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Biomedical subjects

D H Kelly

Publications and source records attributed to D H Kelly.

At least 73 records · Page 4Linked to original sources
PubMed1980

Periodic breathing in siblings of sudden infant death syndrome victims.

To determine the incidence of periodic breathing (PB) episodes during sleep, 48 subsequent sudden infant death syndrome siblings and 48 control infants, matched by sex, gestational age, and chronologic age, were studied by home pneumogram technique. The sudden infant death syndrome siblings had a statistically significant increase in the percent of sleep time spent in PB, in the number of episodes/100 minutes of PB, in the longest episode PB, and in the average duration of all episodes of PB. We conclude that PB is present in a higher amount in sudden infant death syndrome siblings as compared to control infants.

Cheyne-Stokes Respiration↗
PubMed1979

Labetalol and bendrofluazide: comparison of their antihypertensive effects.

A randomized double-blind crossover trial of labetalol, bendrofluazide and placebo was carried out in 18 patients with mild to moderate hypertension. The reduction in blood pressure observed with labetalol and bendrofluazide was similar. The plasma levels of labetalol showed a significant correlation with changes in blood pressure (r = 0.07; P less than 0.021); and plasma level determinations of this drug may be of value in the management of patients who receive antihypertensive agents.

Adult↗
PubMed1979

Motion and vision. I. Stabilized images of stationary gratings.

To demonstrate that eye movements have profound effects on the sine-wave contrast threshold, the author uses a new method of stabilizing the retinal image, in which the Purkinje reflections from the eye move the stimulus pattern displayed on a CRT screen. Calibration of this compensatory motion is very critical; a gain error greater than 1% may produce significant destablization. Under optimum conditions, image stabilization elevates the subject's contrast threshold by a factor of about 20; it also produces after-images with resolution greater than 12 c/deg. These results compare favorably with those obtained by other methods.

Afterimage↗
PubMed1979

Motion and vision. II. Stabilized spatio-temporal threshold surface.

The stabilized contrast-sensitivity function measured at a constant retinal velocity is tuned to a particular spatial frequency, which is inversely related to the velocity chosen. The Fourier transforms of these constant-velocity passbands have the same form as retinal receptive fields of various sizes. At low velocities, in the range of the natural drift motions of the eye, the stabilized contrast-sensitivity function matches the normal, unstablized result. At higher velocities (corresponding to motions of objects in the environment), this curve maintains the same shape but shifts toward lower spatial frequencies. The constant-velocity passband is displaced across the spatio-temporal frequency domain in a manner that is almost symmetric about the constant-velocity plane at v = 2 deg/s. Interpolating these diagonal profiles by a suitable analytic expression, we construct the spatio-temporal threshold surface for stabilized vision, and display its properties in terms of the usual frequency parameters; e.g., at low spatial frequencies, the temporal response becomes nearly independent of spatial frequency, while at low temporal frequencies, the spatial response becomes independent of temporal frequency.

Eye Movements↗
PubMed1979

Periodic breathing in infants with near-miss sudden infant death syndrome.

Twelve-hour nocturnal home recordings of respiration and heart rates were obtained during sleep in 32 infants with near-miss sudden infant death syndrome (SIDS) and in 32 control infants, and the recordings were analyzed for periodic breathing. An episode of periodic breathing was defined as three or more apneic pauses of three or more seconds. The duration of respirations interrupting the pauses was 20 seconds or less. Analysis revealed a statistically significant difference (P less than .001) between the two groups, using criteria of percent of periodic breathing episodes, number of periodic breathing episodes/100 min of recorded sleep time, average duration of all episodes, and duration of the longest episode of periodic breathing. It is concluded that periodic breathing is present in excessive amounts during sleep in infants with near-miss sudden infant death syndrome.

Apnea↗
PubMed1978

Human flicker sensitivity: two stages of retinal diffusion.

A well-known solution of the diffusion equation gives an exponential square-root function as the frequency response for a one-dimensional diffusion or transmission process. When two or more such processes are cascaded, the result is still an exponential square-root characteristic, but with a longer time constant. This seems to explain why flicker thresholds obey the Kelly-Veringa diffusion model at high frequencies, even though the psychophysically inferred diffusion process is much slower than the first stage of visual transduction measured by, for example, late receptor potentials. Two such stages in tandem are sufficient to account for the psychophysical data, because the psychophysical time constant is proportional to the square of the number of stages involved. In addition, the nonlinear behavior of flicker thresholds under intense light adaptation can be explained if the loss factor in the first stage is proportional to the amount of the photopigment bleached. Apparently the flicker thresholds are governed by first- and second-order retinal neurons.

Adaptation, Physiological↗
PubMed1978

Theory of flicker and transient responses. III. An essential nonlinearity.

From our stead-state flicker data, Kelly's (1971) model correctly predicts the transient thresholds for rectangular pulses of variable duration when the (flickering or flashed) stimulus is a 4 cycle/deg grating, but the same prediction fails for a uniform (8 degrees) field. However, if we augment the model with a "hard" nonlinearity, we can fit both types of transient thresholds as well as the steady-state thresholds. The most plausible embodiment of this essential nonlinearity is an asymmetric recifier, which seems to represent the behavior of retinal ganglion cells. Unlike the symmetric models of Roufs and Rashbass, this asymmetry also correctly predicts that the decrement thresholds for some stimuli are smaller than the corresponding increment thresholds.

Animals↗
PubMed1978

Care of infants with near-miss sudden infant death syndrome.

The purpose of this study was to evaluate the effectiveness of home management of life-threatening apnea in infants with near-miss sudden infant death syndrome (SIDS). A total of 84 infants were monitored with apnea monitors for an average of seven months (range 1 to 27). A group of 27 infants had episodes of apnea requiring resuscitation during home monitoring, all of whom were successfully resuscitated by their parents on at least one occasion using bag and mask resuscitation, and 17 infants required more than one resuscitation. Subsequent resuscitation was unsuccessful with four infants. Infants who experienced more than ten episodes of prolonged sleep apnea (apnea longer than 20 seconds) during home monitoring had a significantly increased risk of requiring resuscitation than other infants being studied. With the use of home monitoring of these infants and parents trained in cardiopulmonary resuscitation, the survival rate was 93.4%.

Apnea↗
PubMed1977

Abnormal regulation of ventilation in infants at risk for sudden-infant-death syndrome.

To test whether alveolar hypoventilation and an abnormal ventilatory response to inhaled carbon dioxide explains some episodes of sudden-infant-death syndrome, we assessed ventilatory control during quiet sleep in 12 normal infants and 11 infants who had required at least two resuscitations because of prolonged apnea (greater than 20 seconds) during sleep (aborted form of the syndrome). Infants with the aborted syndrome hypoventilated during quiet sleep (alveolar partial pressure of carbon dioxide, 38.9+/-3.5 mm Hg) as compared to normal infants (35.1+/-1.9, P less than 0.01). In addition, the ventilatory response to carbon dioxide breathing during quiet sleep was impaired (mean change in minute ventilation per change in partial pressure of carbon dioxide 22.1+/-8.9, as compared to 63.1+/-19.1 ml per kilogram per minute per millimeter of mercury in controls [p less than 0.001]). Three infants with the "aborted syndrome" subsequently died during sleep at home; autopsy, done in two, revealed no apparent cause of death. We conclude that infants who have had an episode consistent with sudden-infant-death syndrome have a defect in the regulation of alveolar ventilation.

Apnea↗
PubMed1977

Oral vibrotactile sensation: an evaluation of children with normal and defective articulation.

Lingual vibrotactile thresholds (LVTs) were determined at 125, 250, and 500 Hz for 30 children with defective articulation and 30 children with normal articulation. Secondly, attempts to predict the phonemic and distinctive feature errors from LVTs for defective articulating children is presented. Children with normal articulation show significantly lower (better) LVTs at each frequency than do children with defective articulation. Significant relationships were not found between LVTs and phonemic scores or distinctive feature errors.

Child↗
PubMed1977

The role of the QT interval in the sudden infant death syndrome.

To evaluate the role of QT interval prolongation in the genesis of the sudden infant death syndrome (SIDS), the post-resuscitation electrocardiograms of 21 aborted SIDS infants were reviewed. The infants had been found apneic, cyanotic, limp and unresponsive during sleep and required vigorous physical stimulation and mouth-to-mouth resuscitation. Three subsequently experienced repeat similar episodes from which they could not be resuscitated. Extensive studies eliminated all "known" etiologies for death. The QT intervals of these infants were compared to age and sex matched normal infants as well as to established normal values in the literature; in both the aborted and the subsequent actual SIDS infants, the QT intervals were not significantly different from those of the normal population. Thus, we conclude that QT intervals prolongation does not play a major role in the genesis of the aborted SIDS.

Electrocardiography↗
PubMed1977

Two-band model of heterochromatic flicker.

We have attempted to reconcile the results of several recent chromatic flicker studies. By adjusting the relative amplitudes of red and green sine-wave stimuli that were flickering in opposite phase, we obtained conditions varying from purely chromatic (red-green) stimulation, through each "silent-cone" condition, to purely luminous (homochromatic) stimulation. We also tested the effects of adapting backgrounds in each condition. Our results can be explained in terms of a low-frequency band that represents the opponent-color response, and a high-frequency band that represents the achromatic response. These two bands respond in various proportions, depending on the red-green stimulus ratio. Chromatic adaptation generally affects the low- and high-frequency bands differently and hence changes the shape of the flicker sensitivity curve. However, if the temporally varying waveform and the adapting background are both chosen to stimulate the same cone type, then the opponent-color and achromatic bands are both attenuated by the same amount. In this case, the shapes of the silent-red and silent-green flicker curves are preserved under chromatic adaptation. We conclude that none of these flicker curves are controlled by the temporal characteristics of independent cone types.

Color Perception↗
PubMed1976

Primate flicker sensitivity: psychophysics and electrophysiology.

A quantitative comparison is made between the psychophysical flicker response of man and similar data obtained electrophysiologically from the cones of macaque monkeys. When the psychophysical data are obtained from an eye that is strongly light-adapted, there is excellent agreement between the two sets of data at high frequencies. Under this condition, both kinds of data fit a distributed-parameter model, whose time constant also agrees with that derived from studies of the phosphenes elicited by electrical stimulation of the human eye. On the other hand, psychophysical data obtained with fully modulated stimuli (which minimally adapt the eye) yield a longer time constant for the same model. These results imply that the psychophysical flicker thresholds are normally controlled by a distributed filtering process that is proximal to the receptor stage. This slower, psychophysical process is evidently desensitized by intense adapting lights, so that the faster one that governs the electrophysiological responses can be detected.

Animals↗
PubMed1975

Luminous and chromatic flickering patterns have opposite effects.

When stimulated in phase by a sinusoidally flickering, uniform field, the red and green cone systems tend to inhibit each other. This inhibition is minimized by (i) counterphase (luminance) patterns or (ii) red/green (chromaticity) flicker. However, when (i) and (ii) are combined, the usual flickering-pattern effect is reversed: instead of enhancing chromatic flicker, counterphase patterns tend to suppress it.

Color Perception↗