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Physiology of Respiration

• Respiration involves the movement of air (ventilation) through the airways (trachea, bronchi, bronchioles) to the alveoli, where gas exchange occurs.
• Gas exchange (diffusion) happens at the alveolar-capillary membrane.
• Pulmonary perfusion refers to blood flow through the pulmonary circulation, crucial for effective gas exchange.
• Gravity and alveolar pressure affect perfusion patterns.
• Blood travels from the right ventricle to the pulmonary artery and its branches (right and left pulmonary arteries) to capillary beds surrounding the alveoli.

Mechanism of Breathing

• Inspiration (inhaling) involves diaphragm contraction.
• Expiration (exhaling) involves diaphragm relaxation and arching upward.

Ventilation/Perfusion (V/Q) Ratio

• This ratio represents the balance of air reaching alveoli (ventilation) and blood flow in pulmonary capillaries (perfusion).
• A normal ratio is 1:1, crucial for adequate gas exchange.
• Mismatch can lead to:
  • Inadequate ventilation (shunt): low V/Q ratio (e.g., 0). Pulmonary circulation is adequate, but ventilation is not. Some blood bypasses oxygenation.
  • Inadequate perfusion (dead space): High V/Q ratio (e.g., infinity). Ventilation is normal, but blood flow (perfusion) is reduced.
  • Inadequate ventilation and perfusion (silent unit): combination of both issues.

Respiratory Distress

• Characterized by increased work of breathing, despite normal oxygenation.
• Increased respiratory rate and effort.

Respiratory Failure

• Inability of the respiratory system to adequately exchange oxygen (O2) and carbon dioxide (CO2) between air and blood.
• Diagnosed when:
  • Partial pressure of oxygen (PO2) in arterial blood is < 60 mm Hg.
  • Partial pressure of carbon dioxide (PCO2) in arterial blood is > 50 mm Hg.
  • Insufficient O2 delivery to body tissues (hypoxia)
  • Elevated CO2 in blood (hypercapnia)

Hypoxemia (Low Blood Oxygen)

• Low oxygen levels in the blood.
• Causes:
  • Respiratory system diseases.
  • Neurological system dysfunction.
  • Circulatory issues.
• Leads to:
  • Anaerobic metabolism.
  • Increased serum lactate and metabolic acidosis.
• Consequences:
  • Mild symptoms include tachycardia, vasoconstriction, diaphoresis.
  • Severe symptoms include restlessness, agitation, confusion, coma, cyanosis, slowed heart rate. -Chronic hypoxemia can have insidious symptoms, masking the condition.

Hypercapnia (High Blood Carbon Dioxide)

• High arterial PCO2 due to inadequate ventilation or V/Q mismatch.
• Inversely related to alveolar ventilation

Asthma

• Chronic inflammatory disorder of airways, characterized by unpredictable narrowing and swelling.
• Significant health concern; high hospitalization rates.
• Caused by chronic inflammation from allergens/irritants.
• Results in airflow limitation and hyperresponsiveness.

Asthma Classification

• Mild intermittent, mild persistent, moderate persistent, severe persistent.
• Management varies by severity.

Acute Asthma Episodes

• Characterized by respiratory distress and varying degrees of severity.
• Treated according to response to therapy and severity (measured by flow rates).

Severe Asthma Exacerbations

• High doses and frequency of bronchodilators.
• IV corticosteroids, magnesium sulfate and fluids.
• Continuous monitoring.
• Supplemental oxygen (as needed).

Long-Term Asthma Management

• Control medications for persistent asthma.
• Quick-relief medications for exacerbations.

Drug Classes for Asthma

• Anti-inflammatory drugs (Corticosteroids, leukotriene modifiers, monoclonal antibodies).
• Bronchodilators (β2-adrenergic agonists, methylxanthines, anticholinergics).
• Inhalation devices (MDIs, DPIs, nebulizers)

Patient Education on Drug Therapy

• Proper drug administration crucial for success.
• Inhalation preferred to avoid systemic side effects.
• Spacer use with MDIs improves inhalation.

COPD (Chronic Obstructive Pulmonary Disease)

• Irreversible airflow limitation.
• Generally progressive.
• Inflammatory response to noxious particles/gases.
• Includes chronic bronchitis and emphysema.
• Common in older adults.
• Cigarette smoking a major risk factor.

COPD Pathophysiology

• Irreversible expiratory airflow limitation.
• Airflow obstruction from mucus secretion, mucosal swelling, and bronchospasm.
• Driven by inflammation caused by inhaling noxious particles.
• Damage to lung tissue.