My research focuses on the interactions between the autonomic nervous system and nitric oxide in the regulation of blood pressure, in normal physiology and disease states. In particular, the impact of increased sympathetic activity on impaired nitric oxide function as seen in obesity associated hypertension.

Our group is interested in understanding the role of the interactions between neural and local mechanisms that regulate blood pressure.

We run a complete autonomic laboratory that includes autonomic reflex testing, tilt table testing, microneurography (direct recording of sympathetic traffic), measurement of plasma catecholamines and metabolites, ganglionic blockade to induce transient autonomic failure, and estimation of norepinephrine spillover.

We also perform physiological and pharmacological tests using different techniques that includes determination of peak oxygen consumption, measurement of cardiac output by the re-breathing method and the the perfused forearm technique to asses endothelial function


The following timeline graph is generated from all co-authored publications.

  1. Low-dose propranolol and exercise capacity in postural tachycardia syndrome: a randomized study. Arnold AC, Okamoto LE, Diedrich A, Paranjape SY, Raj SR, Biaggioni I, Gamboa A (2013) Neurology 80(21): 1927-33
    › Primary publication · 23616163 (PubMed) · PMC3716342 (PubMed Central)
  2. Nitric oxide and regulation of heart rate in patients with postural tachycardia syndrome and healthy subjects. Gamboa A, Okamoto LE, Raj SR, Diedrich A, Shibao CA, Robertson D, Biaggioni I (2013) Hypertension 61(2): 376-81
    › Primary publication · 23283362 (PubMed) · PMC3621717 (PubMed Central)
  3. Angiotensin II, independent of plasma renin activity, contributes to the hypertension of autonomic failure. Arnold AC, Okamoto LE, Gamboa A, Shibao C, Raj SR, Robertson D, Biaggioni I (2013) Hypertension 61(3): 701-6
    › Primary publication · 23266540 (PubMed) · PMC3573256 (PubMed Central)
  4. Synergistic effect of norepinephrine transporter blockade and α-2 antagonism on blood pressure in autonomic failure. Okamoto LE, Shibao C, Gamboa A, Choi L, Diedrich A, Raj SR, Black BK, Robertson D, Biaggioni I (2012) Hypertension 59(3): 650-6
    › Primary publication · 22311903 (PubMed) · PMC3312003 (PubMed Central)
  5. Sympathetic activation and nitric oxide function in early hypertension. Gamboa A, Okamoto LE, Diedrich A, Choi L, Robertson D, Farley G, Paranjape S, Biaggioni I (2012) Am J Physiol Heart Circ Physiol 302(7): H1438-43
    › Primary publication · 22287587 (PubMed) · PMC3330790 (PubMed Central)
  6. Neurohumoral and haemodynamic profile in postural tachycardia and chronic fatigue syndromes. Okamoto LE, Raj SR, Peltier A, Gamboa A, Shibao C, Diedrich A, Black BK, Robertson D, Biaggioni I (2012) Clin Sci (Lond) 122(4): 183-92
    › Primary publication · 21906029 (PubMed) · PMC3203411 (PubMed Central)
  7. Comparative efficacy of yohimbine against pyridostigmine for the treatment of orthostatic hypotension in autonomic failure. Shibao C, Okamoto LE, Gamboa A, Yu C, Diedrich A, Raj SR, Robertson D, Biaggioni I (2010) Hypertension 56(5): 847-51
    › Primary publication · 20837887 (PubMed) · PMC2959129 (PubMed Central)
  8. Renal impairment of pure autonomic failure. Garland EM, Gamboa A, Okamoto L, Raj SR, Black BK, Davis TL, Biaggioni I, Robertson D (2009) Hypertension 54(5): 1057-61
    › Primary publication · 19738158 (PubMed) · PMC2796115 (PubMed Central)
  9. Nocturnal blood pressure dipping in the hypertension of autonomic failure. Okamoto LE, Gamboa A, Shibao C, Black BK, Diedrich A, Raj SR, Robertson D, Biaggioni I (2009) Hypertension 53(2): 363-9
    › Primary publication · 19047577 (PubMed) · PMC2665259 (PubMed Central)
  10. Excessive nitric oxide function and blood pressure regulation in patients with autonomic failure. Gamboa A, Shibao C, Diedrich A, Paranjape SY, Farley G, Christman B, Raj SR, Robertson D, Biaggioni I (2008) Hypertension 51(6): 1531-6
    › Primary publication · 18426998 (PubMed) · PMC2497433 (PubMed Central)