Mathematical model of chest wall mechanics: A phenomenological approach

A mathematical model of chest wall mechanics, based on a phenomenological approach to force balances, provides a quantitative framework for analyzing many types of chest wall movements by using orthogonal displacement coordinates. The moveable components of the ventilatory system include the rib cage, diaphragm, and abdomen. A distinction is made between the lung-apposed and diaphragm-apposed actions on the rib cage. The model equations are derived from “pressure” balances and geometrical relations of the compartments; the stress-displacement relations are hyperbolic. With this model we simulated stiff and flaccid chest wall behavior under normal and constrained conditions associated with abdominal compression, a Mueller maneuver, and a diaphragmatic isometric inspiration. We also examined situations that produce paradoxical as well as orthodox inspiratory movements. The results of these simulations were quantitatively consistent with available data from the literature. A phenomenon predicted by the stiff-wall model during quasi-static inspiration is that the rib cage displacement is negligible near residual volume, but then increases dramatically with lung volume. Since this mathematical model has a sound physical basis and is more comprehensive than previous models, it can be used to predict and analyze the behavior of the chest wall under a wide variety of circumstances.     

Treatment Outcomes of West Syndrome in Infants With Down Syndrome

West syndrome constitutes the most frequent of all seizure types in infants with Down syndrome. We retrospectively reviewed records of 12 infants with Down syndrome and West syndrome, accounting for 5% of 239 infants with West syndrome from a comprehensive epilepsy database during a 17-year period. All demonstrated classic hypsarrhythmia on video electroencephalograms. One had clinically responded to clonazepam, and one was not treated because the parents refused any treatment. Seven of 10 infants demonstrated a complete response to high-dose natural adrenocorticotrophic hormone. Four (57%) of these seven infants relapsed. Relapses occurred as long as 2 years after cessation of the initial presentation of infantile spasms. At most recent follow-up (median age, 5 years), 8/12 (67%) were seizure-free, and seven were off any medications. Two of three nonresponders manifested intractable epilepsy and profound mental retardation. Developmentally, 6/8 who could be assessed met criteria for autistic spectrum disorder. Close follow-up is necessary even after successful initial treatment, because relapses are frequent and can occur as long as 2 years later.     

Design and phenomenology of the FEBSTAT study

Purpose: Febrile status epilepticus (FSE) has been associated with hippocampal injury and subsequent hippocampal sclerosis (HS) and temporal lobe epilepsy. The FEBSTAT study was designed to prospectively examine the association between prolonged febrile seizures and development of HS and associated temporal lobe epilepsy, one of the most controversial issues in epilepsy. We report on the baseline phenomenology of the final cohorts as well as detailed aims and methodology. Methods: The “Consequences of Prolonged Febrile Seizures in Childhood” (FEBSTAT) study is a prospective, multicenter study. Enrolled are children, aged 1 month to 6 years of age, presenting with a febrile seizure lasting 30 min or longer based on ambulance, emergency department, and hospital records, and parental interview. At baseline, procedures included a magnetic resonance imaging (MRI) study and electroencephalography (EEG) recording done within 72 h of FSE, and a detailed history and neurologic examination. Baseline development and behavior are assessed at 1 month. The baseline assessment is repeated, with age‐appropriate developmental testing at 1 and 5 years after enrollment as well as at the development of epilepsy and 1 year after that. Telephone calls every 3 months document additional seizures. Two other groups of children are included: a “control” group consisting of children with a first febrile seizure ascertained at Columbia University and with almost identical baseline and 1‐year follow‐up examinations and a pilot cohort of FSE from Duke University. Key Findings: The FEBSTAT cohort consists of 199 children with a median age at baseline of 16.0 months (interquartile range [IQR] 12.0–24.0) and a median duration of FSE of 70.0 min (IQR 47.0–110.0). Seizures were continuous in 57.3% and behaviorally intermittent (without recovery in between) in 31.2%; most were partial (2.0%) or secondary generalized (65.8%), and almost all (98.0%) culminated in a generalized tonic–clonic seizure. Of the 199 children, 86.4% had normal development and 20% had prior febrile seizures. In one third of cases, FSE was unrecognized in the emergency department. The Duke existing cohort consists of 23 children with a median age of FSE onset of 18.0 months (IQR 14.0–28.0) and median duration of FSE of 90.0 min (IQR 50.0–170.0). The Columbia control cohort consists of 159 children with a first febrile seizure who received almost the same workup as the FEBSTAT cohort at baseline and at 1 year. They were followed by telephone every 4 months for a median of 42 months. Among the control cohort, 64.2% had a first simple FS, 26.4% had a first complex FS that was not FSE, and 9.4% had FSE. Among the 15 with FSE, the median age at onset was 14.0 months (IQR 12.0–20.0) and the median duration of FSE was 43.0 min (IQR 35.0–75.0). Significance: The FEBSTAT study presents an opportunity to prospectively study the relationship between FSE and acute hippocampal damage, the development of mesial temporal sclerosis, epilepsy (particularly temporal lobe epilepsy), and impaired hippocampal function in a large cohort. It is hoped that this study may illuminate a major mystery in clinical epilepsy today, and permit the development of interventions designed to prevent the sequelae of FSE.     

Preserved local but disrupted contextual figure-ground influences in an individual with abnormal function of intermediate visual areas

Visual perception depends not only on local stimulus features but also on their relationship to the surrounding stimulus context, as evident in both local and contextual influences on figure-ground segmentation. Intermediate visual areas may play a role in such contextual influences, as we tested here by examining LG, a rare case of developmental visual agnosia. LG has no evident abnormality of brain structure and functional neuroimaging showed relatively normal V1 function, but his intermediate visual areas (V2/V3) function abnormally. We found that contextual influences on figure-ground organization were selectively disrupted in LG, while local sources of figure-ground influences were preserved. Effects of object knowledge and familiarity on figure-ground organization were also significantly diminished. Our results suggest that the mechanisms mediating contextual and familiarity influences on figure-ground organization are dissociable from those mediating local influences on figure-ground assignment. The disruption of contextual processing in intermediate visual areas may play a role in the substantial object recognition difficulties experienced by LG.     

Implicit integration in a case of integrative visual agnosia

We present a case (SE) with integrative visual agnosia following ischemic stroke affecting the right dorsal and the left ventral pathways of the visual system. Despite his inability to identify global hierarchical letters [Navon, D. (1977). Forest before trees: The precedence of global features in visual perception. Cognitive Psychology, 9, 353-383], and his dense object agnosia, SE showed normal global-to-local interference when responding to local letters in Navon hierarchical stimuli and significant picture-word identity priming in a semantic decision task for words. Since priming was absent if these features were scrambled, it stands to reason that these effects were not due to priming by distinctive features. The contrast between priming effects induced by coherent and scrambled stimuli is consistent with implicit but not explicit integration of features into a unified whole. We went on to show that possible/impossible object decisions were facilitated by words in a word-picture priming task, suggesting that prompts could activate perceptually integrated images in a backward fashion. We conclude that the absence of SE's ability to identify visual objects except through tedious serial construction reflects a deficit in accessing an integrated visual representation through bottom-up visual processing alone. However, top-down generated images can help activate these visual representations through semantic links.     

Scaling laws of human interaction activity

Even though people in our contemporary technological society are depending on communication, our understanding of the underlying laws of human communicational behavior continues to be poorly understood. Here we investigate the communication patterns in 2 social Internet communities in search of statistical laws in human interaction activity. This research reveals that human communication networks dynamically follow scaling laws that may also explain the observed trends in economic growth. Specifically, we identify a generalized version of Gibrat''s law of social activity expressed as a scaling law between the fluctuations in the number of messages sent by members and their level of activity. Gibrat''s law has been essential in understanding economic growth patterns, yet without an underlying general principle for its origin. We attribute this scaling law to long-term correlation patterns in human activity, which surprisingly span from days to the entire period of the available data of more than 1 year. Further, we provide a mathematical framework that relates the generalized version of Gibrat''s law to the long-term correlated dynamics, which suggests that the same underlying mechanism could be the source of Gibrat''s law in economics, ranging from large firms, research and development expenditures, gross domestic product of countries, to city population growth. These findings are also of importance for designing communication networks and for the understanding of the dynamics of social systems in which communication plays a role, such as economic markets and political systems.