Endogenous opioids modify dyspnoea during treadmill exercise in patients with COPD.

Exogenous opioid drugs, such as morphine, relieve breathlessness. The present study hypothesis was that endogenous opioids, released during the stress of exercise, modify dyspnoea in patients with chronic obstructive pulmonary disease. After familiarisation, patients performed an incremental treadmill exercise test followed by constant work on the treadmill for 10 min. At subsequent visits (2 to 3 days apart), patients received two puffs of albuterol, had a catheter placed in an arm vein for removal of blood to measure beta-endorphin immunoreactivity, received normal saline or 10 mg of naloxone intravenously in randomised order, and then performed high-intensity constant work rate exercise on the treadmill. The mean+/-sd age of the 17 patients (eight females and nine males) was 63+/-7 yrs, and post-bronchodilator forced expiratory volume in one second was 50+/-17% predicted. In both conditions, beta-endorphin levels increased three-fold from rest to end-exercise. The regression slope of breathlessness as a function of oxygen consumption (primary outcome), mean ratings of breathlessness throughout exercise and peak ratings of breathlessness were significantly higher with naloxone than normal saline. There were no differences in physiological responses throughout exercise between conditions. In conclusion, endogenous opioids modify dyspnoea during treadmill exercise in patients with chronic obstructive pulmonary disease by apparent alteration of central perception.

The effects of added nanoparticles on aqueous kaolinite suspensions II. Rheological effects.

This series examines the effects of added silica nanoparticles on the properties and behavior of an aqueous suspension of kaolinite particles. Part I focused on the structural changes induced by the nanoparticles, primarily through scanning electron microscopy images. In this manuscript, we describe the changes in the rheological behavior of the kaolinite suspensions upon addition of the nanoparticles. In the absence of any additives, kaolinite platelets quickly aggregate and settle. When nanoparticles and salt (NaCl in these experiments) are added together, however, the suspensions begin to stabilize. When the salt and nanoparticle concentrations each exceed specific lower limits, the suspensions undergo a transition to a gel and develop a finite yield stress. Increasing the nanoparticle concentration or added salt concentration substantially increases the measured yield values, such that for the strongest samples, the yield stress exceeds the maximum for the rheometer to shear (3500 Pa). Plots of the complex viscosity, absolute value|eta *, versus time suggest two different time scales for the gelation process-a short, initial time (e.g., less than 2 h) in which absolute value eta * increases rapidly, followed by a gradual rise over a much longer period. Measurement of the phase lag, delta, between the applied stress and response strain indicates that the long-term state of the suspension is either completely viscous (delta = pi/2) or completely elastic (delta = 0). Values of delta between 0 and pi/2 were only seen with suspensions that were transitioning from a liquid to a gel state.

A computer method for assessing satisfaction with hearing aids.

The purpose of this study was to evaluate a new clinical assessment, the Dynamic Assessment of Hearing Aids (DAHA), for a large clinical population. Unlike traditional questionnaire methods, the DAHA has patients use an intuitive graphical computer interface to record visual analogue ratings of satisfaction with various features of their hearing aids (e.g. clarity, cost, appearance). Data were collected from 191 participants.A subset of participants returned for retest. The DAHA items assess satisfaction with hearing aids within four domains: communication, physical features, sound quality, and personal reactions. The concurrent validity was determined by comparing DAHA results to those obtained with the satisfaction with amplification in daily life (SADL). Ratings for personal reactions to hearing aids indicate the most satisfaction, and ratings for communication (especially group conversations and phone use) indicate the least satisfaction. The DAHA total score was found to have good test/retest and high internal consistency. Concurrent validity was supported by a strong correlation between total scores on the DAHA and the SADL. Results suggest the DAHA maybe an effective tool for clinical use.

The effects of added nanoparticles on aqueous kaolinite suspensions. I. Structural effects.

The results of an experimental study focused on the effect of added silica nanospheres on the structure of an aqueous suspension of disc-shaped kaolinite particles are presented. In the absence of any additives, kaolinite particles rapidly aggregate and settle. When only nanoparticles were added to a 14% vol. kaolinite suspension, some stabilization was observed, although a thick, fluid-like sediment still formed. Adding both nanoparticles and salt (NaCl or KCl), however, caused the entire suspension to transition into a solid material that was strong enough to actually be sliced. A phase diagram was constructed showing the concentration of salt and nanoparticles needed to produce this transition. With smaller nanoparticles, the transition occurred at much lower nanoparticle volume fractions. Scanning electron micrographs of both the sediment and solid-like material, obtained by cryogenic drying, showed that the latter consisted of a porous, 'sponge-like' structure. The characteristic size of the pores decreased as the number density of the added nanoparticles increased. Although the nanoparticles were not visible in the SEM images, it is believed that they had separated into the pores of the solid-like material. While a similar type of transition could be produced in suspensions containing only the silica nanospheres, the structure and flow behavior of this material were markedly different from that obtained with the added clay.

Statistical and information properties of head direction cells.

The human channel capacity for identifying sensory stimuli is compared with channel capacities based on neurophysiological findings. Studies have shown that cells in the postsubiculum (PoS) and the anterior dorsal thalamus (ADN) of the rat discharge as a function of the animal's head direction in the horizontal plane. We compute the statistical properties of the firing rates of head direction (HD) cells and the potential amount of information transmitted by these cells according to two theoretical models. The ceU response model for single cells indicates that information transmitted is much less than 0.5 bits. The population response model developed for cell ensembles generates values in the range of 1-3.2 bits, suggesting that a cell population can distinguish between two and nine head directions, depending on the value used for the standard deviation of directions over which a cell fires. These values are similar to those found in human psychophysical studies of the channel capacity for unidimensional sensory attributes.

Midlatency respiratory-related somatosensory activity and perception of oral pressure pulses in normal humans.

A direct relationship exists within subjects between midlatency features (<100 ms poststimulus) of respiratory-related evoked potentials and the perceived magnitude of applied oral pressure pulse stimuli. We evaluated perception in 18 normal subjects using cross-modality matching of applied pressure pulses via grip force and estimated mechanoafferent activity in these subjects by computing the global field power (GFP) from respiratory-related evoked potentials recorded over the right side of the scalp. We compared across subjects 1) the predicted magnitude production for a standard pressure pulse and 2) the slope (beta) and 3) the intercept (INT) of the Stevens power law to the summed GFP over 20-100 ms poststimulus. Both the magnitude production for a standard pressure pulse and the beta showed an inverse relationship with the summed GFP over 20-100 ms poststimulus, although there was no relationship between INT and the summed GFP. This may partially reflect characteristics of the mechanosensors and surely includes aspects of cognitive judgment, because we found and corrected for a high correlation between, respectively, beta (and INT) for pressure pulses and beta (and INT) for estimation of line lengths, a nonrespiratory modality. The relatively shallow, even inverse GFP-to-perception relationship suggests that, despite marked differences in the magnitude of afferent traffic, normal subjects seem to perceive things similarly.

Continuous measurement of breathlessness during exercise: validity, reliability, and responsiveness.

A continuous method for recording changes in breathlessness (dyspnea) during exercise is introduced and compared with the traditional discrete method. In study 1, a category-rating scale was presented on a computer screen, and 14 healthy, young female subjects exercised on a cycle ergometer until exhaustion. Two approaches were used to obtain ratings of breathlessness: a discrete method, in which subjects gave single judgments every minute, and a continuous method, in which subjects throughout exercise moved the mouse so that a bar on the screen extended to the desired location along the scale. Psychophysical results relating measures of breathlessness and the variables of work, oxygen consumption, and minute ventilation were statistically indistinguishable with the two methods, and both methods were highly reliable across test sessions. In study 2, both measurement methods were employed, and the subjects were 14 healthy, young males. In each of two sessions (discrete or continuous method), subjects first rated their breathlessness during an incremental test in which the workload was increased over time and levels of work, and minute ventilation were recorded. Subjects then exercised for 10 min at 60% of the maximal oxygen consumption achieved during the incremental test. At two points during steady-state exercise, a respiratory load was introduced that lasted for 1 min. It was possible to determine the responsiveness of subjects to onset and offset of the respiratory load for the continuous method but not for the discrete method. In study 3, patients with chronic obstructive pulmonary disease employed both methods, and it was found that the continuous method was better at determining whether subjects showed a significant positive slope of the regression line between breathlessness ratings and physiological variables.

Interactive computer method for rating quality of life: comparison of chronic pain patients and healthy controls.

OBJECTIVE: This study presents information on the development of an interactive computer-based rating method of quality of life that assesses the multidimensional impact of chronic pain on the individual. METHOD: A software program assessing 20 categories of quality of life was created and administered to 103 chronic pain patients. Comparison data were obtained from 103 matched healthy controls. RESULTS: High variability was found among pain patients in their ratings of quality of life, and pain patients rated all categories lower than controls. Three groups emerged from a cluster analysis of the data reflecting high, mixed, and low ratings of satisfaction with quality of life. CONCLUSIONS: The rating method was convenient, was easy for the patient to understand, and took very little time to administer. Further investigation of the validity and reliability of this tool is needed.

Descriptors of breathlessness in healthy individuals: distinct and separable constructs.

STUDY OBJECTIVES: We tested the hypothesis that descriptors of breathlessness represent distinct and separable cognitive constructs, and predicted that the use of descriptors of breathlessness by healthy individuals is the same as their use by patients with cardiopulmonary disease. DESIGN: Cluster analyses obtained in healthy individuals were compared with those obtained previously in patients who complained of breathing discomfort. In addition, we used multidimensional scaling (MDS) techniques to analyze relationships among descriptors in healthy individuals. SETTING: Public university. PARTICIPANTS: The participants were 100 healthy individuals (48 men and 52 women) ranging in age between 18 and 65 years (mean, 27.9+/-11.7 years). MEASUREMENTS AND RESULTS: Participants judged the dissimilarity among pairs of 15 descriptors of breathlessness that were used previously to examine the experience of dyspnea in patients who complained of breathing discomfort. Cluster analysis solutions obtained in the healthy individuals were virtually identical to those obtained previously in patients. Three dimensions (attributes) of breathing discomfort were uncovered with MDS: "Depth and frequency of breathing," "Perceived need, or urge, to breathe," and "Difficulty breathing and phase of respiration." The results did not depend on age, sex, levels of education, or the presence of uncomfortable awareness of breathing with activities. CONCLUSIONS: The relations among descriptors of breathlessness obtained in healthy individuals support the contention that the association of different clusters with different disease states reflects distinct and separable cognitive constructs that are not simply dependent on the presence of an underlying pathophysiology or on a specific disease condition. Our results in healthy individuals also suggest that distinct qualities of breathlessness relate to different physiologic mechanisms underlying respiratory discomfort.

The psychophysics of imagery.

A series of experiments considers the extent to which the interrelations among subjective magnitudes aroused by images corresponds to those for subjective magnitudes aroused by physical stimuli. In Experiment 1, 68 undergraduates typed phrases in response to graded categories regarding the imagined magnitude of lights, sounds, and smells. In Experiment 2, 5 undergraduates and, in Experiment 3, 3 graduate students then magnitude estimated the image intensity aroused by each of these stimulus phrases. In Experiments 4 and 5, the same subjects performed cross-modality matches between phrases arousing images for different attributes (light, sound, and smell). Statistical analysis indicates that estimates based on images display many of the same patterns as those based on physical stimuli. The major exception involves sequence effects, present for actual stimuli but not for images.

Magnitude estimation of perceived odor intensity: empirical and theoretical properties.

Four subjects judged the odor intensities of 7 pyridine concentrations and a blank. Computer simulations of a judgment model were compared with the empirical data. The model generates data patterns that closely mimic empirical findings. The following patterns were confirmed: (a) A power function relates magnitude estimates and concentration with an exponent in the range of 0.7 to 1.0 (b) The exponent fluctuates so that the level constant is negatively correlated with the exponent. (c) The standard deviation of the responses is a negatively accelerated function of the mean. (d) The skewness of the responses is relatively high for low concentrations and declines toward zero with increasing concentration. (e) The correlation between responses to successive stimuli is highest when successive concentrations are similar.

Binaural summation after learning psychophysical functions for loudness.

Do response-related processes affect perceptual processes? Sometimes they may: Algom and Marks (1990) produced different loudness exponents by manipulating stimulus range, and thereby also modified the rules of loudness summation determined by magnitude scaling. The present study manipulated exponents by having a dozen subjects learn prescribed power functions with exponents of 0.3, 0.6, or 1.2 (re sound pressure). Subjects gave magnitude estimates of the loudness of binaural signals during training, and of monaural and binaural signals after training. During training, subjects' responses followed the nominal functions reasonably well. Immediately following training, subjects applied the numeric response scales uniformly to binaural and monaural signals alike; the implicit monaural-binaural loudness matches, and thus the basic rules underlying binaural summation, were unaffected by the exponent learned. Comparison of these results with those of Algom and Marks leads us to conclude that changing stimulus range likely influences underlying perceptual events, whereas "calibrating" a loudness scale through pretraining leaves the perceptual processes unaffected.

On the nature and meaning of sinuosity in magnitude-estimation functions.

Magnitude-estimation functions for single observers, derived from multiple judgments of closely spaced stimuli, exhibit a sinuous form in logarithmic coordinates, an observation frequently confirmed since first reported by Luce and Mo (1965). We propose that this can result from reliance on a restricted pool of responses, called "preferred numbers" by Baird and Noma (1975). We describe a model featuring a response band centered on an assumed power function, from which the observer selects from among preferred numbers with equal probability. In simulations, the expected values of these selections oscillate around the underlying power function with an appearance similar to that of Luce-Mo functions. The appearance of these functions depends on values assumed for the scale factor of the power function, the range of intensities considered, and the width of the band from which responses are drawn. We conclude that sinuosity in magnitude-estimation functions does not disconfirm the psychophysical power law.

The effects of size, clutter, and complexity on vanishing-point distances in visual imagery.

The portrayal of vanishing-point distances in visual imagery was examined in six experiments. In all experiments, subjects formed visual images of squares, and the squares were to be oriented orthogonally to subjects' line of sight. The squares differed in their level of surface complexity, and were either undivided, divided into 4 equally sized smaller squares, or divided into 16 equally sized smaller squares. Squares also differed in stated referent size, and ranged from 3 in. to 128 ft along each side. After subjects had formed an image of a specified square, they transformed their image so that the square was portrayed to move away from them. Eventually, the imaged square was portrayed to be so far away that if it were any further away, it could not be identified. Subjects estimated the distance to the square that was portrayed in their image at that time, the vanishing-point distance, and the relationship between stated referent size and imaged vanishing-point distance was best described by a power function with an exponent less than 1. In general, there were trends for exponents (slopes on log axes) to increase slightly and for multiplicative constants (y intercepts on log axes) to decrease as surface complexity increased. No differences in exponents or in multiplicative constants were found when the vanishing-point was approached from either subthreshold or suprathreshold directions. When clutter in the form of additional imaged objects located to either side of the primary imaged object was added to the image, the exponent of the vanishing-point function increased slightly and the multiplicative constant decreased. The success of a power function (and the failure of the size-distance invariance hypothesis) in describing the vanishing-point distance function calls into question the notions (a) that a constant grain size exists in the imaginal visual field at a given location and (b) that grain size specifies a lower limit in the storage of information in visual images.

Stimulus sequence and the exponent of the power function for loudness.

In two experiments, 15 and 13 subjects estimated the loudness of 12 sound-pressure levels (38-104 dB; 6-dB intervals) of a 1000-Hz tone by the method of magnitude estimation with a modulus assigned to the first stimulus presented. The tone duration was 1 sec. and the interstimulus interval was 6 sec. The presentation order was systematically ascending-descending in one experiment and balanced-irregular in the other. The results indicate that (1) loudness is a power function of sound pressure with an exponent of 0.60 for the systematic order and 0.29 for the irregular order. (2) For both the irregular and systematic orders, a large step-size (12 or 18 dB) between the stimulus on Trial n and on Trial n-1 (or n-3) results in a slight assimilation effect. This also occurs for the small step-size (6 dB) in the irregular order. (3) The size of momentary exponents (based on two points, Trials n and n-1 or n-3) depends on the sound pressures of successive stimuli, whether the steps are positive or negative, and whether the stimuli have been presented in systematic or irregular order. For positive steps, the momentary exponent is lower for a soft tone (Trial n) than for a loud tone, whereas for negative steps the momentary exponent is lower for a loud tone than for a soft tone. These effects ar more pronounced when these stimuli are presented in an irregular order. A relative judgment model is offered for magnitude estimation. It assumes that subjects judge the loudness of a stimulus in terms of three reference markers: the minimum and maximum sound pressures as well as the sound pressure of the previous stimulus.

Transformation theory of size judgment.

Perception of size is assessed by having observers adjust a comparison target at a fixed distance to match the size of a standard located at different distances. Results depend on instructions, target orientation, and available stimulus cues. A mathematical theory assumes that the brain performs an inverse transformation on the proximal information impinging on the retina to recover the original distal size of the target. Results depend on the target visual angle, and the effective target distance and orientation applied in performing the inverse transformation. Effective values are linked to instructions, target location, and stimulus cues. Two models are developed and successfully fit to empirical data. One emphasizes the distance parameter; the second, the orientation parameter.

A simple but powerful theory of the moon illusion.

Modification of Restle's theory (1970) explains the moon illusion and related phenomena on the basis of three principles: (1) The apparent sizes of objects are their perceived visual angles. (2) The apparent size of the moon is determined by the ratio of the angular extent of the moon relative to the extents subtended by objects composing the surrounding context, such as the sky and things on the ground. (3) The visual extents subtended by common objects of a constant physical size decrease systematically with increasing distance from the observer. Further development of this theory requires specification of both the components of the surrounding context and their relative importance in determining the apparent size and distance of the moon.

Shift in stimulus range and the exponent of the power function for loudness.

The exponent of the power function for loudness was tracked over the course of 60 trials with one stimulus range and compared to the exponent over the course of 60 subsequent trials with a different stimulus range. Three stimulus sets were used: (1) weak, a short range of relatively soft tones (45-55 dBA); (2) strong, a short range of relatively loud tones (64-74 dBA); and (3) complete, a longer range of soft to loud tones (40-90 dBA). All pairs of stimulus sets were tested, together with three control conditions in which no shift in range occurred. Ten subjects were run in each of the nine groups. For preshift trials, the mean exponent was lowest for the strong stimulus series, highest for the weak series, and at an intermediate value for the complete series. These differences were all significant. Following a shift in stimulus range, the weak series still yielded the highest exponent, but the exponents were not reliably different for the complete and strong series. Postshift exponents also depended significantly on the preshift range experienced by the subjects. These effects were not confined to the period immediately following the shift in range, but persisted for up to 60 trials.