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Abnormal orthostatic changes in blood pressure and heart rate in subjects with intact sympathetic nervous function:
D H Streeten1, G H Anderson, R Richardson
1Department of Medicine, SUNY Health Science Center, Syracuse 13210.
Insights
Idiopathic orthostatic hypotension, causing light-headedness, is often due to venous pooling and hypovolemia. An inflatable pressure suit effectively normalized blood pressure and heart rate in affected individuals.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Function
- Clinical Medicine
Background:
- Orthostatic hypotension (OH) and related circulatory derangements can cause symptoms like light-headedness.
- Idiopathic cases, where known causes are excluded, present diagnostic challenges.
Purpose of the Study:
- To define normal orthostatic circulatory responses.
- To identify and characterize circulatory derangements in patients with idiopathic OH.
- To evaluate the efficacy of external pressure in managing these disorders.
Main Methods:
- Defined normal orthostatic blood pressure and heart rate ranges in 92 healthy individuals.
- Investigated 34 patients with suspected cerebral ischemia due to OH using five potential circulatory derangements.
- Assessed treatment with an inflatable pressure suit (45-50 mm Hg).
- Utilized radiolabeled erythrocytes (Tc 99m) for assessing blood pooling in the legs.
- Measured plasma norepinephrine, red cell mass, plasma volume, and circulating blood volume.
Main Results:
- Identified systolic hypotension, diastolic hypotension, diastolic hypertension, pulse pressure narrowing, and tachycardia in patients.
- The pressure suit normalized orthostatic disorders in most patients.
- Excessive gravitational blood pooling in legs was observed in patients with specific orthostatic disorders.
- Elevated plasma norepinephrine during standing and subnormal blood volumes were noted in some patients.
Conclusions:
- Idiopathic sympathicotonic OH is frequently linked to a venous pooling syndrome.
- Hypovolemia often exacerbates this venous pooling syndrome.
- The underlying causes of hypovolemia in these patients require further investigation.
Abstract:
The normal ranges of orthostatic changes in blood pressure and heart rate have been defined in 92 individuals aged 18 to 64 years. In 34 individuals whose symptoms (especially orthostatic light-headedness) suggested cerebral ischemia, but in whom none of the known causes of orthostatic hypotension could be identified, we have found one or more of five theoretically possible orthostatic circulatory derangements: systolic hypotension, diastolic hypotension, diastolic hypertension, excessive narrowing of the pulse pressure, and tachycardia after standing for at least 3 minutes. The orthostatic disorders of blood pressure and heart rate identified in the 34 patients were significantly reduced, almost always into the normal range, by external pressure of 45 to 50 mm Hg applied through an inflatable pressure suit. After labeling with sodium pertechnetate Tc 99m and reinjecting the erythrocytes contained in 3 to 6 ml blood, external gamma counting over a fixed site in the calf, both in the recumbent and in the standing posture, showed excessive gravitational pooling of blood in the legs of five patients with orthostatic diastolic hypertension, of four with orthostatic narrowing of the pulse pressure, and of 10 with orthostatic tachycardia alone. Plasma norepinephrine concentrations were usually normal in recumbency and elevated above normal limits during standing for 15 to 30 minutes in the 18 patients so observed. Red cell mass, plasma volume, and circulating blood volume were subnormal in more than half the seven patients in whom these measurements were made. We conclude that most of the patients with idiopathic sympathicotonic abnormalities of orthostatic blood pressure control have a venous pooling syndrome often aggravated by hypovolemia, the cause(s) of which remains to be determined.