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Biomedical subjects

D Yager

Publications and source records attributed to D Yager.

At least 55 records · Page 3Linked to original sources
PubMed1991

Airway luminal liquid. Sources and role as an amplifier of bronchoconstriction.

The release of mediators from inflammatory cells into the airway lumen can initiate a series of events leading to airway obstruction, particularly smooth muscle contraction and alteration of endothelial and epithelial permeability leading to mucosal edema and subsequent influx of liquid into the airway lumen. In this report we briefly review the effects of several inflammatory mediators, including eicosanoids, platelet-activating factor, and histamine, as well as the effects of plasma proteins and tachykinins that may be secondarily released because of the presence of inflammatory mediators on endothelial and epithelial permeability. We then consider physical mechanisms whereby the resulting airway luminal liquid could amplify the response of an airway previously constricted because of smooth muscle contraction. Specifically, liquid in the interstices between epithelial projections that are formed during muscular contraction could amplify the degree of luminal compromise by (1) further decreasing luminal cross-sectional area by occupying space, and (2) providing an additional source of inward recoil because of the surface tension of the air-liquid interface.

Animals↗
PubMed1990

'Air hunger' from increased PCO2 persists after complete neuromuscular block in humans.

The tolerance of totally curarized subjects for prolonged breath hold is viewed by many as evidence that respiratory muscle contraction is essential to generate the sensation of breathlessness. Although conflicting evidence exists, none of it was obtained during total neuromuscular block. We completely paralyzed four normal, unsedated subjects with vecuronium (a non-depolarizing neuromuscular blocker). Subjects were mechanically ventilated with hyperoxic gas mixtures at fixed rate and tidal volume. End-expiratory PCO2 (PETCO2) was varied surreptitiously by changing inspired PCO2. Subjects rated their respiratory discomfort or 'air hunger' every 45 sec. At low PETCO2 (median 35 Torr) they felt little or no air hunger. When PETCO2 was raised (median 44 Torr) all subjects reported severe air hunger. They had reported the same degree of air hunger at essentially the same PETCO2 before paralysis. When questioned afterwards all subjects said the sensation could be described by the terms 'air hunger', 'urge to breathe', and 'shortness of breath', and that is was like breath holding. They reported no fundamental difference in the sensation before and after paralysis. We conclude that respiratory muscle contraction is not important in the genesis of air hunger evoked by hypercapnia.

Adult↗
PubMed1989

Impedance of the chest wall during sustained respiratory muscle contraction.

We measured total chest wall impedance (Zw), "pathway impedances" of the rib cage (Zrcpath), and diaphragm-abdomen (Zd-apath), and impedance of the belly wall including abdominal contents (Zbw+) in five subjects during sustained expiratory (change in average pleural pressure [Ppl] from relaxation = 10 and 20 cmH2O) and inspiratory (change in Ppl = -10 and -20 cmH2O) muscle contraction, using forced oscillatory techniques (0.5-4 Hz) we have previously reported for relaxation (J. Appl. Physiol. 66: 350-359, 1989). Chest wall configuration and mean lung volume were kept constant. Zw, Zrcpath, Zd-apath, and Zbw+ all increased greatly at each frequency during expiratory muscle contraction; increases were proportional to effort. Zw, Zrcpath, and Zd-apath increased greatly during inspiratory muscle contraction, but Zbw+ did not. Resistances and elastances calculated from each of the impedances showed the same changes during muscle contraction as the corresponding impedances. Each of the resistances decreased as frequency increased, independent of effort; elastances generally increased with frequency. These frequency dependencies were similar to those measured in relaxed or tetanized isolated muscle during sinusoidal stretching (P.M. Rack, J. Physiol. Lond. 183: 1-14, 1966). We conclude that during respiratory muscle contraction 1) chest wall impedance increases, 2) changes in regional chest wall impedances can be somewhat independent, depending on which muscles contract, and 3) increases in chest wall impedance are due, at least in part, to changes in the passive properties of the muscles themselves.

Adult↗
PubMed1989

Amplification of airway constriction due to liquid filling of airway interstices.

Luminal epithelial projections formed during bronchoconstriction define interstices in which liquid can collect. Liquid in these interstices could amplify the degree of luminal compromise due to muscular contraction in at least two distinct ways. First, the luminal cross-sectional area is reduced by simple filling of the interstices. Second, if the surface tension (gamma) of the air-liquid interface is positive, the pressure drop across the interface produces an additional inward force that can further constrict the airway. We present a theoretical treatment of these two mechanisms together with data which suggest that both may significantly amplify the luminal narrowing due to airway smooth muscle contraction, particularly in small airways when gamma is high. To qualitatively assess the effects of altered gamma, guinea pig lungs with normal and altered airway liquid lining layers were frozen and studied while fully hydrated by low-temperature scanning electron microscopy. Airway gamma was altered in these animals by intratracheal instillation of 0.5 mg lysoplatelet-activating factor (lyso-PAF). The interstices of normal airways were dry, whereas the interstices of airways with altered surface lining layers were liquid filled. In addition, the surfactant inhibitory properties of lyso-PAF, 2-arachidonyl-PAF, and dipalmitoyl phosphatidylcholine (DPPC) were measured with a pulsating bubble surfactometer, using surfactant TA as the model surfactant. Minimal gamma (gamma min) of surfactant TA alone was 4.0 +/- 0.2 dyn/cm; a 5% mixture of lyso-PAF with surfactant TA resulted in a significantly (P less than 0.02) greater gamma min of 8.8 +/- 1.8 dyn/cm. In contrast, 2-arachidonyl-PAF and DPPC had minimal effects on gamma min of surfactant TA.

Animals↗
PubMed1988

Elastic properties of air- and liquid-filled lung parenchyma.

Pressure-volume measurements and the punch indentation test are used to obtain the bulk modulus (kappa) and the shear modulus (mu) of lung parenchyma of air- and liquid-filled rabbit lungs. Plots of kappa and mu vs. transpulmonary pressure obtained from these measurements indicate that there is very little difference between the elastic behavior of the air- and liquid-filled lung, suggesting that the mechanism of resisting deformation in both cases is similar. On the other hand, from plots of kappa and mu vs. lung volume, it appears that the elastic moduli are higher in the air-filled lung than in the liquid-filled lung at the same volume. These differences, referred to as kappa gamma and mu gamma, as well as the difference in transpulmonary pressures (P gamma), are presumably due to the additional elastic recoil of the air-filled lung provided by alveolar surface tension (gamma). No conclusion could be reached about the shape of the kappa gamma vs. P gamma curve. However, the mu gamma vs. P gamma relationship appears to be approximately linear, with a slope of approximately 0.5. This result agrees qualitatively with the model (T. A. Wilson and H. Bachofen, J. Appl. Physiol. 52: 1064-1070, 1982) in which the part of the parenchyma that provides P gamma is pictured as mechanically analogous to an open cell liquid foam, having mu gamma = 0.4P gamma (J. Appl. Mech. Trans. ASME 51: 229-231, 1984), but it is statistically significant only at high lung volumes.

Air↗
PubMed1987

Comparison of perceived spatial frequency between the fovea and the periphery.

A grating viewed in the periphery usually appears to be of higher frequency than the same grating viewed at the fovea, for frequencies below the Nyquist frequency of the periphery. Systematic shifts in perceived frequency between fovea and periphery were found under several experimental conditions: spatially localized or extended sine-wave patterns, test stimuli presented in the superior or the inferior visual field, and stimuli of high or low mean luminance at several different contrasts. A multiple-spatial-frequency channels model can qualitatively account for our results, if it is assumed that each channel has a receptive-field size that increases as a function of eccentricity but has a perceived frequency label that does not change as a function of eccentricity.

Fovea Centralis↗
PubMed1986

Shifts in perceived spatial frequency of low-contrast stimuli: data and theory.

We studied shifts in perceived spatial frequency of foveally viewed stimuli as a function of contrast, using lower contrasts and/or a lower range of spatial frequencies than used previously by others. Reliable shifts in perceived spatial frequency were found, but the direction of the shift at low frequencies was not the same as at high frequencies for some observers. Models based on either light scatter or an early compressive nonlinearity (transducer function) probably cannot account for these results. A multiple spatial-frequency-channels model in which a nonlinear contrast-transfer function (CTF) follows the output of each channel, however, is consistent with most of the results for suprathreshold contrasts. We considered several versions of this latter model, differing in their assumptions about the peak frequencies and bandwidths of the underlying channels, the shape of the CTF, and the combination rule by which the outputs of the channels are labeled and combined according to a weighted average.

Humans↗
PubMed1985

The spatial frequency discrimination function at low contrasts.

Spatial frequency difference thresholds for sinewave gratings near contrast threshold were measured using a two-alternative forced-choice technique, and the threshold frequency differences were plotted as a proportion of standard frequency for standards from 2 to 7 cycles/degree. This function shows reliable local maxima and minima, and these features are more pronounced than they are when stimuli of 30% contrast are used. This result is consistent with the notion that at low contrasts, fewer spatial frequency channels are above threshold in the area of the visual field covered by the stimulus than when the stimulus is at high contrast.

Contrast Sensitivity↗
PubMed1985

Simultaneous measurement of spatial-frequency summation and uncertainty effects.

The predictions for summation and uncertainty effects from several multiple-spatial-frequency-channels models were calculated. The models differed in their assumptions about the shape of the channels' underlying probability-density functions and in the decision rule used to combine the channels' outputs. Varying these assumptions resulted in quite different predictions about the magnitudes of these effects. Simultaneous summation and uncertainty experiments measured the detectability of gratings containing one (simple) or two (compound) spatial frequencies. Performance was assessed in two types of blocks of trials: either each stimulus was in a separate block or three stimuli (two simple gratings and their compound) were randomly intermixed in one block. Quantitative comparisons of the models with the data showed that the increasing-variance Gaussian models (in which the decision variable is the sum of the monitored channels' outputs) provided the best overall fit.

Attention↗
PubMed1984

Detection and identification of spatial frequency: models and data.

Detection and identification of up to four simple sinusoidal gratings were studied. The experimental results were quantitatively compared to predictions from several models. The models all assumed probabilistically independent channels sensitive to different ranges of spatial frequency. The models differed in the shapes of their underlying distributions and, for detection, their decision rule. Detection and identification of far-apart spatial frequencies were consistent with these models. Thus, uncertainty effects for both detection and identification (the decrease in performance with an increase in the number of possible spatial frequencies) can be explained without assuming that attention capacity is limited.

Attention↗
PubMed1984

Spatial-frequency difference thresholds for central and peripheral viewing.

We measured spatial-frequency difference thresholds with a two-alternative forced-choice technique. On each trial a given standard frequency was presented in one temporal interval and a higher or lower frequency in the other. The subject indicated which interval contained the higher frequency of the two presented in that trial. The variable frequencies were chosen using a decision rule combined with a double-random-alternating staircase that converged on stimulus values that produced 70.7% correct choices. The proportional difference in frequency for criterion responding was computed from the mean of all stimulus values presented in a block of trials. This fraction was plotted as a function of standard spatial frequency. The resulting function shows local maxima and minima that are greater than the standard errors of the means across blocks of trials at a given standard. Functions obtained at 10 deg off the fovea showed a greater range of values than those obtained with central viewing. The results are consistent with the notion that there is a limited number of spatial-frequency channels whose bandwidths are narrow relative to their separation in the spatial-frequency spectrum.

Differential Threshold↗
PubMed1977

Visual function in goldfish with unilateral and bilateral tectal ablation.

Following complete bilateral tectal ablation, the ability to detect light recovers in about three weeks. The non-tectal retinal connections which may mediate detection are about one log unit less sensitive than the retinotectal connections. At moderate illumination levels, tectumless fish do not react visually to objects. Tectumless fish integrate luminous flux over a very wide area (at least 25 degrees diameter) while the critical diameter for the normal in this experiment is smaller. Subcortical structures may mediate the interocular transfer of a brightness discrimination. The ipsilateral retinotectal projection following unilateral tectal removal is functional, with normal sensitivity to detection of light.

Animals↗