Spiritual Pain: A Symptom in Search of a Clinical Definition.

We conducted a literature search to identify and compare definitions of the experiential dimension of spiritual pain. Key databases were searched, up to the year 2021 inclusive, for papers with a definition of "spiritual" or "existential" pain/distress in a clinical setting. Of 144 hits, seven papers provided theoretical definitions/descriptions; none incorporated clinical observations or underlying pathophysiological constructs. Based on these findings, we propose a new definition for "spiritual pain" as a "self-identified experience of personal discomfort, or actual or potential harm, triggered by a threat to a person's relationship with God or a higher power." Our updated definition can inform future studies in pain assessment and management.

Optimizing and Accelerating the Development of Precision Pain Treatments for Chronic Pain: IMMPACT Review and Recommendations.

Large variability in the individual response to even the most-efficacious pain treatments is observed clinically, which has led to calls for a more personalized, tailored approach to treating patients with pain (ie, "precision pain medicine"). Precision pain medicine, currently an aspirational goal, would consist of empirically based algorithms that determine the optimal treatments, or treatment combinations, for specific patients (ie, targeting the right treatment, in the right dose, to the right patient, at the right time). Answering this question of "what works for whom" will certainly improve the clinical care of patients with pain. It may also support the success of novel drug development in pain, making it easier to identify novel treatments that work for certain patients and more accurately identify the magnitude of the treatment effect for those subgroups. Significant preliminary work has been done in this area, and analgesic trials are beginning to utilize precision pain medicine approaches such as stratified allocation on the basis of prespecified patient phenotypes using assessment methodologies such as quantitative sensory testing. Current major challenges within the field include: 1) identifying optimal measurement approaches to assessing patient characteristics that are most robustly and consistently predictive of inter-patient variation in specific analgesic treatment outcomes, 2) designing clinical trials that can identify treatment-by-phenotype interactions, and 3) selecting the most promising therapeutics to be tested in this way. This review surveys the current state of precision pain medicine, with a focus on drug treatments (which have been most-studied in a precision pain medicine context). It further presents a set of evidence-based recommendations for accelerating the application of precision pain methods in chronic pain research. PERSPECTIVE: Given the considerable variability in treatment outcomes for chronic pain, progress in precision pain treatment is critical for the field. An array of phenotypes and mechanisms contribute to chronic pain; this review summarizes current knowledge regarding which treatments are most effective for patients with specific biopsychosocial characteristics.

Features and methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system: a Delphi expert consensus study.

ABSTRACT: Classification of musculoskeletal pain based on underlying pain mechanisms (nociceptive, neuropathic, and nociplastic pain) is challenging. In the absence of a gold standard, verification of features that could aid in discrimination between these mechanisms in clinical practice and research depends on expert consensus. This Delphi expert consensus study aimed to: (1) identify features and assessment findings that are unique to a pain mechanism category or shared between no more than 2 categories and (2) develop a ranked list of candidate features that could potentially discriminate between pain mechanisms. A group of international experts were recruited based on their expertise in the field of pain. The Delphi process involved 2 rounds: round 1 assessed expert opinion on features that are unique to a pain mechanism category or shared between 2 (based on a 40% agreement threshold); and round 2 reviewed features that failed to reach consensus, evaluated additional features, and considered wording changes. Forty-nine international experts representing a wide range of disciplines participated. Consensus was reached for 196 of 292 features presented to the panel (clinical examination-134 features, quantitative sensory testing-34, imaging and diagnostic testing-14, and pain-type questionnaires-14). From the 196 features, consensus was reached for 76 features as unique to nociceptive (17), neuropathic (37), or nociplastic (22) pain mechanisms and 120 features as shared between pairs of pain mechanism categories (78 for neuropathic and nociplastic pain). This consensus study generated a list of potential candidate features that are likely to aid in discrimination between types of musculoskeletal pain.

Comparison of the Impacts of Under-Treated Pain and Opioid Pain Medication on Cognitive Impairment.

PURPOSE: To guide clinicians in balancing the risks and benefits of opioids when treating pain, we conducted two systematic reviews: 1) the impact of pain on cognitive function, and 2) the impact of opioids on cognitive function. METHODS: Part one addressed the impact of pain on cognitive impairment; Part two considered the impact of opioids on cognitive impairment. PubMed was used to search for eligible articles. For part one, 1786 articles were identified, of which 23 met our eligibility criteria. For part two, among 584 articles, 18 were found eligible. RESULTS: For part one, 16 studies concluded that patients with chronic pain showed impaired cognitive function; six studies found that chronic pain does not worsen cognitive function; one study concluded that the impact of pain on cognitive function differs based on the underlying cognitive status. For part two, 15 studies found that using opioids to control pain did not cause significant cognitive impairment, while three studies concluded the opposite. Studies evaluating older subjects did not observe different results from those in the whole population for both reviews. CONCLUSION: The published literature indicates that moderate to severe pain can impair cognitive function, and that careful use of opioid analgesics in such subjects does not necessarily worsen cognition. Although our results are insufficient to support clear guidance due to heterogeneity of cohorts and outcomes, this study may assist primary care providers by rendering explicitly the factors to be considered by providers caring for this population with pain when opioids are considered.

Scoping Review of Off-Label Topical Analgesia in Palliative, Hospice and Cancer Care: Towards Flexibility in Evidence-Based Medicine.

PURPOSE: Scoping reviews address the nature of the literature per se rather than inferring evidence-based treatment guidelines. Scoping reviews of the published literature are intended to describe the aggregated nature of the evidence surrounding some agent or intervention, in contrast to systematic reviews that seek when possible to guide clinical practice. We conducted a scoping review to identify reports of potential clinical utility of off-label topical analgesics and adjuvants when FDA-approved treatments have proven inadequate. METHODS: We performed a comprehensive search of three databases (PubMed, Web of Science and Embase) for articles dating from 1947 to the present. Mindful that FDA-approved and WHO-recommended analgesic medications often prove inadequate for individual patients in extremis with palliative, hospice or cancer pain, we used broad, structured inclusion criteria to retrieve articles. RESULTS: We retrieved 12,100 articles; after screening, we had 39 reports addressing 19 different topical agents out of the 32 chemical entities. Our scoping review disclosed evidence about agents that might not have met inclusion criteria for clinical practice guidelines. DISCUSSION: Although generally considered lower quality evidence, case reports or series present suggestions for diverse topical medications to manage pain in challenging circumstances when high-quality evidence for agents and routes of administration is lacking. CONCLUSION: Patients with the greatest need for evidence to identify and guide lesser-used agents during aggressive pain management are the most difficult to enroll and follow in standardized, controlled and/or blinded clinical trials. This scoping review identifies medications, dosages, and routes of topical agents reported to be effective in these often-challenging circumstances. Until larger and higher quality studies are completed, we must rely on the best available evidence even if of lower quality.

Persistent Spinal Pain Syndrome: A Proposal for Failed Back Surgery Syndrome and ICD-11.

OBJECTIVE: For many medical professionals dealing with patients with persistent pain following spine surgery, the term Failed back surgery syndrome (FBSS) as a diagnostic label is inadequate, misleading, and potentially troublesome. It misrepresents causation. Alternative terms have been suggested, but none has replaced FBSS. The International Association for the Study of Pain (IASP) published a revised classification of chronic pain, as part of the new International Classification of Diseases (ICD-11), which has been accepted by the World Health Organization (WHO). This includes the term Chronic pain after spinal surgery (CPSS), which is suggested as a replacement for FBSS. METHODS: This article provides arguments and rationale for a replacement definition. In order to propose a broadly applicable yet more precise and clinically informative term, an international group of experts was established. RESULTS: 14 candidate replacement terms were considered and ranked. The application of agreed criteria reduced this to a shortlist of four. A preferred option-Persistent spinal pain syndrome-was selected by a structured workshop and Delphi process. We provide rationale for using Persistent spinal pain syndrome and a schema for its incorporation into ICD-11. We propose the adoption of this term would strengthen the new ICD-11 classification. CONCLUSIONS: This project is important to those in the fields of pain management, spine surgery, and neuromodulation, as well as patients labeled with FBSS. Through a shift in perspective, it could facilitate the application of the new ICD-11 classification and allow clearer discussion among medical professionals, industry, funding organizations, academia, and the legal profession.

AAAPT Diagnostic Criteria for Acute Neuropathic Pain.

OBJECTIVE: Acute neuropathic pain is a significant diagnostic challenge, and it is closely related to our understanding of both acute pain and neuropathic pain. Diagnostic criteria for acute neuropathic pain should reflect our mechanistic understanding and provide a framework for research on and treatment of these complex pain conditions. METHODS: The Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership with the U.S. Food and Drug Administration (FDA), the American Pain Society (APS), and the American Academy of Pain Medicine (AAPM) collaborated to develop the ACTTION-APS-AAPM Pain Taxonomy (AAAPT) for acute pain. A working group of experts in research and clinical management of neuropathic pain was convened. Group members used literature review and expert opinion to develop diagnostic criteria for acute neuropathic pain, as well as three specific examples of acute neuropathic pain conditions, using the five dimensions of the AAAPT classification of acute pain. RESULTS: AAAPT diagnostic criteria for acute neuropathic pain are presented. Application of these criteria to three specific conditions (pain related to herpes zoster, chemotherapy, and limb amputation) illustrates the spectrum of acute neuropathic pain and highlights unique features of each condition. CONCLUSIONS: The proposed AAAPT diagnostic criteria for acute neuropathic pain can be applied to various acute neuropathic pain conditions. Both the general and condition-specific criteria may guide future research, assessment, and management of acute neuropathic pain.

The revised International Association for the Study of Pain definition of pain: concepts, challenges, and compromises.

ABSTRACT: The current International Association for the Study of Pain (IASP) definition of pain as "An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage" was recommended by the Subcommittee on Taxonomy and adopted by the IASP Council in 1979. This definition has become accepted widely by health care professionals and researchers in the pain field and adopted by several professional, governmental, and nongovernmental organizations, including the World Health Organization. In recent years, some in the field have reasoned that advances in our understanding of pain warrant a reevaluation of the definition and have proposed modifications. Therefore, in 2018, the IASP formed a 14-member, multinational Presidential Task Force comprising individuals with broad expertise in clinical and basic science related to pain, to evaluate the current definition and accompanying note and recommend whether they should be retained or changed. This review provides a synopsis of the critical concepts, the analysis of comments from the IASP membership and public, and the committee's final recommendations for revisions to the definition and notes, which were discussed over a 2-year period. The task force ultimately recommended that the definition of pain be revised to "An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage," and that the accompanying notes be updated to a bulleted list that included the etymology. The revised definition and notes were unanimously accepted by the IASP Council early this year.

Topical Ketamine with Other Adjuvants: Underutilized for Refractory Cancer Pain? A Case Series and Suggested Revision of the World Health Organization Stepladder for Cancer Pain.

Background: Uncontrolled cancer pain is a significant problem in palliative medicine. Opioids are often first-line treatment that increase risks of analgesic tolerance and hyperalgesia. Topical ketamine with other adjuvant pain medications is an often-overlooked treatment, yet may be most effective in difficult-to-treat cancer pain. Objective: We report a case series of hospice patients with uncontrolled cancer pain who were suboptimally treated with opioids and nerve blocks, whose symptoms responded to topical ketamine with other adjuvants. We review the pronociceptive properties of opioids and how topical multimodal treatment of cancer pain can be more effective than standard opioids, other topical adjuvant medications, and nerve blocks. We discuss the shortcomings of the World Health Organization (WHO) stepladder for the treatment of cancer pain and suggest an adjuvant treatment algorithm, directing physicians to appropriate adjuvant pain agents based on pain type and distinct receptor actions. Design: This is a retrospective case series of patients who responded to topical multimodal pain treatment with implementation of findings into an addendum to the WHO stepladder. Subjects: Subjects were from a case series of community-based hospice patients with previously uncontrolled cancer pain. Measurement: Measurement was made by self-report of pain levels using the 10-point numeric pain rating scale. Results: Patients' pain was controlled with topical adjuvant medications with return to previously lost function and prevention of otherwise escalating opioid dosing. Conclusions: These patient cases reveal how ketamine-based topical treatment for cancer pain can be more effective than standard opioids, other topical adjuvant medications, and nerve blocks with no noted side effects and observed reduction in opioid consumption.

Improving Study Conduct and Data Quality in Clinical Trials of Chronic Pain Treatments: IMMPACT Recommendations.

The estimated probability of progressing from phase 3 analgesic clinical trials to regulatory approval is approximately 57%, suggesting that a considerable number of treatments with phase 2 trial results deemed sufficiently successful to progress to phase 3 do not yield positive phase 3 results. Deficiencies in the quality of clinical trial conduct could account for some of this failure. An Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting was convened to identify potential areas for improvement in trial conduct in order to improve assay sensitivity (ie, ability of trials to detect a true treatment effect). We present recommendations based on presentations and discussions at the meeting, literature reviews, and iterative revisions of this article. The recommendations relate to the following areas: 1) study design (ie, to promote feasibility), 2) site selection and staff training, 3) participant selection and training, 4) treatment adherence, 5) data collection, and 6) data and study monitoring. Implementation of these recommendations may improve the quality of clinical trial data and thus the validity and assay sensitivity of clinical trials. Future research regarding the effects of these strategies will help identify the most efficient use of resources for conducting high quality clinical trials. PERSPECTIVE: Every effort should be made to optimize the quality of clinical trial data. This manuscript discusses considerations to improve conduct of pain clinical trials based on research in multiple medical fields and the expert consensus of pain researchers and stakeholders from academia, regulatory agencies, and industry.

Systemic administration of local anesthetic agents to relieve neuropathic pain.

BACKGROUND: Lidocaine, mexiletine, tocainide, and flecainide are local anesthetics which give an analgesic effect when administered orally or parenterally. Early reports described the use of intravenous lidocaine or procaine to relieve cancer and postoperative pain. Interest reappeared decades later when patient series and clinical trials reported that parenteral lidocaine and its oral analogs tocainide, mexiletine, and flecainide relieved neuropathic pain in some patients. With the recent publication of clinical trials with high quality standards, we have reviewed the use of systemic lidocaine and its oral analogs in neuropathic pain to update our knowledge, to measure their benefit and harm, and to better define their role in therapy. OBJECTIVES: To evaluate pain relief and adverse effect rates between systemic local anesthetic-type drugs and other control interventions. SEARCH METHODS: We searched MEDLINE (1966 through 15 May 2004), EMBASE (January 1980 to December 2002), Cancer Lit (through 15 December 2002), Cochrane Central Register of Controlled Trials (2nd Quarter, 2004), System for Information on Grey Literature in Europe (SIGLE), and LILACS, from January 1966 through March 2001. We also hand searched conference proceedings, textbooks, original articles and reviews. SELECTION CRITERIA: We included trials with random allocation, that were double blinded, with a parallel or crossover design. The control intervention was a placebo or an analgesic drug for neuropathic pain from any cause. DATA COLLECTION AND ANALYSIS: We collected efficacy and safety data from all published and unpublished trials. We calculated combined effect sizes using continuous and binary data for pain relief and adverse effects as primary and secondary outcome measurements, respectively. MAIN RESULTS: Thirty-two controlled clinical trials met the selection criteria; two were duplicate articles. The treatment drugs were intravenous lidocaine (16 trials), mexiletine (12 trials), lidocaine plus mexiletine sequentially (one trial), and tocainide (one trial). Twenty-one trials were crossover studies, and nine were parallel. Lidocaine and mexiletine were superior to placebo [weighted mean difference (WMD) = -11; 95% CI: -15 to -7; P < 0.00001], and limited data showed no difference in efficacy (WMD = -0.6; 95% CI: -7 to 6), or adverse effects versus carbamazepine, amantadine, gabapentin or morphine. In these trials, systemic local anesthetics were safe, with no deaths or life-threatening toxicities. Sensitivity analysis identified data distribution in three trials as a probable source of heterogeneity. There was no publication bias. AUTHORS' CONCLUSIONS: Lidocaine and oral analogs were safe drugs in controlled clinical trials for neuropathic pain, were better than placebo, and were as effective as other analgesics. Future trials should enroll specific diseases and test novel lidocaine analogs with better toxicity profiles. More emphasis is necessary on outcomes measuring patient satisfaction to assess if statistically significant pain relief is clinically meaningful.

CONTEXTE: La lidocaïne, le mexilétine, la tocainide et la flécainide sont des anesthésiques locaux qui apportent un effet analgésique lorsqu'ils sont administrés par voie orale ou parentérale. Des études anciennes décrivaient l'utilisation de lidocaïne ou de procaïne par voie intraveineuse pour soulager la douleur due au cancer ou la douleur postopératoire. Un regain d'intérêt a eu lieu quelques décennies plus tard lorsque des séries de patients et des essais cliniques ont rapporté que la lidocaïne par voie parentérale ou ses analogues oraux, tocainide, méxiléine et flécainide, soulageaient la douleur neuropathique chez certains patients. Avec la publication récente d'essais cliniques suivant des normes de qualité, nous avons révisé l'utilisation de lidocaïne systémique et de ses analogues oraux en douleur neuropathique pour mettre à jour nos connaissances, mesurer leurs bénéfices et effets délétères et mieux définir leur rôle dans le traitement. OBJECTIFS: Évaluer le soulagement de la douleur et les effets indésirables entre les médicaments de type anesthésique local systémique et d'autres interventions de contrôle. STRATÉGIE DE RECHERCHE DOCUMENTAIRE: Nous avons effectué une recherche dans MEDLINE (de 1966 au 15 mai 2004), EMBASE (de janvier 1980 à décembre 2002), Cancer Lit (jusqu'au 15 décembre 2002), le registre Cochrane des essais contrôlés (2ème trimestre 2004),le Système pour l'Information en Littérature Grise en Europe (SIGLE), et LILACS, de janvier 1966 à mars 2001. Nous avons également recherché des actes de conférences, des ouvrages, des articles originaux et des revues. CRITÈRES DE SÉLECTION: Nous avons inclus des essais à assignation aléatoire, en double aveugle, avec un plan d'étude parallèle ou croisé. L'intervention de contrôlé était un placebo ou un médicament analgésique contre la douleur neuropathique quelle qu'en soit la cause. RECUEIL ET ANALYSE DES DONNÉES: Nous avons recueilli des données sur l'efficacité et la sécurité à partir de tous les essais publiés et non publiés. Nous avons calculé les quantités d'effet combinées en utilisant les données continues et binaires pour le soulagement de la douleur et les effets indésirables en tant que critères de jugement principal et secondaire, respectivement. RÉSULTATS PRINCIPAUX: Trente­deux essais cliniques contrôlés satisfaisaient aux critères de sélection ; deux d'entre eux étaient des articles en double. Les médicaments de traitement étaient la lidocaïne intraveineuse (16 essais), la mexilétine (12 essais), la lidocaïne plus la mexilétine séquentiellement (un essai) et la tocainide (un essai). Vingt­et­un essais étaient des études croisées et neuf étaient des études parallèles. La lidocaïne et la mexilétine se sont avérées supérieures au placebo [différence moyenne pondérée (DMP) = ­11 ; IC à 95 % : ­15 à ­7 ; P < 0,00001], et des données limitées n'ont mis en évidence aucune différence de l'efficacité (DMP = ­0,6 ; IC à 95 % : ­7 à 6) ou des événements indésirables versus carbamazépine, amantadine, gabapentine ou morphine. Dans ces essais, les anesthésiques locaux systémiques étaient sûrs, avec la non occurrence de toxicités mortelles ou dangereuses. L'analyse de la sensibilité a permis d'identifier la distribution des données dans trois essais comme étant une source probable d'hétérogénéité. Aucun biais de publication n'a été observé. CONCLUSIONS DES AUTEURS: Ces essais cliniques contrôlés sur la douleur neuropathique ont permis de déterminer qu la lidocaïne et ses analogues oraux sont des médicaments sûrs, plus efficaces que le placebo et aussi efficaces que d'autres analgésiques. Les prochains essais devraient porter sur des maladies spécifiques et tester de nouveaux analogues de la lidocaïne avec de meilleurs profils de toxicité. Il est nécessaire de se centrer plus particulièrement sur les résultats mesurant la satisfaction des patients pour déterminer si le soulagement de la douleur significatif du point de vue statistique est pertinent cliniquement.

Current methods and challenges for acute pain clinical trials.

INTRODUCTION: The clinical setting of acute pain has provided some of the first approaches for the development of analgesic clinical trial methods. OBJECTIVES: This article reviews current methods and challenges and provides recommendations for future design and conduct of clinical trials of interventions to treat acute pain. CONCLUSION: Growing knowledge about important diverse patient factors as well as varying pain responses to different acute pain conditions and surgical procedures has highlighted several emerging needs for acute pain trials. These include development of early-phase trial designs that minimize variability and thereby enhance assay sensitivity, minimization of bias through blinding and randomization to treatment allocation, and measurement of clinically relevant outcomes such as movement-evoked pain. However, further improvements are needed, in particular for the development of trial methods that focus on treating complex patients at high risk of severe acute pain.

Cannabis for the Treatment of Chronic Pain in the Era of an Opioid Epidemic: A Symposium-Based Review of Sociomedical Science.

OBJECTIVE: This manuscript reviews medical literature published pertaining to the management of chronic pain with medical marijuana therapy (MMJ), with an emphasis on the social, medical, and legal aspects of therapy. DESIGN: Narrative review of peer-reviewed literature. METHODS: The 3rd Symposium on Controlled Substances and Their Alternatives for the Treatment of Pain was held in Boston on February 27, 2016, with a focus on MMJ for the treatment of chronic pain. Invited speakers had diverse backgrounds, including pain management, addiction psychiatry, neurology, and legal authorities. The purpose of this conference and this subsequent narrative review is to provide a medical, legal, and logistical framework for physicians and other health care providers to refer to when considering the initiation of medical marijuana therapy. RESULTS: The invited speakers each covered a unique aspect of MMJ therapy for the treatment of chronic pain. These presentations highlighted the current data for and against the use of MMJ as a pain therapy. Optimal patient selection and screening, in addition to policy developments, were discussed. CONCLUSIONS: Increasing interest in MMJ for chronic pain underscores a need for primary care and pain physicians to better understand the indications and evidence for its use free from cultural bias. Given a lack of full conclusive clinical utility, continued research is needed to better understand how to best utilize MMJ therapy for the treatment of chronic pain. Policy initiatives, such as enumerated indications, should follow medical science in order to prevent another abused substance epidemic.

Scope and Nature of Pain- and Analgesia-Related Content of the United States Medical Licensing Examination (USMLE).

Background: "The ongoing opioid crisis lies at the intersection of two substantial public health challenges-reducing the burden of suffering from pain and containing the rising toll of the harms that can result from the use of opioid medications" [1]. Improved pain education for health care providers is an essential component of the multidimensional response to both still-unmet challenges [2,3]. Despite the importance of licensing examinations in assuring competency in health care providers, there has been no prior appraisal of pain and related content within the United States Medical Licensing Examination (USMLE). Methods: An expert panel developed a novel methodology for characterizing USMLE questions based on pain core competencies and topical and public health relevance. Results: Under secure conditions, raters used this methodology to score 1,506 questions, with 28.7% (432) identified as including the word "pain." Of these, 232 questions (15.4% of the 1,506 USMLE questions reviewed) were assessed as being fully or partially related to pain, rather than just mentioning pain but not testing knowledge of its mechanisms and their implications for treatment. The large majority of questions related to pain (88%) focused on assessment rather than safe and effective pain management, or the context of pain. Conclusions: This emphasis on assessment misses other important aspects of safe and effective pain management, including those specific to opioid safety. Our findings inform ways to improve the long-term education of our medical and other graduates, thereby improving the health care of the populations they serve.

Sample-Based Models of Protein Energy Landscapes and Slow Structural Rearrangements.

Proteins often undergo slow structural rearrangements that involve several angstroms and surpass the nanosecond timescale. These spatiotemporal scales challenge physics-based simulations and open the way to sample-based models of structural dynamics. This article improves an understanding of current capabilities and limitations of sample-based models of dynamics. Borrowing from widely used concepts in evolutionary computation, this article introduces two conflicting aspects of sampling capability and quantifies them via statistical (and graphical) analysis tools. This allows not only conducting a principled comparison of different sample-based algorithms but also understanding which algorithmic ingredients to use as knobs via which to control sampling and, in turn, the accuracy and detail of modeled structural rearrangements. We demonstrate the latter by proposing two powerful variants of a recently published sample-based algorithm. We believe that this work will advance the adoption of sample-based models as reliable tools for modeling slow protein structural rearrangements.