Peripapillary chorioretinal atrophy: Bruch's membrane changes and photoreceptor loss.

PURPOSE: To determine relationships among Bruch's membrane ultrastructure, photoreceptor degeneration, and choriocapillaris atrophy with respect to zones of retinal pigment epithelium (RPE) degeneration and atrophy adjacent to the optic nerve head, as a function of age. DESIGN: Human tissue study using clinicopathologic correlation. TISSUES: Eyes from patients 36 to 93 years of age lacking clinical evidence of glaucoma, optic nerve abnormalities, severe myopia, age-related macular degeneration, or other macular or peripapillary chorioretinal pathologic condition. METHODS: Sections through the retina-choroid complex at the temporal aspect of the optic nerve head were used for light microscopic histopathologic analysis (n = 17), electron microscopy (n = 9), carbonic anhydrase histochemical analysis (n = 7), and lipid histochemical analysis (n = 22). Retinal whole mounts were used for photoreceptor counts (n = 5). MAIN OUTCOME MEASURES: We determined the width of RPE degeneration and atrophy, the number of eyes with abnormalities of inner Bruch's membrane, and the number of rod and cone photoreceptors within 1 mm of the disc margin. We determined whether Bruch's membrane changes, photoreceptor degeneration, and choriocapillaris atrophy were associated with RPE degeneration and atrophy. RESULTS: All eyes had peripapillary RPE atrophy, degeneration, or both. The zone of RPE atrophy widened significantly after age 75. Thickening of inner Bruch's membrane and abnormalities of the RPE basal lamina were associated with degenerating and atrophic RPE in all eyes. The RPE basal lamina was narrow, reduplicated, or thickened as a basal laminar deposit. All eyes exhibited degeneration and loss of rods but not cones at the peripapillary termination of Bruch's membrane. Diminution of choriocapillaris coverage of Bruch's membrane was associated with RPE degeneration. Complete loss of the choriocapillaris was associated with RPE atrophy. CONCLUSIONS: Our results suggest that peripapillary chorioretinal atrophy is an age-related degeneration of the RPE-Bruch's membrane complex that resembles that found in the macula and periphery of normal eyes.

Heart rate and blood pressure responses to +Gz following varied-duration -Gz.

BACKGROUND: The push-pull effect has been defined previously as decreased +Gz tolerance caused by previous baseline zero or -Gz exposure. Earlier work indicates that the delay in BP (BP) recovery during +Gz is a function of time at -G7, and is due to the lengthened time-course of sympathetically mediated peripheral vasoconstriction. HYPOTHESIS: The purpose of this study was to retrospectively determine whether heart rate (HR) varies with BP as duration at preceding -Gz increased. METHODS: Continuous ECG R-R interval data from 15 s of +2.25Gz after preceding 2, 5, 10, or 15 s at 2Gz obtained from previous experiments were analyzed and compared with the previously reported BP data. Repeated measures ANOVA and regression analyses were used to compare +2.25Gz HR responses after the four -Gz conditions and one control +2.25Gz condition. RESULTS: An initial rapid rise in HR was observed for all conditions with a consistent steady-state plateau achieved after the first 7 s of +2.25Gz. However, there were significant differences in mean HR attained during the +2.25Gz plateau for preceding 15 s -2.0 Gz vs. the control, 2, 5, and 10s -Gz conditions (109+/-1.1 vs. 102+/-1.8, 100+/-2.0, 97+/-1.1 and 101+/-1.1, bpm, respectively; p<0.05). CONCLUSIONS: HR, unlike BP, increases briskly across all preceding -Gz time conditions, adapting within the initial baroreflex-compensatory time frame typically expected for +Gz exposures. These results suggest there may be a threshold effect for HR response. Consequently, vasoconstrictor response is a critical adaptive mechanism during +Gz when preceded by long (>10 s) -Gz exposures.

The effect of varying time at -Gz on subsequent +Gz physiological tolerance (push-pull effect).

INTRODUCTION: Previous studies have demonstrated decreased +Gz tolerance when preceded by 0 Gz or -Gz, referred to as the "push-pull effect." The purpose of this experiment was to observe the effect of varying time duration at -Gz on the push-pull effect. METHODS: During single sessions, six subjects (three men, three women) were subjected to five relaxed exposures to +2.25 Gz on the NAMRL Coriolis Acceleration Platform (CAP). The first and last exposures were control runs that were preceded by +1 Gz. Each experimental run was preceded by -2 Gz for 2, 5, or 15 s. Blood pressure (BP) was monitored using the Finapres at the level of the clavicle. Visual light loss was assessed at +2.25 Gz using a light bar. RESULTS: Mean BP was significantly reduced when the +2.25 Gz exposures were preceded by -2 Gz. Following 15 s of -2 Gz, mean BP decreased more and was slower to recover than for 2 and 5 s of -2 Gz. Reported incidents of visual light loss were: 1 following 2 s, 2 following 5 s, and 4 following 15 s at -2 Gz. There were no reports of visual light loss during control runs. CONCLUSION: During relaxed conditions, the push-pull effect is augmented by increasing duration of the preceding -Gz.

The "push-pull effect".

The purpose of this study was to prove or refute previous authors' suggestions that tolerance to +Gz is reduced when preceded by 0 Gz or -Gz. Six men and six women were subjected to one session of acceleration stresses that varied between -2 and +2.25 Gz on the NAMRL Coriolis Acceleration Platform (CAP). At the beginning and end of each session, we exposed the relaxed subjects to identical control segments that were comprised of +1 Gz for 30 s, followed by +2.25 Gz for 15 s, and then return to +1 Gz. Subjects were also exposed to three experimental segments that were comprised of 0, -1, or -2 Gz for 10 s, followed by +2.25 Gz for 15 s, and then return to +1 Gz. Subjects verbally reported any decrements in peripheral vision during exposure to +2.25 Gz. Blood pressure (BP) was reduced during each 15-s period at +2.25 Gz. The minimum BP was progressively lower during the 15-s period as the preexposure experimental conditions became more negative (+1, 0, -1, and -2 Gz). Episodes of peripheral vision loss increased as the preceding -Gz became more negative. BP during exposure to +Gz was significantly affected by the preceding 10-s exposure to -Gz, and is indicative of reduced +Gz tolerance. As this "push-pull effect" may result in unexpected incapacitation, it has important implications for aviation safety.

The physiological cost of carrying light and heavy loads.

Nine subjects walked on a treadmill with load weights equal to 10% and 40% of body weight carried on the back. Although the speed of the treadmill was selected so that the measured oxygen consumption (VO2) was the same for both load conditions, the heavier load placed an extra strain on the cardiopulmonary system and was perceived by all subjects as harder work than the lighter load. When the subjects worked at their own pace, walking on a level road or climbing stairs with load weights equal to 10% and 40% of body weight, they compensated for the heavier load by decreasing walking speed or climbing rate. Although the energy costs calculated from walking speed, body and load weight for self-paced walking and the external work of stair climbing were the same for both load conditions, the heavier load was again perceived as harder work. These findings are discussed as they relate to the definition of acceptable load weights.