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Resp. Patho

Respiratory Pathophysiology

Primary Function of Respiratory System Exchange gasses between the environment (air) and the blood in the lungs. Deliver oxygen (O2) to tissue and remove waste gas – carbon dioxide (CO2).
Common Problems-airway Obstruction, occlusion
Common Problems-ventilation Gas trapping, ineffective chest excursion,
Common Problems-oxygenation Inability to diffuse gas across alveolar capillary
Defense Mechanisms-Upper respiratory tract mucosa and nasal hairs = humidification, removes particles. Epiglottis = prevents aspiration/foreign bodies from entering trachea/bronchial tree.
Defense Mechanisms-Lower respiratory tract Mucous blanket – protects trachea, bronchi, traps foreign particles. Cilia – propel mucus and entrapped particles upward to oro/nasopharynx. Irritant receptors – nose = sneeze; trachea/bronchi = cough [upper/lower].
Gas-Exchange airways Respiratory bronchioles – no cilia, no goblet cells, little smooth muscle – Alveolar ducts – lead to – Alveoli – primary gasexchange units of the lung
Pulmonary Blood Flow Desaturated blood from right ventricle (RV) to lungs – Capillary beds feed alveoli, exchange gas – Return saturated blood to left atrium (LA)
Pulmonary & Bronchial Circulation Facilitates gas exchange,Delivers nutrients to lung tissue
Systemic Circulation Saturated hemoglobin travels to L heart, then into circulation. At peripheral capillary level, O2 and CO2 exchanged. Returned to R heart
Hemodynamics Low pressure vs. high pressure across lung. Pulmonary catheter used to more precisely measure pressure in R heart as a measure of L heart function.
Lung Volume & Capacities Tital volume (VT)=volume inhaled/exhaled during normal breathing. Expiratory reserve volume (ERV)=volume expired from relaxed lung from forceful exhalation. Inspiratory reserve volume (IRV)=volume of forceful inhalation. Residual volume (RV)=remaining
Muscles & Chest Excursion Expansion of thorax creates negative pleural pressure = ­lung volume. At end of inspiration, normal elasticity retract lung = elastic recoil. Air is moved into and out of lung via the airways in a bellows like fashion.Lungs have natural tendency to
Lung Compliance Measure of lung and chest wall distensibility. Determined by alveolar surface tension and elastic recoil of lung/chest wall. Abnormally high = lung has lost elastic recoil, e.g.emphysema. Abnormally low = “stiff” lung, e.g. ARDS,pneumonia,pulm edema.
Airway resistance Similar to resistance found in blood flow – Related to airway length, area & gas characteristics – Normally low ~ ½ or more from nose – Most common cause is edema, obstruction (mucus plugging), bronchospasm.
Neurological Control of Breathing Automatic and voluntary control – Brain stem – basic automatic rhythm – Medulla – control diaphragm and inspiratory intercostal muscle – CNS chemoreceptors and peripheral chemoreceptors in carotids and aortic bodies respond to D pH, PaCO2, PaO2
Gas Transport - O2 Ventilation of lungs – Diffusion of O2 across alveolocapillary membrane to blood – Attachment of O2 to hemoglobin – Transport via LA/LV of heart to arteries, arterioles, capillaries – Diffusion of O2 across capillaries to cells
Gas Transport - CO2 Diffusion of CO2 from cells to capillaries as carbonic acid – Transport via venous system to RA/RV then to pulmonary artery – Diffusion of CO2 across alveolocapillary membrane – Removal of CO2 through exhalation
Alveolocapillary Membrane Large surface area, very thin membrane.Partial pressure of oxygen is higher in alveolar gas PAO2 than in capillary blood PaO2. Create high diffusion gradient.Blood remains in capillary 0.75 sec but only 0.25 sec needed to equilibrate across cap mem
Arterial Oxygenation During equilibration, O2 dissolves into capillary plasma Binds with available hemoglobin until saturated (SaO2) Small residual dissolved O2 in plasma 20 ml of O2 in 100 ml of blood
Gas Pressure Result of random collisions of gas molecules L-space = ­^ pressure for constant volume ^temperature = ­^pressure for constant volume Sea level barometric pressure = 760 mm Hg (sum of all gasses and water vapor pressure)
Gas Pressure Characteristics Composition of air: O2 = 20.9%, N = 78.1%, trace gasses = remainder Water vapor pressure = 47 mm Hg Partial pressure of O2 at sea level = 0.209 x (760 – 47) = 159 mm Hg
Blood Gasses Arterial PaO2 100 PaCO2 40 SaO2 96-98% Venous PvO2 40 PvCO2 46 SvO2 75%
Oxygen Delivery Cellular respiration ­^ oxygen demand = ­^ cardiac output AND/OR higher tissue uptake (except myocardium and brain tissue) [short term] ^oxygen demand = ­^hemoglobin production [long term]
Oxyhemoglobin In lungs – hemoglobin has affinity for oxygen (oxyhemoglobin association) = saturation At tissues – hemoglobin is release(oxyhemoglobin dissociation) = desaturation Conditions that cause greater release of oxygen -L-pH,H-temp,H-CO2
Diagnostic Tests Spirometry – Arterial blood gas – (mixed-venous continuous monitoring) – Chest XRay or CT scan
Conditions that increase affinity L-temp, L-CO2, carboxyhemoglobin, increase pH
Created by: cmindel