Objective: Haemoglobin is a potential nitric oxide (NO) scavenger. Haemoglobin is associated with blood viscosity and the red blood cell free layer width of microvessels that impact on shear stress in the microcirculation. We hypothesized that haemoglobin modulates retinal vascular function.
Methods: In 139 nondiabetic male patients with haemoglobin levels within the normal range, the vasodilatatory response of retinal capillary blood flow (RCF) to flicker light exposure and the vasoconstrictor response of RCF to infusion of NO synthase inhibitor N-monomethyl-L-arginine (L-NMMA) were assessed. The latter, because of the selective nature of L-NMMA, reflects a parameter of basal NO activity of retinal vasculature. Examinations of retinal parameters were performed noninvasively and in vivo using scanning laser Doppler flowmetry.
Results: Patients with haemoglobin greater or equal the median revealed reduced increase of RCF to flicker light exposure (2.83 ± 12 vs. 9.52 ± 14 (%), P adjusted = 0.002), and greater decrease of RCF to L-NMMA infusion (−7.35 ± 13 vs. −0.92 ± 14 (%), P adjusted = 0.008), compared with patients with haemoglobin below the median. Haemoglobin was negatively related to the percentage change of RCF to flicker light exposure (r = −0.249, P = 0.004) and to L-NMMA infusion (r = −0.201, P = 0.018). In multiple linear regression analysis haemoglobin was an independent determinant of the percentage change of RCF to flicker light exposure (model 1: ß = −0.278, P = 0.003 and model 2: ß = −0.283, P = 0.002) and to L-NMMA infusion (model 1: ß = −0.256, P = 0.005 and model 2: ß = −0.269, P = 0.004).
Conclusion: Haemoglobin emerged as an independent determinant of vascular function in the human retinal vascular bed.
aDepartment of Nephrology and Hypertension, University of Erlangen-Nürnberg, Bavaria, Germany
bDepartment of Human Physiology, University of Warmia and Masuria, Olsztyn, Poland
cDepartment of Ophthalmology, University of Erlangen-Nürnberg, Bavaria, Germany
Correspondence to Professor Dr med. Roland E. Schmieder, MD, Clinical Research Center, Department of Nephrology and Hypertension, University of Erlangen-Nürnberg, Ulmenweg 18, 91054 Erlangen, Germany. Tel: +49 9131 853 6245; fax: +49 9131 853 6215; e-mail: firstname.lastname@example.org
Abbreviations: AFFPIA, Automatic full-field perfusion imaging analysis; L-NMMA, N-monomethyl-L-arginine; NO, nitric oxide; NOS, nitric oxide synthase; RCF, retinal capillary blood flow
Received 23 September, 2012
Revised 26 November, 2012
Accepted 20 December, 2012