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43 Cards in this Set
- Front
- Back
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Define Respiratory Distress
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Labored breathing, characterized by an inappropriate degree of effort to breath based on rate, rhythm, and subjective evaluation of respiratory effort.
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Define dyspnea:
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sensation of arduous, uncomfortable, or difficult breathing that occurs wen the demand for ventilation exceeds the patient's ability to respond. (Is a symptom, not a clinical sign-so dyspnea is not technically applicable to veterinary medicine).
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Clinical Signs of Respiratory Distress:
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flared nostrils, exercise intolerance, inactivity, exaggerated abdominal effort, abnormal respiratory noise (stridor), anxiousness, extended head and neck, cyanosis and synchronis pumping of the anus with the respiratory cycle.
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Respiratory Distress: Causes
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Inefficient exchange of oxygen and carbon dioxide caused by pulmonary disease, airway obstruction, or impairment of muscles and supporting structures necessary for ventilation.
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Causes of increased respiration not related to impaired gas exchange:
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Pain, metabolic acidosis, high environmental temperature.
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Where is the center controller for respiration?
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Medulla
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What does the center controller of respiration control?
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Depth and rate of respiration
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What do central chemoreceptors primarily respond to?
What do peripheral chemoreceptors primarily respond to? |
Central: hypercapnia
Peripheral: hypoxia and hypercapnia/acidemia |
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Concerning Respiration Control: the BBB is permeable to what, impermeable to what?
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Permeable: carbon dioxide
Impermeable: Bicarbonate and hydrogen ions |
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The severity of acidosis in the intracerebral interstitial fluid caused by hyercapnia is amplified by what two features in the CNS?
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1) hypercapnia produces cerebral vasodilation, increasing delivery of CO2 to the CNS
2) cerebrospinal fluid has poor buffering capacity because of low total protein concentrations. |
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What are the most famous peripheral chemoreceptors, where are they located?
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Carotid bodies: bifurcation of the common carotid artery
Aortic bodies: near aortic arch |
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Where do the peripheral chemoreceptors relay info to? How?
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The Central Controller via glossopharyngeal and vagus nerves.
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How does the respiratory pattern differ in hypoxia from hypercapnia?
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Hypoxia: increase in respiratory frequency. Recruitment of inspiratory muscles.
Hypercapnia: Triggers an elevation in tital volume. Potentiates the activity of inspiratory and expiratory muscles. |
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When could oxygen supplementation harm a patient in respiratory distress (not talking paraquat toxicity here).
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In patient suffering from hypoxemia, hypercapnia and acidosis, oxygen will decrease venilatory drive (due to peripheral chemoreceptors), but decreased drive could exacerbate respiratory acidosis.
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How do receptors in the upper and lower respiratory tract respond to mechanical and chemical stimuli?
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Relay afferent info to the central controller via vagus.
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What does expiramental vagal blockade do to horses with tachypnea/pulmonary disease?
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Abolishes tachypnea.
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What do pulmonary stretch receptors do?Where are they located?
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AKA slow adapting stretch receptors, located within the smooth muscle fibersin the walls of the trachea and bronchi. Stimulated by pulmonary inflation and inhibit further inflation of the lung (Hering-Breuer reflex). Conversely, at the end of expiration, they stimulate inspiration.
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Where are irritant receptors? What do they do?
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Believed to be located between epithelial cells of the conducting airways. Stimulation by noxious stimuli triggers bronchoconstriction, cough, tachypnea, mucus production and release of inflammatory mediators.
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How does the vagus nerve contribute to the symptoms of allergic airway disease?
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Vagal-mediated parasympathetic stimulation causes airway narrowing.
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What can you to give rapid relief to horses with COPD?
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Administration of atropine. This demonstrates the important role of parasympathetic bronchoconstriction in the pathogenesis of this disease. Can also give a B2 adrenergic agonist.
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What receptors are upregulated in COPD, and contribute to bronchoconstriction?
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Alpha one.
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What are the pathologic mechanisms of hypoxia?
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1) hypoventilation
2) ventilation-perfusion mismatch 3) right to left shunting 4) diffusion impairment 5) reduced inspired oxygen concentration *The degree of hypercapnia and response to oxygen supplementation varies depending on the mechanism of impaired gas exchange. |
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What is the hallmark of hypoventilation?
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Hypercapnia. (PaCO2 level is inversely proportional to alveolar ventilation)...halving alveolar ventilation doubles PaCO2.
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How is the reduction of arterial oxygen tension related to the increase in CO2?
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Direct proportion: For example an increase in PaCO2 from 40 to 80 mmHg causes the PaO2 to decrease from 100 to 60 mm Hg. Therefore, hypoxemia from hypoventilation is rarely life threatening.
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What is the most significant clinical concern with hypoventilation?
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Not hypoxemia (see previous flashcard). In addition, O2 supplementation easily abolishes hypoxemia. Try acidosis caused by hypercapnia. Can be life threatening.
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What are some disorders that can cause alveolar hypoventilation?
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Mechanical (abdominal distention, trauma to thoracic wall), neuromuscular (botulism, phrenic nerve damage, nutritional muscular dystrophy), dysfx of the diaphragm and intercostal muscles, restrictive diseases (silicosis, pulmonary fibrosis, pneumothorax, pleural effusion) and upper airway obstruction.
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What is ventilation perfusion mismatch?
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Unequal distribution of alveolar ventilation and blood flow.
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What are some things associated with low V-Q ratio?
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(low V-Q ratio is when ventilation cannot adequately perfuse blood)
Examples: COPD, pulmonary atelectasis, and consolidation. |
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What are some diseases associated with high V-Q ratio?
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(high V-Q is when ventilation occurs to poorly perfused units). Pulmonary thromboembolism, shock (low pulmonary arterial pressure).
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What is a protective mechanism by which the body tries to prevent V-Q mismatch?
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Reflex pulmonary arterial constriction (hypoxic vasoconstriction) prevents perfusion of unventilated alveolar units and attempts to redirect blood flow to alveoli that are adequately ventilated.
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What is a "shunt" regarding hypoxemia?
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Defined as blood that is not exposed to ventilated area of lung. Ex: extreme V-Q mismatch, or congenital disease like tetralogy of Fallot.
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What are some examples of diseases that can cause diffusion impairment?
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Pulmonary fibrosis, interstitial pneumonia, silicosis, edema caused by increased width of the barrier or decreased surface area for gas exchange.
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What is the treatment for diffusion impairment?
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Oxygen therapy: increase concentration of oxygen in the alveolus to favor diffusion into blood.
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What is the most common form of obstructive respiratory disease?
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Laryngeal hemiplegia. (COPD also discussed at length).
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What is restrictive pulmonary disease?
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Inhibits pulmonary expansion and leads to inspiratory respiratory distress.
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How is restricitve disease classified?
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Intrapulmonary: pulmonary fibrosis, silicosis, and interstitial pneumonia
Extrapulmonary: pleural effusion, pneumothorax, mediastinal mass, botulism, nutritional muscular dystrophy *the pathophysiologic mechanism for hypoxemia in horses with extrapulmonary restriction is hypoventilation |
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How do horses with restrictive or extrathoracic, nonfixed, obstructive disease present differently from horses with intrathoracic airway obstruction?
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Prolonged inspiration is characteristic of extrathoracic
Difficulty with expiration is characteristic of intrathoracic disease |
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Expiratory wheezes are the hallmark of what disease?
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Obstructive Pulmonary Disease
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Crackles are what? What causes them?
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Intermittent or explosive sounds generated by the bubbling of air through secretions or by equilibration of airway pressure after sudden opening of collapsed airways.
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Crackles occur with what diseases?
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Pneumonia, interstitial fibrosis, COPD, pulmonary edema, atelectasis.
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Wheezes can be categorized how?
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Inspiratory: Oscillation of small airway walls before completely opening
Expiratory: " " completely closing |
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What Is the Work-Up of Respiratory Distress Look Like?
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Hx, PE, EAD
Thoracic auscultation Percussion Arterial Blood Gas (evaluate pulmonary function, alveolar ventilation, and acid-base status)(also monitor response to supplemental O2, bronchodilators, parasympathomimetic or antiinflammatory therapy) Thoracic rads Thoracic ultrasound Endoscopy Transtracheal/bronchial wash |
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What does the cough reflex rely upon? (how is signal sent?)
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Vagal nerves, sensory myelinated nerves inthe larynx respond to mechanical and chemical irritation
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