Evaluation of electromyographic activity and heart rate responses to isometric exercise. The role played by muscular mass and type

The purpose of the present study was to examine the relationship between the electromyographic (EMG) activity and heart rate (HR) responses induced by isometric exercise performed by knee extension (KE) and flexion (KF) in men. Fifteen healthy male subjects, 21 ± 1.3 years (mean ± SD), were submitted to KE and KF isometric exercise tests at 100% of maximal voluntary contraction (MVC). The exercises were performed with one leg (right or left) and with two legs simultaneously, for 10 s in the sitting position with the hip and knee flexed at 90o. EMG activity (root mean square values) and HR (beats/min) were recorded simultaneously both at rest and throughout the sustained contraction. The HR responses to isometric exercise in KE and KF were similar when performed with one and two legs. However, the HR increase was always significantly higher in KE than KF (P<0.05), whereas the EMG activity was higher in KE than in KF (P<0.05), regardless of the muscle mass (one or two legs) involved in the effort. The correlation coefficients between HR response and the EMG activity during KE (r = 0.33, P>0.05) and KF (r = 0.15, P>0.05) contractions were not significant. These results suggest that the predominant mechanism responsible for the larger increase in HR response to KE as compared to KF in our study could be dependent on qualitative and quantitative differences in the fiber type composition found in each muscle group. This mechanism seems to demand a higher activation of motor units with a corresponding increase in central command to the cardiovascular centers that modulate HR control.

Heart rate variability under resting conditions in postmenopausal and young women

The aim of the present study was to compare the modulation of heart rate in a group of postmenopausal women to that of a group of young women under resting conditions on the basis of R-R interval variability. Ten healthy postmenopausal women (mean ± SD, 58.3 ± 6.8 years) and 10 healthy young women (mean ± SD, 21.6 ± 0.82 years) were submitted to a control resting electrocardiogram (ECG) in the supine and sitting positions over a period of 6 min. The ECG was obtained from a one-channel heart monitor at the CM5 lead and processed and stored using an analog to digital converter connected to a microcomputer. R-R intervals were calculated on a beat-to-beat basis from the ECG recording in real time using a signal-processing software. Heart rate variability (HRV) was expressed as standard deviation (RMSM) and mean square root (RMSSD). In the supine position, the postmenopausal group showed significantly lower (P<0.05) median values of RMSM (34.9) and RMSSD (22.32) than the young group (RMSM: 62.11 and RMSSD: 49.1). The same occurred in the sitting position (RMSM: 33.0 and RMSSD: 18.9 compared to RMSM: 57.6 and RMSSD: 42.8 for the young group). These results indicate a decrease in parasympathetic modulation in postmenopausal women compared to young women which was possibly due both to the influence of age and hormonal factors. Thus, time domain HRV proved to be a noninvasive and sensitive method for the identification of changes in autonomic modulation of the sinus node in postmenopausal women.

Induction of interleukin-10 by HIV antigens in peripheral mononuclear cells of health care workers after occupational exposure to HIV-1-positive blood

Evaluation of HIV-induced IL-2 production by peripheral blood mononuclear cells (PBMC) and HIV-specific T helper and cytotoxic T lymphocyte (CTL) responses in health care workers (HCW) occupationally exposed to HIV reveals a high rate of response to HIV among non-seroconverters. IL-10 is also known to interfere with HIV infection in vitro. To evaluate the induction of IL-10 by HIV antigens in HCW occupationally exposed to HIV, 18 HCW with percutaneous injury were enrolled in this study, 9 of them exposed to HIV-contaminated blood, and 9 exposed to HIV-negative blood. PBMC were incubated on plates coated with HIV-1 antigens, and IL-10 was measured in supernatants by ELISA. Five of nine HCW exposed to HIV-contaminated blood presented HIV-induced IL-10. Two of nine HCW exposed to HIV-negative source patients also had detectable levels of HIV-induced IL-10, one of them in the sample obtained on the day of accidental exposure. There was a relationship between the type of device involved in injury and IL-10 production. Individuals exposed to hollow needles or scalpels presented HIV-induced IL-10, whereas those exposed to solid needles and to digital puncture did not, suggesting a relationship between infectious load and IL-10. Although occupational exposure to HIV leads to a low rate of seroconversion, these individuals can develop an antigen-specific immune response characterized in our study by induction of IL-10 in PBMC in vitro.

Effects of aerobic exercise training on heart rate variability during wakefulness and sleep and cardiorespiratory responses of young and middle-aged healthy men

The purpose of the present study was to evaluate the effects of aerobic physical training (APT) on heart rate variability (HRV) and cardiorespiratory responses at peak condition and ventilatory anaerobic threshold. Ten young (Y: median = 21 years) and seven middle-aged (MA = 53 years) healthy sedentary men were studied. Dynamic exercise tests were performed on a cycloergometer using a continuous ramp protocol (12 to 20 W/min) until exhaustion. A dynamic 24-h electrocardiogram was analyzed by time (TD) (standard deviation of mean R-R intervals) and frequency domain (FD) methods. The power spectral components were expressed as absolute (a) and normalized units (nu) at low (LF) and high (HF) frequencies and as the LF/HF ratio. Control (C) condition: HRV in TD (Y: 108, MA: 96 ms; P<0.05) and FD - LFa, HFa - was significantly higher in young (1030; 2589 ms²/Hz) than in middle-aged men (357; 342 ms²/Hz) only during sleep (P<0.05); post-training effects: resting bradycardia (P<0.05) in the awake condition in both groups; VO2 increased for both groups at anaerobic threshold (P<0.05), and at peak condition only in young men; HRV in TD and FD (a and nu) was not significantly changed by training in either groups. The vagal predominance during sleep is reduced with aging. The resting bradycardia induced by short-term APT in both age groups suggests that this adaptation is much more related to intrinsic alterations in sinus node than in efferent vagal-sympathetic modulation. Furthermore, the greater alterations in VO2 than in HRV may be related to short-term APT.

Excitatory amino acid receptor blockade within the caudal pressor area and rostral ventrolateral medulla alters cardiovascular responses to nucleus raphe obscurus stimulation in rats

Pressor responses elicited by stimulation of the nucleus raphe obscurus (NRO) depend on the integrity of the rostral ventrolateral medulla (RVLM). Therefore, to test the participation of excitatory amino acid (EAA) receptors in the cardiovascular responses evoked by NRO stimulation (1 ms, 100 Hz, 40-70 µA, for 10 s), the EAA antagonist kynurenic acid (Kyn) was microinjected at different sites in the ventrolateral medullar surface (2.7 nmol/200 nl) of male Wistar rats (270-320 g, N = 39) and NRO stimulation was repeated. The effects of NRO stimulation were: hypertension (deltaMAP = +43 ± 1 mmHg, P<0.01), bradycardia (deltaHR = -30 ± 7 bpm, P<0.01) and apnea. Bilateral microinjection of Kyn into the RVLM, which did not change baseline parameters, almost abolished the bradycardia induced by NRO stimulation (deltaHR = -61 ± 3 before vs -2 ± 3 bpm after Kyn, P<0.01, N = 7). Unilateral microinjection of Kyn into the CVLM did not change baseline parameters or reduce the pressor response to NRO stimulation (deltaMAP = +46 ± 5 before vs +48 ± 5 mmHg after Kyn, N = 6). Kyn bilaterally microinjected into the caudal pressor area reduced blood pressure and heart rate and almost abolished the pressor response to NRO stimulation (deltaMAP = +46 ± 4 mmHg before vs +4 ± 2 mmHg after Kyn, P<0.01, N = 7). These results indicate that EAA receptors on the medullary ventrolateral surface play a role in the modulation of the cardiovascular responses induced by NRO stimulation, and also suggest that the RVLM participates in the modulation of heart rate responses and that the caudal pressor area modulates the pressor response following NRO stimulation.

Effect of acute nitric oxide synthase inhibition in the modulation of heart rate in rats

Acute nitric oxide synthase inhibition with N G-nitro-L-arginine methyl ester (L-NAME) on chronotropic and pressor responses was studied in anesthetized intact rats and rats submitted to partial and complete autonomic blockade. Blood pressure and heart rate were monitored intra-arterially. Intravenous L-NAME injection (7.5 mg/kg) elicited the same hypertensive response in intact rats and in rats with partial (ganglionic and parasympathetic blockade) and complete autonomic blockade (38 ± 3, 55 ± 6, 54 ± 5, 45 ± 5 mmHg, respectively; N = 9, P = NS). L-NAME-induced bradycardia at the time when blood pressure reached the peak plateau was similar in intact rats and in rats with partial autonomic blockade (43 ± 8, 38 ± 5, 46 ± 6 bpm, respectively; N = 9, P = NS). Rats with combined autonomic blockade showed a tachycardic response to L-NAME (10 ± 3 bpm, P<0.05 vs intact animals, N = 9). Increasing doses of L-NAME (5.0, 7.5 and 10 mg/kg, N = 9) caused a similar increase in blood pressure (45 ± 5, 38 ± 3, 44 ± 9 mmHg, respectively; P = NS) and heart rate (31 ± 4, 34 ± 3, 35 ± 4 bpm, respectively; P = NS). Addition of L-NAME (500 µM) to isolated atria from rats killed by cervical dislocation and rats previously subjected to complete autonomic blockade did not affect spontaneous beating or contractile strength (N = 9). In vivo results showed that L-NAME promoted a tachycardic response in rats with complete autonomic blockade, whereas the in vitro experiments showed no effect on intrinsic heart rate, suggesting that humoral mechanisms may be involved in the L-NAME-induced cardiac response.

Role of nitric oxide of the median preoptic nucleus (MnPO) in the alterations of salivary flow, arterial pressure and heart rate induced by injection of pilocarpine into the MnPO and intraperitoneally

We investigated the effect of L-NAME, a nitric oxide (NO) inhibitor and sodium nitroprusside (SNP), an NO-donating agent, on pilocarpine-induced alterations in salivary flow, mean arterial blood pressure (MAP) and heart rate (HR) in rats. Male Holtzman rats (250-300 g) were implanted with a stainless steel cannula directly into the median preoptic nucleus (MnPO). Pilocarpine (10, 20, 40, 80, 160 µg) injected into the MnPO induced an increase in salivary secretion (P<0.01). Pilocarpine (1, 2, 4, 8, 16 mg/kg) ip also increased salivary secretion (P<0.01). Injection of L-NAME (40 µg) into the MnPO prior to pilocarpine (10, 20, 40, 80, 160 µg) injected into the MnPO or ip (1, 2, 4, 8, 16 mg/kg) increased salivary secretion (P<0.01). SNP (30 µg) injected into the MnPO or ip prior to pilocarpine attenuated salivary secretion (P<0.01). Pilocarpine (40 µg) injection into the MnPO increased MAP and decreased HR (P<0.01). Pilocarpine (4 mg/kg body weight) ip produced a decrease in MAP and an increase in HR (P<0.01). Injection of L-NAME (40 µg) into the MnPO prior to pilocarpine potentiated the increase in MAP and reduced HR (P<0.01). SNP (30 µg) injected into the MnPO prior to pilocarpine attenuated (100%) the effect of pilocarpine on MAP, with no effect on HR. Administration of L-NAME (40 µg) into the MnPO potentiated the effect of pilocarpine injected ip. SNP (30 µg) injected into the MnPO attenuated the effect of ip pilocarpine on MAP and HR. The present study suggests that in the rat MnPO 1) NO is important for the effects of pilocarpine on salivary flow, and 2) pilocarpine interferes with blood pressure and HR (side effects of pilocarpine), that is attenuated by NO.

Influence of Pulsed-Electric Field Irradiation in Crystallization

The growing pharmaceutical interest, among others, in the polymorphic composition of the emerging solid end-products from production processes has been traced to the need for attainment of high product purity. This is more so as the presence of different polymorphs may constitute physical impurity of the product. Hence, the need for optimization of the yield of desired product component(s) through controlled crystallization kinetics for instance. This study was carried out to investigate the impact of pulsed electric field (PEF) irradiation on the crystal morphology of glycine obtained by cooling crystallization (without seeding) from commercial glycine sample in distilled deionized water solution. In doing so, three different pulse frequencies (294, 950 and 145 Hz) and a case without PEF were studied at three cooling rates (5, 10 and 20 ºC/h). The crystal products obtained were analyzed for polymorphic composition by powder x-ray diffraction (PXRD) and Fourier transform infrared (FTIR) spectroscopy while the particles characterization was done on Morphologi G3. The results obtained from this study showed that pulsed electric field irradiation had significant impact on metastability of the aqueous solution as well as on the polymorphic composition of the end product. With increasing PEF frequency applied, nucleation started earlier and the γ-glycine polymorph content of the product crystals increased. These were found to have been aided by cooling rate, as the most significant effect was observed at 5 ºC/h. It was also discovered that PEF application had no measurable impact on the pH of the aqueous solution as well as the size distribution of the particles. Cooling on the contrary was believed to be responsible for the broadening of the particle size distribution with a downward shift of the lower limit of the raw material from about 100 μm to between 10 and 50 μm.

Heart rate variability in athletes and nonathletes at rest and during head-up tilt

The purpose of the present study was to determine if autonomic heart rate modulation, indicated by heart rate variability (HRV), differs during supine rest and head-up tilt (HUT) when sedentary and endurance-trained cyclists are compared. Eleven sedentary young men (S) and 10 trained cyclists (C) were studied. The volunteers were submitted to a dynamic ECG Holter to calculate HRV at rest and during a 70º HUT. The major aerobic capacity of athletes was expressed by higher values of at anaerobic threshold and peak conditions (P < 0.05). At rest the athletes had lower heart rates (P < 0.05) and higher values in the time domain of HRV compared with controls (SD of normal RR interval, SDNN, medians): 59.1 ms (S) vs 89.9 ms (C), P < 0.05. During tilt athletes also had higher values in the time domain of HRV compared with controls (SDNN, medians): 55.7 ms (S) vs 69.7 ms (C), P < 0.05. No differences in power spectral components of HRV at rest or during HUT were detected between groups. Based on the analysis of data by the frequency domain method, we conclude that in athletes the resting bradycardia seems to be much more related to changes in intrinsic mechanisms than to modifications in autonomic control. Also, HUT caused comparable changes in sympathetic and parasympathetic modulation of the sinus node in both groups.

Identification of anaerobic threshold using heart rate response during dynamic exercise

The objective of the present study was to characterize the heart rate (HR) patterns of healthy males using the autoregressive integrated moving average (ARIMA) model over a power range assumed to correspond to the anaerobic threshold (AT) during discontinuous dynamic exercise tests (DDET). Nine young (22.3 ± 1.57 years) and 9 middle-aged (MA) volunteers (43.2 ± 3.53 years) performed three DDET on a cycle ergometer. Protocol I: DDET in steps with progressive power increases of 10 W; protocol II: DDET using the same power values as protocol 1, but applied randomly; protocol III: continuous dynamic exercise protocol with ventilatory and metabolic measurements (10 W/min ramp power), for the measurement of ventilatory AT. HR was recorded and stored beat-to-beat during DDET, and analyzed using the ARIMA (protocols I and II). The DDET experiments showed that the median physical exercise workloads at which AT occurred were similar for protocols I and II, i.e., AT occurred between 75 W (116 bpm) and 85 W (116 bpm) for the young group and between 60 W (96 bpm) and 75 W (107 bpm) for group MA in protocols I and II, respectively; in two MA volunteers the ventilatory AT occurred at 90 W (108 bpm) and 95 W (111 bpm). This corresponded to the same power values of the positive trend in HR responses. The change in HR response using ARIMA models at submaximal dynamic exercise powers proved to be a promising approach for detecting AT in normal volunteers.

Errors in nonword repetition: bridging short- and long-term memory

According to the working memory model, the phonological loop is the component of working memory specialized in processing and manipulating limited amounts of speech-based information. The Children's Test of Nonword Repetition (CNRep) is a suitable measure of phonological short-term memory for English-speaking children, which was validated by the Brazilian Children's Test of Pseudoword Repetition (BCPR) as a Portuguese-language version. The objectives of the present study were: i) to investigate developmental aspects of the phonological memory processing by error analysis in the nonword repetition task, and ii) to examine phoneme (substitution, omission and addition) and order (migration) errors made in the BCPR by 180 normal Brazilian children of both sexes aged 4-10, from preschool to 4th grade. The dominant error was substitution [F(3,525) = 180.47; P < 0.0001]. The performance was age-related [F(4,175) = 14.53; P < 0.0001]. The length effect, i.e., more errors in long than in short items, was observed [F(3,519) = 108.36; P < 0.0001]. In 5-syllable pseudowords, errors occurred mainly in the middle of the stimuli, before the syllabic stress [F(4,16) = 6.03; P = 0.003]; substitutions appeared more at the end of the stimuli, after the stress [F(12,48) = 2.27; P = 0.02]. In conclusion, the BCPR error analysis supports the idea that phonological loop capacity is relatively constant during development, although school learning increases the efficiency of this system. Moreover, there are indications that long-term memory contributes to holding memory trace. The findings were discussed in terms of distinctiveness, clustering and redintegration hypotheses.

Luteal phase of the menstrual cycle increases sweating rate during exercise

The present study evaluated whether the luteal phase elevation of body temperature would be offset during exercise by increased sweating, when women are normally hydrated. Eleven women performed 60 min of cycling exercise at 60% of their maximal work load at 32ºC and 80% relative air humidity. Each subject participated in two identical experimental sessions: one during the follicular phase (between days 5 and 8) and the other during the luteal phase (between days 22 and 25). Women with serum progesterone >3 ng/mL, in the luteal phase were classified as group 1 (N = 4), whereas the others were classified as group 2 (N = 7). Post-exercise urine volume (213 ± 80 vs 309 ± 113 mL) and specific urine gravity (1.008 ± 0.003 vs 1.006 ± 0.002) changed (P < 0.05) during the luteal phase compared to the follicular phase in group 1. No menstrual cycle dependence was observed for these parameters in group 2. Sweat rate was higher (P < 0.05) in the luteal (3.10 ± 0.81 g m-2 min-1) than in the follicular phase (2.80 ± 0.64 g m-2 min-1) only in group 1. During exercise, no differences related to menstrual cycle phases were seen in rectal temperature, heart rate, rate of perceived exertion, mean skin temperature, and pre- and post-exercise body weight. Women exercising in a warm and humid environment with water intake seem to be able to adapt to the luteal phase increase of basal body temperature through reduced urinary volume and increased sweating rate.

Autonomic modulation of heart rate of young and postmenopausal women undergoing estrogen therapy

The aim of the present study was to determine whether estrogen therapy (ET) reduces alterations of the autonomic control of heart rate (HR) due to hypoestrogenism and aging. Thirteen young (24 ± 2.6 years), 10 postmenopausal (53 ± 4.6 years) undergoing ET (PM-ET), and 14 postmenopausal (56 ± 2.6 years) women not undergoing ET (PM) were studied. ET consisted of 0.625 mg/day conjugated equine estrogen. HR was recorded continuously for 8 min at rest in the supine and sitting positions. HR variability (HRV) was analyzed by time (SDNN and rMSSD indices) and frequency domain methods. Power spectral components are reported as normalized units (nu) at low (LF) and high (HF) frequencies, and as LF/HF ratio. Intergroup comparisons: SDNN index was higher in young (median: supine, 47 ms; sitting, 42 ms) than in PM-ET (33; 29 ms) and PM (31; 29 ms) women (P < 0.05). PM showed lower HFnu, higher LFnu and higher LF/HF ratio (supine: 44, 56, 1.29; sitting: 38, 62, 1.60) than the young group in the supine position (61, 39, 0.63) and the PM-ET group in the sitting position (57, 43, 0.75; P < 0.05). Intragroup comparisons: HR was lower in the supine than in the sitting position for all groups (P < 0.05). The HRV decrease from the supine to the sitting position was significant only in the young group. These results suggest that HRV decreases during aging. ET seems to attenuate this process, promoting a reduction in sympathetic activity on the heart and contributing to the cardioprotective effect of estrogen hormones.

Role of the cardiac nerve in the adaptive changes of heart rate in response to an aversive stimulus in Megalobulimus mogianensis

The effect of an aversive stimulus represented by contact with a hot plate on the heart rate of Megalobulimus mogianensis was evaluated with electrocardiogram recording in intact snails (N = 8). All stimulated animals showed an increase in heart rate, with mean values ranging from 35.6 ± 1.2 (basal heart rate) to 43.8 ± 0.9 bpm (post-stimulation heart rate). The cardioacceleration was followed by gradual recovery of the basal heart rate, with mean recovery times varying from 4.3 ± 0.3 to 5.8 ± 0.6 min. Repetition of the stimulus did not affect the magnitude of variation nor did it influence the basal heart rate recovery time. To investigate the role of the cardiac nerve in mediating the heart rate alterations induced by the aversive stimulus, denervated (N = 8) and sham-operated (N = 8) animals were also tested. Although the aversive stimulus caused the heart rate to increase significantly in both experimental groups, the mean increase in heart rate in denervated animals (4.4 ± 0.4 bpm) was 57% of the value obtained in sham-operated animals (7.7 ± 1.3 bpm), indicating that the cardiac nerve is responsible for 43% of the cardioacceleration induced by the aversive stimulus. The cardioacceleration observed in denervated snails may be due to an increase in venous return promoted by the intense muscular activity associated with the withdrawal response. Humoral factors may also be involved. A probable delaying inhibitory effect of the cardiac nerve on the recuperation of the basal heart rate is suggested.

Topographic distribution of the tibial somatosensory evoked potential using coherence

The objective of the present study was to determine the adequate cortical regions based on the signal-to-noise ratio (SNR) for somatosensory evoked potential (SEP) recording. This investigation was carried out using magnitude-squared coherence (MSC), a frequency domain objective response detection technique. Electroencephalographic signals were collected (International 10-20 System) from 38 volunteers, without history of neurological pathology, during somatosensory stimulation. Stimuli were applied to the right posterior tibial nerve at the rate of 5 Hz and intensity slightly above the motor threshold. Response detection was based on rejecting the null hypothesis of response absence (significance level α= 0.05 and M = 500 epochs). The best detection rates (maximum percentage of volunteers for whom the response was detected for the frequencies between 4.8 and 72 Hz) were obtained for the parietal and central leads mid-sagittal and ipsilateral to the stimulated leg: C4 (87%), P4 (82%), Cz (89%), and Pz (89%). The P37-N45 time-components of the SEP can also be observed in these leads. The other leads, including the central and parietal contralateral and the frontal and fronto-polar leads, presented low detection capacity. If only contralateral leads were considered, the centro-parietal region (C3 and P3) was among the best regions for response detection, presenting a correspondent well-defined N37; however, this was not observed in some volunteers. The results of the present study showed that the central and parietal regions, especially sagittal and ipsilateral to the stimuli, presented the best SNR in the gamma range. Furthermore, these findings suggest that the MSC can be a useful tool for monitoring purposes.