E.Fiona Bailey
Professor, BIO5 Institute
Professor, Evelyn F Mcknight Brain Institute
Professor, Physiology
Professor, Speech/Language and Hearing
Primary Department
Department Affiliations
(520) 626-8299
Research Interest
My research focus is the neural control of breathing in human and nonhuman mammals. My earlier work assessed the role of pulmonary stretch receptors and central chemoreceptors in the genesis and relief of dyspnea or shortness of breath in healthy adults. These studies led to studies in the mammalian (rodent) airway that explored the modulation of upper airway muscles activities by chemical and pulmonary afferent feedback and the potential for selective electrical stimulation of the cranial nerve XII to alter airway geometry and volume (NIH/NIDCD RO3). Beginning in 2005, with the support of an NIH/NIDCD K23 I began work in neural control of upper airway muscles using tungsten microelectrodes to record from single motor units in adult human subjects. This work led in turn, to studies of regional (or segmental) muscle and motor unit activities in human subjects under volitional, state-dependent (i.e., wake/sleep) and chemoreceptor drives, in health and disease (NIH/NIDCD RO1). On the basis of the experimental work in muscle and motor units I have pursued additional lines of enquiry focused on clinical respiratory dysfunction in two specific populations a) infants at risk for SIDS and b) adults diagnosed with obstructive sleep apnea (OSA). Both lines of enquiry are highly innovative and have diagnostic and clinical applications. One recent line of enquiry explores the potential for a non-pharmacologic intervention daily to lower blood pressure and to improve sleep in patients diagnosed with mild-moderate obstructive sleep apnea. This training protocol shows promise as a cheap, effective and safe means of lowering blood pressure and improving autonomic-cardiovascular dysfunction in patients who are unwilling or unable to use the standard CPAP therapy.

Publications

Bailey, E. F., Janssen, P. L., & Fregosi, R. F. (2005). PO2-dependent changes in intrinsic and extrinsic tongue muscle activities in the rat. American journal of respiratory and critical care medicine, 171(12), 1403-7.

Historically, respiratory-related research in sleep apnea has focused exclusively on the extrinsic tongue muscles (i.e., genioglossus, hyoglossus, and styloglossus). Until recently, the respiratory control and function of intrinsic tongue muscles (i.e., inferior and superior longitudinalis, transverses, and verticalis), which comprise the bulk of the tongue, were unknown.

Bailey, E. F., & Fregosi, R. F. (2003). Pressure-volume behaviour of the rat upper airway: effects of tongue muscle activation. The Journal of physiology, 548(Pt 2), 563-8.

Our hypothesis was that the simultaneous activation of tongue protrudor and retractor muscles (co-activation) would constrict and stiffen the pharyngeal airway more than the independent activation of tongue protrudor muscles. Upper airway stiffness was determined by injecting known volumes of air into the sealed pharyngeal airway of the anaesthetized rat while measuring nasal pressure under control (no-stimulus) and stimulus conditions (volume paired with hypoglossal (XII) nerve stimulation). Stimulation of the whole XII nerves (co-activation) or the medial XII branches (protrudor activation) effected similar increases in total pharyngeal airway stiffness. Importantly, co-activation produced volume compression (airway narrowing) at large airway volumes (P

Laine, C. M., Nickerson, L. A., & Bailey, E. F. (2012). Cortical entrainment of human hypoglossal motor unit activities. Journal of neurophysiology, 107(1), 493-9.

Output from the primary motor cortex contains oscillations that can have frequency-specific effects on the firing of motoneurons (MNs). Whereas much is known about the effects of oscillatory cortical drive on the output of spinal MN pools, considerably less is known about the effects on cranial motor nuclei, which govern speech/oromotor control. Here, we investigated cortical input to one such motor pool, the hypoglossal motor nucleus (HMN), which controls muscles of the tongue. We recorded intramuscular genioglossus electromyogram (EMG) and scalp EEG from healthy adult subjects performing a tongue protrusion task. Cortical entrainment of HMN population activity was assessed by measuring coherence between EEG and multiunit EMG activity. In addition, cortical entrainment of individual MN firing activity was assessed by measuring phase locking between single motor unit (SMU) action potentials and EEG oscillations. We found that cortical entrainment of multiunit activity was detectable within the 15- to 40-Hz frequency range but was inconsistent across recordings. By comparison, cortical entrainment of SMU spike timing was reliable within the same frequency range. Furthermore, this effect was found to be intermittent over time. Our study represents an important step in understanding corticomuscular synchronization in the context of human oromotor control and is the first study to document SMU entrainment by cortical oscillations in vivo.

Kidder, I. J., Mudery, J. A., & Bailey, E. F. (2014). Neural drive to respiratory muscles in the spontaneously breathing rat pup. RESPIRATORY PHYSIOLOGY & NEUROBIOLOGY, 202, 64-70.

The neonatal rodent serves as useful and appropriate model within which to study respiratory system development. Despite an extensive literature that documents respiratory control in vitro, in vivo studies have relied upon whole body plethysmography to determine measures of respiratory frequency and tidal volume. However, plethysmography restricts access to the animal and thus, respiratory muscle electromyographic (EMG) activities have not been recorded in these studies previously. Electromyography yields accurate information about neural respiratory center output to the musculature and therefore, about the control of breathing in the intact animal. In this case, we documented neural drive to respiratory pump and upper airway muscles, electrocardiogram (ECG) and chest wall motions in rat pups up to 10 days of age noting sighs, spontaneous central apneas and hypopneas in room air and with successive increments in fractional inspired CO2 (F1CO2). Our findings underscore the advantages of EMG recordings for purposes of determining the magnitude and distribution of neural drive to respiratory muscles and for characterizing the full range of breathing behaviors exhibited by rats in the early postnatal period. (C) 2014 Elsevier B.V. All rights reserved.

Bailey, E. F., Huang, Y., & Fregosi, R. F. (2006). Anatomic consequences of intrinsic tongue muscle activation. Journal of applied physiology (Bethesda, Md. : 1985), 101(5), 1377-85.

We recently showed respiratory-related coactivation of both extrinsic and intrinsic tongue muscles in the rat. Here, we test the hypothesis that intrinsic tongue muscles contribute importantly to changes in velopharyngeal airway volume. Spontaneously breathing anesthetized rats were placed in a MRI scanner. A catheter was placed in the hypopharynx and connected to a pressure source. Axial and sagittal images of the velopharyngeal airway were obtained, and the volume of each image was computed at airway pressures ranging from +5.0 to -5.0 cm H2O. We obtained images in the hypoglossal intact animal (i.e., coactivation of intrinsic and extrinsic tongue muscles) and after selective denervation of the intrinsic tongue muscles, with and without electrical stimulation. Denervation of the intrinsic tongue muscles reduced velopharyngeal airway volume at atmospheric and positive airway pressures. Electrical stimulation of the intact hypoglossal nerve increased velopharyngeal airway volume; however, when stimulation was repeated after selective denervation of the intrinsic tongue muscles, the increase in velopharyngeal airway volume was significantly attenuated. These findings support our working hypothesis that intrinsic tongue muscles play a critical role in modulating upper airway patency.