Most hospitalized patients with significant tricuspid regurgitation have advanced disease preventing transcatheter tricuspid valve intervention.

BACKGROUND: More than moderate tricuspid regurgitation (TR) is associated with high mortality. Surgical tricuspid valve repair and replacements are rarely performed due to high operative mortality risk, mainly attributed to late presentation. Novel transcatheter tricuspid valve intervention (TTVI) devices are being developed as an alternative to surgery. The population of patients presenting to tertiary care centers who can benefit from TTVI has not been well defined. METHODS: We retrospectively analyzed 12,677 consecutive 2D echocardiograms completed at our tertiary care center between March 2021 and March 2022 and identified hospitalized patients with more than moderate TR. A total of 569 patients were included in this study. Clinical and echocardiographic data were collected by individual chart review. We used the European Society of Cardiology (ESC) guidelines on the management of valvular disease to retrospectively assign patients to medical, surgical, or transcatheter therapy. RESULTS: 458 patients (80.5 %) were assigned to medical therapy, 57 (10.0 %) were assigned to TTVI, and 54 (9.5 %) were assigned to tricuspid valve surgery. Of note, 75.7 % (431/569) of patients were precluded from any intervention due to advanced disease, and only 4.7 % (27/569) presented too early for intervention, being both asymptomatic and without RV dilatation. CONCLUSION: Only 10.0 % of patients presenting to a tertiary care center with significant TR would be candidates for TTVI when these technologies are approved in the United States. Earlier identification and treatment of TR could increase the number of patients who may benefit from interventions including TTVI.

Activation of orexin-2 receptors in the KÓ§lliker-Fuse nucleus of anesthetized mice leads to transient slowing of respiratory rate.

Orexins are neuropeptides originating from the hypothalamus that serve broad physiological roles, including the regulation of autonomic function, sleep-wake states, arousal and breathing. Lack of orexins may lead to narcolepsy and sleep disordered breathing. Orexinergic hypothalamic neurons send fibers to KÓ§lliker-Fuse (KF) neurons that directly project to the rostroventral respiratory group, and phrenic and hypoglossal motor neurons. These connections indicate a potential role of orexin-modulated KF neurons in functionally linking the control of wakefulness/arousal and respiration. In a reduced preparation of juvenile rats Orexin B microinjected into the KF led to a transient increase in respiratory rate and hypoglossal output, however Orexin B modulation of the KF in intact preparations has not been explored. Here, we performed microinjections of the Orexin B mouse peptide and the synthetic Orexin 2 receptor agonist, MDK 5220, in the KF of spontaneously breathing, isoflurane anesthetized wild type mice. Microinjection of Orexin-2 receptor agonists into the KF led to transient slowing of respiratory rate, which was more exaggerated in response to Orexin-B than MDK 5220 injections. Our data suggest that Orexin B signaling in the KF may contribute to arousal-mediated respiratory responses.

Nucleus Tractus Solitarius Neurons Activated by Hypercapnia and Hypoxia Lack Mu Opioid Receptor Expression.

Impaired chemoreflex responses are a central feature of opioid-induced respiratory depression, however, the mechanism through which mu opioid receptor agonists lead to diminished chemoreflexes is not fully understood. One brainstem structure involved in opioid-induced impairment of chemoreflexes is the nucleus of the solitary tract (NTS), which contains a population of neurons that express mu opioid receptors. Here, we tested whether caudal NTS neurons activated during the chemoreflex challenge express mu opioid receptors and overlap with neurons activated by opioids. Using genetic labeling of mu opioid receptor-expressing neurons and cFos immunohistochemistry as a proxy for neuronal activation, we examined the distribution of activated NTS neurons following hypercapnia, hypoxia, and morphine administration. The main finding was that hypoxia and hypercapnia primarily activated NTS neurons that did not express mu opioid receptors. Furthermore, concurrent administration of morphine with hypercapnia induced cFos expression in non-overlapping populations of neurons. Together these results suggest an indirect effect of opioids within the NTS, which could be mediated through mu opioid receptors on afferents and/or inhibitory interneurons.

Neurochemistry of the Kölliker-Fuse nucleus from a respiratory perspective.

The Kölliker-Fuse nucleus (KF) is a functionally distinct component of the parabrachial complex, located in the dorsolateral pons of mammals. The KF has a major role in respiration and upper airway control. A comprehensive understanding of the KF and its contributions to respiratory function and dysfunction requires an appreciation for its neurochemical characteristics. The goal of this review is to summarize the diverse neurochemical composition of the KF, focusing on the neurotransmitters, neuromodulators, and neuropeptides present. We also include a description of the receptors expressed on KF neurons and transporters involved in each system, as well as their putative roles in respiratory physiology. Finally, we provide a short section reviewing the literature regarding neurochemical changes in the KF in the context of respiratory dysfunction observed in SIDS and Rett syndrome. By over-viewing the current literature on the neurochemical composition of the KF, this review will serve to aid a wide range of topics in the future research into the neural control of respiration in health and disease.