Continuous Arterial Pressure Research Articles

Preeclampsia postpartum: Impairment of cerebral autoregulation and reversible cerebral hyperperfusion.

Preeclampsia is a pregnancy-related hypertensive disorder with endothelial dysfunction. Impaired cerebral autoregulation may lead to symptomatic cerebral hyperperfusion, which sometimes manifests not until after delivery. This study investigated, whether cerebral autoregulation was altered after delivery in healthy and preeclamptic women, and whether this associated with cerebral hyperperfusion. In a prospective study, 35 preeclamptic and 35 healthy women were examined with transcranial Doppler within 10 days postpartum and 6 months later. Continuous arterial blood pressure and cerebral blood flow velocities (CBFV) in the middle (MCA) and posterior cerebral arteries (PCA) were recorded at rest. Dynamic cerebral autoregulation was assessed upon regular breathing at 0.1 Hz via transfer function phase and gain between arterial blood pressure and CBFV oscillations. In preeclamptic women, phase was reduced after delivery in both, MCA and PCA. During the postpartum period, CBFV of the MCA, but not PCA, correlated with higher arterial blood pressure and poorer dynamic cerebral autoregulation. In healthy women with only moderately altered cerebral autoregulation, CBFV remained in the normal range. At both measurements, arterial blood pressure was higher in preeclamptic compared to healthy women. Women with preeclampsia had poorer cerebral autoregulation and an increased risk of transient cerebral hyperperfusion after delivery.

Pharmacological baroreflex testing with fMRI reveals baroreflex mediated brainstem nuclei

BackgroundBrainstem nuclei mediate baroreflex adjustments in efferent sympathetic and parasympathetic traffic. Yet, human brainstem physiology is poorly understood given the lack of suitable methodology. We developed a novel approach combining pharmacological testing, beat‐by‐beat cardiovascular monitoring, and high‐resolution functional magnetic resonance imaging (fMRI) to assess human baroreflex regulation at the level of the brainstem.Method and materialsIn 11 healthy men (30.7 ±6.6 years; 24.1 ±1.9 kg/m2), we monitored continuous finger arterial blood pressure and ECG using customized hardware during multiband fMRI brain acquisitions. We applied repeated intravenous phenylephrine (PHE, 25 and 75 μg, n=8) and nitroprusside (NTP 25 and 75 μg, n=8) boluses using a remote controlled injector. Brainstem and hypothalamus fMRI images were analyzed to identify brainstem nuclei involved in baroreflex‐mediated blood pressure control using with masked general linear model (GLM). BP changes were correlated with the time‐courses of blood‐oxygen‐level dependent (BOLD) signals by mixed‐effects general linear model.ResultsPharmacological baroreflex testing yielded baroreflex sensitivity measurements with typical blood pressure and RR‐interval patterns. Correlation of the baroreflex‐mediated changes in systolic blood pressure with BOLD signals clearly revealed brainstem nuclei. The solitary tract (NTP: 7.3; PHE: 6.0 t‐value), the caudal ventrolateral medulla (PHE: 5.8 t‐value); the rostral ventrolateral medulla (NTP: 5.6; PHE: 7.1 t‐value), the nucleus ambiguus (PHE: 5.8 t‐value), the paraventricular nucleus (NTP:7.1; PHE: 4.5 t‐value), and raphe nuclei (NTP: 5.7; PHE: 6.0 t‐value), were identified with high sensitivity and corrected for multiple comparisons (p < 0.01).ConclusionWe developed novel approach testing baroreflex regulation at the level of the brainstem in humans. The methodology identified baroreflex‐mediated activation and deactivation patterns consistent with previous investigations in animal models. The methodology can be applied to elucidate human physiology and mechanisms of autonomic cardiovascular disease.Support or Funding InformationThis study was funded by the DLR internal cost object 2475023.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Attenuated Mental Stress‐Induced Brachial Artery Hyperemia in Women Relative to Men

While the contributing factors resulting in hypertension and cardiovascular disease (CVD) are multifactorial, vascular dysfunction and exposure to chronic stress are key contributors. In this regard, previous research has indicated that men and women exhibit differential responses to stress. Acute mental stress (MS) elicits increases in peripheral blood flow that are predominately mediated by the actions of nitric oxide (NO) and thus is a technique that can be utilized to assess vascular function. Previous research has focused on sex differences in the response to MS in a variety of physiological variables; however, the impact of sex on the peripheral blood flow response to MS is less clear. Accordingly, the purpose of this study was to investigate the brachial BF hyperemic response during acute MS between men and women. We hypothesized that the hyperemic response to MS would be similar between the groups. Nine women (studied between days 2–7 of the follicular phase of the menstrual cycle) and seventeen men participated in this study. All measurements were obtained in the supine position following a 15 min baseline period. After the baseline period, the left arm was instrumented for continuous assessment of brachial artery diameter and blood velocity, which were used for subsequent calculation of brachial BF. Continuous arterial blood pressure was obtained on the contralateral arm for calculation of forearm vascular conductance (FVC; Flow/MAP). Brachial BF and FVC were continuously calculated during 2 min of baseline and 3 min of MS induced by asking subjects to subtract 7 continuously from a 3‐digit number while attempting to report answers at a pace set by a 60 bpm metronome. Compared to men, women had a reduced baseline blood flow (men: 84.39 ± 49.39 mL/min, women: 36.79 ± 15.41 mL/min; p = 0.01). In response to mental stress, women also had attenuated responses in the following variables: peak BF achieved during MS (men: 244.94 ± 119.06, women: 141.75 ± 86.98 ml/min; p = 0.03), total BF throughout the duration of MS (men: 408.91 ± 131.10, women: 196.84 ± 86.72 ml/min; p < 0.01) and peak FVC achieved during MS (men: 2.86 ± 1.24, women: 1.13 ± 0.63 mL/min/mmHg; p < 0.01). In conclusion, contrary to our hypothesis, these preliminary findings indicate that women had a reduced hyperemic response in the brachial artery during MS relative to men. Further research is warranted to assess mechanisms of these differential responses between sexes.Support or Funding InformationUTA Start‐up funds to R. Matthew BrothersThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Acute and Chronic Anti‐Hypertensive Effects of Plantaginis Semen on Spontaneous Hypertension Rats

Plantaginis semen (PS) is the seed of Plantago asiatica L., and it is widely used as a herbal medicine with antioxidant, diuretic and anti‐inflammatory effects. Hypertension is a cardiovascular disorder and it may lead to many cardiovascular diseases, such as stroke, cardiac hypertrophy, or heart failure. We focused on the acute and chronic anti‐hypertensive effects of Plantaginis semen extract (PSE) on spontaneous hypertensive rat (SHR) and our new inbred spontaneous phase‐1 hypertension (P1‐HT) modeling rats.We used the rats with age of 8~10 weeks. Under anesthesia, continuous femoral arterial pressure of SHR and P1‐HT rats were recorded by intravascular catheter for 5 minutes prior the drug administration. In acute anti‐hypertensive effect test, the rats were orally administered with 0.36 g/kg/ml of PSE that homogenized and suspended in distilled water. The arterial pressure of each rat was consecutively recorded for more than 1hr after drug administration. In chronic anti‐hypertensive effect test, we orally administered the rats with 0.36 g/kg/ml per‐day of PSE for 4 weeks and measured blood pressure. We used Students–t test and one‐way ANOVA to test the effects of PSE treatment on blood pressure.The pretreated mean arterial pressures of animals were 146±10mmHg in SHR rats, and 115±8mmHg in P1‐HT rats. The acute anti‐hypertensive effects of PSE could be observed within 15min after oral gavage and lasting more than 1hr. This acute effect of PSE could significant decrease the mean arterial pressure for 15mmHg on SHR rats, and 22mmHg on P1‐HT rats. The PSE treatment could slow down the heart rhythm significantly in both SHR and P1‐HT rats. The results of acute test of PSE indicate its anti‐hypertensive effects did not only act on diuretic pathway. In chronic tests, daily oral administrated with PSE did not change the pretreated reference value of blood pressure and its anti‐hypertensive effects.In conclusion, our new inbred P1‐HT modeling rats are more sensitive than SHR rats on anti‐hypertensive test of PSE. It may be suitable for other anti‐hypertensive drugs development testing. Oral administrated with PSE may have a rapid anti‐hypertensive effect, and can last for a period of time. Daily administration with PSE can be considered as a treatment strategy for hypertension.Support or Funding InformationNSYSUKMU107‐I001‐3This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Efficacy of a continuous non-invasive arterial blood pressure monitor system for bronchoscope diagnosis and treatment under general anesthesia

Objective To compare continuous non-invasive arterial blood pressure (CNAP) monitoring with non-invasive blood pressure (NIBP) monitoring in anesthesia monitoring application value of bronchoscope diagnosis and treatment, and to find whether the CNAP can improve the detection rate of hypotension and detect low blood pressure earlier so that improve the safety of patients. Methods Twenty patients undergoing bronchoscope diagnosis and treatment under general anesthesia from outpatient were included in this study. The NIBP monitoring was put on one side of the upper limb and the CNAP monitoring was connected to the other side upper limb before inducement of general anesthesia. Both connections were kept until the end of operation. The systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) of the CNAP were recorded one time per minute whereas the SBP, DBP and MAP of NIBP were recorded one time every 3 min. The low blood pressure (SBP<80 mmHg, 1 mmHg=0.133 kPa) frequency of CNAP and NIBP were respectively counted. The low blood pressure detection rate and the hypotension checkout time of NIBP and CNAP were calculated respectively. The consistency and correlation between the two blood pressure measurements were compared. At the same time, the complications of the two methods of monitoring were recorded and compared. Results The low blood pressure detection rate of CNAP and NIBP was 17.2% and 14.7% (P<0.05). The hypotension checkout time of CNAP and NIBP were (1.2±0.4) min and (3.0±0.0) min respectively (P<0.05). The SBP, DBP and MAP bias of CNAP and NIBP measurement were (1.5±8.8), (1.1±8.2) mmHg and (1.3±7.1) mmHg respectively. Consistency limits were -18.70-15.70 mmHg, -17.20-14.90 mmHg and -15.30-12.70 mmHg respectively. The proportion within the scope of the consistency of its corresponding boundary were 96.70%, 97.10% and 97.10% respectively. The correlation coefficients of SBP, DBP and MAP measured by CNAP and NIBP were 0.910, 0.861 and 0.941 respectively (P<0.05). None of the patients had complications. Conclusions CNAP is more sensitive and timely in detecting hypotension. It has higher consistency and more correlation than NIBP. Thus, CNAP can improve the safety of anesthesia monitoring for bronchoscope diagnosis and treatment. Key words: Continuous non-invasive arterial blood pressure monitoring; Bronchoscope diagnosis and treatment; Anesthesia, general

Novel Approach to Elucidate Human Baroreflex Regulation at the Brainstem Level: Pharmacological Testing During fMRI.

Introduction: Brainstem nuclei govern the arterial baroreflex, which is crucial for heart rate and blood pressure control. Yet, brainstem function is difficult to explore in living humans and is therefore mostly studied using animal models or postmortem human anatomy studies. We developed a methodology to identify brainstem nuclei involved in baroreflex cardiovascular control in humans by combining pharmacological baroreflex testing with functional magnetic resonance imaging.Materials and Methods: In 11 healthy men, we applied eight repeated intravenous phenylephrine bolus doses of 25 and 75 μg followed by a saline flush using a remote-controlled injector during multiband functional magnetic resonance imaging (fMRI) acquisition of the whole brain including the brainstem. Continuous finger arterial blood pressure, respiration, and electrocardiogram (ECG) were monitored. fMRI data were preprocessed with a brainstem-specific pipeline and analyzed with a general linear model (GLM) to identify brainstem nuclei involved in central integration of the baroreceptor input.Results: Phenylephrine elicited a pressor response followed by a baroreflex-mediated lengthening of the RR interval (25 μg: 197 ± 15 ms; 75 μg: 221 ± 33 ms). By combining fMRI responses during both phenylephrine doses, we identified significant signal changes in the nucleus tractus solitarii (t = 5.97), caudal ventrolateral medulla (t = 4.59), rostral ventrolateral medulla (t = 7.11), nucleus ambiguus (t = 5.6), nucleus raphe obscurus (t = 6.45), and several other brainstem nuclei [p < 0.0005 family-wise error (few)-corr.].Conclusion: Pharmacological baroreflex testing during fMRI allows characterizing central baroreflex regulation at the level of the brainstem in humans. Baroreflex-mediated activation and deactivation patterns are consistent with previous investigations in animal models. The methodology has the potential to elucidate human physiology and mechanisms of autonomic cardiovascular disease.

Perioperative Quality Initiative consensus statement on the physiology of arterial blood pressure control in perioperative medicine

BackgroundPerioperative arterial blood pressure management is a physiologically complex challenge influenced by multiple factors. MethodsA multidisciplinary, international working subgroup of the Third Perioperative Quality Initiative (POQI) consensus meeting reviewed the (patho)physiology and measurement of arterial pressure as applied to perioperative medicine. We addressed predefined questions by undertaking a modified Delphi analysis, in which primary clinical research and review articles were identified using MEDLINE. Strength of recommendations, where applicable, were graded by National Institute for Health and Care Excellence (NICE) guidelines. ResultsMultiple physiological factors contribute to the perioperative physiological importance of arterial pressure: (i) arterial pressure is the input pressure to organ blood flow, but is not the sole determinant of perfusion pressure; (ii) blood flow is often independent of changes in perfusion pressure because of autoregulatory changes in vascular resistance; (iii) microvascular dysfunction uncouples microvascular blood flow from arterial pressure (haemodynamic incoherence). From a practical clinical perspective, we identified that: (i) ambulatory measurement is the optimal method to establish baseline arterial pressure; (ii) automated and invasive arterial pressure measurements have inherent physiological and technical limitations; (iii) individualised arterial pressure targets may change over time, especially in the perioperative period. There remains a need for research in non-invasive, continuous arterial pressure measurements, macro- and micro-circulatory control, regional perfusion pressure measurement, and the development of sensitive, specific, and continuous measures of cellular function to evaluate blood pressure management in a physiologically coherent manner. ConclusionThe multivariable, complex physiology contributing to dynamic changes in perioperative arterial pressure may be underappreciated clinically. The frequently unrecognised dissociation between arterial pressure, organ blood flow, and microvascular and cellular function requires further research to develop a more refined, contextualised clinical approach to this routine perioperative measurement.

Pulse Arrival Time and Pulse Interval as Accurate Markers to Detect Mechanical Alternans

Mechanical alternans (MA) is a powerful predictor of adverse prognosis in patients with heart failure and cardiomyopathy, but its use remains limited due to the need of invasive continuous arterial pressure recordings. This study aims to assess novel cardiovascular correlates of MA in the intact human heart to facilitate affordable and non-invasive detection of MA and advance our understanding of the underlying pathophysiology. Arterial pressure, respiration, and ECG were recorded in 12 subjects with healthy ventricles during voluntarily controlled breathing at different respiratory rate, before and after administration of beta-blockers. MA was induced by ventricular pacing. A total of 67 recordings lasting approximately 90 s each were analyzed. Mechanical alternans (MA) was measured in the systolic blood pressure. We studied cardiovascular correlates of MA, including maximum pressure rise during systole (dPdtmax), pulse arrival time (PAT), pulse wave interval (PI), RR interval (RRI), ECG QRS complexes and T-waves. MA was detected in 30% of the analyzed recordings. Beta-blockade significantly reduced MA prevalence (from 50 to 11%, p < 0.05). Binary classification showed that MA was detected by alternans in dPdtmax (100% sens, 96% spec), PAT (100% sens, 81% spec) and PI (80% sens, 81% spec). Alternans in PAT and in PI also showed high degree of temporal synchronization with MA (80 ± 33 and 73 ± 40%, respectively). These data suggest that cardiac contractility is a primary factor in the establishment of MA. Our findings show that MA was highly correlated with invasive measurements of PAT and PI. Since PAT and PI can be estimated using non-invasive technologies, these markers could potentially enable affordable MA detection for risk-prediction.

Abstract WP544: Dynamic Cerebral Autoregulation is Impaired in the First Week Postpartum in Women With and Without Preeclampsia

Introduction: Pregnancy, especially when complicated by preeclampsia (PEC), is associated with increased stroke risk in the early postpartum period. Impaired cerebral autoregulation may play a role in the etiology of postpartum stroke. We compared dynamic cerebral autoregulation (DCA) in 3 groups of young women: healthy non-pregnant (HNP), healthy postpartum (HP), and postpartum after severe PEC. Methods: We recruited pregnant women with and without severe PEC and compared them with historical HNP controls. Pregnant women were tested within 1 week postpartum. Subjects were monitored for 10 minutes while breathing spontaneously, using transcranial Doppler to record cerebral blood flow velocity (CBFV) in the bilateral middle cerebral arteries and finger plethysmography to record continuous mean arterial pressure (MAP). We used generalized harmonic wavelets, a combined time-frequency method, to calculate the phase shift in degrees between MAP and CBFV, with higher phase shift indicating better DCA. We compared mean phase shift between the three groups using ANOVA. Results: Data collected from 6 non-pregnant, 5 HP and 5 PEC women were analyzed. Mean phase shift was 46.3 in the HNP, 21.2 in the HP group and 30.0 in the PEC group (p&lt;0.0001). When compared pairwise, the HP and PEC groups each had lower mean phase shift compared to non-pregnant women (p&lt;0.001) (Figure). Conclusion: In the first week postpartum after healthy and PEC-complicated pregnancies, women had poorer DCA capacity compared with healthy young non-pregnant women. The early postpartum period may be associated with impaired autoregulation, leading to increased stroke risk, particularly in women with labile blood pressure such as occurs in PEC.

Sphygmomanometer for Invasive Blood Pressure Monitoring in a Medical Mission.

In patients undergoing high-risk surgery or presenting with major comorbidities, invasive arterial pressure monitoring is often used as the standard of care;1 however, its availability one of the challenges an anesthesiologist may face in remote areas.2 After ultraviolet disinfection, a sphygmomanometer and an intravenous infusion set can be assembled to deliver effective continuous arterial pressure monitoring without a functioning monitor (panel A).This setup described does not allow for a zeroing process. Instead, the heparin solution is injected through the stopcock to make the air column pressure in the tube (shown by the sphygmomanometer) reach the level of the patient’s mean arterial pressure (panel B). When the system is opened to the patient, it can be seen that the sphygmomanometer pointer fluctuates with the cardiac cycle. Its advantages include beat-to-beat blood pressure monitoring and accurate blood pressure reading at low pressures.3 It has the same complications as conventional arterial monitoring, like thrombosis and air embolus. Constant attention is needed to keep the catheter patent, and the tube should be flushed frequently. It also should be noted that this setup can only reflect the trend of mean arterial pressure rather than systolic and diastolic pressures. Simultaneous non-invasive blood pressure monitoring is recommended to overcome this shortcoming. None of these limitations should take away from the usefulness of this device in the field, because only simple pieces of equipment are needed, and the overall trend of pressure will be accurate.The authors acknowledge the support and coordination assistance from the Department of Anesthesiology of Preah Ket Mealea Hospital, Phnom Penh, Cambodia.The authors declare no competing interests.

Noninvasive continuous arterial pressure monitoring with Clearsight during awake carotid endarterectomy: A prospective observational study.

Continuous noninvasive blood pressure (CNBP) measurement using the volume-clamp method is a less invasive alternative compared with invasive intra-arterial monitoring for awake patients during carotid endarterectomy (CEA) under regional anaesthesia. We investigated the agreement of blood pressure (BP) recorded with invasive and CNBP methods during awake CEA. A prospective observational study for assessing agreement with Bland-Altman plots, agreement-tolerability indices (ATI), concordance and interchangeability. Azienda Ospedaliera Universitaria G. Martino, Messina, a University tertiary referral centre in Italy. In 30 consecutive patients, we recorded continuously ipsilateral invasive and noninvasive BPs, from 3 min before carotid cross-clamping to 5 min after unclamping. Primary outcome was bias, 95% limits of agreement, ATI, concordance and interchangeability for mean arterial pressure (MAP). Secondary outcomes were agreements for systolic arterial pressure and diastolic arterial pressure. Tracking of changes was assessed with four-quadrant polar plots and the trend interchangeability method. Optimal bias was defined as 5 mmHg or less. A total of 2672 invasive and CNBP paired measurements (93% of overall data) were analysed, with a median of 92 readings per patient [IQR 76 to 100]. Mean (SD) bias for MAP, systolic arterial pressure and DAP were -6.8 (6.7), -3.0 (9.7) and -9.0 (5.4) mmHg, respectively. The ATIs were 0.88, 0.95 and 0.71, respectively, where ATI of 1.0 or less and at least 2.0 defined acceptable, marginal and unacceptable agreements. The four-quadrant plot analysis for beat-to-beat differences showed concordance rates of 97.3%, 99.98% and 96.4%, respectively. Polar plot analysis showed 95% limits of agreement of -3 to 3, -2 to 2 and -2 to 2 mmHg respectively. Trend interchangeability method showed an interchangeability rate of 95% for MAP. During CEA performed under regional anaesthesia, CNBP offers a less invasive approach for BP monitoring. We found acceptable agreement for MAP defined by an ATI of 0.88 and an excellent 95% global interchangeability rate. A suboptimal bias of 7 mmHg was found with CNBP for MAP.

Revisiting the Sequence Method for Baroreflex Analysis.

The sequence method is an important approach to assess the baroreflex function, mainly because it is based on the spontaneous fluctuations of beat-by-beat arterial pressure (for example, systolic arterial pressure or SAP) and pulse interval (PI). However, some studies revealed that the baroreflex effectiveness index (BEI), calculated through the sequence method, shows an intriguing oscillatory pattern as function of the delay between SAP and PI. It has been hypothesized that this pattern is related to the respiratory influence on SAP and/or PI variability, limiting the SAP ramps to 3 or 4 beats of length. In this study, this hypothesis was tested by assessing the sequence method using raw (original) and filtered series. Results were contrasted to the well-established transfer function, estimated between SAP and PI. Continuous arterial pressure recordings were obtained from healthy rats (N = 61) and beat-by-beat series of SAP and PI were generated. Low-pass (LP) and high-pass (HP) filtered series of SAP and PI were created by filtering the original series with a cutoff frequency of 0.8 Hz. Original series were analyzed by either the sequence method or cross-spectral analysis (transfer function) at low- (LF) and high- (HF) frequency bands, while filtered series were evaluated only by the sequence method. Baroreflex sensitivity (BRS) and BEI of original series, calculated by sequence method, was highly (85–90%) determined by HP series, with no significant association between original and LP series. A high correlation (>0.7) was found between the BRS estimated from original series (sequence method) and HF band (transfer function), as well as for LP series (sequence method) and LF band (transfer function). These findings confirmed the hypothesis that the sequence method quantifies only the high-frequency components of the baroreflex, neglecting the low-frequency influences, such as the Mayer waves. Therefore, we propose using both the original and LP filtered time series for a broader assessment of the baroreflex function using the sequence method.

Estimation of the baroreflex total loop gain by the power spectral analysis of continuous arterial pressure recordings.

Baroreflex dysfunction contributes to the pathogenesis of cardiovascular diseases. The baroreflex comprises a negative feedback loop to stabilize arterial pressure (AP); its pressure-stabilizing capacity is defined as the gain ( G) of the transfer function ( H) of the baroreflex total loop. However, no method exists to evaluate G in a clinical setting. A feedback system with H attenuates pressure disturbance (PD) to PD/(1 + H). We hypothesized that the baroreflex attenuates the power spectrum density (PSD) of AP in the baroreflex functioning frequency range. We created graded baroreflex dysfunction in rats using a modified sinoaortic denervation (SAD) method [SAD; control (no SAD): n = 9; partial SAD (SAD in the right carotid sinus): n = 6, and total SAD (SAD in the bilateral carotid sinuses): n = 6] and evaluated the PSD of 12-h telemetric AP recordings in the light phase. Using the ratio of PSD at 0.01-0.1 Hz (PSD slope), we normalized them with the PSD in rats with complete baroreflex failure and derived the baroreflex index (BRI), which directly reflects G. We compared BRI and G obtained from a baroreflex open-loop experiment (reference G). The PSD slope became steeper with progression of baroreflex dysfunction. BRI (control: 2.00 ± 0.31, partial SAD: 1.28 ± 0.30, and total SAD: 0.06 ± 0.10, P < 0.05) was linearly correlated with reference G ( R2 = 0.91, P < 0.01). BRI accurately estimated G of the baroreflex and may serve as a novel tool for estimating the pressure-stabilizing capacity of the baroreflex in clinical settings. NEW & NOTEWORTHY This study proposed a novel method to estimate the gain of the baroreflex total loop, the so-called "baroreflex index" (BRI). BRI focuses on action potential variability in the frequency domain, considering baroreflex low-pass filter characteristics within 0.01-0.1 Hz. We demonstrated that BRI was linearly correlated with the reference gain of baroreflex in rats. Thus, BRI may contribute greatly to the development of a clinical tool for estimating baroreflex pressure-stabilizing capacity.

The Use of the Abdominal Aortic and Junctional Tourniquet Versus Combat Gauze in a Porcine Hemicorporectomy Model.

Junctional hemorrhage is a potentially preventable cause of death. The Abdominal Aortic and Junctional Tourniquet (AAJT) compresses major vascular structures and arrests blood flow in exsanguinating hemorrhage. In a human model, the AAJT was effective in stopping blood flow in the femoral arteries via compression of the distal aorta. This study compares the ability of AAJT and Combat Gauze (CG) to stop hemorrhagic bleeding from a hemicorporectomy in a swine model. Six anesthetized swine were used. Carotid arterial catheters were placed for continuous mean arterial pressure (MAP) readings. A hemicorporectomy was accomplished with a blade lever device by cutting the animal through both femoral heads transecting the proximal iliac arteries and veins. Hemorrhage control was attempted with the AAJT and regular Kerlix gauze or CG packing and direct pressure followed by Kerlix gauze placed over the CG. The primary outcome measure was survival at 60 minutes. The 60-minute survival was 100% for the AAJT and 0% for the CG group. During the 60-minute monitoring period, only one CG animal achieved hemostasis. For the AAJT group, the mean time to hemostasis was 30 seconds. Initial MAP was higher in the AAJT group (mean, 87mmHg) than the CG group (mean, 70mmHg). The mean 60-minute MAP was 73mmHg for the AAJT group. Mean blood loss at 5 minutes and mean total blood loss were greater in the CG group than in the AAJT group. AAJT is superior to CG in controlling hemorrhage in a junctional wound in a swine model.

Late failure of cerebral autoregulation in hypoxic-ischemic encephalopathy is associated with brain injury: a pilot study

Background: Post-resuscitation reperfusion following hypoxic-ischemia (HIE) is associated with secondary brain injury in neonates. Objective: To quantify the association between perfusion exceeding autoregulatory limits and brain injury. Approach: Continuous mean arterial blood pressure (MABP) and cerebral near-infrared spectroscopy (NIRS) data were prospectively collected from infants with HIE. Cerebral oximetry index (COx) was calculated as a moving correlation coefficient between MABP and NIRS. Upper and lower limits of autoregulation were identified by transition from negative to positive correlation. The proportion of time MABP above (hyperperfusion) and below (hypoperfusion) autoregulatory limits was calculated during therapeutic hypothermia (days 1–3). Main results: Sixteen infants were included; injury was noted in 7/16. There was no significance in hyperperfusion burden between injured and uninjured infants during day one (7% versus 10%, p = 0.88) or two (4% versus 2%, p = 0.88), but there was a marked increase for injured infants on day three (54% versus 14%, p = 0.02). There was a corollary decrease in hypoperfusion for injured versus uninjured infants on day 3 (6% versus 24%, p = 0.05). Significance: HIE infants with brain injury have a late failure of cerebral autoregulation, manifested as a hyperperfusion burden, suggesting pathologic events are active on day 3 of hypothermia. This finding may help to identify infants which might need additional neuroprotection.

An Observational Study of Cerebral Blood Flow Velocity Evaluation in the Prone Position During Posterior Lumbar Surgery.

Prone positioning (PP) is necessary for surgical access during posterior spine procedure. However, physiological changes occur in the PP. Typical findings are a decrease in arterial blood pressure and in cardiac output that could potentially lead to an alteration in cerebral perfusion. Therefore, we decided to study cerebral blood flow velocity (CBFV) with transcranial Doppler ultrasonography to evaluate the effect of the PP on cerebral hemodynamics. Twenty-two patients undergoing spine surgery in the PP were studied. General anesthesia was induced using 250 μg of fentanyl, 2 mg/kg of propofol, and 0.1 mg/kg of vecuronium, and was maintained with 0.25%-0.5% isoflurane, 50% nitrous oxide in oxygen, continuous infusion of 100 μg/kg/min of propofol, 1.5 μg/kg/h of fentanyl, and 0.15 mg/kg/h of ketamine. Continuous invasive arterial blood pressure, heart rate, electrocardiogram, and end-tidal carbon dioxide were monitored. CBFV with transcranial Doppler in the middle cerebral artery was first measured with the patients under general anesthesia in the supine position. Patients were then placed in the PP and remained in this position throughout surgery. CBFV, end-tidal carbon dioxide, heart rate, and blood pressure were measured continuously for 75 minutes after initiation of PP. This coincided with surgical exposure and minimal blood loss. Data were analyzed every 15 minutes for statistical significant change over time. Mean arterial blood pressure decreased 15 minutes after the installation of the PP and onward, but this decrease was not statistically significant. CBFVsyst (the maximal CBFV during the systolic phase of a cardiac cycle) and CBFVmean (the time averaged value of the maximal velocity envelope over 1 cardiac cycle) did not vary at any time points. CBFVdiast (the CBFV just before the acceleration phase [systole] of the next waveform) was lower at T3 (30 minutes after PP) compared to T1 (value derived averaging the first measure in the PP with the ones at 5 and 10 minutes) (P = .01), and the pulsatility index was higher at T5 (60 minutes after PP) compared to T0 (baseline, patient supine under general anesthesia) (P = .04). Data were analyzed at specific time points (T0 and T1). This value was derived by computing an average of the CBFV values collected at the first measure in the PP and at 5 and 10 minutes thereafter: T2, 15 minutes after PP; T3, 30 minutes after PP; T4, 45 minutes after PP; T5, 60 minutes after PP; and T6, 75 minutes after PP. Our data on CBFV during PP for spine surgery demonstrate preservation of cerebral perfusion during stable systemic hemodynamic conditions. The present results do not allow us to determine whether the PP would be similarly tolerated with increasing length of surgery, variations in systemic hemodynamics, and in different patient populations.

Method of deflection corrected tonometry with phantom vessel experiments

BackgroundThe Continuous Non-Invasive measurement of arterial Blood Pressure [CNIBP] is possible via the method of arterial tonometry and the arterial volume clamp methods. Arterial tonometry successfully measures continuous arterial pressure but requires large vessel deformation and a highly miniaturized pressure sensor to obtain a direct calibration of pressure. A properly designed tonometer is capable of achieving pressure accuracy of less than 5% error at the radial artery. The volume clamp method achieves comparable errors but is generally restricted to the very peripheral arteries. Since the brachial or radial arteries are preferable sites to record blood pressure, tonometry is generally preferred. However, due to its strict operating requirements, tonometry requires a highly skilled operator. The greatest source of measurement error results from slight deviation from the artery wall applanation position. In this study, a method for correcting tonometry deflection error is introduced and evaluated using preliminary experiments. Methods-modelingIn prior analysis it has been shown that arterial wall flattening causes contact stress to become uniform and equal to the arterial pressure. In this article, we derive the contact stress for deflections other than the ideal applanation position and to allow variable vessel deflection. This analysis permits the contact stress to be corrected for tonometer positions that are not exact so that pressure accuracy is maintained in spite of less than ideal positioning. This will alleviate the necessity for highly skilled users and allow rapid determination of the pulse pressure. Methods-experimentalExperiments were performed to evaluate applied model corrections for tonometer accuracy versus vessel deflection. Two experiments were performed to evaluate tonometer accuracy when deflection is varied. The first experiment used no deflection correction and the second experiment applied model derived deflection correction. A force sensor was used to deflect a phantom latex vessel of known internal pressure. The corrected contact pressure was then compared with known pressures to evaluate the pressure accuracy. Results-modelinga geometric model was derived for vessel contact area versus deflection. This resulted in a formula that provides contact area continuously for any amount of deflection. Once the contact area is known the average tonometer contact pressure was obtained that corresponds with the vessel internal pressure. Results – experimentalA latex tubing phantom vessel was pressurized to a known amount and was deflected in increments over its full diameter while measuring contact force at each position. The model-derived formula was then used to calculate pressure at each position. The calculated pressure was then compared with known internal pressure to evaluate pressure accuracy for all the phantom pressure and deflection points. ConclusionsA modeling method for tonometer deflection correction was derived and evaluated using a phantom vessel. Average error was significantly reduced over the non-corrected data. The variability of error was also reduced for all data points collected. The experiments reveal that blood pressure measurement error can be reduced to levels obtained in near ideal tonometry conditions without the need for precise position control. The relaxed user precision is anticipated to simplify the use and design requirements for arterial tonometry in practice.

3031Noninvasive identification of baroreflex function from continuous arterial pressure waveform and its clinical application

3031Noninvasive identification of baroreflex function from continuous arterial pressure waveform and its clinical application

Reconstruction of continuous brachial artery pressure wave from continuous finger arterial pressure in humans.

Generalized transfer functions (GTFs) are available to compute the more relevant proximal blood pressure (BP) waveform from a more easily measured peripheral BP waveform. However, GTFs are based on the black box model. This paper presents a practical approach to reconstruct brachial artery pressure (BAP) distally from finger artery pressure (FAP). We assume that continuous BAP can be simply approximated by summing two halves of the continuous FAP shifted by the time delay. We firstly showed that the pressure wave in the finger artery can be considered twice as much as the forward/backward wave in the finger. A simplified individualized transfer function was then derived so as to estimate BAP from FAP. The effectiveness of the method was examined by experiment involving 26 healthy volunteers (26.7 ± 3.8years old) in a resting state. By comparing with a reference BAP, we found that the proposed method can correct the FAP. The errors of the proposed method in estimating systolic and diastolic pressures are - 0.6 ± 6.0 and - 0.6 ± 3.7mmHg, respectively. These results agree with the standard of Association for the Advancement of Medical Instrumentation (AAMI). We also found that the reconstructed BAP from FAP by terminal arterial occlusion technology (TAOT) is comparable to that of the artery occlusion technology (AOT). Our method or TAOT is promising in estimating continuous proximal blood pressure from peripheral blood pressure in practice.

Carbohydrate ingestion induces differential autonomic dysregulation in normal-tension glaucoma and primary open angle glaucoma

BackgroundIt is reported that glaucoma may be associated with vascular dysregulation. Normal tension glaucoma (NTG) and primary open angle glaucoma (POAG), which feature different intraocular pressure levels, may manifest differential features of systemic autonomic dysregulation.Methods and resultsWe investigated autonomic regulation to carbohydrate ingestion and postural change in 37 glaucoma patients (19 NTG and 18 POAG) and 36 controls. Subjects were age and gender-matched, normotensive, and had normal comparable insulin sensitivity. Continuous finger arterial pressure and ECG was recorded in supine and standing positions before and after carbohydrate ingestion. Low frequency (LF, 0.04–0.15Hz) and high frequency (HF, 0.15–0.4Hz) spectral power of heart rate and systolic blood pressure variability (HRV and SBPV) were calculated to estimate sympathovagal function. Overall comparison glaucoma (N = 37) and controls (N = 36) showed an increased sympathetic excitation, vagal withdrawal and unstable mean arterial pressure after carbohydrate ingestion in glaucoma patients. Glaucoma severity by retinal nerve fibre layer (RNFL) thickness is positively correlated to autonomic responses (HRV LF power and HF power in normalised units (nu), and HRV LF/HF ratio) after carbohydrate ingestion. Early (30 minutes) following carbohydrate ingestion, SBP LF power and HRV parameters remained unchanged in controls; while POAG showed abnormal autonomic responses, with a paradoxical vagal enhancement (increased HRV HF power in nu) and sympathetic inhibition (decreased HRV LF power nu and HRV LF/HF ratio), and associated hypotension. Later (60–120 minutes) following carbohydrate ingestion, HRV parameters remained unaltered in controls; whereas NTG manifested vagal withdrawal (reduced HRV HF power nu) and sympathetic hyper-responsiveness (increased HRV LF power nu and HRV LF/HF ratio), despite increased SBP LF power in both controls and NTG. Both NTG and POAG exhibited attenuated autonomic responses to postural stress.ConclusionsNTG and POAG both manifest some systemic autonomic cardiovascular dysregulation. However, the two forms of glaucoma respond differentially to carbohydrate ingestion, irrespective of insulin resistance.