Pharmacologic treatment of intermittent claudication.

Twenty-six patients with severe short-distance claudication underwent a 24-week, randomized, double-blind, parallel-group evaluation of the efficacy of pentoxifylline in the treatment of intermittent claudication. The primary variables analyzed were the initial and absolute claudication distances as determined by standardized treadmill walking. A statistically significant improvement in both parameters was present in the pentoxifylline-treated patients. Nausea was the only drug side effect noted.

The signal-to-noise characteristics of rod-cone interaction.

1. The influence of rods on cone-mediated vision was assessed in eight human observers. To this end, increment threshold functions were obtained by determining thresholds of a cone-detected test flash (25 ms duration, 655 nm wave-length, 13' diameter) as a function of the illuminance of larger, 500 ms duration, rod-detected masking flashes. The type of photoreceptor influenced by each stimulus was carefully checked by means of a series of control procedures involving action spectra and selective rod adaptation.2. When the rod mask was 512 nm in wave-length, 40' in diameter, and less than one scotopic td in illuminance, increment threshold functions show that [Formula: see text], where I(Cth) is cone test threshold, I(R) is rod mask illuminance, and D is a dark noise term similar to that used by Barlow (1956). Further increases in I(R) have no additional influences on cone test threshold until threshold is influenced by the combined action of the mask on both rods and cones. If I(R) is expressed in terms of scotopic flux rather than illuminance, the functional relationship obtained with all rod masks 2 degrees have negligible influence on cone test threshold. We propose that I (inhibitory spatial summator), a neural locus which responds to scotopic flux provided over a very large area, attenuates the activity of E. The combined action of E and I is designated a rod channel. The response of cones and the rod channel summate at a detector. Within the detector, cone signals are distinguished from rod-related activity and intrinsic dark noise on the basis of signal-to-noise discriminations.5. The neural substrate for this rod channel most probably involves the combined action of several neurones which synapse within the inner plexiform layer of the retina. The relationship of this rod channel to other perceptual phenomena is discussed.

The influence of rod light and dark adaptation upon rod-cone interaction.

The influence of a rod-detected mask of illuminance IR on the threshold illuminance of a cone-detected test flash (ICth) was assessed while rods were recovering from the effects of a bleach, and when rods were selectively light adapted. Providing that IR was restricted to within 2 log10 units of rod mask threshold (IRth), results show that ICth/IC0 = K (square root (IR/IRth) + D), where IC0 is cone absolute threshold, D is a dark noise term and K is a proportionality constant. These data were used to obtain 'equivalent background functions' or 'Crawford (1947) transforms' (illuminance of a background field plotted against time in the dark). The same Crawford transform was obtained when either IRth or ICth (in the presence of a fixed illuminance IR) were used as equating variables. All of the foregoing results could be predicted by considering both the influence of light adaptation on rods (see Fain, 1976) and the model developed by Bauer, Frumkes & Nygaard (1982). Under dark-adapted conditions, 40' and 60' diameter rod masks of equal illuminance have very similar influences on ICth. When rods are selectively light adapted 60' masks have smaller influences on ICth. The foregoing results were used to extend the model developed in the previous paper. We suggest that rod adaptation has a distinct influence on neural loci designated E (the excitatory spatial summator) and I (the inhibitory spatial summator), and that E represents a site for both adaptation and spatial summation.