Short-term variability of systolic blood pressure and heart rate in normotensive subjects

Short-term fluctuations in systolic blood pressure (SBP) and heart rate (HR) and their inter-relationship were analysed in a group of normotensive middle-aged men (n = 16) using a multivariate autoregressive modelling technique. This study is the first to evaluate the beat-to-beat variability of SBP and HR in a group of real normotensive subjects. Direct intra-arterial blood pressure was registered together with ECG using an ambulatory tape recording technique (the Oxford method). Power spectrum density estimated (PSD) were used as a measure of the variability. PSDs were calculated over 3-min periods for four basic physiological conditions: during sleep and in the supine, sitting and standing positions. The inter-relationship between the blood pressure and heart rate variabilities was analysed using a closed-loop model. In agreement with results presented earlier in the literature, the beat-to-beat variation in SBP and HR was concentrated in three typical power spectrum regions: the high-frequency (HF = 0.15-0.35 Hz) region (respiration), the mid-frequency (MF = 0.075-0.15 Hz) region (vasomotor oscillation) and the low-frequency (LF = 0.02-0.075 Hz) region (thermoregulation). The variability changes considerably between different situations, especially that of the MF region. The variability was most prominent in the MF region and in the standing position. The variability was generally smallest in the HF region and in sleep. The results also demonstrate that the beat-to-beat variability in SBP and HR can considerably affect one another.     

Heart rate variability, trait anxiety, and perceived stress among physically fit men and women.

BACKGROUND: It is unclear from prior reports whether the relationships between self-ratings of anxiety or emotional stress and parasympathetic nervous system components of heart rate variability are independent of personality and cardiorespiratory fitness. We examined those relationships in a clinical setting prior to a standardized exercise test. METHODS AND RESULTS: Heart rate variability (HRV) was measured during 5 min of supine rest among 92 healthy men (N=52) and women (N=40) who had above-average cardiorespiratory fitness as indicated by peak oxygen uptake measured during grade-incremented treadmill exercise. HRV datasets were decomposed into low-frequency (LF; 0.05-0.15 Hz) and high-frequency (HF; 0.15-0.5 Hz) components using spectral analysis. Self-ratings of trait anxiety and perceived emotional stress during the past week were also assessed. CONCLUSIONS: There was an inverse relationship between perceived emotional stress during the past week and the normalized HF component of HRV (P=0.038). This indicates a lower cardiac vagal component of HRV among men and women who perceived more stress. That relationship was independent of age, gender, trait anxiety, and cardiorespiratory fitness. It was also independent of heart rate; mean arterial blood pressure; and respiration rate, factors which can influence HRV and might be elevated among people reporting anxiety and perceived stress. We conclude that vagal modulation of heart period appears to be sensitive to the recent experience of persistent emotional stress, regardless of a person's level of physical fitness and disposition toward experiencing anxiety.     

The relationships between autonomic function and heart rate in essential hypertension

The circadian variation of blood pressure (BP) may be mediated at least in part by circadian variation of autonomic nervous system activity. In the present study power spectral analysis of hourly R-R intervals for 24 hours was done to obtain the low frequency variability (LF: 0.04 to 0.15Hz) and high frequency variability(HF: 0.15 to 0.40Hz) in 93 patients with untreated essential hypertension. LF/HF ratio and HF were considered to be an index of sympathetic nervous activity and parasympathetic nervous activity, respectively. The relationship between heart rate (HR) and systolic blood pressure (SBP), diastolic blood pressure (DBP), HF, and LF/HF was examined. Both SBP and DBP were correlated positively with HR(r = 0.28, p < 0.05 and r = 0.27, p < 0.05, respectively) in the daytime. HF was correlated negatively and significantly with HR in both daytime and nighttime (r = -0.40, p < 0.05, and r = -0.38, p < 0.05 respectively). After averaging for SBP of 24 hours, HR in the patients whose SBP was 135mmHg or more was significantly higher than that in the patients whose SBP was less than 135mmHg. These results suggest that the decreased parasympathetic nervous activity seems to be responsible for the rise in BP.     

驾驶精神疲劳的心率变异性和血压变异性综合效应分析

驾驶精神疲劳是威胁人们健康与生命安全的严重问题.本研究的目的是基于心率变异性与血压变异性功率谱分析综合评估驾驶员精神疲劳.20个健康男性样本(28.8±4.3)岁参加90 min的模拟驾驶操作实验,实验后计算分析实验样本心率变异性和血压变异性的频域指标,如:低频成分(0.04～0.15 Hz,LF),高频成分(0.15～0.4Hz,HF),代频与高频比值(LF/HF);同时分析反映血流动力学指标的血压和心率.研究表明,样本在实验结束后交感神经兴奋性增强,迷走神经兴奋性减弱,交感迷走平衡性升高;同时,心率变异性与血压变异性的对应指标在实验过程中具有良好的相关性(P＜0.05).研究认为采用多变量综合效应分析方式评价自主神经系统功能是科学和客观的.     

Power spectral analysis of heart rate and blood pressure variability in anaesthetized dogs.

Short-term oscillation of heart rate and blood pressure are mainly regulated by the automatic nervous system. It has been proposed that non-neural factors, such as changes in intrathoracic pressure, can strongly modulate this rhythmicity. Our aim was to evaluate the effect of changing intrathoracic pressure and central autonomic nervous activity on heart rate and blood pressure variability. Evaluation was performed by using spectral analysis techniques with autoregressive modelling. The variability in heart rate and blood pressure remained in animals with open chest or paralysed respiratory muscles. After vagotomy, the variability in heart rate decreased, but not that of blood pressure. Total spinal anaesthesia elicited a decrease in the variability in blood pressure. The pharmacological blockade of alpha- and beta-receptors further decreased both variabilities. It was concluded that in anaesthetized dogs heart rate and blood pressure variability are mainly of central origin and non-neural factors have only minor effect on these central rhythms. High (> 0.15 Hz), medium (0.07-0.15 Hz) and, obviously low (0.00-0.07 Hz) frequency variations in heart rate are mostly mediated vagally. In blood pressure, medium and obviously low frequency variations are modulated by sympathetic nervous system, whereas high frequency variations are secondary to the heart rate variation.     

Blood pressure variability and closed-loop baroreflex assessment in adolescent chronic fatigue syndrome during supine rest and orthostatic stress

Hemodynamic abnormalities have been documented in the chronic fatigue syndrome (CFS), indicating functional disturbances of the autonomic nervous system responsible for cardiovascular regulation. The aim of this study was to explore blood pressure variability and closed-loop baroreflex function at rest and during mild orthostatic stress in adolescents with CFS. We included a consecutive sample of 14 adolescents 12–18 years old with CFS diagnosed according to a thorough and standardized set of investigations and 56 healthy control subjects of equal sex and age distribution. Heart rate and blood pressure were recorded continuously and non-invasively during supine rest and during lower body negative pressure (LBNP) of –20 mmHg to simulate mild orthostatic stress. Indices of blood pressure variability and baroreflex function (α-gain) were computed from monovariate and bivariate spectra in the low-frequency (LF) band (0.04–0.15 Hz) and the high–frequency (HF) band (0.15–0.50 Hz), using an autoregressive algorithm. Variability of systolic blood pressure in the HF range was lower among CFS patients as compared to controls both at rest and during LBNP. During LBNP, compared to controls, α-gain HF decreased more, and α-gain LF and the ratio of α-gain LF/α-gain HF increased more in CFS patients, all suggesting greater shift from parasympathetic to sympathetic baroreflex control. CFS in adolescents is characterized by reduced systolic blood pressure variability and a sympathetic predominance of baroreflex heart rate control during orthostatic stress. These findings may have implications for the pathophysiology of CFS in adolescents.     

Resting and postexercise cardiac autonomic control in trained master athletes

This study used measures of heart rate variability during recovery from high-intensity exercise in trained Master athletes to examine postexercise cardiac autonomic regulation. Seven males (mean age 52.1 +/- 3.3 yr; mass 85.1 +/- 18.0 kg) and 6 females (mean age 50.5 +/- 2.9 yr; mass 63.1 +/- 6.0 kg) performed incremental exercise to an intensity that induced a >4.5 mmol capillary blood lactate concentration, followed by incremental exercise to volitional exhaustion (VO2(max)). A 6 min ECG recording before (Pre) and after (Post) exercise was analyzed in the time (mean rr interval, sd rr) and frequency domains (total power, very low frequency [VLF: 0-0.04 Hz], low frequency [LF: 0.04-0.15 Hz], high frequency [HF: 0.15-0.4 Hz]). VO2(max) for males and females was 49.4 +/- 7.1 ml kg(-1) min(-1) and 45.1 +/- 10.1 ml kg(-1) min(-1), respectively. Lower mean rr interval (Pre: 1,048 +/- 128 ms; Post: 730 +/- 78 ms; P < 0.001) and lower sd rr (Pre: 77 +/- 30 ms; Post: 43 +/- 17 ms; P < 0.001) were recorded following exercise, with no differences based on gender. Total power decreased following exercise (Pre: 6,331 +/- 6,119 ms; Post: 1,921 +/- 1,552 ms). When normalized for changes in total power, a decreased HF component (Pre: 34.52 +/- 14.79 n.u.; Post: 18.49 +/- 13.64 n.u.; P < 0.05) with no change in LF component (Pre: 61.00 +/- 18.66 n.u.; Post: 69.63 +/- 23.97 n.u.; P = 0.34) was recorded. No gender differences in HRV in the frequency domain were recorded. Decreased heart rate variability in both time and frequency domains suggested an increased parasympathetic withdrawal during the autonomic control of postexercise tachycardia in trained Master athletes.     

Baroreceptor reflex sensitivity in human neonates: the effect of postmenstrual age

We performed a cross-sectional study in human infants to determine if indices of R–R interval variability, systolic blood pressure (SBP) variability, and baroreceptor reflex sensitivity change with postmenstrual age (PMA: gestational age + postnatal age). The electrocardiogram, arterial SBP and respiration were recorded in clinically stable infants (PMA, 28–42 weeks) in the quiet sleep state in the first days after birth. (Cross-)spectral analyses of R–R interval series and SBP series were performed to calculate the power of low-frequency (LF, indicating baroreceptor reflex activity, 0.04–0.15 Hz) and high-frequency (HF, indicating parasympathetic activity, individualized between the p-10 and p-90 values of respiratory frequency) fluctuations, and transfer function phase and gain. The mean R–R interval, and LF and HF spectral powers of R–R interval series increased with PMA. The mean SBP increased with PMA, but not the LF and HF spectral powers of SBP series. In the LF range, cross-spectral analysis showed high coherence values (> 0.5) with a consistent negative phase shift between R–R interval and SBP, indicating a ∼3 s lag in R–R interval changes in relation to SBP. Baroreceptor reflex sensitivity, calculated from LF transfer gain, increased significantly with PMA, from 5 (preterm) to 15 ms mmHg⁻¹ (term). Baroreceptor reflex sensitivity correlated significantly with the (LF and) HF spectral powers of R–R interval series, but not with the LF and HF spectral powers of SBP series. The principal conclusions are that baroreceptor reflex sensitivity and spectral power in R–R interval series increase in parallel with PMA, suggesting a progressive vagal maturation with PMA.     

The effect of ventilation on spectral analysis of heart rate and blood pressure variability during exercise

Heart rate variability (HRV) and systolic blood pressure variability (BPV) during incremental exercise at 50, 75, and 100% of previously determined ventilatory threshold (VT) were compared to that of resting controlled breathing (CB) in 12 healthy subjects. CB was matched with exercise-associated respiratory rate, tidal volume, and end-tidal CO(2) for all stages of exercise. Power in the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, >0.15-0.4 Hz) for HRV and BPV were calculated, using time-frequency domain analysis, from beat-to-beat ECG and non-invasive radial artery blood pressure, respectively. During CB absolute and normalized power in the LF and HF of HRV and BPV were not significantly changed from baseline to maximal breathing. Conversely, during exercise HRV, LF and HF power significantly decreased from baseline to 100% VT while BPV, LF and HF power significantly increased for the same period. These findings suggest that the increases in ventilation associated with incremental exercise do not significantly affect spectral analysis of cardiovascular autonomic modulation in healthy subjects.     

Spectral characteristics of heart rate fluctuations during parabolic flight

Parabolic flight is used to create short successive periods of changing gravity in a range between 0 and 1.8 Gz (1 Gz: 9.81 m/s²). The purpose of the present study was to evaluate whether cyclic variations in heart rate during ±20 s periods of stable gravity in parabolic flight reflect autonomic modulation of cardiac chronotropy. During the 29th and 32nd ESA parabolic flight campaign ECG and respiration were recorded in 13 healthy volunteers in both standing and supine postures. We developed and validated a spectral algorithm especially adapted to study frequency components of heart rate among ultrashort (±20 s) stable gravity periods of parabolic flight. A low frequency (LF) component, starting from the lowest measurable frequency (±0.05 Hz) up to 0.15 Hz was distinguished from a high frequency (HF) component, ranging from 0.16 Hz up to 0.4 Hz. Powers were calculated by integration between corresponding limits and represented in normalized units (nu). With our method, we were able to reproduce normal findings in the upright posture at 1 Gz, i.e., less power in the HF component compared to supine (HFnu: 0.18±0.09 vs. 0.40±0.16). These postural related differences are shown to be eliminated at 0 Gz (HFnu: 0.30±0.12 vs. 0.32±0.13) and amplified at 1.8 Gz phases (HFnu: 0.15±0.10 vs. 0.39±0.16) of parabolic flight. In the supine position no coherent differences were shown in the measured variables among different gravity phases. Our observations strongly indicate that spectral characteristics of heart rate fluctuations among stable gravity periods of parabolic flight reflect parasympathetic nervous system control of cardiac chronotropy. At 1 Gz, there is a normal upright situation with less parasympathetic modulation of heart rate compared to supine. This effect is augmented during 1.8 Gz-conditions due to a suppressed parasympathetic control of heart rate in the upright posture. Alternatively, at 0 Gz, increased parasympathetic control in standing position eliminates differences in cardiac chronotropy compared to supine.     

Depressed mood is related to high-frequency heart rate variability during stressors

OBJECTIVE: The purpose of this study was to examine the relationships between depressed mood and parasympathetic control of the heart in healthy men and women at rest and during two stressors. METHODS: Fifty-three healthy college students completed a laboratory stress protocol that included a baseline resting period, a challenging speech task, and a forehead cold pressor task. Depressed mood was assessed using the Beck Depression Inventory (BDI). Parasympathetic cardiac control was measured as the high-frequency (0.12-0.40 Hz) component (HF) of heart rate variability using power spectrum analysis. Blood pressure, respiration rate, and respiration amplitude were measured simultaneously. RESULTS: Participants were categorized as having a high or low depressed mood on the basis of median splits of their BDI scores. Those in the high depressed mood group had significantly greater reductions in HF during the speech task and significantly smaller increases in HF during the forehead cold pressor task than those in the low depressed mood group. Women had significantly greater reductions in HF during the speech task and smaller increases in HF during the forehead cold pressor task than men. However, gender and depressed mood did not interact to predict changes in HF. CONCLUSIONS: Depressed mood is related to the magnitude of decrease in parasympathetic cardiac control during stressors in healthy men and women. These findings extend those of previous studies, in which a similar phenomenon was observed among patients with cardiac disease. Because the participants in this study were healthy, the relationship between depressed mood and parasympathetic cardiac control does not seem to be secondary to cardiovascular disease.     

Vestibular influence on the cardiorespiratory responses to whole-body oscillation after standing

We assessed the influence of vestibular stimulation by whole-body oscillation in the yaw plane on the cardiorespiratory responses after a change of posture from sitting to standing. Eighteen healthy subjects (21–70 years old) and six patients with bilateral vestibular loss (46–59 years old) were tested. For comparison, a subgroup, age matched to the patients, was created from the healthy group. After a 10-min rest, subjects who were sitting, back unsupported, stood on a platform affording en bloc head and body support. The platform was either static or oscillated at 0.1 Hz and 0.5 Hz (20° amplitude) for 2 min. Presentation of the three conditions was counterbalanced. Respiration, ECG, blood pressure and head position were recorded. During oscillation at 0.5 Hz, the respiratory responses were different between groups; healthy subjects showed a significant increase of the respiratory frequency (1.75±2.1 breaths/min), which was not observed in the patients (0.16±0.7 breaths/min) (p<0.05, ANOVA). Absolute changes of heart rate and blood pressure were similar for the three conditions in all the subjects. However, healthy subjects showed a decrease of power spectrum density of the high-frequency ('respiratory') component of heart rate variability on standing during all three conditions. This response was variable among the patients and the age-matched group. The study shows that semicircular canal activation influences the respiratory rhythm during movements in the yaw plane in standing subjects. In addition, we observed that changes of the respiratory influence on heart rate variability during orthostatic stress are not affected by yaw oscillation or chronic vestibular loss, but may be affected by factors related to age. Electronic Publication     

Diet and exercise training reduce blood pressure and improve autonomic modulation in women with prehypertension

Despite mortality from heart disease has been decreasing, the decline in death in women remains lower than in men. Hypertension (HT) is a major risk factor for cardiovascular disease. Therefore, approaches to prevent or delay the onset of HT would be valuable in women. Given this background, we investigated the effect of diet and exercise training on blood pressure (BP) and autonomic modulation in women with prehypertension (PHT). Ten women with PHT (39 ± 6 years, mean ± standard deviation) and ten with normotension (NT) (35 ± 11 years) underwent diet and exercise training for 12 weeks. Autonomic modulation was assessed through heart rate (HR) and systolic BP (SBP) variability, using time and frequency domain analyses. At preintervention, women with PHT had higher SBP (PHT: 128 ± 7 vs. NT: 111 ± 6 mmHg, p < 0.05) and lower HR variability [standard deviation of normal-to-normal beats (SDNN), PHT: 41 ± 18 vs. NT: 60 ± 19 ms, p < 0.05]. At post-intervention, peak oxygen consumption and muscular strength increased (p < 0.05), while body mass index decreased in both groups (p < 0.05). However, SBP decreased (118 ± 8 mmHg, p < 0.05 vs. preintervention) and total HR variability tended to increase (total power: 1,397 ± 570 vs. 2,137 ± 1,110 ms(2), p = 0.08) only in the group with PHT; consequently, HR variability became similar between groups at post-intervention (p > 0.05). Moreover, reduction in SBP was associated with augmentation in SDNN (r = -0.46, p < 0.05) and reduction in low-frequency power [LF (n.u.); r = 0.46, p < 0.05]. In conclusion, diet and exercise training reduced SBP in women with PHT, and this was associated with augmentation in parasympathetic and probably reduction in sympathetic cardiac modulation.     

The beat-to-beat blood pressure response to postural change in young and elderly healthy adult males

Heart rate and blood pressure were studied with the beat-to-beat tracking cuff system in two groups (n=20 per group) of healthy, unmedicated males, one between 60 and 75 years of age and the second between 18 and 29 years of age. The study confirms the previously reported blunted heart rate response to standing and the fact that, when blood pressure is recorded by conventional means, the response exhibited during orthostasis does not differ in healthy groups of young and elderly subjects. With the tracking cuff system, however, the elderly exhibited a smaller immediate systolic and diastolic drop in response to the change to upright posture and less variability in beat-to-beat blood pressure changes. The results have implications for cardiovascular studies, where age and posture can influence both blood pressure and heart rate.This research was supported by National Heart, Lung, and Blood Institute Research Grant HL-31184-05.     

皮质下动脉硬化性脑病血压及心率变异性分析

目的和方法：采用动态检测技术观察３１例皮质下动脉硬化性脑病和对照组３１例健康人血压和心率的变异性。结果：患者均存在动态血压异常，其中平均收缩压、平均舒张压超过正常值者２７例（８７％），夜间基底血压异常升高２２例（７１％），血压异常波动２０例（６４％），昼夜节律逆转４例（１３％）。患者心率变异时域指标２４小时内全部正常心动周期的标准差、２４小时内５分钟节段平均正常心动周期的标准差、在一定时间内相邻两正常心动周期差值大于５０毫秒的个数所占的百分比均明显低于对照组，收缩压与心率无显著相关性。结论：提示血压波动及持续的夜间升压现象在该病中起着一定作用，而这种异常可能与患者植物神经系统功能失调有关     

A comparison of physiological variables in aged and young women during and following submaximal exercise

Previously, we have examined how aging affects the physiological responses of men to endurance exercise. In the present investigation, we aimed to extend our assessment of the influence of aging on exercise‐induced responses by focusing on women. Ten young (20.3 ± 0.3 years; mean ± SE) and 10 aged (75.5 ± 1.2 years) women performed 30 min of cycling at 60–65% of their predetermined peak oxygen uptake. Data for respiratory exchange ratio (RER), heart rate, blood pressure, rectal temperature, and plasma metabolites were collected before exercise, at the 15th and 30th min of exercise, and at 5 and 15 min postexercise. A two‐way, repeated measures ANOVA with main effects of age and time was conducted on each variable. Our findings showed that age affected exercise‐induced responses of each variable quantified. Although RER, heart rate, temperature, and lactate were significantly (P < 0.05) higher among young women, blood pressure and glucose values were greater among aged women. Moreover, unlike previous results noted among men where age‐related differences primarily occurred during postexercise recovery, in women the effect of aging was detected during exercise itself. The data presented here indicate that aging impacts physiological responses of women to prolonged endurance exercise even when relative intensity (% of peak oxygen uptake) is held constant. Combined with our earlier study on men, these findings suggest that gender interacts with aging to determine whether age‐related differences are manifested during exercise itself, or during postexercise recovery. Am. J. Hum. Biol., 2009. © 2009 Wiley‐Liss, Inc.     

Anger inhibition potentiates the association of high end-tidal CO2 with blood pressure in women

OBJECTIVE: High resting end-tidal CO2 (PetCO2) has been shown to be an independent predictor of systolic blood pressure (SBP) in women, particularly older women. The study reported in this article investigated whether the tendency to experience, express, and/or suppress anger contributes to the association of PetCO2 and SBP in women and in men. METHODS: The Spielberger Anger Expression Inventory was administered to 403 healthy male and female participants in the Baltimore Longitudinal Study on Aging. Resting PetCO2 was obtained by means of a respiratory gas monitor, and resting blood pressure was obtained with an oscillometric device. The associations of resting PetCO2 and the anger scales with SBP and diastolic blood pressure (DBP) were investigated using multivariate regression analyses. RESULTS: PetCO2, as well as age and body mass index, was an independent predictor of SBP in women with low, but not high, trait anger and in women with low, but not high, anger-out. PetCO2 was not an independent predictor of SBP in men with either high or low anger. In addition, PetCO2 was not an independent predictor of DBP in either men or women. CONCLUSIONS: The results of this study indicate that inhibition of anger potentiates the relationship of high PetCO2 with SBP in women but not men. Additional studies are needed to determine the origins of the observed gender differences and the psychophysiological pathways by which high resting PetCO2 contributes to elevated resting blood pressure in women.     

Isometric strength,endurance, and the blood pressure and heart rate responses during isometric exercise in healthy men and women,with special reference to age and body fat content

The relationship of sex, age, and body fat content were assessed on the maximal voluntary strength (MVC), the endurance of a sustained contraction held at 40% of the subject's maximal strength, and the associated changes in blood pressure and heart rate. Isometric hand-grip strength was, as expected, greater in men than in women; however, in both sexes, age was inversely related to isometric strength, particularly in women. Body fat content, however, was directly related to strength. In contrast, in both male and female subjects aging was directly related to isometric endurance while body fat content was now inversely related to isometric endurance. The increase in heart rate throughout a fatiguing contraction at 40% MVC was strikingly similar in men and women. Heart rate, which always increased during exercise, attained its highest magnitude during exercise in the subjects who had the highest resting heart rates. However, older subjects displayed a smaller increase in exercising heart rates than younger subjects. The blood pressure at the end of the 40% MVC was directly related to the resting blood pressure. However, aging and body fat content both increased the resting systolic blood pressure in men and women; this aging effect was further exaggerated during the exercise.     

Causal coherence analysis of heart rate variability and systolic blood pressure variability under mental arithmetic task load

Causal coherence analysis based on a closed-loop bivariate autoregressive model was applied to heart rate variability and systolic blood pressure (SBP) variability during mental arithmetic tasks to clarify how mental task load affects the linear closed loop interaction between cardiac and vascular systems. Thirteen normal male subjects performed a mental arithmetic task, button press task, and rest task while measuring their RR interval (RRI) and SBP. The mean value in the low frequency (LF) band (0.04-0.15Hz) of the squared causal coherence function from SBP to RRI during the mental arithmetic task was significantly higher than during the other two control tasks. Conversely, the LF band of the squared causal coherence function from RRI to SBP during the mental arithmetic task tended to be lower than during the rest task. These results suggest that mental arithmetic tasks enhance linear causal coupling from the vascular to cardiac system, and conversely weaken that from the cardiac to vascular system.     

Autonomic cardiac control. II. Noninvasive indices and basal response as revealed by autonomic blockades

Heart period, systolic time intervals, low and high frequency heart period variability, blood pressure, and respiration were measured in female subjects under three drug conditions (saline, atropine sulfate, metoprolol) while sitting and standing on three consecutive days. Following preinfusion baseline recordings, saline, metoprolol (14 mg), or atropine sulfate (2 mg) was infused for 15 min (by using a double-blind procedure). Recordings were taken during a postinfusion baseline and in response to an orthostatic stressor (standing versus sitting postures). At the end of the metoprolol session, atropine sulfate was infused and responses were monitored during the post-infusion (i.e., double blockade) baseline and during orthostatic stressor. Analyses of the blockade data revealed that the preejection period (PEP) reflected sympathetic but not vagal influences on the heart, and high frequency (HF, 0.12–0.40 Hz) heart rate variability (respiratory sinus arrhythmia) reflected vagal but not sympathetic influences on the heart. No other measure provided a specific index of the tonic sympathetic or vagal activation of the heart. Postinfusion PEP under saline predicted individual differences in postinfusion cardiac sympathetic activation, whereas postinfusion heart period (but not HF variability) under saline predicted individual differences in postinfusion cardiac vagal activation.