scholarly journals Blood Pressure Variability and Baroreflex Sensitivity in Premature Newborns—An Effect of Postconceptional and Gestational Age

2021 ◽  
Vol 9 ◽  
Author(s):  
Kamil Javorka ◽  
Katarina Haskova ◽  
Barbora Czippelova ◽  
Mirko Zibolen ◽  
Michal Javorka
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Gestational Age ◽  
High Frequency ◽  
Blood Pressure Variability ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Total Power ◽  
Short Term ◽  
Frequency Power

Introduction: Cardiovascular system is the vitally important system in the dynamical adaptation process of the newborns to the extrauterine environment. To reliably detect immaturity in the given organ system, it is crucial to study the development of the organ functions in relation to maturation process.Objectives: The objective was to determine the changes in the spontaneous short-term blood pressure variability (BPV) and baroreflex sensitivity (BRS) reflecting various aspects of cardiovascular control during the process of maturation in preterm babies and to separate effects of gestational age and postnatal age.Methods: Thirty-three prematurely born infants without any signs of cardio-respiratory disorders (gestational age: 31.8, range: 27–36 weeks; birth weight: 1,704, range: 820–2,730 grams) were enrolled. Continuous peripheral blood pressure signal was obtained by non-invasive volume-clamp photoplethysmography method during supine rest. The recordings of 250 continuous beat-to-beat blood pressure values were processed by spectral analysis of BPV (assessed measures: total power, low frequency and high frequency powers of systolic BPV) and BRS calculation. For each infant we also assessed systolic, diastolic and mean blood pressures, heart rate and respiratory rate.Results: With the postconceptional age, BPV measures decreased (for total power: Spearman correlation coefficient rs = −0.345, P = 0.049; for low frequency power: rs = −0.365, P = 0.037; for high frequency power rs = −0.349; P = 0.046); and BRS increased significantly (rs = 0.448, P = 0.009). The further analysis demonstrated that these effects were more attributable to gestational age than to postnatal age. BRS correlated negatively with BPV magnitude (rs = −0.479 to −0.592, P = 0.001–0.005). Mean blood pressure and diastolic blood pressure increased during maturation (rs = 0.517 and 0.537, P = 0.002 and 0.001, respectively) while heart rate and respiratory rate decreased (rs = −0.366 and −0.516, P = 0.036 and 0.002, respectively).Conclusion: We conclude that maturation process is accompanied by an increased involvement of baroreflex buffering of spontaneous short-term blood pressure oscillations. Gestational age plays a dominant role not only in BPV changes but also in BRS, mean blood pressure, diastolic blood pressure and heart rate changes.

scholarly journals 0461 Blunted Baroreflex Sensitivity and Reduced Morning Parasympathetic Activity in Sleep-Onset Insomnia

SLEEP ◽  
2020 ◽  
Vol 43 (Supplement_1) ◽  
pp. A177-A177
Author(s):  
H Tsai ◽  
T Kuo ◽  
C Yang
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Cardiovascular Events ◽  
Blood Pressure Variability ◽  
Baroreflex Sensitivity ◽  
Sleep Onset ◽  
Low Frequency ◽  
Sleep Structure ◽  
Frequency Power

Abstract Introduction Insomnia is a risk factor for hypertension and cardiovascular events, and this association is strongest for sleep-onset insomnia. However, little is known about insomnia on cardiovascular modulation, especially soon after morning awakening, the peak period of time for cardiovascular incidents. This study explored morning cardiovascular function in individuals with sleep-onset insomnia by analysing heart rate variability, blood pressure variability, and baroreflex sensitivity. Methods Sleep structure of the participants (15 good sleepers and 13 individuals with sleep-onset insomnia) was measured by laboratory polysomnography, followed by continuous recordings of the participant’s blood pressure and heart rate for 10 min in the morning. Results When compared to the good sleepers, the insomnia group showed significant reductions in total sleep time, a longer sleep-onset latency, and reduced sleep efficiency. The sleep structure, including durations of sleep stages, numbers of awakenings and arousal index did not differ between the groups. After morning awakening (averaged time: 12.33 ± 10.48 min), the shorter R-R intervals, lower total power, and lower high-frequency power of heart rate variability were observed among individuals with sleep-onset insomnia, compared with good sleepers. Elevated slopes of systolic and diastolic blood pressure, as well as lower baroreflex sensitivity, were also shown in the insomnia group. Indices of sympathetic activity, including low-frequency percentage of heart rate variability or low-frequency power of blood pressure variability, did not differ between the groups. Conclusion Weak vagal activity and blunted baroreflex sensitivity were evident among sleep-onset insomnia. These findings indicate difficulty in initiating sleep, without significant sleep fragmentation, can independently affect morning cardiovascular function. This study provides a possible link between sleep-onset insomnia and risk of cardiovascular events. Support N/A

Short-term blood pressure variability in renovascular hypertension and in severe and mild essential hypertension

2003 ◽  
Vol 105 (5) ◽  
pp. 609-614 ◽  
Author(s):  
Hanna MUSSALO ◽  
Esko VANNINEN ◽  
Risto IKÄHEIMO ◽  
Tomi LAITINEN ◽  
Juha HARTIKAINEN
Keyword(s):  
Blood Pressure ◽  
Essential Hypertension ◽  
Renovascular Hypertension ◽  
High Frequency ◽  
Blood Pressure Variability ◽  
Total Power ◽  
Control Group ◽  
High Frequency Power ◽  
Short Term ◽  
Frequency Power

This study was designed to examine short-term blood pressure variability (BPV) in patients with different severity and forms of chronic medically treated hypertension. Power spectral analysis of BPV was performed from continuous finger blood pressure (Finapres) recordings. Ten patients with renovascular hypertension (RVHT), 34 with severe essential hypertension (SEHT) and 29 with mild essential hypertension (MEHT) as well as healthy age- and sex-matched control subjects were studied. The RVHT group was characterized by reduced low frequency (LF) power of both systolic and diastolic BPV (P=0.004 and P=0.003 respectively) when compared with the control group. There was also a tendency to lower total power of diastolic BPV (P=0.094). On the contrary, the SEHT group had increased total power of diastolic BPV (P=0.044). However, in the SEHT group, we found no differences in the LF and high frequency power of systolic and diastolic BPV when compared with controls. The MEHT group presented with lower LF power of systolic and diastolic BPV (P=0.028 and P=0.003 respectively) and, in addition, high frequency power of diastolic BPV was lower than in the control group (P=0.020). When the hypertensive groups were compared with each other, total power and LF power of diastolic BPV (P=0.043 and P=0.039 respectively) were lower in the RVHT group than in the SEHT group. In addition, total power of diastolic BPV was lower (P=0.030) in the MEHT group than in the SEHT group. No differences were observed in BPV between the RVHT and MEHT groups. The results show that BPV in hypertensive patients groups behaved differently. This suggests that both the aetiology and severity of hypertension have a significant influence on short-term BPV measured in laboratory conditions and that different control mechanisms are operating in these clinically distinctly different hypertension groups.

Heart rate variability and baroreflex sensitivity are reduced in chronically undernourished, but otherwise healthy, human subjects

2003 ◽  
Vol 104 (3) ◽  
pp. 295-302 ◽  
Author(s):  
Mario VAZ ◽  
A.V. BHARATHI ◽  
S. SUCHARITA ◽  
D. NAZARETH
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
High Frequency ◽  
Baroreflex Sensitivity ◽  
Human Subjects ◽  
Normal Weight ◽  
Autonomic Nerve ◽  
Total Power ◽  
Healthy Human ◽  
Frequency Power

Alterations in autonomic nerve activity in subjects in a chronically undernourished state have been proposed, but have been inadequately documented. The present study evaluated heart rate and systolic blood pressure variability in the frequency domain in two underweight groups, one of which was undernourished and recruited from the lower socio-economic strata [underweight, undernourished (UW/UN); n = 15], while the other was from a high class of socio-economic background [underweight, well nourished (UW/WN); n = 17], as well as in normal-weight controls [normal weight, well nourished (NW/WN); n = 27]. Baroreflex sensitivity, which is a determinant of heart rate variability, was also assessed. The data indicate that total power (0–0.4Hz), low-frequency power (0.04–0.15Hz) and high-frequency power (0.15–0.4Hz) of RR interval variability were significantly lower in the UW/UN subjects (P<0.05) than in the NW/WN controls when expressed in absolute units, but not when the low- and high-frequency components were normalized for total power. Baroreflex sensitivity was similarly lower in the UW/UN group (P<0.05). Heart rate variability parameters in the UW/WN group were generally between those of the UW/UN and NW/WN groups, but were not statistically different from either. The mechanisms that contribute to the observed differences between undernourished and normal-weight groups, and the implications of these differences, remain to be elucidated.

Effect of heavy exercise on spectral baroreflex sensitivity, heart rate, and blood pressure variability in well-trained humans

2008 ◽  
Vol 295 (3) ◽  
pp. H1150-H1155 ◽  
Author(s):  
François Cottin ◽  
Claire Médigue ◽  
Yves Papelier
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Systolic Blood Pressure ◽  
Exercise Test ◽  
Blood Pressure Variability ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Mechanical Effect ◽  
Heavy Exercise ◽  
Gas Exchange Parameters

The aim of the study was to assess the instantaneous spectral components of heart rate variability (HRV) and systolic blood pressure variability (SBPV) and determine the low-frequency (LF) and high-frequency baroreflex sensitivity (HF-BRS) during a graded maximal exercise test. The first hypothesis was that the hyperpnea elicited by heavy exercise could entail a significant increase in HF-SBPV by mechanical effect once the first and second ventilatory thresholds (VTs) were exceeded. It was secondly hypothesized that vagal tone progressively withdrawing with increasing load, HF-BRS could decrease during the exercise test. Fifteen well-trained subjects participated in this study. Electrocardiogram (ECG), blood pressure, and gas exchanges were recorded during a cycloergometer test. Ventilatory equivalents were computed from gas exchange parameters to assess VTs. Spectral analysis was applied on cardiovascular series to compute RR and systolic blood pressure power spectral densities, cross-spectral coherence, gain, and α index of BRS. Three exercise intensity stages were compared: below (A1), between (A2), and above (A3) VTs. From A1 to A3, both HF-SBPV (A1: 45 ± 6, A2: 65 ± 10, and A3: 120 ± 23 mm2Hg, P < 0.001) and HF-HRV increased (A1: 20 ± 5, A2: 23 ± 8, and A3:40 ± 11 ms2, P < 0.02), maintaining HF-BRS (gain, A1: 0.68 ± 0.12, A2: 0.63 ± 0.08, and A3: 0.57 ± 0.09; α index, A1: 0.58 ± 0.08, A2: 0.48 ± 0.06, and A3: 0.50 ± 0.09 ms/mmHg, not significant). However, LF-BRS decreased (gain, A1: 0.39 ± 0.06, A2: 0.17 ± 0.02, and A3: 0.11 ± 0.01, P < 0.001; α index, A1: 0.46 ± 0.07, A2: 0.20 ± 0.02, and A3: 0.14 ± 0.01 ms/mmHg, P < 0.001). As expected, once VTs were exceeded, hyperpnea induced a marked increase in both HF-HRV and HF-SBPV. However, this concomitant increase allowed the maintenance of HF-BRS, presumably by a mechanoelectric feedback mechanism.

Age dependency of cardiovascular autonomic responses to head-up tilt in healthy subjects

2004 ◽  
Vol 96 (6) ◽  
pp. 2333-2340 ◽  
Author(s):  
Tomi Laitinen ◽  
Leo Niskanen ◽  
Ghislaine Geelen ◽  
Esko Länsimies ◽  
Juha Hartikainen
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
High Frequency ◽  
Healthy Subjects ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Upright Position ◽  
Vascular Responses ◽  
Autonomic Responses ◽  
Head Up Tilt

In elderly subjects, heart rate responses to postural change are attenuated, whereas their vascular responses are augmented. Altered strategy in maintaining blood pressure homeostasis during upright position may result from various cardiovascular changes, including age-related cardiovascular autonomic dysfunction. This exploratory study was conducted to evaluate impact of age on cardiovascular autonomic responses to head-up tilt (HUT) in healthy subjects covering a wide age range. The study population consisted of 63 healthy, normal-weight, nonsmoking subjects aged 23–77 yr. Five-minute electrocardiogram and finger blood pressure recordings were performed in the supine position and in the upright position 5 min after 70° HUT. Stroke volume was assessed from noninvasive blood pressure signals by the arterial pulse contour method. Heart rate variability (HRV) and systolic blood pressure variability (SBPV) were analyzed by using spectral analysis, and baroreflex sensitivity (BRS) was assessed by using sequence and cross-spectral methods. Cardiovascular autonomic activation during HUT consisted of decreases in HRV and BRS and an increase in SBPV. These changes became attenuated with aging. Age correlated significantly with amplitude of HUT-stimulated response of the high-frequency component ( r = -0.61, P < 0.001) and the ratio of low-frequency to high-frequency power of HRV ( r = -0.31, P < 0.05) and indexes of BRS (local BRS: r = -0.62, P < 0.001; cross-spectral baroreflex sensitivity in the low-frequency range: r = -0.38, P < 0.01). Blood pressure in the upright position was maintained well irrespective of age. However, the HUT-induced increase in heart rate was more pronounced in the younger subjects, whereas the increase in peripheral resistance was predominantly observed in the older subjects. Thus it is likely that whereas the dynamic capacity of cardiac autonomic regulation decreases, vascular responses related to vasoactive mechanisms and vascular sympathetic regulation become augmented with increasing age.

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.

Abstract WP301: Noninvasive Beat-to-Beat Assessment of Blood Pressure Variability, Heart Rate Variability and Baroreflex Sensitivity: Which Parameters Best Predict Clinical Outcome After Acute Ischemic Stroke?

Stroke ◽  
2016 ◽  
Vol 47 (suppl_1) ◽  
Author(s):  
Li Xiong ◽  
Ge Tian ◽  
Xiangyan Chen ◽  
Howan Leung ◽  
Thomas Leung ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Ischemic Stroke ◽  
Clinical Outcome ◽  
Blood Pressure Variability ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Prognostic Information ◽  
Power Spectral

Background and Objectives: Blood pressure variability (BPV), heart rate variability (HRV) and baroreflex sensitivity (BRS) as measures of autonomic function might provide prognostic information in ischemic stroke. We aimed to study noninvasive beat-to-beat assessment of BPV, HRV and BRS in the acute phase of ischemic stroke to determine whether any of them predicted clinical outcome. Methods & Patients: Consecutive ischemic stroke patients within 7 days of symptom onset were enrolled. The frequency components of BPV and HRV by means of power spectral analysis [very low frequency (VLF; < 0.04 Hz); low frequency (LF; 0.04-0.15 Hz); high frequency (HF; 0.15-0.40 Hz); power spectral density (PSD; <0.40 Hz) and LF/HF ratio] were calculated from 10-minute recordings of beat-to-beat blood pressure and heart rate monitoring. The baroreflex slope and baroreflex effectiveness index (BEI) were determined using the sequence method for BRS. Clinical outcome was assessed at 3 months after stroke onset as good or poor by modified Rankin Scale (mRS) (good outcome, mRS ≤ 2). Results: 82 patients were recruited (mean age, 64.6 ± 9.9 years; 89.3% males). Univariate analysis showed that there were significant differences in National Institutes of Health Stroke Scale (NIHSS) at recruitment, VLF diastolic BPV, VLF, HF and PSD systolic BPV, and down ramp BEI between the good and poor outcome groups (all P < 0.05). After adjusting for NIHSS, multivariate logistic regression showed that only HF systolic BPV (OR 1.320; 95% CI, 1.050-1.659; P=0.017) and down BEI (OR 0.950; 95% CI, 0.912-0.990; P=0.014) were independently correlated with poor functional outcome. Conclusions: Beat-to beat highly variable systolic blood pressure and impaired BRS as evaluated by decreased down BEI are associated with an unfavorable functional outcome after acute ischemic stroke. Important prognostic information can be readily obtained from a short period of noninvasive hemodynamics monitoring in the acute stroke patient.

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.

Cardioautonomic control in healthy singleton and twin pregnancies

2020 ◽  
Author(s):  
Victoria L. Meah ◽  
Miranda L. Kimber ◽  
Rshmi Khurana ◽  
Rachelle Howse ◽  
Lisa K. Hornberger ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
High Frequency ◽  
Total Power ◽  
High Frequency Power ◽  
Singleton Pregnancy ◽  
Minute Period ◽  
Twin Pregnancies ◽  
Frequency Power ◽  
Singleton Pregnancies

In conjunction with significant cardiovascular adaptation, changes in cardioautonomic balance, specifically greater sympathetic activation and vagal withdrawal, are considered normal adaptations to healthy singleton pregnancy. Cardiovascular adaptation to twin pregnancy is more profound than that of singleton pregnancies; however, the changes in cardioautonomic control during multifetal gestation are unknown. To address this gap, beat-by-beat blood pressure (photoplethysmography) and heart rate (lead II electrocardiogram) were measured continuously in 25 twin pregnancies and 25 singleton pregnancies (matched for age, pre-pregnancy BMI and gestational age) during 10-minutes of rest. Data extracted from a 3- to 5-minute period was used to analyze heart rate variability (HRV), blood pressure variability (BPV), cardiovagal baroreflex gain and cardiac intervals as indicators of cardioautonomic control. Independent t-tests were used to determine statistical differences between groups (α=0.05) and the false rate discovery was determined to adjust for multiple comparisons. Resting heart rate was greater in twin compared to singleton pregnancies (91±10 vs. 81±10 bpm; P=0.001), but blood pressure was not different. Individuals with twin pregnancies had lower HRV, evidenced by lower standard deviation of R-R intervals (32±11 vs. 47±18 ms; P=0.001), total power (1035±810 vs. 1945±1570 ms2; P=0.004) and high frequency power (224±262 vs. 810±806 ms2; P<0.001) compared to singleton pregnancies. There were no differences in cardiac intervals, BPV and cardiovagal baroreflex gain between groups. Our findings suggest that individuals with twin pregnancies have greater sympathetic and lower parasympathetic contributions to heart rate and that cardiac, but not vascular, autonomic control is impacted during twin compared to singleton pregnancy.

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.

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