The Relationship Between Cortical Activation in Response to Anorectal Stimuli and Continence Behavior in Freely Behaving Rats Before and After Application of Sacral Nerve Stimulation.

BACKGROUND: Changes in anorectal sensation have been reported in patients with fecal incontinence, and there is limited evidence that sacral nerve stimulation can restore normal sensation. OBJECTIVE: The aims of the present study were to investigate changes in the transmission of sensory anorectal stimuli in a rodent model of fecal incontinence and to study the effects of sacral nerve stimulation on defecation behavior. DESIGN: An established model of fecal incontinence was utilized for this study. INTERVENTION: Pudendal nerve stretch and compression were used in 16 adult female Wistar rats and were monitored for 3 weeks: 6 rats received sacral nerve stimulation for 1 week by using an implantable neurostimulator and 10 rats had nonfunctioning "dummy" devices inserted. Five additional rats were sham operated. Anorectal cortical evoked potentials were used as a surrogate marker for anorectal sensory function. MAIN OUTCOME MEASURES: The primary outcomes measured were fecal incontinence index, evoked potential amplitude, and latency. RESULTS: Fifty percent of rats showed behavioral signs of fecal incontinence measured by the Fecal Incontinence Index (>0.20), calculated by using the pellet distribution outside the cage's latrine area. Anorectal evoked potential amplitude was reduced in rats with a Fecal Incontinence Index >0.20 (p = 0.019). The amplitude of forepaw evoked potentials recorded as a control was not different between groups. Chronic sacral nerve stimulation using the fully implantable device and custom rodent lead was safe and stable during this chronic prospective study. Incontinent rats (n = 3) that received sacral nerve stimulation showed an improvement of Fecal Incontinence Index and an increase of evoked potential amplitude to anorectal stimulation compared with the dummy implant controls (n = 5). LIMITATIONS: The main limitation is the small number of animals that received sacral nerve stimulation. CONCLUSIONS: Chronic sacral nerve stimulation is feasible in rats when miniature telemetric devices are used. Behavioral signs of fecal incontinence were positively correlated with the latency of anorectal evoked potentials. See Video Abstract at http://links.lww.com/DCR/B712.RELACIÓN ENTRE LA ACTIVACIÓN CORTICAL EN RESPUESTA A LOS ESTÍMULOS ANORRECTALES Y EL COMPORTAMIENTO DE CONTINENCIA EN RATAS QUE SE COMPORTAN LIBREMENTE ANTES Y DESPUÉS DE LA APLICACIÓN DE ESTIMULACIÓN DEL NERVIO SACRO. ANTECEDENTES: Se han informado cambios en la sensación anorrectal en pacientes con incontinencia fecal y hay evidencia limitada de que la estimulación del nervio sacro puede restaurar la sensación normal. OBJETIVO: Los objetivos del presente estudio fueron investigar los cambios en la transmisión de estímulos anorrectales sensoriales en un modelo de roedor de incontinencia fecal y estudiar los efectos de la estimulación del nervio sacro en la conducta de defecación. DISEO: Un modelo establecido de incontinencia fecal. INTERVENCIN: Se utilizó estiramiento y compresión del nervio pudendo en 16 ratas Wistar hembras adultas y se les realizó un seguimiento durante 3 semanas: seis ratas recibieron estimulación del nervio sacro durante 1 semana utilizando un neuroestimulador implantable y diez ratas tuvieron insertados dispositivos "ficticios" no funcionantes. Se operaron simuladamente cinco ratas adicionales. Los potenciales evocados corticales anorrectales se utilizaron como marcador subrogado de la función sensorial anorrectal. PRINCIPALES MEDIDAS DE RESULTADO: Índice de incontinencia fecal, amplitud de potenciales evocados y latencia. RESULTADOS: El cincuenta por ciento de las ratas mostró signos de comportamiento de incontinencia fecal medidos por el Índice de incontinencia fecal (> 0.20), calculado utilizando la distribución de heces fuera del área de la letrina de la jaula. La amplitud del potencial evocado anorrectal se redujo en ratas con un índice de incontinencia fecal >0.20 (p = 0.019). La amplitud de los potenciales evocados de la pata delantera registrados como control no fue diferente entre los grupos. La estimulación crónica del nervio sacro utilizando un dispositivo totalmente implantable y un cable de roedor personalizado fue segura y estable durante este estudio prospectivo crónico. Las ratas con incontinencia (N = 3) que recibieron estimulación del nervio sacro mostraron una mejora del índice de incontinencia fecal y un aumento de la amplitud del potencial evocado a la estimulación anorrectal en comparación con los controles de implante ficticio (N = 5). LIMITACIONES: La principal limitación es el pequeño número de animales que recibieron estimulación del nervio sacro. CONCLUSIONES: La estimulación crónica del nervio sacro es factible en ratas cuando se utilizan dispositivos telemétricos en miniatura. Los signos conductuales de incontinencia fecal se correlacionaron positivamente con la latencia de los potenciales evocados anorrectales. Consulte Video Resumen en http://links.lww.com/DCR/B712. (Traducción-Dr. Jorge Silva Velazco).

Distribution and morphology of sensory and autonomic fibres in the subendocardial plexus of the rat heart.

Cardiac reflexes originating from sensory receptors in the heart ensure blood supply to vital tissues and organs in the face of constantly changing demands. Atrial volume receptors are mechanically sensitive vagal afferents which relay to the medulla and hypothalamus, affecting vasopressin release and renal sympathetic activity. To date, two anatomically distinct sensory endings have been identified which may subserve cardiac mechanosensation: end-nets and flower-spray endings. To map the distribution of atrial receptors in the subendocardial space, we have double-labelled rat right atrial whole mounts for neurofilament heavy chain (NFH) and synaptic vesicle protein 2 (SV2) and generated high-resolution maps of the rat subendocardial neural plexus at the cavo-atrial region. In order to elucidate the nature of these fibres, double labelling with synaptophysin (SYN) and either NFH, calcitonin gene-related peptide (CGRP), choline acetyltransferase (ChAT) or tyrosine hydroxylase (TH) was performed. The findings show that subendocardial nerve nets are denser at the superior cavo-atrial junction than the mid-atrial region. Adluminal plexuses had the finest diameters and stained positively for synaptic vesicles (SV2 and SYN), CGRP and TH. These plexuses may represent sympathetic post-ganglionic fibres and/or sensory afferents. The latter are candidate substrates for type B volume receptors which are excited by stretch during atrial filling. Deeper nerve fibres appeared coarser and may be cholinergic (positive staining for ChAT). Flower-spray endings were never observed using immunohistochemistry but were delineated clearly with the intravital stain methylene blue. We suggest that differing nerve fibre structures form the basis by which atrial deformation and hence atrial filling is reflected to the brain.

Simulating Tissues with 3D-Printed and Castable Materials.

Manufacturing technologies continue to be developed and utilized in medical prototyping, simulations, and imaging phantom production. For radiologic image-guided simulation and instruction, models should ideally have similar imaging characteristics and physical properties to the tissues they replicate. Due to the proliferation of different printing technologies and materials, there is a diverse and broad range of approaches and materials to consider before embarking on a project. Although many printed materials' biomechanical parameters have been reported, no manufacturer includes medical imaging properties that are essential for realistic phantom production. We hypothesize that there are now ample materials available to create high-fidelity imaging anthropomorphic phantoms using 3D printing and casting of common commercially available materials. A material database of radiological, physical, manufacturing, and economic properties for 29 castable and 68 printable materials was generated from samples fabricated by the authors or obtained from the manufacturer and scanned with CT at multiple tube voltages. This is the largest study assessing multiple different parameters associated with 3D printing to date. These data are being made freely available on GitHub, thus affording medical simulation experts access to a database of relevant imaging characteristics of common printable and castable materials. Full data available at: https://github.com/nmcross/Material-Imaging-Characteristics .

Design and implementation of a low cost, modular, adaptable and open-source XYZ positioning system for neurophysiology.

In recent years, open-source 3D printing technologies have become increasingly applied to biological research. We have created a fully open-source, versatile and low cost XYZ positioning system using 3D printer components. As this system is controlled by a Python3 based operating system running on a Raspberry Pi 3 Model B, its behaviour can be adapted to meet multiple needs in neurophysiology. We have developed two main applications of this system. First, we have created an automated microscopy script that links seamlessly with image stitching plugins in ImageJ (Fiji) allowing the user to create high resolution montages. Second, we have created a series of movement scripts allowing the application of graded rates of stretch to muscle spindles. Here we outline the construction and implementation of this system and discuss how we have utilised this tool in our research.

The projection of anorectal afferents to cortex of the rat: Comparison of two methods of cortical mapping.

BACKGROUND: The rat has served usefully as a model for fecal incontinence and exploration of the mechanism of action of sacral neuromodulation. However, there is a gap in knowledge concerning representation(s) on the primary sensory cortex of this anatomical region. METHODS: Multi-electrode array (32 channels) and intrinsic optical signal (IOS) processing were used to map cortical activation sites following anorectal electrical stimulation in the rat. A simple method for expanding a 32-electrode array to a virtual 2700 array was refined. KEY RESULTS: The IOS method identified activation of parietal cortex following anorectal or first sacral nerve root (S1) stimulation; however, the signal was poorly localized and large spontaneous vasomotion was observed in pial vessels. In contrast, the resulting high-density maps showed two anatomically distinct cortical activation sites to anorectal stimulation. CONCLUSIONS & INFERENCES: There are two distinct sites of activation on the parietal cortex following anorectal stimulation in the rat. The implications for sacral neuromodulation as a therapy for fecal incontinence are discussed.

The projection of anorectal afferents to spinal cord and effect of sacral neuromodulation on dorsal horn neurons which receive such input in the rat.

BACKGROUND: The rat has served usefully as a model for fecal incontinence and exploration of the mechanism of action of sacral neuromodulation (SNM). There remains a deficit in information regarding the location and type of spinal neurons which receive anorectal input and the effect of SNM on those neurons. METHODS: Single neuronal extracellular recordings of neurons receiving anorectal input were made at the S1 level of the spinal cord using sharp glass electrodes. SNM at S1 was delivered at 2 Hz for 3 minutes and its effect on discharge was quantified. KEY RESULTS: In total, 31 units (n = 14 animals) receiving anorectal synaptic input were recorded at the first sacral (S1) segmental level in either lamina III or IV of the dorsal horn. The inputs were classified according to afferent fiber conduction speed (16 Aδ, 11 Aß, and 4 C-fiber). The baseline firing frequency (ie, the mean firing frequency before the application of SNM) was 0.48 Hz ± 0.49 (mean ± SD) and 58% of units responded to acute SNM with either an increase or decrease in mean firing frequency. CONCLUSIONS & INFERENCES: In this study, the majority of spinal neurons receiving anorectal input changed their activity in response to SNM. These findings provide the basis for future studies which aim to explore the precise cellular mechanism of action of SNM on this fecal continence pathway.

Bands of Fontana are caused exclusively by the sinusoidal path of axons in peripheral nerves and predict axon path; evidence from rodent nerves and physical models.

The precise cause of the bands of Fontana, striations on peripheral nerves visible to the naked eye, has been the subject of debate for hundreds of years. Some researchers have described them as reflecting the sinuous course of nerve fibres passing through nerves, and others have proposed that endoneurial collagen and sheaths surrounding nerves play a role in their appearance. We hypothesised that the bands are caused exclusively by reflection of light from the surfaces of nerve fibres travelling in phase in sinusoidal waveforms through peripheral nerves. We aligned images of obliquely illuminated nerves with confocal images of axons in those nerves, and the numbers and positions of the bands precisely matched the axonal waves. We also developed three-dimensional models of nerves with representations of the sinusoidal path of axons at their surface. We observed patterns resembling the bands of Fontana when these models were obliquely illuminated. This provides evidence that the bands of Fontana can be caused by light reflected sinusoidal path of axons alone. We subsequently describe a mechanism of band production based on our observations of both nerves and models. We report that smaller diameter nerves such as phrenic nerves and distal branches of sciatic nerves have shorter band intervals than larger nerves, such as proximal trunks of sciatic nerves, and that shorter band intervals correlate with longer axons per unit length of nerve, which suggests a greater tolerance to stretch. Inspection of banding patterns on peripheral nerves may permit prediction of axon length within nerves, and assist in the interpretation of nerve conduction data, especially in diseases where axon path has become altered.

Additive Manufacture of Composite Soft Pneumatic Actuators.

This article presents a direct additive manufacturing method for composite material soft pneumatic actuators that are capable of performing a range of programmable motions. Commonly, molding is the method used to manufacture soft fluidic actuators. This is material, labor, and time intensive and lacks the design freedom to produce custom actuators efficiently. This article proposes an alternative semiautomated method of designing and manufacturing composite soft actuators. An affordable, open-source, desktop three-dimensional (3D) printer was modified into a four-axis, combined, fused deposition modeling, and paste extrusion printer. A Grasshopper 3D algorithm was devised to implement custom actuator designs according to user inputs, resulting in a G-code print file. Bending, contracting, and twisting motion actuators were parametrically designed and subsequently additively manufactured from silicone and thermoplastic elastomer (TPE) materials. Experimental testing was completed on these actuators along with their constitutive materials. Finite element models were created to simulate the actuator's kinematic performance. Having a platform method to digitally configure and directly additively manufacture custom-motion, composite soft actuators has the potential to accelerate the development of more intricate designs and lead to potential impacts in a range of areas, including in-clinic personalization of soft assistive devices and patient-specific biomedical devices.

Efficacy and mechanism of sub-sensory sacral (optimised) neuromodulation in adults with faecal incontinence: study protocol for a randomised controlled trial.

BACKGROUND: Faecal incontinence (FI) is a substantial health problem with a prevalence of approximately 8% in community-dwelling populations. Sacral neuromodulation (SNM) is considered the first-line surgical treatment option in adults with FI in whom conservative therapies have failed. The clinical efficacy of SNM has never been rigorously determined in a trial setting and the underlying mechanism of action remains unclear. METHODS/DESIGN: The design encompasses a multicentre, randomised, double-blind crossover trial and cohort follow-up study. Ninety participants will be randomised to one of two groups (SNM/SHAM or SHAM/SNM) in an allocation ratio of 1:1. The main inclusion criteria will be adults aged 18-75 years meeting Rome III and ICI definitions of FI, who have failed non-surgical treatments to the UK standard, who have a minimum of eight FI episodes in a 4-week screening period, and who are clinically suitable for SNM. The primary objective is to estimate the clinical efficacy of sub-sensory SNM vs. SHAM at 32 weeks based on the primary outcome of frequency of FI episodes using a 4-week paper diary, using mixed Poisson regression analysis on the intention-to-treat principle. The study is powered (0.9) to detect a 30% reduction in frequency of FI episodes between sub-sensory SNM and SHAM stimulation over a 32-week crossover period. Secondary objectives include: measurement of established and new clinical outcomes after 1 year of therapy using new (2017 published) optimised therapy (with standardised SNM-lead placement); validation of new electronic outcome measures (events) and a device to record them, and identification of potential biological effects of SNM on underlying anorectal afferent neuronal pathophysiology (hypothesis: SNM leads to increased frequency of perceived transient anal sphincter relaxations; improved conscious sensation of defaecatory urge and cortical/subcortical changes in afferent responses to anorectal electrical stimulation (main techniques: high-resolution anorectal manometry and magnetoencephalography). DISCUSSION: This trial will determine clinical effect size for sub-sensory chronic electrical stimulation of the sacral innervation. It will provide experimental evidence of modifiable afferent neurophysiology that may aid future patient selection as well as a basic understanding of the pathophysiology of FI. TRIAL REGISTRATION: International Standard Randomised Controlled Trial Number: ISRCTN98760715 . Registered on 15 September 2017.

An animal model of faecal incontinence and sacral neuromodulation.

The pudendal nerves can be injured during traumatic vaginal childbirth and result in faecal incontinence. Some of these incontinent patients benefit from chronic sacral neuromodulation and the mechanism of action of this therapy has been a focus of many studies. In 2008, a rodent model of neuropathic faecal incontinence was introduced and subsequently validated through a series of investigations. This review summarizes the decade-long contribution of Professor Ronan O'Connell to the inception and application of this rodent model of faecal incontinence and sacral neuromodulation.

Dual-extrusion 3D printing of anatomical models for education.

Two material 3D printing is becoming increasingly popular, inexpensive and accessible. In this paper, freely available printable files and dual extrusion fused deposition modelling were combined to create a number of functional anatomical models. To represent muscle and bone FilaFlex3D flexible filament and polylactic acid (PLA) filament were extruded respectively via a single 0.4 mm nozzle using a Big Builder printer. For each filament, cubes (5 mm3 ) were printed and analyzed for X, Y, and Z accuracy. The PLA printed cubes resulted in errors averaging just 1.2% across all directions but for FilaFlex3D printed cubes the errors were statistically significantly greater (average of 3.2%). As an exemplar, a focus was placed on the muscles, bones and cartilage of upper airway and neck. The resulting single prints combined flexible and hard structures. A single print model of the vocal cords was constructed which permitted movement of the arytenoids on the cricoid cartilage and served to illustrate the action of intrinsic laryngeal muscles. As University libraries become increasingly engaged in offering inexpensive 3D printing services it may soon become common place for both student and educator to access websites, download free models or 3D body parts and only pay the costs of print consumables. Novel models can be manufactured as dissectible, functional multi-layered units and offer rich possibilities for sectional and/or reduced anatomy. This approach can liberate the anatomist from constraints of inflexible hard models or plastinated specimens and engage in the design of class specific models of the future. Anat Sci Educ 11: 65-72. © 2017 American Association of Anatomists.

Systematic Review of Animal Models Used in Research of Origins and Treatments of Fecal Incontinence.

BACKGROUND: Fecal incontinence is a common disorder, but its pathophysiology is not completely understood. OBJECTIVE: The aim of this review is to present animal models that have a place in the study of fecal incontinence. DATA SOURCES: A literature review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines performed in August 2016 revealed 50 articles of interest. Search terms included fecal/faecal incontinence and animal model or specific species. STUDY SELECTION: Articles not describing an animal model, in vitro studies, veterinary literature, reviews, and non-English articles were excluded. MAIN OUTCOME MEASURES: The articles described models in rats (n = 31), dogs (n = 8), rabbits (n = 7), and pigs (n = 4). RESULTS: Different fecal incontinence etiologies were modeled, including anal sphincter lesions (33 articles) ranging from a single anal sphincter cut to destruction of 50% of the anal sphincter by sharp dissection, electrocautery, or diathermy. Neuropathic fecal incontinence (12 articles) was achieved by complete or incomplete pudendal, pelvic, or inferior rectal nerve damage. Mixed fecal incontinence (5 articles) was modeled either by the inflation of pelvic balloons or an array of several lesions including nervous and muscular damage. Anal fistulas (2 articles), anal sphincter resection (3 articles), and diabetic neuropathy (2 articles) were studied to a lesser extent. LIMITATIONS: Bias may have arisen from the authors' own work on fecal incontinence and the absence of blinding to the origins of articles. CONCLUSIONS: Validated animal models representing the main etiologies of fecal incontinence exist, but no animal model to date represents the whole pathophysiology of fecal incontinence. Therefore, the individual research questions still dictate the choice of model and species.

Fabrication and assessment of 3D printed anatomical models of the lower limb for anatomical teaching and femoral vessel access training in medicine.

For centuries, cadaveric dissection has been the touchstone of anatomy education. It offers a medical student intimate access to his or her first patient. In contrast to idealized artisan anatomical models, it presents the natural variation of anatomy in fine detail. However, a new teaching construct has appeared recently in which artificial cadavers are manufactured through three-dimensional (3D) printing of patient specific radiological data sets. In this article, a simple powder based printer is made more versatile to manufacture hard bones, silicone muscles and perfusable blood vessels. The approach involves blending modern approaches (3D printing) with more ancient ones (casting and lost-wax techniques). These anatomically accurate models can augment the approach to anatomy teaching from dissection to synthesis of 3D-printed parts held together with embedded rare earth magnets. Vascular simulation is possible through application of pumps and artificial blood. The resulting arteries and veins can be cannulated and imaged with Doppler ultrasound. In some respects, 3D-printed anatomy is superior to older teaching methods because the parts are cheap, scalable, they can cover the entire age span, they can be both dissected and reassembled and the data files can be printed anywhere in the world and mass produced. Anatomical diversity can be collated as a digital repository and reprinted rather than waiting for the rare variant to appear in the dissection room. It is predicted that 3D printing will revolutionize anatomy when poly-material printing is perfected in the early 21st century.

A review of sacral nerve stimulation parameters used in the treatment of faecal incontinence.

Sacral nerve stimulation (SNS) was originally developed in the field of urinary incontinence. Without adaptation, it was subsequently applied to treat faecal incontinence. SNS has now become a first line therapy for this socially disabling condition, however the mechanism of action is unknown. This review examines the evidence for stimulation parameters currently used for SNS in humans and considers the potential electrophysiological effects of changing these parameters. However, without a proper understanding of the physiology of SNS, changing stimulation parameters remains empirical.

Normal nerve striations are altered in the trembler-J mouse, a model of Charcot-Marie-Tooth disease.

INTRODUCTION: This study was initiated because it was noted that the peripheral nerves of Trembler-J mice (a model of human Charcot-Marie-Tooth disease) appear to lack normal striations. METHODS: We performed confocal microscopy of whole sciatic nerves and tested the effect of axial stress on impulse conduction. RESULTS: We found that the axons of mutant mice were longer than those of the wild-type (1.55 mm of axon/mm length of nerve vs. 1.28 mm/mm respectively). This axonal elongation altered the helical nerve striations (bands of Fontana). As nerves were stretched axially, the conduction distance became correspondingly shorter. The effect on latency was significantly greater in the more coiled nerves of Trembler-J mice (P = 0.038). CONCLUSIONS: The finding that mice with a mutated peripheral myelin protein 22 (PMP22) possess excessively long axons may be related to the excess Schwann cell numbers found in this disorder.

Increased cardiac output contributes to the development of chronic intermittent hypoxia-induced hypertension.

Chronic intermittent hypoxia (CIH) in animal models has been shown to result in hypertension and elevation of sympathetic nervous system activity. Sympathetically mediated vasoconstriction is believed to be the primary mechanism underpinning CIH-induced hypertension; however, the potential contribution of the heart is largely overlooked. We sought to determine the contribution of cardiac output (CO) and lumbar sympathetic control of the hindlimb circulation to CIH-induced hypertension. Male Wistar rats (n = 64) were exposed to 2 weeks of CIH [cycles of 90 s hypoxia (5% O2 nadir) and 210 s normoxia] or normoxia for 8 h day(-1). Under urethane anaesthesia, CIH-treated animals developed hypertension (81.4 ± 2.2 versus 91.6 ± 2.4 mmHg; P < 0.001), tachycardia (397 ± 8 versus 445 ± 7 beats min(-1); P < 0.001) and an increased haematocrit (42.4 ± 0.4 versus 45.0 ± 0.4%; P < 0.001). Echocardiography revealed that CIH exposure increased the CO [19.3 ± 1.7 versus 25.8 ± 2.6 ml min(-1) (100 g)(-1); P = 0.027] with no change in total peripheral resistance (4.93 ± 0.49 versus 4.17 ± 0.34 mmHg ml(-1) min(-1); P = 0.123). Sympathetic ganglionic blockade revealed that sympathetic control over blood pressure was not different (-27.7 ± 1.6 versus -32.3 ± 2.9 mmHg; P = 0.095), and no chronic vasoconstriction was found in the hindlimb circulation of CIH-treated animals (39.4 ± 2.5 versus 38.0 ± 2.4 µl min(-1) mmHg(-1); P = 0.336). Lumbar sympathetic control over the hindlimb circulation was unchanged in CIH-treated animals (P = 0.761), although hindlimb arterial sympathetic density was increased (P = 0.012) and vascular sensitivity to phenylephrine was blunted (P = 0.049). We conclude that increased CO is sufficient to explain the development of CIH-induced hypertension, which may be an early adaptive response to raise O2 flow. We propose that sustained elevated cardiac work may ultimately lead to heart failure.

Effect of chronic intermittent hypoxia on the reflex recruitment of the genioglossus during airway obstruction in the anesthetized rat.

We sought to test the hypothesis that chronic intermittent hypoxia (CIH)-a feature of sleep-disordered breathing in humans-impairs reflex recruitment of the genioglossus (GG, pharyngeal dilator) during obstructive airway events. Adult male Wistar rats were exposed to 20 cycles of normoxia and hypoxia (5% O2 at nadir) per hour, 8h a day for 7 days (CIH, N=7). The sham group (N=7) were exposed to normoxia in parallel. Following gas treatments, rats were anesthetized with an i.p. injection of urethane (1.5g/kg; 20%, w/v). Fine concentric needle electrodes were inserted into the GG and the costal diaphragm. Discriminated GG motor unit potentials and whole electromyograph (EMG), together with arterial blood pressure and arterial O2 saturation, were recorded during quiet basal breathing and during nasal airway occlusion. Airway occlusion significantly increased GG EMG activity in all animals; but there was no difference in the reflex response to airway occlusion between sham and CIH-treated animals (+105±22% vs. +105±17%, mean±SEM for area under the curve of integrated GG EMG, % increase from baseline, p=0.99). Occluded breaths were characterized by a significant increase in the firing frequency of phasically active units and the recruitment of large motor units that were quiescent under basal conditions. Though there are reports of impaired control of the upper airway following CIH in the rat, we conclude that reflexly evoked motor discharge to the GG is not affected by 7 days of CIH, a paradigm that we have shown increases apnea index in sleeping rats.

Effects of sustained hypoxia on sternohyoid and diaphragm muscle during development.

Sustained hypoxia is a dominant feature of respiratory disease. Despite the clinical significance, the effects of sustained hypoxia on the form and function of respiratory muscle during development are relatively underexplored. Wistar rats were exposed to 1 week of sustained hypoxia (ambient pressure 450 mmHg) or normoxia at various time points during development. Sternohyoid and diaphragm muscle contractile and endurance properties were assessed in vitro. Muscle succinate dehydrogenase and myosin heavy chain composition were determined. The role of reactive oxygen species in hypoxia-induced muscle remodelling was assessed. Sustained hypoxia increased sternohyoid muscle force and fatigue in early but not late development, effects that persisted after return to normoxia. Hypoxia-induced sternohyoid muscle fatigue was not attributable to fibre type transitions or to a decrease in oxidative capacity. Chronic supplementation with the superoxide scavenger tempol did not prevent hypoxia-induced sternohyoid muscle fatigue, suggesting that mechanisms unrelated to oxidative stress underpin hypoxia-induced maladaptation in sternohyoid muscle. Sustained hypoxia had no effect on diaphragm muscle fatigue. We conclude that there are critical windows during development for hypoxia-induced airway dilator muscle maladaptation. Sustained hypoxia-induced impairment of upper airway muscle endurance may persist into later life. Upper airway muscle dysfunction could have deleterious consequences for the control of pharyngeal airway calibre in vivo.