Spontaneous Blood Pressure Research Articles

Heart rate variability and spontaneous baroreflex sequences in supine healthy volunteers subjected to nasal positive airway pressure

To determine the dynamic effects of short-term nasal positive airway pressure (nPAP) on cardiovascular autonomic control, continuous recordings of noninvasively obtained hemodynamic measurements and heart rate variability (HRV) were obtained in 10 healthy subjects during frequency-controlled breathing (between 0.20 and 0.24 Hz) in supine posture under different pressures of nPAP ranging from 3 to 20 cmH(2)O. HRV was assessed using spectral analysis of the R-R interval. The slope of the regression line between spontaneous systolic blood pressure and pulse interval changes was taken as an index of the sensitivity of arterial baroreflex modulation of heart rate (sequence method). Application of nPAP resulted in a pressure-dependent decrease of cardiac output and stroke volume (P < 0.05, ANOVA) and in an increase in total peripheral resistance (P < 0.03, ANOVA). Hemodynamic changes under increasing nPAP were accompanied by a decrease in total power of HRV despite mean R-R interval remaining unchanged. The overall decrease in HRV was accompanied by a reduction across all frequency bands when absolute units were used (P < 0.01). When the power of low frequency and high frequency was calculated in normalized units, a diminished high frequency and an increased low-to-high frequency ratio were observed (P < 0.05). Compared with low levels of nPAP, pressure levels of >10 cmH(2)O were associated with a significant decline in the mean slope of spontaneous baroreceptor sequences (P < 0.04). These findings indicate that short-term administration of nPAP in normal subjects exerts significant alterations in R-R interval variability and spontaneous baroreflex modulation of heart rate.

High spontaneous fluctuation in arterial blood pressure improves the assessment of cerebral autoregulation

Cerebral autoregulation maintains a relatively constant blood flow despite changes of blood pressure in the brain. Linear models have been extensively applied to identify this mechanism, using spontaneous arterial blood pressure (ABP) fluctuation as input and cerebral blood flow velocity (CBFV) change as output. Although valuable measurements have been achieved by these models, accuracy and consistency are of great concern due to the large variability of results. We therefore investigated whether more reliable measurements can be achieved by selecting only those recordings (or parts of recordings) with relatively high spontaneous variability of ABP. Twenty-four recordings, 7 from hypercapnia and 17 from normocapnia, of ABP and CBFV from 9 healthy adults were analyzed. Two conventional autoregulatory parameters were used to assess cerebral autoregulation. In the absence of a ‘gold’ standard for the study of dynamic cerebral autoregulation, lower variability of the parameters and higher correlation with pCO2 were considered as criteria for identifying improved measures of autoregulation. Both significantly lower variability of the parameters, and higher correlation between the parameters and pCO2 were achieved from the data with higher variability of blood pressure. We therefore conclude that ABP with high variability may effectively stimulate regulatory response in blood flow resulting in improved assessment of cerebral autoregulation.

Arterial baroreflex control of heart rate: determining factors and methods to assess its spontaneous modulation

Arterial baroreflex control of heart rate: determining factors and methods to assess its spontaneous modulation

Interval training in elderly men increases both heart rate variability and baroreflex activity

Autonomic nervous system activity decreases continuously with age and appears to be a powerful predictor of disease and death. Attempts are thus made to reactivate autonomic drive with the intent of improving health. We assessed maximal oxygen consumption (VO2max), autonomic nervous system activity by heart rate variability (HRV) analysis and spontaneous cardiac baroreflex activity (SBR) in eleven elderly men (73.5+/-4.2 years) before and after a 14-week program of intensive cycloergometer interval training. The standard HRV indices were calculated using time domain (mean RR, PNN50, RMSSD, SDNN, SDANN and SDNNIDX), and Fourier transform (total power, ULF,VLF, LF, LFnu, HF, HFnu and LF/HF) analyses of 24-hour, daytime and nighttime Holter recordings. The SBR was calculated from 15-minute recordings of spontaneous blood pressure and RR interval variations using the sequence (slope, slSBR) and cross-spectral (alphaSBRHF and alphaSBRLF) methods. After the training period,VO2max increased by 18.6 % (26.8+/-4.4 to 31.8+/-5.2 ml.kg(-1).min(-1), p<0.01). The nocturnal parasympathetic indices of HRV increased (PNN50: 3.05+/-2.21 to 5.00+/-2.87%, RMSSD: 29.1+/-7.6 to 38.8+/-10.9 ms, HF: 117+/-54 to 194+/-116 ms2/Hz, all p<0.05) as did the SBR indices (slSBR: 7.0+/-1.8 to 9.8+/-2.1 ms.mmHg(-1), p<0.01; alphaSBRHF: 6.9+/-2.2 to 10.5+/-3.7 ms.mmHg(-1), p<0.05; alphaSBRLF: 5.3+/-2.3 to 6.9+/-3.1 ms.mmHg(-1), p=0.22). Intensive endurance training in elderly men enhanced parasympathetic parameters of HRV and, interestingly, of SBR. Physiological mechanisms and long-term clinical effects on health status should be further investigated.

Baroreceptor reflex control of heart rate in rats studied by induced and autogenic changes in arterial pressure

The function of the arterial baroreflex has traditionally been assessed by measurement of reflex changes in heart rate (HR) or sympathetic nerve activity resulting from experimenter-induced manipulation of arterial blood pressure (the Oxford method, also termed the pharmacological method). However, logistical and flexibility limitations of this technique have promoted the development of new methods for assessing baroreflex function such as the evaluation of changes in spontaneous arterial pressure and HR. Although this new spontaneous method has been validated in dogs and humans, it has not been rigorously tested in rats. In the present study, the method of correlating spontaneous changes in systolic blood pressure and HR was evaluated in resting, normotensive Sprague-Dawley rats. This technique was found to be neither reliable nor valid under the conditions employed in the present protocol. We also tested a variation of the spontaneous method that evaluates particular sequences of data during which arterial pressure and pulse interval are changing in the same direction for at least three consecutive heartbeats (the sequence method). The sequence method did not provide extra reliability or validity over the spontaneous method. We conclude that due to the restricted range of variability obtained by measuring spontaneous blood pressure fluctuations, the spontaneous and sequence techniques do not provide data that are comparable to the traditional method of assessing HR changes triggered by arterial blood pressure increases and decreases induced by vasoactive drugs. However, it is possible that surgical stress obscured the relationship between blood pressure and HR, and therefore additional studies are needed to determine whether the spontaneous and sequence methods can be applied to rats during different behavioral states.

Effect of the arterial hypertension and captopril treatment on the angiotensin II content in the subfornical organ. A study in SHR rats

We studied the effects of spontaneous high blood pressure and the captopril treatment on the subfornical organ (SFO) of rats. The brains of control Wistar-Kyoto rats (WKY), WKY rats treated with captopril (WKY-T), spontaneously hypertensive rats (SHR) and SHR rats treated with captopril (SHR-T) were processed immunohistochemically using anti-angiotensin II as primary antibody. Immunorective material (IRM) for angiotensin II was observed in a group of neurons and some cells of the ependymal layer of the SFO in WKY rats. The angiotensin II immunoreactive (AGII-ir) in the SHR rats was decreased, showing positive reaction only in a few neurons, while captopril treatment induced an increase in immunoreactive material in hypertensive rats, but contrarily, the expression of AGII-ir in the WKY-T group was scarce. The variations of the angiotensin II observed in the SFO could be owing to an interaction between the hypertension and its captopril treatment.

Time-domain cross-correlation baroreflex sensitivity: performance on the EUROBAVAR data set.

To test a new method (cross-correlation baroreflex sensitivity, xBRS) for the computation of time-domain baroreflex sensitivity on spontaneous blood pressure and heart interval variability using the EUROBAVAR data set. We applied xBRS to the 42 records in the EUROBAVAR data set, obtained from 21 patients in the lying and standing positions. One patient had a recent heart transplant and one was diabetic with evident cardiac autonomic neuropathy. xBRS computes the correlation between beat-to-beat systolic blood pressure and R-R interval, resampled at 1 Hz, in a sliding 10 s window, with delays of 0-5 s for interval. The delay with the greatest positive correlation is selected and, when significant at P = 0.01, slope and delay are recorded as one xBRS value. Each 1 s of the recording is the start of a new computation. Non-parametric tests are used. With patients in the lying position, xBRS yielded a value of 12.4 ms/mmHg compared with the EUROBAVAR sequential 16.2 ms/mmHg, and for the standing positions the respective values were 6.2 and 6.7 ms/mmHg, giving lying to standing ratios of 1.96 and 2.10, respectively. xBRS yielded results for all files, with 20 values per minute on average at a lower within-patient variance. Best delays were 0, 1 and 2 s, and the delay increased by 102 ms when the patient was in the standing position. The xBRS method was successful in the patients with diabetes and the heart transplant. The xBRS method should be considered for experimental and clinical use, because it yielded values that correlated strongly with and were close to the EUROBAVAR averages, yielded more values per minute, had lower within-patient variance and measured baroreflex delay.

Highly selective iNOS inhibition and sphincter of Oddi motility in the Australian possum.

Inducible nitric oxide synthase (iNOS) plays a major role in acute pancreatitis. Selective inhibitors of iNOS are being developed as therapeutic agents. Sphincter of Oddi (SO) dysfunction may cause pancreatitis and nitric oxide is necessary for SO relaxation. A new highly selective iNOS inhibitor, AR-C102222AA (AR-C), is evaluated together with the established iNOS inhibitor, L-N(6)-(1-iminoethyl)lysine (L-NIL), and the selective neuronal nitric oxide synthase (nNOS) blocker S-methyl-l-thiocitrulline (SMTC). In anaesthetized Australian Brush-tailed possums, the effect of topical, i.v. or i.a. administration of these drugs was evaluated on spontaneous SO motility, blood pressure (BP) and pancreatic vascular perfusion. SO motility was recorded by manometry and pancreatic vascular perfusion by laser Doppler fluxmetry. Also, the effect of SMTC and AR-C on electrical field stimulation (EFS)-induced non-cholinergic non-adrenergic (NANC) SO relaxation in vitro was evaluated. Infusion of AR-C (0.1-30 micromol kg(-1)) increased SO contraction frequency (P = 0.026) only at the two highest doses. L-NIL infusion (0.15 to 14.7 micromol kg(-1)) also increased SO contraction frequency at 8.8 micromol kg(-1) (P < 0.05) and reduced SO contraction amplitude at the two highest doses (P < 0.05). SMTC injections (0.5 nmol-2.4 micromol) produced a dose-dependent increase in SO contraction frequency (P = 0.009), but no effect was seen on the other parameters. In vitro SMTC (40-400 microm) inhibited EFS-induced NANC relaxation in a dose-dependent manner (P < 0.0005). In contrast AR-C (10-500 microm) had no effect on EFS-induced NANC relaxation (P > 0.05). At low doses, AR-C does not effect SO motility or EFS-induced NO mediated relaxation. However, high doses of AR-C and L-NIL in vivo influenced SO motility by inhibiting nNOS activity and these effects need be considered in relation to therapeutic doses of this agent.

P.2.16 The influence of spontaneous blood pressure elevations on the QT dispersion in patients with hypertension and after myocardial infarction

P.2.16 The influence of spontaneous blood pressure elevations on the QT dispersion in patients with hypertension and after myocardial infarction

P.2.16 The influence of spontaneous blood pressure elevations on the QT dispersion in patients with hypertension and after myocardial infarction

P.2.16 The influence of spontaneous blood pressure elevations on the QT dispersion in patients with hypertension and after myocardial infarction

P.2.16 The influence of spontaneous blood pressure elevations on the QT dispersion in patients with hypertension and after myocardial infarction

P.2.16 The influence of spontaneous blood pressure elevations on the QT dispersion in patients with hypertension and after myocardial infarction

Sympathetic and cardiac baroreflex function in panic disorder.

Recent reports have demonstrated increased cardiac risk, and an association with essential hypertension in patients with panic disorder. The cause is not known, but possibly involves sympathetic nervous activation. In this study, we evaluated the arterial baroreflex control of vascular sympathetic nervous outflow and cardiac baroreflex function in panic disorder patients. We studied nine patients suffering from panic disorder and ten healthy subjects. Microneurographic recording of muscle sympathetic nerve activity (MSNA) was made with simultaneous recording of blood pressure (BP) and electrocardiogram (ECG). The relationship between MSNA and spontaneous diastolic BP (DBP) changes was assessed at rest and was defined as the arterial baroreflex control of MSNA. Cardiac baroreflex function was assessed using the sequence method. Anxiety was assessed using Spielberger's anxiety state and trait inventory. The slopes of the relationship between MSNA and DBP were more negative (steeper) in the panic disorder group compared with the control subjects (-5.97 +/- 0.45 versus -3.06 +/- 0.43 bursts/100 heart beats per mmHg, P < 0.001). Panic disorder patients had significantly higher state and trait anxiety scores. The slope of the relationship between MSNA and diastolic BP was significantly related to the trait anxiety of the subjects. There was no difference between the cardiac baroreflex sensitivity between the two groups. Patients with panic disorder exhibit enhanced reflex gain of the arterial baroreflex control of MSNA but no change in the cardiac baroreflex. While any clinical significance this observation might have in relation to increased cardiac risk in panic disorder, or to concordance with essential hypertension, remains to be elucidated, increased reactivity of vasoconstricting sympathetic nerves may be a trait characteristic in this cohort.

Cardiac baroreflex control in humans during and immediately after brief exposure to simulated high altitude.

To examine the baroreflex response in humans during and immediately after acute hypoxia exposure, the cardiac baroreflex sensitivity (BRS) was studied using adaptation of RR intervals in response to spontaneous systolic blood pressure fluctuations (sequences methodology) in 11 unacclimatized subjects. All measurements were made under fixed breathing rate, and realized consecutively at baseline level (20 min), at an inspired oxygen concentration of 11% (15 min) and again under normoxic conditions (20 min; recovery period). The spontaneous baroreflex response decreases progressively during hypoxic exposure, causing a tachycardic response at this FiO2 without any significant alteration of the systolic or diastolic blood pressure. The magnitude of decrease for this variable at the end of exposure averaged 42.9 +/- 15.6%. The simultaneous spectral analysis of heart rate (HR) variability in hypoxic condition confirmed an alteration in the parasympathetic activity (HFnu: -17.8 +/- 30.9% versus basal conditions, P < 0.01) counterbalanced by an exaggerated sympathetic activity (LFnu: +33 +/- 42.4%, P < 0.05) at the sinus node. Interestingly, we could observe an enhanced cardiac baroreflex response during the period following the inhalation of the hypoxic mixture (+130.6 +/- 15.6% of basal conditions, P < 0.001). There is a relationship with a significant and abrupt increase in the parasympathetic control of HR (mean HR reached 111 +/- 8.1% of the mean basal HR, P < 0.01). These results suggest that brief exposure to hypoxia under rate-controlled ventilation is associated with a significant alteration in the spontaneous cardiac baroreflex. This important cardiac autonomic imbalance is followed by a significant increase in the cardiac parasympathetic drive even after the disappearance of the hypoxic stimulus.

Mechanism of blood pressure and R-R variability: insights from ganglion blockade in humans.

Spontaneous blood pressure (BP) and R-R variability are used frequently as 'windows' into cardiovascular control mechanisms. However, the origin of these rhythmic fluctuations is not completely understood. In this study, with ganglion blockade, we evaluated the role of autonomic neural activity versus other 'non-neural' factors in the origin of BP and R-R variability in humans. Beat-to-beat BP, R-R interval and respiratory excursions were recorded in ten healthy subjects (aged 30 +/- 6 years) before and after ganglion blockade with trimethaphan. The spectral power of these variables was calculated in the very low (0.0078-0.05 Hz), low (0.05-0.15 Hz) and high (0.15-0.35 Hz) frequency ranges. The relationship between systolic BP and R-R variability was examined by cross-spectral analysis. After blockade, R-R variability was virtually abolished at all frequencies; however, respiration and high frequency BP variability remained unchanged. Very low and low frequency BP variability was reduced substantially by 84 and 69 %, respectively, but still persisted. Transfer function gain between systolic BP and R-R interval variability decreased by 92 and 88 % at low and high frequencies, respectively, while the phase changed from negative to positive values at the high frequencies. These data suggest that under supine resting conditions with spontaneous breathing: (1) R-R variability at all measured frequencies is predominantly controlled by autonomic neural activity; (2) BP variability at high frequencies (> 0.15 Hz) is mediated largely, if not exclusively, by mechanical effects of respiration on intrathoracic pressure and/or cardiac filling; (3) BP variability at very low and low frequencies (< 0.15 Hz) is probably mediated by both sympathetic nerve activity and intrinsic vasomotor rhythmicity; and (4) the dynamic relationship between BP and R-R variability as quantified by transfer function analysis is determined predominantly by autonomic neural activity rather than other, non-neural factors.

Dynamic cerebral autoregulation and beat to beat blood pressure control are impaired in acute ischaemic stroke

Objectives: Hypertension and chronic cerebrovascular disease are known to alter static cerebral autoregulation (CA) but the effects of acute stroke on dynamic CA (dCA) have not been studied in detail....

Advanced analysis of spontaneous baroreflex sensitivity, blood pressure and heart rate variability in patients with dilated cardiomyopathy

Advanced analysis of spontaneous baroreflex sensitivity, blood pressure and heart rate variability in patients with dilated cardiomyopathy

Advanced analysis of spontaneous baroreflex sensitivity, blood pressure and heart rate variability in patients with dilated cardiomyopathy

Baroreflex sensitivity (BRS) is an important parameter in the classification of patients with reduced left ventricular function. This study aimed at investigating BRS in patients with dilated cardiomyopathy (DCM) and in healthy subjects (controls), as well as comparing the values of BRS parameters with parameters of heart rate variability (HRV) and blood pressure variability (BPV). ECG, continuous blood pressure and respiration curves were recorded for 30 min in 27 DCM patients and 27 control subjects. The Dual Sequence Method (DSM) includes the analysis of spontaneous fluctuations in systolic blood pressure and the corresponding beat-to-beat intervals of heart rate to estimate bradycardic, opposite tachycardic and delayed baroreflex fluctuations. The number of systolic blood pressure/beat-to-beat interval fluctuations in DCM patients was reduced in comparison with controls (DCM patients: male, 154.4+/-93.9 ms/mmHg; female, 93.7+/-40.5 ms/mmHg; controls: male, 245.5+/-112.9 ms/mmHg; female, 150.6+/-55.8 ms/mmHg, P<0.05). The average slope in DCM patients was lower than in controls (DCM, 5.3+/-1.9 ms/mmHg; controls, 8.0+/-5.4 ms/mmHg; P<0.05). Discriminant function analysis showed that, in the synchronous range of the standard sequence method, the DCM and control groups could be discriminated to only 76% accuracy, whereas the DSM gave an improved accuracy of 84%. The combination of six parameters of HRV, BPV and DSM gives an accuracy of classification of 96%, whereas six parameters of HRV and BPV could separate the two groups to only 88% accuracy. Thus the DSM leads to an improved characterization of autonomous regulation in order to differentiate between DCM patients and healthy subjects. BRS in DCM patients is significantly reduced and apparently less effective.

Blood pressure and heart rate variability and baroreflex sensitivity before and after brain death

OBJECTIVESTo evaluate spontaneous blood pressure and heart rate variability and spontaneous baroreflex sensitivity before and after brain death.METHODSSpontaneous variability of arterial blood pressure and heart rate—estimated by power spectra of...

Assessment of cerebral autoregulation using time-domain cross-correlation analysis

Time domain cross-correlation analysis of pre-filtered mean arterial blood pressure (MABP) and mean cerebral blood flow velocity (MCBFV) was applied to assess the cerebral autoregulation (CA). Beat-to-beat time series of spontaneous arterial blood pressure and cerebral blood flow velocity were obtained from 13 young normal volunteers with the Finapres device and the transcranial Doppler for periods of approximately 5 min in the supine position. Cross-correlation functions (CCFs) were estimated using a 64 beat wide moving window. Mean CCF patterns were obtained for each subject and for the entire population. The MABP and MCBFV signals were bandpass filtered in the very low-frequency range (VLF, 0.015– 0.07 Hz ), low-frequency range (LF, 0.07– 0.15 Hz ) and high-frequency range (HF, 0.15– 0.40 Hz ) before applying CCF for the purpose of studying the effect of different bandwidths on the resulting mean CCFs. Results revealed that the corresponding time lags of the peak values of the MABP–MCBFV CCFs increased significantly between the LF and HF frequency ranges (LF: −1.20±0.91 s , HF: −0.07±0.42 s, p<0.001 ; paired sign test). The left-shift (negative lag) of the CCF peak between MABP and MCBFV is a result of the phase-lead property. The increasing time lag of the CCF peak indicated evidence of the autoregulatory disturbance. The CCF of pre-filtered spontaneous MABP and MCBFV could be a useful tool to estimate the CA dynamic response.

Effects of alterations in arterial CO2 tension on cerebral blood flow during acute intracranial hypertension in rats.

Cerebrovascular reactivity to CO2 in clinical and experimental studies has been found to be impaired during increased intracranial pressure (ICP). However, from previous study results it has not been possible to estimate whether the impairment was caused by elevated ICP, or caused by decreased cerebral perfusion pressure (CPP). The current study was carried out in a group of unmanipulated control rats and in six investigation groups of six rats each: two groups with elevated ICP (30 and 50 mm Hg) and spontaneous arterial blood pressure (MABP), two groups with spontaneous ICP and arterial hypotension (77 and 64 mm Hg), and two groups with elevated ICP (30 and 50 mm Hg) and arterial hypertension (124 mm Hg). Intracranial hypertension was induced by continuous infusion of lactated Ringer's solution into the cisterna magna, arterial hypotension by controlled bleeding, and arterial hypertension by continuous administration of norepinephrine intravenously. Cerebral blood flow (CBF) was measured repetitively by the intraarterial 133Xe method at different levels of arterial PCO2. In each individual animal, CO2 reactivity was calculated from an exponential regression line obtained from the corresponding CBF/PaCO2 values. By plotting each individual value of CO2 reactivity against the corresponding CPP value from the seven investigation groups, CPP was significantly and directly related to CO2 reactivity of CBF (P < .001). No correlation was found by plotting CO2 reactivity values against the corresponding MABP values or the corresponding ICP values. Thus, the results show that CO2 reactivity is at least partially determined by CPP and that the impaired CO2 reactivity observed at intracranial hypertension and arterial hypotension may be caused by reduced CPP.