Pulmonary Pathophysiology I: Obstructive Lung Diseases

Pulmonary Pathophysiology I: Obstructive Lung Diseases

• Lecture objectives include discussing the anatomy and physiology of the respiratory system, pathophysiological hallmarks of COPD, asthma, emphysema, and bronchitis, and pharmacologic interventions for exacerbations.

Respiratory System Role

• The respiratory system's overall role is oxygen and carbon dioxide exchange.
• It regulates blood pH through bicarbonate buffer system.
• Carboxyhemoglobin formation is also part of the system.
• Adjusting gas levels offsets changes in pH.
• It is involved with phonation for speech production.
• Movement of mucus (phlegm) throughout the respiratory tract is important to combat infections.

CO2-O2 Exchange in the Lungs

• CO2 diffuses from the blood into the alveoli.
• O2 diffuses from the alveoli into the blood.
• The process involves the bicarbonate buffer system, carbonic anhydrase, and hemoglobin.

Hemoglobin Dissociation Curve

• Conditions necessitating oxygen unloading shift the curve to the right.
• Higher oxygen partial pressure is needed for complete oxygen occupancy in hemoglobin.
• Hemoglobin releases oxygen more easily to peripheral tissues.
• Conditions that would shift the curve to the right include sepsis, systemic inflammatory response, hypoxia, hypotension, hyperthermia, acidosis and hyperglycemia/DKA.

Organization of the Pulmonary System

• The trachea divides into right and left mainstem bronchi.
• Mainstem bronchi branch into secondary bronchi.
• Secondary bronchi further branch into tertiary bronchi.
• Tertiary bronchi become bronchioles, culminating in alveoli.
• Alveoli are highly vascularized, facilitating gas exchange.

Alveoli

• Alveoli cluster together, with specialized functions.
• Type I alveoli are directly involved in gas exchange.
• Type II alveoli secrete surfactant, keeping alveoli open for gas exchange.
• Surfactant lowers surface tension, preventing alveolar collapse.
• Emphysema damages Type II alveoli, leading to irreversible alveolar collapse.
• ARDS (Acute Respiratory Distress Syndrome) can be caused by surfactant loss, resulting in collapsed alveoli.

Alveoli and Pulmonary Capillaries

• Diagrammatic view shows the relationship between alveoli and pulmonary capillaries.
• Smooth and elastic fibers surround the alveoli.
• Capillaries surround alveoli for efficient gas exchange.

Mechanics of Respiration

• Air moves from high pressure areas to low pressure areas.
• Contraction of inspiratory muscles expands the thoracic cavity, decreasing lung pressure, and drawing air in.
• Expiration results from the relaxation of these muscles, increasing lung pressure and expelling air.
• Pressure decreases facilitate air movement into the lungs.
• Volume and pressure are inversely proportional.

Other Factors in Breathing

• Surface tension, lung compliance, and airway resistance all impact breathing mechanics.

Surface Tension

• Type II alveolar cells produce surfactant, decreasing surface tension.
• This prevents alveolar collapse, ensuring efficient gas exchange.

Lung Compliance

• Compliance is the lungs' ability to expand in response to pressure changes.
• Decreased compliance, due to things like restrictive lung diseases, makes expansion more difficult.

Airway Resistance

• Airway resistance is determined by airway size.
• Larger airways have less resistance, facilitating air movement.
• Smaller airways have higher resistance, making breathing more difficult.
• Obstructive lung diseases increase airway resistance due to narrowing of airways.

Neurological Control of Breathing

• The pons and medulla control respiration.
• The pons helps maintain rhythmic breathing, while the medulla modulates respiratory muscle contraction.
• The medulla is involved in regulating the respiratory response to changing CO2 and oxygen levels.
• Brainstem strokes can disrupt these neurological functions, affecting breathing and adaptation to CO2 levels.

Diseases of the Respiratory Tract

• Upper airway diseases, obstructive lung diseases, restrictive lung diseases, and infections were discussed.

"Obstructive Versus Restrictive" Lung Disease

• "Restrictive lung disease" is characterized by reduced lung expansion due to low compliance, while "obstructive lung diseases" involve increased airway resistance.

Obstructive Lung Diseases

• Examples include asthma, COPD, and bronchiectasis.
• These diseases are due to increased airflow obstruction from larger to smaller airways.
• Clinical signs/symptoms include wheezing, cough, sputum production, cyanosis, and chest tightness.

Cor Pulmonale

• https://www.youtube.com/watch?v=zaYxtKYthDk

Asthma

• Asthma is a chronic hyperreactive airway disease.
• Triggers include allergies, environmental factors, or tobacco exposure.
• Pathophysiology involves acute attacks due to exposure, causing bronchospasms and histamine release and IgE.
• Other cytokines like leukotrienes, interleukins, stimulate inflammation.
• The cough reflex, via the vagus nerve, can trigger bronchoconstriction.
• Chronically, inflammatory stress leads to airway remodeling and bronchial wall hypertrophy.

Asthma, Pathophysiology

• Trigger factors like allergens initiate airway inflammation.
• This leads to airway muscle contraction, bronchial swelling, and mucus production.
• The immune system plays a key role in the inflammatory response.

Molecular Mechanisms of Asthma

• Activation of immune cells (e.g., T cells, B cells, mast cells) following antigen presentation leads to release of inflammatory mediators.
• This causes bronchoconstriction and excessive mucus production.

Diagnosis of Asthma

• Pulmonary Function Tests (PFTs) measure FEV1/FVC ratio to assess the degree of airflow limitation.
• FEV1 is forced expiratory volume in one second.
• FVC is forced vital capacity.
• Bronchodilator testing confirms reduced airflow limitation is reversible.
• Laboratory assays like hypereosinophilia or elevated IgE levels aid in diagnosis.

Asthma Management

• Rescue medications (e.g., short-acting beta agonists) treat acute attacks.
• Maintenance medications (e.g., inhaled corticosteroids) manage chronic symptoms.

Chronic Obstructive Pulmonary Disease (COPD)

• COPD is a hybrid disease, encompassing chronic bronchitis, emphysema, and airway hyperreactivity.
• Epidemiology features high prevalence in smokers aged 40-45.
• Alpha-1 antitrypsin deficiency is a genetic factor.
• Chronic airway hyperreactivity leads to large-scale mucus production.
• Emphysema causes irreversible alveolar destruction, compromising gas exchange.
• Increased airflow obstruction leads to chronic hypoxia.
• Prolonged vascular constriction can lead to cor pulmonale (isolated right-sided heart failure).

Pathophysiology of COPD

• The pathophysiology involves similar to asthma, but with increased mucus secretion, ciliary dysfunction, and damaged alveolar walls.
• Oxidative and inflammatory damage plays a role.
• Increased susceptibility to bacterial pneumonia.
• Air trapping results in problems in respiration and oxygen transport.

COPD Clinical Findings and Diagnosis

• Clinical signs include productive cough with thick, light-brown sputum, wheezing, and chest tightness.
• Diagnosis uses PFTs, showing a low FEV1/FVC ratio.
• Chest X-rays and CT scans help identify emphysema or pneumonia.
• Basic blood tests can assess for underlying infections.
• Echocardiograms are helpful for evaluating cor pulmonale suspected.

COPD Management

• COPD management mirrors asthma management for acute episodes.
• Chronic management often includes inhaled bronchodilators and inhaled corticosteroids, often with combination inhalers.
• Antibiotics are considered if pneumonia is suspected.
• Oxygen supplementation is targeted at low oxygen saturations (<88%).

Why Oxygen Therapy Isn't Always Suitable for COPD Patients

• The medulla's "set point" for respiration is adjusted to mildly elevated CO2 and low O2 levels in COPD patients.
• Peripheral chemoreceptors become desensitized.
• High supplemental oxygen may suppress the respiratory drive leading to respiratory failure.

This quiz covers the anatomy and physiology of the respiratory system, focusing on obstructive lung diseases such as COPD, asthma, emphysema, and bronchitis. It also addresses the pathophysiology of these conditions and the pharmacologic treatments available for exacerbations. Test your knowledge on respiratory gas exchange and related mechanisms.