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Biomedical subjects

D H Kelly

Publications and source records attributed to D H Kelly.

At least 37 records · Page 2Linked to original sources
PubMed1987

Increased respiratory frequency and variability in high risk babies who die of sudden infant death syndrome.

We have tested the hypothesis that autonomic instability, reflected in increased variability of heart rate and respiratory frequency, characterized high risk babies who died of sudden infant death syndrome. Using computer-based methods, we compared the power spectra of instantaneous heart rate and respiration on coded tape recordings from seven asymptomatic siblings and 10 babies with symptomatic apnea who died of sudden infant death syndrome to 34 age- and sex-matched controls. We confirmed our previous observation of increased respiratory bandwidth, an index of variability in respiratory frequency (p = 0.009) but failed to confirm our finding of increased low frequency fluctuations in heart rate (p = 0.18). In addition, we found an increase in mean respiratory frequency during quiet breathing (p = 0.001) and a significant relationship between respiratory bandwidth and mean respiratory frequency (r = 0.604, p = 0.0002). These variables along with those from a previous analysis of the same data base yield a discriminant function with 82% sensitivity and 100% specificity. These results confirm previous suggestions that high risk babies who die of sudden infant death syndrome exhibit autonomic instability.

Autonomic Nervous System↗
PubMed1987

Long-term follow-up of children with congenital central hypoventilation syndrome.

The long-term clinical course of six patients with congenital central hypoventilation syndrome is described. During the neonatal period, the patients had prolonged apneas and hypoventilation, in the absence of cardiac, pulmonary, or neuromuscular disease. After an initial period of respirator dependency, they became able to sustain normal gas exchange while awake. During sleep, however, profound hypoventilation developed, and tracheostomy and mechanical ventilation were required. Ventilatory responses to hypercapnia and hypoxia were depressed or absent and did not improve with time. One patient was able, at 2 years of age, to breathe spontaneously during sleep with only moderate hypoventilation. The others, now 4 to 14 years of age, still need ventilatory support during sleep. Complications, such as cardiac failure and hypoxic seizures, mostly occurred early in the course and resolved with correction of insufficient mechanical ventilation. Speech acquisition was possible with the use of a special stoma plug. All patients were managed at home, and with appropriate support, the parents were able to provide safe ventilatory care with low morbidity and no mortality.

Developmental Disabilities↗
PubMed1987

Familial occurrence of sudden infant death syndrome and apnea of infancy.

We sought to determine the outcome of infants born to families with multiple victims of sudden infant death syndrome (SIDS) and/or apnea of infancy. Seventy-three infants, born to families who had two or more previous siblings who had either died of SIDS or who were monitored at home for apnea of infancy or for abnormal results on polysomnogram and/or pneumogram recording, were prospectively monitored. The infants underwent polysomnogram and pneumogram recordings and were subsequently monitored at home with a cardiorespiratory monitor. All episodes of apnea were immediately reviewed. Thirteen infants (18%) had subsequent severe episodes of apnea and five other infants (7%) died during a subsequent episode. All deaths occurred in families who had two or more SIDS victims. The outcome for the 17 infants who were half siblings was similar to the outcome for full siblings. Clinical data of the infants and results of evaluation were not predictive of outcome.

Female↗
PubMed1986

Pneumograms in infants who subsequently died of sudden infant death syndrome.

Victims of sudden infant death syndrome (SIDS) have occasionally been reported to have had prolonged apnea or an increased frequency of short apnea prior to their deaths. To examine the extent of these abnormalities, we compared pneumograms obtained in 17 infants who subsequently died of SIDS (10 with history of apnea) with those of 34 age- and sex-matched controls. The recordings were analyzed by a computer program that avoided observer bias. SIDS infants had significantly greater mean heart rate (P less than 0.05) and periodic breathing during quiet time (P less than 0.003) than control infants had. The apnea in SIDS infants tended to be more periodic than in control infants (P less than 0.002). In addition, the incidence of bradycardia was greater in SIDS (three infants) than in controls (none) (P less than 0.03). These differences suggest a disturbance of autonomic function prior to death in some victims of SIDS.

Apnea↗
PubMed1986

Analysis of heart rate and respiratory patterns in sudden infant death syndrome victims and control infants.

Retrospective analyses of patterns of breathing and heart rate variability obtained by visual inspection and spectral analysis of ECG and respiratory activity have provided markers associated with subsequent death in a referred population of infants at high risk for sudden infant death syndrome (SIDS). Such markers include breathing patterns characterized by excessive apneic pauses and periodic breathing, heart rate spectra characterized by increased low frequency oscillations, and respiratory activity spectra characterized by a widened "bandwidth" during regular breathing. To test whether such measurements could distinguish SIDS cases and randomly selected controls from a population study the data from 10 cases and 100 age-matched control subjects were analyzed blind. The code was disclosed after completion of the analysis. We found that none of the markers served to distinguish the SIDS cases from the controls in the population at large. This observation may indicate important physiological differences between infants destined to die in the referred high risk population and infants who die of SIDS at large. The possible reasons for our inability to identify the group of SIDS in the general population, as compared to the group of deaths in the referred high risk group are: (1) different disease processes in the two groups, (2) difference responses to the same disease process in the two groups, (3) a response reflecting the psychosocial setting of the referred high risk population, (4) methodological differences between this and previous studies. We conclude that these markers are not of value in screening the population at large.

Heart Rate↗
PubMed1985

Receptive-field-like functions inferred from large-area psychophysical measurements.

By means of quasi-sinusoidal, circular stimulus patterns, frequency modulated to correct for the radial component of retinal inhomogeneity, we attempt to make all eccentricities within a 16-deg field contribute equally to the threshold response. Wide-field contrast-sensitivity data obtained with these frequency-modulated stimuli are modeled using a canonical form of local contrast sensitivity function (CSF), scaled linearly with eccentricity. Calculating Fourier transforms of the constant-velocity, local CSF, we obtain line-spread and point-spread functions that can also be interpreted as receptive-field responses at various eccentricities. These results are compared to other data on local spatial processing in the retina.

Fovea Centralis↗
PubMed1985

Visual processing of moving stimuli.

This review covers a period bracketed by two OSA Symposia--"Vision under Stabilized Image Conditions," held in San Francisco in 1978, and "Motion and Vision in Man and Machine," held in New Orleans in 1983--during which image stabilization came of age as a standard technique of visual psychophysics. It seems clear that the first spatiotemporal signal-processing step in the visual system depends on image motion; e.g., a constant velocity effectively provides the mathematical convolution of stimulus patterns with retinal receptive fields. Thus the motion of the stimulus pattern at the retina is an important experimental variable over which we have only recently gained full control. We can now replace the haphazard behavior of the subject's natural eye movements by simpler forms of motion that are known and controlled by the experimenter. Results obtained in our laboratory with such stabilized fixation control include threshold measurements for moving lines and gratings, comparison of contrast sensitivities with natural and artificial eye movements, effects of orientation on moving-grating thresholds, models of the stabilized spatiotemporal threshold surface, and effects of retinal inhomogeneity on selectivity for spatial frequency and velocity. Other experiments, too numerous to include here, have also used these techniques.

Eye Movements↗
PubMed1985

Retinal inhomogeneity. III. Circular-retina theory.

By introducing a local contrast-sensitivity function, defined as the Fourier transform of the local point-spread function, we have constructed a model of retinal inhomogeneity that predicts the contrast sensitivity for circular homogeneous or inhomogeneous sinusoidal targets up to 16 degrees in diameter. This model assumes that (1) contrast sensitivity is mediated by a standard, receptive-field-type filter function (one that fits our data somewhat better than available receptive-field models); (2) retinal inhomogeneity is circularly symmetric; i.e., receptive-field size varies only with eccentricity; (3) this size variation is governed by a linear scaling factor out to at least 8 degrees eccentricity; and (4) the local contrast sensitivities at different parts of the retina combine in accord with a fourth-power probability-summation rule. The parameters of the model were determined by fitting contrast-sensitivity data for a new class of stimulus patterns: locally sinusoidal, circularly symmetric targets with radially varying spatial frequency (but constant amplitude). The model also fits contrast thresholds for circular cosine disks and annuli of various sizes and eccentricities. (Predictions for noncircular patterns require a minor extension.) The results suggest that the uniform, homogeneous sinusoidal patterns used throughout the literature provide surprisingly little information about the form of receptive fields.

Humans↗
PubMed1984

Incidence and significance of primary abnormalities of cardiac rhythm in infants at high risk for sudden infant death syndrome.

The exact relationship between cardiac arrhythmias and sudden infant death syndrome (SIDS) is uncertain. Several reports have implicated both ventricular and supraventricular arrhythmias in isolated cases, but there have been no studies of the incidence or type of arrhythmias that occur in populations at risk for SIDS. Of 1699 infants at high risk for SIDS, 60 (4%) were found to have a primary cardiac arrhythmia (i.e., not associated with disordered respiration or apnea). The incidence of atrial and ventricular premature beats, supraventricular tachycardia, and Wolff-Parkinson-White syndrome was similar to the incidence found in normal infants. Primary bradycardia (defined as a heart rate less than 60 for greater than 10 s not associated with abnormal respiration) was the most common arrhythmia, occurring with a frequency and severity not seen in normal infants. Thirty-two infants experienced periodic bradycardia. In 19 of these latter infants, there were symptoms associated with these bradyarrhythmias that necessitated treatment. Heart rates as low as 20 beats/min were recorded. One infant presented with an episode of ventricular fibrillation and on further evaluation was noted to have recurrent bradyarrhythmias. In no infant was there abnormal prolongation of the QT interval. Primary bradyarrhythmias are seen at an increased incidence in infants at high risk for SIDS and may play a causal role in this syndrome. Most symptomatic infants can be adequately controlled with sympathomimetic or parasympatholytic therapy. Other cardiac arrhythmias occur at a rate similar to that in normal infants and are therefore unlikely to play a major role in SIDS.

Arrhythmias, Cardiac↗
PubMed1984

Retinal inhomogeneity. I. Spatiotemporal contrast sensitivity.

Spatiotemporal sine-wave contrast thresholds were measured at four retinal eccentricities: 0 degrees, 3 degrees, 6 degrees, and 12 degrees. Threshold functions of spatial frequency were determined for each eccentricity at two selected temporal frequencies, and functions of temporal frequency at two selected spatial frequencies. Fixation was controlled by stabilizing the retinal image. The stimulus patterns were circular cosine targets confined to annular zones, so that stimulation occurred in all meridians simultaneously. In spite of these unusual conditions, our results were in good agreement with unstabilized, single-meridian data from other laboratories. The spatial-frequency functions obtained at both high and low flicker rates scaled with eccentricity in the same way. For the bandpass functions obtained at 0.5 Hz, the reciprocal of the peak spatial frequency varied linearly with eccentricity. Measured with spatial patterns chosen in accord with this scaling relation, both sets of temporal-frequency functions were essentially independent of eccentricity. Threshold functions at constant velocity were also consistent with the same scaling relation.

Fixation, Ocular↗
PubMed1984

Retinal inhomogeneity. II. Spatial summation.

Effects of spatial probability summation were measured with concentric cosine forming a set of contiguous annular zones having mean eccentricities of 0 degrees, 2.8 degrees, and 6.1 degrees. To detect these small effects reliably we measured contrast thresholds for all eccentricities at one spatial frequency in each experimental session by an interleaved-staircase method. Sharp edges were eliminated by truncating each zone at a zero crossing of the pattern, and fixation was controlled by stabilizing the retinal image. Under these conditions, each local region of the retina contributes to the sensitivity of larger regions by a standard, fourth-power summation rule, regardless of the number or contiguity of the component regions involved. This was experimentally confirmed with three nested zones for spatial frequencies from 0.5 to 5 cycles/degree. Together with the results of Part I of this series [D. H. Kelly, J. Opt. Soc. Am. A 1, 107 (1984)], the summation rule predicts that, over a large range, target size should have no effect on contrast sensitivity at high spatial frequencies, and this was also confirmed. Similar predictions were extrapolated to other contrast-sensitivity data for which empirical tests are not available.

Fixation, Ocular↗
PubMed1984

Role of local adaptation in the fading of stabilized images.

We provide evidence that the fading of stabilized images and the formation of negative afterimages result from the same local adaptive process. We measure thresholds for stabilized, static, sine-wave gratings and for stabilized flickering sine-wave gratings. We then measure the contrasts of the negative afterimages formed by the threshold-contrast stabilized, static stimuli. (The threshold-contrast flickering gratings produce no visible afterimages.) We find that the difference between the thresholds for stabilized, static gratings and the thresholds for slowly flickering gratings is equal to the contrasts of the afterimages produced by the stabilized, static gratings. We conclude that the fading of these stabilized gratings can be accounted for completely by local adaptation (the process underlying the formation of negative afterimages.

Adaptation, Ocular↗
PubMed1984

Lingual vibrotactile perception: lingual pressure effects on neuro-sensory response.

A calibrated pressure transducer, embedded within a lower tongue clamp disk, enabled the application of specific tongue pressures during lingual threshold measurement. Thresholds were obtained for five tongue pressures (2, 5, 8, 11, and 14 PSIA ) at three frequencies (125, 250, and 500 Hz). Thresholds varied as a function of tongue pressure. As pressure increased from 2 to 8 PSIA thresholds decreased. As pressure increased above 8 PSIA thresholds increased. Tongue pressure did not influence frequency function.

Adult↗
PubMed1984

Critical problems in spatial vision.

In recent years the study of spatial vision seems to have come almost full circle. Localized stimuli (such as lines, bars, and edges) were abandoned in favor of textured patterns (such as sinusoidal gratings), a trend that was accelerated by the discovery that gratings of sufficiently different spatial frequencies or orientations (stimuli localized in the Fourier domain) were detected independently. This led to various attempts to model form vision in terms of spatial frequency analysis. More recently there has been a shift toward models that include, once again, the local aspects of spatial processing; this trend is more consistent with both retinal and cortical physiology. (Still surviving is the notion of a complete set of orthonormal basis functions, but not sinusoidal ones.) Other important developments include attempts to model spatiotemporal interaction, and the discovery that spatial processing takes on an entirely different character in the absence of any temporal variation (i.e., when the retinal image is stabilized). We attempt to trace these developments in terms of a selected group of representative studies, which we examine in some depth.

Biomedical Engineering↗
PubMed1984

Apnea of infancy and subsequent neurologic, cognitive, and behavioral status.

A pilot study investigated the neurologic, cognitive, and behavioral consequences of nonfatal infancy apnea. Fifteen formerly apneic, monitored children were compared with age-similar siblings and with age-sex matched playmates. Significant impairment in gross motor development and mild cognitive deficiencies were observed when those who had had apnea were compared with their siblings but not when contrasted with their playmates. Lack of difference between those who had had apnea and playmates might have been due to a selection bias involving assortive friendships. The frequency and the severity of apneic episodes were associated but neither one showed a clear gradient of risk for poor outcome in the areas under study, indicating the possibility that apnea may have a threshold effect on subsequent development.

Apnea↗
PubMed1983

Spatiotemporal variation of chromatic and achromatic contrast thresholds.

Moving the retinal image of a sinusoidal grating at a constant velocity (compensated for eye movements) provides controlled spatial and temporal frequencies at every point in the stimulus field. Using this controlled-velocity technique, we have measured the detection threshold for isoluminance, red/green gratings as a function of their spatial and temporal frequencies. The chromatic contrast-threshold surface obtained in this way is analogous to the achromatic contrast-threshold surface measured previously, but the results are quite different. For very low temporal frequencies (below 0.2 Hz), the chromatic sensitivity decreases steadily with decreasing temporal frequency. Below 0.01 Hz, chromatic patterns disappear completely even at maximum contrast (although achromatic or homochromatic patterns do not). In the region above 0.2 Hz, both achromatic and chromatic thresholds can be explained by the same receptive-field-like model. When the center and the surround components of this model are additively combined, they form the chromatic threshold surface; when the sign of either component is reversed, they form the achromatic one.

Color Perception↗