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APS Physiology in Medicine reviews, 1998-2011

Review articles explicating basic science for clinicians. From the American Physiological Society.

Physiology in Medicine

Physiology in Medicine: Review articles from the American Physiological Society

Physiology in Medicine (PIM) appeared as a bimonthly series of articles published jointly by APS and Annals of Internal Medicine. It was published in Annals through 2010.

The aim of this series is to provide practicing MDs and/or researchers an up-to-date physiological understanding of disease with the proper application of new molecular models and tools. Articles published in this series are intended to provide a thoughtful and lucid linkage of science to the patient.

Future PIM articles will be published in the various APS journals, with each journal soliciting PIM articles in their area of focus.

Physiology in Medicine: 2012-present

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Cheung, K., Rathbone, A., Melanson, M., Trier, J., Ritsma, B. R., & Allen, M. D. (2021). Pathophysiology and management of critical illness polyneuropathy and myopathyJournal of Applied Physiology130(5), 1479–1489.

Critical illness-associated weakness (CIAW) is an umbrella term used to describe a group of neuromuscular disorders caused by severe illness. It can be subdivided into three major classifications based on the component of the neuromuscular system (i.e. peripheral nerves or skeletal muscle or both) that are affected. This includes critical illness polyneuropathy (CIP), critical illness myopathy (CIM), and an overlap syndrome, critical illness polyneuromyopathy (CIPNM). It is a common complication observed in people with critical illness requiring intensive care unit (ICU) admission. Given CIAW is found in individuals experiencing grave illness, it can be challenging to study from a practical standpoint. However, over the past 2 decades, many insights into the pathophysiology of this condition have been made. Results from studies in both humans and animal models have found that a profound systemic inflammatory response and factors related to bioenergetic failure as well as microvascular, metabolic, and electrophysiological alterations underlie the development of CIAW. Current management strategies focus on early mobilization, achieving euglycemia, and nutritional optimization. Other interventions lack sufficient evidence, mainly due to a dearth of large trials. The goal of this Physiology in Medicine article is to highlight important aspects of the pathophysiology of these enigmatic conditions. It is hoped that improved understanding of the mechanisms underlying these disorders will lead to further study and new investigations for novel pharmacologic, nutritional, and exercise-based interventions to optimize patient outcomes.

Habashi, N. M., Camporota, L., Gatto, L. A., & Nieman, G. (2021). Functional pathophysiology of SARS-CoV-2-induced acute lung injury and clinical implicationsJournal of Applied Physiology130(3), 877–891.

The worldwide pandemic caused by the SARS-CoV-2 virus has resulted in over 84,407,000 cases, with over 1,800,000 deaths when this paper was submitted, with comorbidities such as gender, race, age, body mass, diabetes, and hypertension greatly exacerbating mortality. This review will analyze the rapidly increasing knowledge of COVID-19-induced lung pathophysiology. Although controversial, the acute respiratory distress syndrome (ARDS) associated with COVID-19 (CARDS) seems to present as two distinct phenotypes: type L and type H. The "L" refers to low elastance, ventilation/perfusion ratio, lung weight, and recruitability, and the "H" refers to high pulmonary elastance, shunt, edema, and recruitability. However, the LUNG-SAFE (Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure) and ESICM (European Society of Intensive Care Medicine) Trials Groups have shown that ∼13% of the mechanically ventilated non-COVID-19 ARDS patients have the type-L phenotype. Other studies have shown that CARDS and ARDS respiratory mechanics overlap and that standard ventilation strategies apply to these patients. The mechanisms causing alterations in pulmonary perfusion could be caused by some combination of 1) renin-angiotensin system dysregulation, 2) thrombosis caused by loss of endothelial barrier, 3) endothelial dysfunction causing loss of hypoxic pulmonary vasoconstriction perfusion control, and 4) hyperperfusion of collapsed lung tissue that has been directly measured and supported by a computational model. A flowchart has been constructed highlighting the need for personalized and adaptive ventilation strategies, such as the time-controlled adaptive ventilation method, to set and adjust the airway pressure release ventilation mode, which recently was shown to be effective at improving oxygenation and reducing inspiratory fraction of oxygen, vasopressors, and sedation in patients with COVID-19.

Nanduri, J., Semenza, G. L., & Prabhakar, N. R. (2017). Epigenetic changes by DNA methylation in chronic and intermittent hypoxia. American Journal of Physiology. Lung Cellular and Molecular Physiology313(6), L1096–L1100.

DNA methylation of cytosine residues is a well-studied epigenetic change, which regulates gene transcription by altering accessibility for transcription factors. Hypoxia is a pervasive stimulus that affects many physiological processes. The circulatory and respiratory systems adapt to chronic sustained hypoxia, such as that encountered during a high-altitude sojourn. Many people living at sea level experience chronic intermittent hypoxia (IH) due to sleep apnea, which leads to cardiovascular and respiratory maladaptation. This article presents a brief update on emerging evidence suggesting that changes in DNA methylation contribute to pathologies caused by chronic IH and potentially mediate adaptations to chronic sustained hypoxia by affecting the hypoxia-inducible factor (HIF) signaling pathway.

Varyani, F., Fleming, J. O., & Maizels, R. M. (2017). Helminths in the gastrointestinal tract as modulators of immunity and pathologyAmerican Journal of Physiology. Gastrointestinal and Liver Physiology312(6), G537–G549.

Helminth parasites are highly prevalent in many low- and middle-income countries, in which inflammatory bowel disease and other immunopathologies are less frequent than in the developed world. Many of the most common helminths establish themselves in the gastrointestinal tract and can exert counter-inflammatory influences on the host immune system. For these reasons, interest has arisen as to how parasites may ameliorate intestinal inflammation and whether these organisms, or products they release, could offer future therapies for immune disorders. In this review, we discuss interactions between helminth parasites and the mucosal immune system, as well as the progress being made toward identifying mechanisms and molecular mediators through which it may be possible to attenuate pathology in the intestinal tract.

Nieman, G. F., Satalin, J., Kollisch-Singule, M., Andrews, P., Aiash, H., Habashi, N. M., & Gatto, L. A. (2017). Physiology in Medicine: Understanding dynamic alveolar physiology to minimize ventilator-induced lung injuryJournal of Applied Physiology122(6), 1516–1522.

Acute respiratory distress syndrome (ARDS) remains a serious clinical problem with the main treatment being supportive in the form of mechanical ventilation. However, mechanical ventilation can be a double-edged sword: if set improperly, it can exacerbate the tissue damage caused by ARDS; this is known as ventilator-induced lung injury (VILI). To minimize VILI, we must understand the pathophysiologic mechanisms of tissue damage at the alveolar level. In this Physiology in Medicine paper, the dynamic physiology of alveolar inflation and deflation during mechanical ventilation will be reviewed. In addition, the pathophysiologic mechanisms of VILI will be reviewed, and this knowledge will be used to suggest an optimal mechanical breath profile (MBP: all airway pressures, volumes, flows, rates, and the duration that they are applied at both inspiration and expiration) necessary to minimize VILI. Our review suggests that the current protective ventilation strategy, known as the "open lung strategy," would be the optimal lung-protective approach. However, the viscoelastic behavior of dynamic alveolar inflation and deflation has not yet been incorporated into protective mechanical ventilation strategies. Using our knowledge of dynamic alveolar mechanics (i.e., the dynamic change in alveolar and alveolar duct size and shape during tidal ventilation) to modify the MBP so as to minimize VILI will reduce the morbidity and mortality associated with ARDS.

Wang, T., Gross, C., Desai, A. A., Zemskov, E., Wu, X., Garcia, A. N., Jacobson, J. R., Yuan, J. X., Garcia, J. G., & Black, S. M. (2017). Endothelial cell signaling and ventilator-induced lung injury: molecular mechanisms, genomic analyses, and therapeutic targetsAmerican journal of physiology. Lung cellular and molecular physiology312(4), L452–L476.

Mechanical ventilation is a life-saving intervention in critically ill patients with respiratory failure due to acute respiratory distress syndrome (ARDS). Paradoxically, mechanical ventilation also creates excessive mechanical stress that directly augments lung injury, a syndrome known as ventilator-induced lung injury (VILI). The pathobiology of VILI and ARDS shares many inflammatory features including increases in lung vascular permeability due to loss of endothelial cell barrier integrity resulting in alveolar flooding. While there have been advances in the understanding of certain elements of VILI and ARDS pathobiology, such as defining the importance of lung inflammatory leukocyte infiltration and highly induced cytokine expression, a deep understanding of the initiating and regulatory pathways involved in these inflammatory responses remains poorly understood. Prevailing evidence indicates that loss of endothelial barrier function plays a primary role in the development of VILI and ARDS. Thus this review will focus on the latest knowledge related to 1) the key role of the endothelium in the pathogenesis of VILI; 2) the transcription factors that relay the effects of excessive mechanical stress in the endothelium; 3) the mechanical stress-induced posttranslational modifications that influence key signaling pathways involved in VILI responses in the endothelium; 4) the genetic and epigenetic regulation of key target genes in the endothelium that are involved in VILI responses; and 5) the need for novel therapeutic strategies for VILI that can preserve endothelial barrier function.

Polverino, F., Seys, L. J., Bracke, K. R., & Owen, C. A. (2016). B cells in chronic obstructive pulmonary disease: moving to center stage. American journal of physiology. Lung cellular and molecular physiology, 311(4), L687–L695.

Chronic inflammatory responses in the lungs contribute to the development and progression of chronic obstructive pulmonary disease (COPD). Although research studies focused initially on the contributions of the innate immune system to the pathogenesis of COPD, more recent studies have implicated adaptive immune responses in COPD. In particular, studies have demonstrated increases in B cell counts and increases in the number and size of B cell-rich lymphoid follicles in COPD lungs that correlate directly with COPD severity. There are also increases in lung levels of mediators that promote B cell maturation, activation, and survival in COPD patients. B cell products such as autoantibodies directed against lung cells, components of cells, and extracellular matrix proteins are also present in COPD lungs. These autoantibodies may contribute to lung inflammation and injury in COPD patients, in part, by forming immune complexes that activate complement components. Studies of B cell-deficient mice and human COPD patients have linked B cells most strongly to the emphysema phenotype. However, B cells have protective activities during acute exacerbations of COPD by promoting adaptive immune responses that contribute to host defense against pathogens. This review outlines the evidence that links B cells and B cell-rich lymphoid follicles to the pathogenesis of COPD and the mechanisms involved. It also reviews the potential and limitations of B cells as therapeutic targets to slow the progression of human COPD.

Allen, M. D., Doherty, T. J., Rice, C. L., & Kimpinski, K. (2016). Physiology in Medicine: neuromuscular consequences of diabetic neuropathy. Journal of applied physiology121(1), 1–6.

Diabetic polyneuropathy (DPN) refers to peripheral nerve dysfunction as a complication of diabetes mellitus. This condition is relatively common and is likely a result of vascular and/or metabolic disturbances related to diabetes. In the early or less severe stages of DPN it typically results in sensory impairments but can eventually lead to major dysfunction of the neuromuscular system. Some of these impairments may include muscle atrophy and weakness, slowing of muscle contraction, and loss of power and endurance. Combined with sensory deficits these changes in the motor system can contribute to decreased functional capacity, impaired mobility, altered gait, and increased fall risk. There is no pharmacological disease-modifying therapy available for DPN and the mainstay of treatment is linked to treating the diabetes itself and revolves around strict glycemic control. Exercise therapy (including aerobic, strength, or balance training-based exercise) appears to be a promising preventative and treatment strategy for patients with DPN and those at risk. The goal of this Physiology in Medicine article is to highlight important and overlooked dysfunction of the neuromuscular system as a result of DPN with an emphasis on the physiologic basis for that dysfunction. Additionally, we sought to provide information that clinicians can use when following patients with diabetes or DPN including support for the inclusion of exercise-based therapy as an effective, accessible, and inexpensive form of treatment.

Stabler, C. T., Lecht, S., Mondrinos, M. J., Goulart, E., Lazarovici, P., & Lelkes, P. I. (2015). Revascularization of decellularized lung scaffolds: principles and progressAmerican journal of physiology. Lung cellular and molecular physiology, 309(11), L1273–L1285.

There is a clear unmet clinical need for novel biotechnology-based therapeutic approaches to lung repair and/or replacement, such as tissue engineering of whole bioengineered lungs. Recent studies have demonstrated the feasibility of decellularizing the whole organ by removal of all its cellular components, thus leaving behind the extracellular matrix as a complex three-dimensional (3D) biomimetic scaffold. Implantation of decellularized lung scaffolds (DLS), which were recellularized with patient-specific lung (progenitor) cells, is deemed the ultimate alternative to lung transplantation. Preclinical studies demonstrated that, upon implantation in rodent models, bioengineered lungs that were recellularized with airway and vascular cells were capable of gas exchange for up to 14 days. However, the long-term applicability of this concept is thwarted in part by the failure of current approaches to reconstruct a physiologically functional, quiescent endothelium lining the entire vascular tree of reseeded lung scaffolds, as inferred from the occurrence of hemorrhage into the airway compartment and thrombosis in the vasculature in vivo. In this review, we explore the idea that successful whole lung bioengineering will critically depend on 1) preserving and/or reestablishing the integrity of the subendothelial basement membrane, especially of the ultrathin respiratory membrane separating airways and capillaries, during and following decellularization and 2) restoring vascular physiological functionality including the barrier function and quiescence of the endothelial lining following reseeding of the vascular compartment. We posit that physiological reconstitution of the pulmonary vascular tree in its entirety will significantly promote the clinical translation of the next generation of bioengineered whole lungs.

Mulugeta, S., Nureki, S., & Beers, M. F. (2015). Lost after translation: insights from pulmonary surfactant for understanding the role of alveolar epithelial dysfunction and cellular quality control in fibrotic lung diseaseAmerican journal of physiology. Lung cellular and molecular physiology309(6), L507–L525.

Dating back nearly 35 years ago to the Witschi hypothesis, epithelial cell dysfunction and abnormal wound healing have reemerged as central concepts in the pathophysiology of idiopathic pulmonary fibrosis (IPF) in adults and in interstitial lung disease in children. Alveolar type 2 (AT2) cells represent a metabolically active compartment in the distal air spaces responsible for pulmonary surfactant biosynthesis and function as a progenitor population required for maintenance of alveolar integrity. Rare mutations in surfactant system components have provided new clues to understanding broader questions regarding the role of AT2 cell dysfunction in the pathophysiology of fibrotic lung diseases. Drawing on data generated from a variety of model systems expressing disease-related surfactant component mutations [surfactant proteins A and C (SP-A and SP-C); the lipid transporter ABCA3], this review will examine the concept of epithelial dysfunction in fibrotic lung disease, provide an update on AT2 cell and surfactant biology, summarize cellular responses to mutant surfactant components [including endoplasmic reticulum (ER) stress, mitochondrial dysfunction, and intrinsic apoptosis], and examine quality control pathways (unfolded protein response, the ubiquitin-proteasome system, macroautophagy) that can be utilized to restore AT2 homeostasis. This integrated response and its derangement will be placed in the context of cell stress and quality control signatures found in patients with familial or sporadic IPF as well as non-surfactant-related AT2 cell dysfunction syndromes associated with a fibrotic lung phenotype. Finally, the need for targeted therapeutic strategies for pulmonary fibrosis that address epithelial ER stress, its downstream signaling, and cell quality control are discussed.

Maraki, M. I., & Sidossis, L. S. (2015). Physiology in Medicine: update on lifestyle determinants of postprandial triacylglycerolemia with emphasis on the Mediterranean lifestyleAmerican journal of physiology. Endocrinology and metabolism309(5), E440–E449.

This review updates the effect of lifestyle on plasma triacylglycerols (TAG) in the postprandial state, commonly reported as postprandial lipemia (PPL), an independent risk factor for cardiovascular diseases (CVD). Numerous studies have shown that Mediterranean diet may reduce PPL. However, most of these studies were focused on the type of fat (i.e., monounsaturated fat from olive oil), and the other components of the Mediterranean lifestyle were neglected. Physical activity, an integral part of this lifestyle, is widely investigated on its own and shown to reduce PPL. In addition, preliminary results of studies examining other Mediterranean "ingredients", such as legumes, fish, and herbs, showed additional benefits; however, data on the long-term effects are limited. More studies are needed to confirm short-term results and investigate the effects of the whole Mediterranean lifestyle on PPL and whether these effects mediate its protective role on CVD. Moreover, investigation of the effects in nonhealthy populations and the underlying mechanisms would be clinically helpful in individualizing the appropriate intervention.

Luks A. M. (2015). Physiology in Medicine: A physiologic approach to prevention and treatment of acute high-altitude illnesses. Journal of applied physiology118(5), 509–519.

With the growing interest in adventure travel and the increasing ease and affordability of air, rail, and road-based transportation, increasing numbers of individuals are traveling to high altitude. The decline in barometric pressure and ambient oxygen tensions in this environment trigger a series of physiologic responses across organ systems and over a varying time frame that help the individual acclimatize to the low oxygen conditions but occasionally lead to maladaptive responses and one or several forms of acute altitude illness. The goal of this Physiology in Medicine article is to provide information that providers can use when counseling patients who present to primary care or travel medicine clinics seeking advice about how to prevent these problems. After discussing the primary physiologic responses to acute hypoxia from the organ to the molecular level in normal individuals, the review describes the main forms of acute altitude illness--acute mountain sickness, high-altitude cerebral edema, and high-altitude pulmonary edema--and the basic approaches to their prevention and treatment of these problems, with an emphasis throughout on the physiologic basis for the development of these illnesses and their management.

Potoka, K. P., & Gladwin, M. T. (2015). Vasculopathy and pulmonary hypertension in sickle cell diseaseAmerican journal of physiology. Lung cellular and molecular physiology308(4), L314–L324.

Sickle cell disease (SCD) is an autosomal recessive disorder in the gene encoding the β-chain of hemoglobin. Deoxygenation causes the mutant hemoglobin S to polymerize, resulting in rigid, adherent red blood cells that are entrapped in the microcirculation and hemolyze. Cardinal features include severe painful crises and episodic acute lung injury, called acute chest syndrome. This population, with age, develops chronic organ injury, such as chronic kidney disease and pulmonary hypertension. A major risk factor for developing chronic organ injury is hemolytic anemia, which releases red blood cell contents into the circulation. Cell free plasma hemoglobin, heme, and arginase 1 disrupt endothelial function, drive oxidative and inflammatory stress, and have recently been referred to as erythrocyte damage-associated molecular pattern molecules (eDAMPs). Studies suggest that in addition to effects of cell free plasma hemoglobin on scavenging nitric oxide (NO) and generating reactive oxygen species (ROS), heme released from plasma hemoglobin can bind to the toll-like receptor 4 to activate the innate immune system. Persistent intravascular hemolysis over decades leads to chronic vasculopathy, with ∼10% of patients developing pulmonary hypertension. Progressive obstruction of small pulmonary arterioles, increase in pulmonary vascular resistance, decreased cardiac output, and eventual right heart failure causes death in many patients with this complication. This review provides an overview of the pathobiology of hemolysis-mediated endothelial dysfunction and eDAMPs and a summary of our present understanding of diagnosis and management of pulmonary hypertension in sickle cell disease, including a review of recent American Thoracic Society (ATS) consensus guidelines for risk stratification and management.

Gonzalez, L. M., Moeser, A. J., & Blikslager, A. T. (2015). Animal models of ischemia-reperfusion-induced intestinal injury: progress and promise for translational researchAmerican journal of physiology. Gastrointestinal and liver physiology308(2), G63–G75.

Research in the field of ischemia-reperfusion injury continues to be plagued by the inability to translate research findings to clinically useful therapies. This may in part relate to the complexity of disease processes that result in intestinal ischemia but may also result from inappropriate research model selection. Research animal models have been integral to the study of ischemia-reperfusion-induced intestinal injury. However, the clinical conditions that compromise intestinal blood flow in clinical patients ranges widely from primary intestinal disease to processes secondary to distant organ failure and generalized systemic disease. Thus models that closely resemble human pathology in clinical conditions as disparate as volvulus, shock, and necrotizing enterocolitis are likely to give the greatest opportunity to understand mechanisms of ischemia that may ultimately translate to patient care. Furthermore, conditions that result in varying levels of ischemia may be further complicated by the reperfusion of blood to tissues that, in some cases, further exacerbates injury. This review assesses animal models of ischemia-reperfusion injury as well as the knowledge that has been derived from each to aid selection of appropriate research models. In addition, a discussion of the future of intestinal ischemia-reperfusion research is provided to place some context on the areas likely to provide the greatest benefit from continued research of ischemia-reperfusion injury.

Koo, P., Gartman, E. J., Sethi, J. M., & McCool, F. D. (2015). Physiology in Medicine: physiological basis of diaphragmatic dysfunction with abdominal hernias-implications for therapy. Journal of applied physiology118(2), 142–147.

An incisional hernia is a common complication after abdominal surgery. Complaints of dyspnea in this population may be attributed to cardiopulmonary dysfunction or deconditioning. Large abdominal incisional hernias, however, may cause diaphragm dysfunction and result in dyspnea, which is more pronounced when standing (platypnea). The use of an abdominal binder may alleviate platypnea in this population. We discuss the link between diaphragm dysfunction and the lack of abdominal wall integrity and how abdominal wall support partially restores diaphragm function.

Chatterjee, S., Nieman, G. F., Christie, J. D., & Fisher, A. B. (2014). Shear stress-related mechanosignaling with lung ischemia: lessons from basic research can inform lung transplantationAmerican journal of physiology. Lung cellular and molecular physiology307(9), L668–L680.

Cessation of blood flow represents a physical event that is sensed by the pulmonary endothelium leading to a signaling cascade that has been termed "mechanotransduction." This paradigm has clinical relevance for conditions such as pulmonary embolism, lung bypass surgery, and organ procurement and storage during lung transplantation. On the basis of our findings with stop of flow, we postulate that normal blood flow is "sensed" by the endothelium by virtue of its location at the interface of the blood and vessel wall and that this signal is necessary to maintain the endothelial cell membrane potential. Stop of flow is sensed by a "mechanosome" consisting of PECAM-VEGF receptor-VE cadherin that is located in the endothelial cell caveolae. Activation of the mechanosome results in endothelial cell membrane depolarization that in turn leads to activation of NADPH oxidase (NOX2) to generate reactive oxygen species (ROS). Endothelial depolarization additionally results in opening of T-type voltage-gated Ca(2+) channels, increased intracellular Ca(2+), and activation of nitric oxide (NO) synthase with resultant generation of NO. Increased NO causes vasodilatation whereas ROS provide a signal for neovascularization; however, with lung transplantation overproduction of ROS and NO can cause oxidative injury and/or activation of proteins that drive inflammation and cell death. Understanding the key events in the mechanosignaling cascade has important lessons for the design of strategies or interventions that may reduce injury during storage of donor lungs with the goal to increase the availability of lungs suitable for donation and thus improving access to lung transplantation.

Seccombe, L. M., & Peters, M. J. (2014). Physiology in medicine: acute altitude exposure in patients with pulmonary and cardiovascular diseaseJournal of applied physiology116(5), 478–485.

Travel is more affordable and improved high-altitude airports, railways, and roads allow rapid access to altitude destinations without acclimatization. The physiology of exposure to altitude has been extensively described in healthy individuals; however, there is a paucity of data pertaining to those who have reduced reserve. This Physiology in Medicine article discusses the physiological considerations relevant to the safe travel to altitude and by commercial aircraft in patients with pulmonary and/or cardiac disease.

Dempsey, J. A., Xie, A., Patz, D. S., & Wang, D. (2014). Physiology in medicine: obstructive sleep apnea pathogenesis and treatment--considerations beyond airway anatomyJournal of applied physiology116(1), 3–12.

We review evidence in support of significant contributions to the pathogenesis of obstructive sleep apnea (OSA) from pathophysiological factors beyond the well-accepted importance of airway anatomy. Emphasis is placed on contributions from neurochemical control of central respiratory motor output through its effects on output stability, upper airway dilator muscle activation, and arousability. In turn, we consider the evidence demonstrating effective treatment of OSA via approaches that address each of these pathophysiologic risk factors. Finally, a case is made for combining treatments aimed at both anatomical and ventilatory control system deficiencies and for individualizing treatment to address a patient's own specific risk factors.

Muller, M. D., Reed, A. B., Leuenberger, U. A., & Sinoway, L. I. (2013). Physiology in medicine: peripheral arterial disease. Journal of applied physiology, 115(9), 1219–1226.

Peripheral arterial disease (PAD) is an atherosclerotic condition that can provoke symptoms of leg pain ("intermittent claudication") during exercise. Because PAD is often observed with comorbid conditions such hypertension, dyslipidemia, diabetes, cigarette smoking, and/or physical inactivity, the pathophysiology of PAD is certainly complex and involves multiple organ systems. Patients with PAD are at high risk for myocardial infarction, stroke, and all-cause mortality. For this reason, a better physiological understanding of the pathogenesis and treatment options for PAD patients is necessary and forms the basis of this Physiology in Medicine review.

Chan, M. V., & Wallace, J. L. (2013). Hydrogen sulfide-based therapeutics and gastrointestinal diseases: translating physiology to treatmentsAmerican journal of physiology. Gastrointestinal and liver physiology, 305(7), G467–G473.

Hydrogen sulfide (H2S) is a gaseous meditator that has various physiological and pathophysiological roles in the body. It has been shown to be an important mediator of gastrointestinal (GI) mucosal defense and contributes significantly to repair of damage and resolution of inflammation. Synthesis of H2S increases markedly after mucosal injury, and inhibition of H2S in such circumstances leads to delayed healing and exacerbated inflammation. The beneficial effects of H2S may be attributable to its ability to elevate mucosal blood flow, prevent leukocyte-endothelial adhesion, reduce oxidative stress, and stimulate angiogenesis. The use of H2S-donating agents and inhibitors of the key enzymes contributing to H2S synthesis have provided strong evidence for the importance of H2S in enhancing mucosal resistance to damage, as well as modulating inflammation and repair. In recent years, significant evidence has been generated to support the notion that these positive aspects of H2S can be exploited in drug design, particularly for arthritis, inflammatory bowel disease, and colon cancer chemoprevention. Thus novel H2S-based therapies have been shown to be effective anti-inflammatories that can promote the resolution of inflammation and accelerate the healing of GI ulcers. Encouraging results have already been seen experimentally with a mesalamine derivative and with H2S-releasing derivatives of nonsteroidal anti-inflammatory drugs.

Christiaans, S. C., Wagener, B. M., Esmon, C. T., & Pittet, J. F. (2013). Protein C and acute inflammation: a clinical and biological perspectiveAmerican journal of physiology. Lung cellular and molecular physiology305(7), L455–L466.

The protein C system plays an active role in modulating severe systemic inflammatory processes such as sepsis, trauma, and acute respiratory distress syndrome (ARDS) via its anticoagulant and anti-inflammatory properties. Plasma levels of activated protein C (aPC) are lower than normal in acute inflammation in humans, except early after severe trauma when high plasma levels of aPC may play a mechanistic role in the development of posttraumatic coagulopathy. Thus, following positive results of preclinical studies, a clinical trial (PROWESS) with high continuous doses of recombinant human aPC given for 4 days demonstrated a survival benefit in patients with severe sepsis. This result was not confirmed by subsequent clinical trials, including the recently published PROWESS-SHOCK trial in patients with septic shock and a phase II trial with patients with nonseptic ARDS. A possible explanation for the major difference in outcome between PROWESS and PROWESS-SHOCK trials is that lung-protective ventilation was used for the patients included in the recent PROWESS-SHOCK, but not in the original PROWESS trial. Since up to 75% of sepsis originates from the lung, aPC treatment may not have added enough to the beneficial effect of lung-protective ventilation to show lower mortality. Thus whether aPC will continue to be used to modulate the acute inflammatory response in humans remains uncertain. Because recombinant human aPC has been withdrawn from the market, a better understanding of the complex interactions between coagulation and inflammation is needed before considering the development of new drugs that modulate both coagulation and acute inflammation in humans.

Munir, K. M., Chandrasekaran, S., Gao, F., & Quon, M. J. (2013). Mechanisms for food polyphenols to ameliorate insulin resistance and endothelial dysfunction: therapeutic implications for diabetes and its cardiovascular complicationsAmerican journal of physiology. Endocrinology and metabolism305(6), E679–E686.

The rising epidemic of diabetes is a pressing issue in clinical medicine worldwide from both healthcare and economic perspectives. This is fueled by overwhelming increases in the incidence and prevalence of obesity. Obesity and diabetes are characterized by both insulin resistance and endothelial dysfunction that lead to substantial increases in cardiovascular morbidity and mortality. Reciprocal relationships between insulin resistance and endothelial dysfunction tightly link metabolic diseases including obesity and diabetes with their cardiovascular complications. Therefore, therapeutic approaches that target either insulin resistance or endothelial dysfunction alone are likely to simultaneously improve both metabolic and cardiovascular pathophysiology and disease outcomes. Moreover, combination therapies with agents targeting distinct mechanisms are likely to have additive or synergistic benefits. Conventional therapies for diabetes and its cardiovascular complications that are both safe and effective are insufficient to meet rising demand. Large, robust, epidemiologic studies demonstrate beneficial metabolic and cardiovascular health effects for many functional foods containing various polyphenols. However, precise molecular mechanisms of action for food polyphenols are largely unknown. Moreover, translation of these insights into effective clinical therapies has not been fully realized. Nevertheless, some functional foods are likely sources for safe and effective therapies and preventative strategies for metabolic diseases and their cardiovascular complications. In this review, we emphasize recent progress in elucidating molecular, cellular, and physiological actions of polyphenols from green tea (EGCG), cocoa (ECG), and citrus fruits (hesperedin) that are related to improving metabolic and cardiovascular pathophysiology. We also discuss a rigorous comprehensive approach to studying functional foods that is essential for developing novel, effective, and safe medications derived from functional foods that will complement existing conventional drugs.

Noah, D. L., & Noah, J. W. (2013). Adapting global influenza management strategies to address emerging virusesAmerican journal of physiology. Lung cellular and molecular physiology305(2), L108–L117.

Death by respiratory complications from influenza infections continues to be a major global health concern. Antiviral drugs are widely available for therapy and prophylaxis, but viral mutations have resulted in resistance that threatens to reduce the long-term utility of approved antivirals. Vaccination is the best method for controlling influenza, but vaccine strategies are blunted by virus antigenic drift and shift. Genetic shift in particular has led to four pandemics in the last century, which have prompted the development of efficient global surveillance and vaccination programs. Although the influenza pandemic of 2009 emphasized the need for the rapid standardization of global surveillance methods and the preparation and dissemination of global assay standards for improved reporting and diagnostic tools, outbreaks of novel influenza strains continue to occur, and current efforts must be enhanced by aggressive public education programs to promote increased vaccination rates in the global population. Recently, a novel H7N9 avian influenza virus with potential to become a pandemic strain emerged in China and was transmitted from animals to humans with a demonstrated >20% mortality rate. Sporadic outbreaks of highly lethal avian virus strains have already increased public awareness and altered annual vaccine production strategies to prevent the natural adaption of this virus to human-to-human transmission. Additional strategies for combating influenza include advancement of new antivirals for unexploited viral or host cellular targets; novel adjuvants and alternate vaccine delivery systems; and development of universal protein, DNA, or multivalent vaccines designed to increase immune responsiveness and enhance public health response times.

Vogiatzis, I., & Zakynthinos, S. (2013). The physiological basis of rehabilitation in chronic heart and lung disease. Journal of applied physiology115(1), 16–21.

Cardiopulmonary rehabilitation is recognized as a core component of management of individuals with congestive heart failure (CHF) or chronic obstructive pulmonary disease (COPD) that is designed to improve their physical and psychosocial condition without impacting on the primary organ impairment. This has lead the scientific community increasingly to believe that the main effects of cardiopulmonary rehabilitative exercise training are focused on skeletal muscles that are regarded as dysfunctional in both CHF and COPD. Accordingly, following completion of a cardiopulmonary rehabilitative exercise training program there are important peripheral muscular adaptations in both disease entities, namely increased capillary density, blood flow, mitochondrial volume density, fiber size, distribution of slow twitch fibers, and decreased lactic acidosis and vascular resistance. Decreased lactic acidosis at a given level of submaximal exercise not only offsets the occurrence of peripheral muscle fatigue, leading to muscle task failure and muscle discomfort, but also concurrently mitigates the additional burden on the respiratory muscles caused by the increased respiratory drive, thereby reducing dyspnea sensations. Furthermore in patients with COPD, exercise training reduces the degree of dynamic lung hyperinflation leading to improved arterial oxygen content and central hemodynamic responses, thus increasing systemic muscle oxygen availability. In patients with CHF, exercise training has beneficial direct and reflex sympathoinhibitory effects and favorable effects on normalization of neurohumoral excitation. These physiological benefits apply to all COPD and CHF patients independently of the degree of disease severity and are associated with improved exercise tolerance, functional capacity, and quality of life.

Wagner P. D. (2013). Physiology in Medicine--Déjà vu all over againJournal of applied physiology114(7), 833.