In autonomic failure (AF), blood pressure (BP) falls upon standing which is commonly ascribed to defective vasoconstriction and excessive pooling. Observations on the amount of pooling in AF are... Show moreIn autonomic failure (AF), blood pressure (BP) falls upon standing which is commonly ascribed to defective vasoconstriction and excessive pooling. Observations on the amount of pooling in AF are contradictory. We evaluated pooling using strain-gauge plethysmography (SGP) during head-up tilt (HUT) with a parachute harness fixed to the tilt table to avoid muscle tension in the lower limbs and thus to maximise pooling. 23 healthy subjects and 12 patients with AF were tilted for 5 min. BP and calf volume changes, as measured by SGP, were measured continuously. Multiple regression analysis was used to examine the effect of AF on orthostatic fluid shifts after adjustment for potential confounders. Patients did not differ from controls with respect to the increase of calf volume after 5 min HUT. The acute (0-1 min) and the prolonged (1-5 min) phases of calf volume responses to HUT were also similar between patients and controls. No correlation was found between the degree of orthostatic hypotension and the orthostatic calf volume change in AF. In one patient an additional measurement was made before rising from bed in the early morning demonstrating a greater albeit small increase of calf volume upon HUT. Orthostatic fluid shifts at the level of the calf in AF are not augmented during the course of the day despite marked hypotension. However, a small increase of pooling may be expected when the patient first gets out of bed in the morning probably due to the absence of oedema. Show less
This thesis contains various studies on syncope. The first part of the thesis systematically reviews the terminology of syncope and related conditions. The second part of the thesis questions... Show moreThis thesis contains various studies on syncope. The first part of the thesis systematically reviews the terminology of syncope and related conditions. The second part of the thesis questions whether orthostatic hypotension in autonomic failure is associated with increased venous pooling upon standing. In the third part the role hyperventilation in the pathophysiology of syncope is examined. Furthermore the potential of respiratory manoeuvres to combat orthostatic hypotension in autonomic failure is evaluated. The final part of the thesis contains various clinical studies, including the assessment of the accuracy of eyewitness accounts in transient loss of consciousness. Show less
