Research Interests

Our laboratory’s research focus entails the investigation of neural cardiovascular control at rest and during exercise in humans with a specific emphasis on the sympathetic branch of the autonomic nervous system. Ongoing studies involve assessing sympathetic responses during various physiological manipulations including isometric and aerobic forms of exercise, lower body negative pressure to simulate the effect of gravity when one stands up, and infusions of pharmacological agents. Studies are performed in normal healthy subjects as well as in patients with various pathophysiological conditions such as heart failure and hypertension. Our laboratory obtains direct measures of sympathetic neural firing using the technique of microneurography. This measurement allows for the assessment of moment-to-moment as well as long term changes in sympathetic nerve activity. Also, with the application of partial autospectral and time series analyses to muscle sympathetic neurograms we are beginning to investigate the central origin(s) and pattern(s) of sympathetic discharge in humans.

Our current research focus is on the neural mechanisms that contribute to exercise-induced sympathoexcitation as well as the peripheral modulators of sympathetically-mediated vasoconstriction in contracting skeletal muscle with a particular emphasis on the potential roles of free radicals and changes in nitric oxide signaling in altering these responses. Considering the continually increasing population of elderly individuals, our future direction will be to begin to examine age related alterations in neural cardiovascular control during exercise. Research in this area has been limited and is extremely important considering that an exaggerated blood pressure response to exercise increases the risk for mortality in otherwise healthy adults.

Professional Background

• B.S. in Physical Education, Brooklyn College, Brooklyn, NY
• M.S. in Clinical Exercise Physiology, Northeastern University, Boston, MA
• Ph.D. in Biomedical Sciences, UNT Health Science Center, Fort Worth, TX
• Completed postdoctoral training at UT Southwestern Medical Center, Dallas, TX
• Recipient of New Investigator Award, UT Southwestern Allied Health Sciences School
• Recipient of American Physiological Society, Neural Control & Autonomic Regulation Section Michael J. Brody Young Investigator Award
• Recipient of American Physiological Society, Research Career Enhancement Award
• Recipient of American Physiological Society, Caroline tum Suden/Frances A. Hellebrandt Professional Opportunity Award

Selected Publications

• Fadel, P.J., Z. Wang, H. Watanabe, D. Arbique, W. Vongpatanasin, and G.D. Thomas. Augmented Sympathetic Vasoconstriction in Exercising Forearms of Postmenopausal Women is Reversed by Oestrogen Therapy. Journal of Physiology, 561.3: 893-901, 2004.
• Fadel, P.J., S.M. Barman, S.W. Phillips, and G.L. Gebber. Fractal Fluctuations in Human Respiration. Journal of Applied Physiology, 97: 2056-2064, 2004.
• Fadel, P.J., D.M. Keller, H. Watanabe, P.B. Raven and G.D. Thomas. Noninvasive Assessment of Sympathetic Vasoconstriction in Human and Rodent Skeletal Muscle Using Near Infrared Spectroscopy and Doppler Ultrasound. Journal of Applied Physiology, 96: 1323-1330, 2004.
• Fadel, P.J., H.S. Orer, S.M. Barman, W. Vongpatanasin, R.G. Victor, and G.L. Gebber. Fractal Properties of Human Muscle Sympathetic Nerve Activity. AJP: Heart and Circulatory Physiology, 286: H1076-H1087, 2004.
• Abbas, A., P.J. Fadel, Z. Wang, D. Arbique, I. Jialal, and W. Vongpatanasin. Contrasting Effects of Oral vs. Transdermal Estrogen on Serum Amyloid A (SAA) and HDL-SAA in Postmenopausal women. Arterioscler Thromb Vasc Biol, 24: 1-4, 2004.
• Wray, D.W., P.J. Fadel, M.L. Smith, P.B. Raven, and M. Sander. Inhibition of Alpha Adrenergic Vasoconstriction in Exercising Human Thigh Muscles. Journal of Physiology, 555.2: 545-563, 2004.
• Fadel, P.J., Z. Wang, M. Tuncel, H. Watanabe, A. Abbas, D. Arbique, W. Vongpatanasin, R.W. Haley, R.G. Victor, G.D. Thomas. Reflex Sympathetic Activation during Static Exercise is Severely Impaired in Patients with Myophosphorylase Deficiency. Journal of Physiology, 548: 983-993, 2003.
• Fadel, P.J., M. Stromstad, D.W. Wray, S.A. Smith, P.B. Raven and N.H Secher. New Insights into Differential Baroreflex Control of Heart Rate in Humans. AJP: Heart and Circulatory Physiology, 284: H735-H743, 2003.
• Ogoh, S., P.J. Fadel, P. Nissen, O. Jans, C. Selmer, N.H. Secher, and P.B. Raven. Baroreflex-Mediated Changes in Cardiac Output and Vascular Conductance in Response to Alterations in Carotid Sinus Pressure during Exercise in Humans. Journal of Physiology, 550.1: 317-324, 2003.

Methodology/Techniques

An invaluable tool for my research is the technique of microneurography, whereby sympathetic neurograms are obtained from the placement of a tungsten microelectrode into the peroneal nerve near the fibular head or popliteal fossa of the lower leg. By obtaining such a direct and continuous measure of sympathetic neural firing, we can assess moment-to-moment as well as long term changes in sympathetic nerve activity. Other techniques available in the laboratory include typical laboratory stressors for assessing reflex control of the autonomic nervous system in humans as well as various analytical procedures to evaluate the oscillations and patterns of sympathetic nerve activity.