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The beneficial symptomatic and objective effects of postural treatment at night in patients with debilitating [[orthostatic hypotension]] due to autonomic failure were confirmed in several case series <cite>7</cite><cite>8</cite><cite>9</cite>. A consistent finding in these reports is that if a high salt diet or fludrocortisone were added to head-up sleeping the beneficial effects on orthostatic tolerance were enhanced. | The beneficial symptomatic and objective effects of postural treatment at night in patients with debilitating [[orthostatic hypotension]] due to autonomic failure were confirmed in several case series <cite>7</cite><cite>8</cite><cite>9</cite>. A consistent finding in these reports is that if a high salt diet or fludrocortisone were added to head-up sleeping the beneficial effects on orthostatic tolerance were enhanced. | ||
An excessive fall in cardiac output underlie the impairment in tolerance to standing after a night’s sleep on a flat bed, systemic vascular resistance does not change <cite>10</cite>. Although nocturnal polyuria is a typical feature of patients with autonomic failure the degree of impairment in | An excessive fall in cardiac output underlie the impairment in tolerance to standing after a night’s sleep on a flat bed, systemic vascular resistance does not change <cite>10</cite>. Although nocturnal polyuria is a typical feature of patients with autonomic failure the degree of impairment in orthostatic tolerance after a night's sleep cannot be explained only by the nocturnal polyuria. Marked diurnal variation in orthostatic tolerance can also be found in patients with small diurnal differences in body weight. Transcapillary fluid shifts are thought to play an important role in these patients <cite>10</cite><cite>11</cite><cite>12</cite>. Despite this, treatment with the vasopressin analogue desmopressin has been found effective in reducing both nocturnal polyuria and the postural BP fall in the morning <cite>13</cite>. Adding to complexity, confinement to bed did not substantially alter the diurnal BP changes <cite>14</cite>. Thus various factors may play a role in the diurnal BP changes including orthostatic fluid shifts, transcapillary fluid shifts and neurohumoral rhythms causing changes in sodium and water excretion | ||
==Physiological mechanisms== | ==Physiological mechanisms== | ||