Spectral Analysis Of Blood Pressure Research Articles

The impact of total sleep deprivation upon supine and head up tilt hemodynamics using non-linear analysis in firefighters

PurposeThe impact of 31 h of total sleep deprivation (TSD) on cardiovascular autonomic modulation was evaluated in 46 volunteers all professional fire brigade units officers (all men, mean age = 32.11 ± 6.4). MethodsHemodynamic examination was obtained at baseline and after 31 h of Total Sleep Deprivation (TSD). Each measurement period included supine and head-up tilt (HUT) test response. Continuous beat-to-beat systolic blood pressure (sBP), diastolic blood pressure (dBP) and mean blood pressure (mBP), heart rate (HR), stroke volume (SV), left ventricular ejection time (LVET) and cardiac output (CO) were calculated in rest supine position and in response to HUT. Nonlinear analyses were conducted using Permutation Entropy (PE), Amplitude Aware Permutation Entropy (AAPE) and Fractal Dimension (FD). ResultsSupine increase of HR and decrease in RRI, LVET and entropy of LVET were observed after 31-h of TSD. Increase in entropy of mBP was indicated by AAPE and PE methods. Response to HUT, values of spectral analysis of blood pressure (normalized units of high frequency of sBP and dBP) was altered. Permutation entropy of mBP in response to HUT were significantly changed after 31-h of TSD. ConclusionsTSD alters autonomic nervous system modulation of cardiac and vascular functioning while supine and in response to orthostatic stress. TSD resulted in changes in cardiac and both spectral and two methods of analysis of entropy of blood pressure when supine. Values of spectral analysis of blood pressure and permutation entropy of mean blood pressure in response to HUT were significantly changed after 31 h of TSD.

Vasopressin and v1br gene expression is increased in the hypothalamic pvn of borderline hypertensive rats.

Vasopressin (VP) is a neurohypophyseal peptide best known for its role in maintaining osmotic and cardiovascular homeostasis. The main sources of VP are the supraoptic and paraventricular (PVN) nuclei of the hypothalamus, which coexpress the vasopressin V1a and V1b receptors (V1aR and V1bR). Here, we investigated the level of expression of VP and VP receptors in the PVN of borderline hypertensive rats (BHRs), a key integrative nucleus for neuroendocrine cardiovascular control. Experiments were performed in male BHRs and Wistar rats (WRs) equipped with a radiotelemetry device for continuous hemodynamic recording under baseline conditions and after saline load without or with stress. Autonomic control of the circulation was evaluated by spectral analysis of blood pressure (BP) and heart rate (HR) variability and baroreceptor reflex sensitivity (BRS) using the sequence method. Plasma VP was determined by radioimmunoassay, and VP, V1aR, and V1bR gene expression was determined by RT-qPCR. Under baseline conditions, BHRs had higher BP, lower HR, and stronger BRS than WRs. BP and HR variability was unchanged. In the PVN, overexpression of the VP and V1bR genes was found, and plasma VP was increased. Saline load downregulated V1bR mRNA expression without affecting VP mRNA expression or plasma VP and BP. Adding stress increased BP, HR, and low-frequency sympathetic spectral markers and decreased plasma VP without altering the level of expression of VP and VP receptors in the PVN. It follows that overexpression of VP and V1bR in the PVN is a characteristic trait of BHRs and that sympathetic hyperactivity underlies stress-induced hypertension.

Advantages of individual approach to chronotherapy in Yamal hypertensive shift workers

Objective. To compare efficiency of the chronotherapy based on spectral analysis of blood pressure (BP) with chronotherapy based on the results of 24-hour BP monitoring. Design and methods. Ninety-three men, transpolar shift workers, with hypertension (HTN) II stage, 1–2 degree were divided into 2 subgroups: in the 1st group daily BP profile was assessed once («dipper», «non-dipper», «over-dipper», «night-peaker», «Standard treatment» group, n = 57), in the 2nd group BP chronotype was considered (group «Chrono», n = 36). Standard analysis and cosinor-analysis of 24‑hour BP monitoring were performed. Lisinopril (LP) 5 mg per day was prescribed for 2 weeks followed by second assessment. Results. Chronotherapy based on the chronotype of daily BP and its spectral characteristics is more efficient and allows better BP control. It leads to a better compliance and achievement of the target BP level, normalization of daily dynamics of BP and heart rate. Conclusions. In shift workers living in the Far North, chronotherapy of HTN is a promising method used due to the early change of daily BP dynamics. Individual chronotherapy is recommended as a rational approach to treat “northern” HTN and contributes to a better patients’ compliance.

Continuous Cuffless Blood Pressure Estimation Using Pulse Transit Time and Photoplethysmogram Intensity Ratio.

Pulse transit time (PTT) has attracted much interest for cuffless blood pressure (BP) measurement. However, its limited accuracy is one of the main problems preventing its widespread acceptance. Arterial BP oscillates mainly at high frequency (HF) because of respiratory activity, and at low frequency (LF) because of vasomotor tone. Prior studies suggested that PTT can track BP variation in HF range, but was inadequate to follow the LF variation, which is probably the main reason for its unsatisfactory accuracy. This paper presents a new indicator, the photoplethysmogram intensity ratio (PIR), which can be affected by changes in the arterial diameter, and, thus, trace the LF variation of BP. Spectral analysis of BP, PTT, PIR, and respiratory signal confirmed that PTT was related to BP in HF at the respiratory frequency, while PIR was associated with BP in LF range. We, therefore, develop a novel BP estimation algorithm by using both PTT and PIR. The proposed algorithm was validated on 27 healthy subjects with continuous Finapres BP as reference. The results showed that the mean ± standard deviation (SD) for the estimated systolic, diastolic, and mean BP with the proposed method against reference were -0.37 ±5.21, -0.08 ±4.06, -0.18 ±4.13 mmHg, and mean absolute difference (MAD) were 4.09, 3.18, 3.18 mmHg, respectively. Furthermore, the proposed method outperformed the two most cited PTT algorithms for about 2 mmHg in SD and MAD. These results demonstrated that the proposed BP model using PIR and PTT can estimate continuous BP with improved accuracy.

Current Approaches to Quantifying Tonic and Reflex Autonomic Outflows Controlling Cardiovascular Function in Humans and Experimental Animals.

The role of the autonomic nervous system in the pathophysiology of human and experimental models of cardiovascular disease is well established. In the recent years, there have been some rapid developments in the diagnostic approaches used to assess and monitor autonomic functions. Although most of these methods are devoted for research purposes in laboratory animals, many have still found their way to routine clinical practice. To name a few, direct long-term telemetry recording of sympathetic nerve activity (SNA) in rodents, single-unit SNA recording using microneurography in human subjects and spectral analysis of blood pressure and heart rate in both humans and animals have recently received an overwhelming attention. In this article, we therefore provide an overview of the methods and techniques used to assess tonic and reflex autonomic functions in humans and experimental animals, highlighting current advances available and procedure description, limitations and usefulness for diagnostic purposes.

58. Cardiovascular responses in patients with symptoms of orthostatic intolerance

The inability to stand without orthostatic hypotension is the typical disabling clinical symptom of both Postural Tachicardia Syndrome (POTS) and Orthostatic Intolerance (OI). The increase of sinus heart rate of 30 beats/min or greater occurring within 10 min of head-up tilt test or standing, or a heart rate while upright of >120 beats/min. discriminates between the two conditions. To verify if others criteria, beside the difference in heart rate increase, can distinguish the two groups, we analyzed the cardiovascular responses during active standing and head – up tilt test. We analyzed 10 patients with POTS and 10 with OI. Power spectral analysis of blood pressure and heart rate variability, in resting condition and during a period of 30 min of head – up tilt test to 60°, was performed. Both clinical conditions were compared with each other and with a control group using the Student t test. During the head – up tilt both groups of patients showed a marked and comparable increase of LF-RRI and LF/HF ratio in the power spectrum of R–R interval compared to the baseline. This could suggest the hypothesis of OI as a condition preceding POTS.

From the First Spectral Analysis of Blood Pressure Variability in the World to the Present Time: Contribution of the Department of Physiology of the Faculty of Medicine, Masaryk University, Brno

The review shows the significance of blood pressure regulation studies conducted during several decades at the Department of Physiology, Faculty of Medicine, Masaryk University, Brno. Continuous non-invasive blood pressure measurement was first introduced and patented here and, with the obtained data, the first spectral analysis of blood pressure was performed. This method was used in many different physiological studies on the relationship of blood pressure regulation to circulatory parameters, breathing, and baroreflex sensitivity. The article deals with studies on risk stratification of sudden cardiac death according to decreased baroreflex sensitivity, 24-hour heart rate variability, the amount of extrasystoles and late potentials. Importance of the new method of determination of one summation risk index is described here. A summary of the new conception of the relationship between low baroreflex sensitivity and hypertension is presented. Here, not only pathological changes of the vessel wall but also increased sympathetic activity and genetic predisposition play a role. Importance of studies conducted in young adults is highlighted, as inherited BRS decrease contributes to earlier blood pressure increase in the young. This research is highly topical, since prevention of hypertension in childhood is possible. Recent studies are dedicated to blood pressure regulation in young diabetics.

Cardiovascular variability in Parkinson’s disease and extrapyramidal motor slowing

Parkinson's disease (PD) is a degenerative neurological condition, associated with cardiovascular dysfunction. Many studies have utilised heart rate variability (HRV) to assess the autonomic nervous system in PD, but blood pressure variability (BPV) has received less attention. The purpose of the present study was to compare HRV and BPV between participants with established PD, extrapyramidal motor slowing (EPMS) (not reaching clinical criteria for PD), older healthy controls (OHC), and young healthy controls (YHC), in order to ascertain whether either of these measures can be used as an early marker of non-motor symptoms in PD. HRV was assessed at rest and during 2 min of slow deep breathing in 97 participants, divided into four groups: YHC (20-30 years; n = 19); OHC (67-83 years; n = 28); EPMS (59-91 years; n = 25) and PD (61-84 years; n = 25). Spectral analysis of blood pressure was performed on stable non-invasive recordings of blood pressure obtained in 76 of the participants. Low frequency (LF) and high frequency (HF) components, and the LF/HF ratio, were measured. Significant differences were only seen between the YHC and the three older groups. For HRV this was seen at rest and during 2 min of slow deep breathing, whereas for BPV this was only seen during 2 min of slow deep breathing. These data indicate that there are only age-related changes in HRV and BPV, and that neither technique is sensitive enough to provide an index of pre-clinical PD.

Artificial gravity with ergometric exercise as a countermeasure against cardiovascular deconditioning during 4 days of head-down bed rest in humans

We have shown previously that combined short-arm centrifuge and aerobic exercise training preserved several physiologically important cardiovascular functions in humans. We hypothesized that artificial gravity (AG) and exercise is effective to prevent changes of physical problems during head-down bed rest (HDBR). To test this hypothesis, 12 healthy male subjects had undergone 4 days of 6° HDBR. Six of them were exposed to AG of an alternating 2-min intervals of +1.0 and +2.0 Gz at foot level for 30 min twice per day with ergometric exercise of 40 W as a countermeasure during bed rest (CM group), while the remaining six served as untreated controls (no-CM group). Before and after 4 days of bed rest, leg venous hemodynamics was assessed by venous occlusion plethysmography and autonomic cardiovascular control estimated by power spectral analysis of blood pressure and heart rate. Further, orthostatic tolerance was evaluated by a 75° head-up tilt test and physical working capacity was surveyed by near maximal physical working capacity test before and after bed rest. The data showed that combined centrifuge and exercise applied twice daily for a total of 60 min during 4 days of HDBR prevented (a) a decrease in working capacity, (b) autonomic dysfunction (a decrease in the activity of parasympathetic cardiac innervation) and (c) an increase in leg venous flow resistance. The combination of a 30 min alternating of +1.0 and +2.0 Gz for twice per day of AG with 40 W ergometric exercise may offer a promising countermeasure to short duration simulated microgravity.

Reduction of heart rate, but not heart rate variability, in diabetic rats

Reduction of heart rate is an early event in type 1 diabetes mellitus (DM) in a number of species including rats, rabbits, and humans. This reduction has been attributed to baroreflex dysfunction resulting from increased parasympathetic tone (McDowell et al AJP 1994; 266: H235). DM was induced by streptozotocin in Long Evans rats (intact, n=5 & DM n=7). Systolic pressure did not differ between the groups. 24h average heart rate declined from 362 ± 4 at control to 356 ± 3 at week 3 and 346 ± 4 min−1 at week 11 in intact rats and from 370 ± to 328 ± 6 and 300 ± 6 min−1 in DM (decline p < 0.00003 versus intact). However, heart rate variability, expressed as coefficient of variation, was unchanged. We had previously shown that spectral analysis of blood pressure from heart rate (~6 Hz) to circadian (0.0000115 Hz) readily detects the roughly fivefold increase in blood pressure (BP) spectral power induced by chemoreceptors‐sparing partial baroreceptor denervation. This increase occurs only in the interval from 0.08 Hz out to 0.0004 Hz. Here we used spectral analysis of inter‐beat interval (one hour record) and of BP to compare intact and DM rats at the three time points. Repeated measures ANOVA was used to compare intact and DM rats in the frequency band noted above and in standard very low frequency (0.02 ‐ 0.2 Hz), low frequency (0.2 ‐ 0.6 Hz), and high frequency (0.6 ‐ 3 Hz) bands. As expected there were no differences between groups in the control condition. However there were also no differences between the intact and DM rats at weeks 3 and 11. To the extent that this analysis probes arterial baroreflex is, we can detect no differences between intact and diabetic rats. Funded by Heart & Stroke Fdn of BC & Yukon

Hindlimb unloading elicits anhedonia and sympathovagal imbalance

The hindlimb-unloaded (HU) rat model elicits cardiovascular deconditioning and simulates the physiological adaptations to microgravity or prolonged bed rest in humans. Although psychological deficits have been documented following bed rest and spaceflight in humans, few studies have explored the psychological effects of cardiovascular deconditioning in animal models. Given the bidirectional link established between cardiac autonomic imbalance and psychological depression in both humans and in animal models, we hypothesized that hindlimb unloading would elicit an alteration in sympathovagal tone and behavioral indexes of psychological depression. Male, Sprague-Dawley rats confined to 14 days of HU displayed anhedonia (a core feature of human depression) compared with casted control (CC) animals evidenced by reduced sucrose preference (CC: 81 +/- 2.9% baseline vs. HU: 58 +/- 4.5% baseline) and reduced (rightward shift) operant responding for rewarding electrical brain stimulation (CC: 4.4 +/- 0.3 muA vs. 7.3 +/- 1.0 muA). Cardiac autonomic blockade revealed elevated sympathetic [CC: -54 +/- 14.1 change in (Delta) beats/min vs. HU: -118 +/- 7.6 Delta beats/min] and reduced parasympathetic (CC: 45 +/- 11.8 Delta beats/min vs. HU: 8 +/- 7.3 Delta beats/min) cardiac tone in HU rats. Heart rate variability was reduced (CC: 10 +/- 1.4 ms vs. HU: 7 +/- 0.7 ms), and spectral analysis of blood pressure indicated loss of total, low-, and high-frequency power, consistent with attenuated baroreflex function. These data indicate that cardiovascular deconditioning results in sympathovagal imbalance and behavioral signs consistent with psychological depression. These findings further elucidate the pathophysiological link between cardiovascular diseases and affective disorders.

Renal blood flow and dynamic autoregulation in conscious mice

Autoregulation of renal blood flow (RBF) occurs via myogenic and tubuloglomerular feedback (TGF) mechanisms that are engaged by pressure changes within preglomerular arteries and by tubular flow and content, respectively. Our understanding of autoregulatory function in the kidney largely stems from experiments in anesthetized animals where renal perfusion pressure is precisely controlled. However, normally occurring variations in blood pressure are sufficient to engage both myogenic and TGF mechanisms, making the assessment of autoregulatory function in conscious animals of significant value. To our knowledge, no studies have evaluated the dynamics of RBF in conscious mice. Therefore, we used spectral analysis of blood pressure and RBF and identified dynamic operational characteristics of the myogenic and TGF mechanisms in conscious, freely moving mice instrumented with ultrasound flow probes and arterial catheters. The myogenic response generates a distinct resonance peak in transfer gain at 0.31 +/- 0.01 Hz. Myogenic-dependent attenuation of RBF oscillations, indicative of active autoregulation, is apparent as a trough in gain below 0.3 Hz (-6.5 +/- 1.3 dB) and a strong positive phase peak (93 +/- 9 deg), which are abolished by amlodipine infusion. Operation of TGF produces a local maximum in gain at 0.05 +/- 0.01 Hz and a positive phase peak (62.3 +/- 12.3 deg), both of which are eliminated by infusion of furosemide. Administration of amlodipine eliminated both myogenic and TGF signature peaks, whereas furosemide shifted the myogenic phase peak to a slower operational frequency. These data indicate that myogenic and TGF dynamics may be used to investigate the effectiveness of renal autoregulatory mechanisms in conscious mice.

Dynamic renal autoregulation in conscious, freely moving mice

Myogenic (MYO) and tubuloglomerular feedback (TGF) mechanisms control renal blood flow (RBF) autoregulation. MYO and TGF operate with specific dynamic properties to regulate RBF in response to spontaneous fluctuations in blood pressure (BP). Developing a method to evaluate MYO and TGF control systems in conscious mice would allow RBF autoregulation to be studied in available genetic models. Using spectral analysis of BP and RBF, we identified dynamic operational characteristics of MYO and TGF in conscious, freely moving mice (NZW, n=10), instrumented with ultrasound flow probes and arterial catheters. We found that MYO generates a distinct resonance peak in transfer gain at 0.31±0.01 Hz. MYO‐dependent attenuation of RBF oscillations, indicative of active autoregulation, is apparent as a trough in gain below 0.3 Hz (−6.3±1.5 dB) and a strong positive phase peak (87±8 deg), which are abolished by amlodipine infusion (3.3±1.1 dB p<0.01; 14±1 deg p<0.01). Operation of TGF produces a local maximum in gain at 0.77±0.8 Hz and a positive phase peak (60.4±14.3 deg), both of which are removed by infusion of furosemide. Administration of amlodipine eliminated both MYO and TGF signature peaks, whereas furosemide did not alter MYO operational characteristics. These data indicate that MYO and TGF dynamics may be used to investigate the effectiveness of renal autoregulatory mechanisms in conscious mice. (Supported by R01HL085907 MJR, R01HL069194 JFR)

Spectral analysis of blood pressure and heart rate variability in baboons with a normal, low or high RBC sodium‐lithium countertransport phenotype

Spectral analysis of blood pressure and heart rate variability in baboons with a normal, low or high RBC sodium‐lithium countertransport phenotype

Assessment of Cardiovascular Autonomic Function in Patients with Liver Cirrhosis Using Heart Rate Variability, Blood Pressure Variability and Baroreflex Sensitivity

Background: Liver cirrhosis is associated with several hemodynamic abnormalities, including an impairment of autonomic nervous system reflexes, but very few have compared the disease severity with cardiovascular autonomic dysfunction assessed by spectral analysis of blood pressure and electrocardiogram. The aim of this study was to investigate the relationship between Child-Turcotte-Pugh (CTP) score and autonomic indices in patients with liver cirrhosis using the heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS). Methods: Fifty patients scheduled for liver transplantation recipients under general anesthesia were enrolled in the study. Beat-to-beat blood pressure and RR interval were measured for five minutes before anesthesia induction. HRV and BPV were estimated by power spectral analysis of RR interval and systolic blood pressure. BRS was estimated by both the sequence method (Sequence BRS) and high frequency (HF) gain of transfer function analysis (HF BRS). Results: Significant inverse correlations between CTP score and Sequence BRS (r = -0.61), HF BRS (r = -0.59), low frequency (LF) and HF power of HRV (r = -0.57, r = -0.46), LF power of BPV (r = -0.37) were found. However, no significant correlations were observed between CTP score and LF/HF ratio of HRV (r = -0.02) and HF power of BPV (r = 0.27). Conclusions: These results showed that autonomic dysfunction assessed by spectral analysis was associated with increasing severity of liver cirrhosis. Further study will be needed to clarify relationship between our findings and hemodynamic fluctuations during anesthesia for liver transplantation.

Higher Plasma Homocysteine Concentration Is Associated with More Advanced Systemic Arterial Stiffness and Greater Blood Pressure Response to Stress in Hypertensive Patients

Hyperhomocysteinemia has been reported to be associated with both vascular structure alteration and increased cardiovascular risk. This study examined whether hyperhomocysteinemia causes increased systemic arterial stiffness, thereby enhancing blood pressure response to stress in hypertensive patients. In 50 treated hypertensive patients, we studied brachial-ankle pulse wave velocity (PWV), a new measure for arterial stiffness, blood pressure response to stress, and blood pressure recovery after stress. Autonomic nervous activities were examined by spectral analysis of blood pressure and RR interval variabilities. Total plasma homocysteine and neurohumoral parameters were determined from fasting blood. Brachial-ankle PWV correlated with age (r=0.64, p<0.001), plasma homocysteine concentration (r=0.35, p<0.05), and systolic blood pressure (SBP) (r=0.62, p<0.001). Higher plasma homocysteine concentration was independently associated with greater brachial-ankle PWV (beta=0.388, p=0.01). We classified the subjects into high homocysteine (7.3 nmol/ml or over) and low homocysteine (7.2 nmol/ml or below) groups. Baseline SBP, plasma renin activity, aldosterone, and norepinephrine concentrations were similar between the two groups. However, the SBP values during stress and the recovery periods were higher in the high homocysteine group than the low homocysteine group even after adjusting for sex and age. The behavior of sympathetic vasomotor activity did not differ between the two groups. These data suggest that higher plasma homocysteine concentration is associated with increased systemic arterial stiffness, which may enhance blood pressure reactivity to stress in hypertensive patients.

Effects of Salt Sensitivity on Neural Cardiovascular Regulation in Essential Hypertension

Salt-sensitive hypertensive subjects, as defined by conventional categorical classification, exhibit alterations of autonomic cardiovascular control. The aim of our study was to explore whether, in hypertensive subjects, the degree of autonomic dysfunction and the level of salt sensitivity are correlated even when the latter is only mildly elevated and displays under-threshold values. Salt sensitivity of 34 essential hypertensive subjects was assessed on a continuous basis by the salt sensitivity index after low- and high-sodium diet. Beat-by-beat finger blood pressure was recorded after each diet period. Autonomic cardiovascular control was evaluated by spectral analysis of blood pressure and pulse interval and by assessment of spontaneous baroreflex sensitivity (sequence technique). Salt sensitivity and baroreflex sensitivity showed a negative relationship during low and high sodium intake, starting from low values of the salt sensitivity index. All spectral indexes of pulse interval, except the ratio between low- and high-frequency powers, were inversely related to salt sensitivity index after high sodium intake. In subjects with lower salt sensitivity, baroreflex sensitivity and pulse interval power in the high-frequency band were higher after high sodium intake than after low sodium intake. In contrast, subjects with a higher salt sensitivity index showed lower values of baroreflex sensitivity and pulse interval power in the high-frequency band, uninfluenced by salt intake. Our results provide the first demonstration of an impairment of parasympathetic cardiac control in parallel with the increase in the degree of salt sensitivity, also in subjects who were not ranked as salt-sensitive by the conventional categorical classification.

Impaired response of cardiac autonomic nervous system to glucose load in severe obesity

Objective This study was undertaken to further analyze the response of the cardiovascular autonomic nervous system (ANS) to changes in plasma insulin concentration induced by an oral glucose load. We hypothesized that, as a consequence of insulin resistance, an inability of insulin to increase the sympathetic modulation of heart rate (HR) and blood pressure (BP) would be observed in normotensive obese patients. Methods We used spectral analysis to measure simultaneously the short-term variability of HR and BP in 23 never-obese subjects and in 70 normotensive overweight or obese patients subdivided into 3 subgroups: (1) overweight group (body mass index [BMI], 25-29.9 kg/m 2), n = 23; (2) class I-II obese group (BMI, 30-39.9 kg/m 2), n = 23; (3) class III obese group (BMI, ≥40 kg/m 2), n = 23. Results Oral glucose ingestion and the related increased insulinemia caused significant changes in the indices of sympathetic modulation (low-frequency [LF] power and LF/high-frequency ratio) of both HR and BP in normal weight, overweight, and obese subjects. However, the LF increments gradually decreased with the BMI classes, suggesting that sympathetic nervous system modulation in these subjects may be insulin-resistant. Conclusion Obesity could develop resistance to the sympatho-excitatory effects of insulin that might play a role in the etiology of obesity. Spectral analysis of BP and HR can be used in research to evaluate the reactivity of the sympathetic nervous system in a manner that represents another feature of the obesity/insulin-resistance syndrome.

The Influence of One‐Year Treatment by Angiotensin Converting Enzyme Inhibitor on Baroreflex Sensitivity and Flow‐Mediated Vasodilation of the Brachial Artery in Essential Hypertension—Comparison with Calcium Channel Blockers

Background. Both baroreflex sensitivity and flow‐mediated vasodilator function have been recognized to have prognostic significance in cardiovascular diseases. Long‐term antihypertensive treatment effects on these parameters, however, remain unclear. Subjects and Methods. We examined the effects of long‐term treatment by angiotensin converting enzyme inhibitors (ACEI) or calcium channel blockers (CCB) on baroreflex and flow‐mediated vasodilator function in patients with essential hypertension (EH). We recruited 36 patients aged 56 ± 11 years, with systolic blood pressure ≧160 mmHg and/or diastolic blood pressure ≧95 mmHg. Patients were assigned either to treatment by long‐acting ACEI (n = 12) or CCB (n = 24). All patients were followed for 12 months. Optimal BP was achieved by two optional increases in treatment: dose‐doubling of the primary drug during the first three months and the addition of diuretics or β‐blockers thereafter. Target blood pressure was 140/90 mmHg or a fall ≧20/10 mmHg. Baroreflex sensitivity was examined by spectral analysis of blood pressure and RR interval variabilities before treatment and after 3 and 12 months of treatment. The flow‐mediated vasodilator function was determined before and 12 months after treatment by measuring the change in brachial artery diameter during increases in flow induced by reactive hyperemia. Results. Baseline blood pressures were similar between the ACEI and CCB groups (172 ± 5/103 ± 2 vs. 172 ± 4/101 ± 3 mmHg). Blood pressures after 3 and 12 months of treatment also did not differ between the ACEI and CCB groups (149 ± 4/91 ± 2 vs. 145 ± 2/ 85 ± 2 mmHg, and 133 ± 5/84 ± 2 vs. 133 ± 2/81 ± 2 mmHg, respectively). Baseline baroreflex sensitivity was similar between the groups (6.7 ± 0.8 vs. 5.9 ± 0.6 msec/mmHg). This parameter remained unchanged at three months but increased after 12 months of treatment in both the ACEI (9.5 ± 1.6 msec/mmHg, p = 0.05) and CCB (9.1 ± 1.2 msec/mmHg, p = 0.006) groups. Percent increases in brachial arterial diameter and flow during reactive hyperemia increased in the group treated with ACEI (12.4 ± 3.5 vs. 25.8 ± 6.3% and 618 ± 72 vs. 953 ± 166, p < 0.05 for both) but both parameters remained unchanged in the group treated with CCB. Conclusion. These data suggest that long‐term blood pressure control with modern antihypertensive drugs improves baroreflex function. Treatment with ACEI may be more favorable for flow‐mediated vasodilator function than treatment with CCB.

Usefulness of daily +2Gz load as a countermeasure against physiological problems during weightlessness

Adaptation to head-down-tilt bed rest as a simulated microgravity leads to an abnormality of reflex control of circulation, hypovolemia and reduction of exercise capacity. We hypothesized that this cardiovascular deconditioning and reduction of exercise capacity could be prevented by a daily 1 hr centrifugation at +2Gz. To test this hypothesis, twenty healthy male subjects underwent 4 day of 6° head-down-tilt bed rest. Ten of them were exposed to a +2Gz load for up to 30 min twice per day (the Gz group). The remaining 10 were not exposed to a Gz load (the no-Gz group). We estimated autonomic cardiovascular control by power spectral analysis of blood pressure and R-R interval variability, and baroreflex regulation by the transfer function analysis and the sequence method, before and after bed rest. Further, we measured hematocrit as an index of changes in plasma volume and maximal oxygen consumption as an index of exercise capacity, before and after bed rest. Result: In the no-Gz group, heart rate increased after bed rest. The high frequency power of R-R interval variability as an index of cardiac parasympathetic nervous activity, baroreflex gains estimated by transfer function analysis and the sequence method as index of the integrated arterial-cardiac baroreflex function decreased significantly. Associated with these changes, the ratio of low to high frequency power of R-R as an indicator of cardiac sympathovagal balance tended to increase after bed rest in the no-Gz group. However, those showed no significant changes after bed rest in the Gz group. Hematocrit increased after bed rest in the no-Gz group. It also tended to increase in the Gz group, however it did not achieve statistical significance. Maximal oxygen consumption decreased significantly to similar extent in both the groups. Conclusion: This result suggested that 1) a daily 1hr +2Gz load produced by a centrifuge might eliminate the changes in autonomic cardiovascular control during simulated weightlessness; 2) furthermore, it might partly reverse hypovolemia induced by bed rest; 3) however, it could not prevent the decreases in exercise capacity.