Effect of metformin pretreatment on myocardial injury during coronary artery bypass surgery in patients without diabetes (MetCAB): a double-blind, randomised controlled trial

BACKGROUND

During coronary artery bypass graft (CABG) surgery, ischaemia and reperfusion damage myocardial tissue, and increased postoperative plasma troponin concentration is associated with a worse outcome. We investigated whether metformin pretreatment limits cardiac injury, assessed by troponin concentrations, during CABG surgery in patients without diabetes.

METHODS

We did a placebo-controlled, double-blind, single-centre study in an academic hospital in Nijmegen (Netherlands) in adult patients without diabetes undergoing an elective on-pump CABG procedure. We randomly assigned patients (1:1) in blocks of ten via a computer-generated randomisation sequence to either metformin hydrochloride (500 mg three times per day) or placebo (three times per day) for 3 days before surgery. The last dose was given roughly 3 h before surgery. Patients, investigators, trial staff, and the statistician were all masked to treatment allocation. The primary endpoint was the plasma concentration of high-sensitive troponin I at 6, 12, and 24 h postreperfusion after surgery, analysed in the per-protocol population with a mixed-model analysis using all these timepoints. Secondary endpoints included the occurrence of clinically relevant arrhythmias within 24 hours after reperfusion, the need for inotropic support, time to detubation, duration of stay in the intensive-care unit, and postoperative use of insulin. This study is registered with ClinicalTrials.gov, number NCT01438723.

FINDINGS

Between Nov 8, 2011, and Nov 22, 2013, we randomly assigned 111 patients to treatment (57 to metformin and 54 to placebo). Five patients dropped out from the metformin group, and six from the placebo group. 52 patients in the metformin group and 48 patients in the placebo group were included in the per-protocol analysis. Geometric mean high-sensitivity troponin I increased from 0 μg/L to 3·67 μg/L (95% CI 3·06-4·41) with metformin and to 3·32 μg/L (2·75-4·01) with placebo at 6 h after reperfusion; 2·84 μg/L (2·37-3·41) and 2·45 μg/L (2·02-2·96), respectively, at 12 h; and to 1·77 μg/L (1·47-2·12) and 1·60 μg/L (1·32-1·94) at 24 h. The concentrations did not differ significantly between the groups (difference 12·3% for all timepoints [95% CI -12·4 to 44·1] p=0·35). Occurrence of arrhythmias did not differ between groups (three [5·8%] of 52 patients who received metformin vs three [6·3%] of 48 patients who received placebo; p=1·00). There was no difference between groups in the need for inotropic support, time to detubation, duration of stay in the intensive-care unit, or postoperative use of insulin. No patients died within 30 days after surgery. Occurrence of gastrointestinal discomfort (mostly diarrhoea) was significantly higher with metformin than with placebo (11 [21·2%] of 52 vs two [4·2%] of 48 patients; p=0·01).

INTERPRETATION

Short-term metformin pretreatment, although safe, does not seem to be an effective strategy to reduce periprocedural myocardial injury in patients without diabetes undergoing CABG surgery.

FUNDING

Netherlands Organisation for Health Research and Development and Netherlands Heart Foundation.

Salvia Miltiorrhiza Root Water-Extract (Danshen) Has No Beneficial Effect on Cardiovascular Risk Factors. A Randomized Double-Blind Cross-Over Trial

Purpose

Danshen is the dried root extract of the plant Salvia Miltiorrhiza and it is used as traditional Chinese medicinal herbal product to prevent and treat atherosclerosis. However, its efficacy has not been thoroughly investigated. This study evaluates the effect of Danshen on hyperlipidemia and hypertension, two well known risk factors for the development of atherosclerosis.

Methods

This was a randomized, placebo-controlled, double-blind crossover study performed at a tertiary referral center. Participants were recruited by newspaper advertisement and randomized to treatment with Danshen (water-extract of the Salvia Miltiorrhiza root) or placebo for 4 consecutive weeks. There was a wash out period of 4 weeks. Of the 20 analysed participants, 11 received placebo first. Inclusion criteria were: age 40-70 years, hyperlipidemia and hypertension. At the end of each treatment period, plasma lipids were determined (primary outcome), 24 hours ambulant blood pressure measurement (ABPM) was performed, and vasodilator endothelial function was assessed in the forearm.

Results

LDL cholesterol levels were 3.82±0.14 mmol/l after Danshen and 3.52±0.16 mmol/l after placebo treatment (mean±SE; p<0.05 for treatment effect corrected for baseline). Danshen treatment had no effect on blood pressure (ABPM 138/84 after Danshen and 136/87 after placebo treatment). These results were further substantiated by the observation that Danshen had neither an effect on endothelial function nor on markers of inflammation, oxidative stress, glucose metabolism, hemostasis and blood viscosity.

Conclusion

Four weeks of treatment with Danshen (water-extract) slightly increased LDL-cholesterol without affecting a wide variety of other risk markers. These observations do not support the use of Danshen to prevent or treat atherosclerosis.

Trial Registration

ClinicalTrials.gov NCT01563770

Cardiovascular pharmacotherapy: Innovation stuck in translation

Systematic reviews of animal studies have revealed serious limitations in internal and external validity strongly affecting the reliability of this research. In addition inter-species differences are likely to further limit the predictive value of animal research for the efficacy and tolerability of new drugs in humans. Important changes in the research process are needed to allow efficient translation of preclinical discoveries to the clinic, including improvements in the laboratory and publication practices involving animal research and early incorporation of human proof-of-concept studies to optimize the interpretation of animal data for its predictive value for humans and the design of clinical trials.

Shortcomings of protocols of drug trials in relation to sponsorship as identified by Research Ethics Committees: analysis of comments raised during ethical review

BACKGROUND

Submission of study protocols to research ethics committees (RECs) constitutes one of the earliest stages at which planned trials are documented in detail. Previous studies have investigated the amendments requested from researchers by RECs, but the type of issues raised during REC review have not been compared by sponsor type. The objective of this study was to identify recurring shortcomings in protocols of drug trials based on REC comments and to assess whether these were more common among industry-sponsored or non-industry trials.

METHODS

Retrospective analysis of 226 protocols of drug trials approved in 2010-2011 by three RECs affiliated to academic medical centres in The Netherlands. For each protocol, information on sponsorship, number of participating centres, participating countries, study phase, registration status of the study drug, and type and number of subjects was retrieved. REC comments were extracted from decision letters sent to investigators after review and were classified using a predefined checklist that was based on legislation and guidelines on clinical drug research and previous literature.

RESULTS

Most protocols received comments regarding participant information and consent forms (n = 182, 80.5%), methodology and statistical analyses (n = 160, 70.8%), and supporting documentation, including trial agreements and certificates of insurance (n = 154, 68.1%). Of the submitted protocols, 122 (54.0%) were non-industry and 104 (46.0%) were industry-sponsored trials. Non-industry trials more often received comments on subject selection (n = 44, 36.1%) than industry-sponsored trials (n = 18, 17.3%; RR, 1.58; 95% CI, 1.01 to 2.47), and on methodology and statistical analyses (n = 95, 77.9% versus n = 65, 62.5%, respectively; RR, 1.18; 95% CI, 1.01 to 1.37). Non-industry trials less often received comments on supporting documentation (n = 72, 59.0%) than industry-sponsored trials (n = 82, 78.8%; RR, 0.83; 95% CI, 0.72 to 0.95).

CONCLUSIONS

RECs identified important ethical and methodological shortcomings in protocols of both industry-sponsored and non-industry drug trials. Investigators, especially of non-industry trials, should better prepare their research protocols in order to facilitate the ethical review process.

The effect of eplerenone on adenosine formation in humans in vivo: a double-blinded randomised controlled study

Background

It has been suggested that mineralocorticoid receptor antagonists have direct cardioprotective properties, because these drugs reduce mortality in patients with heart failure. In murine models of myocardial infarction, mineralocorticoid receptor antagonists reduce infarct size. Using gene deletion and pharmacological approaches, it has been shown that extracellular formation of the endogenous nucleoside adenosine is crucial for this protective effect. We now aim to translate this finding to humans, by investigating the effects of the selective mineralocorticoid receptor antagonist eplerenone on the vasodilator effect of the adenosine uptake inhibitor dipyridamole, which is a well-validated surrogate marker for extracellular adenosine formation.

Methods and Results

In a randomised, double-blinded, placebo-controlled, cross-over study we measured the forearm blood flow response to the intrabrachial administration of dipyridamole in 14 healthy male subjects before and after treatment with placebo or eplerenone (50 mg bid for 8 days). The forearm blood flow during administration of dipyridamole (10, 30 and 100 µg·min⁻¹·dl⁻¹) was 1.63 (0.60), 2.13 (1.51) and 2.71 (1.32) ml·dl⁻¹·min⁻¹ during placebo use, versus 2.00 (1.45), 2.68 (1.87) and 3.22 (1.94) ml·dl⁻¹·min⁻¹ during eplerenone treatment (median (interquartile range); P = 0.51). Concomitant administration of the adenosine receptor antagonist caffeine attenuated dipyridamole-induced vasodilation to a similar extent in both groups. The forearm blood flow response to forearm ischemia, as a stimulus for increased formation of adenosine, was similar during both conditions.

Conclusion

In a dosage of 50 mg bid, eplerenone does not augment extracellular adenosine formation in healthy human subjects. Therefore, it is unlikely that an increased extracellular adenosine formation contributes to the cardioprotective effect of mineralocorticoid receptor antagonists.

Trial Registration

ClinicalTrials.gov, NCT01837108

Impact of metformin on endothelial ischemia-reperfusion injury in humans in vivo: a prospective randomized open, blinded-endpoint study

INTRODUCTION

Large prospective studies in patients with type 2 diabetes mellitus have demonstrated that metformin treatment improves cardiovascular prognosis, independent of glycemic control. Administration of metformin potently limits infarct size in murine models of myocardial infarction. This study examined, for the first time in humans, whether metformin limits ischemia-reperfusion (IR) injury in vivo using a well-validated forearm model of endothelial IR-injury.

METHODS

Twenty-eight healthy volunteers (age 41±6 years, 10 male/16 female) were randomized between pretreatment with metformin (500 mg three times a day for 3 days) or no treatment in a Prospective Randomized Open Blinded Endpoint study. Brachial artery flow mediated dilation (FMD) was measured before and after 20 minutes of forearm ischemia and 20 minutes of reperfusion. FMD analysis was performed offline by investigators blinded for the treatment arm.

RESULTS

Baseline FMD did not differ between metformin pretreatment and no pretreatment (6.9±3.6% and 6.1±3.5%, respectively, p = 0.27, n = 26). FMD was significantly lower after forearm IR in both treatment arms (4.4±3.3% and 4.3±2.8%, respectively, P<0.001 in both conditions). A linear mixed model analysis revealed that metformin treatment did not prevent the decrease in FMD by IR.

CONCLUSION

A 3 day treatment with metformin in healthy, middle-aged subjects does not protect against endothelial IR-injury, measured with brachial artery FMD after forearm ischemia. Further studies are needed to clarify what mechanism underlies the cardiovascular benefit of metformin treatment.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01610401.

The cardioprotective effects of mineralocorticoid receptor antagonists

Despite state-of-the-art reperfusion therapy, morbidity and mortality remain significant in patients with an acute myocardial infarction. Therefore, novel strategies to limit myocardial ischemia-reperfusion injury are urgently needed. Mineralocorticoid receptor (MR) antagonists are attractive candidates for this purpose, since several clinical trials in patients with heart failure have reported a survival benefit with MR antagonist treatment. MRs are expressed by several cells of the cardiovascular system, including cardiomyocytes, cardiac fibroblasts, vascular smooth muscle cells, and endothelial cells. Experiments in animal models of myocardial infarction have demonstrated that acute administration of MR antagonists, either before ischemia or immediately at the moment of coronary reperfusion, limits infarct size. This action appears to be independent of the presence of aldosterone and cortisol, which are the endogenous ligands for the MR. The cardioprotective effect is mediated by a nongenomic intracellular signaling pathway, including adenosine receptor stimulation, and activation of several components of the Reperfusion Injury Salvage Kinase (RISK) pathway. In addition to limiting infarct size, MR antagonists can improve scar healing when administered shortly after reperfusion and can reduce cardiac remodeling post myocardial infarction. Clinical trials are currently being performed studying whether early administration of MR antagonists can indeed improve prognosis in patients with an acute myocardial infarction, independent of the presence of heart failure.

Role of Endogenous Vascular Endothelial Growth Factor in Endothelium-Dependent Vasodilation in Humans

Angiogenesis inhibitors have remarkably improved the outcome of patients with several types of cancer. Hypertension is the most reported side effect of angiogenesis inhibitors interfering with vascular endothelial growth factor signaling. In this study, we test the hypothesis that circulating vascular endothelial growth factor at physiological concentrations is essential to preserve normal endothelial control of vasomotor tone. In 7 healthy male volunteers, infusion of bevacizumab (monoclonal vascular endothelial growth factor antibody) into the brachial artery for 15 minutes (144 μg/dL forearm volume per minute) did not affect forearm vasodilator tone as measured with venous occlusion strain gauge plethysmography. In a separate group of 12 male volunteers, a similar bevacizumab infusion reduced the vasodilator response to 2 dosages of acetylcholine from (mean±SE) 440±157% and 926±252% to 169±40% and 612±154% ( P <0.05). Finally, in a third group of 12 volunteers, bevacizumab did not alter the percentage increase in forearm blood flow during infusion of sodium nitroprusside at dosages equipotent to acetylcholine. Bevacizumab acutely and specifically reduced endothelium-mediated vasodilation at local concentrations that resemble plasma concentrations after systemic exposure to bevacizumab. This observation suggests a physiological role for vascular endothelial growth factor in maintaining normal endothelial control of vasomotor tone. The role of the endothelium in the mechanism of bevacizumab-induced hypertension deserves further exploration.

Aging attenuates the protective effect of ischemic preconditioning against endothelial ischemia-reperfusion injury in humans

Reperfusion is mandatory after ischemia but also triggers ischemia-reperfusion (I/R) injury. Ischemic preconditioning (IPC) can limit endothelial I/R injury. Nonetheless, translation of IPC to the clinical arena is often disappointing. Since application of IPC typically relates to older patients, efficacy of IPC may be attenuated with aging. Our objective was to examine the impact of advanced age on the ability of IPC to protect against endothelial dysfunction due to I/R injury. We included 15 healthy young (20-25 yr) and 15 older (68-77 yr) men. We examined brachial artery endothelial function using flow-mediated dilation (FMD) before and after arm I/R (induced by inflation of an upper-arm blood pressure cuff for 20 min and 15 min of reperfusion). In a randomized order, I/R was preceded by IPC or a control intervention consisting of three cycles of 5 min upper-arm cuff inflation to 220 or 20 mmHg, respectively. As a result, in young men, FMD decreased significantly after I/R (6.4 ± 2.7 to 4.4 ± 2.5%). This decrease was not present when I/R was preceded by IPC (5.9 ± 2.3 to 5.6 ± 2.5%). IPC-induced protection appeared to be significantly reduced in the elderly patients (P = 0.04). Although FMD decreased after I/R in older men (3.5 ± 1.7 to 2.5 ± 1.0%), IPC could not prevent this (3.7 ± 2.1 to 2.2 ± 1.1%). In conclusion, this study is the first to observe in humans in vivo that older age is associated with an abolished effect of IPC to protect against endothelial dysfunction after I/R in the brachial artery. This provides a possible explanation for the problematic translation of strategies that reduce I/R injury from preclinical work to the clinical arena.

[Clopidogrel plus acetylsalicylic acid: a deadly combination]

In the recently published SPS3 trial, clopidogrel plus aspirin increased mortality compared with aspirin alone in patients with lacunar cerebral infarcts. A detailed review of currently available trial data on this dual-antiplatelet strategy, having taken the between-trial variation in mortality in the various control groups into account, indicates lethal toxicity which also occurs in patients with coronary atherosclerosis. The recently observed benefit of an alternative P2Y12 receptor antagonist (ticragelor) on survival as compared with clopidogrel suggests that the toxicity of the clopidogrel/aspirin combination likely results from an 'off-target' effect. The exact nature of this 'off-target' effect is currently unknown. The lack of a survival benefit in combination with the frequent occurrence of serious bleeding complications requires the cessation of the use of clopidogrel in combination with aspirin. The question whether clopidogrel should be replaced by an alternative P2Y12 receptor antagonist needs to be answered by future trials.

Improved resistance to ischemia and reperfusion, but impaired protection by ischemic preconditioning in patients with type 1 diabetes mellitus: a pilot study

Background

In patients with type 1 diabetes mellitus (T1DM), cardiovascular events are more common, and the outcome following a myocardial infarction is worse than in nondiabetic subjects. Ischemic or pharmacological preconditioning are powerful interventions to reduce ischemia reperfusion (IR)-injury. However, animal studies have shown that the presence of T1DM can limit these protective effects. Therefore, we aimed to study the protective effect of ischemic preconditioning in patients with T1DM, and to explore the role of plasma insulin and glucose on this effect.

Methods

^99mTechnetium-annexin A5 scintigraphy was used to detect IR-injury. IR-injury was induced by unilateral forearm ischemic exercise. At reperfusion, Tc-annexin A5 was administered, and IR-injury was expressed as the percentage difference in radioactivity in the thenar muscle between the experimental and control arm 4 hours after reperfusion. 15 patients with T1DM were compared to 21 nondiabetic controls. The patients were studied twice, with or without ischemic preconditioning (10 minutes of forearm ischemia and reperfusion). Patients were studied in either normoglycemic hyperinsulinemic conditions (n = 8) or during hyperglycemic normoinsulinemia (n = 7). The controls were studied once either with (n = 8) or without (n = 13) ischemic preconditioning.

Results

Patients with diabetes were less vulnerable to IR-injury than nondiabetic healthy controls (12.8 ± 2.4 and 11.0 ± 5.1% versus 27.5 ± 4.5% in controls; p < 0.05). The efficacy of ischemic preconditioning to reduce IR-injury, however, was lower in the patients and was even completely abolished during hyperglycemia.

Conclusions

Patients with T1DM are more tolerant to forearm IR than healthy controls in our experimental model. The efficacy of ischemic preconditioning to limit IR-injury, however, is reduced by acute hyperglycemia.

Trial Registration

The study is registered at www.clinicaltrials.gov (NCT00184821)

Targeting adenosine receptors in the development of cardiovascular therapeutics

Adenosine receptor stimulation has negative inotropic and dromotropic actions, reduces cardiac ischemia-reperfusion injury and remodeling, and prevents cardiac arrhythmias. In the vasculature, adenosine modulates vascular tone, reduces infiltration of inflammatory cells and generation of foam cells, and may prevent the development of atherosclerosis as a result. Modulation of insulin sensitivity may further add to the anti-atherosclerotic properties of adenosine signaling. In the kidney, adenosine plays an important role in tubuloglomerular feedback and modulates tubular sodium reabsorption. The challenge is to take advantage of the beneficial actions of adenosine signaling while preventing its potential adverse effects, such as salt retention and sympathoexcitation. Drugs that interfere with adenosine formation and elimination or drugs that allosterically enhance specific adenosine receptors seem to be most promising to meet this challenge.

Abstract 1693: Bevacizumab acutely decreases endothelium dependent vasodilation in healthy volunteers

Introduction: Angiogenesis inhibitors have remarkably improved the outcome of patients with several types of cancer. One of the most reported side effects of angiogenesis inhibitors is hypertension. In patients treated with bevacizumab, a monoclonal antibody against vascular endothelial growth factor (VEGF), hypertension has an overall incidence up to 32%. Understanding the pathogenesis of this side effect is essential for optimal treatment with this class of drugs. Microvascular endothelial dysfunction is involved in the pathogenesis of hypertension. Our hypothesis is that bevacizumab (BVZ) induced hypertension is caused by an acute reduction of endothelium-mediated vasodilation. Methods: BVZ was infused intra-arterially to separate direct local effects of VEGF inhibition from systemic actions, such as hypertension, that could indirectly interfere with endothelial function. At first, in seven volunteers the acute vasomotor effect of BVZ was studied. During 15 minutes BVZ 144 μg/dl forearm volume/min was infused in the brachial artery of the non-dominant arm while assessing forearm blood flow (FBF) with venous strain gauge plethysmography. During BVZ infusion venous blood was collected from both arms to measure local and systemic concentrations of BVZ. Subsequently the acute vasodilator response to intra-arterial acetylcholine (Ach, endothelium-dependent vasodilator) alone and during simultaneous infusion of BVZ was studied, in another group of 12 volunteers. Finally, the effect of BVZ on the response to an endothelium-independent vasodilator nitroprusside (SNP) was studied in a similar experimental set up, in a third group of 12 volunteers. Results: In the experimental arm during infusion BVZ reached a concentration of 135±10,7μg/ml (± SD; n=8), resembling systemic exposure to BVZ in patients treated with 5mg BVZ i.v./kg. BVZ concentration in the control arm was 6,7±1,1 μg/ml (n=10). Intra-arterial BVZ did not directly alter forearm vascular tone. Infusion of BVZ significantly reduced the percentage increase in forearm blood flow during infusion of two dosages of acetylcholine from (mean±SE) 440±157 and 926±252 to 169±154 and 612±40 (p&lt;0,05, ANOVA for repeated measures on log-transformed data). In the absence of BVZ, the vasodilator response to SNP equaled the response to ACh. BVZ did not alter the percentage increase in forearm blood flow during infusion of SNP (n=12). Conclusion: Although BVZ did not alter baseline forearm vascular tone, it acutely and specifially reduced endothelium-mediated vasodilation. Although this observation suggests a minor role for the muscle vascular bed, a similar acute effect in other organs such as the kidney could very well be involved in the pathogenesis of BVZ-induced hypertension.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1693. doi:1538-7445.AM2012-1693

Atorvastatin does not affect ischaemia-induced phosphatidylserine exposition in humans in-vivo

AIM

Statins can induce pharmacologic preconditioning and thereby reduce infarct size. Cellular phosphatidylserine (PS) exposition occurs in the course of ischaemia and reperfusion and has been associated with injury. In this experiment we studied the effect of atorvastatin on PS exposition after a standardised ischaemia and reperfusion challenge.

METHODS

In a double-blind randomised cross-over trial 30 healthy volunteers were allocated to 3 day treatment with atorvastatin (80 mg/day) and placebo (n = 24), or placebo treatment twice (n = 6). At the end of each treatment period, volunteers underwent 10 minutes of forearm ischaemic exercise. At reperfusion radiolabeled annexin A5 was administered intravenously and Gamma camera imaging of both hands was performed 1 and 4 hours after reperfusion.

RESULTS

Annexin A5 targeting was not different between atorvastatin treatment (26.1 ± 9.8% and 24.0 ± 9.5% respectively at 1 and 4 hours after reperfusion) and placebo treatment (25.6 ± 11.0% and 24.5 ± 10.7%) (p = 0.99). Our time control experiment did not reveal a carry-over effect.

CONCLUSIONS

Our results show that treatment with atorvastatin 80 mg does not reduce forearm PS exposition after ischaemic exercise. This suggests that the role of PS exposure in the prevention of ischemia and reperfusion injury by short term treatment with atorvastatin is limited.

The cardioprotective effects of metformin

PURPOSE OF REVIEW

In patients with type 2 diabetes mellitus, treatment with metformin is associated with a lower cardiovascular morbidity and mortality, compared with alternative glucose-lowering drugs. It has been suggested that metformin might exert direct protective effects on the heart.

RECENT FINDINGS

This review appraises recent experimental animal studies on the effect of metformin on myocardial ischaemia-reperfusion injury and remodeling. In murine models of myocardial infarction, the administration of metformin potently limits infarct size. Activation of adenosine monophosphate-activated protein kinase, increased formation of adenosine, and the prevention of opening of the mitochondrial permeability transition pore at reperfusion all contribute to this cardioprotective effect. In addition, metformin therapy attenuates postinfarction cardiac remodeling. There is evidence that activation of adenosine monophosphate-activated protein kinase and endothelial nitric oxide synthase, and a reduced collagen expression are crucial for this effect.

SUMMARY

The finding that metformin limits myocardial infarct size and remodeling in animal models of myocardial infarction suggests that patients suffering from myocardial ischaemia could benefit from treatment with metformin, even when these patients do not have diabetes. Currently, several clinical trials are being performed to test this hypothesis.

Effect of different sympathetic stimuli-autonomic dysreflexia and head-up tilt-on leg vascular resistance in spinal cord injury

OBJECTIVE

To compare the effect of different sympathetic stimuli, that is, exaggerated sympathetic activity and orthostatic challenges, on the increase in leg vascular resistance in persons with spinal cord injury (SCI) without and controls with supraspinal sympathetic control.

DESIGN

Case-control intervention study.

SETTING

Physiology research laboratory.

PARTICIPANTS

Persons with SCI (N=9; motor and sensory complete spinal cord lesion above the sixth thoracic spinal segment) and able-bodied controls (N=9).

INTERVENTIONS

In persons with SCI, exaggerated sympathetic activity was evoked by autonomic dysreflexia, and in controls, by using a cold pressor test (CPT). A 30° head-up tilt (HUT) was performed in both groups.

MAIN OUTCOME MEASURE

Leg blood flow was measured by using venous occlusion plethysmography during the different sympathetic stimuli. Leg vascular resistance was calculated as the arterial-venous pressure gradient divided by blood flow.

RESULTS

In persons with SCI, leg vascular resistance significantly increased during autonomic dysreflexia and 30° HUT (25±20 and 24±13 arbitrary units [AU], respectively), with no difference (P=.87) between stimuli. In controls, leg vascular resistance significantly increased during CPT and 30° HUT (15±13 and 29±12AU, respectively) with no difference (P=.03) between stimuli. There were no differences (P=.22) in increase in leg vascular resistance during the different sympathetic stimuli between persons with SCI and controls.

CONCLUSIONS

The increase in leg vascular resistance during autonomic dysreflexia in persons with SCI is not different from that during 30° HUT, which might be caused by a limited vasoconstrictor reserve. Despite the lack of supraspinal sympathetic control in persons with SCI, the increase in leg vascular resistance during exaggerated sympathetic activity was not different from controls.