Description of the PiCCO cardiac output monitor and the related physiology of the cardiovascular system and oxygen delivery.
about 10 years ago
I just wondered if any of you guys out there could help me out on this problem. I know that if systemic vascular resistance is decreased, the afterload will also decrease. Does this mean that stroke volume will therefore increase? What effect will it have on heart rate?
over 8 years ago
This month’s case is by Barbara J. Mroz, M.D. and Robin R. Preston, Ph.D., author of Lippincott’s Illustrated Reviews: .Physiology (ISBN: 9781451175677). For more information, or to purchase your copy, visit: http://tiny.cc/PrestonLIR, with 15% off using the discount code: MEDUCATION. The case below is followed by a choice of diagnostic tests. Select the one lettered selection that would be most helpful in diagnosing the patient’s condition. The Case A 54-year-old male 2 pack-per-day smoker presents to your office complaining of cough and shortness of breath (SOB). He reports chronic mild dyspnea on exertion with a daily cough productive of clear mucus. During the past week, his cough has increased in frequency and is now productive of frothy pink-tinged sputum; his dyspnea is worse and he is now short of breath sometimes even at rest. He has had difficulty breathing when lying flat in bed and has spent the past two nights sleeping upright in a recliner. On physical examination, he is a moderately obese male with a blood pressure of 180/80 mm Hg, pulse of 98, and respiratory rate of 22. His temperature is 98.6°F. He becomes winded from climbing onto the exam table. Auscultation of the lungs reveals bilateral wheezing and crackles in the lower posterior lung fields. There is pitting edema in the lower extremities extending up to the knees. Question Which if the following tests would be most helpful in confirming the correct diagnosis? A. Spirometry B. Arterial blood gas C. Complete blood count D. B-type natriuretic peptide blood test E. Electrocardiogram Answer? The correct answer is B-type natriuretic peptide blood test. Uncomfortable breathing, or feeling short of breath, is a common medical complaint with multiple causes. When approaching a patient with dyspnea, it is helpful to remember that normal breathing requires both a respiratory system that facilitates gas exchange between blood and the atmosphere, and a cardiovascular system that transports O2 and CO¬2 between the lungs and tissues. Dysfunction in either system may cause dyspnea, and wheezing (or bronchospasm) may be present in both cardiac and pulmonary disease. In this patient, the presence of lower extremity edema and orthopnea (discomfort when lying flat) are both suggestive of congestive heart failure (CHF). Elevated blood pressure (systolic of 180) and a cough productive of frothy pink sputum may also be associated symptoms. While wheezing could also be caused by COPD (chronic obstructive pulmonary disease) in the setting of chronic tobacco use, the additional exam findings of lung crackles and edema plus systolic hypertension are all more consistent with CHF. What does the B-type natriuretic peptide blood test tell us? When the left ventricle (LV) fails to maintain cardiac output (CO) at levels required for adequate tissue perfusion, pathways are activated to increase renal fluid retention. A rising plasma volume increases LV preload and sustains CO via the Frank-Starling mechanism. Volume loading also stimulates cardiomyocytes to release atrial- (ANP) and B-type (BNP) natriuretic peptides. BNP has a longer half-life than ANP and provides a convenient marker for volume loading. Plasma BNP levels are measured using immunoassay; levels >100 pg/mL are suggestive of overload resulting in heart failure. How does heart failure cause dyspnea? Increasing venous pressure increases mean capillary hydrostatic pressure and promotes fluid filtration from the vasculature. Excess filtration from pulmonary capillaries causes fluid accumulation within the alveoli (pulmonary edema) and interferes with normal gas exchange, resulting in SOB. Physical signs and symptoms caused by high volume loading include: (1) Lung crackles, caused by fluid within alveoli (2) Orthopnea. Reclining increases pulmonary capillary hydrostatic pressure through gravitational effects, worsening dyspnea when lying flat. (3) Pitting dependent edema caused by filtration from systemic capillaries, an effect also influenced by position (causing edema in the lower legs as in our ambulatory patient or in dependent areas like the sacrum in a bedridden patient). What would an electrocardiogram show? Heart failure can result in LV hypertrophy and manifest as a left axis deviation on an electrocardiogram (ECG), but some patients in failure show a normal ECG. An ECG is not a useful diagnostic tool for dyspnea or CHF per se. Wouldn’t spirometry be more suitable for diagnosing the cause of dyspnea in a smoker? Simple spirometry will readily identify the presence of airflow limitation (obstruction) as a cause of dyspnea. It's a valuable test to perform in any smoker and can establish a diagnosis of chronic obstructive pulmonary disease (COPD) if abnormal. While this wheezing patient is an active smoker who could have airflow obstruction, the additional exam findings above point more to a diagnosis of CHF. What would an arterial blood gas show? An arterial blood gas measures arterial pH, PaCO¬2, and PaO2. While both CHF and COPD could cause derangements in the values measured, these abnormalities would not necessarily be diagnostic (e.g., a low PaO2 could be seen in both conditions, as could an elevated PaCO¬2). Would a complete blood count provide useful information? A complete blood count could prove useful if anemia is a suspected cause of dyspnea. Test result BNP was elevated (842 pg/mL), consistent with CHF. Diuretic treatment was initiated to help reduce volume overload and an afterload reducing agent was started to lower blood pressure and improve systolic function.
Lippincott Williams & Wilkins
about 8 years ago
This book has been specifically designed with the needs of the student in mind. Lengthy explanations are avoided and the material is presented in a concise form that not only makes it easy to understand but also easy to remember and reproduce, which is precisely what the student needs. Key features - Short chapters are organized in the sequence preferred by most physiology teachers - The contents of each chapter are tailored to provide just enough material for a single lecture (occasionally two lectures), making it very handy for teachers. (The book contains 120 chapters) - Basics of relevant physics and chemistry are made extremely simple. This is welcomed by both physiology teachers and students, for efficient teaching and learning - Schematic diagrams in 3D perspective are employed to elucidate difficult anatomical concepts, including the gross structure of the brain - Simple analogies of difficult concepts are given, often comically illustrated. Apparent paradoxes are highlighted and simple answers are provided - Difficult topics are presented with elegant simplicity and brevity without compromising on the core concepts. These include membrane electrophysiology, electromyography, hemostatic balance, electrocardiography, cardiac output, hemodynamics, respiratory mechanics, counter-current multiplier system, body fluid and electrolyte balance, gastric acid secretion, calcitropic hormones, fetoplacental unit, memory and learning, synaptic transmission and sensorimotor mechanisms
about 6 years ago
Circulatory System Functions of the Heart Blood flow Through the Heart Cardiac Muscle Cells Intrinsic Conduction System Cardiac impulse Excitation-Contraction Conduction Pathway Electrocardiogram Cardiac Cycle Heart Sounds Cardiac Output Factors Affecting Cardiac Output -- Preload -- --Contractility -----Afterload Regulation of the Heart Primary control factors of the heart Congestive Heart Failure
over 5 years ago