The effect of posture and of compression of the neck on excretion of electrolytes and glomerular filtration; further studies

Compression of the neck of the sitting subject caused increase in urinary sodium output without change in glomerular filtration (creatinine clearance) or apparent cardiac output (electrokymograph). The possible existence of an intracranial mechanism sensitive to alterations in volume of extracellular fluid and regulating the volume of extracellular fluid is suggested.

The effect of posture and of congestion of the head on sodium excretion in normal subjects

In healthy young subjects the sodium excretion is decidedly less in the sitting than in the recumbent posture. The difference can be partially overcome by compression of the neck in the sitting position. Some possible implications of these observations will be considered in the subsequent communications.

Effect of body posture on lung volumes

The changes produced by body posture on total lung capacity and its subdivisions have been reported for all positions except the prone position. Twenty normal subjects, twelve males and eight females, had determinations of total lung capacity in the three body positions, sitting, supine and prone. Tidal volume, minute ventilation and O2 consumption were also measured. The changes found on assumption of the supine position from the sitting position were similar to those previously reported. For the prone position, a smaller inspiratory capacity and a larger expiratory reserve volume were found. The mean values were changed, respectively, –8% and +37%. Associated with these changes was a significant increase of the functional residual capacity by 636 ml. Ventilation did not change significantly from that found during sitting, unlike the findings associated with the supine position, in which position the tidal volume was decreased. Respiratory frequency remained the same for all positions.

Submitted on April 5, 1960

Blood pressure during supine exercise in idiopathic orthostatic hypotension

The arterial blood pressure was measured during exercise in six patients with idiopathic orthostatic hypotension. In five there was a pronounced fall of arterial pressure while the subjects exercised in the supine position on a horizontal table. The systolic and diastolic pressures fell by an average of 50 and 32 mm. of mercury, respectively. During comparable exercise with the table tilted 15 degrees head downward, the pressures fell to a similar degree. Thus, an abnormal response of blood pressure occurred under conditions in which venous pooling was unlikely to be present.

It is suggested that the fall in blood pressure during exercise in the supine position was the result of failure of compensatory constriction of other vascular beds and not of failure of the cardiac output to increase. Thus, the net peripheral resistance in such patients is less than that in normal persons performing comparable exercise.

Effects of posture on plasma volume and some blood constituents

When the posture was changed from horizontal to vertical, or the reverse, the alteration in plasma volume and in the levels of haematocrit, haemoglobin, and plasma protein was much greater in patients with oedema or low plasma protein or albumin concentrations ("the pathological group") than in patients without these abnormalities ("the control group"). This larger fluid shift, and the larger concentration changes dependent on it, are explained in terms of Starling's hypothesis. In the control group there was scarcely any change in the total mass of intravascular plasma protein with change in posture, but in the pathological group this was often considerable. This was interpreted as indicating increased permeability of the capillaries to protein. Attention is drawn to the influence of uncontrolled alterations in posture on biochemical and haematological measurements and a recommendation is made in order to standardize conditions before taking blood for the analysis of non-diffusible constituents.

VESTIBULAR HABITUATION DURING REPETITIVE COMPLEX STIMULATION: A STUDY OF TRANFER EFFECTS

Thirty-two men were rotated at 7.5 rev/min while facing the center of the Pensacola slow rotation room for several hours. The men were seated 4 ft from the center of rotation; direction of rotation was toward the subject's left. During rotation, subjects were immobile except for series of measured head movements restricted to the frontal plane and to a particular quadrant of that plane for each subject. Nystagmus, illusory phenomena, and nausea were reduced by this procedure, but this habituation did not transfer to other forms of vestibular stimulation including that induced by head movements in an “unpracticed” quadrant of the same plane. Residual effects exhibited in “static tests” after the habituation program were primarily restricted to the practiced quadrant.

habituation; nystagmus; vestibular function

Submitted on January 15, 1964