Continuous Blood Pressure Signals Research Articles

Optimization of respiratory-gated auricular vagus afferent nerve stimulation for the modulation of blood pressure in hypertension.

The objective of this pilot study was to identify frequency-dependent effects of respiratory-gated auricular vagus afferent nerve stimulation (RAVANS) on the regulation of blood pressure and heart rate variability in hypertensive subjects and examine potential differential effects by sex/gender or race. Twenty hypertensive subjects (54.55 ± 6.23 years of age; 12 females and 8 males) were included in a within-person experimental design and underwent five stimulation sessions where they received RAVANS at different frequencies (i.e., 2 Hz, 10 Hz, 25 Hz, 100 Hz, or sham stimulation) in a randomized order. EKG and continuous blood pressure signals were collected during a 10-min baseline, 30-min stimulation, and 10-min post-stimulation periods. Generalized estimating equations (GEE) adjusted for baseline measures were used to evaluate frequency-dependent effects of RAVANS on heart rate, high frequency power, and blood pressure measures, including analyses stratified by sex and race. Administration of RAVANS at 100 Hz had significant overall effects on the reduction of heart rate (β = -2.03, p = 0.002). It was also associated with a significant reduction of diastolic (β = -1.90, p = 0.01) and mean arterial blood pressure (β = -2.23, p = 0.002) in Black hypertensive participants and heart rate in female subjects (β = -2.83, p = 0.01) during the post-stimulation period when compared to sham. Respiratory-gated auricular vagus afferent nerve stimulation exhibits frequency-dependent rapid effects on the modulation of heart rate and blood pressure in hypertensive patients that may further differ by race and sex. Our findings highlight the need for the development of optimized stimulation protocols that achieve the greatest effects on the modulation of physiological and clinical outcomes in this population.

Evening Binge Alcohol Disrupts Cardiovagal Tone and Baroreflex Function During Polysomnographic Sleep Stages

Evening alcohol consumption has been shown to attenuate nocturnal cardiovagal baroreflex sensitivity (cvBRS) and vagal tone, but the impact of alcohol on cvBRS during specific polysomnographic sleep stages remains unclear. We hypothesized that binge alcohol consumption would decrease nocturnal cardiovagal tone and cvBRS, particularly during slow wave (SWS) and rapid eye movement (REM) sleep due to their reported impact on cardiovascular health. Sixteen volunteers (9 women, 7 men; 25±1 years; 28±1 kg/m2) participated in this study. Utilizing a randomized, crossover design, participants arrived to the laboratory for two testing nights (alcohol vs. fluid control) separated by one month. The alcohol condition simulated a binge drinking episode by consuming a 4-5 drink equivalent within two hours. The alcohol dose was based on National Institute of Alcohol Abuse & Alcoholism (NIAAA) definitions of binge drinking, which includes differences based upon body weight and sex (1g/kg men, 0.85g/kg women). Overnight polysomnography (Natus, Middleton, WI), two-lead electrocardiogram (ECG), and dual-finger plethysmography (Finapres NOVA, Netherlands) were recorded during an 8-hour in-laboratory sleep acquisition period. The nocturnal ECG and continuous blood pressure signals were imported into custom software (WinCPRS, Absolute Aliens, Finland) for heart rate variability (HRV) and cvBRS analyses. A ten-minute period of stable sleep was selected in each participant for each sleep stage, and was verified by a board-certified sleep physician. Each segment of stable sleep was free of any scorable arousal, apneic event, and limb movement. Cardiovagal activity was assessed via fast-Fourier transform and quantified as high frequency (HF; 0.15-0.4 Hz), and cvBRS was assessed using up-up (vagal activation) and down-down (vagal withdrawal) sequence analyses. Evening binge alcohol consumption reduced HF during SWS (1429±279 vs. 698±146 ms2, p>0.001) and REM (1114±238 vs. 599±151 ms2, p=0.022), but not stage II (1619±453 vs. 901±258 ms2, p=0.137). Evening binge alcohol consumption decreased cvBRS during stage II (up-up, 21±3 vs. 15±3 ms/mmHg, p=0.035; down-down, 23±2 vs. 14±2 ms/mmHg, p=0.001) and REM sleep (up-up, 21±4 vs. 15±3 ms/mmHg, p=0.008; down-down, 19±3 vs. 12±2 ms/mmHg, p=0.008), but did not alter cvBRS during SWS (up-up, 21±3 vs. 15±3 ms/mmHg, p=0.224; down-down, 22±2 vs. 17±4 ms/mmHg, p=0.225). Taken together, our results indicate that the deleterious cardiovascular effects of binge alcohol consumption may be present across multiple sleep stages, but particularly during stable REM sleep.

27 Cerebral Autoregulation Associated with Falls in Older Persons with Orthostatic Hypotension?

Abstract Background It is considered well-established that orthostatic hypotension (OH) is associated with falls, population-based studies have found that a large proportion of community-dwelling older adults fulfill the criteria for OH without experiencing falls. It is therefore postulated that older individuals with OH may only experience fall if cerebral autoregulation, which is the mechanism by which the brain blood flow is maintained constant through a autoregulatory range, is impaired. Objective To evaluate the relationship between cerebral autoregulation and OH in older individuals with and without a history of falls. Method Individuals aged 3 60 years were recruited from medical clinics, by word of mouth, and from existing research registries. Baseline sociodemographics, detailed medical history and medication history were obtained. Bilateral middle cerebral artery (MCA) blood flow were recorded using transcranial Doppler ultrasound (TCD) synchronized with non-invasive continuous blood pressure and ECG recordings. Synchronized brain blood flow signals, heart trace and blood pressure signals were first recorded during 10 minutes’ supine rest. Participants were then be asked to perform a standard set of mathematical calculations, a Valsalva maneuver and to stand up from a seated position. Results 36 participants have been evaluated to date (13 fallers, 23 non-Fallers). There is no statistically significant difference in gender, ethnicity or height and weight between groups. Fluctuations in MCA flow velocity were observed with spontaneous fluctuations in blood pressure at rest and with induced blood pressure changes during the challenge maneuvers. Visual inspection of the signals obtained suggested that changes in MCA flow velocity were more marked among fallers and non-fallers. Conclusion Synchronization of cerebral blood flow and continuous blood pressure signals opens up numerous new possibilities in research and clinical practice. Our preliminary findings suggest that cerebral autoregulation does play a role in determining the presence of symptomats in older individuals with OH.

Electroencephalographic Slow-Wave Activity During Sleep in Different Phases of Blood Pressure and Respiration Oscillations.

Sleep is characterized by dynamic coupling between central (CNS) and peripheral autonomic (ANS) nervous systems. However, further research is needed to better understand the multiple interactions occurring among electroencephalographic (EEG) features and respiratory and cardiovascular (CV) outputs modulated by the ANS during sleep. Here, we developed new methods to study EEG slow-wave activity (SWA) during non-rapid eye movement (NREM) sleep with respect to the phases of peripheral oscillations. EEG, respiration, and continuous blood pressure signals recorded from 20 participants were analyzed. Digital filters, designed to decompose the signals into different frequency bands, and the Hilbert transform were applied to estimate the instantaneous phases and frequencies of the peripheral oscillations. The peripheral oscillations were categorized into four phases representing up and down states. EEG delta power (synchronized SWA) was computed and compared across these phases during NREM sleep. Results show that EEG delta power is higher during down phases of slow and respiratory frequency components of blood pressure and during up phases of respiration, suggestive of CNS-ANS coupling during NREM sleep. The developed techniques provide the preliminary framework to further analyze and interpret complex interactions between cortical and cardiac oscillations and their synchrony.

Instantaneous Frequencies of Continuous Blood Pressure a Comparison of the Power Spectrum, the Continuous Wavelet Transform and the Hilbert–Huang Transform

Continuous biological signals, like blood pressure recordings, exhibit nonlinear and nonstationary properties which must be considered during their analysis. Heart rate variability analyses have identified several frequency components and their autonomic origin. There is need for more knowledge on the time-changing properties of these frequencies. The power spectrum, continuous wavelet transform and Hilbert–Huang transform are applied on a continuous blood pressure signal to investigate how the different methods compare to each other. The Hilbert–Huang transform shows high ability to analyze such data, and can, by identifying instantaneous frequency shifts, provide new insights into the nature of these kinds of data.

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This paper proposes a new algorithm for sleep apnea detection based on stroke volume. It is very important to detect sleep apnea since it is a common and serious sleep-disordered breathing (SDB). In the previous studies, methods for sleep apnea detection using heart rate variability, airflow and blood oxygen saturation, tracheal sound have been proposed, but a method using stroke volume has not been studied. The proposed algorithm consists of detection of characteristic points in continuous blood pressure signal, estimation of stroke volume and detection of sleep apnea. To evaluate the performance of algorithm, the MIT-BIH Polysomnographic Database provided by Phsio- Net was used. As a result, the sensitivity of 85.99%, the specificity of 72.69%, and the accuracy of 84.34%, on the average were obtained. The proposed method showed comparable or higher performance compared with previous methods.

Correlation dimension estimation: can this nonlinear description contribute to the characterization of blood pressure control in rats?

The application of correlation dimension estimation to the study of cardiovascular control, via the blood pressure (BP) time series was investigated. We chose to calculate the Grassberger-Procaccia (GP) correlation dimension. In order to obtain a reliable estimate of the correlation dimension, we studied impact of various parameters such as the appropriate sampling rate, the time delays, the embedding dimension, the minimal trace length required, and the number of points needed as reference points. We developed a recipe for the reliable treatment of the continuous BP signal in rats, our animal model, and discussed the possible pitfalls which demand special attention. Next, we applied the surrogate data method to a BP time series, looking for the existence of nonlinear components, in order to test whether the nonlinear modeling is necessary for accurately describing the system. We found that, indeed, the correlation dimension does reveal information which cannot be unveiled by the commonly used power spectral technique, thus, making the nonlinear modeling an important approach, providing additional insight into the cardiovascular control system.

Finger‐to‐brachial comparability of ‘modelflow’stroke volume improves after pulsewave reconstruction

Modelflow is a method that determines stroke volume (SV) from central or peripheral continuous blood pressure signals. Pulsewaves are changed along the arterial tree; distortion occurs as the mean pressure level gradually declines. These changes might jeopardize the determination of SV from a distal measurement site. Techniques have been assessed to reconstruct brachial artery pressures (BAPs) from non-invasive finger blood pressure (FIN) waveforms. In this study, we determined the effect of different forms of brachial reconstruction techniques on the comparability of modelflow SV from FIN and BAP. Supine resting FIN and BAP were measured simultaneously in 57 subjects, covering a wide range of blood pressures and degrees of vascular disease. SV from the two sites were compared before correction and after correction for pulsewave distortion or pressure gradient. The latter was determined by a regression formula and by a return to flow (RTF) method, using the brachial cuff pressure at the moment of reappearance of FIN during cuff deflation. SV from unfiltered FIN exceeded BAP-derived SV by 4.6 (SD 11) ml. This difference was positively related to the subjects' age. Correction for pulsewave distortion increased the average difference to 13 (12) ml (P < 0.05 to the unfiltered condition). Adjustment for the pressure gradient reduced the difference to -2.5 (7) ml (P < 0.01). RTF had no additional effect. We concluded that the FIN-to-BAP comparability can be increased by brachial reconstruction techniques, which correct for the pressure gradient. This can be adequately performed without additional measurements, allowing its application to measurements already taken.