This work was supported by a University of Texas at Arlington Interdisciplinary Research Program grant.

This protocol follows the guidelines of the institutional review board at the University of Texas at Arlington and conforms to the standards set by the latest version of the Declaration of Helsinki. Accordingly, written informed consent was (and should be) obtained prior to commencement of research procedures.
1. Instrumentation
NOTE: The following instrumentation description is based on the near-infrared (NIR) spectrometer and data acquisition system used in our lab ...

<ol>
	<li>Huang, A. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Predictive+value+of+reactive+hyperemia+for+cardiovascular+events+in+patients+with+peripheral+arterial+disease+undergoing+vascular+surgery.">Predictive value of reactive hyperemia for cardiovascular events in patients with peripheral arterial disease undergoing vascular surgery.</a> Arterioscler Thromb Vasc Biol. 27 (10), 2113-2119 (2007).</li><li>Suryapranata, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Predictive+value+of+reactive+hyperemic+response+on+reperfusion+on+recovery+of+regional+myocardial+function+after+coronary+angioplasty+in+acute+myocardial+infarction.">Predictive value of reactive hyperemic response on reperfusion on recovery of regional myocardial function after coronary angioplasty in acute myocardial infarction.</a> Circulation. 89 (3), 1109-1117 (1994).</li><li>Richardson, R. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Muscle+Blood-Flow+in+Man+-+Is+Maximal+O2+Extraction+Compromised.">High Muscle Blood-Flow in Man - Is Maximal O2 Extraction Compromised.</a> J of Appl Physiol. 75 (4), 1911-1916 (1993).</li><li>Clifford, P. S., Hellsten, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vasodilatory+mechanisms+in+contracting+skeletal+muscle.">Vasodilatory mechanisms in contracting skeletal muscle.</a> J Appl Physiol. 97 (1), 393-403 (2004).</li><li>Hansen, J., Thomas, G. D., Jacobsen, T. N., Victor, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Muscle+metaboreflex+triggers+parallel+sympathetic+activation+in+exercising+and+resting+human+skeletal+muscle.">Muscle metaboreflex triggers parallel sympathetic activation in exercising and resting human skeletal muscle.</a> Am J Physiol. 266 (6 Pt 2), H2508-H2514 (1994).</li><li>Thomas, G. D., Victor, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nitric+oxide+mediates+contraction-induced+attenuation+of+sympathetic+vasoconstriction+in+rat+skeletal+muscle.">Nitric oxide mediates contraction-induced attenuation of sympathetic vasoconstriction in rat skeletal muscle.</a> J Physiol. 506 (Pt 3), 817-826 (1998).</li><li>Hansen, J., Thomas, G. D., Harris, S. A., Parsons, W. J., Victor, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+sympathetic+neural+control+of+oxygenation+in+resting+and+exercising+human+skeletal+muscle.">Differential sympathetic neural control of oxygenation in resting and exercising human skeletal muscle.</a> J Clin Invest. 98 (2), 584-596 (1996).</li><li>Rosenmeier, J. B., Fritzlar, S. J., Dinenno, F. A., Joyner, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exogenous+NO+administration+and+alpha-adrenergic+vasoconstriction+in+human+limbs.">Exogenous NO administration and alpha-adrenergic vasoconstriction in human limbs.</a> J Appl Physiol. 95 (6), 2370-2374 (2003).</li><li>Fadel, P. J., Keller, D. M., Watanabe, H., Raven, P. B., Thomas, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Noninvasive+assessment+of+sympathetic+vasoconstriction+in+human+and+rodent+skeletal+muscle+using+near-infrared+spectroscopy+and+Doppler+ultrasound.">Noninvasive assessment of sympathetic vasoconstriction in human and rodent skeletal muscle using near-infrared spectroscopy and Doppler ultrasound.</a> J Appl Physiol. 96 (4), 1323-1330 (2004).</li><li>Nelson, M. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PDE5+inhibition+alleviates+functional+muscle+ischemia+in+boys+with+Duchenne+muscular+dystrophy.">PDE5 inhibition alleviates functional muscle ischemia in boys with Duchenne muscular dystrophy.</a> Neurology. 82 (23), 2085-2091 (2014).</li><li>Nelson, M. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sodium+nitrate+alleviates+functional+muscle+ischaemia+in+patients+with+Becker+muscular+dystrophy.">Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy.</a> J Physiol. 593 (23), 5183-5200 (2015).</li><li>Remensnyder, J. P., Mitchell, J. H., Sarnoff, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+sympatholysis+during+muscular+activity.+Observations+on+influence+of+carotid+sinus+on+oxygen+uptake.">Functional sympatholysis during muscular activity. Observations on influence of carotid sinus on oxygen uptake.</a> Circ Res. 11, 370-380 (1962).</li><li>Kodama, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiorespiratory+fitness+as+a+quantitative+predictor+of+all-cause+mortality+and+cardiovascular+events+in+healthy+men+and+women:+A+meta-analysis.">Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: A meta-analysis.</a> JAMA. 301 (19), 2024-2035 (2009).</li><li>Westerblad, H., Place, N., Yamada, T., Rassier, D. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Muscle Biophysics: From Molecules to Cells. , 279-296 (2010).</li><li>Tyni-Lenn&#233;, R., Gordon, A., Jansson, E., Bermann, G., Sylv&#233;n, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skeletal+muscle+endurance+training+improves+peripheral+oxidative+capacity,+exercise+tolerance,+and+health-related+quality+of+life+in+women+with+chronic+congestive+heart+failure+secondary+to+either+ischemic+cardiomyopathy+or+idiopathic+dilated+cardiomyopathy.">Skeletal muscle endurance training improves peripheral oxidative capacity, exercise tolerance, and health-related quality of life in women with chronic congestive heart failure secondary to either ischemic cardiomyopathy or idiopathic dilated cardiomyopathy.</a> Am J of Cardiol. 80 (8), 1025-1029 (1997).</li><li>Cabalzar, A. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Muscle+function+and+quality+of+life+in+the+Crohn's+disease.">Muscle function and quality of life in the Crohn's disease.</a> Fisioter Mov. 30, 337-345 (2017).</li><li>Esch, B. T., Scott, J. M., Warburton, D. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Construction+of+a+lower+body+negative+pressure+chamber.">Construction of a lower body negative pressure chamber.</a> Adv Physiol Educ. 31 (1), 76-81 (2007).</li><li>Ryan, T. E., Southern, W. M., Reynolds, M. A., McCully, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+cross-validation+of+near-infrared+spectroscopy+measurements+of+skeletal+muscle+oxidative+capacity+with+phosphorus+magnetic+resonance+spectroscopy.">A cross-validation of near-infrared spectroscopy measurements of skeletal muscle oxidative capacity with phosphorus magnetic resonance spectroscopy.</a> J Appl Physiol. 115 (12), 1757-1766 (2013).</li><li>Ryan, T. E., Brophy, P., Lin, C. T., Hickner, R. C., Neufer, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+in+vivo+skeletal+muscle+mitochondrial+respiratory+capacity+in+humans+by+near-infrared+spectroscopy:+a+comparison+with+in+situ+measurements.">Assessment of in vivo skeletal muscle mitochondrial respiratory capacity in humans by near-infrared spectroscopy: a comparison with in situ measurements.</a> J Physiol. 592 (15), 3231-3241 (2014).</li><li>Adami, A., Rossiter, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Principles,+insights+and+potential+pitfalls+of+the+non-invasive+determination+of+muscle+oxidative+capacity+by+near-infrared+spectroscopy.">Principles, insights and potential pitfalls of the non-invasive determination of muscle oxidative capacity by near-infrared spectroscopy.</a> J Appl Physiol. , (2017).</li><li>Corretti, M. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Guidelines+for+the+ultrasound+assessment+of+endothelial-dependent+flow-mediated+vasodilation+of+the+brachial+artery+-+A+report+of+the+International+Brachial+Artery+Reactivity+Task+Force.">Guidelines for the ultrasound assessment of endothelial-dependent flow-mediated vasodilation of the brachial artery - A report of the International Brachial Artery Reactivity Task Force.</a> J Am Coll Cardiol. 39 (2), 257-265 (2002).</li><li>Thijssen, D. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+flow-mediated+dilation+in+humans:+a+methodological+and+physiological+guideline.">Assessment of flow-mediated dilation in humans: a methodological and physiological guideline.</a> Am J Physiol Heart Circ Physiol. 300 (1), H2-H12 (2011).</li><li>Green, D. J., Jones, H., Thijssen, D., Cable, N. T., Atkinson, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow-mediated+dilation+and+cardiovascular+event+prediction:+does+nitric+oxide+matter?.">Flow-mediated dilation and cardiovascular event prediction: does nitric oxide matter?.</a> Hypertension. 57 (3), 363-369 (2011).</li><li>Southern, W. M., Ryan, T. E., Reynolds, M. A., McCully, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reproducibility+of+near-infrared+spectroscopy+measurements+of+oxidative+function+and+postexercise+recovery+kinetics+in+the+medial+gastrocnemius+muscle.">Reproducibility of near-infrared spectroscopy measurements of oxidative function and postexercise recovery kinetics in the medial gastrocnemius muscle.</a> Appl Physiol Nutr Metab. 39 (5), 521-529 (2014).</li><li>Ryan, T. E., Erickson, M. L., Brizendine, J. T., Young, H. J., McCully, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Noninvasive+evaluation+of+skeletal+muscle+mitochondrial+capacity+with+near-infrared+spectroscopy:+correcting+for+blood+volume+changes.">Noninvasive evaluation of skeletal muscle mitochondrial capacity with near-infrared spectroscopy: correcting for blood volume changes.</a> J Appl Physiol. 113 (2), 175-183 (2012).</li><li>Ryan, T. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skeletal+muscle+oxidative+capacity+in+amyotrophic+lateral+sclerosis.">Skeletal muscle oxidative capacity in amyotrophic lateral sclerosis.</a> Muscle Nerve. 50 (5), 767-774 (2014).</li><li>Mayeur, C., Campard, S., Richard, C., Teboul, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+four+different+vascular+occlusion+tests+for+assessing+reactive+hyperemia+using+near-infrared+spectroscopy.">Comparison of four different vascular occlusion tests for assessing reactive hyperemia using near-infrared spectroscopy.</a> Crit Care Med. 39 (4), 695-701 (2011).</li><li>McLay, K. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vascular+responsiveness+determined+by+near-infrared+spectroscopy+measures+of+oxygen+saturation.">Vascular responsiveness determined by near-infrared spectroscopy measures of oxygen saturation.</a> Exp Physiol. 101 (1), 34-40 (2016).</li><li>McLay, K. M., Nederveen, J. P., Pogliaghi, S., Paterson, D. H., Murias, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Repeatability+of+vascular+responsiveness+measures+derived+from+near-infrared+spectroscopy.">Repeatability of vascular responsiveness measures derived from near-infrared spectroscopy.</a> Physiol Rep. 4 (9), (2016).</li><li>Ryan, T. E., Southern, W. M., Brizendine, J. T., McCully, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activity-induced+changes+in+skeletal+muscle+metabolism+measured+with+optical+spectroscopy.">Activity-induced changes in skeletal muscle metabolism measured with optical spectroscopy.</a> Med Sci Sports Exerc. 45 (12), 2346-2352 (2013).</li><li>Southern, W. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduced+skeletal+muscle+oxidative+capacity+and+impaired+training+adaptations+in+heart+failure.">Reduced skeletal muscle oxidative capacity and impaired training adaptations in heart failure.</a> Physiol Rep. 3 (4), (2015).</li><li>Ryan, T. E., Brizendine, J. T., McCully, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comparison+of+exercise+type+and+intensity+on+the+noninvasive+assessment+of+skeletal+muscle+mitochondrial+function+using+near-infrared+spectroscopy.">A comparison of exercise type and intensity on the noninvasive assessment of skeletal muscle mitochondrial function using near-infrared spectroscopy.</a> J Appl Physiol. 114 (2), 230-237 (2013).</li><li>Adami, A., Cao, R., Porszasz, J., Casaburi, R., Rossiter, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reproducibility+of+NIRS+assessment+of+muscle+oxidative+capacity+in+smokers+with+and+without+COPD.">Reproducibility of NIRS assessment of muscle oxidative capacity in smokers with and without COPD.</a> Respir Physiol Neurobiol. 235, 18-26 (2017).</li><li>Lacroix, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reproducibility+of+near-infrared+spectroscopy+parameters+measured+during+brachial+artery+occlusion+and+reactive+hyperemia+in+healthy+men.">Reproducibility of near-infrared spectroscopy parameters measured during brachial artery occlusion and reactive hyperemia in healthy men.</a> J Biomed Opt. 17 (7), 077010 (2012).</li><li>Bopp, C. M., Townsend, D. K., Warren, S., Barstow, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relationship+between+brachial+artery+blood+flow+and+total+[hemoglobin+myoglobin]+during+post-occlusive+reactive+hyperemia.">Relationship between brachial artery blood flow and total [hemoglobin+myoglobin] during post-occlusive reactive hyperemia.</a> Microvasc Res. 91, 37-43 (2014).</li><li>Willingham, T. B., Southern, W. M., McCully, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+reactive+hyperemia+in+the+lower+limb+using+near-infrared+spectroscopy.">Measuring reactive hyperemia in the lower limb using near-infrared spectroscopy.</a> J Biomed Opt. 21 (9), 091302 (2016).</li><li>Kragelj, R., Jarm, T., Erjavec, T., Presern-Strukelj, M., Miklavcic, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parameters+of+postocclusive+reactive+hyperemia+measured+by+near+infrared+spectroscopy+in+patients+with+peripheral+vascular+disease+and+in+healthy+volunteers.">Parameters of postocclusive reactive hyperemia measured by near infrared spectroscopy in patients with peripheral vascular disease and in healthy volunteers.</a> Ann Biomed Eng. 29 (4), 311-320 (2001).</li><li>Gurley, K., Shang, Y., Yu, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Noninvasive+optical+quantification+of+absolute+blood+flow,+blood+oxygenation,+and+oxygen+consumption+rate+in+exercising+skeletal+muscle.">Noninvasive optical quantification of absolute blood flow, blood oxygenation, and oxygen consumption rate in exercising skeletal muscle.</a> J Biomed Opt. 17 (7), 075010 (2012).</li></ol>

The authors declare that they have no competing financial interests.

The methods described herein enable non-invasive, clinical evaluation of reactive hyperemia, neurovascular coupling, and skeletal muscle oxidative capacity in a single clinic or laboratory visit.
Critical Considerations
Although NIRS is relatively robust and easy to use, collection of these data require careful placement of the optodes directly over the muscle belly, secured tightly in place to avoid movement artifact, and covered with a bl...

The hyperemic response to a brief period of tissue ischemia has emerged as a key non-invasive measure of (micro)vascular function. During occlusion of a conduit artery, downstream arterioles dilate in an effort to offset the ischemic insult. Upon release of the occlusion, the decreased vascular resistance results in hyperemia, the magnitude of which is dictated by one&#39;s ability to dilate the downstream microvasculature. While reactive hyperemia is a strong independent predictor of cardiovascular events1,2&#160;and therefore a clinically significant endpoint, its functional significance to exercise tolerance and quality of life is less clear.
Indeed, dynamic exercise represents a major cardiovascular stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic demand. For example, skeletal muscle blood flow can increase nearly 100-fold during isolated muscle contractions3, which would overwhelm the pumping capacity of the heart if such a hemodynamic response were extrapolated to whole-body exercise. Accordingly, to avoid severe hypotension, sympathetic (i.e., vasoconstrictor) nervous activity increases to redistribute cardiac output away from inactive and visceral tissues and towards active skeletal muscle4. Sympathetic outflow is also directed to the exercising skeletal muscle5; however, local metabolic signaling attenuates the vasoconstrictor response in order to ensure adequate tissue oxygen delivery6,7,8,9,10,11. Collectively, this process is termed functional sympatholysis12, and is imperative to the normal regulation of skeletal muscle blood flow during exercise. Since skeletal muscle blood flow is a key determinant of aerobic capacity &#8212; an independent predictor of quality of life and cardiovascular disease morbidity and mortality13&#8212; understanding the control of skeletal muscle blood flow and tissue oxygen delivery during exercise is of great clinical significance.
Oxygen delivery is only half of the Fick equation, however, with oxygen utilization satisfying the other half of the equation. Among the major determinates of oxygen utilization, mitochondrial oxidative phosphorylation plays an essential role in supplying adequate energy for cellular processes both at rest and during exercise. Indeed, impairments in muscle oxidative capacity can limit functional capacity and quality of life14,15,16. Various measures are commonly used to provide an index of muscle oxidative capacity, including invasive muscle biopsies and expensive and time-consuming magnetic resonance spectroscopy (MRS) techniques.
Here, we propose a novel, non-invasive approach, using near-infrared spectroscopy (NIRS), to assess each of these three major clinical endpoints (reactive hyperemia, sympatholysis, and muscle oxidative capacity) in a single clinic or laboratory visit. The major advantages of this approach are three-fold: First, this technique is easily portable, relatively low cost, and easy to perform. Current Doppler ultrasound approaches for measuring reactive hyperemia are highly operator-dependent &#8212; requiring extensive skill and training &#8212; and require sophisticated, high-cost, data acquisition hardware and post-processing software. Moreover, this could conceivably be introduced into the clinic and/or large clinical trials for bedside monitoring or testing therapeutic efficacy. Second, by virtue of the methodology, this technique focuses specifically on the skeletal muscle microvasculature, increasing the overall specificity of the technique. Alternative approaches using Doppler ultrasound focus entirely on upstream conduit vessels and infer changes downstream, which can dampen the signal. Third, this technique is completely non-invasive. Skeletal muscle oxidative capacity is traditionally assessed with invasive and painful muscle biopsies, and functional sympatholysis may be assessed with intra-arterial injection of sympathomimetics and sympatholytics. This approach avoids these requirements all together.

<table border="0" cellpadding="0" cellspacing="0" width="836">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:328px;">Dual-channel OxiplexTS Near-infrared spectroscopy machine</td>
			<td style="width:223px;">Iss Medical</td>
			<td align="right" style="width:119px;">101</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">NIRS muscle sensor</td>
			<td style="width:223px;">Iss Medical</td>
			<td align="right" style="width:119px;">201.2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">E20 Rapid cuff inflation system</td>
			<td style="width:223px;">Hokanson</td>
			<td style="width:119px;">E20</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">AG101 Air Source</td>
			<td style="width:223px;">Hokanson</td>
			<td style="width:119px;">AG101</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">Smedley Handgrip dynometer (recording)</td>
			<td style="width:223px;">Stolting</td>
			<td align="right" style="width:119px;">56380</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">Powerlab 16/35, 16 Channel Recorder</td>
			<td style="width:223px;">ADInstruments</td>
			<td style="width:119px;">PL3516</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">Human NIBP Set</td>
			<td style="width:223px;">ADInstruments</td>
			<td style="width:119px;">ML282-SM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">Bio Amp</td>
			<td style="width:223px;">ADInstruments</td>
			<td style="width:119px;">FE132</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">Quad Bridge Amp</td>
			<td style="width:223px;">ADInstruments</td>
			<td style="width:119px;">FE224</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">Connex Spot Monitor</td>
			<td style="width:223px;">Welch Allyn</td>
			<td style="width:119px;">71WX-B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:328px;">Origin(Pro) graphing software</td>
			<td style="width:223px;">OrignPro</td>
			<td style="width:119px;">Pro</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:328px;">Lower body negative pressure chamber</td>
			<td style="width:223px;">Physiology Research Instruments</td>
			<td style="width:119px;">standard unit</td>
			<td></td>
		</tr>
	</tbody>
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skeletal muscle neurovascular coupling, oxidative capacity, and microvascular function with 'one stop shop' near-infrared spectroscopy

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic demand. Reactive hyperemia (in response to a brief period of tissue ischemia) is an independent predictor of cardiovascular events and provides important insight into vascular health and vasodilatory capacity. Skeletal muscle oxidative capacity is equally important in health and disease, as it determines the energy supply for myocellular processes. Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess each of these major clinical endpoints (reactive hyperemia, neurovascular coupling, and muscle oxidative capacity) during a single clinic or laboratory visit. Unlike Doppler ultrasound, magnetic resonance images/spectroscopy, or invasive catheter-based flow measurements or muscle biopsies, our approach is less operator-dependent, low-cost, and completely non-invasive. Representative data from our lab taken together with summary data from previously published literature illustrate the utility of each of these end-points. Once this technique is mastered, application to clinical populations will provide important mechanistic insight into exercise intolerance and cardiovascular dysfunction.

Skeletal muscle oxidative capacity
Figure 2 illustrates a representative participant response during a NIRS-derived skeletal muscle oxidative capacity assessment. Panel A shows the tissue saturation profile during a 5 min arterial cuff occlusion protocol, handgrip exercise, and intermittent arterial occlusion during recovery from exercise. Panel B illustrates the expected t...

Watch this Scientific Journal Video about Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy at JoVE.com

Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with &#039;One Stop Shop&#039; Near-infrared Spectroscopy

Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess reactive hyperemia, neurovascular coupling and skeletal muscle oxidative capacity in a single clinic or laboratory visit.

Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic ...

The specific goals of this experiment are to noninvasively assess skeletal muscle oxidative capacity, to assess exercise skeletal muscle blood flow regulation, and to measure reactive hyperemia. These methods can help answer important questions related to the pathophysiology of exercise intolerance and cardiovascular disease. The main advantage of this technique is that we can noninvasively assess macro and micro vascular function and skeletal oxidative capacity in any clinical or laboratory setting.Generally, individuals new to this method will struggle because of the operator-dependent nature of near-infrared spectroscopy. It is important to achieve consistent and accurate placement of the probe, as small deviations from optimal placement could have a large impact on signal quality. Begin with instructing the subject to lie supine with their legs inside an LBNP chamber so that their belt line is approximately even with the opening of the LBNP box.Next, optimally place three electrocardiogram electrodes on the subject, two in an inferior midclavicular location and one on the subject's left side medial to the iliac crest. To proceed, place a non-invasive blood pressure monitor module on the subject's dominant wrist. Make use of properly-calibrated finger blood pressure cuffs.Place them on each finger. Now instruct the subject to grasp an HGD with their nondominant hand in a slightly abducted position. Have the subject position their arm comfortably on the bedside table, then adjust the distance and angle of the HGD for optimal grip strength with minimal arm movement.Then secure the HGD to a bedside table. Next, measure the maximum voluntary contraction of the subject. Tell the participant that when prompted to squeeze the HGD as hard as possible, only utilizing the muscles in the hand and forearm.The subject must refrain from recruiting their upper arm, chest, shoulder, or abdominal muscles. Take three measurements separated by 60 seconds and record the highest force exerted. Next, place a rapid inflation cuff around the upper arm of the exercising hand.Connect the air line from the rapid inflation controller to the cuff. Then palpate for the flexor digitorum profundus and mark its borders. Then clean the skin over the muscle with an alcohol prep wipe and place the NIR probe over the center of the belly of the muscle.Proper identification of the flexor digitorum profundus is crucial for the correct placement of the near-infrared probe. To do this, instruct the subject to perform a light grip on the dynamometer while palpating the anterior medial aspect of the forearm. Affix the probe securely to the forearm and wrap it with dark cloth to minimize interference from ambient light.After completing the instrumentation, instruct the subject to lie still for two minutes and record the initial baseline value of tissue saturation prior to the cuff occlusion. Then inflate the upper arm cuff to at least 30 millimeters of mercury above systolic for five minutes. It is very important that the subject be still and relaxed during all cuff inflations and deflations to minimize motion artifacts.Now record the lowest value of tissue saturation during the cuff occlusion. After deflating the cuff, let the subject return to the resting baseline values. Once the subject has maintained a resting baseline for at least one full minute, instruct the subject to squeeze and maintain an isometric hand grip at 50%of their maximum voluntary contraction.Encourage the subject to maintain their isometric contraction until the tissue desaturates by 50%Then tell the subject to relax their hand and that no more exercise or movement is needed. Within three to five seconds, administer a rapid cuff occlusion series consisting of 18 inflations and deflations of progressively greater durations. After the 18th series, instruct the subject to rest and stay as still as possible.Once saturation has returned to baseline for at least two minutes, repeat the 18 cuff occlusions once more. Instrument the subject as before and seal the subject into the LBNP chamber. Ensure that the seal is airtight.Then with the subject lying still and at rest collect three minutes of baseline data. At the three minute mark, turn on the vacuum to drop the chamber pressure by 20 to 30 millimeters of mercury. Run the vacuum for two minutes while monitoring the subject's response.At the five minute mark, turn off the vacuum and allow the subject to rest for three minutes. Then at the eight minute mark, initiate a voice prompt guiding the subject through a rhythmic hand grip exercise at 20%maximum voluntary contraction. Observe that the subject is maintaining a consistent squeeze at 20%of maximum and relaxing completely between grips.Do this until the 11 minute mark. Then turn on the vacuum while the subject continues the exercise. After two minutes turn off the vacuum and have the subject continue the exercise for two more minutes.When this is over, have the subject rest quietly and lie still. The NIRS-derived skeletal muscle oxidative capacity assessment includes a tissue saturation profile during a five minute arterial cuff occlusion protocol, hand grip exercise, and intermittent arterial occlusion during recovery from exercise. The expected tissue desaturation-resaturation profile shows that during the intermittent arterial occlusions during the recovery period, the rate of desaturation is directly proportional to the rate of muscle oxygen consumption.The calculated muscle oxygen consumption recovery data should fit to a mono-exponential curve and the recovery time constant derived. The NIRS-derived reactive hyperemia profile provides valuable insight into vascular reactivity and the test is easily adaptable and clinically meaningful. In a healthy control subject, when LBNP is superimposed on a mild hand grip the reflex decrease in muscle oxygenation is attenuated by about 50%Failure to attenuate sympathic nerve activity during exercise disrupts the balance between oxygen delivery and utilization, and causes functional muscle ischemia.After watching this video you should have a good understanding of how to noninvasively assess skeletal muscle oxidative capacity, reactive hyperemia, and functional sympatholysis using commercially available near-infrared spectroscopy. While attempting this procedure, it's important to allow subjects to recover adequately between each stimulus. Once mastered, this data collection can be completed in 60 minutes or less.Following this procedure, other methods like diffuse correlation spectroscopy which assesses microvascular perfusion, can be incorporated to provide further mechanistic insight into skeletal muscle oxygen delivery and utilization.

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12.4K Görüntüleme.  University of Texas at Arlington. The specific goals of this experiment are to noninvasively assess skeletal muscle oxidative capacity, to assess exercise skeletal muscle blood flow regulation, and to measure reactive hyperemia. These methods can help answer important questions related to the pathophysiology of exercise intolerance and cardiovascular disease. The main advantage of this technique is that we can noninvasively assess macro and micro vascular function and skeletal oxidative capacity in any clinical or laboratory ...