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The effect of short term high salt diet on cerebrovascular reactivity in response to orthostatic position change in young healthy subjects

Introduction: Brain tissue is protected from variations in blood pressure by cerebral autoregulation (CA), maintaining stable cerebral perfusion and brain tissue oxygenation in spite of these variations (1). It is well accepted that increased dietary salt intake is positively correlated with incidence of stroke (2). High salt (HS) diet, even short termed, impairs endothelium-dependent vasodilator responses in many vascular beds, including cerebral microcirculation (3). The present study aimed to evaluate the effect of short term HS diet on middle cerebral artery (MCA) reactivity to orthostatic position change in healthy human subjects. Methods: 25 persons were included (men:6, women:19) in this study. The study was designed as prospective, “crossover” study with repeated measurements. Participants took low salt (LS) diet for 1 week (<2, 3g kitchen salt/day) followed by 1 week of HS diet (>11, 2 g kitchen salt/day). 24h urine samples were collected and analyzed for sodium excretion after diet protocols. Measurements of MCA reactivity during sitting in a relaxed state and in response to orthostatic position change (standing up and sitting down) were performed after LS and HS diet protocols by Transcranial Doppler (TCD) Flowmetry. Blood pressure (BP), heart rate (HR), R-R interval, mean cerebral blood flow (CBF), systolic CBF (sCBF), diastolic CBF (dCBF), velocity time integral (VTI), cerebral vasomotor reactivity (CVR) and cerebral pulsatility index (CPI) were simultaneously recorded during TCD measurements. This study was approved by the Ethical Committee of the Faculty of Medicine University of Osijek Results: Changes in 24h urinary sodium excretion confirmed that subjects conformed to the diet protocols. CBF, sCBF and dCBF decrease during sitting down was significantly more pronounced after HS diet compared to measurements taken after LS diet (relative CBF change -0.0518 vs. -0.00109, P=0.011 ; sCBF -0.0286 vs. -0.0021, P=0.019 ; dCBF -0.0662 vs. -0.00412, P=0.015). VTI was significantly decreased during sitting down after HS diet, whereas in the period after LS diet there was significant increase during sitting down from the measurement conducted in the relaxed sitting state (relative VTI change -0.0344 vs. 0.0309, P=0.036). sCBF decrease after standing up was also significantly more prominent after HS diet compared to the decrease during standing up measured after LS diet (-0.0536 vs. -0.0222, P=0.050). Changes of HR, R-R interval, CVR and CPI during orthostatic position changes were not significantly affected by the HS diet compared to LS diet. Furthermore, HS diet did not significantly affect any of the arterial BP values. Conclusion: One week of HS diet can impair the cerebrovascular reactivity in humans, even without affecting BP values.

high salt diet ; cerebral blood vessels ; vascular reactivity ; orthostatic position change

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