Quantitative endoscopy: initial accuracy measurements.

The geometric optics of an endoscope can be used to determine the absolute size of an object in an endoscopic field without knowing the actual distance from the object. This study explores the accuracy of a technique that estimates absolute object size from endoscopic images. Quantitative endoscopy involves calibrating a rigid endoscope to produce size estimates from 2 images taken with a known traveled distance between the images. The heights of 12 samples, ranging in size from 0.78 to 11.80 mm, were estimated with this calibrated endoscope. Backup distances of 5 mm and 10 mm were used for comparison. The mean percent error for all estimated measurements when compared with the actual object sizes was 1.12%. The mean errors for 5-mm and 10-mm backup distances were 0.76% and 1.65%, respectively. The mean errors for objects <2 mm and > or =2 mm were 0.94% and 1.18%, respectively. Quantitative endoscopy estimates endoscopic image size to within 5% of the actual object size. This method remains promising for quantitatively evaluating object size from endoscopic images. It does not require knowledge of the absolute distance of the endoscope from the object, rather, only the distance traveled by the endoscope between images.

Slow weight gain is associated with increased periodic breathing in healthy infants.

To investigate the hypothesis that weight gain can influence periodic breathing in healthy infants, we prospectively studied, by nocturnal pneumogram technique, respiration and heart rate in 99 full-term infants during the first month of life. Eighty-eight infants had a repeat study at about 2 months of age. Pneumograms were analyzed visually for percent periodic breathing (%PB), and by computer for mean respiratory rate and mean heart rate. We found a median %PB of 0.9 initially and of 0.3 at about 2 months of age. The 95th percentile was 13.5 at 2 weeks and 7.3 at 2 months, higher than previously reported. Between the two ages tested, %PB was inversely correlated with weight gain (P < 0.001, < 0.03, respectively). Infants with greater weight gain had a greater fall in %PB (P < 0.03). We conclude that in the first 2 months of life, slow weight gain is associated with increased periodic breathing.

Cardiorespiratory recordings from infants dying suddenly and unexpectedly at home.

OBJECTIVE: Little is known about the mechanism of death during sudden infant death. To study the mechanism, we obtained data on six infants who died while on a memory-equipped cardiorespiratory monitor. METHODS: Waveforms of respiration and heart rate trend were available for five infants; an alarm log only was available for the sixth. These printouts were reviewed with attention to mechanism and time to death. RESULTS: All infants were born prematurely; autopsies reported the cause of death as sudden infant death syndrome in three cases and bronchopulmonary dysplasia in the others. Bradycardia, which played a more prominent role than central apnea, was preceded by tachycardia in two deaths. Resuscitation occurred within 1 minute in four cases; no response to alarms occurred in the other two cases, apparently because the parents were desensitized by prior meaningless alarms. Five patients died within 20 minutes, whereas one death due to sudden infant death syndrome was prolonged. CONCLUSION: Bradycardia is an important feature in all six of these infant deaths. Although its etiology is unknown, hypoxemia or obstructive apnea may precede bradycardia. Home monitors equipped to detect these possible antecedents will yield further insight into sudden infant death.

Measurements of chromatic and achromatic afterimages.

Several types of measurement were made of the negative afterimages formed by viewing chromatic and achromatic sine-wave conditioning gratings that were stabilized on the retina. We varied the spatial frequency, contrast, and duration of the conditioning stimulus and the interval between its offset and the afterimage measurement. Different methods of measuring afterimage contrast were also compared. We conclude that (1) an isoluminant chromatic stimulus creates an isoluminant chromatic afterimage; (2) afterimage contrast is linearly related to conditioning contrast; (3) chromatic and achromatic afterimages have similar low-pass spatial-frequency characteristics; (4) both types of afterimage build up and decay exponentially, with a (1/e) time constant of 4-8 s; (5) most important, both chromatic and achromatic afterimages raise the threshold for a chromatic flashed grating, but neither affects the threshold for an achromatic flashed grating; (6) we can explain these results by postulating that negative afterimages are subserved only by the sustained, or parvocellular, pathways.

Apnea and periodic breathing in healthy full-term infants, 12-18 months of age.

Many children older than 12 months of age are now on home monitors. Home pneumograms performed on normal infants have established standards, and have been used to evaluate infants during their first year. However, no standards have been described for infants older than 12 months. We, therefore, recorded the standard pneumogram on 88 full-term healthy infants who were 12-18 months of age. We analyzed the recordings for average respiratory and heart rates, apnea (greater than or equal to 6 seconds) density, longest apnea, periodic breathing, and bradycardia for 12 hours. We compared the values in males vs. females and in infants 12-14.9 months vs. 15.0-18.0 months of age. Since there was no difference in any parameter measured in any group, we combined the values to determine the normal values for this population.

Moving gratings and microsaccades.

This paper reports an extended study of anomalous (enhanced) sensitivity to moving gratings in the range of 1-10 cycles per degree, at high temporal frequencies (greater than 20 Hz), i.e., in the high-frequency corner of the spatiotemporal threshold surface. The effect is very robust. All subjects (n = 5) show the effect with moving or flickering gratings and with or without stabilization of the retinal image. After eliminating various types of potential artifacts, the phenomenon was finally attributed to a form of transient destabilization associated with microsaccadic eye movements. In the unstabilized condition, microsaccades and voluntary saccades both interact with the grating motion to produce visible flashes. With image stabilization, the (1-msec) delay of the Purkinje-image eyetracker interacts with these saccades in a way that increases the visibility of the associated flashes. The form of the threshold data suggests that the size of the saccades may vary with the spatial period of the moving grating.

Prospective pneumogram recordings in preterm infants with and without clinical apnea and bradycardia.

Recordings of breathing movements and heart rate (pneumograms) were obtained prospectively in 89 preterm infants at 0-28 days of age to determine if those who develop apnea and/or bradycardia with cyanosis (Group 1) differ from those who do not (Group 2). The 148 pneumograms were blindly analyzed for periodic breathing, bradycardia, longest apnea, and quiet time. Pneumograms were compared between groups at weekly intervals during the first 4 weeks. Significant differences were found among infants who had pneumograms recorded during the 1st week of life. Although mean gestational age and mean postconceptional age at recording were similar, birthweight and weight at recording were significantly lower in Group 1 infants. Total time spent in periodic breathing and the longest episode of periodic breathing were significantly greater in Group 1 infants. Logistic regression analysis revealed significant independent relationships between birthweight and periodic breathing at less than or equal to 7 days of age and the occurrence of symptomatic apnea and/or bradycardia. It is concluded that preterm infants who develop apnea and/or bradycardia with cyanosis have a lower mean birthweight and mean weight at recording at less than or equal to 7 days of age than similar asymptomatic preterm infants. Periodic breathing at less than or equal to 7 days of age is associated with the occurrence of clinical symptoms of apnea and/or bradycardia. Normal pneumogram values for groups of 6-21 asymptomatic preterm infants are provided for the first 4 weeks of life.

Does lithium carbonate affect the ion transport abnormality in cystic fibrosis?

Lithium is known to affect several aspects of cellular regulation which may be related to ion channel function in epithelial cells. To determine whether the ion transport abnormality in cystic fibrosis (CF) is affected by lithium with resultant changes in clinical status, 36 CF patients, 12-37 years old, were enrolled in a 14 week, double-blind, placebo-controlled trial. Eighteen patients were randomly assigned to receive lithium carbonate for 10 weeks. At the end of therapy their average serum lithium concentration was 0.56 +/- 0.06 mmol (SEM) per liter. Their sweat chloride concentration fell from 92.1 +/- 4.8 mmol per liter to 87.4 +/- 4.0 mmol per liter after 10 weeks of therapy (P = 0.07) and rose to 94.4 +/- 3.5 mmol per liter 4 weeks after end of therapy (P less than 0.001 compared to results at end of therapy). Their forced vital capacity (FVC) fell from 72 +/- 5.3% of predicted to 66 +/- 5.1% of predicted after 4 weeks of therapy (P less than 0.01), and their forced expiratory volume in one second (FEV1) fell from 56 +/- 5.5% of predicted to 51 +/- 5.5% of predicted after 4 weeks of therapy (P less than 0.01). In a non-blind assessment, performed 19 weeks after the end of therapy, their FVC and FEV1 had risen and were not significantly different from baseline. Sweat chloride, FVC, and FEV1 remained unchanged in the placebo group throughout the period of study.(ABSTRACT TRUNCATED AT 250 WORDS)

Opponent-color receptive-field profiles determined from large-area psychophysical measurements.

By compensating for retinal inhomogeneity and using the opponent-color characteristics of retinal receptive fields, some of the problems associated with previous methods of inferring local spatial-processing properties from sine-wave contrast-sensitivity measurements can be eliminated. Forced-choice contrast detection thresholds were obtained for circular frequency-modulated patterns, over a wide range of spatial and temporal frequencies, with three subjects. Eye-movement artifacts were minimized by image stabilization. The luminance contrast sensitivity (L) for a given isochromatic stimulus and the chromatic contrast sensitivity (C) for the corresponding isoluminance stimulus were measured in rapid succession, under identical conditions, using red and green components with accurately known spectral distributions. Receptive-field center (E) and surround (I) frequency functions were then calculated from the L and C data by solving two linear equations in two unknowns, with coefficients given by the spectral characteristics of the stimuli and the long-wave and middle-wave cone pigments. The results depend on the small differences of large numbers inherent in opponent-color responses, so they are somewhat noisy, but the forms of these (E-I) spatial profiles are similar to those obtained by other methods.

Pneumogram recordings in infants resuscitated for apnea of infancy.

Infants who sustained a spell of apnea of infancy during which they were resuscitated have been shown to be at increased risk for sudden infant death syndrome. To determine the value of the pneumogram as a predictor of outcome in this population, the first pneumogram obtained of 51 such infants was analyzed. The infants were grouped on the basis of subsequent outcome during a course of monitoring: group 1--infants who died during a subsequent event; group 2--infants who received resuscitation or vigorous stimulation to terminate a subsequent spell; group 3--infants who survived and did not have a significant subsequent episode. The results for these infants were compared with those of a control group matched for age and sex. A detailed, blinded computer analysis revealed no significant difference in the results of the pneumogram analysis between the three groups. It did not identify the infants in whom apneic spells necessitating resuscitation subsequently developed or those who died. However, when compared with the control group, infants with apnea of infancy had significantly higher mean respiratory rates, heart rates, and tachycardia indexes. It is concluded that, although the first pneumogram does not predict the risk of an adverse outcome in a population of infants with severe apnea of infancy, it does reveal subtle cardiorespiratory differences between study and control infants.

Transplacentally acquired caffeine and the occurrence of apnea, bradycardia, and periodic breathing in preterm infants: preliminary communication.

Cord blood caffeine concentrations were measured by high-pressure liquid chromatography in 79 preterm infants. Eleven infants (14%) had detectable caffeine concentrations ranging from 1.1 to 3.7 micrograms/mL (means +/- SD = 2.5 +/- 0.8), and 68 infants had no measurable caffeine. Seven infants with detectable caffeine (group 1) had impedance pneumograms recorded before 2 weeks of age. Each infant in group 1 was matched with two infants without detectable caffeine by birthweight, gestational age, and chronologic age at pneumogram recording to yield a control group (group 2) of 14 infants. Comparison of the groups using quantitative measures of apnea, bradycardia, and periodic breathing obtained from pneumogram analysis and the incidence of monitor alarms on bedside nursing records showed no significant differences. Thus, caffeine was present infrequently and at low concentrations at birth in 79 preterm infants. The amount of apnea, bradycardia, and periodic breathing experienced before 2 weeks of age in 7 preterm infants with detectable cord blood caffeine was not different from that in 14 similar infants without caffeine. Future studies are planned to examine the relationship between postnatal changes in transplacentally acquired methylxanthine concentrations and quantitative measures of apnea, bradycardia, and periodic breathing in a larger number of preterm infants without cardiorespiratory disease.

Retinal inhomogeneity and motion in depth.

The relation between retinal inhomogeneity and motion in depth was explored by means of a circularly symmetric but nonuniform stimulus pattern, designed to fit the inhomogeneity of the subject's retina. Radial motion of the quasi-sinusoidal rings of this target evokes an illusion of motion in depth: forward if the frontal-plane motion is centrifugal, backward if it is centripetal. Like the Plateau spiral, this stimulus produces strong motion aftereffects (MAE's) over a wide range of spatial and temporal frequencies. Over a much more limited frequency range, the forward MAE is significantly more adaptable than the backward MAE. This forward effect was found to occur only at very low spatial frequencies (approximately 0.05-0.5 cycles/deg at the fovea) and velocities near 20 deg/sec. The effect was destroyed by decentering the target or by varying its homogeneity so that it no longer matched the retina. These results suggest a hard-wired collision-avoidance system.

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.

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.

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.