Chapter 17
Gas Exchange and Respiratory Function
● Definition: The process by which oxygen (O₂) is delivered to the blood and carbon
dioxide (CO₂) is expelled from the body.
● Key Components:
● Alveoli:
○ Thin-walled air sacs where gas exchange occurs.
○ Surrounded by capillaries.
● Alveolar-Capillary Membrane:
○ Junction between the respiratory and circulatory systems.
○ Site of diffusion of O₂ into the blood and CO₂ out of the blood.
● Pulmonary Circulation:
○ Delivers deoxygenated blood to the lungs for reoxygenation.
● Physiological Process:
○ Inhalation (Ventilation): O₂ enters the alveoli.
■ Active Process:
● Requires contraction of the diaphragm and intercostal muscles.
● Creates negative pressure to draw air in.
○ Diffusion: O₂ moves from alveoli → capillaries. CO₂ moves from capillaries →
alveoli.
○ Exhalation: CO₂ is expelled from the body.
■ Passive Process:
● Relies on lung recoil and relaxation of respiratory muscles.
Ventilation and Perfusion
● Ventilation (V): The process of moving air in and out of the lungs. Inspiration: Active
process requiring muscle contraction. Expiration: Passive process driven by lung recoil.
○ Dependent on Neuromuscular and Musculoskeletal Integrity:
■ Central Nervous System (CNS):
● Medulla and Pons monitor CO₂ and O₂ levels in the blood.
● Adjust the rate and depth of respiration based on gas levels.
■ Musculoskeletal System:
● Supports respiration by facilitating movement of the chest wall and
lungs:
○ Diaphragm: Main respiratory muscle.
○ Intercostal Muscles: Expand and contract the rib cage.
○ Accessory Muscles: Scalene, sternomastoid, trapezius,
and abdominal muscles assist during increased respiratory
demand.
● Perfusion (Q): The process of blood flow through the pulmonary vasculature. Ensures
oxygen (O₂) enters the bloodstream and carbon dioxide (CO₂) is expelled.
○ Role of Alveoli in Perfusion:
■ Gas Exchange Site: Alveoli must be adequately expanded with air to
facilitate contact with hemoglobin for effective gas exchange.
■ Ventilation (V)/Perfusion (Q) Mismatch:
, ● Adequate ventilation, poor exchange:
○ Occurs when alveoli are filled with edema or secretions,
preventing proper O₂ and CO₂ exchange.
● Poor ventilation, adequate blood flow:
○ Occurs when alveoli are not expanded adequately, despite
normal perfusion.
● V/Q Ratio: The balance between ventilation and perfusion, crucial for efficient gas
exchange.
● Clinical Relevance: Imbalances in V/Q can lead to respiratory and circulatory issues,
such as hypoxia or pulmonary embolism.
Age Related Changes of the Respiratory System
● Increased Airspace: Alveolar enlargement reduces gas exchange efficiency.
● Increased Apoptosis: Loss of alveolar cells decreases lung surface area.
● Decreased Elasticity: Reduced alveolar elasticity impairs lung expansion and
contraction.
● Decreased Lung Function: These changes contribute to a decline in respiratory
efficiency, increasing disease risk.
Respiratory Assessment
● Thorax and Lungs (general overview)
○ 1. Inspection:
■ Observe chest symmetry, respiratory rate, rhythm, and depth.
■ Check for accessory muscle use, cyanosis, or deformities.
■ Respiratory Rate, Depth, and Rhythm
● Normal vs. Abnormal:
● Tachypnea: Fast breathing
● Bradypnea: Slow breathing
● Orthopnea: Difficulty breathing when lying flat
● Apnea: Absence of breathing
● Hyperpnea: Deep breathing
■ Thoracic Size and Symmetry
● Size/Shape: Barrel chest, kyphosis, or pectus excavatum?
● Expansion/Symmetry: Even chest wall movement during
inspiration.
■ Use of Accessory Muscles
● Evidence of labored breathing (e.g., neck, intercostal, or
abdominal muscle use).
■ Skin and Extremities Color:
● Pallor or cyanosis?
● Appearance: Any mottling or unusual discoloration?
● Clubbing: Enlarged fingertips, a sign of chronic hypoxia.
■ Neck Inspection
● Tracheal Deviation: Midline or displaced? A sign of pneumothorax
or mass
○ 2. Palpation:
, ■ Assess for tenderness, chest wall expansion, and tactile fremitus
(vibration during speech).
■ 1. Assess for Abnormalities
● Tenderness: Identify areas of pain or sensitivity.
● Masses or Lesions: Check for lumps, bumps, or irregularities on
the chest wall.
■ 2. Thoracic Expansion
● Evaluate symmetry of chest wall movement during deep
inspiration.
● Place hands on the lower rib cage and observe for equal
movement.
■ 3. Tactile Fremitus
● Assess vibrations when the patient speaks ("99").
○ Increased fremitus: May indicate consolidation (e.g.,
pneumonia).
○ Decreased fremitus: May suggest air or fluid (e.g., pleural
effusion, pneumothorax).
○ 3. Percussion:
■ Identify normal resonance or abnormalities (e.g., dullness in fluid
accumulation or hyperresonance in air trapping).
■ Percuss across lung fields to identify:
● Resonance: Normal lung sound.
● Dullness: Indicates fluid or solid mass (e.g., pleural effusion,
consolidation).
● Hyperresonance: Suggests air trapping (e.g., pneumothorax,
emphysema).
○ 4. Auscultation
■ Listen for breath sounds in key areas:
● Bronchial: Over trachea; loud and high-pitched.
● Bronchovesicular: Near major bronchi; moderate pitch and
intensity.
● Vesicular: Peripheral lung fields; soft and low-pitched
■ 1. Crackles
● Fine Crackles: Soft, high-pitched, and brief (e.g., in pulmonary
fibrosis, CHF).
● Coarse Crackles: Loud, low-pitched, bubbling sounds (e.g., in
pneumonia, COPD, or fluid overload).
■ 2. Wheezes
● High-pitched, musical sounds caused by narrowed airways (e.g.,
in asthma, bronchitis).
■ 3. Stridor
● Harsh, high-pitched sound during inspiration, often caused by
upper airway obstruction (e.g., croup, foreign body).
■ 4. Pleural Friction Rub
, ● Grating sound caused by inflamed pleural layers rubbing together
(e.g., in pleuritis or pleural effusion). i.e. sandpaper blocks rubbing
together
■ Abnormal Voice Sounds
● Lung consolidation occurs when air in the lungs is replaced by
fluid, blood, pus, or other substances.
○ Egophony: Patient says "ee" but it sounds like "ay" over
areas of consolidation.
○ Bronchophony: Patient says "99"; louder and clearer over
consolidation.
○ Whispered Pectoriloquy: Patient whispers "1, 2, 3"; sounds
amplified over consolidation.
Abnormal Breathing Patterns
● Cheyne-Stokes Respiration: Breaths alternate between shallow and deep, followed by
periods of apnea.
○ Causes:
■ Severe brain pathology (e.g., brain stem herniation).
■ Increased intracranial pressure (ICP).
■ Compression of the brain stem. Heart failure.
○ This breathing pattern is considered a normal part of the dying process in some
cases, signaling significant systemic decline. It can be distressing for families, so
providing education and reassurance is important.
■ Decreased perfusion to the brain or brainstem dysfunction.
■ Heart failure, which disrupts normal circulation and oxygen delivery.
■ End-of-life changes: As the body shuts down, breathing patterns often
become irregular, including Cheyne-Stokes.
● Kussmaul’s Breathing: Pattern: Deep, rapid, and labored breathing. Greater than 20
breaths per minute (bpm).
○ Causes
■ Metabolic Acidosis: Body attempts to "blow off" CO₂ to compensate for
low pH.
■ Renal Failure: Accumulation of acids in the blood.
■ Diabetic Ketoacidosis (DKA): Excess ketones cause severe acidosis.
○ Clinical Significance: A hallmark of severe metabolic derangements. Requires
urgent intervention to address the underlying cause.
Respiratory Modalities
● 1. Pulmonary Function Tests (PFTs)- Routinely used in patients with chronic lung
disorders. Assesses respiratory function, disease severity, and response to therapy.
○ Screening for:
■ Hazardous occupational exposures.
■ Pre-surgical clearance.
■ Performed by: Respiratory therapists using a spirometer.
● 2. Diagnostic Labs
○ Arterial Blood Gases (ABGs):
Gas Exchange and Respiratory Function
● Definition: The process by which oxygen (O₂) is delivered to the blood and carbon
dioxide (CO₂) is expelled from the body.
● Key Components:
● Alveoli:
○ Thin-walled air sacs where gas exchange occurs.
○ Surrounded by capillaries.
● Alveolar-Capillary Membrane:
○ Junction between the respiratory and circulatory systems.
○ Site of diffusion of O₂ into the blood and CO₂ out of the blood.
● Pulmonary Circulation:
○ Delivers deoxygenated blood to the lungs for reoxygenation.
● Physiological Process:
○ Inhalation (Ventilation): O₂ enters the alveoli.
■ Active Process:
● Requires contraction of the diaphragm and intercostal muscles.
● Creates negative pressure to draw air in.
○ Diffusion: O₂ moves from alveoli → capillaries. CO₂ moves from capillaries →
alveoli.
○ Exhalation: CO₂ is expelled from the body.
■ Passive Process:
● Relies on lung recoil and relaxation of respiratory muscles.
Ventilation and Perfusion
● Ventilation (V): The process of moving air in and out of the lungs. Inspiration: Active
process requiring muscle contraction. Expiration: Passive process driven by lung recoil.
○ Dependent on Neuromuscular and Musculoskeletal Integrity:
■ Central Nervous System (CNS):
● Medulla and Pons monitor CO₂ and O₂ levels in the blood.
● Adjust the rate and depth of respiration based on gas levels.
■ Musculoskeletal System:
● Supports respiration by facilitating movement of the chest wall and
lungs:
○ Diaphragm: Main respiratory muscle.
○ Intercostal Muscles: Expand and contract the rib cage.
○ Accessory Muscles: Scalene, sternomastoid, trapezius,
and abdominal muscles assist during increased respiratory
demand.
● Perfusion (Q): The process of blood flow through the pulmonary vasculature. Ensures
oxygen (O₂) enters the bloodstream and carbon dioxide (CO₂) is expelled.
○ Role of Alveoli in Perfusion:
■ Gas Exchange Site: Alveoli must be adequately expanded with air to
facilitate contact with hemoglobin for effective gas exchange.
■ Ventilation (V)/Perfusion (Q) Mismatch:
, ● Adequate ventilation, poor exchange:
○ Occurs when alveoli are filled with edema or secretions,
preventing proper O₂ and CO₂ exchange.
● Poor ventilation, adequate blood flow:
○ Occurs when alveoli are not expanded adequately, despite
normal perfusion.
● V/Q Ratio: The balance between ventilation and perfusion, crucial for efficient gas
exchange.
● Clinical Relevance: Imbalances in V/Q can lead to respiratory and circulatory issues,
such as hypoxia or pulmonary embolism.
Age Related Changes of the Respiratory System
● Increased Airspace: Alveolar enlargement reduces gas exchange efficiency.
● Increased Apoptosis: Loss of alveolar cells decreases lung surface area.
● Decreased Elasticity: Reduced alveolar elasticity impairs lung expansion and
contraction.
● Decreased Lung Function: These changes contribute to a decline in respiratory
efficiency, increasing disease risk.
Respiratory Assessment
● Thorax and Lungs (general overview)
○ 1. Inspection:
■ Observe chest symmetry, respiratory rate, rhythm, and depth.
■ Check for accessory muscle use, cyanosis, or deformities.
■ Respiratory Rate, Depth, and Rhythm
● Normal vs. Abnormal:
● Tachypnea: Fast breathing
● Bradypnea: Slow breathing
● Orthopnea: Difficulty breathing when lying flat
● Apnea: Absence of breathing
● Hyperpnea: Deep breathing
■ Thoracic Size and Symmetry
● Size/Shape: Barrel chest, kyphosis, or pectus excavatum?
● Expansion/Symmetry: Even chest wall movement during
inspiration.
■ Use of Accessory Muscles
● Evidence of labored breathing (e.g., neck, intercostal, or
abdominal muscle use).
■ Skin and Extremities Color:
● Pallor or cyanosis?
● Appearance: Any mottling or unusual discoloration?
● Clubbing: Enlarged fingertips, a sign of chronic hypoxia.
■ Neck Inspection
● Tracheal Deviation: Midline or displaced? A sign of pneumothorax
or mass
○ 2. Palpation:
, ■ Assess for tenderness, chest wall expansion, and tactile fremitus
(vibration during speech).
■ 1. Assess for Abnormalities
● Tenderness: Identify areas of pain or sensitivity.
● Masses or Lesions: Check for lumps, bumps, or irregularities on
the chest wall.
■ 2. Thoracic Expansion
● Evaluate symmetry of chest wall movement during deep
inspiration.
● Place hands on the lower rib cage and observe for equal
movement.
■ 3. Tactile Fremitus
● Assess vibrations when the patient speaks ("99").
○ Increased fremitus: May indicate consolidation (e.g.,
pneumonia).
○ Decreased fremitus: May suggest air or fluid (e.g., pleural
effusion, pneumothorax).
○ 3. Percussion:
■ Identify normal resonance or abnormalities (e.g., dullness in fluid
accumulation or hyperresonance in air trapping).
■ Percuss across lung fields to identify:
● Resonance: Normal lung sound.
● Dullness: Indicates fluid or solid mass (e.g., pleural effusion,
consolidation).
● Hyperresonance: Suggests air trapping (e.g., pneumothorax,
emphysema).
○ 4. Auscultation
■ Listen for breath sounds in key areas:
● Bronchial: Over trachea; loud and high-pitched.
● Bronchovesicular: Near major bronchi; moderate pitch and
intensity.
● Vesicular: Peripheral lung fields; soft and low-pitched
■ 1. Crackles
● Fine Crackles: Soft, high-pitched, and brief (e.g., in pulmonary
fibrosis, CHF).
● Coarse Crackles: Loud, low-pitched, bubbling sounds (e.g., in
pneumonia, COPD, or fluid overload).
■ 2. Wheezes
● High-pitched, musical sounds caused by narrowed airways (e.g.,
in asthma, bronchitis).
■ 3. Stridor
● Harsh, high-pitched sound during inspiration, often caused by
upper airway obstruction (e.g., croup, foreign body).
■ 4. Pleural Friction Rub
, ● Grating sound caused by inflamed pleural layers rubbing together
(e.g., in pleuritis or pleural effusion). i.e. sandpaper blocks rubbing
together
■ Abnormal Voice Sounds
● Lung consolidation occurs when air in the lungs is replaced by
fluid, blood, pus, or other substances.
○ Egophony: Patient says "ee" but it sounds like "ay" over
areas of consolidation.
○ Bronchophony: Patient says "99"; louder and clearer over
consolidation.
○ Whispered Pectoriloquy: Patient whispers "1, 2, 3"; sounds
amplified over consolidation.
Abnormal Breathing Patterns
● Cheyne-Stokes Respiration: Breaths alternate between shallow and deep, followed by
periods of apnea.
○ Causes:
■ Severe brain pathology (e.g., brain stem herniation).
■ Increased intracranial pressure (ICP).
■ Compression of the brain stem. Heart failure.
○ This breathing pattern is considered a normal part of the dying process in some
cases, signaling significant systemic decline. It can be distressing for families, so
providing education and reassurance is important.
■ Decreased perfusion to the brain or brainstem dysfunction.
■ Heart failure, which disrupts normal circulation and oxygen delivery.
■ End-of-life changes: As the body shuts down, breathing patterns often
become irregular, including Cheyne-Stokes.
● Kussmaul’s Breathing: Pattern: Deep, rapid, and labored breathing. Greater than 20
breaths per minute (bpm).
○ Causes
■ Metabolic Acidosis: Body attempts to "blow off" CO₂ to compensate for
low pH.
■ Renal Failure: Accumulation of acids in the blood.
■ Diabetic Ketoacidosis (DKA): Excess ketones cause severe acidosis.
○ Clinical Significance: A hallmark of severe metabolic derangements. Requires
urgent intervention to address the underlying cause.
Respiratory Modalities
● 1. Pulmonary Function Tests (PFTs)- Routinely used in patients with chronic lung
disorders. Assesses respiratory function, disease severity, and response to therapy.
○ Screening for:
■ Hazardous occupational exposures.
■ Pre-surgical clearance.
■ Performed by: Respiratory therapists using a spirometer.
● 2. Diagnostic Labs
○ Arterial Blood Gases (ABGs):
