MENG, AND MILTON ELKIN. Validation of use of xenon 133 to measure intrarenal distribution of blood flow. Am. J. Physiol. 219(Z) : 440-444. 1970.-The gamma camera has been used to evaluate the distribution of radioxenon in man after injection into the renal artery. Combined gas-washout curves performed according to the method of Thorburn and associates and gamma-camera studies confirm the relationship between the first component of the gas-washout curve and clearing of radioactivity from the renal cortex. The mean cortical renal blood flow in patients with no known renal disease on a normal diet was 413 ml/min per 100 g of kidney =t 27 (SE). This represented 76.4% =t 2.7 of the total renal blood flow. The method was found to be reproducible and safe. These studies suggest that the xenon washout study is a reliable method for the determination of the intrarenal distribution of blood flow in man.

The intrarenal distribution of blood flow measured by the 183 xenon washout method and the renin activity of renal venous blood were determined in 16 patients with early essential hypertension. None of the patients had evidence of systemic disease except for the elevation in blood pressure (> 150/100 mm Hg). Fifteen of the subjects received a controlled sodium diet during 7 to 9 days before study, at the time of renal angiography. An inverse relationship was noted between the cortical component of the renal blood flow and renin activity of renal venous blood (r = 0.64, P <0.02). Renin secretion rates were also calculated in 12 patients confirming the inverse relationship between cortical distribution of blood flow and renin secretion (r = 0.763, P<0.01). The cortical renal blood flow in 10 patients on a low salt intake was 79.6% ± 2.6 (SE) of the total renal blood flow. The cortical blood flow in five patients on a high salt diet was 87.6%±1.9 (SE); the statistical difference between the two groups is significant (P<0.05). A direct relationship was noted between cortical blood flow and the logarithm of the 24-hour urinary sodium excretion from the day preceding the study (r = 0.54, P<0.05). Renin secretion rate and renin in renal venous blood were directly correlated (r = 0.813, P<0.01). Changes in corticomedullary distribution of flow were inversely related to the changes in cortical distribution. The degree of reduction of cortical renal blood flow correlated with the degree of increase in renin secretion and in renin activity in renal venous blood. Our data are compatible with reduced cortical renal blood flow mediating renin release or vice versa. Either mechanism would result in more efficient conservation of salt and water by the kidney. ADDITIONAL KEY WORDSrenin release human hypertension low salt intake sodium excretion xenon washout cortical blood flow corticomedullary blood flow• The majority of pathologic conditions which are accompanied by consistent alterations in renal blood flow are also associated with changes in peripheral renin activity. Renovascular hypertension (1), acute renal failure (2), and hemorrhagic hypotension (3) are each associated with increased peripheral renin activity and with a reduction in the total

A total of 24 children between the ages of 65/;, and 11 l/i yr. tapped on a key in groups of 3 taps, each tap triggering a click SO db above the threshold of normal hearing. The design of the experiment permitted the click to be heard synchronously with the tap or with a delay which varied from 0 to 1,000 msec., in 100-msec. steps. The effects of delay on the force of taps, the total time for 30 taps, the time during which the finger actually rested on the key, and grouping errors were computed for the synchronous timing and for each of the delay times. Delay had significant disruptive effects on all four parameters. The disruptive effect o n total time, time on the key, and grouping errors increased as a function of length of delay, the 1,000-msec. delay being more disruptive than any below 700 msec. The increase in force was significant at all delay times, regardless of the length of delay. Age did not affect sensitivity to delay. The results of our study are surprising in view of the a'ell-established fact that in normal adults speech is most effectively disrupted by a delay time of 160 to 200 msec. The reasons for the difference in findings are as yet con jecrural.Smooth motor performance requires repeated adjusrmenrs so that a fine balance can be maintained berween the individual parrs of the limb throughout the range of motion. Feedback informarion arising from receptors in the moving part, e.g., sense of pressure, couch, muscle tension, and joinr position, as well as visual and auditory cues, flows toward the central nervous sysrem as the movement is being made. This feedback, it is thought, is sampled while the sequential impulses for the movement are being released in the brain and is used to initiate corrective reflexes. A decrease of available information in one or several feedback channels may impair motor performance; thus, persons with acquired hearing losses often speak too loudly, and those with proprioceptive sensory impairments become ataxic.Distorrion in feedback information disruprs motor performance even more effectively than does decreased feedback

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