Ronald M. Harper, Ph.D. - US grants

Our hypothesis is that sleep influences on breathing result partially from regional activity changes in ventral medullary surface (VMS) areas which participate in chemoreceptor afferent processing, alter blood pressure influences on breathing, and change facilitatory influences on other respiratory regions. The regional alterations in VMS activity may result from changes in descending supramedullary influences, which are enhanced or reduced by different sleep states. We will test these possibilities in intact animals by 1) relating respiratory changes during different sleep- waking states to "spontaneous" activity on VMS sites and in the paraventricular hypothalamus, which projects to the medullary surface; 2) applying resistive breathing, hypercapnic, hypoxic, peripheral chemoreceptor stimulation by cyanide, and blood pressure challenges during states, and mapping resulting VMS surface and hypothalamic activity while charting respiratory and cardiovascular responses; and 3) electrically stimulating hypothalamic regions during different states, and examining resultant influences on the VMS and on respiratory musculature and cardiovasculature activity. Microelectrodes and optical imaging probes will be placed in the paraventricular hypothalamus and on VMS areas that have a demonstrated potential to modify respiration or blood pressure, and thus may mediate state-related respiratory and cardiovascular effects. Single cell discharge, together with images of scattered 660 and 415 nm light (to measure activity by membrane movement and perfusion) will be collected during baseline and challenges within each sleep and waking state. Correlations of overall and regional changes in scattered light to upper airway and diaphragmatic respiratory muscle and cardiovascular patterns will be calculated using analog cross correlation, frequency- domain and event-related potential measures for optical recordings, and point-process techniques for cell discharge.

Check all data tapes furnished by the Government for conditions of the tapes, completeness of data, and accuracy of specifications. Data tapes will be received from the completed contract with Boston University; data tapes from the SIDS Project Institute, London, England, will be used for the performance of this project.

The objective is to examine the mechanisms by which rostral brain areas affect respiratory control during sleep in the developing animal so that mechanisms of respiratory failure can be understood in victims of the sudden infant death syndrome (SIDS). We suggest that state influences modify descending input from rostral brain regions to specific respiratory areas of the midbrain and medulla, and place the developing organism at risk for obstructive sleep apnea by differentially enhancing diaphragmatic over upper airway action. We further suggest that the extent of influence from rostral areas changes with development. A newly described limbic arousal system that project to the nucleus of the solitary tract, parabrachial pons, and periaqueductal gray may underlie a large component of arousal-mediated upper airway muscle activation, and we plan to examine contributions to respiratory patterns at 3 ages in the kitten. The role of rostral structures in respiratory development will be studied by 1) examining "spontaneous" neuronal activity in particular regions of the ventral forebrain, midbrain, and medulla during sleep and waking, and relating this activity to upper airway nad diaphragmatic patterning, and 2) evoking activity in rostral regions and examining the resultant influence on neuronal activity in respiratory brainstem regions and on respiratory activity. Micro- and microelectrodes will be placed in rostral regions that have a demonstrated effect on respiratory patterning in the waking state and subserve functions altered by different states, and thus may be a component of the respiratory stimulus of "wakefulness." Neuronal discharge and slow-wave activity will be recorded in rostral hypothalamic regions implicated in temperature control, hippocampal regions related to motor patterning, and the central nucleus of the amygdala, an area implicated in "affective" arousal. We will record neurons in midbrain projection sites of these regions, the caudal lateral periaqueductal gray (which projects to premotor cells of facial, genioglossal, laryngeal, and abdominal motoneurons), the nucleus parabrachiales, and the Kolliker-Fuse nuclei of the parabrachial pons, as well as in the retroambiguus nucleus of the medulla. Respiratory pattern dependencies will be determined from cross- correlations of cell discharge with aspects of patterning of the diaphragm, a laryngeal abductor ( the cricothyroid), and an upper airway dilator (the posterior cricoarytenoid); regression procedures will determine relationships with aspects of the respiratory cycle and with blood pressure, measured with an implanted catheter. Phase-plane plots will be used to assess nonlinear aspects of respiratory patterning and neuronal discharge. Evoked activity will include warming and cooling of the preoptic region to manipulate temperature "drive" to respiration during each sleep-waking state.

This project will examine the development of physiological measures and sleep states in normal infants and in infants at risk for the sudden infant death syndrome (SIDS). The objective is to find physiological characteristics that differentiate infants who later succumbed from those who survived, and apply these characteristics to a yet-unexamined group at risk for SIDS. Infants who later succumbed to SIDS, and two groups of infants at increased risk of SIDS, siblings of SIDS victims and infants who experienced a life-threatening event, will be compared with age-matched controls using data already collected. The objectives are based on the assumptions 1) that SIDS victims succumb from a failure of mechanisms that normally allow a state transition when the infant is exposed to a life- threatening challenge, and 2) that physiological signs, measured during different states, will provide suggestions of the mechanisms that lead to a failure to respond adequately to challenges. Instantaneous and long term changes in cardiac and respiratory intervals, obtained during each sleep- waking state, will be assessed over the first 6 months of life in normal infants and AIDS-siblings, and in single recordings of infants who experienced a life threatening event or subsequently died of SIDS. The interaction between physiological variables that define sleep states will be assessed using linear time-domain filtering procedures and frequency- domain spectral techniques, together with nonlinear dynamic procedures including phase-plane plots, to determine if development of moment-to- moment activity and interactions between variables are altered in infants at risk. The temporal characteristics of sleep-walking states, including distribution of states across the night, state transition probabilities, periodic organization, and time of night modulation of sleep and waking physiology will be compared between control infants and infants at risk. Relationships of moment-to-moment physiological alterations in activity to the 3-4 h "feeding rhythm" and to time-of-night will be quantified for each group. Assessment of instantaneous variation in cardiac and respiratory intervals will include Poincare procedures and phase-plane plots, together with ANOVA assessment of dispersion at different rates. Multivariate statistical procedures, including stepwise logistic regression and discriminant analysis, will also be used to assess differences among risk groups.

The objective of these studies is to examine central neural control over respiratory and cardiac patterning following acute cocaine administration in freely moving cats. This objective is based on the assumption that cocaine alters activity in limbic system structures which normally have an influence on cardiac and respiratory patterning, and that death from cocaine administration may result from CNS effects on either the upper airway or diaphragmatic musculature, or from central effects on cardiac rhythms, perhaps compounded by peripheral vasoconstriction or hyperthermia induced by cocaine Dose-responses of cocaine will be assessed in relation to patterning of the upper airway musculature and the diaphragm, as well as to blood pressure, heart rate, and arrhythmias. EEG and single-neuron discharge will be examined in limbic and brainstem structures while have been demonstrated to have roles in cardiovascular and respiratory patterning. These structures include the central nucleus of the amygdala, the nucleus parabrachialis medialis of the pons, the nucleus of the solitary tract, and the hypoglossal nucleus. Electromyograhic activity of upper airway muscles including the posterior cricoarytenoid muscles, the major laryngeal dilator, and the thyroarytenoid muscle, a laryngeal constrictor, will be recorded, together with activity of the costal diaphragm. Arterial pressure will be recorded from an indwelling carotid cannula, and the ECG will be acquired from the diaphragmatic EMG leads. Core and anterior hypothalamic temperature will be monitored with miniaturized themprobes. Low, medium, and high doses of cocaine or control saline will be injected IV, and electrophysiological activity will be recorded for 24 hr post delivery. Pontine and amygdala sites will be reversibly blockaded by cooling following cocaine administration to examine the role of these structures in mediating cardiac and respiratory effects. Data will be written on a polygraph, digitized on a PDP 11/73 computer, and analyzed with respect to dose-related 1) inspiratory and expiratory timing alterations in the upper airway and diaphragm, 2) obstruction of the upper airway, 3) apneustic or apneic activity of the diaphragm, 4) alterations in phasic or tonic arterial pressure, 5) cardiac arrhythmias, 6) hyperpyrexia, 7) activated EMG or seizure discharge in limbic and brainstem areas, and 8) respiratory-related single neuron discharge in limbic and brainstem areas.

DESCRIPTION (Adapted from applicant's description): The objective is to identify the brain structures that are deficient in patients afflicted with Congenital Central Hypoventilation Syndrome (CCHS), a disorder characterized by absence of central chemoreception, loss of breathing drive during sleep, and occasional waking hypotonia. Brain areas will be visualized with functional magnetic resonance procedures in normal subjects and CCHS patients during baseline conditions and during challenges of mild hypoxia, hypercapnia, and transient elevation of blood pressure. Blood oxygen level dependent (BOLD) functional magnetic resonance images will be collected from fifteen CCHS patients and 15 age-matched controls during baseline, and 100% 02, 5% CO2 in 95% 02, and 15% 02 ventilatory challenges, and during Valsalva pressor maneuvers, while respiration, heart rate and variability, non-invasive blood pressure, and an index of sympathetic outflow (sweating) are measured. Brain images from baseline conditions will be subtracted from images collected during experimental challenges. The extent of activation and time course of changes in activated brain regions during challenges and recovery will be compared in CCHS patients and controls. The timing of activation of different brain sites will be correlated with physiological changes accompanying the challenges.

The objectives are to determine, using functional magnetic resonance (fMRI) techniques, the location and time course of activation of brain structures activated during obstructive sleep apnea. We hypothesize that particular regions of the orbital frontal cortex, rostral hypothalamus, amygdala, locus coeruleus, midline raphe, and dorsal and ventral pons, which activate to simulated obstructive apnea in waking control subjects, will fail to activate, or respond with reduced activity during sleep apnea events of patients, but will continue to activate during simulated obstructive apnea during sleep in controls. Other regions involved in the suppression of muscle tone may show excessive activation in patients, thereby inducing obstructive apnea. A time series of 30 repetitions of 20 image slices across the entire brain will be obtained in the sagittal plane using blood oxygen level dependent (BOLD) Echo Planar-Imaging pulse sequences, optimal for sensing perfusion alterations, in 20 obstructive apnea patients and 20 age- and sex-matched controls during apnea events of sleep (patients) and during inspiratory loads (20 cM water) applied at the onset of an inspiratory effort during sleep (controls). To partition effects of sleep, both groups will undergo a baseline waking recording, followed by inspiratory loading, and Valsalva pressor challengers, which simulate sensory and autonomic aspects of obstructive apnea. Heart rate, flow, non-invasive blood pressure, arm sweating, and digit oximetry will be measured concurrently with image scans. The MR signal changes will be assessed with software optimized for fMRI processing to gauge regional activation changes during apneic events, inspiratory loading and sympathetic challenges. Cross correlations of regional image changes with respiratory, cardiovascular and sympathetic outflow induces will be calculated. The studies have the potential to identify brain regions involved in mediating upper airway atonia, to provide insights into pharmacologic intervention for obstructive sleep apnea, and to determine the neural sites involved in autonomic concomitants of airway obstruction.

DESCRIPTION (provided by applicant): The objective is to identify deficient structure and function within brain areas, which control breathing and blood pressure in early life, and thus assist determination of failure mechanisms in the Sudden Infant Death Syndrome (SIDS). Brain structures identified as showing neuroanatomic and functional neural deficits in a condition characterized by failure to breathe during sleep and deficient blood pressure control, Congenital Central Hypoventilation Syndrome (CCHS), will be evaluated for defects in axonal integrity and ability of selected areas to respond with appropriate timing to autonomic and ventilatory challenges. The brain areas selected for study showed circumscribed anatomical deficits in cerebellar structures and regions encompassing fiber bundles interconnecting limbic structures; these areas mediate the perception of air hunger, regulation of blood pressure lowering or elevation, and detection of CO2 and hypoxia. We will use diffusion tensor imaging to evaluate axonal integrity and distribution within areas which showed cellular or axonal damage in the syndrome, including fibers 1) of the cingulum bundle, 2) extending caudally from the caudate nucleus, and ventrally to the basal forebrain, 3) projecting to the mid-hippocampus, and 4) from the inferior olive to Purkinje neurons of the cerebellar cortex and deep nuclei in 53 CCHS patients and 53 age-and gender-matched controls. We will examine timing of cerebellar, pontine, posterior thalamic and limbic responses with functional magnetic resonance imaging procedures to successive hypercapnia and Valsalva maneuvers to evaluate coordination of activity within these areas. The studies can reveal whether aberrant brain structure responses to breathing and blood pressure challenges result from nerve fiber loss, and whether deficient timing of brain structure action accompanies stimulation of chemoreceptor and blood pressure regulation sites. Since SIDS may result from hypotension or failure to enhance breathing to hypoxia, the studies may describe mechanisms of failure in the syndrome.

DESCRIPTION (provided by applicant): Sleep-disordered breathing (SDB) is common in heart failure (HF) patients and associated with increased morbidity and mortality. Current treatments for SDB have not been shown to improve survival and often have high non-compliance, lack of efficacy in SDB alleviation, and/or associated with pain. Passive foot movement, the rhythmic movement of feet without voluntary effort, is known to increase ventilation but has not been examined in HF patients. We hypothesize that passive foot movement will decrease SDB (decrease in Apnea-Hypopnea Index [AHI]) with little or no impact on sleep state (fewer arousals during sleep), better sleep (measured by the Pittsburgh Sleep Quality Index Questionnaire) and greater preference for passive foot movement compared to continuous/biphasic positive airway pressure (CPAP/BiPAP - traditional SDB treatment methods). Using a one-group, quasi-experimental, pre- and post-test design, we will examine 26 subjects with advanced HF (left ventricular ejection fraction <0.40, dilated systolic dysfunction, not in acute HF, age 40-65 years) and SDB (AHI >5 via overnight polysomnography in the previous 6 months) who will be randomized to undergo passive foot movement either during the first or last half of the night during overnight polysomnography. The specific aims for this study are to: 1) Examine the association between SDB (as indicated by AHI), blood oxygen desaturation, carbon dioxide blood levels and passive foot movement;2) Examine the association between passive foot movement and changes in sleep stage during an overnight sleep study (polysomnography) in HF patients with SDB;3) Determine the impact of passive foot movement on subjective reports of sleep quality in HF patients with a history of SDB. The objective is of this study is to determine the relationships between a novel treatment option, passive foot movement, and SDB in HF patients. If passive foot movement decreases SDB and is tolerable to persons with HF, this intervention could have change clinical practice and improve outcomes in this high risk patient population. PUBLIC HEALTH RELEVANCE: Sleep-disordered breathing is common in heart failure and is associated with increased morbidity and mortality. Current treatments for sleep-disordered breathing have not demonstrated improvement in heart failure outcomes and often are associated with high non-compliance, ineffectiveness, and/or increased risk for pain. Passive foot movement is the rhythmic movement of the feet without voluntary effort, which results in increased ventilation. It is an innovative treatment option for sleep-disordered breathing which has the potential to effectively treat heart failure patients with dramatically decreased risk of adverse effects. If effective, passive foot movement could have important impact on heart failure disease progression and survival.

DESCRIPTION (provided by applicant): Children and young adults with spinal cord injury (SCI) commonly show sleep-disordered breathing (SDB), which is associated with increased morbidity and mortality, with an incidence conservatively reported at over 30%. Current treatments for SDB have high non-compliance due to associated discomfort or lack of efficacy. The most common intervention, continuous positive airway pressure, poses special problems with children and young adolescents, since the necessary masks distort developing facial bone structure over time, often forcing surgical reconstruction, and are difficult to fit as the child grows. Passive limb movement, the rhythmic movement of extremities without voluntary effort, increases ventilation during sleep in subjects with intact spinal cords; the impact of this intervention in complete thoracic SCI (paraplegic) patients lacking sensory information from the lower limbs is unknown. We hypothesize that passive limb movement (PLM) in these SCI patients with intact spinal cords above the thoracic cord region will decrease SDB [decrease the Apnea- Hypopnea Index (AHI)] for both obstructive and central apnea events, improve ventilation and oxygenation, and do so without arousing subjects during the night.. Using a one-group, quasi-experimental, pre- and post- test design, we will perform overnight polysomnography on 26 pediatric and young adults with complete thoracic spinal cord injury (ASIA A paraplegia, age 12-25 years), earlier screened to show SDB, who will be randomized to undergo passive limb (hand) movement either during the first or last half of the night during overnight polysomnography. The specific aims for this study are to: 1) Determine whether PLM therapy in pediatric and young adults with complete thoracic SCI (complete paraplegia) with SDB will improve SDB (as indicated by apnea-hyperpnoea index), ventilation (end-tidal carbon dioxide), and oxygen saturation; and 2) Compare number of arousals in pediatric and young adults with complete thoracic SCI during baseline sleep and during sleep when they are receiving PLM therapy. The objective of this study is to determine whether a novel treatment, passive limb movement, will improve ventilation in complete thoracic SCI adolescents and young adults with SDB, and do so with minimal disturbance to sleep. If passive limb movement improves ventilation and is tolerable to SCI patients, the intervention will provide an inexpensive, non-invasive therapy that could change clinical practice and significantly improve quality of life and outcomes in this high risk patient population. PUBLIC HEALTH RELEVANCE: Sleep-disordered breathing is common in children and adult spinal cord injury patients, and is associated with increased risk for high blood pressure, learning disorders, anxiety, and depression. Current treatments for sleep-disordered breathing are associated with high non-compliance, ineffectiveness, and discomfort. Upper limb cyclic movement (passive limb movement) may assist breathing in patients with spinal cord lesions below the cervical vertebrae (paraplegia). Passive limb movement is an innovative treatment option for sleep- disordered breathing which has the potential to effectively treat both children and adults with paraplegia.

? DESCRIPTION (provided by applicant): Individuals with intractable epilepsy have a ~1% annual risk of Sudden Unexpected Death in Epilepsy (SUDEP). Pre-mortem risk factors are unknown; however, evidence suggests autonomic nervous system (ANS) failure, sustained apnea/hypoxemia, or some combination of respiratory and cardiovascular (CV) collapse underlies the fatal event. Adverse ANS signs are prominent in epilepsy, with ANS-driven cardiac arrhythmias (bradycardia, asystole, tachyarrhythmias) in ~72% of epilepsy patients, hypotension, impaired baroreflex sensitivity (potentially compromising cerebral blood flow), enhanced sympathetic outflow, expressed as increased sweating and decreased inter-ictal nocturnal heart rate variability (HRV) common. EEG characteristics, including post-ictal generalized EEG suppression (PGES) is suggestive of high SUDEP-risk, strongly correlate with increased sweating and decreased HRV, and is typically accompanied by profound hypotension. Neural mechanisms underlying these patterns need to be defined. Our findings of damage to pulvinar thalamic CO2 and O2 integration areas, and to left insular parasympathetic regulatory structures in SUDEP victims suggest that an impaired ability to integrate respiratory sensory signals, combined with exaggerated parasympathetic action, inducing hypotension, thus resulting in cerebral hypoperfusion leading to the EEG signs of PGES, contribute to a fatal scenario. Deficits in other respiratory and ANS regulatory areas may participate, but those sites must be determined. We propose to relate focal brain structural changes in persons with epilepsy to particular peri-ictal autonomic and breathing patterns recognized as indices of risk for death. We found, in other syndromes exhibiting sudden death, e.g., heart failure, significant lateralized neural injury in brainstem and forebrain ANS and respiratory areas. Such unilateral injury can induce asymmetric ANS, and especially, sympathetic drive, establishing a scenario for potentially fatal arrhythmia or hypotension. We will determine peri-ictal physiological pattern of EEG, and especially PGES, blood pressure, HRV, baroreflex sensitivity, cardiac arrhythmia, and breathing that lead to risk of SUDEP, collect high resolution T1-weighted, diffusion tensor, and kurtosis images, and relate extent and laterality of injury to the physiological patterns. The studies will provide insights into mechanisms of failure in SUDEP, and suggest pre-mortem indications of characteristics that lead to a fatal scenario that are suitable for targeted intervention.

? DESCRIPTION (provided by applicant): Individuals with intractable epilepsy have a ~1% annual risk of Sudden Unexpected Death in Epilepsy (SUDEP). Pre-mortem risk factors are unknown; however, evidence suggests autonomic nervous system (ANS) failure, sustained apnea/hypoxemia, or some combination of respiratory and cardiovascular (CV) collapse underlies the fatal event. Adverse ANS signs are prominent in epilepsy, with ANS-driven cardiac arrhythmias (bradycardia, asystole, tachyarrhythmias) in ~72% of epilepsy patients, hypotension, impaired baroreflex sensitivity (potentially compromising cerebral blood flow), enhanced sympathetic outflow, expressed as increased sweating and decreased inter-ictal nocturnal heart rate variability (HRV) common. EEG characteristics, including post-ictal generalized EEG suppression (PGES) is suggestive of high SUDEP-risk, strongly correlate with increased sweating and decreased HRV, and is typically accompanied by profound hypotension. Neural mechanisms underlying these patterns need to be defined. Our findings of damage to pulvinar thalamic CO2 and O2 integration areas, and to left insular parasympathetic regulatory structures in SUDEP victims suggest that an impaired ability to integrate respiratory sensory signals, combined with exaggerated parasympathetic action, inducing hypotension, thus resulting in cerebral hypoperfusion leading to the EEG signs of PGES, contribute to a fatal scenario. Deficits in other respiratory and ANS regulatory areas may participate, but those sites must be determined. We propose to relate focal brain structural changes in persons with epilepsy to particular peri-ictal autonomic and breathing patterns recognized as indices of risk for death. We found, in other syndromes exhibiting sudden death, e.g., heart failure, significant lateralized neural injury in brainstem and forebrain ANS and respiratory areas. Such unilateral injury can induce asymmetric ANS, and especially, sympathetic drive, establishing a scenario for potentially fatal arrhythmia or hypotension. We will determine peri-ictal physiological pattern of EEG, and especially PGES, blood pressure, HRV, baroreflex sensitivity, cardiac arrhythmia, and breathing that lead to risk of SUDEP, collect high resolution T1-weighted, diffusion tensor, and kurtosis images, and relate extent and laterality of injury to the physiological patterns. The studies will provide insights into mechanisms of failure in SUDEP, and suggest pre-mortem indications of characteristics that lead to a fatal scenario that are suitable for targeted intervention.