Citations

Abstract The mammalian neuromuscular junction (NMJ) comprises a presynaptic terminal, a postsynaptic receptor region on the muscle fiber (endplate), and the perisynaptic (terminal) Schwann cell. As with any synapse, the purpose of the NMJ is to transmit signals from the nervous system to muscle fibers. This neural control of muscle fibers is organized as motor units, which display distinct structural and functional phenotypes including differences in pre‐ and postsynaptic elements of NMJs. Motor units vary considerably in the frequency of their activation (both motor neuron discharge rate and duration/duty cycle), force generation, and susceptibility to fatigue. For earlier and more frequently recruited motor units, the structure and function of the activated NMJs must have high fidelity to ensure consistent activation and continued contractile response to sustain vital motor behaviors (e.g., breathing and postural balance). Similarly, for higher force less frequent behaviors (e.g., coughing and jumping), the structure and function of recruited NMJs must ensure short‐term reliable activation but not activation sustained for a prolonged period in which fatigue may occur. The NMJ is highly plastic, changing structurally and functionally throughout the life span from embryonic development to old age. The NMJ also changes under pathological conditions including acute and chronic disease. Such neuroplasticity often varies across motor unit types. © 2022 American Physiological Society. Compr Physiol 12: 3731–3766, 2022.

Abstract In this article, we highlight the contributions of passive experiments that address important exercise‐related questions in integrative physiology and medicine. Passive experiments differ from active experiments in that passive experiments involve limited or no active intervention to generate observations and test hypotheses. Experiments of nature and natural experiments are two types of passive experiments. Experiments of nature include research participants with rare genetic or acquired conditions that facilitate exploration of specific physiological mechanisms. In this way, experiments of nature are parallel to classical “knockout” animal models among human research participants. Natural experiments are gleaned from data sets that allow population‐based questions to be addressed. An advantage of both types of passive experiments is that more extreme and/or prolonged exposures to physiological and behavioral stimuli are possible in humans. In this article, we discuss a number of key passive experiments that have generated foundational medical knowledge or mechanistic physiological insights related to exercise. Both natural experiments and experiments of nature will be essential to generate and test hypotheses about the limits of human adaptability to stressors like exercise. © 2023 American Physiological Society. Compr Physiol 13:4879‐4907, 2023.

Abstract Heart transplantation (HT) is one of the prodigious achievements in modern medicine and remains the cornerstone in the treatment of patients with advanced heart failure. Advances in surgical techniques, immunosuppression, organ preservation, infection control, and allograft surveillance have improved short‐ and long‐term outcomes thereby contributing to greater clinical success of HT. However, prolonged allograft and patient survival following HT are still largely restricted by the development of late complications, including allograft rejection, infection, cardiac allograft vasculopathy (CAV), and malignancy. The introduction of mTOR inhibitors early after HT has demonstrated multiple protective effects against CAV progression, renal dysfunction, and tumorigenesis. Therefore, several HT programs increasingly use mTOR inhibitors with partial or complete withdrawal of calcineurin inhibitor (CNI) in stable HT patients to reduce complications risk and improve long‐term outcomes. Furthermore, despite a substantial improvement in exercise capacity and health‐related quality of life after HT as compared to advanced heart failure patients, most HT recipients remain with a 30% to 50% lower peak oxygen consumption (Vo 2 ) than that of age‐matched healthy subjects. Several factors, including alterations in central hemodynamics, HT‐related complications and alterations in the musculoskeletal system, and peripheral physiological abnormalities, presumably contribute to the reduced exercise capacity following HT. Cardiac denervation and subsequent loss of sympathetic and parasympathetic regulation are responsible for various physiological alterations in the cardiovascular system, which contributes to restricted exercise tolerance. Restoration of cardiac innervation may improve exercise capacity and quality of life, but the reinnervation process is only partial even several years after HT. Multiple studies have shown that aerobic and strengthening exercise interventions improve exercise capacity by increasing maximal heart rate, chronotropic response, and peak Vo 2 after HT. Novel exercise modalities, such as high‐intensity interval training (HIT), have been proven as safe and effective for further improvement in exercise capacity, including among de novo HT recipients. Further developments have recently emerged, including donor heart preservation techniques, noninvasive CAV and rejection surveillance methods, and improvements in immunosuppressive therapies, all aiming at increasing donor availability and improving late survival after HT. © 2023 American Physiological Society. Compr Physiol 13:4719‐4765, 2023.

Abstract Extracellular vesicles (EVs) are membrane‐bound nanoparticles released by cells and are an important means of intercellular communication in physiological and pathological states. We provide an overview of recent advances in the understanding of EV biogenesis, cargo selection, recipient cell effects, and key considerations in isolation and characterization techniques. Studies on the physiological role of EVs have relied on cell‐based model systems due to technical limitations of studying endogenous nanoparticles in vivo . Several recent studies have elucidated the mechanistic role of EVs in liver diseases, including nonalcoholic fatty liver disease, viral hepatitis, cholestatic liver disease, alcohol‐associated liver disease, acute liver injury, and liver cancers. Employing disease models and human samples, the biogenesis of lipotoxic EVs downstream of endoplasmic reticulum stress and microvesicles via intracellular activation stress signaling are discussed in detail. The diverse cargoes of EVs including proteins, lipids, and nucleic acids can be enriched in a disease‐specific manner. By carrying diverse cargo, EVs can directly confer pathogenic potential, for example, recruitment and activation of monocyte‐derived macrophages in NASH and tumorigenicity and chemoresistance in hepatocellular carcinoma. We discuss the pathogenic role of EVs cargoes and the signaling pathways activated by EVs in recipient cells. We review the literature that EVs can serve as biomarkers in hepatobiliary diseases. Further, we describe novel approaches to engineer EVs to deliver regulatory signals to specific cell types, and thus use them as therapeutic shuttles in liver diseases. Lastly, we identify key lacunae and future directions in this promising field of discovery and development. © 2023 American Physiological Society. Compr Physiol 13:4631‐4658, 2023.

ABSTRACTObjectiveThe primary objective of this study is to review the evidence for aspirin use to prevent the growth of vestibular schwannomas (VS) and to propose a prospective trial to determine the progression‐free survival of VS patients after up to 42 months of treatment with aspirin. Secondary study objectives are to determine the effect of aspirin on VS growth, hearing function, serum biomarker levels, and the quality of life, as well as to determine the tolerability of aspirin treatment and whether serum biomarker and salicylate levels predict the response to aspirin.Study DesignLiterature review.SettingSix academic and private medical centers.MethodsReview of recent English literature regarding prophylactic aspirin use for VS.ResultsThe retrospective reviews on the utility of aspirin to prevent VS growth are inconclusive. Eighty‐four patients have been enrolled in a prospective double‐blinded, placebo‐controlled trial thus far to determine the effect of aspirin on VS.ConclusionsCompletion of a robust study design is necessary. The current aspirin dose has been well tolerated, with minimal adverse events to date.Level of EvidenceReview of retrospective studies: Level 4; Proposed randomized, placebo‐controlled, double‐blinded clinical trial: Level 2.

Abstract Objectives The aim of this study was to compare the measured physiological factors that limit running performance with real marathon results from world-class distance runners, evaluating the compatibility between measured data and predicted results based on the previously suggested model. Methods Four world-class East African marathon runners (three male, one female) underwent physiological running assessments to predict marathon performance times using a model based on V ˙ $\dot {\mathrm{V}}$ O 2 peak, percentage of V ˙ $\dot {\mathrm{V}}$ O 2 peak at the second ventilatory threshold, and running economy. Predictions were then compared to participants’ best marathon times. Results The measured V ˙ $\dot {\mathrm{V}}$ O 2 peak of the world-class runners was 75.1 ± 2.7 mL/kg/min. The second ventilatory threshold occurred at 85 ± 3 % of the peak, with a running economy of 63.7 ± 2.4 mL/kg/min at 19.6 ± 0.9 km/h. The predicted marathon performance time was 2:06:51 ± 0:03:17 h:min:s for the males and 2:17:36 h:min:s for the female. Comparing these predictions to their personal best times, the average difference was 00:55 ± 00:51 min:s (range: 00:20-02:08). Conclusions This research provides laboratory data on world-class road running athletes, reinforcing the link between marathon performance and V ˙ $\dot {\mathrm{V}}$ O 2 peak, the percentage of V ˙ $\dot {\mathrm{V}}$ O 2 peak at the second ventilatory threshold, and running economy. The examined athletes had lower V ˙ $\dot {\mathrm{V}}$ O 2 peak compared to predicted values, highlighting the importance of running economy and fractional utilization of V ˙ $\dot {\mathrm{V}}$ O 2 peak in achieving such performances. Future studies should continue to advance the field by including additional bioenergetic parameters measured during race conditions and expanding the participant cohort of elite marathoners, encompassing both sexes.

AbstractObjectiveNeuromodulation for pediatric refractory epilepsy (PRE) is preferred when the seizure onset zone is not amenable to surgical resection, due to multifocal onset or involvement of eloquent cortex. Given its rapidly evolving landscape, we describe our institutional experience with neurostimulation therapies including deep brain stimulation (DBS) of the anterior nucleus (DBS‐ANT), the centromedian nucleus (DBS‐CM), responsive neurostimulation (RNS), and chronic subthreshold stimulation (CSS) to treat PRE.MethodsA retrospective chart review was conducted to identify pediatric patients (≤18 years of age) who presented to our institution with PRE. Patients were included who had at least 1 year of follow‐up after neurostimulation was started. Patients with ≥50% seizure frequency reduction at last follow‐up compared to baseline were classified as responders.ResultsA total of 35 patients (21 females) were included in the series. Nine patients underwent DBS‐ANT, 9 underwent DBS‐CM (+ ANT in 7 patients), 5 underwent RNS, and 12 underwent CSS. The median age at seizure onset and surgery was 8 and 16 years, respectively. Structural lesions were the most common etiology of epilepsy (54%). Eighteen patients had prior interventions and 13 received invasive EEG. Post‐operative complications following neurostimulation implantation were noted in three patients (9%). However, no permanent deficits were noted. Median follow‐up time was 46 months (range 13–162 months). Twenty‐three patients (59%) were responders (3/9 DBS‐ANT; 7/9 DBS‐CM; 4/5 RNS; 9/12 CSS). Further, median seizure reduction was 25% (DBS‐ANT), 89% (DBS‐CM), 87% (RNS), and 88% (CSS) across the cohort. Six patients (17%) had improved subjective neurocognitive outcomes while the other 29 had stable neurocognitive outcomes.SignificanceDBS, RNS, and CSS are safe and effective options for PRE. An understanding of treatment approaches can optimize results by tailoring therapy to individual patients.Plain Language SummaryThis study investigates the use of various neurostimulation therapies for treating pediatric refractory epilepsy (PRE) including deep brain stimulation (DBS), responsive neurostimulation (RNS), and chronic subthreshold stimulation (CSS). Overall, neuromodulation was found to be effective in reducing seizures in most patients, with 59% of patients showing at least a 50% reduction in seizure frequency. Additionally, the treatments were generally safe, with few complications and no instances of permanent deficits.

Abstract Background: Resilience, quantified by the brief resilience scale (BRS), has been recognized for its role in pain and symptomatology in musculoskeletal conditions. The role of psychological factors in the clinical presentation and outcomes of FAI surgery continues to be poorly understood. Methods: This is a prospective multicenter study of FAI patients undergoing primary hip arthroscopy. PROMs were administered at baseline, 3-, and 6-months post-op and included the Patient Reported Outcomes Measurement Information System (PROMIS) domains of anxiety and depression, as well as Hip Disability and Osteoarthritis and Outcome Score (HOOS), modified Harris Hip Score (mHHS), and International Hip Outcome Tool (iHOT-12). Resilience was characterized by BRS score and divided into low (“L”, score<3), normal (“N”, score 3-4.3), and high resilience (“H”, score>4.3). Results: 675 patients were included with a mean age of 24.9±7.8 years and female predominance (56%). Mean BRS scores were 3.7±0.7 (1.5-5.0). 13.8% (n=93) had low resilience, 65.9% (n=445) had normal resilience, and 20.3% (n=137) had high resilience. Lower resilience had more severe symptoms in HOOS pain (p<0.001), HOOS sports (p=0.003), HOOS ADL (p<0.001), HOOS QoL (p<0.001), iHOT-12 (p=0.002), and mHHS (p<0.001). Anxiety (L: 50.5%/N: 14.4%/H: 2.2%) and depression (L: 38.7%/N: 8.8%/H: 2.9%) were higher in lower resilience groups (all p<0.001) and this trend stayed consistent in female and male sub-analyses with females having greater anxiety and depression symptoms. The follow-up cohort with 3- and 6-months follow-up was 487 patients and had similar baseline characteristics as the baseline cohort. Lower resilience had lower postoperative PROs (with similar change) (p<0.05). After treatment, rates of anxiety or depression decreased from 22.1% to 15.6% with the low resilience group having the highest change from 62.9% to 45.9%. Conclusion: Low resilience correlates with more severe symptoms and predicts anxiety/depression in FAI. 13.8% had low resilience while 20.3% had high resilience. Lower resilience had worse postoperative PROs. Particularly in patients with low resilience at presentation, rates of anxiety or depression symptoms decreased postoperatively. Further studies are needed to understand the role of resilience in longer-term outcomes of FAI and whether concurrent psychological treatment will help improve patient outcomes after hip arthroscopy for FAI.