Finger Arterial Pressure Research Articles

Examining temporal changes in model-optimized parameters using longitudinal hemodynamic measurements

BackgroundWe previously applied hemodynamic data to personalize a mathematical model of the circulation expressed as physically interpretable parameters. The aim of this study was to identify patterns in the data that could potentially explain the estimated parameter changes. This included investigating whether the parameters could be used to track the effect of physical activity on high blood pressure. Clinical trials have repeatedly detected beneficial changes in blood pressure after physical activity and uncovered changes in lower level phenotypes (such as stiffened or high-resistance blood vessels). These phenotypes can be characterized by parameters describing the mechanical properties of the circulatory system. These parameters can be incorporated in and contextualized by physics-based cardiovascular models of the circulation, which in combination can become tools for monitoring cardiovascular disease progression and management in the future.MethodsClosed-loop and open-loop models of the left ventricle and systemic circulation were previously optimized to data from a pilot study with a 12-week exercise intervention period. Basal characteristics and hemodynamic data such as blood pressure in the carotid, brachial and finger arteries, as well as left-ventricular outflow tract flow traces were collected in the trial. Model parameters estimated for measurements made on separate days during the trial were used to compute parameter changes for total peripheral resistance, systemic arterial compliance, and maximal left-ventricular elastance. We compared the changes in these cardiovascular model-based estimates to changes from more conventional estimates made without the use of physics-based models by correlation analysis. Additionally, ordinary linear regression and linear mixed-effects models were applied to determine the most informative measurements for the selected parameters. We applied maximal aerobic capacity (measured as VO2max\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{VO2max}$$\\end{document}) data to examine if exercise had any impact on parameters through regression analysis and case studies.Results and conclusionsParameter changes in arterial parameters estimated using the cardiovascular models correlated moderately well with conventional estimates. Estimates based on carotid pressure waveforms gave higher correlations (0.59 and above when p<0.05\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$<0.05$$\\end{document}) than those for finger arterial pressure. Parameter changes over the 12-week study duration were of similar magnitude when compared to short-term changes after a bout of intensive exercise in the same parameters. The short-term changes were computed from measurements made immediately before and 24 h after a cardiopulmonary exercise test used to measure VO2max\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{VO2max}$$\\end{document}. Regression analysis indicated that changes in VO2max\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{VO2max}$$\\end{document} did not account for any substantial amount of variability in total peripheral resistance, systemic arterial compliance, or maximal left-ventricular elastance. On the contrary, changes in stroke volume contributed to far more explained variability. The results suggest that more research is required to be able to accurately track exercise-induced changes in the vasculature for people with pre-hypertension and hypertension using lumped-parameter models.

Rapid changes in cerebrovascular compliance during vasovagal syncope.

The compensatory mechanisms supporting cerebral perfusion throughout head-up tilt (HUT) in patients with vasovagal syncope (VVS) remain unclear. We tested the hypothesis that increased cerebrovascular compliance (Ci) and decreased cerebrovascular resistance (CVR) support cerebral blood velocity (CBV) during pre-syncope in VVS. Finger arterial blood pressure (ABP) and right middle cerebral artery blood velocity (CBV) were recorded in 15 individuals diagnosed with VVS (n = 11 female, mean age: 40 ± 16years, mean body mass index: 24.9 ± 4.0kg/m2) at supine rest and during HUT (80 degree angle). Individual ABP and CBV waveforms during VVS were input into a modified Windkessel model to calculate Ci and ohmic CVR. Gosling's pulsatility index (Pi; pulse amplitude/mean CBV) was calculated. Diastolic ABP, systolic ABP, mean ABP (72 ± 11 to 51 ± 12mmHg), and CVR decreased progressively during presyncope (all P ≤ 0.04). As expected, systolic CBV was sustained (all P ≥ 0.29) while diastolic and mean CBV (51 ± 13 to 38 ± 13mmHg) fell during presyncope (all P ≤ 0.04). Both Ci and Pi increased during presyncope (128 ± 97 and 60 ± 41%, respectively; all P ≤ 0.049) and were positively correlated (R2 = 0.79, P < 0.01). Increased Ci contributed to changes in mean CBV (P < 0.01) but decreased CVR did not (P = 0.28). These data provide evidence that Ci increases during presyncope in patients with VVS and is likely involved in the maintenance of systolic CBV during a fall in diastolic CBV. However, this regulation is not sufficient to preserve CBV in the presence of such extreme and progressive reductions in ABP.

Cerebrovascular Compliance during Progressive Hypotension in Patients with Autonomic Failure

Background: Cerebral perfusion during reductions in arterial pressure (AP) can be supported transiently by a Windkessel mechanism that increases cerebrovascular compliance (Ci). This defense mechanism exists in healthy participants during rapid standing and in patients during vasovagal syncope. However, it remains unknown whether the rise in Ci with falling AP exhibits a threshold effect. Thus, we tested the hypothesis that increased Ci is passive to a reduction in AP and starts to increase only after a threshold has been reached. To test this hypothesis, it was necessary to study a population that tolerates progressive large reductions in BP without a loss of consciousness. Therefore, we analyzed Ci changes during a graded head-up tilt (HUT) from patients with autonomic failure (AF). Methods: Finger AP and right middle cerebral artery blood velocity (MCAv) were recorded from 5 AF patients (n = 5 male, 61 ± 23 years, 25 ± 5 kg/m2) at supine rest and during graded-HUT (30, 45, 60 degrees). Tilt gradients increased incrementally every 5 minutes until AP reached a critically low value prompting termination of HUT. The total time in HUT was 11 ± 4 min. Individual AP and MCAv waveforms during supine rest and graded HUT (one waveform every 5 s) were assessed with a modified Windkessel model to calculate Ci and cerebrovascular resistance (CVR). Pulse pressure (PP) was calculated as systolic AP − diastolic AP. A threshold value for the increase in Ci was determined as five consecutive cardiac cycles greater than the average supine Ci plus 2 standard deviations. Results: Graded HUT resulted in an overall reduction in AP (85 ± 18 to 50 ± 7 mmHg), PP (72 ± 22 to 32 ± 19 mmHg), mean MCAv (62 ± 12 to 35 ± 7 cm/s), and CVR (1.4 ± 0.1 to 1.0 ± 0.3 mmHg/cm/s; all p &lt; 0.05 vs supine). Ci increased by 905 ± 756% (p = 0.04 vs supine). The threshold effect was evident as Ci began to increase progressively after PP fell by 15 ± 3 mmHg and AP fell by 12 ± 2 mmHg. Conclusions: Our results provide evidence that Ci increases after a threshold reduction in PP and AP in the apparent absence of autonomic support. These data support the idea that increasing Ci during reductions in AP represents a pressure-dependent Windkessel mechanism. Of interest, our findings provide clinical insight into how AF patients compensate for such large reductions in pressure without the assistance of CVR as a defense mechanism. NSERC USRA — Western University, Natural Sciences and Engineering Research Council of Canada (NSERC, Grant No. RGPIN-2018-06255). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Comparison between Speckle Plethysmography and Photoplethysmography during Cold Pressor Test Referenced to Finger Arterial Pressure.

Speckle Plethysmography (SPG) and Photoplethysmography (PPG) are different biophotonics technologies that allow for measurement of haemodynamics. As the difference between SPG and PPG under low perfusion conditions is not fully understood, a Cold Pressor Test (CPT-60 s full hand immersion in ice water), was used to modulate blood pressure and peripheral circulation. A custom-built setup simultaneously derived SPG and PPG from the same video streams at two wavelengths (639 nm and 850 nm). SPG and PPG were measured at the right index finger location before and during the CPT using finger Arterial Pressure (fiAP) as a reference. The effect of the CPT on the Alternating Component amplitude (AC) and Signal-to-Noise Ratio (SNR) of dual-wavelength SPG and PPG signals was analysed across participants. Furthermore, waveform differences between SPG, PPG, and fiAP based on frequency harmonic ratios were analysed for each subject (n = 10). Both PPG and SPG at 850 nm show a significant reduction during the CPT in both AC and SNR. However, SPG showed significantly higher and more stable SNR than PPG in both study phases. Harmonic ratios were found substantially higher in SPG than PPG. Therefore, in low perfusion conditions, SPG seems to offer a more robust pulse wave monitoring with higher harmonic ratios than PPG.

Noninvasive finger plethysmography for continuous blood pressure monitoring in patients with left ventricular assist device.

Accurate blood pressure (BP) measurement remains challenging in patients with HeartMate 3™ left ventricular assist devices (HM3 LVADs). The Finapres® NOVA is a promising non-invasive continuous BP monitor that uses the volume clamp method via a finger cuff, so here we aimed to validate the instrument in HM3 patients. In a single-center cohort, BP was monitored in 15 patients within 72 h following HM3 implantation. A radial artery catheter quantified arterial blood pressure (ABP), while the NOVA measured finger arterial pressure (fiAP) and reconstructed brachial artery pressure (reBAP). Waveforms were recorded for 10 min, and mean values were calculated in 15-s intervals. fiAP and ABP were moderately correlated during both the first (ICC 0.61, p = 0.04) and final measurements (ICC 0.66, p = 0.03). reBAP and ABP were strongly correlated during both the first (ICC 0.81, p = 0.002) and final measurements (ICC 0.83, p = 0.001). Both NOVA-derived values may underestimate low BP values while overestimating relatively high BP values. The reBAP was within 5 mm Hg of the ABP in 40% of patients (and within 10 mm Hg in 67%). This pilot represents the first evidence in support of the Finapres® NOVA for non-invasive BP measurement in select patients with HM3 LVADs. The instrument may provide useful data during BP medication adjustments or pump titration, but despite the correlation between the non-invasive reBAP and invasive ABP, individual-level inaccuracy may be clinically meaningful. Further investigation is needed to clarify these limitations and optimize accuracy before widespread adoption in this unique patient population.

Monitoring variability in parameter estimates for lumped parameter models of the systemic circulation using longitudinal hemodynamic measurements

BackgroundPhysics-based cardiovascular models are only recently being considered for disease diagnosis or prognosis in clinical settings. These models depend on parameters representing the physical and physiological properties of the modeled system. Personalizing these parameters may give insight into the specific state of the individual and etiology of disease. We applied a relatively fast model optimization scheme based on common local optimization methods to two model formulations of the left ventricle and systemic circulation. One closed-loop model and one open-loop model were applied. Intermittently collected hemodynamic data from an exercise motivation study were used to personalize these models for data from 25 participants. The hemodynamic data were collected for each participant at the start, middle and end of the trial. We constructed two data sets for the participants, both consisting of systolic and diastolic brachial pressure, stroke volume, and left-ventricular outflow tract velocity traces paired with either the finger arterial pressure waveform or the carotid pressure waveform.ResultsWe examined the feasibility of separating parameter estimates for the individual from population estimates by assessing the variability of estimates using the interquartile range. We found that the estimated parameter values were similar for the two model formulations, but that the systemic arterial compliance was significantly different (p < 10^{-6}) depending on choice of pressure waveform. The estimates of systemic arterial compliance were on average higher when using the finger artery pressure waveform as compared to the carotid waveform.ConclusionsWe found that for the majority of participants, the variability of parameter estimates for a given participant on any measurement day was lower than the variability both across all measurement days combined for one participant, and for the population. This indicates that it is possible to identify individuals from the population, and that we can distinguish different measurement days for the individual participant by parameter values using the presented optimization method.

Comparing Remote Speckle Plethysmography and Finger-Clip Photoplethysmography with Non-Invasive Finger Arterial Pressure Pulse Waves, Regarding Morphology and Arrival Time.

The goal was to compare Speckle plethysmography (SPG) and Photoplethysmography (PPG) with non-invasive finger Arterial Pressure (fiAP) regarding Pulse Wave Morphology (PWM) and Pulse Arrival Time (PAT). Healthy volunteers (n = 8) were connected to a Non-Invasive Blood Pressure (NIBP) monitor providing fiAP pulse wave and PPG from a clinical transmission-mode SpO2 finger clip. Biopac recorded 3-lead ECG. A camera placed at a 25 cm distance recorded a video stream (100 fps) of a finger illuminated by a laser diode at 639 nm. A chest belt (Polar) monitored respiration. All signals were recorded simultaneously during episodes of spontaneous breathing and paced breathing. Post-processing was performed in Matlab to obtain SPG and analyze the SPG, PPG and fiAP mean absolute deviations (MADs) on PWM, plus PAT modulation. Across 2599 beats, the average fiAP MAD with PPG was 0.17 (0-1) and with SPG 0.09 (0-1). PAT derived from ECG-fiAP correlated as follows: 0.65 for ECG-SPG and 0.67 for ECG-PPG. Compared to the clinical NIBP monitor fiAP reference, PWM from an experimental camera-derived non-contact reflective-mode SPG setup resembled fiAP significantly better than PPG from a simultaneously recorded clinical transmission-mode finger clip. For PAT values, no significant difference was found between ECG-SPG and ECG-PPG compared to ECG-fiAP.

Respiratory Sinus Arrhythmia is Mainly Driven by Central Feedforward Mechanisms in Healthy Humans.

Heart rate variability (HRV) has prognostic and diagnostic potential, however, the mechanisms behind respiratory sinus arrhythmia (RSA), a main short-term HRV, are still not well understood. We investigated if the central feedforward mechanism or pulmonary stretch reflex contributed most to RSA in healthy humans. Ventilatory support reduces the centrally mediated respiratory effort but remains the inspiratory stretch of the pulmonary receptors. We aimed to quantify the difference in RSA between spontaneous breathing and ventilatory support. Nineteen healthy, young subjects underwent spontaneous breathing and non-invasive intermittent positive pressure ventilation (NIV) while we recorded heart rate (HR, from ECG), mean arterial pressure (MAP) and stroke volume (SV) estimated from the non-invasive finger arterial pressure curve, end-tidal CO2 (capnograph), and respiratory frequency (RF) with a stretch band. Variability was quantified by an integral between 0.15–0.4 Hz calculated from the power spectra. Median and 95% confidence intervals (95%CI) were calculated as Hodges–Lehmann’s one-sample estimator. Statistical difference was calculated by the Wilcoxon matched-pairs signed-rank test. RF and end-tidal CO2 were unchanged by NIV. NIV reduced HR by 2 bpm, while MAP and SV were unchanged in comparison to spontaneous breathing. Variability in both HR and SV was reduced by 60% and 75%, respectively, during NIV as compared to spontaneous breathing, but their interrelationship with respiration was maintained. NIV reduced RSA through a less central respiratory drive, and pulmonary stretch reflex contributed little to RSA. RSA is mainly driven by a central feedforward mechanism in healthy humans. Peripheral reflexes may contribute as modifiers of RSA.

Beyond the Baroreflex: A New Measure of Autonomic Regulation Based on the Time-Frequency Assessment of Variability, Phase Coherence and Couplings.

For decades the role of autonomic regulation and the baroreflex in the generation of the respiratory sinus arrhythmia (RSA) - modulation of heart rate by the frequency of breathing - has been under dispute. We hypothesized that by using autonomic blockers we can reveal which oscillations and their interactions are suppressed, elucidating their involvement in RSA as well as in cardiovascular regulation more generally. R-R intervals, end tidal CO2, finger arterial pressure, and muscle sympathetic nerve activity (MSNA) were measured simultaneously in 7 subjects during saline, atropine and propranolol infusion. The measurements were repeated during spontaneous and fixed-frequency breathing, and apnea. The power spectra, phase coherence and couplings were calculated to characterise the variability and interactions within the cardiovascular system. Atropine reduced R-R interval variability (p < 0.05) in all three breathing conditions, reduced MSNA power during apnea and removed much of the significant coherence and couplings. Propranolol had smaller effect on the power of oscillations and did not change the number of significant interactions. Most notably, atropine reduced R-R interval power in the 0.145-0.6Hz interval during apnea, which supports the hypothesis that the RSA is modulated by a mechanism other than the baroreflex. Atropine also reduced or made negative the phase shift between the systolic and diastolic pressure, indicating the cessation of baroreflex-dependent blood pressure variability. This result suggests that coherent respiratory oscillations in the blood pressure can be used for the non-invasive assessment of autonomic regulation.

Stroke volume variation as an index of fluid responsiveness can be impaired by mental stress.

Cardiac stroke volume variation (SVV) measurement is one of the techniques to detect fluid-responsive hypovolemia in patients under mechanical ventilation. There is an ongoing effort to apply SVV for this purpose also in conscious patients. However, the effect of mental stress often occurring in conscious patients as a potential confounding factor on SVV is not known. The aim of our study was to compare effect of simulated hypovolemia and mental stress on SVV in healthy volunteers in the context of potential confounders - breathing pattern, respiratory sinus arrhythmia magnitude and sex. We examined 102 young healthy volunteers (58 females), mean age 18.6 years. Finger arterial blood pressure was recorded by volume-clamp photoplethysmographic method (Finometer Pro, FMS, Amsterdam, Netherland). From the blood pressure curve, a built in ModelFlow algorithm calculated stroke volume values (SV) for each heartbeat. Respiratory volume was recorded using calibrated respiratory inductive plethysmography (RespiTrace, NIMS, Miami Beach, FL, USA). During four phases of examination protocol (supine rest, head-up tilt (HUT), supine recovery, mental arithmetic task (MA)) we analyzed SVV related to respiratory activity. While during HUT we found an expected increase in SVV together with mean SV decrease, SVV significantly decreased during MA. The observed changes during MA could be attributed to an increased respiratory rate and/or decreased respiratory sinus arrhythmia. Sex related differences in SVV responses to HUT and MA were observed. We conclude that mental stress together with respiratory sinus arrhythmia and respiratory pattern changes can significantly influence SVV as a potential index of fluid responsiveness in conscious patients.

Assessment of baroreceptor reflex sensitivity in young obese Saudi males at rest and in response to physiological challenges.

Autonomic imbalance in overweight/obese persons could lead to an increased risk of cardiovascular complications including hypertension and arrhythmias. Baroreceptor reflex sensitivity is a sensitive indicator to detect an altered sympathovagal balance in overweight/obese individuals. This study investigated the effects of overweight/obesity on baroreceptor sensitivity in young Saudi males at rest and in response to physiological challenges.Subjects and methodsIn this cross‐sectional study, spontaneous baroreceptor sensitivity at rest and in response to deep breathing, isometric hand grip exercise and moderate intensity isotonic exercise were recorded in 20 normal weight and 20 overweight/obese subjects. Finger arterial blood pressure signal, recorded through Finometer, was used to calculate baroreceptor sensitivity through cross‐correlation method. The baroreceptor sensitivity data were log transformed before application of parametric tests.ResultsThe spontaneous baroreceptor sensitivity was similar in both groups at baseline, but exhibited a significant increase during deep breathing only in normal weight (p < .001). Immediately after the isotonic exercise the baroreceptor sensitivity was significantly lower than baseline in both normal weight and overweight/obese and remained significantly lower in overweight/obese individuals compared to normal weight (p < .05) throughout the recovery period. There was a significant rise in baroreceptor sensitivity after isometric exercise in overweight/obese group only (p = .001). Pearson's correlation showed a significant negative correlation of baroreceptor sensitivity with body mass index during deep breathing (r = −.472, p = .004) and in post‐isotonic exercise recovery period (r = −.414, p = .013).ConclusionA significantly reduced baroreceptor sensitivity response to deep breathing, reduced baroreceptor sensitivity recovery after isotonic exercise, and an exaggerated shoot up after isometric exercise in overweight/obese suggests an altered sympathovagal balance. Baroreceptor sensitivity measurements in response to physiological challenges, deep breathing, and isotonic exercise, may be more sensitive investigations for detection of early attenuation of cardiac autonomic function. This would enable timely intervention thereby delaying complications and improving the quality of life.

Changes in Heart Rate Variability and Baroreflex Sensitivity During Daytime Naps.

Background and ObjectivesChanges in autonomic cardiac activity during night sleep are well documented. However, there is limited information regarding changes in the autonomic cardiac profile during daytime naps. Heart rate variability (HRV) and baroreflex sensitivity (BRS) are reliable measures of autonomic cardiac activity. The purpose of this study was to determine the changes in HRV and BRS during daytime naps in healthy men.MethodsThis was a cross-sectional study of 25 healthy men. Polysomnographic recording with electrocardiogram monitoring was conducted for all volunteers during a 50–80 min nap between 3.30 pm and 5.30 pm. Five-minute segments during pre-nap wakefulness, non-rapid eye movement (NREM) sleep stages (N1, N2, and N3), rapid eye movement (REM) sleep stage, and post-nap wakefulness were used to measure changes in the variation in HRV parameters, including inter-beat interval (RR-interval), total spectral power (TP), high-frequency power (HF), low-frequency power (LF), and low frequency/high-frequency ratio (LF/HF). BRS was also measured for 10 min during pre- and post-nap wakefulness using finger arterial pressure measurement (Finometer Pro ®).ResultsHRV increased significantly during NREM sleep compared with that during pre-nap wakefulness (p < 0.05), as reflected by RR-interval prolongation, higher HF, and increased HFnu (normalized units). Furthermore, there was a parallel reduction in TP, LF, and LF/HF ratio during NREM sleep, indicating parasympathetic predominance over cardiac autonomic activity. HF and HFnu were significantly reduced during REM sleep compared with that during NREM sleep (p < 0.05). BRS did not show significant differences between pre- and post-nap wakefulness.ConclusionWe observed a progressive increase in parasympathetic activity during daytime sleep as NREM sleep deepened compared with that during wakefulness and REM sleep. Daytime nap may have a favorable cardiovascular impact.

“Comparison of cardiovascular autonomic activity (heart rate variability and baroreceptor sensitivity) in young healthy females during fasting and hyperglycaemia”

Background and AimThe present study compared cardiovascular autonomic activity and reactivity during fasting (FS) and hyperglycemia (HS) states in young healthy females. MethodsThis case crossover study was conducted on 30 females recruited by convenient sampling. Blood glucose levels were measured in FS and after oral glucose load i.e., HS. Finger arterial blood pressure (BP) and ECG were recorded constantly to monitor baroreceptor sensitivity (BRS) and heart rate variability (HRV). Autonomic reactivity was tested with deep breathing (DB), Valsalva manoeuvre (VM), and head-up-tilt (HUT) test under FS and HS. HRV parameters not normally distributed were natural log (ln) transformed. ResultsSignificantly reduced Valsalva ratio and higher heart rate and BP were observed in HS that continued during HUT (P < 0.05). The lnSDNN (standard deviation of normal-to-normal intervals) and lnRMSSD (root mean square of successive differences) were significantly lower (p < 0.05) in HS during HUT. After HUT, lnRMSSD remained lower (P = 0.031), whereas lnLF/HF (low frequency/high frequency power) ratio (P = 0.042) and LFnu (normalized units) (P = 0.024) were higher in HS. BRS was significantly lower in supine position in HS compared to FS and further reduced in HUT position in both FS and HS (P < 0.05). ConclusionCompared to FS, the HS exhibited heightened sympathetic activity with attenuation of parasympathetic activity and this phenomenon was further accentuated by HUT. BRS was more sensitive indicator of autonomic effects of hyperglycemia in resting state. In addition to standard tests, autonomic reactivity in vulnerable young subjects could be useful to detect autonomic imbalance at an early stage.

Differences in effects of task repetition in three modalities Go/No‐go paradigams.

Previous studies suggested that learning, habituation, mental fatigue, or reduced motivation due to task repetition (time‐on‐task) decreased the peak amplitude and/or latency of components of event‐related potentials (ERPs), but the mechanism remains unclear. Also, the effect of the sensory modality on those changes has not been clarified. The difference in modality could modify cerebral blood flow or its distribution in the brain. We hypothesized that the effect of task repetition on ERPs was related to the sensory modality, and the changes in cerebral blood flow contributed to the difference. Subjects performed 6 sessions of Go/No‐go paradigms for 5 minutes with visual, auditory, and somatosensory stimuli on different days, and were allowed to rest for 5 minutes between sessions. In addition to electroencephalography, middle cerebral artery blood mean velocity and finger arterial pressure were continuously measured to evaluate dynamic cerebral autoregulation via transfer function analysis. The amplitude of P300 decreased with the time‐on‐task in all three modalities, and the latency of P300 delayed with the time‐ontask only with somatosensory stimuli. The reductions in amplitude were the greatest with the visual stimuli among the three modalities. The reductions in the amplitude of P300 were greater with No‐go stimuli than Go stimuli across the three modalities. Contrary to our hypothesis, dynamic cerebral autoregulation did not change throughout the trials. These results suggest that the effects of task repetition on ERPs were sensory modality‐dependent, while dynamic cerebral autoregulation during cognitive tasks might not contribute to changes in ERPs.Support or Funding InformationJapan Society for the Promotion of Science 18H03166

Single-digit cold-induced vasodilation adaptations during an Antarctic expedition

An increasing number of people are spending time in Polar Regions for work and tourism and this can increase the risk of tissue injuries, e.g. frostbite. The risk would be reduced if beneficial peripheral blood flow adaptions occurred but data regarding the trainability of the cold-induced vasodilation (CIVD) response are equivocal. Five healthy males spent almost 8 months in Antarctica; five of them at a semi-permanent camp (− 44 °C; 2752 m). CIVD tests (30 min index finger immersion into 0 °C water) were performed on the 12th, 39–40th, 67–68th, 179th and 234th days of the expedition in a climate-controlled caboose. Heart rate (HR), thermal sensation of the finger, pain sensation, and mean arterial pressure (MAP) were recorded. Minimum, maximum, and mean finger temperature were greater, onset time was earlier (r = 0.34), and amplitude was greater (r = 0.55) on day 234 than day 12 suggesting that adaptation occurred. Time-point data suggested that the adaptations were progressive. Cardiovascular and perceptual data also showed some adaptation. MAP was lower on day 234 than day 12 (r = 0.47 and r = 0.47) but mean HR was higher (r = 0.55). Mean and peak thermal sensation (r = 0.31–0.59; r = 0.31) and perceived pain (r = 0.58; r = 0.36) both improved over the course of the expedition. Of interest to Polar Region visitors, beneficial peripheral and perceptual adaptations to prolonged Antarctic exposure can occur with 2 h of daily outdoor exposure although the rates at which adaptation occurs differ.

The cardiovascular response to ambient temperature changes within the human thermoneutral zone

IntroductionThe human temperature control within the thermoneutral zone (TNZ) depends on the regulation of skin blood flow to hands and feet (acral skin) [1]. The acral skin blood flow is regulated by absolute level and fluctuations in arterio‐venous anastomoses’ vasculature resistance. We hypothesized that a change in ambient temperature would not affect the hemodynamic responses within the TNZ in healthy humans.MethodsTwenty‐four young healthy human subjects were exposed to three ambient temperatures (20°C, 26°C and 32°C) while supine and lightly dressed in a climate chamber. Each temperature plateau lasted for 40 minutes. The protocol either started at 20°C or 32°C, with a subsequent increase or decrease in temperature, respectively, and the order was randomized. Beat‐by‐beat blood flux from both index fingers and the left forearm were recorded simultaneously by laser Doppler flowmetry (DRT4, Moor Instruments, Devon, UK), together with heart rate (HR, from ECG). Non‐invasive finger arterial blood pressure (Finometer, Finapres Medical System, Netherlands; calibrated at each temperature plateau) was recorded continuously from the right middle finger, providing mean arterial pressure (MAP) and estimated beat‐to‐beat cardiac stroke volume (SV). The medians and their corresponding 95% confidence intervals were calculated by Hodges‐Lehmann’s estimates. Wilcoxon signed rank sum test for paired samples tested differences between states.Preliminary resultsIncreasing ambient temperature from 20°C to 32°C caused a five‐fold increase in left fingertip flux (p&lt;0.003) while left forearm flux doubled (p&lt;0.008). The fluctuations in the bilateral fingertip flux were maximum correlated at 26°C (&gt;0.82) and significantly higher than the correlation at 32°C (0.73, p&lt;0.01 as compared to 26°C). The hemodynamic variables changed significantly within the TNZ. MAP decreased from 74 (70,77) mmHg at 20°C to 64 (60,68) mmHg at 32°C (p&lt;0.0001). SV decreased from 102 (93, 113) ml at 20°C to 97 (86, 106) ml at 32°C (p&lt;0.0004). HR increased minimally from 20°C (56 bpm (52, 59) to 32°C (58 bpm (56, 61) (p=0.01).ConclusionsThe marked changes in acral skin blood flow within TNZ affected the central hemodynamic variables, with the vasodilation reflected in MAP decrease coinciding with an increase in ambient temperature. HR and SV showed minimal changes within TNZ.Support or Funding InformationThe Research Council of Norway (grant no: 230354)

Reconstruction of Continuous Brachial Arterial Pressure From Continuous Finger Arterial Pressure Using a Two-Level Optimization Strategy.

We attempt to reconstruct brachial arterial pressure (BAP) waves from finger arterial pressure waves measured using the vascular unloading technique without arm-cuff calibration. A novel method called two-level optimization (TOP) strategy is proposed as follows. We first derive a simplified transfer function (TF) based on a tube-load model with only two parameters to be estimated, a coefficient B and a time delay ∆t. Then, at level one, two minimization problems are formulated to estimate the optimal coefficient Bopt and time delay ∆topt. Then, we can derive an optimal TF hopt(t). However, this derivation requires true (or reference) BAP waves. Therefore, at level two, we apply multiple linear regression (MLR) to further model the relationship between the derived optimal parameters and subjects' physiologic parameters. Hence, eventually, one can estimate coefficient BMLR and time delay ∆tMLR from subject's physiologic parameters to derive the MLR-based TF hMLR(t) for the BAP reconstruction. Twenty-one volunteers were recruited for the data collection. The mean ± standard deviation of the root mean square errors between the reference BAP waves and the BAP waves reconstructed by hopt(t), hMLR(t), and a generalized transfer function (GTF) were 3.46 ± 1.42mmHg, 3.61 ± 2.28mmHg, and 6.80 ± 3.73mmHg (significantly larger with p < 0.01), respectively. The proposed method can be considered as a semi-individualized TF which reconstructs significantly better BAP waves than a GTF. The proposed TOP strategy can potentially be useful in more general reconstruction of proximal BP waves.

Effect of energy drink consumption on baroreceptor sensitivity in young normal weight and overweight/obese males

Objectives:There is lack of evidence exploring sympathetic effect by baroreceptor sensitivity in obese consuming energy drink. The purpose of this study was to investigate the acute effect of energy drink on individuals baroreceptor sensitivity in young healthy normal weight and overweight/obese males.Methods:This cross-sectional study was performed in the Department of Physiology, Imam Abdulrahman Bin Faisal University, Kingdom of Saudi Arabia. After getting ethical approval, 25 male participants were recruited by convenient sampling and informed consent was obtained. Participants were grouped into normal weight and overweight/obese on basis of body mass index. Finger arterial blood pressure was recorded with Finometer® at baseline, 30min and 60 minutes in the post-energy drink period and baroreceptor sensitivity was calculated. As data was not normally distributed it was log transformed.Results:The baseline baroreceptor sensitivity was lower (P<0.05) in overweight/obese compared to normal weight participants. Baroreceptor sensitivity reduced significantly (P<0.05) at 60 minutes after energy drink consumption in the whole cohort of both normal weight and overweight/obese. Baroreceptor sensitivity remained lower in overweight/obese compared to normal weight at 60min but the difference was not significant.Conclusion:Consumption of energy drink acutely reduced baroreceptor sensitivity in both normal weight and obese young healthy males with an earlier onset of effect in overweight/obese indicating enhanced sympathetic activity. Energy drinks consumption could place the obese in a more vulnerable state to hypertension and arrhythmia.

Effects of inspiratory muscle-training intensity on cardiovascular control in amateur cyclists.

Chronic effects of inspiratory muscle training (IMT) on autonomic function and baroreflex regulation are poorly studied. This study aims at evaluating chronic effects of different IMT intensities on cardiovascular control in amateur cyclists. A longitudinal, randomized, controlled blind study was performed on 30 recreational male cyclists undergoing IMT for 11 wk. Participants were randomly allocated into sham-trained group (SHAM, n = 9), trained group at 60% of the maximal inspiratory pressure (MIP60, n = 10), and trained group at critical inspiratory pressure (CIP, n = 11). Electrocardiogram, finger arterial pressure, and respiratory movements were recorded before (PRE) and after (POST) training at rest in supine position (REST) and during active standing (STAND). From the beat-to-beat series of heart period (HP) and systolic arterial pressure (SAP), we computed time domain markers, frequency domain indexes in the low frequency (0.04-0.15 Hz) and high frequency (HF, 0.15-0.4 Hz) bands, an entropy-based complexity index (CI), and baroreflex markers estimated from spontaneous HP-SAP sequences. Compared with SHAM, the positive effect of MIP60 over the HP series led to the HF power increase during REST (PRE: 521.2 ± 447.5 ms2; POST: 1,161 ± 878.9 ms2) and the CI rise during STAND (PRE: 0.82 ± 0.18; POST: 0.97 ± 0.13). Conversely, the negative effect of CIP took the form of the decreased HP mean during STAND (PRE: 791 ± 71 ms; POST: 737 ± 95 ms). No effect of IMT was visible over SAP and baroreflex markers. These findings suggest that moderate-intensity IMT might be beneficial when the goal is to limit cardiac sympathetic hyperactivity at REST and/or in response to STAND.

Abstract 041: Hypoxic Peripheral Chemoreceptor Activation Engages Sympathetic Brainstem and Hypothalamic Nuclei in Human Subjects

Peripheral carotid chemoreceptors, which raise sympathetic activation at the brainstem level, may serve as targets for antihypertensive therapy. However, human peripheral chemoreflex regulation in the brainstem is poorly understood due to lack of suitable methodologies. Therefore, we combined measurements of beat-by-beat blood pressure and SpO 2 , and high-resolution functional magnetic resonance imaging (fMRI) to elucidate human brainstem circuits engaged through hypoxic peripheral chemoreceptor activation. We submitted 12 healthy men (29.7 ±6.6 years; 24.0 ±1.86 kg/m 2 ) to five hypoxic episodes by breathing 10% oxygen for 180 seconds followed by 90 seconds normoxia during multiband fMRI brain acquisitions. We monitored continuous finger arterial blood pressure using customized hardware, ECG, and SpO 2 . Brainstem and hypothalamus fMRI images were analyzed to identify nuclei involved in peripheral chemoreflex processing. Systolic blood pressure (SBP) and SpO 2 time courses were correlated with the blood-oxygen-level dependent signals with a general linear model. With hypoxia, SpO 2 decreased by 12.32 ±3.68% (p &lt; 0.01), heart rate increased 13.86 ±3.47 bpm (p &lt; 0.01), and SBP decreased with hypoxia 5.45 ±5.5 mmHg (p &lt; 0.01). In the brainstem, the nucleus tractus solitarii (t-values: SpO 2 : 5.9; SBP: 4.79), the caudal ventrolateral medulla (SpO 2 : 5.61; SBP: 5.59), intermediate reticular nucleus (SpO 2 : 4.7, SBP: 5.98), nucleus ambiguus (SpO 2 : 5.03, SBP: 5.59), dorsal motor nucleus of the vagal nerve (SBP: 4.79), and inferior olive (SpO 2 : 4.7, SBP: 6.16) were identified with high sensitivity and corrected for multiple comparisons (p &lt; 0.01). Furthermore, we observed activation of the following hypothalamic nuclei: paraventricular nucleus (SpO 2 : 7.67), anterior and lateral hypothalamic area (SpO 2 : 7.67, SBP: 4.79), supraoptic nucleus, and tuberomammillary nucleus (SpO 2 : 7.07). High-resolution brainstem fMRI during repeated hypoxia traces brainstem circuits engaged by peripheral chemoreceptors. The methodology can be applied to study peripheral chemoreceptor contributions to human cardiovascular disease and may have utility in identifying patients likely to respond to peripheral chemoreceptor modulation.