estimated from the lines generally ranged from four to six cycles per degree, with slightly greater estimates from data from the descending probe series. There were no systematic changes in response bias as a function of grating spatial frequency.

Journal Article↗
PubMed1994

Aerobic capacity and anaerobic threshold of wheelchair basketball players.

This study evaluated the aerobic capacity and anaerobic threshold of national level Israeli wheelchair basketball players. Subjects were tested working on a wheelchair rolling on a motor driven treadmill and on an arm cycle ergometer. Metabolic and cardiopulmonary parameters were measured during graded maximal exercise tests. Blood lactic acid (LA) concentration was measured in the intervals between loads during the test on the wheelchair. Heart rate (HR) and % heart rate reserve (%HRR) corresponding to the anaerobic threshold (4 mM blood LA) were evaluated while working on the wheelchair rolling on a motor driven treadmill. While working on the wheelchair the following peak exercise values were obtained: VO2 = 24.7 ml.kg/min, VE = 92.09 l/min HR = 181.5 b/min and R = 1.22. Values corresponding to the anaerobic threshold were found to be, HR = 139 b/min and %HRR = 57.02. Low correlations were obtained between peak exercise VO2 and VE measured while working on the wheelchair and those measured with arm cycle ergometer (r = 0.57 p = 0.137 and r = 0.4 p = 0.233 respectively). As athletes, subjects in the present study may be classified as having a low aerobic capacity and anaerobic threshold. It is also concluded that the ergometer type may have an important influence on test results.

Adult↗
PubMed2006

A model for the dynamics of human weight cycling.

The resolution to lose weight by cognitive restraint of nutritional intake often leads to repeated bouts of weight loss and regain, a phenomenon known as weight cycling or "yo-yo dieting". A simple mathematical model for weight cycling is presented. The model is based on a feedback of psychological nature by which a subject decides to reduce dietary intake once a threshold weight is exceeded. The analysis of the model indicates that sustained oscillations in body weight occur in a parameter range bounded by critical values. Only outside this range can body weight reach a stable steady state. The model provides a theoretical framework that captures key facets of weight cycling and suggests ways to control the phenomenon. The view that weight cycling represents self-sustained oscillations has indeed specific implications. In dynamical terms, to bring weight cycling to an end, parameter values should change in such a way as to induce the transition of body weight from sustained oscillations around an unstable steady state to a stable steady state. Maintaining weight under a critical value should prevent weight cycling and allow body weight to stabilize below the oscillatory range.

Humans↗
PubMedDate not supplied

Induction of electrical heterogeneity impairs ventricular defibrillation: an effect specific to regional conduction velocity slowing.

BACKGROUND: This study determined whether dispersion of conduction velocity, refractoriness, or excitability increases biphasic shock defibrillation energy requirements (DERs). METHODS AND RESULTS: Twenty-four swine were instrumented with a mid-LAD perfusion catheter for regional infusion of lidocaine 0.75 mg. kg(-1). h(-1) (n=7), low-dose d-sotalol (0.16 mg. kg(-1). h(-1)) (n=4), high-dose d-sotalol (0.5 mg. kg(-1). h(-1)) (n=6), or saline (n=7). Effective refractory periods (ERPs) were determined at 5 myocardial sites, and regional conduction velocity was determined in LAD-perfused and -nonperfused regions. Regional lidocaine infusion increased DER values by 84% (P=0.008) and slowed conduction velocity by 23% to 35% (P<0.01) but did not affect ERP. Conversely, regional low- and high-dose d-sotalol infusion did not alter DER values or conduction velocity but increased regional ERP by 14% to 17% (P<0.001). Regional lidocaine increased conduction velocity dispersion by 100% to 200% (P=0.01) but did not change ERP dispersion, whereas d-sotalol increased ERP dispersion by 140% (P<0.001) without affecting conduction velocity dispersion. Lidocaine infusion induced ventricular fibrillation (VF) in 6 of 7 animals, whereas regional d-sotalol was not proarrhythmic. Regional infusion of lidocaine and d-sotalol prolonged VF cycle length by 23% to 41% (P<0.05) in the perfused region and increased VF cycle length dispersion by 85% to 240% (P<0.05). Both agents increased pacing threshold (excitability) in the perfused region by 93% to 116% (P<0.05). CONCLUSIONS: Regional conduction velocity slowing increased DER values, which was probably a result of spatial dispersion of conduction velocity. Increasing refractory period dispersion without changing conduction velocity did not alter DFT values. Thus, dispersion of conduction velocity may be a more likely regulator of defibrillation efficacy than dispersion of refractoriness.

Action Potentials↗
PubMed1984

The role of lipid and antioxidant exchanges in cell division synchronization (mathematical model).

Cell-cycle synchronization of two diffuse-coupled cells has been studied in the framework of the membrane model for the cell division cycle, proposed by Chernavskii et al. (1977). It has been shown semi-analytically (using the averaging principle) and by computer stimulation that a) if the duration of the G1-phase (TG1) for two identical cells is comparable with the duration of the remaining cycle (TS + G2 + M), the lipid (L)-exchange results in a synchronization with phase difference phi = 0. The antioxidant (A)-exchange leads to a phase-locking with phi = T0/2 (where T0 is the cell cycle period; b) if TG1 much greater than TS + G2 + M (or TG1 much less than TS + G2 + M) the L-exchange makes synchronization possible both with phi = 0 and phi = T0/2 while the A-exchange results in phase-locking with phi confined to the region 0 to T0/2; c) for non-identical cells differing in the values of kinetic parameters, the locking band narrows as the population density increases (when some model parameters are close to the bifurcation thresholds). We expect that the cells selected artificially at a definite phase of cycle might maintain the synchronous division for a long time if the lipid exchange between cells were stimulated.

Antioxidants↗
PubMed1982

Cell-cycle kinetics and ultraviolet light survival in UV-1, a Chinese hamster ovary cell mutant defective in post-replication recovery.

UV-I, an ultraviolet-sensitive mutant of CHO-KI, is abnormally slow to recover from the inhibition of DNA synthesis caused by u.v. irradiation. When synchronized UV-I cells are irradiated in G1, their movement into S phase is unaltered, but thymidine incorporation is depressed (compared with that in the parent cell similarly treated). When irradiated in S phase, again incorporation is more depressed, and S phase suffers a greater delay in UV-I than in the parent cell. UV-I and its parent have similar capacities for excision repair of u.v.-induced damage inflicted in G1, and so enter S phase with similar amounts of unrepaired damage. The single-cell survival was measured after irradiation at different points in the cell cycle. The mutant and parent cells have similar values of D0 (mean lethal dose) except in mitosis, when the parent cell shows markedly greater resistance to u.v. irradiation. Dq (quasi-threshold dose) is fairly constant for the parent cell, but in UV-I it falls to a minimum in S phase. The responses of UV-I to u.v. irradiation are generally consistent with its known defect in the process of post-replication recovery, i.e. the ability to join up the abnormally small DNA fragments synthesized on a u.v.-damaged template.

Animals↗
PubMed1999

The effect of dynamic exercise on resting cold thermoregulatory responses measured during water immersion.

The purpose of this study was to evaluate the effect of exercise on the subsequent post-exercise thresholds for vasoconstriction and shivering measured during water immersion. On 2 separate days, seven subjects (six males and one female) were immersed in water (37.5 degrees C) that was subsequently cooled at a constant rate of approximately 6.5 degrees C x h(-1) until the thresholds for vasoconstriction and shivering were clearly established. Water temperature was then increased to 37.5 degrees C. Subjects remained immersed for approximately 20 min, after which they exited the water, were towel-dried and sat in room air (22 degrees C) until both esophageal temperature and mean skin temperature (Tsk) returned to near-baseline values. Subjects then either performed 15 min of cycle ergometry (at 65% maximal oxygen consumption) followed by 30 min of recovery (Exercise), or remained seated with no exercise for 45 min (Control). Subjects were then cooled again. The core temperature thresholds for both vasoconstriction and shivering increased significantly by 0.2 degrees C Post-Exercise (P < 0.05). Because the Tsk at the onset of vasoconstriction and shivering was different during Pre- and Post-Exercise Cooling, we compensated mathematically for changes in skin temperatures using the established linear cutaneous contribution of skin to the control of vasoconstriction and shivering (20%). The calculated core temperature threshold (at a designated skin temperature of 32.0 degrees C) for vasoconstriction increased significantly from 37.1 (0.3) degrees C to 37.5 ( 0.3) degrees C post-exercise (P < 0.05). Likewise, the shivering threshold increased from 36.2 (0.3) degrees C to 36.5 (0.3) degrees C post-exercise (P < 0.05). In contrast to the post-exercise increase in cold thermal response thresholds, sequential measurements demonstrated a time-dependent similarity in the Pre- and Post-Control thresholds for vasoconstriction and shivering. These data indicate that exercise has a prolonged effect on the post-exercise thresholds for both cold thermoregulatory responses.

Adult↗
PubMed1997

An interpretation of the internal desynchronizations based on dynamics of the two-process model.

Daan's two-process model is known to be one of the most powerful models, covering various situations from free-running to sleep deprivation. In this study, bifurcation properties of the model dynamics are clarified using a circle map. In addition, the two-process model is applied to simulate the two distinct patterns (the period-prolonged: I and the period-shortened: II) of sleep-wake cycles during internal desynchronizations. We propose the novel interpretation that types I and II could be regarded as mutual entrainments between the body temperature rhythm and the sleep-wake cycle with the period ratios 3:4 and 3:2, respectively. From the bifurcation properties of the two-process model obtained above, the model is shown to be able to generate the respective type of mutual entrainment with an appropriate range of a parameter value, i.e, a gap between thresholds. The variable behavior of human circadian rhythm is suggested to be systematically understood based on the bifurcation properties of the two-process model.

Activity Cycles↗
PubMed1997

Fatigue effects on body balance.

Body sway variables (sway area and sway path) were recorded by a dynamometric platform in 13 young subjects, standing quiet with feet together, with eyes open (EO) and eyes closed (EC), prior to and following two types of physical exercise (treadmill walking and cycle ergometer pedalling). Each exercise was performed under both fatiguing (above anaerobic threshold) and non-fatiguing conditions. Following fatiguing treadmill exercise, we observed a significant increase in body sway with respect to pre-exercise values. The increase was present under both visual conditions, affected both sway area and sway path and lasted until about 15 min from the end of the exercise. The Romberg quotient (the ratio of EC/EO of sway area, or sway path) significantly increased after the fatiguing exercise with respect to the non-fatiguing exercise. The mean position of the centre of foot pressure (CFP) was unchanged after the exercise. Fatigue induced an increase in the median frequency of oscillation of the centre of foot pressure, independent of the amplitude of sway. Non-fatiguing treadmill exercise induced no significant changes in sway or in its frequency content. Following fatiguing cycle ergometer exercise, a negligible increase or a decrease (under eyes closed condition) in body sway were observed. Non-fatiguing cycling exercise induced no significant changes or a decrease in sway. Control experiments showed that simple repetition of successive stance trials (without intercalated exercise) was able by itself to induce a decrease in sway. By taking this effect into account, both types of cycling exercises revealed a mild capacity to increase sway. We concluded that body sway increased after strenuous physical exercise, but was little affected by exercise performed below the estimated anaerobic threshold. The effects of fatigue on sway were short-lasting and of moderate extent, and therefore were not liable to seriously threaten body equilibrium.

Adolescent↗
PubMed2005

Cyclic effects on experimental pain response in women with temporomandibular disorders.

AIMS: Since cyclic effects on experimental pain response in women with temporomandibular disorders (TMD) have not been adequately studied, the aim of this study was to assess variations in experimental pain response at 4 phases of the menstrual cycle. METHODS: Eighteen normally cycling women with TMD, 25 women with TMD and taking oral contraceptives (OC), 25 normally cycling pain-free controls, and 26 pain-free controls taking OC underwent 3 experimental pain procedures at 4 phases during each of 3 menstrual cycles. These procedures included algometer palpations at fixed amounts of pressure and pressure pain thresholds at several body sites, and an ischemic arm pain task. Repeated measures analysis of variance was used to compare cycle phase, TMD group, and OC status differences in experimental pain response. RESULTS: Significant phase-related differences were seen for palpation intensity measures (P values < .05). Normally cycling women with TMD showed higher palpation pain intensity at menses and midluteal phases, while women with TMD taking OC showed stable palpation pain intensity ratings at menses, ovulatory, and midluteal phases, with increased intensity at the late luteal phase. TMD subjects had greater palpation pain and ischemic pain intensity and lower pressure pain thresholds compared to controls. CONCLUSION: Phase-related differences in experimental pain response were not strong and were more often found for experimental stimuli with greater clinical relevance (ie, palpation pain) compared with an ischemic pain task.

Adolescent↗
PubMed1993

Skin nerve stimulation caused by low frequency electric field.

The most known result of the influence of the VLF and LF electric fields on a human being is pain due to stimulation of the skin nerves. The threshold of nerve stimulation is related to a value of electric current flowing across a small area of the skin being in contact with the surface of a metallic object. It is shown in this paper that the following set of important parameters corresponds to fingertip threshold perception of the current which from the value of 0.5 mA at 1 kHz increases linearly up to the value of 50 mA at 100 kHz: charge transported across the skin during one duty cycle (0.225 microC), product of the voltage drop on the skin and the surface of the contact electrode (1 mVm2), product of the power dissipated in the skin under the contact electrode and the surface of the contact electrode (0.5 microW m2), electric field intensity of vertical polarization (1.6 kV/m).

Electric Stimulation↗
PubMed2004

Effect of a 15% increase in preferred pedal rate on time to exhaustion during heavy exercise.

The aim of this study was to evaluate the effect of a 15% increase in preferred pedal rate (PPR) on both time to exhaustion and pulmonary O(2) uptake (VO(2)) response during heavy exercise. Seven competitive cyclists underwent two constant-power tests (CPT) at a power output that theoretically requires 50% of the difference in VO(2) between the second ventilatory threshold and VO(2)max (Pdelta50). Each cyclist cycled a CPT at PPR (CPTPPR) and a CPT at +15% of PPR (CPT+15%) in a randomized order. The average PPR value was 94 +/- 4 rpm, and time to exhaustion was significantly longer in CPTPPR compared with CPT+15% (465 +/- 139 vs. 303+/- 42 s, respectively; p = 0.01). A significant decrease in VO(2) values in the first minutes of exercise and a significant increase in VO(2) slow component was reported in CPT+15% compared with CPT(PPR). These data indicate that the increase of 15% PPR was associated with a decrease in exercise tolerance and a specific VO(2) response, presumably due to an increase of negative muscular work, internal work, and an altering of motor unit recruitment patterns.

Adult↗
PubMed1997

Comparison of five cell cycle analysis models applied to 1414 flow cytometric DNA histograms of fresh frozen breast cancer.

Conflicting prognostic results with regard to DNA flow cytometric variables have been reported for breast cancer patients. Reasons for this can be found mainly on the different levels of methodology, including the interpretation of the DNA-histograms. Several computer programs based on different fitting models are available for cell cycle analyses which result in different %S-phase calculations. The present study evaluated the influence of 5 different cell cycle analysis models on several cell cycle variables (%S-phase, %G2M-phase, %diploid cells, DNA-index, %debris) derived from flow cytometric DNA-histograms obtained from breast cancers. DNA-histograms obtained from 1414 fresh frozen breast cancers were interpreted using 5 different cell cycle analysis models using the computer program MultiCycle AV. Model 1 used the zero order S-phase calculation and "sliced nuclei" debris correction, model 2 added fixed G0/G1 and G2/M-phase ratio, and model 3 added correction for aggregates. Model 4 applied the first order S-phase calculation and sliced nuclei debris correction. Model 5 fixed the CVs of the G0/G1 and G2/M-phase in addition to applying the sliced nuclei debris correction and zero-order S-phase calculation. Using all cases, it was shown that when the aggregates correction was included (model 3) in the analysis, on average, significantly lower mean values were obtained for %S-phase cells, and %debris, and %G2M-phase cells of the first cell cycle. No significant differences were observed for the other variables. Analyzing the DNA-diploid, tetraploid, and aneuploid cases separately, similar results were obtained. Linear regression analysis showed only moderately strong correlations for the %S-phase and %G2M-phase variables between the different models, indicating that for individual DNA-histograms the cell cycle analysis results may vary. In conclusion, quite different values can be obtained for especially the %S-phase cells using different cell cycle analysis models in individual cases. Correction for aggregates results on average in significantly lower %S-phase values. This clearly has implications for comparing %S-phase results from studies using aggregate correction or not, especially with regard to prognostic thresholds. Large follow-up studies are necessary to derive at the prognostically best model.

Breast Neoplasms↗