Recording Of Blood Flow Research Articles

Time–Frequency Approaches for the Detection of Interactions and Temporal Properties in Renal Autoregulation

We compare the influence of time-frequency methods on analysis of time-varying renal autoregulation properties. Particularly, we examine if detection probabilities are similar for amplitude and frequency modulation for a modulated simulation signal among five time-frequency approaches, and if time-varying changes in system gain are detected using four approaches for estimating time-varying transfer functions. Detection of amplitude and frequency modulation varied among methods and was dependent upon background noise added to the simulated data. Three non-parametric time-frequency methods accurately detected modulation at low frequencies across noise levels but not high frequencies; while the converse was true for a fourth, and a fifth non-parametric approach was not capable of modulation detection. When applied to estimation of time-varying transfer functions, the parametric approach provided the most accurate estimations of system gain changes, detecting a 1dB step increase. Application of the appropriate methods to laser Doppler recordings of cortical blood flow and arterial pressure data in anesthetized rats reaffirm the presence of time-varying dynamics in renal autoregulation. An increase in the peak system gain and detection of amplitude modulation of the Myogenic mechanism both occurred after inhibition of nitric oxide synthase, suggesting a connection between the operation of underlying regulators and system performance.

Peripheral Microcirculation and Endothelial Function in Comas Induced by Acute Cerebrovascular Accident

Objective: to study the state of systemic microcirculation and endothelial function in comas induced by acute cerebrovascular accident (ACA). Subjects and methods. The study was conducted within the first 7 days of ACA in 38 coma patients, who were divided into groups according to the etiology of stroke: Group 1 comprised 20 patients with hemorrhagic stroke; their mean age was 56.6±2.3 years; Group 2 consisted of 18 patients with ischemic stroke; their mean age was 58.5±2.2 years. A control group included 34 apparently healthy individuals; their mean age was 55.1±2.1 years. The microcirculatory bed was evaluated within 7 days, by applying cutaneous laser Doppler flowmetry using a LAKK-02 capillary blood flow laser analyzer made in Russia (LAZMA Research-and-Production Association, the Russian Federation). Coincidentally with recording of the microcirculatory blood flow, blood samples were collected to explore the serum concentrations of endothelin-1, stable nitric oxide metabolites, van Willebrand factor, and thrombomodulin. Results. Throughout the study, the patients with coma induced by ACA were found to have microcirculatory disorders consisting in higher microperfusion along with the markedly increased influence of active modulators of vascular tone, as well as endothelial functional structural changes. Conclusion. The data obtained in the study suggest that there were uniform changes in the state and regulation of systemic microcirculation in patients with ACA irrespective of the type of stroke (hemorrhagic or ischemic). Key words: stroke, microcirculation, microvascular bed, micro blood flow, tissue perfusion, endothelium.

Recording of Amplitude-Integrated Electroencephalography, Oxygen Saturation, Pulse Rate, and Cerebral Blood Flow during Massage of Premature Infants

Stimulation of the nervous system plays an important role in brain function and psychomotor development of children. Massage can benefit premature infants, but has limitations. The authors conducted a study to verify the direct effects of massage on amplitude-integrated electroencephalography (aEEG), oxygen saturation (SaO(2)), and pulse analyzed by color cerebral function monitor (CCFM) and cerebral blood flow assessed by the Doppler technique. The amplitude of the aEEG trend during massage significantly increased. Massage also impacted the dominant frequency δ waves. Frequency significantly increased during the massage and return to baseline after treatment. SaO(2) significantly decreased during massage. In four premature infants, massage was discontinued due to desaturation below 85%. Pulse frequency during the massage decreased but remained within physiological limits of greater than 100 beats per minute in all infants. Doppler flow values in the anterior cerebral artery measured before and after massage did not show statistically significant changes. Resistance index after massage decreased, which might provide greater perfusion of the brain, but this difference was not statistically significant. Use of the CCFM device allows for monitoring of three basic physiologic functions, namely aEEG, SaO(2), and pulse, and increases the safety of massage in preterm infants.

Involvement of the Median Preoptic Nucleus in the arterial blood pressure regulation

Studies have been shown that Median Preoptic Nucleus (MnPO) neurons have a great influence in the cardiovascular responses induced by changes in circulating volume. The present study sought to determine the participation of MnPO in the cardiovascular control. Male Wistar normotensive (NT) and spontaneously hypertensive (SH) rats (280–320g) were anesthetized with urethane (1.2 g/kg, i.v.) and instrumented for mean arterial blood pressure (MAP) and renal blood flow (RBF) recordings. Renal vascular conductance (RVC) was calculated as the ratio RBF/MAP and expressed as percentage of baseline. In NT rats (n=7), inhibition of MnPO nucleus produced a significant hypotension (−7 ± 1.5 mmHg) and renal vasodilation (5.3 ± 1.2% above baseline). In SH rats (n=8), hypotension response was significantly greater (−15 ± 2.7 mmHg, p<0.05) than NT rats. We also observed an increase of RVC (8.4 ± 2.4% above baseline) in HT rats. Analysis of the spread of dye nanoinjected at the end of the experiment showed that the drug injection sites were confined to the MnPO. We conclude that the MnPO nucleus is involved in the tonic regulation of blood pressure in NT rats. Moreover, the increase of neuronal activity in the MnPO may contribute to sympathoexcitation and maintenance of hypertension in SH rats. Supported by CNPq (477832/2010‐5; GRP).

Application of implantable telemetry in swine heart failure models

Swine animal models are commonly used to study the mechanism of heart failure (HF) and to develop new therapies. Continuous recordings of blood flow, ventricular and systemic blood pressures in awake, free‐roaming animals without the effects of anesthesia will provide valuable data on the progression and treatment of HF. The objective of this study was to evaluate simultaneous, totally implantable, telemetric measurements of these parameters in swine HF models. Solid‐state blood pressure catheters were placed in the right or left ventricle and descending aorta for pressure measurements while Doppler probes were placed around the LAD and branchocephalic arteries for blood flow velocity measurements. ECG electrodes were attached to the left ventricle. Each telemetry unit was implanted subcutaneously for up to 6 weeks into various HF models including A‐V fistula, aortic banding and high‐rate pacing. Sudden and chronic changes of hemodynamics were captured during the progression of HF. Systemic pressure progressively decreased within first 2 weeks in HF with pacing and recovered by 4 weeks; while the pressure increased progressively in HF with aortic banding for 4 weeks. The pressure did not significantly change within first 4 weeks, but LAD flow increased within 2 weeks in animals with A‐V fistula. The results showed that this biotelemetry system is capable of long‐term accurate monitoring of simultaneous blood flow, pressure and ECG. This system will have significant utility in chronic models of cardiovascular physiology and pathology.

The Effect of Exercise on Pulpal and Gingival Blood Flow in Physically Active and Inactive Subjects as Assessed by Laser Doppler

The effects of exercise on pulpal and gingival blood flow are undefined. The autonomic nervous system response suggests that they could increase or decrease with exercise, and they may be independent of each other. This study attempts to answer these questions.Materials and Methods:15 “physically active” subjects and 15 “physically inactive” subjects exercised on a treadmill. Laser Doppler recordings of pulpal and gingival blood flow were taken before and after exercise.Results:There was a mean increase of approximately 50% in both pulpal (range -66%-+509%) and gingival (-72%- +1022%) blood flow after exercise, with wide variations, with no significant differences between the two groups of subjects.Conclusion:Exercise could increase pulpal and/or gingival blood flow as part of the overall increase in cardiac output with exercise, or could decrease pulpal and/or gingival blood flow due to diversion of blood to the somatic muscles during exercise. This study suggests that the former physiological phenomenon usually takes place at both sites,though there were some contradictory results.

Anti-Angiogenic Effect of P2X7 Receptor Antagonist Oxidized ATP as a Mechanism of Anti-Tumor Growth

Extracellular ATP accumulated in tumor microenvironment activates P2X7 receptor on cellular membrane of cancer cells. Recently, an importance of P2X7 receptor in cancer growth or malignancy has been suggested. We have reported an inhibitory effect of oxidized ATP (oxATP), which is an irreversible antagonist of P2X7 receptor, on melanoma growth. However, the mechanism has not yet been established. In this study, we investigated the effect of oxATP on angiogenesis in vitro and in vivo to reveal the mechanism of anti-tumor growth by oxATP. We found that oxATP strongly suppressed cell migration and wound healing in mouse endothelium b.End3 cells, indicating the suppressive effect of oxATP on angiogenesis in vitro. We further investigate the effect of oxATP on angiogenesis in vivo. We performed ligation of the femoral artery and vein of BALB/c mouse, and a laser doppler perfusion image analyzer recorded blood flow postoperatively. The blood flow of hind limb was significantly decreased by the operation and recovered within 1-2 weeks, indicating angiogenesis. However, administration of oxATP to mice significantly suppressed the recovery of blood flow. Increase of serum matrix metalloproteinases (MMPs) and vascular endothelial growth factor (VEGF) levels contribute to angiogenesis. The serum MMP-2, MMP-9, and VEGF levels were lower in oxATP-treated mice than in control mice. Moreover, production of VEGF in RBL-2H3 mast cells was suppressed by treatment with oxATP. These results suggest that oxATP inhibited angiogenesis in vivo via suppression of MMP-2, MMP-9 and VEGF production. We conclude that oxATP has an anti-angiogenic effect, which would contribute to suppression of cancer growth.

Assessment of Skin Microvascular Function and Dysfunction With Laser Speckle Contrast Imaging

In recent years, skin microcirculation has been considered an easily accessible and potentially representative vascular bed to evaluate and understand the mechanisms of microvascular function and dysfunction.1–3 Vascular dysfunction (including impaired endothelium-dependent vasodilation) induced by different pathologies is evident in the cutaneous circulation.4–7 It has been suggested that the skin microcirculation may mirror generalized systemic vascular dysfunction in magnitude and underlying mechanisms.1 Furthermore, minimally invasive skin-specific methodologies using laser systems make the cutaneous circulation a useful translational model for investigating mechanisms of skin physiology and skin pathophysiology induced either by skin disease itself or by other diseases such as vascular, rheumatologic, and pneumologic. To date, the skin has been used as a circulation model to investigate vascular mechanisms in a variety of diseased states, including hypercholesterolemia,8 Alzheimer disease,9 carpal tunnel syndrome,10 schizophrenia,11 hypertension,6 renal disease,12 type 2 diabetes,13 peripheral vascular disease,14 atherosclerotic coronary artery disease,2 heart failure,15 systemic sclerosis,16 obesity,17 primary aging,18,19 and sleep apnea.20 Assessment of skin microvascular function can be done by both invasive and noninvasive techniques. Among noninvasive techniques, laser systems are mainly used.21 The recent development of the laser speckle contrast imaging (LSCI) technique for monitoring skin microvascular function enables its use as a surrogate end point in clinical trials. LSCI allows for noncontact, real-time, and noninvasive monitoring of cutaneous blood flow changes.22,23 Recent evidence has shown that the LSCI technique dramatically reduces the variability of clinical measurements compared with laser Doppler flowmetry (LDF), making the technique a fascinating tool to facilitate microvascular studies in clinical routine.23,24 In this review, we describe …

Assessment of uterine artery and aortic isthmus Doppler recordings as predictors of necrotizing enterocolitis

The purpose of this study was to evaluate whether changes of uterine arteries and aortic isthmus Doppler blood flow recordings could enhance the prediction of necrotizing enterocolitis. Doppler characteristics of the uterine artery, umbilical and middle cerebral arteries, ductus venosus, and aortic isthmus were reviewed in 123 growth-restricted fetuses who were then divided into 2 groups: with and without necrotizing enterocolitis. Twelve of 123 newborn infants (9%) expressed necrotizing enterocolitis. This group showed significant association between necrotizing enterocolitis and bilateral notching on the uterine artery (83.3% vs 29.7%; P < .001), uterine artery mean resistance index (83.3% vs 36.9%; P < .002), aortic isthmus diastolic blood flow velocity integrals (Z score: -7.32 vs -3.99; P = .028), and absent or negative "a" wave on the ductus venosus (17% vs 1.8%; P = .021). With the use of logistic regression, uterine bilateral notching could predict necrotizing enterocolitis with a sensitivity of 83.3% and a specificity of 70.3%. More than any other variable, uterine bilateral notching should be recognized as a strong risk factor for necrotizing enterocolitis.

Functional near-infrared spectroscopy (fNIRS) of brain function during active balancing using a video game system

Functional near-infrared spectroscopy (fNIRS) is a portable, non-invasive, brain imaging technology that uses low levels of non-ionizing light to record changes in cerebral blood flow in the brain through optical sensors placed on the surface of the scalp. These signals are recorded via flexible fiber optic cables, which allow neuroimaging experiments to be conducted on participants while performing tasks such as standing or walking. FNIRS has the potential to provide new insights into the evolution of brain activation during ambulatory motor learning tasks and standing tasks to probe balance and vestibular function. In this study, a 32 channel fNIRS system was used to record blood flow changes in the frontal, motor, sensory, and temporal cortices during active balancing associated with playing a video game simulating downhill skiing (Nintendo Wii™; Wii-fit™). Using fNIRS, we found activation of superior temporal gyrus, which was modulated by the difficulty of the balance task. This region had been previously implicated in vestibular function from other animal and human studies.

Laser Doppler Imaging: Usefulness in Chronic Pain Medicine

Sympathetic nervous system dysfunction is thought to be a factor in neuropathic pain conditions such as Complex Regional Pain Syndrome and in vascular conditions such as Raynaud’s phenomenon. Laser Doppler fluxmetry has been used as a fast non-invasive method to quantify changes in skin capillary blood flow which reflect activation of sympathetically mediated vasoconstriction of the arterioles that supply the capillaries. Studies of dynamic change of skin capillary blood flow with sympathetic activation such as cold or inspiratory gasp have generally used single point laser Doppler systems where the probe is in contact with the skin. The results are a single line tracing representing the capillary flow at a single point on the skin a few millimeters in diameter. Laser Doppler imaging (moorLDI laser Doppler imager, Moor Instruments Ltd.) allows for non-contact recording of skin blood flow of an area as large as 50 centimeters square with a resolution of 256 by 256 pixels and 4 milliseconds per pixel. Most work with laser Doppler imaging has studied changes that occur between successive scans. We have found it useful to look at changes that occur during a scan. In this way we obtain data that is comparable to the time resolution of single point laser Doppler methods, but with the larger spatial information that is available with laser Doppler imaging. We present a small series of case reports in which inspiratory gasp during laser Doppler imaging was able to provide quick, useful and unequivocal clinical information regarding the status of regional bilateral skin capillary response to sympathetic activation. This may be useful for distinguishing sympathetically mediated from sympathetically independent pain. We believe the methods described may provide the basis for future quantitative studies similar to those that use single point laser Doppler methods. Key words: Laser doppler, laser Doppler imaging, sympathetically maintained pain, Raynaud’s phenomen, complex regional pain syndrome

Distance between laser head and skin does not influence skin blood flow values recorded by laser speckle imaging

BackgroundLaser Speckle contrast imaging (LSCI) allows non-contact, real-time recording of cutaneous blood flow (CBF). Different distances from laser-head to skin (distancesL–S) can be chosen by the operator to perform these recordings. We aimed to evaluate the impact of different DistancesL–S on the analysis of rest blood flow and post-occlusive reactive hyperemia (PORH). MethodsFour distancesL–S (10, 15, 20, and 30cm) were evaluated in a random order in 11 healthy subjects. We analyzed the concordance between each recording at each distanceL–S. We compared CBF results (absolute values and cutaneous vascular conductance (CBF divided by mean arterial pressure)) obtained for each distanceL–S. The intra-subject coefficients of variation due to distancesL–S (intra-CV, in%) were also studied. ResultsThe mean “r” (standard deviation) cross-correlation coefficient was 0.99 (0.00) between each CBF trace issued from different distanceL–S. Both kinds of CBF results, at rest and for PORH peak, show non-significant differences when the distanceL–S is modified. The intra-CV varies from 5.9% to 8.6% at rest and from 5.6% to 9.1% for the PORH peak. ConclusionDistanceL–S neither influences SBFR at rest, nor at peak post-occlusive hyperemia in the 10–30cm interval using LSCI.

Unraveling the human cerebral circulation: insights from cerebral blood pressure and flow recordings

a.c. burton once commented that the relation of pressure to flow is the “central problem in hemodynamics” ([2][1]). This proposition remains true today, as it did more than 50 years ago when revolutionary concepts such as “vascular impedance” and “autoregulation” of regional organ

Parameters of Microcirculation in Paired Formations after Single Aspirin Administration: Laser Doppler Flowmetry Data

Laser Doppler flowmetry showed that aspirin can induce blood flow reduction and transitory manifold increase or decrease in vascular tone in rat skin and kidneys. The dynamics is more illustrative when parameters of individual animals are evaluated and depends on the areas of blood flow recording. Deaths and reduction of narcotic sleep duration were noted in concomitant use of nembutal and aspirin.

Increasing the “region of interest” and “time of interest”, both reduce the variability of blood flow measurements using laser speckle contrast imaging

Objective Both spatial variability and temporal variability of skin blood flow are high. Laser speckle contrast imagers (LSCI) allow non-contact, real-time recording of cutaneous blood flow on large skin surfaces. Thereafter, the observer can define different sizes for the region of interest (ROI) in the images to decrease spatial variability and different durations over which the blood flow values are averaged (time of interest, TOI) to decrease temporal variability. We aimed to evaluate the impact of the choices of ROI and TOI on the analysis of rest blood flow and post occlusive reactive hyperemia (PORH). Methods Cutaneous blood flow (CBF) was assessed at rest and during PORH. Three different sizes of ROI (1 mm 2, 10 mm 2 and 100 mm 2), and three different TOI (CBF averaged over 1 s, 15 s, and 30 s for rest, and over 1 s, 5 s and 10 s for PORH peak) were evaluated. Inter-subjects and intra-subjects coefficient of variations (inter-CV and intra-CV) were studied. Results The inter-subject variability of CBF is about 25% at rest and is moderately improved when the size of the ROI increases (inter-CV = 31%, for 1 s and 1 mm 2 versus inter-CV = 23%, for 15 s and 100 mm 2). However, increasing the TOI does not improve the results. The variability of the PORH peak is lower with an inter-CV varying between 11.4% (10 s and 100 mm 2) and 21.6% (5 s and 1 mm 2). The lowest intra-CV for the CBF at rest was 7.3% (TOI of 15 s on a ROI of 100 mm 2) and was 3.1% for the PORH peak (TOI of 10 s on a ROI of 100 mm 2). Conclusion We suggest that a size of ROI larger than 10 mm 2 and a TOI longer than 1 s are required to reduce the variability of CBF measurements both at rest and during PORH peak evaluations at the forearm level. Many technical aspects such as comparison of laser speckle contrast imaging and laser Doppler imaging or the effect of skin to head distance on recorded values with LCSI are required to improve future studies using this fascinating clinical tool.

Use of a simple arm-raising test with a portable laser Doppler blood flow meter to detect dehydration

Using micro electromechanical systems (MEMS) technologies, the authors have developed the world’s smallest, lightest, and least power-consuming laser Doppler blood flow meter. Unlike commercial fibre-type blood flow instruments, the new blood flow meter is invulnerable to any movements of the person wearing it and has a wireless transmitter. Utilizing the characteristics of the blood flow meter, the authors attempted to detect dehydration by having a subject simply raise an arm (arm-raising test) with the flow meter attached to a fingertip. Healthy young volunteers (20 men and two women, mean age 22.9, age range 21–27 years) were instructed to perspire in a sauna until they became dehydrated. The target dewatering ratio was 2 per cent, which was calculated from the body weight measured using a weight scale. Four markers were compared: mean blood flow (MBF) before arm-raising, MBF during arm-raising, maximum amplitude (MA) of the pulse wave during arm-raising, and inclination of reflex (IR) wave calculated from the recorded blood flow data for the non-dehydrated (before sauna) and dehydrated (3 h after sauna) states in the arm-raising test. Each of the mean total markers (MBF during arm-raising, MA, and IR) was significantly lower ( P &lt; 0.05) during the dehydrated state than the non-dehydrated. These results suggest that three markers could detect dehydration and the blood flow meter devised has the potential to be used as a portable device for detecting dehydration.

A novel mathematical approach for blood flow signal analyses

We performed continuous synchronized recordings of the blood flow in the brachial artery, electrocardiogram (ECG) and respiration, in different body positions, using a newly developed photoplethysmograph (PPG) sensor. Study of the arterial blood flow was done using a novel mathematical method developed for this purpose. The analyses of 5-minute recording sessions, at constant breathing frequency, showed a high correlation between the arterial blood flow and the heart rate. In addition, the analyses of blood flow recordings from the carotid artery revealed a significant correlation with the heart rate, despite the signal disturbance induced by neck muscle movement during the respiratory circle. Along with arterial blood flow, we performed recordings of peripheral blood flow using an identical PPG sensor. The analyses demonstrate that the arterial blood flow is in better correlation with the heart rate than the peripheral blood flow.

Feed-forward changes in carotid blood flow velocity during active standing

Orthostatic changes induce temporary loss of circulatory regulation. Feedback systems react to cardiovascular alterations to compensate for the instability. To clarify the existence of anticipatory cardiovascular regulation during active standing, we continuously recorded blood flow velocity (BFV) in the common carotid artery and cerebral blood volume (CBV) in healthy men. The maximum BFV value decreased significantly before standing in the reaction-time condition. The decrease significantly correlated with the change in systolic blood pressure that accompanies upright standing from a supine position. The anticipatory BFV decrease disappeared during self-paced standing, and all BFV parameters significantly declined after the self-paced standing. The CBV recording showed a significant increase in oxyhemoglobin levels before standing in the reaction-time condition. Our study suggests that some feed-forward cardiovascular regulation triggered by central command could be activated before standing, and it may play a functional role in the maintenance of cerebral perfusion during standing.

Effect Of PPADS On Mesenteric Arterial And Portal Venous Flow Responses To Splanchnic Nerve Stimulation

Our previous work suggested that splanchnic nerve stimulation may exert differential effects on mesenteric arterial and portal venous hemodynamics. This study tested the hypothesis that ATP contributes to the differences in mesenteric arterial and portal venous responses to splanchnic nerve stimulation.Spontaneously hypertensive rats (SHR) were anesthetized with urethane/chloralose and fitted with catheters to record arterial pressure. The rats were also instrumented for splanchnic nerve stimulation and for mesenteric arterial and portal venous blood flow recording. Frequency response curves (1–15 Hz) were constructed before and after treatment with pyridoxal‐phosphate‐6‐azophenyl‐2′,4′‐disulfonate (PPADS; 20 mg/kg), an ATP P2X receptor antagonist.Splanchnic nerve stimulation caused frequency dependent decreases in mesenteric arterial and portal venous blood flow. Treatment with PPADS caused a rightward displacement of the frequency response curves for both mesenteric arterial flow and portal venous flow. The magnitude of this displacement was less than that observed following omega conotoxin treatment.Collectively, these data suggest that ATP contributes to both mesenteric arterial and portal venous responses to splanchnic nerve stimulation. Supported by NIH #2RO1HL63053‐ARRA (DM) and USD SSOM bridge funds.

Effects of spinal cord stimulation with “standard clinical” and higher frequencies on peripheral blood flow in rats

Background: It is unclear whether spinal cord stimulation (SCS) at higher frequencies induces further increases in vasodilation and enhances clinical efficacy. Objectives: This study investigated effects of SCS at both a normal frequency (as used clinically) and two higher frequencies on peripheral vasodilation. Methods: A unipolar ball electrode was placed on the left dorsal column at the lumbar 2–3 spinal cord segments (L2–L3) in sodium pentobarbital anesthetized, paralyzed, and artificially ventilated rats. Cutaneous blood flow recordings from both ipsilateral (left) and contralateral (right) hind foot pads were measured with laser Doppler flow perfusion monitors. SCS at frequencies of 50, 200, or 500 Hz was applied at 30%, 60%, and 90% of motor threshold (MT) using standard square waves. Resiniferatoxin (RTX: an ultrapotent analog of capsaicin) and a calcitonin gene-related peptide (CGRP) receptor blocker (CGRP 8–37) was also used to elucidate mechanisms of SCS vasodilation at these higher frequencies. Results: SCS applied with the three frequencies produced similar MT ( n = 22). SCS at 500 Hz significantly increased cutaneous blood flow and decreased vascular resistance compared to changes induced by frequencies of 50 and 200 Hz ( P < 0.05, n = 8). RTX (2 μg/kg, i.v.) as well as CGRP 8–37 (2.37 mg/kg, i.v.) significantly reduced SCS-induced vasodilation at 500 Hz ( P < 0.05, n = 6) as compared to responses prior to administrations of these drugs. Conclusion: SCS at 500 Hz significantly increased SCS-induced vasodilation without influencing MT. Furthermore, effects of SCS at 500 Hz are mediated via activation of TRPV1-containing fibers and a release of CGRP.