Impact of the COVID-19 Pandemic on a Clinical Trial: A Quantitative Report on Study Engagement and Strategies.

INTRODUCTION: The COVID-19 pandemic impacted clinical research worldwide potentially altering research findings. The study purpose was to measure the effect of the pandemic on recruitment, retention, assessment, and intervention completion rates. METHODS: Enrollment and participation data from a clinical trial evaluating efficacy of a physical therapy intervention for high-risk preterm infants were compared across 3 pandemic periods (February 2019 through November 2021). RESULTS: Recruitment, retention, assessment, and intervention completion rates were lowest during the peak pandemic period. CONCLUSIONS: In compliance with the Human Subjects Review Board, and for the participants' and staff safety, transition from in-person to telehealth or hybrid visits was required to continue this longitudinal study. Despite the negative effect of the pandemic, parental resilience and commitment to the study was clear. Flexibility, quick action, dedication, and efficiency of the research team were key elements enabling study continuation with successful transition to telehealth assessments/interventions during the peak pandemic period.

Effect of a NICU to Home Physical Therapy Intervention on White Matter Trajectories, Motor Skills, and Problem-Solving Skills of Infants Born Very Preterm: A Case Series.

Infants born very preterm (VPT; ≤29 weeks of gestation) are at high risk of developmental disabilities and abnormalities in neural white matter characteristics. Early physical therapy interventions such as Supporting Play Exploration and Early Development Intervention (SPEEDI2) are associated with improvements in developmental outcomes. Six VPT infants were enrolled in a randomised clinical trial of SPEEDI2 during the transition from the neonatal intensive care unit to home over four time points. Magnetic resonance imaging scans and fixel-based analysis were performed, and fibre density (FD), fibre cross-section (FC), and fibre density and cross-section values (FDC) were computed. Changes in white matter microstructure and macrostructure were positively correlated with cognitive, motor, and motor-based problem solving over time on developmental assessments. In all infants, the greatest increase in FD, FC, and FDC occurred between Visit 1 and 2 (mean chronological age: 2.68-6.22 months), suggesting that this is a potential window of time to optimally support adaptive development. Results warrant further studies with larger groups to formally compare the impact of intervention and disparity on neurodevelopmental outcomes in infants born VPT.

Longitudinal Changes in the Sensorimotor Pathways of Very Preterm Infants During the First Year of Life With and Without Intervention: A Pilot Study.

Objective: Evaluate longitudinal changes in brain microstructure and volumes in very preterm infants during the first year of life with and without intervention.Design: Descriptive pilot study.Methods: Five preterm infants in a three-arm clinical trial, one SPEEDI Early, two SPEEDI Late, and two usual care. Brain structural and diffusion MRI's were acquired within 72 hours after neonatal intensive care unit discharge (n = 5), three months post-baseline (n = 5), and six months post-baseline (n = 3). Fractional anisotropy (FA), Mean diffusivity (MD), and volume metrics were computed for five brain regions.Results: More than 60% of eligible participants completed 100% of the scheduled MRIs. FA and volume increased from baseline to six months across all brain regions. Rate of white matter volume change from baseline to six months was highest in SPEEDI Early.Conclusions: Non-sedated longitudinal MRI is feasible in very preterm infants and appears to demonstrate longitudinal changes in brain structure and connectivity.

Polyneuronal innervation of single muscle fibers in cat eye muscle: inferior oblique.

Single muscle fibers with multiple axonal endplates (multiply innervated fibers) are normally present in adult extraocular muscles (EOMs), while most other mammalian skeletal muscles contain fibers with a single myoneural junction. Recent findings by others led us to investigate for the presence of polyneuronal innervation (innervation of a single muscle fiber by >1 motoneuron) in the inferior oblique (IO) muscle of pentobarbital anesthetized cats. The IO muscle nerve branches, as they coursed through the orbit, were further divided for independent or simultaneous electrical stimulation with bipolar electrodes. Four of five established tests for polyneuronal innervation gave positive results. The sum of the twitch (1) and tetanic (2) tensions in response to individual nerve branch stimulation was greater than that for simultaneous (whole) nerve stimulation. The summed electromyographic (EMG) responses (3) gave a similar positive result. The result for crossed tetanic potentiation (4) was negative for polyneuronal innervation while the crossed fatigue (5) test was positive. These results are consistent with recent studies. That the EOMs exhibit polyneuronal innervation further explains the eye-movement system's functional integrity during some neuromuscular disorders as well as its ability to operate with precision after the loss of numerous motoneurons.

The importance of saccular function to motor development in children with hearing impairments.

Children with hearing deficits frequently have delayed motor development. The purpose of this study was to evaluate saccular function in children with hearing impairments using the Vestibular Evoked Myogenic Potential (VEMP). The impact of the saccular hypofunction on the timely maturation of normal balance strategies was examined using the Movement Assessment Battery for Children (Movement ABC). Thirty-three children with bilateral severe/profound hearing impairment between 4 and 7 years of age were recruited from a three-state area. Approximately half of the sample had one or bilateral cochlear implants, one used bilateral hearing aids, and the rest used no amplification. Parents reported whether the hearing impairment was diagnosed within the first year or after 2 years of age. No VEMP was evoked in two thirds of the hearing impaired (HI) children in response to the bone-conducted stimulus. Children who were reportedly hearing impaired since birth had significantly poorer scores when tested with the Movement ABC.

Anatomic and physiological characteristics of the ferret lateral rectus muscle and abducens nucleus.

The ferret has become a popular model for physiological and neurodevelopmental research in the visual system. We believed it important, therefore, to study extraocular whole muscle as well as single motor unit physiology in the ferret. Using extracellular stimulation, 62 individual motor units in the ferret abducens nucleus were evaluated for their contractile characteristics. Of these motor units, 56 innervated the lateral rectus (LR) muscle alone, while 6 were split between the LR and retractor bulbi (RB) muscle slips. In addition to individual motor units, the whole LR muscle was evaluated for twitch, tetanic peak force, and fatigue. The abducens nucleus motor units showed a twitch contraction time of 15.4 ms, a mean twitch tension of 30.2 mg, and an average fusion frequency of 154 Hz. Single-unit fatigue index averaged 0.634. Whole muscle twitch contraction time was 16.7 ms with a mean twitch tension of 3.32 g. The average fatigue index of whole muscle was 0.408. The abducens nucleus was examined with horseradish peroxidase conjugated with the subunit B of cholera toxin histochemistry and found to contain an average of 183 motoneurons. Samples of LR were found to contain an average of 4,687 fibers, indicating an LR innervation ratio of 25.6:1. Compared with cat and squirrel monkeys, the ferret LR motor units contract more slowly yet more powerfully. The functional visual requirements of the ferret may explain these fundamental differences.

Effects of artificial rearing on contractile properties of genioglossus muscle in Sprague-Dawley rat.

Mammals suckle from a nipple during the early neonatal period to obtain nourishment. The genioglossus muscle helps position and move the tongue for efficient suckling. The purpose of this study was to examine the contractile properties and myosin heavy chain (MHC) phenotype of the genioglossus following an early period of artificial rearing, which reduced nutritive suckling. Beginning at 3 days of age, rats were fed via gastric cannula until postnatal day 14 (P14). At P14, artificially reared rat pups were either allowed to grow to postnatal day 42 (P42) or anaesthetised and prepared for experimentation. Comparisons were made between artificially reared and dam reared groups at P14 and P42. At P14 maximum tetanic tension and fatigue index were lower in the artificially reared group than the dam reared group. By P42, artificially reared rats had a higher fatigue index and lower percentage of MHCIIa than dam reared rats. The artificial rearing technique employed in this study was adequate to produce chronic changes in fatigue resistance and MHC distribution in genioglossus muscle of rat; the changes observed here may be similar to changes that occur in premature human infants requiring early artificial feedings.

Contractile properties and myosin heavy chain composition of rat tongue retrusor musculature show changes in early adulthood after 19 days of artificial rearing.

Previously, we showed that artificial rearing using the "pup in a cup" model results in decreased tongue activity and caused some minor alterations in the tongue retrusor musculature. However, the artificial rearing time frame previously chosen was brief (11 days). The purpose of the present investigation was to extend the artificial rearing period from postnatal days 3 to 21 (P21) to determine whether significant alterations occur as a result of this reduced tongue use. Several changes in contractile properties due to the artificial rearing process were observed, which fully recovered by postnatal days 41 to 42 (P41-2). These changes included a shorter twitch contraction time, shorter twitch half-relaxation time, and decreased fatigue resistance. Styloglossus muscle exhibited more neonatal myosin heavy chain (MHC) isoform at P21 for the artificially reared (AR) group. Changes that were persistent at P41-2 were also observed. Maximum tetanic tension was lower for the AR group at P21 and P41-2 compared with their dam-reared counterparts. Twitch tension was also lower by P41-2 in the AR group. At P41-2, the AR group exhibited an increase in MHC IIa and a decrease in MHC IIb for the styloglossus muscle. In addition, the AR group exhibited a decreased MHC IIb for the long head of the biceps brachii at P41-2. Our results are similar to other models of hindlimb immobilization and suspension. By extending our artificial rearing period, this reduced tongue activity induced acute changes and alterations in the tongue retrusor musculature that persisted into early adulthood.

Myosin heavy chain and fibre diameter of extrinsic tongue muscles in rhesus monkey.

OBJECTIVE: The purpose of this investigation was to identify the myosin heavy chain (MHC) phenotype and fibre diameters of hypoglossal innervated extrinsic tongue muscles in rhesus monkey. METHODS: Genioglossus, styloglossus and hyoglossus muscle samples obtained from three female rhesus monkeys were analysed for MHC isoforms via gel electrophoresis and stained with MHC antibodies to measure least mean diameters. RESULTS: MHC phenotypes were consistent for all three muscles. Each muscle was predominantly composed of MHC type IIa and I. All three isoforms were significantly different from each other in fibre diameter for styloglossus and genioglossus (IIb>IIa and IIx>I; P<0.001). For hyoglossus, the MHC type II isoforms had larger diameters than the MHC type I isoform (P<0.001). CONCLUSIONS: While the extrinsic tongue muscle MHC and/or muscle fibre type composition may be different between mammalian species, there are consistent similarities between the intrinsic and extrinsic tongue muscles. We suggest this is necessary for the highly coordinated activities performed by the tongue such as mastication, respiration and swallowing. The differences in fibre diameters among MHC isoforms suggest a large force gradation, which would be consistent with the coordination of these activities. The similarities among primates in MHC and/or muscle fibre composition as well as similar cortical inputs to the hypoglossal nucleus, suggest that we could expect to see similar MHC phenotype for extrinsic tongue muscles in human.

Lateral rectus muscle changes after bilateral neonatal labyrinthectomy in the ferret.

The vestibular system is essential to the coordination of eye movements during head movements. Exercise, such as the eye movements mediated by the vestibular system, is a major factor in the development of muscle fiber types and the strength of muscle. In this study, the contents of the inner ear were removed (labyrinthectomy) from (LAB) ferrets at postnatal day 10 (P10) and raised with control (SHAM) animals. At P30, the lateral rectus muscles (LR) were removed to analyze the expression of myosin heavy chain (MHC) isoforms and to measure the least diameter of the developmental, slow and fast type muscle fibers. Another set of animals were sacrificed at P120 to analyze MHC isoform expression and muscle fiber diameters, as well as the contractile characteristics of the LR were measured prior to sacrifice. The average LAB LR was significantly stronger than the SHAM LR and the muscle fibers of the LAB animals were larger in diameter. The LAB animals expressed more type IIx and less slow type MHC. These results support the hypothesis that input from the inner ear influence the development of strength and muscle diameter in the ferret extraocular muscles.

Neonatal bilabyrinthectomy leads to changes in skeletal muscle fiber form and function.

Children with hypoactive semicircular canals commonly have delayed motor development. We studied ferrets whose vestibular labyrinths were removed at postnatal day 10 (P10) to evaluate 1) development of motor behavior, 2) soleus contractile characteristics, 3) muscle fiber diameter, and 4) the expression of myosin heavy chain (MHC) isoforms. At P30 labyrinthectomized (LAB) ferrets exhibited a significant delay in motor development. At P120, the LAB ferrets continued to have significantly more difficulty with dynamic balance than the SHAM ferrets. At P30, the muscle fibers were about the same diameter as those in the sham operated ferrets (SHAM) at the same age but significantly more developmental MHC isoforms were expressed in the LAB soleus muscle. At P120, both the LAB soleus and medial gastrocnemius expressed significantly more type IIX MHC. The P120 LAB soleus muscle was significantly weaker and the muscle fibers were significantly smaller. These results support the hypothesis that vestibular receptors are important to the development of upright posture and balance activities, and influence muscle fiber development and MHC expression in postural muscles.

Stimulation-evoked eye movements with and without the lateral rectus muscle pulley.

Recent studies have suggested that extraocular muscle (EOM) pulleys, composed of collagen, elastin, and smooth muscle, are among the tissues surrounding the eye. High-resolution magnetic-resonance imaging appears to indicate that the pulleys serve to both constrain and alter the pulling paths of the EOMs. The active pulley hypothesis suggests that the orbital layer of the EOMs inserts on the pulley and serves to control it. Based on anatomical data, the active pulley hypothesis also suggests that the orbital layer does not rotate the eye within the orbit; this is done by the global layer of the muscle. However, no physiological data exist to confirm this hypothesis. Here we used stimulation-evoked eye movements in anesthetized monkeys and cats before and after destruction of the lateral rectus muscle pulley by removal of the lateral bony orbit and adjacent orbital tissue. The absence of these structures resulted in increased lateral, in the primate, and medial, in the cat, eye-movement amplitude and velocity. Vertical eye movements in the cat were not significantly affected. The results indicate that these increases, confined to horizontal eye-movement amplitude and velocity, may be attributed to passive properties within the orbit. In relation to the active pulley hypothesis, we could discern no clear impact (in terms of amplitude or velocity profile of the movements) of lateral eye exposure that could be directly attributable to the active lateral pulley system.

Effect of artificial rearing on the contractile properties and myosin heavy chain isoforms of developing rat tongue musculature.

This study's purpose was to examine the influence of an altered activity level, via artificial rearing, on the contractile properties, myosin heavy chain phenotypes (MHC), and muscle fiber sizes of the developing rat tongue retractor musculature. Artificially reared rat pups were fed through a gastric cannula, eliminating nutritive suckling from postnatal day 4 to postnatal day 14. Rat pups were observed immediately following artificial rearing (postnatal day 14) and after a 1-mo resumption of function (postnatal day 42). The contractile characteristics of the tongue retractor musculature were measured in response to stimulation of the hypoglossal nerve. At postnatal day 14, artificially reared rat pups demonstrated significantly longer twitch half-decay times, lower fusion frequencies, and a marked decrease in fatigue resistance. These contractile speed and fatigue characteristics were fully recovered following a 1-mo resumption of function. MHC phenotypes of the styloglossus muscle (a tongue retractor) were determined by gel electrophoresis. At postnatal day 14, artificial rearing had not altered the MHC phenotype or muscle fiber sizes of the styloglossus muscle. However, following a 1-mo resumption of function artificially reared rat pups demonstrated a small but significant increase in MHCIIa expression and decrease in MHCIIb expression compared with dam-reared rats. These results support artificial rearing as a useful model for altering the activity level of the tongue and suggest that normal suckling behavior is necessary for the normal postnatal development of the tongue retractor musculature. This may also be the case for premature infants necessarily fed artificially.

Extraocular motor unit and whole-muscle contractile properties in the squirrel monkey. Summation of forces and fiber morphology.

In order to understand the neural control of movement, many investigations have examined the contractile properties of single motor units contracting in isolation, and a great majority of those studies have been done in the cat. Fewer studies, again primarily in the cat, have examined motor units acting in concert in both hind-limb and extraocular muscles. It has been shown, in general, that when individual motor unit forces are added together they do not always add linearly, which makes our understanding of motor control somewhat more complicated. In addition, complex neuronal firing patterns can yield unexpected force outputs or muscle positions whether those patterns occur naturally or are induced through motoneuron stimulation. The current investigation extends these findings of nonlinearity to the primate extraocular system. In studies of the squirrel monkey lateral rectus muscle and its motor units, we show that individual units lose an average of 45% of their force output when they fire in concert with a small number of other motor units. Also, when individual motor units are stimulated at a constant rate of 100 Hz, the force output is most often dramatically different if that constant 100-Hz stimulation is preceded by brief (25 ms), high-frequency stimulation burst or pulse, as occurs during saccades. The force at 100 Hz is usually significantly higher than when no pulse is delivered. However, we now show that an identical stimulation pattern applied to a number of motor units simultaneously does not always yield these force differences. These "nonlinearities" are addressed in terms of the complex muscle architecture that we show in the squirrel monkey lateral rectus muscle. Muscle fibers do not always run in parallel from tendon to tendon. Instead, they may branch or attach to each other laterally or end to end, serially.

Short-term effects of botulinum toxin on the lateral rectus muscle of the cat.

Botulinum toxin type A (BTX) is often used as an alternative to surgery for the treatment of strabismus and many other motor or cosmetic problems. Although numerous studies established BTX as a powerful transmission-blocking agent at the neuromuscular junction, no evaluation of extraocular muscle (EOM) contractile properties after administration of BTX exists. Some anatomical studies on EOM fiber types suggested a long-term preferential effect of BTX on orbital layer, singly innervated muscle fibers. In this study, we examined the short-term effects of BTX on the contractile properties of normal lateral rectus muscle to determine the functional effect of BTX on muscle-force output over time. Measurements of muscle tension and the corresponding EMG evoked by stimulation of nerve VI were made hourly for up to 18 h following BTX administration. An intramuscular BTX injection of 2 U caused a dramatic decrease in maximum twitch and tetanic tension of the muscle in response to different frequencies of stimulation. This suppression developed gradually over time, with a concomitant reduction of EMG amplitude. No significant changes in muscle-speed-related characteristics (e.g., twitch contraction time, fusion frequency) were found. The results suggest a functional effect of BTX on all muscle fiber types, although, with the dose used, we did not observe complete muscle paralysis within the time of recording. The time course of muscle tension suppression by BTX also was frequency dependent, with the lower stimulation frequencies being more affected, suggesting that implementation of higher frequencies could still produce adequate eye movements.