Blood flow effects of percutaneous peripheral nerve stimulation. A blinded, randomized clinical trial.

BACKGROUND: The vasculature function is mainly regulated by the autonomic nervous system. Importantly, the sensory-motor nervous system also innervates peripheral vessels and has the capacity to modulate vascular tone. Here we investigated the effects of electrical stimulation of a mixed nerve trunk on blood flow in deep arteries and muscle perfusion. Our hypothesis is that stimulation of a mixed nerve can modify blood flow. METHODS: Twenty-nine healthy participants were included into a randomized-crossover and blinded clinical trial. Each subject received a placebo and two percutaneous peripheral nerve stimulation (pPNS) protocols on the median nerve: Pain Threshold continuous Low Frequency (PT-cLF) and Sensory Threshold burst High Frequency (ST-bHF). Blood flow was then assessed bilaterally using Power Doppler Ultrasonography at the main arteries of the arm, and blood perfusion at the forearm muscles. Afterwards, blood flow was quantified using a semi-automatized software, freely shared here. RESULTS: Placebo, consisting in needle insertion, produced an immediate and generalized reduction on peak systolic velocity in all arteries. Although nerve stimulation produced mainly no effects, some significant differences were found: both protocols increased the relative perfusion area of the forearm muscles, the ST-bHF protocol prevented the reduction in peak systolic velocity and TAMEAN of the radial artery produced by the control protocol and PT-cLF produced a TAMEAN reduction of the ulnar artery. CONCLUSIONS: Therefore, the arterial blood flow in the arm is mainly impervious to the electrical stimulation of the median nerve, composed by autonomic and sensory-motor axons, although it produces mild modifications in the forearm muscles perfusion.

Simpatectomía de la arteria radial y ulnar en contexto de úlcera digital secundaria a esclerosis sistémica cutánea localizada / Radial and ulnar artery sympathectomy in the context of digital ulcer secondary to localized cutaneous systemic sclerosis

SPeripheral sympathectomy is a procedure which has shown high rates of decreasing ischemic pain, recover functionality and wound healing, preventing the progression of the disease and further complications. We present a female patient with severe Raynaud´s phenomenon secondary to localized cutaneous systemic sclerosis complicated who presented digital ulcer treated with a sympathectomy of the radial and ulnar artery at the wrist level, undergoing post-operative follow-up.

Ultrasonographic Evaluation of a Patient With a Successful Digital Sympathectomy in Raynaud Phenomenon: A Case Report.

Selective periarterial sympathectomy in Raynaud phenomenon (RP) has not been adequately studied as there was no reliable method to evaluate outcomes. However, dynamic Doppler ultrasonography may have clinical value in the management and follow-up of patients with RP; but few reports describe using the device to assess surgical outcomes. Here, we report a case of successful digital sympathectomy in a single digit and the postoperative evaluation using ultrasonography. A 23-year-old patient with secondary RP underwent surgery targeting both common digital artery (ulnar side) and the proper digital artery (radial side). The procedure yielded immediate pain relief and the improvement of recurrent fingertip ulceration. The 1-year postoperative assessment with dynamic Doppler ultrasonography using a hockey-stick probe was performed with a cold provocation test and revealed peak systolic velocity improvement comparable to the nontreated ulnar side but prominent fibrosis on the radial aspect. We anticipate that Doppler ultrasonography may be an effective tool for the postoperative assessment of patients who underwent digital sympathectomy for treatment of RP.

Vascular branches from cutaneous nerve of the forearm and hand: Application to better understanding raynaud's disease.

Cutaneous nerves have branches called vascular branches (VBs) that reach arteries. VBs are thought to be involved in arterial constriction, and this is the rationale for periarterial sympathectomy as a treatment option for Raynaud's disease. However, the branching patterns and distribution areas of the VBs remain largely unclear. The aim of the present study was to investigate the anatomical structures of the VBs of the cutaneous nerves. Forty hands and forearms were examined to assess the branching patterns and distribution areas of the VBs of the superficial branch of the radial nerve (SBRN), the lateral antebrachial cutaneous nerve (LACN), the medial antebrachial cutaneous nerve (MACN), and the palmar cutaneous branch of the ulnar nerve (PCUN). VBs reaching the radial and ulnar arteries were observed in all specimens. The branching patterns were classified into six types. The mean distance between the radial styloid process and the point where the VBs reached the radial artery was 34.3 ± 4.8 mm in the SBRN and 38.5 ± 15.8 mm in the LACN. The mean distance between the ulnar styloid process and the point where the VBs reached the ulnar artery was 60.3 ± 25.9 mm in the MACN and 43.8 ± 26.0 mm in the PCUN. This study showed that the VBs of the cutaneous nerves have diverse branching patterns. The VBs of the SBRN had a more limited distribution areas than those of the other nerves. Clin. Anat. 31:734-741, 2018. © 2017 Wiley Periodicals, Inc.

Evaluation of hand circulation with CardioWaves photoplethysmograph device during Allen test in healthy volunteers.

OBJECTIVE: Radial artery occlusion is a potential complication of transradial procedures and its occurrence ranges from 0.8 to 30%. It is virtually always asymptomatic but the functional and sensorial consequences of a long acting hand hypoperfusion could go underestimated. CardioWaves is a novel photoplethysmograh device that allows us to detect the pulse wave amplitude of the blood flowing to the hand. Our objective was to assess in normal subjects the hand blood flow supplied by radial arteries and ulnopalmar arches, respectively, by using CardioWaves device during modified Allen's test (MAT). PATIENTS AND METHODS: MAT was performed on both hands of 60 normal subjects, age ranging 21 to 66 years, without any cardiovascular factor risk. RESULTS: Photoplethysmograh and MAT showed a high positive linear correlation (r=0.93). Despite that, MAT tends to give a higher reading by between 1.05 and 1.6 sec. 11 of 120 readings (9%) by CardioWaves showed values of radial/ulnar pulse amplitude ratio more than mean + 1 SD, suggesting a significant decrease in ulnopalmar arterial circulation when radial blood flow supply would ceased. CONCLUSIONS: The CardioWaves device allows us an accurate reading of the flow because of its independency from respiratory changes. Furthemore, the evaluation of radial and ulnar pulse wave amplitude and the ratio between them would reveal an insufficient blood flow supply by the ulnar artery irrespective of the MAT results. We suggest that their assessment before performing coronary angiography and interventions may reduce potential complication of transradial access.

Modulation of noradrenergic neurotransmission in isolated rat radial artery.

The present study was designed to characterize the neurogenic contraction of rat radial artery. Electrical field stimulation (EFS) evoked frequency-dependent contraction that was abolished by tetrodotoxin (neuronal Na(+) channel blocker), guanethidine (sympathetic neuron blocker), or phentolamine (alpha-adrenoceptor blocker). The alpha(1)-adrenoceptor antagonist prazosin inhibited endothelium-independent contractions to EFS, noradrenaline (NA), and the alpha(1)-adrenoceptor agonist phenylephrine. Rauwolscine, an alpha(2)-adrenoceptor antagonist, augmented nerve-mediated contractions and reduced sensitivity to NA and the alpha(2)-adrenoceptor agonist BHT-920. The beta-adrenoceptor antagonist propranolol diminished EFS-elicited contractions, while sensitivity to NA was enhanced by propranolol. Relaxations evoked by isoproterenol, a beta-adrenoceptor agonist, were abolished by propranolol. N(G)-Nitro-L-arginine (L-NOARG), a nitric oxide (NO) synthase inhibitor, increased both nerve-mediated and NA-induced responses in endothelium-intact, but not in endothelium-denuded arteries. Moreover, endothelium-dependent responses to BHT-920 and isoproterenol were modified by L-NOARG. Tetraethylammonium (TEA) or 4-aminopyridine, the Ca2+-activated (K(Ca)) or voltage-dependent K+ (K(V)) channel blockers, respectively, enhanced the neurogenic contractions observed. TEA but not 4-aminopyridine increased NA-induced contractions. The ATP-sensitive K+ (K(ATP))-channel blocker glibenclamide failed to modify adrenergic contractions. Blockade of capsaicin-sensitive primary afferents increased EFS-induced contractions. In conclusion, adrenergic contractions are predominantly mediated by muscular alpha(1)-adrenoceptors, while endothelial alpha(2)- and beta-adrenoceptors play a minor role. Presynaptic alpha(2)- and beta-adrenoceptors cannot be precluded. Noradrenergic neurotransmission in rat radial artery seems to be modulated by both stimulation of endothelial NO, K(Ca), and K(V) channels and sensory C-fiber activation.

Baroreflex sensitivity of an arterial wall during rotary blood pump assistance.

It is well known that the baroreflex system is one of the most important indicators of the pathophysiology in hypertensive patients. We can check the sensitivity of the baroreflex by observing heart rate (HR) responses; however, there is no simple diagnostic method to measure the arterial behavior in the baroreflex system. Presently, we report the development of a method and associated hardware that enables the diagnosis of baroreflex sensitivity by measuring the responses of both the heart and the artery. In this system, the measurements are obtained by monitoring an electrocardiogram and a pulse wave recorded from the radial artery or fingertip. The arterial responses were measured in terms of the pulse wave velocity (PWV) calculated from the pulse wave transmission time (PTT) from the heart to the artery. In this system, the HR change corresponding to the blood pressure change in time series sequence was observed. Slope of the changes in blood pressure and HR indicated the sensitivity of the baroreflex system of the heart. This system could also measure the sensitivity of the baroreflex system of an artery. Changes in the PWV in response to the blood pressure changes were observed. Significant correlation was observed in the time sequence between blood pressure change and PWV change after calculating the delay time by cross-correlation. The slope of these parameter changes was easily obtained and it demonstrated the sensitivity of the baroreflex system of an artery. We evaluated this method in animal experiments using rotary blood pump (RBP) with undulation pump ventricular assist device, and PTT elongation was observed in response to increased blood pressure with RBP assistance. Furthermore, when tested clinically, decreased sensitivity of the baroreflex system in hypertensive patients was observed. This system may be useful when we consider the ideal treatment and follow-up of patients with hypertension.

Neurological status and tissue perfusion changes after radial artery harvesting for myocardial revascularization: importance of the Allen test.

OBJECTIVE: Although radial artery (RA) removal for coronary revascularization is considered safe, there is still considerable suspicion concerning adequate hand perfusion. We investigated the blood flow alterations in the donor forearm by quantitative perfusion scintigraphy tests in patients with RA conduits, and compared the results between the patients using different Allen test refill lengths . METHODS: 50 patients undergoing coronary artery bypass graft surgery with RA grafts were investigated. Perfusion studies and a detailed physical examination of the donor hand were performed preoperatively, and repeated early before the patient was discharged and six months after operation. Forearm perfusion scintigraphy was performed by 370 MBq Technetium-99m Methoxyisobutyl isonitrile (MIBI). Perfusion index (PI) and blood pool index (BPI) were calculated by dividing the computed data from obtained images of the donor side by that of the non-donor side. Comparisons of the indices were initially performed within all patients, then through dividing the patients into three groups according to their Allen test refill length using ANOVA. RESULTS: The incidence of any neurological symptoms was 32 % in the early postoperative period. Preoperative measurements of both PI and BPI in all patients were not statistically significant when compared with the values obtained from the postoperative course. Indices of patients with long Allen test refill lengths were significantly lower than those of other patients' data in the first week after surgery. No statistical difference was observed at six months after the operation. CONCLUSION: According to our results, removal of the RA for coronary revascularization is safe. Although a significant decline in hand perfusion was observed during the early postoperative period in patients with long Allen test refill, compensatory mechanisms provide a dramatic amelioration in digital blood flow leading to good functional and neurological outcomes in the late course.

Comparison of ultrasonically activated scalpel and traditional technique in radial artery harvesting: clinical research.

BACKGROUND: Use of the radial artery (RA) as a conduit in coronary artery bypass grafting (CABG) has become increasingly popular in recent years. The aim of this study was to compare the results of two different RA harvesting techniques. Use of the harmonic scalpel is suggested to be safe and additionally reduces spasm rates. MATERIAL AND METHODS: From January 2000, the first 200 consecutive patients who underwent RA harvesting for CABG were enrolled in this study. Patients were divided into two groups. RA was harvested by means of electrocautery + hemoclips in Group I and by harmonic scalpel + hemoclips in Group II. 30 patients (30 %) in Group I and 25 patients (25 %) in Group II were female. Mean age was 53.9 +/- 9.3 and 53.5 +/- 8.4 years in Group I and Group II, respectively. Hand circulation and ulnar collateral flow was assured with a modified Allen test in all patients preoperatively. During the operation perfusion of the hand was monitored by oximetric plethysmography. The distal end of RA was also explored and clamped with a soft vascular clamp to evaluate the saturation values in the groups. During the clamping period, oxygen saturation values did not decrease so we harvested RAs in all patients. RESULTS: There were no statistically significant differences between the groups with the exception of the RA harvesting times, the postoperative analgesia requirements, the rate of vasospasm and the need for hemostatic clips. CONCLUSION: Harmonic scalpel usage in RA harvesting causes less trauma to adjacent tissues; the analgesia requirements, the rate of vasospasm, the RA harvesting time and the need of hemostatic clips decreases. We conclude that the use of a harmonic scalpel for radial artery harvesting is safer and faster than the routine technique.

Does preemptive stellate ganglion blockage increase the patency of radiocephalic arteriovenous fistula?

OBJECTIVE: Radio-cephalic arteriovenous fistulas (AVFs) have high early failure ratio. Increased sympathetic activity and spasm of radial artery during the surgery may responsible for early occlusion rate. DESIGN: Fifty patients were randomized to two groups (each containing 25 patients). Stellate Ganglion Blockade (SGB) was performed in Group 1. Another group was considered as control group (Group 2) to make statistical comparisons. All AVFs were performed under local anesthesia in both groups. RESULTS: Average fistula flow was 201.4+/-40.4 ml/min in Group 1 and 155.6+/-27.4 ml/min in Group 2 (p < 0.001). While average peak velocity of radial artery was 167.1+/-31.3 cm/sec in Group 1, it was 107.8+/-15.8 cm/sec in Group 2 (p < 0.001). Thrill was found in all Group 1 patients, but there was thrill only 13 of the Group 2 patients (p < 0.001). Mean maturation time was 41.4+/-6.8 days after surgery in Group 1 and 77.1+/-10.5 days in Group 2 (p < 0.001). Adequate vascular access was obtained 19 patients in Group 1 and 12 patients in Group 2 (p = 0.041). CONCLUSION: AVF occlusion rate is much more common in early postoperative period. Diminished sympathetic tonus by preemptive SGB not only increases early patency rate but also increases fistula maturation rate.

Arterial stiffening influence of sympathetic nerve activity: evidence from hand transplantation in humans.

Studies in animals and humans suggest that sympathetic activity exerts a stiffening influence on large and middle-sized artery walls. We sought to obtain further evidence on this issue by measuring radial artery distensibility in an allotransplanted and thus denervated hand using the contralateral artery as control. In 2 men, blood pressure was measured by a semiautomatic device (Dinamap). Diastolic diameter, systo-diastolic diameter excursion (ultrasound Wall Track system), and distensibility (Reneman formula) of both radial arteries were measured at a level corresponding to 4 cm below the suture of the transplanted hand 40 days after surgery and every 4 weeks for the next 6 months. After surgery, systo-diastolic diameter excursion and distensibility were much greater in the transplanted radial artery than in the contralateral vessel, reaching values similar to the contralateral ones after 4 months, when signs of reinnervation of the transplanted hands had appeared. Radial deinnervation was accompanied by an increased arterial distensibility, which provides further evidence of the sympathetic stiffening effect on arterial wall in humans.

Neuropeptide Y is released from human mammary and radial vascular biopsies and is a functional modulator of sympathetic cotransmission.

The role of neuropeptide Y (NPY) as a modulator of the vasomotor responses mediated by sympathetic cotransmitters was examined by electrically evoking its release from the perivascular nerve terminals of second- to third-order human blood vessel biopsies and by studying the peptide-induced potentiation of the vasomotor responses evoked by exogenous adenosine 5' triphosphate (ATP) and noradrenaline (NA). Electrical depolarization of nerve terminals in mammary vessels and radial artery biopsies elicited a rise in superfusate immunoreactive NPY (ir-NPY), which was chromatographically identical to a standard of human NPY (hNPY); a second peak was identified as oxidized hNPY. The amount released corresponds to 4-6% of the total NPY content in these vessels. Tissue extracts also revealed two peaks; hNPY accounted for 68-85% of the ir-NPY, while oxidized hNPY corresponded to 7-15%. The release process depended on extracellular calcium and on the frequency and duration of the electrical stimuli; guanethidine blocked the release, confirming the peptide's sympathetic origin. Assessment of the functional activity of the oxidized product demonstrated that while it did not change basal tension, the NA-evoked contractions were potentiated to the same extent as with native hNPY. Moreover, NPY potentiated both the vasomotor action of ATP or NA alone and the vasoconstriction elicited by the simultaneous application of both cotransmitters. RT-PCR detected the mRNA coding for the NPY Y(1) receptor. In summary, the release of hNPY or its oxidized species, elicited by nerve terminal depolarization, coupled to the potentiation of the sympathetic cotransmitter vasomotor responses, highlights the modulator role of NPY in both arteries and veins, strongly suggesting its involvement in human vascular sympathetic reflexes.

Comparison of continuous wave Doppler ultrasound of the radial artery and laser Doppler flowmetry of the fingertips with sympathetic stimulation.

Laser Doppler is widely used to evaluate sympathetic vasoconstrictor function. Continuous wave (cw)-Doppler of the radial artery may be an alternative but less expensive approach to quantify sympathetically induced resistance changes in the peripheral vascular system. In order to compare the power of both methods, this study was performed with simultaneous assessment of cw Doppler and laser Doppler flowmetry in volunteers. Twenty-five healthy subjects (median age years, range 20-27) rested in a relaxed supine position and were asked to perform a deep inspiratory gasp and a commanded cough (DIG + C). Radial artery blood flow was assessed with a standard cw Doppler device, arteriolar blood flow was assessed simultaneously employing a single point laser Doppler perfusion monitor at the fingertips. We quantified the latency between stimulus and onset of vasoconstriction, the latency to the maximum vasoconstriction and the duration of response. The decrease in flow velocities (cw Doppler) after stimulus was compared with the decrease in capillary flow (laser Doppler). While the flow profile as measured with laser Doppler remained monophasic after stimulation, cw Doppler showed biphasic flow (or absent diastolic flow) in all subjects after DIG + C. The latencies between stimulus and onset of reaction were significantly shorter when measured with laser Doppler (1.8 s vs. 2 s, p = 0.049), the latencies till the maximum extent of the reaction was reached did not differ significantly (3.2 vs. 3.3 s). The duration of the response was significantly shorter when measured by laser Doppler (12.0 vs. 14.5 s (p < 0.0001). While skin blood flow in the laser Doppler measurement decreased after stimulation from 654 flux units (FU) to 319 FU (-59%), mean flow velocities in the radial artery declined from 1.07 kHz to 0.14 kHz (-87%). This relative change was significantly different (p < 0.0001). The correlation between the decline of flux units as measured by laser Doppler and cw Doppler changes was r = 0.616 (p = 0.004). Both methods are feasible to monitor flow changes due to sympathetic stimulation. Latencies and relative quantitative changes were closely correlated.Thus, cw Doppler is a valid alternative approach to laser Doppler flowmetry in healthy volunteers.

Sympathetic vasomotor response of the radial artery in patients with diabetic foot syndrome.

OBJECTIVE: Neurophysiological assessment of the peripheral autonomic system is characterized by various limitations. An alternative approach to laser Doppler and venous plethymography is the assessment of the sympathetic vasomotor response of the radial artery obtained by continuous wave Doppler sonography. Nomogram data have been established and demonstrate the temporary disappearance of diastolic flow after coughing or deep inspiration. RESEARCH DESIGN AND METHODS: We assessed the sympathetic vasomotor response in 25 patients (mean age 64 years, range 43-76) with diabetic foot syndrome. The Doppler data were correlated with nerve conduction studies of the median and peroneal nerve, the extent of radiologically diagnosed media sclerosis, and compared with nomogram values (n = 41). RESULTS: Although similar mean flow velocities were found under baseline conditions, the flow pattern was characterized by higher pulsatility in the diabetic group (resistance index [RI] 1.1 vs. 0.7). No significant difference in RI was observed after coughing. The latency of onset of the response was prolonged (2.1 vs. 1.5 s), while the duration of the response did not differ (18 vs. 15 s). Only the nerve conduction velocity of the peroneal nerve correlated inversely with the RI. The extent of radiologically proven calcification tended to correlate with the pulsatility of the baseline signal and the response latencies. CONCLUSIONS: The data obtained by this study suggest the concurrent existence of reduced vessel elasticity due to media sclerosis and dysfunction of the autonomic vasomotor system.

[Periarterial sympathectomy of the radial and ulnar arteries in Raynaud's phenomenon--a preliminary study]. / Denervierung der A. radialis und der A. ulnaris bei sekundärem Raynaud-Syndrom--erste Ergebnisse.

PURPOSE: Assessment of the post-operative results of peripheral sympathectomy in Raynaud's phenomenon. METHODS: Six patients with therapy refractory Raynaud's phenomenon underwent a 4 cm long adventitial stripping of the radial and ulnar arteries proximal to the wrist. The nerve of Henle was followed up to the surface of the palmar arch and resected. The pre- and postoperative examinations were performed using the help of a questionnaire, telethermography and infra-red laser reflexion rheography. RESULTS: All but two patients (two hands) were free of complaints (four patients, six hands), the three ulcers on the finger tips healed well. According to the questionnaire there was a dramatic improvement in the quality of life of the patients. CONCLUSION: In the follow-up period of two years, there was no recurrence. Adventitial stripping of the radial and ulnar arteries and resection of the nerve of Henle proximal to the wrist have demonstrated favourable results in the treatment of therapy-resistant complaints in Raynaud's phenomenon.

Continuous wave Doppler ultrasound for evaluation of vasomotor tone of the radial artery.

OBJECTIVE: At present, the sympathetic skin response (SSR) is the only routinely employed technique for evaluating the autonomic function of peripheral nerves. The present study was conducted in order to compare SSR to continuous wave Doppler (CWD) of the radial artery in both healthy control subjects and patients with lower brachial plexus lesions. METHODS: Both methods were performed in 50 healthy volunteers (aged 23 to 70 years; mean age and standard deviation, 39.6+/-14.3 years) and six patients presenting with severe lesions of the lower brachial plexus (aged 22 to 60 years; mean age, 37.6+/-16.0 years). RESULTS: In each control subject, a SSR could be evoked with a mean latency of 1.2+/-0.2 s and a mean amplitude of 2.9+/-1.5 mV. In 45 healthy subjects, CWD revealed both a reduction of systolic, diastolic, and mean peak blood flow velocity after electrical (ES) and acoustic (AS) stimulation as well as after inspiratory cough (IC). The mean latencies to the decrease in flow velocity decrease amounted to 1.8+/-0.7, 2.0+/-0.7, and 1. 4+/-0.4 s, respectively. The resistance (Pourcelot) index increased significantly. CWD failed to show changes of blood flow velocity in five healthy subjects due to high sympathetic tone (no baseline diastolic blood flow) or instability of blood flow caused by respiration. In patients with lower brachial plexus lesions, SSR was diminished and changes in blood flow could not be observed on the affected side. CONCLUSION: CWD sonography allows easy quantitative assessment of arteriolar tone in healthy subjects and patients with autonomic nerve lesions of the limbs.

Comparison of the sympathetic skin response and continuous wave Doppler sonography of the radial artery.

The value of neurophysiological tests of the autonomic nerve system is limited. One of the clinically most commonly applied test is the skin sudomotor response, frequently referred to as 'sympathetic skin response' (SSR). However, the SSR is a more qualitative than quantitative evaluation technique. Continuous wave (cw) Doppler sonography of the radial artery may be an alternative quantitative approach. We studied 41 age matched volunteers (23 female, 18 male; 16-82 years (mean age 53 years)). The stimulus was a loud and unexpected acoustic signal, alternatively a cough. SSR evaluation included the latency of onset, the duration and the amplitude of the response. Doppler evaluation also included flow velocity and resistance index (RI) changes with adequate stimulation. SSRs were observed in 36 volunteers (88%), Doppler responses in 35 (85%). The latency between stimulus and response onset was 1.35 s with SSR and 1.52 s with ultrasound (n.s.). The mean SSR amplitude was 1.3 mV, systolic velocities decreased by 20% and diastolic velocities by 124% (flow reversal). RI increased from 0.85 to 1.25 with no correlation between SSR amplitude and flow velocity changes. SSR and cw Doppler are complementary methods. Doppler sonography offers an additional approach of autonomic nerve evaluation.

Sympathetic modulation of radial artery compliance in congestive heart failure.

Animal studies have suggested that arterial compliance can be modulated by adrenergic influences. Whether this adrenergic modulation also occurs in humans is still a matter of debate. In the present article we address this issue by examining the relationships between sympathetic tone and arterial compliance in a variety of physiological and pathophysiological conditions. We have found that cigarette smoking, ie, an action that produces a marked sympathetic activation, causes a significant reduction in radial artery compliance, as measured by an echotracking device capable of providing continuous beat-to-beat evaluation of this hemodynamic variable. When expressed as compliance index, ie, as the ratio between the area under the compliance-pressure curve and pulse pressure, the reduction amounted to 35.7 +/- 4.8% (mean +/- SEM) and was independent of the smoking-related blood pressure increase. Furthermore, pharmacological stimulation of adrenergic receptors located in the arterial wall was also shown to affect arterial compliance because the radial artery compliance index was markedly reduced (- 29.5 +/- 3.9%) during phenylephrine infusion in the brachial artery at doses devoid of any systemic blood pressure effect. Evidence was also obtained that the relationship between sympathetic activation and arterial compliance has pathophysiological relevance, because in 17 patients with congestive heart failure (New York Heart Association classes II through IV) there was a significant inverse correlation (r = .62, P < .01) between muscle sympathetic nerve activity (directly measured by microneurography in the peroneal nerve) and radial artery compliance.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of sympathetic tone on mechanical properties of muscular arteries in humans.

Although smooth muscle tone is a key determinant of mechanical properties of arteries in animal experiments, it has not yet been studied in humans because of technical limitations. To assess the influence of tone on arterial properties in humans and to emphasize the interest of calculation at specific stress, we used echo tracking and photoplethysmographic measurement of arterial pressure to study radial arterial mechanics during a cold pressor test (CPT) in 12 healthy volunteers (28 +/- 2 yr). During CPT, mean arterial pressure rose from 83 +/- 3 to 106 +/- 5 mmHg (P < 0.05), internal diameter decreased from 2.75 +/- 0.15 to 2.54 +/- 0.14 mm (P < 0.05), and wall thickness increased from 0.576 +/- 0.027 to 0.634 +/- 0.029 mm (P < 0.05). At a specific pressure (105 mmHg), midwall stress and incremental modulus decreased whereas arterial compliance increased. The incremental modulus of elasticity and compliance were fitted as functions of pressure and of midwall stress. CPT decreased the modulus about equally at all wall stresses measured. The modulus decreased and the compliance increased at every level of pressure measured. At all levels of midwall stress, the compliance was decreased. Thus acute sympathetic stimulation induced by CPT decreases the wall stiffness of human arteries in vivo. This may be explained by an unloading of stiffer wall components during active arterial constriction.