Carotid Arterial Pressure Research Articles

The effect of intermittent intraabdominal pressure elevations and low cardiac output on the femoral to carotid arterial blood pressure difference in piglets.

Our previous work in a laparoscopic setting in piglets revealed that the systolic femoral artery pressure was approximately 5% higher than its carotid counterpart, whereas the mean and diastolic values showed no significant difference. This remained idem when the intraabdominal pressure (IAP) was gradually increased. In this study, we aimed to investigate the effect of (1) intermittent IAP elevations and (2) a low cardiac output (CO) on the blood pressure (BP) difference cranially (carotid artery) and caudally (femoral artery) of a capnoperitoneum (ΔP=P a fem-P a carot). A total of twenty-two piglets (mean body weight 11.0kg; range 8.9-13.3kg) were studied. Of these, 14 underwent intermittent IAP elevations at 8 and 16mmHg, and ΔP was measured. In another 8 piglets, a model of reduced CO was created by introducing an air embolism (2ml/kg over 30s) in the inferior caval vein (VCI) at 12mmHg IAP to further assess the influence of this variable on ΔP. Systolic ΔP remained at a mean of 5.6mmHg and was not significantly affected by insufflation or exsufflation up to an IAP of 16mmHg. Diastolic and mean values showed no differences between P a carot and P a fem. P a fem, systol remained higher than its carotid counterpart as long as the cardiac index (CI) was above 1.5l/min/m2, but fell significantly below P a carot, systol at a low CI. There was no CO-dependent effect on diastolic and mean ΔP. Repeated IAP elevations do not significantly influence ΔP. Intermittent IAP elevations do not significantly influence ΔP. Despite of a CO-dependent inversion of systolic ΔP, mean BP measurements at the leg during laparoscopy remain representative even at low CO values.

The Relationship between Carotid Stump Pressure and Changes in Motor-Evoked Potentials in Carotid Endarterectomy Patients.

Background The threshold of ischemic tolerance has not been completely identified in human clinical studies. Distal carotid artery pressure can be easily measured through the internal shunt tube during carotid endarterectomy (CEA). To confirm the critical threshold of intracranial arterial pressure and its maximum duration, we investigated the distal internal carotid artery (ICA) pressure and motor-evoked potential (MEP) changes during ICA clamping. Material and Methods Between September 2012 and March 2014, 9 patients (10 sides) with carotid stenosis (70-99%) were surgically treated at our hospital. All CEAs were performed under general anesthesia, and we routinely used a carotid shunt with the intraoperative MEP monitors. When the MEP amplitude decreased to < 50% of the control during carotid clamping, the MEP amplitude was defined as significantly reduced. Results The MEP amplitude significantly decreased in 2 of the 10 procedures (20%) during ICA clamping. The mean distal ICA pressure varied widely, ranging from 13 to 48 mm Hg. In seven cases with a mean distal ICA pressure > 20 mm Hg, there were no significant changes in the MEP during ICA clamping. However, there were three cases with a mean distal ICA pressure < 20 mm Hg, and the MEP amplitude significantly decreased in two of those three patients from 4 to 5 minutes after clamping. Conclusions The present study provides considerable information about a higher incidence of MEP amplitude deterioration in CEA patients with a mean distal ICA pressure < 20 mm Hg during ICA clamping.

Role of catestatin in 2K1C-induced renal hypertension in rats and the underlying mechanism

To investigate the roles of catestatin (CST) in 2-kidney-1 clip (2K1C)-induced renal hypertension in rats, and to explore the underlying mechanism. Thirty six male SD rats were randomly divided into Sham group (n=15) and Model group(n=21).The model group was performed by 2K1C operation. For 2K1C operation, the left renal arteries were narrowed by cotton thread. The Sham group was treated with the same condition as the 2K1C group except the renal artery was narrowed. Tail-cuff systemic blood pressure of rats was measured before and every weeks after 2K1C operation. Six weeks after 2K1C operation, a carotid artery catheter was inserted to measure blood pressure of rats under anesthesia. Then, the model group was randomly subdivided into 2K1C group (n=15) and 2K1C+CST group (n=6). The rats of 2K1C+CST group were intravenous given CST (80 μg/100 g) and the rats of Sham or 2K1C group were given normal saline. All rats were sacrificed after blood pressure was measured and blood was collected. Then, the left ventricular plus interventricular septum weight (LV+S) was weighted and the ratio of (LV+S)/body weight(BW) was calculated as the index of left ventricular hypertrophy. Norepinephrine (NE) contents in plasma were determined by high performance liquid chromatography(HPLC) and CST contents in plasma by ELISA. The nitrite/nitrate contents in the left ventricular tissue and plasma were measured by nitrate reduction method to represent nitric oxide (NO)contents.Expression levels of CST in the left ventricle, kidney, medulla oblongata and adrenal gland,as well as eNOS and iNOS, were tested by Western blot. ①The 2K1C group had higher tail-artery blood pressure(P<0.01) and were more marked presence of right ventricular hypertrophy than those of sham group (P<0.01). Compared with Sham group, plasma CST content in 2K1C group was decreased by 226% (P<0.01), while plasma NE content in 2K1C group was increased by 246% (P<0.01), expression levels of chromograminA(Chga) in medulla oblongata of 2K1C group were increased by 108%, in leftventricle and kidneywere decreased by 60% and 30%, respectively (P<0.05).the content of NO in left ventricular and plasmawere increased by 46% and 24% respectively. ②The carotid arterial blood pressure of 2K1C group markedly reduced after administration of CST.③Compared with 2K1C group, the content of NO in left ventricul and plasma of 2K1C+CST group were increased by 35% and 19% respectively(P<0.05). The expression of eNOS in left ventricular of 2K1C+CST group were also obviously increased. The CST expression of 2K1C-induced renal hypertension rats is reduced and the effects of exogenous CST lowering their blood pressure may be related to NO/NOS system.Therefore, we speculate CST could contribute to the pathogenesis and progression of renal hypertension.

Cardiovascular Adaptation in Response to Chronic Hypoxia in Awake Rats.

To examine how cardiovascular adaptation to chronic hypoxia might evolve, the responses to blood pressure (Pt) and hematocrit (Ht) during long-term systemic exposure to hypoxia were observed in awake rats. Furthermore, the total peripheral vascular resistance (TPR) was estimated using direct measurements of systemic blood pressure (Ps) and blood flow (Qs) in carotid artery based on Darcy's law (TPR=Ps/Qs) to evaluate the remodeling procedure in the microcirculation. BP and Ht under normoxic conditions were kept almost constant, while hypoxic exposure immediately increased Ht to 58% and, thereafter, it remained stable. The TPR values showed no significant differences between hypoxic and normoxic conditions. These results suggest that effects of high viscosity caused by increasing Ht on peripheral vascular resistance can be compensated by inducing microvascular remodeling with the arteriolar dilation and capillary angiogenesis.

Risk factors for neurological worsening and symptomatic watershed infarction in internal carotid artery aneurysm treated by extracranial-intracranial bypass using radial artery graft.

OBJECT The revascularization technique, including bypass created using the external carotid artery (ECA), radial artery (RA), and M2 portion of middle cerebral artery (MCA), has remained indispensable for treatment of complex aneurysms. To date, it remains unknown whether diameters of the RA, superficial temporal artery (STA), and C2 portion of the internal carotid artery (ICA) and intraoperative MCA blood pressure have influences on the outcome and the symptomatic watershed infarction (WI). The aim of the present study was to evaluate the factors for the symptomatic WI and neurological worsening in patients treated by ECA-RA-M2 bypass for complex ICA aneurysm with therapeutic ICA occlusion. METHODS The authors measured the sizes of vessels (RA, C2, M2, and STA) and intraoperative MCA blood pressure (initial, after ICA occlusion, and after releasing the RA graft bypass) in 37 patients. Symptomatic WI was defined as presence of the following: postoperative new neurological deficits, WI on postoperative diffusion-weighted imaging, and ipsilateral cerebral blood flow reduction on SPECT. Neurological worsening was defined as the increase in 1 or more modified Rankin Scale scores. First, the authors performed receiver operating characteristic curve analysis for continuous variables and the binary end point of the symptomatic WI. The clinical, radiological, and physiological characteristics of patients with and without the symptomatic WI were compared using the log-rank test. Then, the authors compared the variables between patients with and without neurological worsening at discharge and at the 12-month follow-up examination or last hospital visit. RESULTS Symptomatic WI was observed in 2 (5.4%) patients. The mean MCA pressure after releasing the RA graft (< 55 mm Hg; p = 0.017), mean (MCA pressure after releasing the RA graft)/(initial MCA pressure) (< 0.70 mm Hg; p = 0.032), and mean cross-sectional area ratio ([RA/C2 diameter](2) < 0.40 mm [p < 0.0001] and [STA/C2 diameter](2) < 0.044 mm [p < 0.0001]) were related to the symptomatic WI. All preoperatively independent patients remained independent (modified Rankin Scale score < 3). After adjusting for age and sex, left operative side (p = 0.0090 and 0.038) and perforating artery ischemia (p = 0.0050 and 0.022) were related to neurological worsening at discharge (11 [29%] patients) and at the 12-month follow-up or last hospital visit (8 [22%] patients). CONCLUSIONS Results of the present study showed that the vessel diameter and intraoperative MCA pressure had impacts on the symptomatic WI and that operative side and perforating artery ischemia were related to neurological worsening in patients with complex ICA aneurysms treated by ECA-RA-M2 bypass.

혈관 유연성을 고려한 경동맥 분기부 모델 혈류역학 해석

Blood flow simulations in an realistic carotid bifurcation model with considering wall compliance were carried out to investigate the effect of wall elasticity on the wall shear stress and wall solid stress. Canonical waveforms of flow rates and pressure in carotid arteries were imposed for boundary conditions. Compared to a rigid wall model, we found an increased recirculation region at the carotid bulb and an overall reduction of wall shear stress in a compliant model. Additionally, there was appreciable change of flow rate and pressure wave in longitudinal direction. Both solid and wall shear stress concentration occur at the bifurcation apex.

Carotid artery corrected flow time measurement via bedside ultrasonography in monitoring volume status

PurposeThe purpose of this study is to investigate the possible correlation between corrected flow time (FTc) in carotid artery and changes in volume status. Materials and methodsNinety-three patients with end-stage renal failure who underwent fluid removal via hemodialysis were enrolled prospectively. The volume of fluid removed as well as prehemodialysis and posthemodialysis measures of FTc in the carotid artery, heart rate, and mean arterial pressure was evaluated. All imaging measurements were performed with patients at supine position, 15 minutes before and after the hemodialysis session, by evaluating the right common carotid artery at the level of the lower border of thyroid cartilage. ResultsThe mean FTc before fluid removal was 345.07 ± 37.19 milliseconds. This measure decreased significantly after the volume removal with a posthemodialysis mean of 307.77 ± 31.76 milliseconds (P < .0001). There was a statistically significant and negative association between the volume of fluid removed by hemodialysis and the changes in FTc (Pearson correlation, −0.39; P < .0001). ConclusionThe assessment of changes in FTc of carotid artery via Doppler waveform analysis may predict the changes in intravascular volume. The use of this diagnostic modality may be an accurate and noninvasive alternative to currently available methods.

Hypotensive effect of alpha-lipoic acid after a single administration in rats

Objective:The effect of alpha-lipoic acid on blood pressure was investigated many times in chronic studies, but there are no studies on the effect of this compound after a single administration. Alpha-lipoic acid is a drug used in diabetic neuropathy, often in obese patients, to treat hypertension. Therefore, knowledge of the potential antihypertensive effect of alpha-lipoic acid even after a single dose and possibly too much pressure reduction is interesting and useful.Methods:The mechanism of the hypotensive effect of alpha-lipoic acid was examined in normotensive rats in vivo after a single intraperitoneal administration, blood pressure in the left carotid artery of the rats was measured prior to the administration of the compounds (alpha- lipoic acid and/or glibenclamide) and 80 min thereafter.Results:Alpha-lipoic acid at a dosage of 50 mg/kg b.w. i.p. significantly decreased the blood pressure from the 50th min after drug administration. This cardiovascular effect of this compound was reversed by glibenclamide, a selective KATP blocker. Glibenclamide alone at this dose did not significantly affect the blood pressure. Statistical significance was evaluated using two-way ANOVA.Conclusion:This suggests that alpha-lipoic acid affects ATP-dependent potassium channels. It is possible that this is an indirect effect of hydrogen sulfide because alpha-lipoic acid can increase its concentration. The results obtained in this study are very important because the patients taking alpha-lipoic acid may be treated for co-existing hypertension. Therefore, the possibility of blood pressure lowering by alpha-lipoic acid should be taken into account, although it does not lead to excessive orthostatic hypotension.

Effects of chest compressions on cardiovascular and cerebral hemodynamics in asphyxiated near-term lambs.

Chest compressions (CC) and adrenaline administration are recommended in asphyxiated newborns with persistent bradycardia despite effective ventilation. The effects of CC on cerebral blood flow in newborns at birth are unknown. Our aim was to determine the effects of CC, with or without adrenaline administration, on the return of spontaneous circulation, carotid blood flow (CBF), and carotid arterial pressure (CAP) in asphyxiated near-term lambs. Asphyxia was induced in near-term lambs by clamping the umbilical cord and delaying ventilation onset until spontaneous circulation ceased. Lambs were then resuscitated by positive pressure ventilation along with CC followed by adrenaline administration. CAP and CBF were continuously recorded. Mean CAP did not increase significantly during CC and only increased following adrenaline administration. CC did not increase mean CBF but increased CBF amplitude due to increased peak flow and the onset of retrograde flow during diastole. Adrenaline increased mean CBF from 1 ± 2 to 15 ± 5 ml/kg/min and abolished retrograde diastolic CBF, leading to the return in spontaneous circulation. We conclude that CC with adrenaline administration was required to increase CBF and restore spontaneous circulation in asphyxiated lambs. Low CBF and retrograde diastolic CBF during CC indicate hypoperfusion to the brain.

Carotid Artery Applanation Tonometry Does Not Cause Significant Baroreceptor Activation.

Carotid artery applanation tonometry is widely used in estimating local carotid artery pressure waveforms and carotid-femoral pulse wave velocity. However, the substantial pressure applied locally to the carotid artery with applanation tonometry might well evoke a baroreceptor response, resulting in bradycardia and hypotension. Therefore, when carotid and femoral tonometry are performed sequentially, baroreceptor activation could lead to different hemodynamic conditions between carotid and femoral acquisitions. Combining those acquisitions into one pulse wave velocity measure would be erroneous. In this study, we assessed whether carotid applanation tonometry has an influence on heart rate and blood pressure. In 26 hypertensive subjects, heart rate and blood pressure were assessed by continuous finger pulse waveform recording during carotid as well as femoral applanation tonometry. Both carotid and femoral acquisitions were measured in alternation and in triplicate. Median averaging over the 3 carotid and femoral measurements, respectively, was used to obtain a subject's median heart rate and blood pressure during carotid as well as femoral tonometry. Difference in heart rate during carotid and femoral tonometry was -0.7±2.2 bpm. Differences in systolic, pulse, and diastolic blood pressure were -0.7±6.8, -0.1±3.8, and -0.3±3.5mm Hg, respectively. All differences were statistically nonsignificant. Confidence intervals were used to calculate the maximum absolute difference at 95% certainty, which was 1.6 bpm for heart rate and ≤3.5mm Hg for all blood pressures. We conclude that in our study, carotid artery applanation tonometry as performed by an experienced researcher did not cause clinically significant baroreceptor activation.

The effect of oxygen content during an initial sustained inflation on heart rate in asphyxiated near-term lambs

ObjectiveAt birth, an initial sustained inflation (SI) uniformly aerates the lungs, increases arterial oxygenation and rapidly improves circulatory recovery in asphyxiated newborns. We hypothesised that lung aeration, in the absence...

Telemetric Recording of Renal and Carotid Blood Flow Velocity and Arterial Blood Pressure Simultaneously in Rats

Hypertension‐induced barotrauma without or with concomitant vasoconstriction, tissue ischemia and hypoxia has been postulated to initiate and drive the pathogenic cascades that lead to hypertension induced tissue injury. Yet the precise temporal relationship between arterial pressure and tissue blood flow over time as causative mechanisms for barotrauma remain unresolved and controversial. A major technical limitation has been the absence of methods allowing simultaneous high fidelity long‐term measurement of blood flow and arterial pressure in conscious animals. Transonic has developed a cutting edge technology to continuously evaluate arterial blood pressure and two blood flow velocity's simultaneously in conscious rats. Here, we report the first demonstration of recording renal and carotid blood flow and arterial pressure using this new multi‐variable telemetric system. A solid state pressure sensor was placed in the abdominal aorta and 0.8mm and 0.5mm in diameter flow probes were sutured on the renal and carotid artery, respectively, in Wistar rats. Both flow velocity signals correlated with the arterial pressure signal and exhibited constant lag times. After 5 min of carbogen breathing carotid vascular resistance decreased by 31±4% while renal vascular resistance decreased by 7±1%. These experiments demonstrate the feasibility of the technique for high fidelity temporal profiling of both blood pressure and blood flows to renal and carotid vascular beds simultaneously in conscious rats. British Heart Foundation funded research.

0159 : Increased NOX4 expression in mice knockdown of angiopoietin-like 2 worsens pressure overload-induced cardiac dysfunction but preserves vascular endothelial integrity

Angiopoietin-like 2 (angptl2) is a pro-inflammatory and pro-oxidative protein that induces endothelial dysfunction in mice. The impact of angptl2 on cardiac function is still unknown. We hypothesized that angptl2 could contribute to cardiac dysfunction and that knocking-down angptl2 would be protective against pressure overload. We investigated both cardiac and vascular endothelial functions in angptl2 knockdown mice (KD) versus wild-type (WT) littermates, in response to a 6-week pressure overload induced by transverse aortic constriction (TAC). TAC increased systolic pressure in the right carotid artery by 60% in WT, but only 28% in KD mice. In TAC-WT, but not in -KD mice, carotid and posterior cerebral arteries isolated from the highpressure right side displayed increased wall thickness, a remodeling associated with endothelial dysfunction. In contrast, and contrary to our hypothesis, TAC induced a more severe cardiac remodeling in KD than in WT mice: TAC-KD mice displayed a greater heart weight / tibia length ratio, as well as a higher gene expression of hypertrophic remodeling molecular markers, (ANP, BNP, MyoHβ/MyoHα) when compared to TAC-WT mice. Cardiac function measured by Millar catheter also showed greater alteration of the left ventricular relaxation in TAC-KD mice (increased minimal and end diastolic pressures, 25% reduced relaxation rate), suggesting cardiac contractile dysfunction. Finally, we observed, only in hearts from TAC-KD mice, an increase in mRNA and protein expression of NOX4 which is known to produce H 2 O 2 , a deleterious hypertrophic stimulus in cardiomyocytes, but is a vasodilatory factor. This is the first demonstration that angptl2 knockdown paradoxically worsens cardiac hypertrophy and contractile dysfunction induced by pressure overload, contrasting with the preserved arterial wall structure and endothelial integrity. Up-regulation of NOX4 could, at least partly, contribute to these opposite effects in angptl2 KD mice.

Reduced Common Carotid Artery Blood Flow in Spontaneously Hypertensive Rats is Unaffected by Aging and/or Chronic In Vivo Resveratrol Treatment

This study examined common carotid artery (CCA) blood flow (using a perivascular flowprobe) and pressure (using a catheter‐tip transducer) in anesthetized Adult (20‐24 wk old) and Aging (60‐70 wk old) Wistar Kyoto rats (WKY) and Spontaneously Hypertensive rats (SHR) following 28‐days of in vivo treatment (in drinking water, ab libitum) with either no trans resveratrol (RSV; No‐RSV), a moderate RSV dose (Mod‐RSV; ~0.075 mg/kg/day; to mimic daily red wine consumption), or a high RSV dose (High‐RSV; ~7.5 mg/kg/day). CCA mean, maximal systolic, minimum diastolic, and pulse pressure, and heart rate, were all significantly elevated in SHR vs. WKY (p&lt;0.01). Aging was associated with a significant increase in pulse pressure in WKY (p&lt;0.01). CCA mean, maximal systolic, and minimum diastolic blood flow, and vascular conductance, were all significantly reduced in SHR vs. WKY (p&lt;0.05). Aging did not have a significant effect on the flow parameters in either SHR or WKY. Neither Mod‐RSV nor High‐RSV treatment had a significant effect on the CCA blood pressure and blood flow variables measured. These data demonstrate that the reduction in CCA blood flow found in SHR is unaffected by aging or chronic in vivo RSV treatment. Further investigation into what can account for and alter the reduced CCA blood flow found in SHR is warranted.Funded by NSERC.

Critical buckling pressure in mouse carotid arteries with altered elastic fibers

Arteries can buckle axially under applied critical buckling pressure due to a mechanical instability. Buckling can cause arterial tortuosity leading to flow irregularities and stroke. Genetic mutations in elastic fiber proteins are associated with arterial tortuosity in humans and mice, and may be the result of alterations in critical buckling pressure. Hence, the objective of this study is to investigate how genetic defects in elastic fibers affect buckling pressure. We use mouse models of human disease with reduced amounts of elastin (Eln+/−) and with defects in elastic fiber assembly due to the absence of fibulin-5 (Fbln5−/−). We find that Eln+/− arteries have reduced buckling pressure compared to their wild-type controls. Fbln5−/− arteries have similar buckling pressure to wild-type at low axial stretch, but increased buckling pressure at high stretch. We fit material parameters to mechanical test data for Eln+/−, Fbln5−/− and wild-type arteries using Fung and four-fiber strain energy functions. Fitted parameters are used to predict theoretical buckling pressure based on equilibrium of an inflated, buckled, thick-walled cylinder. In general, the theoretical predictions underestimate the buckling pressure at low axial stretch and overestimate the buckling pressure at high stretch. The theoretical predictions with both models replicate the increased buckling pressure at high stretch for Fbln5−/− arteries, but the four-fiber model predictions best match the experimental trends in buckling pressure changes with axial stretch. This study provides experimental and theoretical methods for further investigating the influence of genetic mutations in elastic fibers on buckling behavior and the development of arterial tortuosity.

Effects of baicalin on collagen Ι and collagen ΙΙΙ expression in pulmonary arteries of rats with hypoxic pulmonary hypertension.

The synthesis and accumulation of collagen play an important role in the formation and progression of hypoxic pulmonary hypertension. Baicalin has been reported to prevent bleomycin-induced pulmonary fibrosis. However, the role of baicalin in the treatment of pulmonary hypertension remains unknown. A disintegrin and metalloprotease with thrombospondin type-1 motif (ADAMTS-1) is a secreted enzyme that acts on a wide variety of extracellular matrix (ECM) substrates associated with vascular diseases. In this study, we aimed to investigate the effects of baicalin on the synthesis of collagen I in rats with pulmonary hypertension induced by hypoxia and the changes in ADAMTS-1 expression. A total of 24 Sprague Dawley rats were randomly assigned to 3 groups as follows: the control group (C), the hypoxia group (H) and the hypoxia + baicalin group (B). The rats in groups H and B were kept in a normobaric hypoxic chamber for 4 weeks, and the rats in group C were exposed to room air. We measured the hemodynamic indexes, including mean pulmonary artery pressure (mPAP), mean systemic (carotid) artery pressure (mSAP), and then calculated the mass ratio of right ventricle to left ventricle plus septum [RV/(LV + S)] to reflect the extent of right ventricular hypertrophy. We measured the mRNA and protein expression levels of type I collagen, type III collagen and ADAMTS-1 by hybridization in situ, and immunohistochemistry and western blot analysis, respectively. The results revealed that treatment with baicalin significantly reduced pulmonary artery pressure and attenuated the remodeling of the pulmonary artery under hypoxic conditions by increasing the expression of ADAMTS-1, so that the synthesis of type I collagen and its mRNA expression were inhibited. In conclusion, baicalin effectively inhibits the synthesis of collagen I in pulmonary arteries and this is associated with an increase in the expression of ADAMTS-1. Thus, treatment with baicalin may be an effective method for lowering pulmonary artery pressure and preventing pulmonary artery remodeling.

A preliminary study on cerebellar acetylcholine-mediated blood pressure regulation in young and old rats

Cholinergic innervation of the cerebellar cortex can modulate cerebellar functions. However, the role of acetylcholine (ACh) in cerebellar regulation of blood pressure (BP) has not been examined. Moreover, the effect of aging on this regulation remains unexplored. In this study, carotid arterial pressure was measured in young (2months) and old (16–20months) rats after ACh was microinjected into the cerebellar cortex. The results show a concentration-dependent effect of ACh (30, 100, and 300mM) on mean arterial pressure (MAP), maximal decreased MAP (MDMAP) and reactive time (all Ps<0.05). However, responses in the old animals were significantly attenuated compared to the young (Ps<0.05). The results indicate that cerebellar cholinergic innervation exerts depressor effects on BP regulation, and such effects undergo retrogression with aging. Further studies concerning the mechanism are needed to confirm these preliminary findings.

Evaluation of accuracy of invasive and non-invasive blood pressure monitoring in relation to carotid artery pressure in anaesthetised ponies

Invasive blood pressure measurement (IBP) using peripheral arteries is a commonly used technique in equine anaesthesia, although the accuracy has not been demonstrated. Non-invasive blood pressure monitoring (NIBP) may be indicated for field anesthesia, short procedures and foal anaesthesia. In the present report, the agreement of various IBP and NIBP measuring sites compared to carotid artery pressure was tested in anaesthetised experimental ponies. Six ponies were anaesthetised in lateral recumbency with sevoflurane and received either saline or dexmedetomidine boli followed by constant rate infusion (CRI). Invasive blood pressure measurements were obtained simultaneously from the carotid, facial and metatarsal arteries. NIBP measurements over both median arteries, metatarsal and middle coccygeal arteries were performed in random order. All blood pressure readings obtained were compared to carotid pressure by Bland-Altman analysis. Non-invasive blood pressure measurements had larger bias and poorer limits of agreement compared to IBP measurements. NIBP measurement from the coccygeal artery had the best repeatability and best limits of agreement of all NIBP positions and was not affected by the use of dexmedetomidine. The facial artery had smaller limits of agreement with dexmedetomidine treatment. There was no difference between the facial and metatarsal arteries during dexmedetomidine treatment in MAP and DAP. Systolic arterial pressures from the metatarsal artery showed larger bias and larger limits of agreement compared to facial artery. In conclusion, NIBP measurement from the tail artery is a reliable alternative to direct arterial blood pressure measurement. Both the metatarsal and facial arteries have acceptable agreement with carotid artery pressure so the choice can be based on the logistics of the procedure.

Biomechanical model of cerebral vascular dynamics and their effect on CSF dynamics

With advancing age venous wall thickness increases going along with a loss of elastic properties, the arterioles curl and capillary density decreases leading to a reduction of cross sectional area [1]. Even in healthy individuals these changes influence vascular and CSF dynamics, as a reduction of total cerebral blood flow, aqueduct and cervical stroke volume are reported [2]. In NPH these dynamics seem to be altered in a different way, as aqueduct stroke volume [2] and ICP amplitude are increased and arteriovenous delay is drastically reduced compared to normal aging [3]. However it is not clear in what way the described vascular alterations influence the pressure propagation inside the vessels and impact CSF dynamics. So far no biomechanical model exists that investigates the influence of macroscopic and microscopic changes of cerebral blood vessels. That is why we put a model up for discussion that simulates vascular pressure propagation and enables the investigation of altered vascular properties in the context of NPH. A Matlab Simulink model was developed reproducing each vessel section by a distensible compartment. Therefore the cerebral vascular tree was divided into 13 sections from carotid artery to venous sinuses and the pulsatile carotid artery and sinus pressure were inputted as Fourier series. The cross sectional area was varied according to literature data and flow resistance was implemented taking into account the rheological characteristics of blood. The Windkessel function and relaxation properties of vascular walls were integrated by a Voigt model, enabling the variation of wall properties for each section individually. Due to the distensible vessel walls each section interacts with the CSF compartment and autoregulation was implemented by a simple proportional controller. After parameterisation mean pressure and pressure amplitude in the vessel sections showed good accordance with literature values [4]. We have proposed a model of vascular dynamics that is able to identify the impact of altered vascular wall properties and structural changes. Furthermore the effect of different arterial and venous input pressure profiles can be analysed. These parameter analyses are part of our ongoing research.

Piezoelectric sensor to non-invasively detect age associated changes in human carotid pulse

The arterial pressure waveform reflects the physics of blood flow in the arterial tree. There are definite changes that occur in the vasculature with age and cause changes in the shape of arterial waveforms. These changes are mainly attributed to increase in the pulse wave velocity caused by the arterial stiffness that causes the reflected wave to return early. Arterial waveforms can be used to non-invasively detect the condition of the cardiac system. There are various methods that have been used to non-invasively detect the arterial pressure waveform like the applanation tonometry, ausculcatory method, palpatory method etc. The developed work presents a simple and cost-effective method wherein carotid artery pressure waveform of subjects of different age groups is recorded using piezoelectric sensor and then analysed using MATLAB to find the systolic, diastolic and inflection points. These points are used to calculate augmentation index and find the changes that occur in the augmentation index with age.