Hyperinsulinemia produces cardiac vagal withdrawal and nonuniform sympathetic activation in normal subjects

1999 ◽  
Vol 276 (1) ◽  
pp. R178-R183 ◽  
Author(s):  
Philippe Van De Borne ◽  
Martin Hausberg ◽  
Robert P. Hoffman ◽  
Allyn L. Mark ◽  
Erling A. Anderson
Keyword(s):  
High Frequency ◽  
Sympathetic Activity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Low Frequency ◽  
Power Spectral Analysis ◽  
Normal Subjects ◽  
Power Spectral ◽  
Low Frequency Variability ◽  
High Frequency Variability

The exact mechanisms for the decrease in R-R interval (RRI) during acute physiological hyperinsulinemia with euglycemia are unknown. Power spectral analysis of RRI and microneurographic recordings of muscle sympathetic nerve activity (MSNA) in 16 normal subjects provided markers of autonomic control during 90-min hyperinsulinemic/euglycemic clamps. By infusing propranolol and insulin ( n = 6 subjects), we also explored the contribution of heightened cardiac sympathetic activity to the insulin-induced decrease in RRI. Slight decreases in RRI ( P < 0.001) induced by sevenfold increases in plasma insulin could not be suppressed by propranolol. Insulin increased MSNA by more than twofold ( P < 0.001), decreased the high-frequency variability of RRI ( P< 0.01), but did not affect the absolute low-frequency variability of RRI. These results suggest that reductions in cardiac vagal tone and modulation contribute at least in part to the reduction in RRI during hyperinsulinemia. Moreover, more than twofold increases in MSNA occurring concurrently with a slight and not purely sympathetically mediated tachycardia suggest regionally nonuniform increases in sympathetic activity during hyperinsulinemia in humans.

Impact of Changes in Respiratory Frequency and Posture on Power Spectral Analysis of Heart Rate and Systolic Blood Pressure Variability in Normal Subjects and Patients with Heart Failure

1996 ◽  
Vol 91 (1) ◽  
pp. 35-43 ◽  
Author(s):  
John E. Sanderson ◽  
Leata Y. C. Yeung ◽  
Dickens T. K. Yeung ◽  
Richard L. C. Kay ◽  
Brian Tomlinson ◽  
...  
Keyword(s):  
Heart Failure ◽  
Blood Pressure ◽  
Heart Rate ◽  
Spectral Analysis ◽  
High Frequency ◽  
Low Frequency ◽  
Power Spectral Analysis ◽  
Normal Subjects ◽  
Power Spectral ◽  
Patients With Heart Failure

1. Autonomic dysfunction is a major feature of congestive cardiac failure and may have an important role in determining progression and prognosis. The low-frequency/high-frequency ratio derived from power spectral analysis of heart rate variability has been proposed as a non-invasive method to assess sympatho-vagal balance. However, the effects of different respiratory rates or posture are rarely accounted for, but may be relevant in patients with heart failure in whom clinical improvement is accompanied by a fall in respiratory rate and an increased proportion of the day in the upright position. 2. We have assessed the effect of controlled respiration at different rates (10, 15, 20 breaths/min or 0.17, 0.25 and 0.33 Hz), while supine and standing, on power spectral analysis of heart rate and blood pressure variability in 11 patients with heart failure and 10 normal subjects. 3. Heart rate variance and low-frequency power (normalized units) were reduced in patients with heart failure (absent in six). During controlled breathing while supine, the power of the high-frequency component was significantly greater at 10 breaths/min than at 20 breaths/min in patients with heart failure, whether expressed in absolute units (P = 0.005) or percentage of total power (P = 0.03). 4. On standing, controlled breathing in patients with heart failure produced less change in high-frequency power (P = 0.054), but the low-frequency/high-frequency ratio at lower respiratory rates was reduced (P = 0.05). In normal subjects, as expected, respiratory rate had a highly significant effect on high-frequency power. Also, in normal subjects there was the expected increase in heart rate low-frequency power (P = 0.04) moving from supine to standing with an increase in the low-frequency/high-frequency ratio (P = 0.003), while in the patients with heart failure this was absent, reflecting blunted cardiovascular reflexes. 5. Systolic blood pressure low- and high-frequency components and their ratio were significantly affected by respiration (P > 0.03) and change in posture (P > 0.03) in both patients with heart failure and normal subjects, with a significant increase in the low-frequency/high-frequency ratio (P = 0.03) on standing in patients with heart failure, indicating that autonomic modulation of blood pressure is still operating in heart failure. 6. Thus, respiratory rate and changes in posture have a significant effect on measurements derived from spectral analysis of heart rate and blood pressure variability. Studies that use power spectral analysis as a measure of sympatho-vagal balance should control for these variables.

Relation between QT interval variability and muscle sympathetic nerve activity in normal subjects

2015 ◽  
Vol 309 (7) ◽  
pp. H1218-H1224 ◽  
Author(s):  
Fatima El-Hamad ◽  
Elisabeth Lambert ◽  
Derek Abbott ◽  
Mathias Baumert
Keyword(s):  
Supine Position ◽  
Sympathetic Nerve ◽  
Qt Interval ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Low Frequency ◽  
Normal Subjects ◽  
Nerve Activity ◽  
Head Up Tilt ◽  
Low Frequency Power

Beat-to-beat variability of the QT interval (QTV) is sought to provide an indirect noninvasive measure of sympathetic nerve activity, but a formal quantification of this relationship has not been provided. In this study we used power contribution analysis to study the relationship between QTV and muscle sympathetic nerve activity (MSNA). ECG and MSNA were recorded in 10 healthy subjects in the supine position and after 40° head-up tilt. Power spectrum analysis was performed using a linear autoregressive model with two external inputs: heart period (RR interval) variability (RRV) and MSNA. Total and low-frequency power of QTV was decomposed into contributions by RRV, MSNA, and sources independent of RRV and MSNA. Results show that the percentage of MSNA power contribution to QT is very small and does not change with tilt. RRV power contribution to QT power is notable and decreases with tilt, while the greatest percentage of QTV is independent of RRV and MSNA in the supine position and after 40° head-up tilt. In conclusion, beat-to-beat QTV in normal subjects does not appear to be significantly affected by the rhythmic modulations in MSNA following low to moderate orthostatic stimulation. Therefore, MSNA oscillations may not represent a useful surrogate for cardiac sympathetic nerve activity at moderate levels of activation, or, alternatively, sympathetic influences on QTV are complex and not quantifiable with linear shift-invariant autoregressive models.

Effect of provocative maneuvers on heart rate variability in subjects with quadriplegia

1995 ◽  
Vol 268 (6) ◽  
pp. H2239-H2245 ◽  
Author(s):  
D. R. Grimm ◽  
R. E. DeMeersman ◽  
R. P. Garofano ◽  
A. M. Spungen ◽  
W. A. Bauman
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Sympathetic Activity ◽  
Spectral Component ◽  
Low Frequency ◽  
Power Spectral Analysis ◽  
Parasympathetic Activity ◽  
Power Spectral ◽  
Spectral Components ◽  
Male Subjects

This study investigated heart rate variability (HRV) in individuals with quadriplegia who have disruption of autonomic control of the heart. Seven male subjects with neurological complete quadriplegia and seven with incomplete quadriplegia were studied at rest and during provocation. HRV was measured by power spectral analysis using a fast Fourier transform. Two spectral components were generated: 1) the high-frequency (HF) peak, a reflection of parasympathetic activity, and 2) the low-frequency (LF) peak, primarily sympathetic activity with some parasympathetic input. Results of the provocative maneuvers were grouped into one composite variable. Significant differences in the LF spectral component were found between the groups with complete and incomplete lesions in the supine position and after provocation (LF supine: P = 0.01; LF provocation: P = 0.002). After provocation, significant differences were demonstrated in the HF spectral component between these groups (P = 0.005). In contrast to previous findings, a LF component in subjects with complete quadriplegia was observed; this LF component decreased after provocation, suggesting the parasympathetic component withdrew during stressful maneuvers. There also appeared to be general downregulation of parasympathetic activity to the heart in subjects with complete quadriplegia. The presence of an increased LF spectral component during provocation in those with incomplete lesions implies sympathetic stimulation of the heart and may be used as a marker of sympathetic activity in individuals with quadriplegia.

scholarly journals The nature of the extreme X-ray variability in the NLS1 1H 0707-495

2021 ◽  
Author(s):  
M L Parker ◽  
W N Alston ◽  
L Härer ◽  
Z Igo ◽  
A Joyce ◽  
...  
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Emission Lines ◽  
Intrinsic Variability ◽  
Low Velocity ◽  
Strong Suppression ◽  
X Ray ◽  
Low Frequency Variability ◽  
High Frequency Variability ◽  
Long Timescales

Abstract We examine archival XMM-Newton data on the extremely variable narrow-line Seyfert 1 (NLS1) active galactic nucleus (AGN) 1H 0707-495. We construct fractional excess variance (Fvar) spectra for each epoch, including the recent 2019 observation taken simultaneously with eROSITA. We explore both intrinsic and environmental absorption origins for the variability in different epochs, and examine the effect of the photoionised emission lines from outflowing gas. In particular, we show that the unusual soft variability first detected by eROSITA in 2019 is due to a combination of an obscuration event and strong suppression of the variance at 1 keV by photoionised emission, which makes the variance below 1 keV appear more extreme. We also examine the variability on long timescales, between observations, and find that it is well described by a combination of intrinsic variability and absorption variability. We suggest that the typical extreme high frequency variability which 1H 0707-495 is known for is intrinsic to the source, but the large amplitude, low frequency variability that causes prolonged low-flux intervals is likely dominated by variable low-ionisation, low velocity absorption.

Contrasting effects of phentolamine and nitroprusside on neural and cardiovascular variability

2001 ◽  
Vol 281 (2) ◽  
pp. H559-H565 ◽  
Author(s):  
Philippe van de Borne ◽  
Mohsen Rahnama ◽  
Silvia Mezzetti ◽  
Nicola Montano ◽  
Alberto Porta ◽  
...  
Keyword(s):  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Low Frequency ◽  
Normal Subjects ◽  
Neural Oscillator ◽  
Adrenergic Blockade ◽  
Sympathetic Activation ◽  
Nerve Activity ◽  
Cardiovascular Variability ◽  
Adrenergic Transmission

The relative contributions of a central neural oscillator and of the delay in α-adrenergic transmission within the baroreflex loop in the predominance of low-frequency (LF) cardiovascular variability during sympathetic activation in humans are unclear. We measured R-R interval (RR), muscle sympathetic nerve activity (MSNA), blood pressure (BP), and their variability in 10 normal subjects during sympathetic activation achieved by BP lowering with sodium nitroprusside (SNP) and α-adrenergic blockade using phentolamine. SNP and phentolamine induced comparable reductions in BP ( P > 0.25). Despite tachycardia and sympathetic activation with both SNP and phentolamine, LF variability in RR, MSNA, and BP increased during SNP and decreased during phentolamine (SNP: RR +20 ± 6%, MSNA +3 ± 5%, systolic BP +9 ± 6%, diastolic BP +7 ± 5%; phentolamine: RR −2 ± 7%, MSNA −34 ± 6%, systolic BP −16 ± 8%, diastolic BP −13 ± 4%, P< 0.05 except systolic BP, where P = 0.09). Thus LF variability is reduced when sympathetic activation is induced by α-adrenergic blockade. This suggests that α-adrenergic transmission within the baroreflex loop may contribute importantly to the predominance of LF cardiovascular variability associated with sympathetic excitation in humans.

Power spectral analysis of heart rate variability in traumatic quadriplegic humans

1990 ◽  
Vol 258 (6) ◽  
pp. H1722-H1726 ◽  
Author(s):  
K. Inoue ◽  
S. Miyake ◽  
M. Kumashiro ◽  
H. Ogata ◽  
O. Yoshimura
Keyword(s):  
Spectral Analysis ◽  
High Frequency ◽  
Low Frequency ◽  
Power Spectral Analysis ◽  
Center Frequency ◽  
Control Group ◽  
Climatic Chamber ◽  
Power Spectral ◽  
Spectral Components ◽  
Chamber Temperature

This study investigated the spontaneous beat-to-beat variabilities in R-R intervals of six traumatic neurologically complete quadriplegic (QP) males and six age-matched healthy males (control) while they were at rest in the supine position in a climatic chamber (temperature 30 degrees C, relative humidity 60%) by means of autoregressive power spectral analysis. As shown by earlier studies, in the control group there were two major spectral components, a high-frequency (HF) component [center frequency 0.30 +/- 0.02 (SE) Hertz equivalent (Hz eq), power 767.5 +/- 384.6 ms2] and a low-frequency (LF) component (0.11 +/- 0.01 Hz eq, 707.5 +/- 198.8 ms2). On the contrary, in the QP group, only the HF component was observed (0.30 +/- 0.02 Hz eq, 421.8 +/- 134.7 ms2). The results suggest that 1) the disappearance of the LF component in the QP subject is presumably caused by the interruption of the spinal pathways linking supraspinal cardiovascular centers with the peripheral sympathetic outflow, and 2) the cervical spinal sympathetic pathways may be instrumental in the genesis of the LF component in humans.

Carotid baroreceptor-muscle sympathetic relation in humans

1987 ◽  
Vol 253 (6) ◽  
pp. R929-R934 ◽  
Author(s):  
R. F. Rea ◽  
D. L. Eckberg
Keyword(s):  
Sympathetic Activity ◽  
Healthy Subjects ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Normal Subjects ◽  
Threshold Level ◽  
Sigmoid Function ◽  
Nerve Activity ◽  
Carotid Baroreceptor ◽  
Neck Pressure

The purpose of this study was to define the relation between carotid distending pressure and muscle sympathetic activity in humans. Carotid baroreceptors of nine healthy subjects were compressed or stretched for 5 s with graded neck pressure or suction (+40 to -65 mmHg), and muscle sympathetic nerve activity was recorded. The results delineate several features of human baroreflex function. First, the carotid-muscle sympathetic relation is well described by an inverse sigmoid function. Second, a linear relation exists between carotid distending pressure and sympathetic outflow over a range of approximately 25 mmHg. Third, sympathetic responses to changes of carotid pressures are asymmetric; increases of sympathetic activity during carotid compression are much greater than reductions of sympathetic activity during carotid stretch. Fourth, at rest, normal subjects operate near the threshold level for sympathetic excitation. Thus the carotid-muscle sympathetic baroreflex is poised to oppose reductions more effectively than elevations of arterial pressure, and the range of pressures over which the reflex is active is wider than thought hitherto.

scholarly journals Power spectral analysis of heart rate variability in Bangladeshi healthy male and female

2016 ◽  
Vol 43 (3) ◽  
pp. 146-150
Author(s):  
Qazi Farzana Akhter ◽  
Qazi Shamima Akhter ◽  
Farhana Rahman ◽  
Sybilla Ferdousi ◽  
Susmita Sinha
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
High Frequency ◽  
Low Frequency ◽  
Power Spectral Analysis ◽  
Autonomic Nerve ◽  
Age Group ◽  
Power Spectral

Heart rate variability (HRV) has been considered as an indicator of autonomic nerve function status. We aimed to find out the reference values of heart rate variability by power spectral analysis in our healthy population of both sex. This cross sectional study was conducted in the Department of Physiology, Dhaka Medical College, Dhaka from the period of July 2012 to June 2013. For this, 180 subjects were selected with the age ranging from 15-60 years. All the study subjects were divided into 3 different groups according to age (Group A: 15-30 years; Group B: 31-45 years; Group C: 46-60 years). Each group contained 60 subjects of which 30 were male and 30 were female. Analysis of HRV parameters were done in Department of Physiology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka. Systolic blood pressure, diastolic blood pressure, low frequency normalized unit, low frequency / high frequency ratio were significantly higher in male than female. Again high frequency power, high frequency normalized unit were significantly higher in female than male of same age group. This study concludes that male showed higher cardiac sympathetic activities while female showed higher cardiac parasympathetic activities in different age groups.Bangladesh Med J. 2014 Sep; 43 (3): 146-150

Physiology and Pathophysiology of Heart Rate and Blood Pressure Variability in Humans: Is Power Spectral Analysis Largely An Index of Baroreflex Gain?

1995 ◽  
Vol 88 (1) ◽  
pp. 103-109 ◽  
Author(s):  
Peter Sleight ◽  
Maria Teresa La Rovere ◽  
Andrea Mortara ◽  
Gianni Pinna ◽  
Roberto Maestri ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Spectral Analysis ◽  
High Frequency ◽  
Blood Pressure Variability ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Power Spectral Analysis ◽  
Autonomic Balance ◽  
Baroreflex Control ◽  
Power Spectral

1. It is often assumed that the power in the low-(around 0.10 Hz) and high-frequency (around 0.25 Hz) bands obtained by power spectral analysis of cardiovascular variables reflects vagal and sympathetic tone respectively. An alternative model attributes the low-frequency band to a resonance in the control system that is produced by the inefficiently slow time constant of the reflex response to beat-to-beat changes in blood pressure effected by the sympathetic (with or without the parasympathetic) arm(s) of the baroreflex (De Boer model). 2. We have applied the De Boer model of circulatory variability to patients with varying baroreflex sensitivity and one normal subject, and have shown that the main differences in spectral power (for both low and high frequency) between and within subjects are caused by changes in the arterial baroreflex gain, particularly for vagal control of heart rate (R—R interval) and left ventricular stroke output. We have computed the power spectrum at rest and during neck suction (to stimulate carotid baroreceptors). We stimulated the baroreceptors at two frequencies (0.1 and 0.2 Hz), which were both distinct from the controlled respiration rate (0.25 Hz), in both normal subjects and heart failure patients with either sensitive or poor baroreflex control. 3. The data broadly confirm the De Boer model. The low-frequency (0.1 Hz) peak in either R—R or blood pressure variability) was spontaneously generated only if the baroreflex control of the autonomic outflow was relatively intact. With a large stimulus to the carotid baroreceptor it was possible to influence the low-frequency R—R but not low-frequency blood pressure variability. This implies that it is too simplistic to use power spectral analysis as a simple measure of autonomic balance its underlying modulation is more complex than generally believed. 4. It may be that power spectral analysis is more a sensitive indicator of baroreflex control, particularly of vagal control, than direct evidence of autonomic balance. of course, there is often a correlation between the gain of the reflex and the autonomic balance of vagus and sympathetic. These considerations may help our understanding of some conditions, such as exercise or heart failure, when the power spectral analysis method fails to identify increased sympathetic discharge; this failure may partly be explained by the decrease in baroreflex sensitivity which occurs in these two conditions.

Nonrandom variability in respiratory cycle parameters of humans during stage 2 sleep

1990 ◽  
Vol 69 (2) ◽  
pp. 630-639 ◽  
Author(s):  
M. Modarreszadeh ◽  
E. N. Bruce ◽  
B. Gothe
Keyword(s):  
High Frequency ◽  
Minute Ventilation ◽  
Power Spectra ◽  
Low Frequency ◽  
Neural Mechanism ◽  
Normal Subjects ◽  
Feedback Loops ◽  
Low Frequency Oscillations ◽  
Stage 2 Sleep ◽  
Correlated Components

We analyzed breath-to-breath inspiratory time (TI), expiratory time (TE), inspiratory volume (VI), and minute ventilation (Vm) from 11 normal subjects during stage 2 sleep. The analysis consisted of 1) fitting first- and second-order autoregressive models (AR1 and AR2) and 2) obtaining the power spectra of the data by fast-Fourier transform. For the AR2 model, the only coefficients that were statistically different from zero were the average alpha 1 (a1) for TI, VI, and Vm (a1 = 0.19, 0.29, and 0.15, respectively). However, the power spectra of all parameters often exhibited peaks at low frequency (less than 0.2 cycles/breath) and/or at high frequency (greater than 0.2 cycles/breath), indicative of periodic oscillations. After accounting for the corrupting effects of added oscillations on the a1 estimates, we conclude that 1) breath-to-breath fluctuations of VI, and to a lesser extent TI and Vm, exhibit a first-order autoregressive structure such that fluctuations of each breath are positively correlated with those of immediately preceding breaths and 2) the correlated components of variability in TE are mostly due to discrete high- and/or low-frequency oscillations with no underlying autoregressive structure. We propose that the autoregressive structure of VI, TI, and Vm during spontaneous breathing in stage 2 sleep may reflect either a central neural mechanism or the effects of noise in respiratory chemical feedback loops; the presence of low-frequency oscillations, seen more often in Vm, suggests possible instability in the chemical feedback loops. Mechanisms of high-frequency periodicities, seen more often in TE, are unknown.

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