Important Physiological Concepts Research Articles

Integration of physiology in a curriculum on human structure: a snapshot of the cardiovascular block.

With the gradual shift from discipline-based to competency-based medical education, the integrated curriculum has become a popular model for connecting basic science and clinical content in undergraduate medical education. Despite its popularity, there are concerns that important physiological concepts are not adequately addressed. We describe the spiral integration of physiology content in the 5-week Cardiovascular block of our Homeostasis course at the Zucker School of Medicine. We also describe our approach to incorporating physiology into an integrated, constructed response, short-answer assessment format. Our approach to spiral integration consists of rotating lab stations that highlight the distinction between normal and abnormal states, linked with appropriate clinical interventions. Physiology is at the core of integration in any curriculum and the basis of all applied fields of medicine, hence our approach is that teaching structural relationships would not be valuable without consideration of its functions, which can then be utilized in discussion of clinical presentations, imaging, and relevant pathologies. Likewise, our integrated assessments require the students to compose their answers to the questions from scratch, which creates a shift in mode of students' preparation from rote memorizations to more cognitive processing that enhances critical thinking.

Comprehensive Review of Current Pain Management in Rib Fractures With Practical Guidelines for Clinicians.

Rib fractures are present in 15% of all traumas and 60% of patients with chest traumas. Rib fractures are not life-threatening in isolation, but they can be quite painful which leads to splinting and compromise of respiratory function. Splinting limits the ability of a patient to take a deep breath, which leads to atelectasis, atelectasis to poor secretion removal, and poor secretion removal leads to pneumonia. Pneumonia is the common pathway to respiratory failure in patients with rib fractures. It is noted that in the elderly, each rib fracture increases developing pneumonia by 27% and the risk of dying by 19%. From a public health perspective, rib fractures have long-term implications with only 59% of patients returning to work at 6 months. In this review we will examine the state of art as it currently exists with regard to the management of pain associated with rib fractures. Included in this overview will be a brief review of the anatomy of the thorax and some important physiologic concepts, the latest trends in pharmacologic and noninvasive means of managing rib pain, a special section on epidural anesthesia, some other alternative invasive methods of pain control, and a review of the recent literature on rib plating. Finally, a practical, easy to follow guideline, to manage the patient with pain from rib fractures will be presented.

Oxygen supply capacity in animals evolves to meet maximum demand at the current oxygen partial pressure regardless of size or temperature.

The capacity to extract oxygen from the environment and transport it to respiring tissues in support of metabolic demand reportedly has implications for species' thermal tolerance, body size, diversity and biogeography. Here, we derived a quantifiable linkage between maximum and basal metabolic rate and their oxygen, temperature and size dependencies. We show that, regardless of size or temperature, the physiological capacity for oxygen supply precisely matches the maximum evolved demand at the highest persistently available oxygen pressure and this is the critical PO2 for the maximum metabolic rate, Pcrit-max For most terrestrial and shallow-living marine species, Pcrit-max is the current atmospheric pressure, 21 kPa. Any reduction in oxygen partial pressure from current values will result in a calculable decrement in maximum metabolic performance. However, oxygen supply capacity has evolved to match demand across temperatures and body sizes and so does not constrain thermal tolerance or cause the well-known reduction in mass-specific metabolic rate with increasing body mass. The critical oxygen pressure for resting metabolic rate, typically viewed as an indicator of hypoxia tolerance, is, instead, simply a rate-specific reflection of the oxygen supply capacity. A compensatory reduction in maintenance metabolic costs in warm-adapted species constrains factorial aerobic scope and the critical PO2 to a similar range, between ∼2 and 6, across each species' natural temperature range. The simple new relationship described here redefines many important physiological concepts and alters their ecological interpretation.

Effect of a small-group, active learning, tutorial-based, in-course enrichment program on student performance in medical physiology.

Physiology is one of the major foundational sciences for the medical curriculum. This discipline has proven challenging for students to master due to ineffective content acquisition and retention. Preliminary data obtained from a survey completed by "low-performance" students (those maintaining a grade average below the passing mark of 70%) at Morehouse School of Medicine reported that students lacked the ability to adequately recognize and extract important physiological concepts to successfully navigate multiple-choice assessments. It was hypothesized that a specially designed, small-group, active learning, physiology in-course enrichment program would minimize course assessment failure rates by enhancing the ability of low-performance students to effectively identify important course content, successfully perform on multiple-choice assessments, and, thereby, improve overall course performance. Using self-report surveys, study skills and test-taking deficiencies limiting successful comprehension of course material and examination performance were identified. Mini-quiz assessments and assignments in formulating multiple-choice examination questions were given to help students recognize and solidify core concepts and improve test-taking ability. Lastly, self-report surveys evaluated the effectiveness of the enrichment program on overall course performance. Results showed a marked improvement in student confidence levels with regards to approaching multiple-choice assessments, and a significant improvement in grades achieved in the physiology component of the first-year curriculum, as 100% of participants achieved a final passing grade average of ≥70%. It was concluded that students became more proficient in identifying, understanding, and applying core physiological concepts and more successful in mastering multiple-choice questions.

Advances in coronary physiology.

Pressure-wire technology, most typically fractional flow reserve (FFR), has provided interventional cardiologists with a means of determining the physiological importance of a stenosis during angiography. There has been renewed interest in coronary physiology in the light of guideline recognition, ongoing clinical research and new technologies changing the paradigm of how assessment is performed in the catheter laboratory. We reflect on FFR, with regards the potential effects of changing hemodynamics on FFR and the latest evidence with regards to outcomes. We also review the instantaneous wave-free ratio (iFR), a new pressure-only index, measured at rest, that is under active evaluation in several international randomized controlled trials. We review the accumulated evidence and discuss the important physiological concepts between pressure and flow that underlie the approach to using resting indices. Finally we investigate future developments, including physiological mapping with iFR-Pullback and the potential to predict the hemodynamic effect of stenting.

Cardiovascular support in preterm infants: A survey of practices in Australia and New Zealand

Management of haemodynamic instability in premature neonates and selection of inotropic therapy are protocol driven, and therapeutic choices lack scientific validation. The aim of this study was to characterise practices related to the management of haemodynamic instability in premature infants. An electronic web-based questionnaire was emailed to all neonatologists and advanced trainees in Australia and New Zealand. Respondents were presented with a series of questions related to the management of hypotension in a 1-day-old, extremely low birthweight infant, and opinions were collected. Survey response rate was 65% (114/176). Haemodynamically significant ductus arteriosus, systemic blood flow and left ventricular afterload were considered the most important physiologic concepts by 81, 68 and 50%, respectively. After initial crystalloid replacement, the next step in management reported included a second bolus (35%), dobutamine (28%), dopamine (17%) or clinician-performed cardiac ultrasound (CPCU) (20%). In the setting of hypotension resistant to dobutamine and dopamine, the most common strategies were to perform CPCU (57%), or administer hydrocortisone (39%), epinephrine (3.5%) or milrinone (<1%). The majority (66%) of respondents felt that premature infants are over-treated on the basis of presumed hypotension, while 83% felt that performing a CPCU would enhance clinical decision-making. Wide variation in the approach to management of haemodynamic instability in extremely low birthweight infants was identified. Haemodynamic information provided by a CPCU was considered highly desirable by the majority of the respondents.

Issues Involved in the Process of Developing a Medical Food

The creation of a medical food with potential health benefits for a particular patient population is a surprisingly complex process. Fortunately, the developmental process for a specific medical food is not as rigorous or as tightly regulated as that of a pharmaceutical agent. However, numerous factors unique to the enteral formulation of a new product come into play, such as physical/chemical compatibility, pH, stability, bioavailability, decay, and even palatability. Additional considerations such as strength of health benefit claims, packaging or presentation, and marketability determine the ultimate commercialization and whether a product ends up being released to the public. A full understanding of the development, substantiation, and commercialization of a medical food is necessary for important physiologic concepts in nutrition therapy to end up as part of the therapeutic regimen at the bedside of the critically ill obese patient.

Obesity and the lung: 3 · Obesity, respiration and intensive care

Obesity is a major problem from a public health perspective and a difficult practical matter for intensivists. The obesity pandemic has required treating clinicians to develop an appreciation of the...

Passing on the legacy: teaching capillary filtration and developing presentation skills using classic papers

Capillary filtration is a key area in the understanding of cardiovascular function and has both physiological and pathophysiological relevance in nearly every organ system. This article describes how classic papers in the Legacy collection of American Physiological Society publications can be used in a teaching symposium exploring the evidence supporting current concepts of capillary fluid exchange. Individual students are given papers to read, edit, and present to the class. The appropriate selection and sequencing of these papers allows the development of important physiological concepts to be tracked. A series of papers concerned with capillary filtration is suggested, and the contribution of each to the developing story is outlined. This approach allows students to develop critical and presentation skills and provides them with a case study of the scientific method as it is applied to physiology as well as establishing an appropriate knowledge base concerning the role of hydrostatic and oncotic forces in capillary fluid exchange. Relevant teaching points are explored further using questions based on a figure from one of the three classic papers used: "Microinjection studies of capillary permeability: II. The relationship between capillary pressure and the rate at which fluid passes through the walls of single capillaries," by E. M. Landis (Am J Physiol 82: 217-238, 1927).

Formative assessment can be fun as well as educational

An understanding of the hormonal basis of normal growth and development, including the changes occurring at puberty, is important foundation knowledge for contemporary medical practice in most fields of medicine. A quiz, testing the important physiological concepts of growth and puberty, was designed using the format of the well-known television game "Who Wants to Be a Millionaire." An evaluation of this formative assessment activity revealed that a cohort of first-year undergraduate medical students valued learning with peers in an enjoyable, interactive environment, where they were able to admit to uncertainties and clarify answers. It also showed that making an educational activity fun need not detract from the focus of giving feedback on learning. Formative assessment, known to produce learning gains in a range of educational settings, is an important activity in contemporary medical education. With a greater emphasis on self-directed learning and less well-defined curriculum boundaries, feedback helps students to understand and apply the important physiological concepts that underpin the practice of medicine.

Emerging Concepts in the Evaluation of Ventilatory Limitation During Exercise: The Exercise Tidal Flow-Volume Loop

Traditionally, ventilatory limitation (constraint) during exercise has been determined by measuring the ventilatory reserve or how close the minute ventilation (VE) achieved during exercise (i.e., ventilatory demand) approaches the maximal voluntary ventilation (MVV) or some estimate of the MVV (i.e., ventilatory capacity). More recently, it has become clear that rarely is the MVV breathing pattern adopted during exercise and that the VE/MVV relationship tells little about the specific reason(s) for ventilatory constraint. Although it is not a new concept, by measuring the tidal exercise flow-volume (FV) loops (extFVLs) obtained during exercise and plotting them according to a measured end-expiratory lung volume (EELV) within the maximal FV envelope (MFVL), more specific information is provided on the sources (and degree) of ventilatory constraint. This includes the extent of expiratory flow limitation, inspiratory flow reserve, alterations in the regulation of EELV (dynamic hyperinflation), end-inspiratory lung volume relative to total lung capacity (or tidal volume/inspiratory capacity), and a proposed estimate of ventilatory capacity based on the shape of the MFVL and the breathing pattern adopted during exercise. By assessing these types of changes, the degree of ventilatory constraint can be quantified and a more thorough interpretation of the cardiopulmonary exercise response is possible. This review will focus on the potential role of plotting the extFVL within the MFVL for determination of ventilatory constraint during exercise in the clinical setting. Important physiologic concepts, measurements, and limitations obtained from this type of analysis will be defined and discussed.

Integration of reflex responses in the control of blood pressure and vascular resistance

This overview presents four important concepts related to integration of cardiovascular reflexes. 1. 1. Activation of sympathetic efferent activity to various organs is nonuniform. Simultaneous activation of both sympathetic and parasympathetic efferent pathways may occur. These effects are evident in the responses to diving and stimulation of chemoreceptors. Both diving and stimulation of chemoreceptors decrease heart rate and myocardial oxygen demand and cause intense peripheral vasoconstriction, which limits oxygen delivery to the periphery. Stimulation of chemoreceptors also causes active coronary vasodilatation favoring an optimal distribution of blood flow to the heart. 2. 2. When two groups of sensory afferents that cause opposing responses are activated simultaneously, the effect of one sensory afferent system will override the other. During hypotension caused by occlusion of the circumflex coronary artery, the reflexes originating in cardiac vagal afferents are inhibitory and reverse the effect of unloading of arterial baroreceptors. The net effect is not simply blockade of sympathetic vasoconstrictor effects, but withdrawal of sympathetic tone. Thus, the cardiac “reflex” overrides the effects of arterial hypotension. 3. 3. The reflex response to activation of one group of sensory afferents may be dependent on the input from other groups of afferents to the medullary neurons. At low carotid sinus pressure, the “gains” of the chemoreceptor and somatic reflexes are augmented. The cardiopulmonary vagal afferents modulate the arterial baroreceptor reflex as well as the chemoreceptor and somatic reflexes. The cardiopulmonary vagal afferents, when activated, suppress the sympathetic excitatory response to arterial hypotension, to chemoreceptor stimulation and to somatic afferent stimulation. Another important interaction is that of the thermal receptors which, when activated by heat, suppress the vasoconstrictor response to arterial hypotension in cutaneous more than in muscular beds. 4. 4. Stimulation of sensory afferent receptors may be modified by drugs or humoral factors acting on the receptor itself or on the chemical and mechanical characteristics of the tissues surrounding the receptor. Acetylstrophanthidin injected into the circumflex coronary artery potentiates the sympathetic inhibitory response to activation of cardiac sensory afferents (vagal afferents) by volume loading and by occlusion of the circumflex. The sensitization may explain in part the action digitalis has on the peripheral circulation in heart failure. The clinical implications of these four important physiologic concepts are discussed.

Disorders of the Respiratory System,

Cumming and Semple have undertaken a formidable task in attempting to write a text that encompasses a discussion of both normal lung physiology and human lung disease. Despite their admirable intentions, they have failed to produce a book that will be of value as a standard reference for either medical students or graduate physicians. This book is divided into two sections—normal lung structure and function, and pathophysiology and human disease. Both sections are subject to the same general criticism. In attempting to write a text of such broad scope while at the same time applying reasonable limits to the length of the book, the authors have been forced to discuss all topics in a very general, superficial manner. Although they are aiming primarily at medical students, this lack of critical discussion detracts markedly from the value of the book for any audience. In the initial section, important physiologic concepts are