Asthma: Clinical Findings

Yu Yan – Asthma – Final.pptx
Episodic dyspnea (shortness of breath)Asthma: Clinical FindingsLegend:Published December 17, 2012 on www.thecalgaryguide.comMechanismPathophysiologySign/Symptom/Lab FindingComplicationsAuthor: Yan YuReviewers:Jason BasermanJennifer AuNaushad Hirani** MD at time of publicationNoseConjunctivitisPatients need to voluntarily contract their expiratory muscles faster and more forcefully to effectively expireEosinophils infiltrate:Associated allergic eosinophil responseExpiratory Wheeze(high-pitched expiratory sound)Runny nose, sneezing, etcEyes? oxygenation of blood (hypoxemia)Narrower airways ? turbulent airflow, heard on auscultationIf severe:? ventilation of alveoli Respiratory centers ? rate of breathing to compensateDuring expiration, positive pleural pressure squeezes on airways ? ?? airway obstructionVariable, sporadic airway obstruction in response to triggersDuring severe attacks:Prolonged expiratory phase of breathingRhinitis/ sinusitisChest tightnessNote: Asthma attacks often have two phases: An immediate attack (within 0-2 hours of the trigger, due to acute release of histamine from mast cells)A delayed attack (4-12 hours after exposure to the trigger, due to eosinophil infiltration of airways).Keep the possibility of a delayed attack in mind when treating patients in Emergency!Red itchy eyes, visual blurringSkinSkin rash, hivesAtopic dermatitisPatient compensates by activating accessory respiratory muscles to ? thoracic volumeVisible contraction of neck muscles (Scalene, sternocleidomastoids)??? airway obstruction on expiration, lungs take more time to emptyTachypneaHeart rate ? to improve perfusion of tissueTachycardiaNote: Asthma should be suspected in children experiencing dyspnea with multiple episodes of Upper Respiratory Tract Infections or Croup.Asthma Episodic airway constriction and airflow obstruction, due to hyper-responsiveness to certain triggers (see slide on asthma pathogenesis)Note: Symptoms often worse at night or early in the morning.Gas is trapped within alveoli ? hyperinflates lungsVentilating larger lungs needs more effort
Agonizing acetylcholine receptors on bronchial smooth muscle will constrict airways if they are “hyper-responsive”Normal PFT, CXRAsthma: Findings on InvestigationsLegend:Published December 17, 2012 on www.thecalgaryguide.comMechanismPathophysiologySign/Symptom/Lab FindingComplicationsAuthor: Yan YuReviewers:Jason BasermanJennifer AuNaushad Hirani** MD at time of publicationDuring an asthma attack:FEV1 <80%, FEV1/FVC < 0.7(on spirometry)Asthma Episodic airway constriction and airflow obstruction, due to hyper-responsiveness to certain triggers (see slide on asthma pathogenesis)Total expiration time takes longer than normalPatients can present when they are not suffering from an attackDuring expiration, positive pleural pressure squeezes on airways ? ? obstructionAbbreviations:PFT: pulmonary function testFEV1: Forced expiratory volume in 1 secondFVC: Forced vital capacityPaO2: partial pressure of O2 in arterial bloodPaCO2: partial pressure of CO2 in arterial bloodStimulate airway smooth muscle dilation with a short-acting beta agonist (SABA) (Bronchodilator response test)Large ? in FEV1 (>15-20%, often fully restored)Investigations for Asthma include:Spirometry (Pulmonary function test), before and after bronchodilatorBronchial hyper-responsiveness testArterial Blood Gasses (ABGs)Chest X-Ray (CXR): frontal and lateralMucus plugs airways/alveoliPeak Expiratory Flow (PEF) meter given to patients, to monitor lung function over several daysVariablity in PEF >20% day to dayEpisodic asthma attacks ? variable expiratory flow rates on different daysSpirometry and chest x-rays can be doneBronchial hyper-responsivenessTest (high sensitivity!)In asthma, airway smooth muscle is not so physically damaged; thus responsive to SABAMethacholine, an acetylcholine-receptor agonist, is inhaledIf low doses can? FEV1 by 20%If high doses cannot ? FEV1 by 20%Rules out asthma (airways not hyper-responsive)Suggests asthma(high false positive rate)? oxygenation of blood (hypoxemia)? ventilation of alveoli Respiratory centers ? breathing rate to try to ? PaO2Airway smooth muscle constrictsHyperventilation ? breath out more CO2Hypocapnia (? PaCO2)Caution: if PaCO2 is normal or high during an asthma attack, be alarmed: this means the patient’s respiratory muscles are getting tired, and patient is ventilating/ breathing less, which may lead to respiratory failure (see relevant slide)? PaO2 (usually mild)Respiratory AlkalosisLess arterial CO2 ? blood acidity? airway lumen diameter
Asthma: PathogenesisLegend:Published December 17, 2012 on www.thecalgaryguide.comMechanismPathophysiologySign/Symptom/Lab FindingComplicationsAuthor: Yan YuReviewers:Jason BasermanJennifer AuNaushad Hirani** MD at time of publicationAsthma: Defined as airway hyper-responsiveness causing variable and reversible airflow obstructionDelayed response (4-12 hrs)Environmental factors(i.e. excess hygiene, fewer siblings, antibiotics within the first two years)Genetic factors(i.e. HLA gene mutations, defects in bronchial airway epithelium)Upper respiratory tract infections (URTIs)Atopy: predisposition to allergic hyper-sensitivity in airwaysFirst exposure to triggers* sensitizes helper T cellsSecond exposure to triggersAllergens (pollen, animal dander, dust, mold, etc)Cold airExerciseAir pollution, cigarette smoke, other chemicalsTriggers of airway hyper-responsiveness include:Stimulation of B-cells to produce IgE, which binds to mast cell surfacesAllergens cross-link IgEs on mast cellsActivated Helper-T cells & IgE-sensitized mast cells now line the airwaysMast cells release histamines, leukotrienes, and other inflammatory mediatorsBronchial smooth muscle contractionVasodilation ? edemaAirway obstructionEarly response (0-2 hrs)Activated mast cells & helper T cells release cytokinesInduce maturation of granular WBCs like eosinophilsEosinophils migrate into:AirwaysEyesNoseBronchiole constrictionConjunctivitisRhinitisAsthmaGoblet cell hyperplasia ? ? mucus secretionDrugs (aspirin, NSAIDs, Beta-blockers)
113 kB / 719 words