Transcutaneous Electrical Nerve Stimulation Improves Vascular Conductance After Coronary Artery Bypass Graft Surgery

Study Overview
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Brief Summary
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The investigators will test the hypothesis that transcutaneous electrical nerve stimulation (TENS) may attenuate peripheral vasoconstriction and to improve blood flow redistribution during handgrip exercise in acute myocardial infarction (AMI) patients after Coronary Arterial Bypass Graft Surgery (CABG).

Detailed Description
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Thirty-eight patients will be randomized to a (4 times/day; 30 min/session) for 5-day program of TENS (n = 20) or to placebo-TENS (P-TENS, n = 18) applied on cervical region (C7-T4). Acute sympathetic stimulation by cold pressor test (CPT), Maximal voluntary contraction (MVC), Femoral blood flow (FBF) and femoral vascular conductance (FVC) will be measured as primary outcome pre and post-CABG, even as the 6-minute walk test (6-MWT), Inspiratory and expiratory muscle strength (PImax and PEmax) and β-endorphin as a secondary clinical parameters. In addition, amount of opioid analgesic and pain intensity also will be measured throughout at first 24 hours after CABG (immediately, 6, 12 and 24 hours).

Official Title
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Transcutaneous Electrical Nerve Stimulation Improves Vascular Conductance After Coronary Artery Bypass Graft Surgery

Conditions
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Acute Myocardial Infarction

Intervention / Treatment
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* Device: Transcutaneous electrical nerve stimulation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: a previous history of more than 1 vessel coronary artery disease, lifelong abstinence from tobacco, and formal indication for CABG, according to established guideline. Exclusion Criteria: Patients older than 70 years of age, with chronic renal failure, or with unstable angina in the 48 h prior to CABG, moderate or severe valve disease, complex cardiac arrhythmias, stroke, and/or inability to exercise the lower limbs.

Ages Eligible for Study
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Minimum Age: 48 Years
Maximum Age: 70 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: TENS CABG<br>Eligible patients will be randomized to a transcutaneous electrical nerve stimulation program (TENS; n = 20) or to placebo-TENS (P-TENS; n = 18). All patients were followed by their own physicians, received routine nursing assistance, and were visited daily by one of the investigators, but P-TENS group will be not exposed to any specific electrical stimulation or motor physical intervention. | Device: Transcutaneous electrical nerve stimulation<br>* Patients will be treated with conventional TENS (ENDOMED 684 Device, ENRAF-Nonius B.V., Rotterdam, Netherlands) for 5 days (4 times/day; 30 min/session) applied on cervical region (C7-T4). TENS intervention was applied as described elsewhere.<br>* Other names: electrical stimulation;|
| Placebo Comparator: P-TENS CABG<br>Patients will be treated with placebo-TENS (P-TENS) condition for 5 days (4 times/day; 30 min/session) applied on cervical region (C7-T4). P-TENS device underwent modifications in its internal programming: the control capacitor of the time constant was changed and the active time between pulses was modified from 330 milliseconds to 33 seconds, in order to prevent an analgesic effect (33). | Device: Transcutaneous electrical nerve stimulation<br>* Patients will be treated with conventional TENS (ENDOMED 684 Device, ENRAF-Nonius B.V., Rotterdam, Netherlands) for 5 days (4 times/day; 30 min/session) applied on cervical region (C7-T4). TENS intervention was applied as described elsewhere.<br>* Other names: electrical stimulation;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Blood flow redistribution - baseline and 5 days later | The ultrasound Doppler system will be equipped with two linear array transducers operating at an imaging frequency of 7- 8 megahertz (MHz). The common femoral artery of the left leg will be insonated distal to the inguinal ligament, 2-3 cm proximal to the bifurcation. Using femoral artery diameter and mean blood velocity (MBF), femoral blood flow (FBF) was calculated as MBF π x (vessel diameter/2)2 x 60. Femoral vascular resistance (FVR) and femoral vascular conductance (FVC) were calculated as (MBP/FBF) and (FBF/MBP * 100 mm Hg), the conductance multiplied by 100 mmHg so that the conductance units will be similar to the units of femoral blood flow (10, 45). The magnitude of reduction FVC (expressed in %) was calculated as vascular conductance during exercise (% change) - conductance at rest (% change) expressed by % of baseline. | 1 day | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Inspiratory and Expiratory Muscle Function | Inspiratory and expiratory muscle strength testing were performed using a pressure transducer (MVD-500 V.1.1 Micro Hard System, Global Med, Porto Alegre, Brazil). Maximal inspiratory (PImax), and maximal static expiratory pressure (PEmax) were measured as previously described. | 5 day | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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exercise, neuromodulation, blood flow, exercise capacity