Salt Supplementation Improves Orthostatic Cerebral and Peripheral Vascular Control in Patients With Syncope

Abstract

Abstract-Salt supplementation improves orthostatic tolerance in many patients with posturally related syncope (PRS).This study aimed to examine whether in those patients who responded to salt loading there was also evidence of improved cerebral autoregulation and more powerful peripheral vasoconstriction during orthostasis. Eleven PRS patients were studied before and after ingestion of 100 mmol/d slow sodium for 2 months. Subjects underwent an orthostatic stress test of combined head-up tilting and lower body suction. We continuously monitored heart rate (ECG), blood pressure (Finapres), forearm and cerebral blood flow velocities (Doppler ultrasound), and end-tidal carbon dioxide (CO 2 ). Forearm vascular resistance was calculated from pressure divided by velocity. Cerebral autoregulation was assessed from the correlation coefficient of the relationship between cerebral blood pressure and velocity. Salt loading had no effect on resting heart rate or blood pressure. Symptoms and orthostatic tolerance significantly improved in 10 of the patients. This was associated with a significant increase in the maximal forearm vasoconstriction from 64.4%Ϯ13.7% (SEM) Key Words: sodium Ⅲ vascular resistance P revious work from our laboratory, including a doubleblind placebo-controlled trial, has demonstrated that salt supplementation improves orthostatic tolerance in patients with posturally related syncope (PRS). [1][2][3] This increase in tolerance to orthostatic stress was attributed partly to increases in plasma volume 1 and partly to increased baroreceptor sensitivity. 3 We have also shown that the increase in vascular resistance in response to an orthostatic stress is significantly smaller in patients with poor orthostatic control than in healthy volunteers. Impaired responses were seen in patients with PRS 4,5 and in those with the postural tachycardia syndrome. 5 Because subjects with better orthostatic tolerance show larger responses of forearm vascular resistance to postural changes, the first aim of the present study was to examine whether an improvement in orthostatic tolerance induced by salt loading might be associated with larger vascular resistance responses.We have also recently reported evidence of impaired cerebral autoregulation in patients with PRS. 6 In another study, we demonstrated that water ingestion improved orthostatic tolerance in healthy control subjects 7 and that this improvement in tolerance was associated with an improvement in cerebral autoregulation. Thus, the second aim of this study was to determine whether cerebral autoregulation in this group of PRS patients was improved after salt supplementation. Methods SubjectsSubjects for this study were recruited from patients referred to the laboratory for orthostatic stress testing because of recurrent attacks of syncope or near syncope. To be considered suitable for salt loading, patients needed to satisfy the following criteria: (1) a clinical history suggestive of posturally related hypotension; (2) no other clinical disorder, excluded by app...

Orthostatic hypotension following spinal cord injury: understanding clinical pathophysiology

“…In the upright position, there is normally a baroreceptor-mediated vasoconstriction, via an increase in tonic sympathetic outflow, in order to maintain blood pressure and cerebral perfusion. It has been demonstrated previously that these vascular resistance responses play a crucial role in cardiovascular control during orthostatic stress, [46][47][48] and any impairment in vascular resistance responses following SCI will predispose to orthostatic intolerance. 46,47 In the light of the alterations mentioned above, it is surprising that blood pressure control during orthostatic stress is not more severely impaired following SCI.…”

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“…In able-bodied individuals, orthostatic tolerance and postural blood pressure control are known to be greatly influenced by plasma volume, 31 whereby larger plasma and/or blood volumes are associated with better tolerance to orthostasis. 32 In patients with chronic SCI, there is evidence of impaired water and sodium retention, which is confounded by limited salt and water intake. 33 There is only limited information available on circulating volume following SCI; however, it has also been shown that total blood volume and hemoglobin mass are decreased in individuals with SCI with a lesion above T4.…”

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“…Counselling focuses on educating the patient and the family to understand the condition, emphasizing the benign prognosis and trigger avoidance. Hydration and liberalizing salt intake improves orthostatic tolerance to tilt testing in small acute or short-term studies, increasing plasma volume, cerebrovascular and peripheral vascular control [11,12]. No long-term, controlled evidence exists for any conservative treatment.…”