Module 8: Chapter 5 Pathophysiology of Pulmonary Conditions

Respiratory System Overview

Two Divisions:

1. Air Conduction:

   • Function: Delivers warm and moistened air to the lungs to enhance gas exchange and protect the pulmonary surfaces from irritation.

   • Components: Nose, mouth, trachea, bronchi, and bronchioles, each playing a crucial role in ensuring air is filtered, humidified, and warmed before reaching the alveoli.

2. Gas Exchange:

   • Function: Exchanges vital gases, oxygen, and carbon dioxide between air and blood to maintain homeostasis and support cellular metabolism.

   • Components: Alveoli and capillaries, where the diffusion of gases occurs across the alveolar membrane into the bloodstream.

Key Structures of the Respiratory System

Anatomy:

• Nasal Cavity: Filters, warms, and humidifies the air.

• Throat (Pharynx): A passage that carries air to the larynx and food to the esophagus.

• Nose and Mouth: Entry points for air, with the nose having a greater role in filtration due to cilia and mucus.

• Esophagus: Not part of the respiratory system but runs parallel and serves as a food passage.

• Larynx: Contains vocal cords and acts as a passageway for air while preventing food aspiration.

• Trachea: Also known as the windpipe, it directs air into the bronchi.

• Lungs (Left and Right): Main organs of respiration, each comprising lobes and alveoli where gas exchange occurs.

• Alveoli: Tiny air sacs that increase surface area for gas exchange.

• Capillary Venule Network: Surrounds alveoli, facilitating gas transport to and from blood.

• Bronchiole and Bronchi: Airways that lead to the lungs, branching further into smaller bronchioles.

• Diaphragm: A critical muscle that assists in breathing mechanics by contracting and relaxing to facilitate inhalation and exhalation.

Gas Exchange Mechanism

Requirements:

• Adequate ventilation (air delivery) and perfusion (blood flow) are essential for effective gas exchange.

Normal Values:

• Normal ventilation = 4 L/min.

• Normal perfusion = 5 L/min.

• Ventilation/perfusion (VQ) ratio: Normal range = 0.8, crucial for determining lung efficiency.

Factors Influencing VQ Ratio:

• Alveolar and capillary surface area and thickness significantly affect the efficiency of gas exchange and the overall VQ ratio.

Gas Transportation

Oxygen Transport:

• Mechanism: Oxygen is carried by hemoglobin (forming oxyhemoglobin), which easily releases oxygen to tissues influenced by local pH and temperature changes.

Carbon Dioxide Transport:

• Carbon dioxide is primarily transported as bicarbonate ions (HCO3-), and its removal from the body is crucial for maintaining acid-base balance.

Lung Compliance

Importance:

• Lung compliance, defined as the stretchability of lung tissue, is essential. High compliance indicates easier inflation, while low compliance can make breathing laborious.

Role of Surfactant:

• Surfactant is a lipoprotein coating the alveoli, preventing collapse, reducing surface tension, and promoting reinflation during exhalation.

Pressure System:

• Lungs function as a negative pressure system, facilitating airflow into the pulmonary pathways.

Breathing Process

Control:

• The breathing process is largely involuntary, primarily managed by the medulla oblongata, which responds to changes in carbon dioxide and oxygen levels in the blood.

• Chemoreceptors and Stretch Receptors: These regulate breathing rhythm and depth based on current physiological demands.

Inspiration:

• Occurs through the contraction of the diaphragm and intercostal muscles, creating negative pressure that draws air into the lungs.

Expiration:

• Typically a passive process that relies on the elastic recoil of lung tissue; active components may be involved during forceful expiration.

Hypoxic Drive with Chronic Elevated PCO2 Levels

Mechanism:

• In patients with chronic elevated carbon dioxide (PCO2) levels, a hypoxic drive can develop, where low oxygen (PO2) levels stimulate increased respiration rates as a compensatory mechanism.

Pulmonary Function Tests (PFT)

Key Measurements:

• Tidal Volume: ~500 mL, the amount of air inhaled or exhaled in a normal breath.

• Minute Respiratory Volume: ~6 L, total volume of air inhaled and exhaled in one minute.

• Inspiratory Reserve Volume: 2–3 L, additional air that can be inhaled after a normal inspiration.

• Expiratory Reserve Volume: 1–1.5 L, additional air that can be forcibly exhaled after a normal expiration.

• Vital Capacity: Total of tidal volume plus both reserves, representing the maximum amount of air a person can expel from the lungs.

• Residual Volume: 1–1.5 L left after forced expiration, indicating the air that remains in the lungs to keep the alveoli open.

• FEV1 vs. Forced Vital Capacity: Used in diagnosing and classifying obstructive and restrictive lung diseases.

Role in pH Balance

Regulation:

• The rate and depth of breathing modulate the body’s pH levels by controlling carbon dioxide concentration in the blood.

• Increased Breathing: Results in the expulsion of CO2, raising pH (alkalosis).

• Decreased Breathing: Causes CO2 retention, lowering pH (acidosis).

Conditions of the Respiratory System

Lung Sounds:

• Variations in lung sounds, including rales, crackles, wheezes, rhonchi, pleural friction rubs, and stridor, provide diagnostic insight into underlying conditions.

Influenza Overview

Nature:

• Influenza is a viral infection affecting both the upper and lower respiratory tracts, leading to systemic symptoms.

Types:

• Type A: Most severe and prevalent, often responsible for pandemics.

• Type B: Generally less severe, seasonal outbreaks.

• Type C: Causes mild respiratory illness, less common than A and B.

US Flu Season:

• Typically spans from October through March, with peaks in December and February.

Manifestations:

• Symptoms include low-grade fever, headache, dry cough, body aches, nasal congestion, chills, fatigue, and in some cases, secondary bacterial infections.

Diagnosis:

• Based on patient history, physical examination, rapid antigen testing, and viral culture.

Treatment:

• Antiviral medications, hydration, plenty of rest, antipyretics to reduce fever, and analgesics for pain relief.

Prevention:

• Key methods include proper handwashing, avoiding crowded places during outbreaks, and annual vaccinations.

Pneumonia Overview

Definition:

• Pneumonia is defined as an infection and inflammation of the lung parenchyma, leading to impaired gas exchange.

Causes:

• Caused by infectious agents such as bacteria and viruses, and lung secretion stasis.

Types:

• Viral Pneumonia: Generally mild, but can lead to secondary bacterial pneumonia.

• Bacterial Pneumonia: Most common type; frequently caused by Streptococcus pneumoniae.

Complications:

• Can lead to septicemia, pulmonary edema, lung abscess, and Acute Respiratory Distress Syndrome (ARDS).

Diagnosis and Treatment:

• Diagnosis is based on clinical signs and symptoms, with management focusing on supportive care and antibiotics if bacterial.

Tuberculosis (TB)

Causative Agent:

• Mycobacterium tuberculosis, a slow-growing, aerobic bacterium.

Transmission:

• Primarily through airborne droplets generated when an infected person coughs or sneezes.

Manifestations:

• May include a productive cough, hemoptysis (coughing up blood), night sweats, weight loss, and fatigue.

Diagnosis:

• Conducted using the Mantoux test, chest X-ray, and sputum culture for confirmation.

Treatment:

• Involves a combination of antimicrobial therapy for a minimum of six months to eradicate the bacteria and prevent resistance.

Asthma Overview

Definition:

• Asthma is a chronic disorder characterized by intermittent airway obstruction caused by inflammation, bronchospasm, and increased mucus production.

Types:

• Types include extrinsic (allergic), intrinsic (non-allergic), nocturnal, exercise-induced, occupational, and drug-induced asthma.

Stages of an Asthma Attack:

• Stage One: Bronchospasms occur, leading to coughing and shortness of breath.

• Stage Two: Airway edema and mucus production increase, further obstructing airflow.

Manifestations:

• Common symptoms include wheezing, dyspnea (difficulty breathing), and chest tightness, which may increase during an attack.

Chronic Obstructive Pulmonary Disease (COPD)

Overview:

• COPD encompasses a group of debilitating chronic disorders characterized by irreversible tissue degeneration affecting lung function.

Main Types:

• Chronic Bronchitis: Features include a productive cough with increased mucus due to chronic inflammation.

• Emphysema: Involves the destruction of the alveolar walls, leading to decreased surface area for gas exchange.

Case Study Analysis

Mr. Lansing:

• Key Symptoms: Flushed skin, shortness of breath, diminished breath sounds, and no cough despite a significant smoking history.

Key Questions:

• Diagnostic tests that are likely to be ordered include arterial blood gases (ABGs), complete blood count (CBC), and chest X-ray, aiming to identify underlying disease processes based on presented symptoms and clinical history.

Additional Respiratory Conditions

Pleural Effusion:

• Refers to the accumulation of fluid in the pleural space, which can impair breathing and gas exchange.

Pneumothorax:

• Air trapped in the pleural cavity, which can lead to lung collapse (atelectasis) and respiratory distress.

Pulmonary Embolism (PE):

• A blockage in the pulmonary artery that commonly arises from deep vein thrombosis (DVT), resulting in acute respiratory compromise and possible infarction of lung tissue.

Acute Respiratory Distress Syndrome (ARDS):

• A severe inflammatory response leading to fluid accumulation in the alveoli, resulting in rapid onset of respiratory failure and requiring intensive medical management.

Cystic Fibrosis:

• A genetic disorder characterized by thick mucus production that obstructs airflow and leads to recurrent lung infections and damage.

Legionnaire's Disease and Pneumocystis Jirovecii Pneumonia:

• Specific infectious agents known for causing pneumonia, particularly in immunocompromised patients and individuals with weakened immune systems.