Ventilatory chemosensitivity in parents of infants with sudden infant death syndrome

Alterations of functional connectivities associated with autism spectrum disorder symptom severity: a multi-site study using multivariate pattern analysis

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder. The estimation of ASD severity is very important in clinical practice due to providing a more elaborate diagnosis. Although several studies have revealed some resting-state functional connectivities (RSFCs) that are related to the ASD severity, they have all been based on small-sample data and local RSFCs. The aim of the present study is to adopt multivariate pattern analysis to investigate a subset of connectivities among whole-brain RSFCs that are more contributive to ASD severity estimation based on large-sample data. Regression estimation shows a Pearson correlation value of 0.5 between the estimated and observed severity, with a mean absolute error of 1.41. The results provide obvious evidence that some RSFCs undergo notable alterations with the severity of ASD. More importantly, these selected RSFCs have an abnormality in the connection modes of the inter-network and intra-network connections. In addition, these selected abnormal RSFCs are mainly associated with the sensorimotor network, the default mode network, and inter-hemispheric connectivities, while exhibiting significant left hemisphere lateralization. Overall, this study indicates that some RSFCs suffer from abnormal alterations in patients with ASD, providing additional evidence of large-scale functional network alterations in ASD.

Rethinking Measures of Functional Connectivity via Feature Extraction

Functional magnetic resonance imaging (fMRI)-based functional connectivity (FC) commonly characterizes the functional connections in the brain. Conventional quantification of FC by Pearson's correlation captures linear, time-domain dependencies among blood-oxygen-level-dependent (BOLD) signals. We examined measures to quantify FC by investigating: (i) Is Pearson's correlation sufficient to characterize FC? (ii) Can alternative measures better quantify FC? (iii) What are the implications of using alternative FC measures? FMRI analysis in healthy adult population suggested that: (i) Pearson's correlation cannot comprehensively capture BOLD inter-dependencies. (ii) Eight alternative FC measures were similarly consistent between task and resting-state fMRI, improved age-based classification and provided better association with behavioral outcomes. (iii) Formulated hypotheses were: first, in lieu of Pearson’s correlation, an augmented, composite and multi-metric definition of FC is more appropriate; second, canonical large-scale brain networks may depend on the chosen FC measure. A thorough notion of FC promises better understanding of variations within a given population.

Common brain disorders are associated with heritable patterns of apparent aging of the brain

Common risk factors for psychiatric and other brain disorders are likely to converge on biological pathways influencing the development and maintenance of brain structure and function across life. Using structural MRI data from 45,615 individuals aged 3-96 years, we demonstrate distinct patterns of apparent brain aging in several brain disorders and reveal genetic pleiotropy between apparent brain aging in healthy individuals and common brain disorders.

Oxygen sensing: applications in humans

Our concepts of oxygen sensing have been transformed over the years. We now appreciate that oxygen sensing is not a unique property limited to “chemoreceptors” but is a common property of tissues and that responses to changes in oxygen levels are not static but can change over time. Respiratory responses initiated at the carotid body are modified by the excitatory and depressant effects of hypoxia at the brain and on the pathways connecting the carotid body to the brain. Equally important is that we are beginning to use our understanding of the cellular and molecular pathways triggered by hypoxia and hyperoxia to identify therapeutic targets to treat diseases such as cancer. We also have a better understanding of the complexities of the human respiratory responses to hypoxia; however, major deficiencies remain in our ability to alter or even measure human ventilatory responses to oxygen deficiency.

Neurotransmitters in central respiratory control

A diverse group of processes are involved in central control of ventilation. Both fast acting neurotransmitters and slower acting neuromodulators are involved in the central respiratory drive. This review deals with fast acting neurotransmitters that are essential centrally in the ventilatory response to H(+)/CO(2) and to acute hypoxia. Data are reviewed to show that the central response to H(+)/CO(2) is primarily at sites in the medulla, the most prominent being the ventral medullary surface (VMS), and that acetylcholine is the key neurotransmitter in this process. Genetic abnormalities in the cholinergic system lead to states of hypoventilation in man and that knock out mice for genes responsible for neural crest development have none or diminished CO(2) ventilatory response. In the acute ventilatory response to hypoxia the afferent impulses from the carotid body reach the nucleus tractus solitarius (NTS) releasing glutamate which stimulates ventilation. Glutamate release also occurs in the VMS. Hypoxia is also associated with release of GABA in the mid-brain and a biphasic change in concentration of another inhibitory amino acid, taurine. Collectively changes in these amino acids can account for the ventilatory output in response to acute hypoxia. Future studies should provide more data on molecular and genetic basis of central respiratory drive and the role of neurotransmitter in this essential function.

The ventilatory response to carbon dioxide in high risk infants

PURPOSE

To examine the ventilatory response to inspired carbon dioxide in infants considered to be at risk for sudden infant death syndrome or apnea.

DESIGN

Clinical data measurement.

SETTING

Infant apnea evaluation program of a university division of neonatology.

PATIENTS

Fifty nine infants were full term characterized by the following diagnoses; siblings of infants who had died from sudden infant death syndrome (SIDS) (n = 7), apparent life threatening event (ALTE) (n = 24), apnea/cyanosis in the newborn nursery (n = 21), and controls. Sixty-nine infants were preterm and consisted of patients suffering from idiopathic apnea (n = 61), and bronchopulmonary dysplasia (n = 8).

MEASUREMENTS

The ventilatory response to carbon dioxide was measured with a computerized waveform analyzer.

MAIN RESULTS

Among full term infants no significant differences in the ventilatory slope in response to CO2 was seen. The range of mean slope was 19.4 +/- 7.6 in siblings of SIDS and 36 +/- 17 in control infants. Greater number of sibling of SIDS had slopes less than 20 ml/kg/min/mmHg in comparison to control infants. Sibling of SIDS had less increase in minute ventilation and inspiratory flow in response to CO2 administration in comparison to control infants. Preterm infants had similar slopes with a mean of 33 ml/kg/min/mmHg in infants with idiopathic apnea and 28 ml/kg/min/mmHg in infants with bronchopulmonary dysplasia.

CONCLUSIONS

The large intragroup variability in the ventilatory response to inspired CO2, confirming previously reported data, comprises the benefit of this test. Thus, ventilatory response to CO2 administration is not useful in unselected patients at risk of SIDS or apnea.

Hypercapnic and hypoxic ventilatory and cardiac responses in school-aged siblings of sudden infant death syndrome victims

Siblings of sudden infant death syndrome (SIDS) victims have been shown to have abnormal ventilatory patterns and altered responses to respiratory stimuli during infancy. To evaluate whether these abnormalities persist, we studied ventilatory responses in 20 older SIDS siblings (9.8 +/- 0.9 (mean +/- SEM) years of age) and 20 control subjects (10.2 +/- 0.9 years of age). To evaluate hypercapnic ventilatory responses, we had subjects rebreathe 5% carbon dioxide and 95% oxygen until end-tidal carbon dioxide tension reached 65 mm Hg. Instantaneous minute ventilation, mean inspiratory flow, and respiratory rate were calculated breath by breath. Hypercapnic responses did not differ between SIDS siblings (2.08 +/- 0.14 L/min per mm Hg) and control subjects (1.90 +/- 0.10 L/min per mm Hg; not significant). To assess hypoxic ventilatory responses, we asked subjects to rebreathe 13% oxygen and 7% carbon dioxide, with the balance nitrogen, at mixed-venous end-tidal carbon dioxide tension, until arterial oxygen saturation by pulse oximetry fell to 75%. No differences in hypoxic ventilatory responses were found between the SIDS siblings (-1.39 +/- 0.15 L/min/% saturation) and the control subjects (-1.22 +/- 0.17 L/min/% saturation; not significant). The mean inspiratory flow, tidal volume, respiratory rate, and heart rate responses to hypercapnia and hypoxia were also similar in the two groups. We conclude that there is no difference in hypercapnic and hypoxic ventilatory and cardiac responses, as assessed by rebreathing techniques, between school-aged SIDS siblings and control subjects. We speculate that in SIDS siblings the control of breathing is immature during infancy and that they achieve maturity of control and resolution of breathing abnormalities with time.

Case-control studies in pediatric epidemiology: parent surrogates and potential pitfalls of inaccurate and selective recall

The case-control study is quite popular as a study design for exploring associations between risk factors and disease in pediatric epidemiology. Since data concerning exposures to the child are often collected through interviews with parents or other surrogates, researchers should be aware of the opportunities for bias due to inaccurate or incomplete recall. Methods which exist for the control of this problem are presented. These include: the selection of control groups with childhood conditions of similar etiologic uncertainty as the disease being studied; collecting exposure data from both parents; collection of data from children where possible; diligent interviewer training; reviewing clinical records; and use of validity scales. Strengths and weaknesses of these strategies are discussed.