1. Chapter 8 Postural Hypotension and Syncope Michael J. Aminoff
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Figure 8-1 Anatomy of the autonomic pathways involved in maintaining the blood pressure on standing.
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Figure 8-2 Sequence of events that ensure maintenance of the blood pressure after adoption of the upright posture. Only the immediate cardiovascular changes are shown. As indicated in the text, a variety of other humoral mechanisms are also activated.
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Figure 8-3 Heart rate responses to standing in a normal subject. Immediately on standing, there is a rapid increase in heart rate that is maximal at approximately the fifteenth beat after standing.
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Figure 8-4 Cardiovascular responses to the Valsalva maneuver, as recorded with an intra-arterial needle. A, Normal response. B, Abnormal response in a patient with multiple system atrophy.
(From Aminoff MJ: Electromyography in Clinical Practice. 3rd Ed. Churchill Livingstone, New York, 1998, p. 206, with permission.)
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Figure 8-5 Valsalva maneuver as recorded using an electrocardiograph (ECG) or heart rate monitor in a normal subject. The tachycardia that occurs during the forced expiratory maneuver is clearly evident, as is the compensatory bradycardia that occurs when the maneuver is released.
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Figure 8-6 Normal variation in heart rate that occurs in response to deep breathing.
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Figure 8-7 Variation in blood volume after a deep inspiration in a normal subject, measured photoplethysmographically by means of an infrared emitter and detector placed on the pad of the index finger. The bottom trace represents the sensor output after it has been amplified by the photoplethysmographic module of a computerized autonomic testing system; it is a function of the absolute blood volume in the finger. Each peak represents a heartbeat, and the amplitude of each wave reflects blood volume in the area about the sensor. The apparent shift of the direct-current signal component is due to the long time constant that is necessary so that signal information is not lost. The relative voltage, representing the amplitude of each pulse, is shown in the upper trace. It is evident in both traces that after the deep inspiration there is a reduction in digital blood flow (i.e., reduced amplitude of the waveforms in the lower trace and a corresponding decline in the upper trace).
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Figure 8-8 Thermoregulatory sweat tests. A, An increase in body temperature leads normally to sweating over the entire body. An indicator powder becomes discolored (purple) by the moisture. It was not placed on the face and head, so that no discoloration is seen in these regions. B, In a patient with a length-dependent neuropathy involving the sudomotor fibers, sweating is absent in a stocking-and-glove-pattern. C, A patient with multiple system atrophy and almost complete anhidrosis, showing only small scattered areas of sweating.
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Figure 8-9 Sweating induced through an axon reflex. Iontophoresed acetylcholine stimulates sweat gland production locally and—by an axon reflex—in adjacent areas.
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Figure 8-10 Renal responses to fluid deprivation for 36 hours of five dysautonomic patients with multiple system atrophy (right panels) and four control subjects with Parkinson disease and preserved autonomic reflexes (left panels). Deprivation commenced at 6 P.M. Mean results for each successive 4-hour period are shown for urine osmolality (blue) and volume (red) in A, and for sodium (blue) and potassium excretion (red) in B. Subjects were recumbent during the night (10 P.M. to 10 A.M.; shaded area) and were up and about during the day (10 A.M. to 10 P.M.). In the control subjects, urine volume declined and osmolality increased during the period of fluid deprivation; sodium excretion was unchanged whereas potassium excretion was greater during the day than night. In the dysautonomic subjects, similar changes were seen during the day; during recumbency at night, however, a considerable increase occurred in urinary volume and sodium and potassium excretion, and urinary osmolality declined.
(Data from Wilcox CS, Aminoff MJ, Penn W: Basis of nocturnal polyuria in patients with autonomic failure. J Neurol Neurosurg Psychiatry 37:677, 1974.)
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