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A. Benavente-Perez, S. L. Hosking, N. S. Logan; Exacerbated Systemic Response to Hypercapnia in Young Smokers Triggers Ocular Haemodynamic Response. Invest. Ophthalmol. Vis. Sci. 2009;50(13):383.
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Cigarette smoking is a major risk factor for respiratory pathologies and it is associated with a 2-4 fold increased risk of coronary heart disease and stroke related mortality. Smoking also affects the vascular autoregulatory features of the eye; however, limited studies to date have assessed the various ocular vascular beds and the systemic circulation to prevent the confounding effects of age and blood pressure. The purpose of this study was to evaluate the systemic and ocular vascular response to isoxic hypercapnia in young smokers.
The retrobulbar, pulsatile and microcirculatory ocular circulation were assessed using the Colour Doppler Imaging, Heidelberg Retinal Flowmeter and Ocular Blood Flow Analyser at two sessions: baseline (B1, breathing room air) and isoxic hypercapnia (IH: breathing CO2 enriched air until end tidal pCO2 increased 15% above B1 with constant O2 supply).B1: one eye of each of 42 participants grouped into smokers and non-smokers were assessed: 21 smokers (mean age 26.79 ± 4.09 years, smoking Fagerström Tolerance Questionnaire, FTQ score 7.38) and 21 non-smokers (mean age, 26.52 ± 5.17 years, FTQ score 0 points).IH: subgroups comprising 11 non-smokers (mean age 25.00 ± 2.93 years, FTQ score 0) and 11 smokers (mean age 25.81 ± 3.70 years, FTQ score 6.63) were evaluated.Blood pressure (BP), intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP) and body mass index (BMI) were measured.
B1: no differences in BP, MAP, OPP or ocular haemodynamics were found between smokers and non-smokers. H1: hypercapnia induced a significant increase in BP, MAP and OPP only in smokers. After controlling for the effects of OPP there was no significant response to hypercapnia in the pulsatile, retrobulbar or microretinal circulation of either smokers or non-smokers. FTQ score correlated significantly with the percentage changes induced by hypercapnia in the ophthalmic artery (R=-0.63 p=0.05) and central retinal artery velocity ratios (R=-0.65 p=0.04).
Under normal breathing resting conditions there is no significant difference in baseline flow between smokers and non-smokers. During stress testing, only smokers exhibited significant changes to systemic blood pressure which may be indicative of systemic hypoxia or autonomic dysregulation.
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