Visual properties of cells in anterior dorsal ventricular ridge of turtle.

Single units in the anterior dorsal ventricular ridge (ADVR), a structure in the major afferent visual pathway of turtle, were investigated electrophysiologically for response properties to varied light patterns. The majority of cells responded to a broad range of spatially, temporally, and chromatically varied stimuli over most of the monocular visual field. One category of cells, seemingly specialized for 'novelty' detection, indicates one possible role for ADVR in visual sensory processing.

Photoreceptor input and temporal summation in turtle retinal ganglion cells.

The relation between photoreceptor input and temporal summation in ganglion cells was investigated in the optical nerve of fresh-water turtle, Pseudemys. Action spectra derived for constant, high-criterion responses showed most cells to be maximally sensitive to 620 nm light, indicating dominant input from red-sensitive cones. At a lower criterion, sensitivity to 520 nm light greatly increased indicating an increase in rod input. Temporal summation curves for these intensity-dependent cells showed reciprocity between flash intensity and duration up to 128 msec for high-criterion summation curves. Low-criterion summation curves showed reciprocity up to the critical duration of 285 msec. Cells maximally sensitive to 620 nm light at all intensities often showed secondary sensitivity to 560 nm light, and were fitted by action spectra taken from red- and green-sensitive cones. Temporal summation curves for these cells had critical durations near 100 msec. Some cells responded best to light near 520 nm at all intensities and demonstrated little or no input from red-sensitive cones. These cells were fitted well by the action spectrum of rods and showed the longest critical durations of all at 375 msec. Chromatic input and temporal characteristics are intimately related: red-cone-dominated ganglion cells have the shortest critical durations while rod-dominated cells shows much longer ones. These findings are in keeping with psychophysical determinations of critical durations in this same animal.

An automated apparatus for the determination of visual thresholds in turtles.

An automated apparatus is described that permits precise and reliable measurements of visual thresholds in turtles using a conditioned avoidance technique. The entire sequence of stimulus management and the collection of response data are under programmed control.

The first DRG: lessons from the end stage renal disease program for the prospective payment system.

When Medicare implemented the diagnosis related group (DRG) method of reimbursement for hospitals in 1983, it already had a decade of experience using a prospective payment arrangement for its end stage renal disease (ESRD) program. We reviewed this experience to determine the lessons for Medicare's reimbursement of hospital services. The use of a fixed price for renal dialysis encouraged the introduction of cost-saving techniques. Failure to reduce the price for dialysis in keeping with the cost reductions, however, prevented the government from realizing the full benefits of prospective payment. In addition, there were important changes in medical practice that had independent effects on the program. Similar influences are likely to shape the impact of prospective payment on hospital behavior.

The iron lung: halfway technology or necessary step?

The iron lung is often used to epitomize the costly halfway technologies of modern-day medicine that fail to cure and only prolong a seriously compromised existence. Historical evidence indicates that the iron lung was not a costly instrument of last resort; instead, it was a lifesaving device that played a critical role in the evolution of modern respirators and respiratory care. Contrary to the prevailing views of the biomedical research community, the creation of new devices and instruments is often as important a source of technical change in medicine as are advances in the biological sciences.

Effects of conditioning on exertional rhabdomyolysis and serum creatine kinase after severe exercise.

This study determined the effects of different conditioning levels on exertional rhabdomyolysis after severe exercise. 15 well-conditioned men were randomly divided into three conditioning groups, i.e. 0, 4 and 8 miles on alternate days for 1 month. They were physically stressed by running 14 miles at 8 min/mile after 1 month of training. The effects of the different levels of conditioning on exertional rhabdomyolysis after the test run were determined by assaying serum samples for creatine kinase (CK) and myoglobin levels. Serum CK levels increased 98-294% above pre-conditioning control values after the 14-mile test run while serum myoglobin levels increased 52-405%. The most marked increases occurred in those subjects who trained less than 8 miles on alternate days. These results suggest that these quantitative indices are useful in determining the amount of conditioning necessary to prevent significant rhabdomyolysis after severe exercise.

Photoreceptor signals at visual threshold.

Electrical responses of cone photoreceptors in the retina of the freshwater turtle have been characterised for flashes and steps of light in darkness and in the presence of background light. These intracellular measurements have been combined with the behavioural increment threshold curve to yield an estimate of 5-10 muV for the signal developed in a cone when the turtle can just detect an increment flash. The signal developed when the cones under the stimulus image are dark-adapted is of interest, for its measurement would help to explain how known physiological processes subserve visual detection for a variety of photic conditions. The effective quantal absorption of dark-adapted, red-sensitive cones of Pseudemys scripta elegans for a stimulus that the turtle can just detect is reported here. By combining this result with previous electrical measurements on red-sensitive cones of this species, an estimate of 35-70 muV is obtained for the signal developed in a dark-adapted cone at behavioural threshold. This larger signal required for detection of a flash in darkness is of particular interest in view of the recent observation that the intrinsic noise of turtle cones in darkness is larger than that of illuminated cones.

Economic incentives and organizational realities: managing hospitals under DRGs.

Diagnosis-related Groups (DRGs) offer hospitals financial incentives to improve efficiency. To be effective, DRGs require a realignment of management so that physicians' use of resources can be disciplined by administrators. The constituency for altering power relationships within hospitals, however, is, at best, a weak one: administrators see their primary task as the protection of physicians' clinical autonomy. Constraints imposed on hospitals by regulators can be accommodated by minor adjustments in behavior that ensure neither gains in efficiency nor changes in decision-making authority.