About

Ravinder Mittal is a Professor of Medicine at UCSD, with a background in medical education from Delhi University and clinical training from Maulana Azad Medical College, New York Medical College, Lincoln Hospital, and Yale University. His research focuses on gastrointestinal motility, esophageal and anorectal function, and related disorders. He has led numerous clinical trials and research projects investigating mechanisms of esophageal dysfunction, fecal incontinence, and reflux disease, utilizing advanced imaging and novel methodologies. His work includes exploring the molecular basis of mechanosensitivity in esophageal neurons, the biomechanics of the antireflux barrier, and the development of innovative diagnostic techniques for esophageal and anorectal disorders. Dr. Mittal has contributed significantly to understanding the pathophysiology of conditions such as achalasia, functional dysphagia, and fecal incontinence, and has been involved in translating research findings into clinical applications.

Research topics

• Medicine
• Internal medicine
• Gastroenterology
• Geology
• Remote sensing
• Intensive care medicine

Selected publications

• A Review of Vagus Nerve Stimulation for Disease: Comprehensive Theory and Evidence for Mechanisms of Action

  Comprehensive physiology · 2026-03-04 · 1 citations

  articleOpen access

  Vagus nerve stimulation (VNS) is an established neuromodulatory therapy approved for epilepsy, depression, obesity, stroke rehabilitation, rheumatoid arthritis, migraine, and cluster headaches. Its therapeutic potential has expanded dramatically, with growing evidence supporting its efficacy across a wide spectrum of neurological, psychiatric, cardiovascular, immunological, metabolic, and gastrointestinal disorders. Despite this progress, the field has lacked a comprehensive synthesis that unifies mechanistic insights with translational applications across organ systems. This review addresses that gap by systematically integrating current knowledge in the multifactorial mechanisms through which VNS modulates central and peripheral functions, including neuromodulator release, synaptic plasticity, autonomic regulation, neuroimmune control, and endocrine integration. In addition, this review identifies key limitations of VNS, including biological heterogeneity, technical constraints, and methodological variability, and proposes future innovations such as selective fiber targeting, closed-loop systems, and artificial intelligence-guided personalization. By providing a rigorous, system-level overview of VNS mechanisms and their translational relevance, this article serves as a foundational resource for advancing the science and clinical deployment and helping illustrate future directions for precision neuromodulation and bioelectronic medicine.

  PublisherDOI

• Tu1238: REVERSAL OF CRURAL DIAPHRAGM DYSFUNCTION IN INTERSTITIAL LUNG DISEASE AFTER LUNG TRANSPLANT

  Gastroenterology · 2025-05-01

  articleSenior author
  PublisherDOI

• Genesis of Bolus Pressure During Primary Peristalsis: Key to Understanding “Functional Dysphagia”

  Neurogastroenterology & Motility · 2025-09-30 · 1 citations

  articleSenior authorCorresponding

  ABSTRACT Background During swallowing, the bolus passes through the esophagus during the relaxation phase of peristalsis—termed the bolus domain (BD)—before being cleared by sequential contractions. Bolus pressure (BP) in BD results from the compartmentalization of the bolus between the advancing contraction and the lower esophageal sphincter. This study aimed to evaluate the genesis of BP in the BD using high‐resolution impedance manometry (HRMZ), distension‐contraction plots, and high‐frequency ultrasound imaging in healthy subjects and “functional dysphagia (FD)” patients. Methods We analyzed HRMZ recordings from 30 healthy controls and 30 FD patients. Swallows of 5 mL and 10 mL saline were recorded in the supine and Trendelenburg positions. BP was measured in the BD (from upper esophageal sphincter relaxation to the 20‐mmHg isocontour onset of contraction). Automated tools extracted BP, luminal cross‐sectional area (CSA), and the percentage of BD area with CSA ≤ 50 mm 2 (no‐bolus area). Ultrasound images evaluated the timing of luminal distension and wall changes during the bolus domain and contraction. Key Results Controls showed luminal distension in most of the BD. On the other hand, FD patients exhibited higher BP and a significantly larger percentage of no‐bolus areas in the BD ( p < 0.001) compared to controls. ROC analysis revealed high diagnostic accuracy in distinguishing patients from controls (AUC = 0.898) for the percentage of no‐bolus area in the BD; a 16.5% threshold yielding 86.7% sensitivity and 80.0% specificity. Ultrasound imaging confirmed luminal collapse during the bolus domain in patients with FD. Conclusions & Inferences In patients with FD, bolus pressure is partly related to the compression of the manometry catheter by the esophageal wall. The proportion of BP‐positive, bolus‐negative areas in the BD distinguishes FD patients and controls.

  PublisherDOI

• Hysteresis of the lower esophageal sphincter: relevance to the pathogenesis of esophageal achalasia and its phenotypes

  American Journal of Physiology-Gastrointestinal and Liver Physiology · 2025-08-13

  articleOpen accessSenior author

  Hysteresis, a key biomechanical property of the esophagogastric junction (EGJ), may play a crucial role in achalasia pathogenesis. Using functional lumen imaging probe (FLIP) topography, we demonstrate that EGJ distensibility increases with repeated distensions, with subtype-dependent variability. Our findings suggest that hysteresis is associated with achalasia progression and treatment outcomes, offering novel insights into esophageal biomechanics. These results may guide refinements in FLIP-based diagnostics and inform future therapeutic approaches targeting determinants of hysteresis.

  PublisherOA PDFDOI

• Fibrosis in the Hiatus of Esophagus in Patients With Primary Esophageal Motor Disorders: Radiomic Analysis

  Neurogastroenterology & Motility · 2025-05-20 · 2 citations

  articleOpen access1st authorCorresponding

  INTRODUCTION: In normal subjects, the esophagus and crus of the diaphragm slide relative to each other during esophageal peristalsis, which is not the case in patients with achalasia esophagus. OBJECTIVE: To examine the tissue characteristics of the esophageal hiatus in patients with achalasia esophagus, high amplitude esophageal contractions (HAEC), esophagogastric junction outflow obstruction (EGJOO), and normal subjects using radiomics analysis of the CT images. METHODS: A large number of medical records (1221 controls, 409 achalasia, 562 EGJOO, and 349 HAEC) were screened to identify subjects with a CT scan of the abdomen/chest in their record that met the pre-determined criteria. Using multiplanar rotation of CT images, the esophageal hiatus was visualized in a 2D plane. The grayscale intensity distributions (GSID) of the three regions of interest, i.e., (1) subcutaneous adipose tissue, (2) a posterior spine muscle (marker of fibro-connective tissue), and (3) esophageal hiatus were determined. RESULTS: No differences in the mean GSID of subcutaneous adipose tissue and muscle were found among the four groups. On the other hand, the esophageal hiatus mean GSID was significantly higher in the three patient groups compared to controls. The GSIDs were higher in achalasia patients than in HAEC and EGJOO patients. The mean GSI of the hiatus was closer to that of the muscle with greater overlap between the hiatus and muscle in the three patient groups; the overlap was greater in achalasia as compared to HAEC and EGJOO patients. CONCLUSION: A higher GSI of the hiatus with greater overlap between the hiatus and muscle suggests an increase in fibro-connective tissue in the esophageal hiatus of patients with primary esophageal motility disorders (EMD). We propose that fibrosis in the esophageal hiatus restricts axial separation between the LES and crural diaphragm, which may be important in the pathogenesis of esophageal motor disorders.

  PublisherOA PDFDOI

• In Memoriam: Richard W. <scp>McCallum</scp> , <scp>MD</scp> , <scp>FACP</scp> , <scp>FRACP</scp> ( <scp>AUST</scp> ), <scp>FACG</scp> —A Legend in Gastric Physiology and Pathophysiology

  Neurogastroenterology & Motility · 2025-09-17

  articleOpen access

  Richard W. McCallum, MD, Professor and Founding Chair of the Department of Internal Medicine, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center at El Paso, Texas, an accomplished physician scientist, mentor, doctor of doctors, pioneer, and an esteemed member of the ANMS, passed away peacefully on August 21st, 2025. He was 80 years old and led a full life. A native of Brisbane, Australia, Richard's father, Dr. Norman McCallum, was a distinguished dermatologist. Richard received his medical degree from the Queensland Medical School, University of Queensland, and then moved to the USA to pursue postgraduate medical education, with the intent of returning to Australia. He interned at the Charity Hospital (New Orleans) and then completed his internal medicine residency at Barnes Hospital (St. Louis). Here, he met and married his lifelong bride, Mary Beth. He completed his gastroenterology fellowship at the University of California, Los Angeles, under the tutelage of Drs. Morton Grossman, John Walsh, Charlie Code, and Jon Isenberg, the “kings” of GI physiology, followed by a short faculty stint at UCLA. Thereafter, he was recruited to Yale University, where he served as a faculty member for almost a decade. In 1985, he was appointed chief of gastroenterology at the University of Virginia in Charlottesville, VA, and was endowed with the Paul Janssen Professorship in Medicine. The next 10 years were his golden decade as he built a strong clinical and basic science GI division. In an era when nobody believed that Helicobacter pylori could cause peptic ulcer disease, Dr. McCallum had the foresight to recruit Dr. Barry Marshall, who proved this link and was subsequently awarded the Nobel Prize in Physiology or Medicine. In 1995, Dr. McCallum was recruited to Kansas University Medical Center as Chief of Gastroenterology/Hepatology, and in 2009 became Professor and Founding Chair of the Department of Internal Medicine at El Paso, Texas. In 2015, he was also appointed an honorary Professor of Medicine at his alma mater, University of Queensland, Brisbane, Australia. A true out-of-the-box thinker, he transformed ideas into innovations that changed the lives of countless patients. He collaborated with Dr. Jiande Chen to develop a portable gastric pacemaker. Later, under Dr. McCallum's direction, the first gastric electrical stimulation (GES) system, “Enterra” for gastroparesis was implanted on April 1, 1998, at Kansas University. Since then, tens of thousands of patients have received this therapy—a testament to his foresight as a pioneer. Under his leadership, his team has carried out a large number of clinical trials, testing new pharmacologic treatments and pushing forward cutting-edge diagnostic tools such as wireless motility capsules for neurogastroenterology and motility diseases. As one of the founding members of the NIH/NIDDK Gastroparesis Clinical Research Consortium, Dr. McCallum was continuously funded for more than 15 years and helped to raise awareness of gastroparesis. In the consortium, he spearheaded research on domperidone, joint hypermobility syndrome and gastroparesis, and evaluation of Carnett's sign for abdominal pain in gastroparesis. He was often the highest enroller in clinical trials. He was extremely nurturing of colleagues, an example of which is Drs. Irene Sarosiek and Jerzy Sarosiek, who worked with him for more than 30 years, as well as inspiring others including Ravinder Mittal, MD, and Jiande Chen, PhD. He has authored more than 500 peer-reviewed articles, 130 textbook chapters, and has edited over 15 scientific textbooks, including the widely used Handbook on Gastrointestinal Motility and Disorders of Gut-Brain Interactions, which he co-edited with Drs. Satish Rao and Henry Parkman. He held multiple patents. The impact of Dr. McCallum's work is reflected by the many honors and awards he has received throughout his distinguished career. This includes the Chancellor's Council Distinguished Research Award from the Texas Tech University System (2015), the Gold Medal for Excellence in Academic Medicine from the Texas Medical Association (2016), and the Washington University Medical Center Resident/Fellow Alumni Achievement Award (2017). Perhaps the best recognition of Dr. McCallum's legacy was the Neurogastroenterology & Motility (NGM) Section Research Mentor Award from the American Gastroenterological Association Institute Council (2018) and the Mentor of the Year from the Southern Society of Clinical Investigation (2017). He also received the Founders' Medal from the Southern Society for Clinical Investigation, the ACP Laureate Award, and the Award for Service to the El Paso Community for creating and championing the RotaCare Clinic, El Paso. He served as the President of the Southern Society for Clinical Investigation, the International Society of Electrogastrography, the Kansas GI Society, and the El Paso County Medical Society. He was also Editor-in-Chief of an international online journal (Gastrointestinal Disorders) and the Journal of Investigative Medicine (JIM), the official publication for the American Federation for Clinical Research. Richard will be sorely missed for his clinical acumen, sharp intellect, his joie de vivre, and inimitable presence at the scientific meetings. Dr. McCallum's legacy lives on through the countless patients he cared for and the lives he saved; the innumerable trainees he mentored, and the enduring impact of his work in gastrointestinal motility. Beyond academia, he was an ardent sports enthusiast who never missed an NCAA basketball game, Kansas football match, or Australian cricket test. He took pride in sharing his NCAA bracket each year and fiercely competed with young and old alike. A passionate tennis player, he also loved to travel, meet friends, ballroom dance, attend the symphony, and even body surf. Well-known for his tireless work ethic, it was not uncommon to receive emails from him after midnight, his most productive time of the day! He is survived by his beloved wife Mary Beth, his daughters Elizabeth and Heather, sons-in-law Marshall and Franklin, his son Yates and daughter-in-law Lexi, and his most cherished grandchildren: Summer, Huck, Zeke, Colette, Ren, and Dash, and sister Sue Roberts. All authors have contributed equally for this article. The authors declare no conflicts of interest.

  PublisherOA PDFDOI

• Tu1278: FUNCTIONAL DYSPHAGIA WITH REDUCED ESOPHAGEAL DISTENSION: THE POSSIBLE ROLE OF THE STRIATED MUSCLE REGION IN ESOPHAGEAL DISTENSION

  Gastroenterology · 2025-05-01

  article
  PublisherDOI

• Tu1250: GENESIS OF BOLUS PRESSURE DURING PERISTALSIS: KEY TO UNDERSTANDING “FUNCTIONAL DYSPHAGIA”

  Gastroenterology · 2025-05-01

  articleSenior author
  PublisherDOI

• Crural and costal diaphragm function during emesis

  American Journal of Physiology-Gastrointestinal and Liver Physiology · 2025-05-17

  articleOpen access

  Although the diaphragm is known as a primary respiratory muscle, the two diaphragm sections, the costal and crural, have notably different functions. This study elucidates the essential role of the crural diaphragm during emesis, a gastrointestinal process. During emesis, the crural diaphragm abandons respiratory function and transmutes to act as an esophageal sphincter. Meanwhile, the costal diaphragm continues ventilatory function.

  PublisherDOI

• Striated Muscle Contractility and Distal Esophageal Distensibility Define Novel Subtypes of Functional Dysphagia

  Clinical Gastroenterology and Hepatology · 2025-12-01

  article
  PublisherDOI

Recent grants

• Anal Sphincter Morphology & Function Assessed with Novel MR Imaging Techniques

  NIH · $1.7M · 2011–2016

• Novel Electrical Impedance Methodology to Understand Functional Dysphagia

  NIH · $2.5M · 2016–2022

• NIH Grant R03DK052094

  NIH · $151k · 2000

• Novel Applications of Sarcomere Length to Improve Anal Continence

  NIH · 2009–2012

• NIH Grant R01DK051604

  NIH · $1.2M · 2003

Frequent coauthors

• Valmik Bhargava

  112 shared

• Ali Zifan

  University of California, San Diego

  86 shared

• Yanfen Jiang

  Huazhong University of Science and Technology

  56 shared

• Jianmin Liu

  Shandong University

  45 shared

• Arash Babaei

  Shiraz University of Medical Sciences

  40 shared

• Richard W. McCallum

  Texas Tech University

  38 shared

• Melissa M. Ledgerwood

  University of California, San Diego

  29 shared

• Melissa M. Ledgerwood-Lee

  University of California, San Diego

  28 shared

Education

• Ph.D., Molecular and Computational Biology

  University of California, San Diego

  2005

• M.S., Molecular and Computational Biology

  University of California, San Diego

  2001

• B.S., Biology

  University of California, San Diego

  1999