Local Viscoelasticity of Biopolymer Solutions

1996 ◽  
Vol 463 ◽  
Author(s):  
B. Schnurr ◽  
F. Gittes ◽  
P. D. Olmsted ◽  
C. F. Schmidt ◽  
F. C. Mackintosh
Keyword(s):  
Shear Modulus ◽  
Low Frequency ◽  
Thermal Fluctuations ◽  
High Frequency Power ◽  
Scaling Exponents ◽  
Complex Shear ◽  
High Resolution Technique ◽  
Micrometer Scale ◽  
The Relationship ◽  
Frequency Power

AbstractWe describe a new, high-resolution technique for determining the local viscoelastic response of polymer gels on a micrometer scale. This is done by monitoring thermal fluctuations of embedded probe particles. We derive the relationship between the amplitude of fluctuations and the low-frequency storage modulus G′, as well as the relationship between the fluctuation power spectrum, measured between 0.1 Hz and 25kHz, and the complex shear modulus G((ω). For both, semiflexible F-actin solutions and flexible polyacrylamide (PAAm) gels we observe high-frequency power-law dependence in the spectra, which reflects the behavior of the shear modulus. However, we observe distinctly different scaling exponents for G((ω) in F-actin and PAAm gels—presumably due to the semiflexible nature of the actin filaments.

Elevated heart rate variability in physically active postmenopausal women: a cardioprotective effect?

1996 ◽  
Vol 271 (2) ◽  
pp. H455-H460 ◽  
Author(s):  
K. P. Davy ◽  
N. L. Miniclier ◽  
J. A. Taylor ◽  
E. T. Stevenson ◽  
D. R. Seals
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Postmenopausal Women ◽  
High Frequency ◽  
Low Frequency ◽  
Total Power ◽  
High Frequency Power ◽  
Fat Percentage ◽  
Physically Active ◽  
Frequency Power

Coronary heart disease (CHD) and cardiac sudden death (CSD) incidence accelerates after menopause, but the incidence is lower in physically active versus less active women. Low heart rate variability (HRV) is a risk factor for CHD and CSD. The purpose of the present investigation was to test the hypothesis that HRV at rest is greater in physically active compared with less active postmenopausal women. If true, we further hypothesized that the greater HRV in the physically active women would be closely associated with an elevated spontaneous cardiac baroreflex sensitivity (SBRS). HRV (both time and frequency domain measures) and SBRS (sequence method) were measured during 5-min periods of controlled frequency breathing (15 breaths/min) in the supine, sitting, and standing postures in 9 physically active postmenopausal women (age = 53 +/- 1 yr) and 11 age-matched controls (age = 56 +/- 2 yr). Body weight, body mass index, and body fat percentage were lower (P < 0.01) and maximal oxygen uptake was higher (P < 0.01) in the physically active group. The standard deviation of the R-R intervals (time domain measure) was higher in all postures in the active women (P < 0.05) as were the high-frequency, low-frequency, and total power of HRV. SBRS also was higher (P < 0.05) in the physically active women in all postures and accounted for approximately 70% of the variance in the high-frequency power of HRV (P < 0.05). The results of the present investigation indicate that physically active postmenopausal women demonstrate higher levels of HRV compared with age-matched, less active women. Furthermore, SBRS accounted for the majority of the variance in the high-frequency power of HRV, suggesting the possibility of a mechanistic link with cardiac vagal modulation of heart rate. Our findings may provide insight into a possible cardioprotective mechanism in physically active postmenopausal women.

Increase in electromyogram low-frequency power in nonfatigued contracting skeletal muscle

1986 ◽  
Vol 61 (3) ◽  
pp. 1012-1017 ◽  
Author(s):  
A. R. Bazzy ◽  
J. B. Korten ◽  
G. G. Haddad
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Biceps Brachii ◽  
Low Frequency ◽  
Biceps Brachii Muscle ◽  
Power Spectral ◽  
Loaded Breathing ◽  
Low Frequency Power ◽  
The Relationship ◽  
Frequency Power

We studied the relationship between changing elbow joint angle and the power spectral density of the biceps brachii muscle electromyogram (EMG) during submaximal isometric contractions. For this purpose, we recorded the EMG of the biceps brachii muscle with surface electrodes in 13 subjects. Each subject held a 2.8-kg weight and contracted the biceps isometrically for 30 s at one of two lengths. The length of the muscle was changed by flexing the forearm toward the upper arm to form an angle of 135 degrees (L1) or 45 degrees (L2). We found that the mean centroid frequency (fc) of the EMG power spectral density was 26% lower at L1 than at L2 (P less than 0.01). For each subject there was no significant change in fc during the isometric contraction at either angle. In addition, in nine subjects who sustained fatiguing contractions of the biceps with a 6-kg load, fc decreased by 15% (P less than 0.025). These data suggest that a change in the length at which a muscle contracts isometrically can alter or induce indirectly an alteration in the frequency content of its EMG. This finding may have important implications for the assessment of respiratory muscle EMG especially during loaded breathing.

Effects of oral arsenic trioxide therapy on QT intervals in patients with acute promyelocytic leukemia: implications for long-term cardiac safety

Blood ◽  
2006 ◽  
Vol 108 (1) ◽  
pp. 103-106 ◽  
Author(s):  
Chung-Wah Siu ◽  
Wing-Yan Au ◽  
Cindy Yung ◽  
Cyrus R. Kumana ◽  
Chu-Pak Lau ◽  
...  
Keyword(s):  
Arsenic Trioxide ◽  
High Frequency ◽  
Peak Plasma ◽  
Low Frequency ◽  
Holter Monitoring ◽  
Cardiac Safety ◽  
High Frequency Power ◽  
Qt Intervals ◽  
Frequency Power

Ventricular tachyarrhythmias may occur during intravenous arsenic trioxide (As2O3). This has not happened during oral As2O3. Sixteen patients were studied by electrocardiography and 24-hour Holter monitoring at baseline, during and after oral As2O3 (As2O3-ON, As2O3-OFF). QT and corrected QT (QTc) were significantly longer during As2O3-ON than in As2O3-OFF, but QT and QTc dispersions were comparable. The patients' 24-hour heart rates were higher during As2O3-ON than in As2O3-OFF. QTc intervals at each hour were longer during As2O3-ON than in As2O3-OFF. However, QTc prolongation of more than 30 milliseconds only occurred at one time point (2 hours) after oral As2O3, resulting in QTc of more than 500 milliseconds in 3 of 16 patients, all within 4 hours of oral As2O3. Although the standard deviation of normal RR interval was lower during As2O3-ON, ratios of low frequency to high frequency power for As2O3-ON and As2O3-OFF were comparable. No ventricular proarrhythmias were observed. These observations, due to the lower peak plasma arsenic reached during oral As2O3, may explain the relative cardiac safety of oral As2O3. (Blood. 2006;108:103-106)

A Plateau in the Relationship between High-Frequency Power and R-R intervals at Low Heart Rates

2004 ◽  
Vol 36 (Supplement) ◽  
pp. S128-S129
Author(s):  
Antti M. Kiviniemi ◽  
Arto J. Hautala ◽  
Timo H. Mäkikallio ◽  
Raija T. Laukkanen ◽  
Seppo Nissilä ◽  
...  
Keyword(s):  
High Frequency ◽  
High Frequency Power ◽  
Heart Rates ◽  
The Relationship ◽  
Frequency Power

Cardiovascular variability after arousal from sleep: time-varying spectral analysis

2003 ◽  
Vol 95 (4) ◽  
pp. 1394-1404 ◽  
Author(s):  
Anna Blasi ◽  
Javier Jo ◽  
Edwin Valladares ◽  
Barbara J. Morgan ◽  
James B. Skatrud ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
High Frequency ◽  
Low Frequency ◽  
Sleep Time ◽  
Respiratory Pattern ◽  
Time Varying ◽  
High Frequency Power ◽  
Low Frequency Power ◽  
Frequency Power

We performed time-varying spectral analyses of heart rate variability (HRV) and blood pressure variability (BPV) recorded from 16 normal humans during acoustically induced arousals from sleep. Time-varying autoregressive modeling was employed to estimate the time courses of high-frequency HRV power, low-frequency HRV power, the ratio between low-frequency and high-frequency HRV power, and low-frequency power of systolic BPV. To delineate the influence of respiration on HRV, we also computed respiratory airflow high-frequency power, the modified ratio of low-frequency to high-frequency HRV power, and the average transfer gain between respiration and heart rate. During cortical arousal, muscle sympathetic nerve activity and heart rate increased and returned rapidly to baseline, but systolic blood pressure, the ratio between low-frequency and high-frequency HRV power, low-frequency HRV power, the modified ratio of low-frequency to high-frequency HRV power, and low-frequency power of systolic BPV displayed increases that remained above baseline up to 40 s after arousal. High-frequency HRV power and airflow high-frequency power showed concommitant decreases to levels below baseline, whereas the average transfer gain between respiration and heart rate remained unchanged. These findings suggest that 1) arousal-induced changes in parasympathetic activity are strongly coupled to respiratory pattern and 2) the sympathoexcitatory cardiovascular effects of arousal are relatively long lasting and may accumulate if repetitive arousals occur in close succession.

scholarly journals The Effect of Massage Therapy on Autonomic Activity in Critically Ill Children

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Ling Guan ◽  
Jean-Paul Collet ◽  
Nataliya Yuskiv ◽  
Peter Skippen ◽  
Rollin Brant ◽  
...  
Keyword(s):  
Low Frequency ◽  
Pediatric Intensive Care ◽  
Frequency Domain Analysis ◽  
Clinical Severity ◽  
Critically Ill Children ◽  
Percentage Increase ◽  
Low Frequency Power ◽  
Study Intervention ◽  
The Relationship ◽  
Frequency Power

Objectives. Our main objective was to describe the effect of foot and hand (F&H) massage on the autonomic nervous system (ANS) activity in children hospitalized in a pediatric intensive care unit (PICU); the secondary objectives were to assess the relationship between ANS function and the clinical severity and to explore the effects of repeated massage sessions on the ANS.Methods. Design was a descriptive experimental study. Intervention was single or six session(s) of F&H massage. ANS function was assessed through the frequency-domain analysis of heart rate variability. Main metrics included high and low frequency power (HF and LF), HF + LF, and LF/HF ratio.Results. Eighteen children participated in the study. A strong Spearman’s correlation (ρ=-0.77) was observed between HF + LF and clinical severity. During massage, the parasympathetic activity (measured by HF) increased significantly from baseline (P=0.04) with a mean percentage increase of 75% (95% CI: 20%∼130%). LF increased by 56% (95% CI: 20%∼92%) (P=0.026). Repeated sessions were associated with a persistent effect on HF and LF which peaked at the second session and remained stable thereafter.Conclusions. HF + LF is positively correlated with clinical severity. F&H massage can improve the ANS activity and the effect persists when repeated sessions are offered.

A Plateau in the Relationship between High-Frequency Power and R-R intervals at Low Heart Rates

2004 ◽  
Vol 36 (Supplement) ◽  
pp. S128???S129
Author(s):  
Antti M. Kiviniemi ◽  
Arto J. Hautala ◽  
Timo H. M??kikallio ◽  
Raija T. Laukkanen ◽  
Seppo Nissil?? ◽  
...  
Keyword(s):  
High Frequency ◽  
High Frequency Power ◽  
Heart Rates ◽  
The Relationship ◽  
Frequency Power

scholarly journals Heart Rate Variability during Face Cooling in Concussed Adolescents

Neurology ◽  
2019 ◽  
Vol 93 (14 Supplement 1) ◽  
pp. S8.1-S8
Author(s):  
Mohammad Haider ◽  
Charles Wilber ◽  
Kaitlin Viera ◽  
Itai Bezherano ◽  
John Leddy
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
High Frequency ◽  
Low Frequency ◽  
High Frequency Power ◽  
Clinical Recovery ◽  
Face Cooling ◽  
Ratio Measure ◽  
Frequency Power ◽  
Mean Heart Rate

ObjectiveWe measured heart rate variability (HRV) during physiological stimuli in acutely concussed adolescents (CX) and after clinical recovery, and compared with healthy controls (HC).BackgroundConcussion is associated with autonomic dysfunction. Face Cooling (FC) triggers the trigeminal nerve to evoke transient increases in cardiac parasympathetic (PNS) activity.Design/Methods11 CX (14.8 ± 0.9 years, 6 male, 7 days since injury) and 11 HC (16.1 ± 1.1 years, 9 male) participated. We calculated mean heart rate (HR), standard deviation of root mean square (RMSSD, measure of PNS tone) and low-frequency to high-frequency power ratio (LF/HF ratio, measure of sympathetic [SNS] tone) at rest and 3-minute FC test.ResultsCX at Visit 1 and 2 had significantly lesser increase in HR (p = 0.02) and RMSSD (p = 0.038) than HC on FC.ConclusionsThese data show that acutely concussed participants have an attenuated PNS response to physiological stimuli which continues after clinical recovery.

scholarly journals Bispectral Index™ Alterations Have Associations with Autonomic Changes during Hypnosis in Trauma Center Researchers: A Formative Evaluation (Preprint)

2020 ◽  
Author(s):  
C. Michael Dunham ◽  
Amanda L. Burger ◽  
Barbara M. Hileman ◽  
Elisha A. Chance ◽  
Amy E. Hutchinson
Keyword(s):  
Respiratory Rate ◽  
Skin Conductance ◽  
High Frequency ◽  
Trauma Center ◽  
Formative Evaluation ◽  
Low Frequency ◽  
High Frequency Power ◽  
Interbeat Interval ◽  
Low Frequency Power ◽  
Frequency Power

BACKGROUND Hypnosis was induced to enhance reductions in Bispectral Index™ (BIS) values. OBJECTIVE Autonomic monitoring was used to assess physiologic relaxation and explore their associations with BIS values. METHODS Each session consisted of reading a 4-minute baseline neutral script and playing an 18-minute hypnosis tape to 3 researchers involved in the BIS neurofeedback study. In addition to BIS monitoring, autonomic monitoring was performed and included measures of electromyography, skin temperature, skin conductance, respiratory rate, expired carbon dioxide, and heart rate variability. The t-test, correlation analyses, and multivariate linear regression analyses were used in data analysis. RESULTS Hypnosis was associated with reductions in BIS (P<.001), electromyography (P<.001), respiratory rate (P<.001), skin conductance (P=.006), and very low frequency power (P=.04) and with increases in expired carbon dioxide (P<.001), skin temperature (P=.04), high frequency power (P<.001), and successive heart interbeat interval difference (P=.04) values. Decreased BIS values were associated with reduced electromyography measures (R=.76; P<.001), respiratory rate (R=.35; P=.004), skin conductance (R=.57; P<.001), and low frequency power (R=.32; P=.01) and with increased high frequency power (R=-.53; P<.001), successive heart interbeat interval difference (R=-.32; P=.009), and standard deviation of heart interbeat interval (R=-.26; P=.04) values. CONCLUSIONS Hypnosis appeared to induce mental and physical relaxation, enhance parasympathetic neural activation, and attenuate sympathetic nervous system activity, changes that were associated with BIS values. Findings of the preliminary formative evaluation suggest that the current hypnosis model may be useful for assessing autonomic physiological associations with changes in BIS values, thus motivating us to proceed with a larger investigation in trauma center nurses and physicians. CLINICALTRIAL None

Sign in / Sign up

Export Citation Format

Share Document