Respiratory System Structures and Functions

Structures and Functions of Respiratory System

• Primary purpose: gas exchange — transfer of oxygen (O₂) and carbon dioxide (CO₂) between atmosphere and blood.
• Two parts:
  • Upper respiratory tract
  • Lower respiratory tract
• Adequate O₂ and a healthy, functioning respiratory system are necessary for life.

Upper Respiratory Tract

• Structures: Nose, Mouth, Pharynx, Epiglottis, Larynx, Trachea.
• Functions:
  • Nose: warm, filter, humidify inspired air.
  • Septum and Turbinates: contribute to filtration and air conditioning.
  • Pharynx subdivided into Nasopharynx, Oropharynx, Laryngopharynx.
• Notable features:
  • Epiglottis, Larynx, Trachea.
  • Trachea approximately 5 inches long x 1 inch wide.
  • Carina — bifurcation of the trachea.
  • Angle of Louis (sternal angle) used as a landmark.
  • Vigorous coughing with suctioning may be performed.

Lower Respiratory Tract

• Structures: Bronchi, Bronchioles, Alveolar ducts, Alveoli.
• Lobes of lungs: Right lung — 3 lobes; Left lung — 2 lobes.
• Additional landmarks:
  • Hilus: entry point of bronchi, pulmonary vessels, and nerves into the lungs.
  • Right main bronchus is shorter, wider, and straighter than the left; aspiration more likely in the right lung.
• Functional concepts:
  • Bronchoconstriction and bronchodilation as regulation of airway diameter.
• Structures of the lower airways (anatomic dead space):
  • Trachea and bronchi — no gas exchange.
  • Bronchioles — contain smooth muscle that constricts/dilates.
  • Alveoli — end part of respiratory tract; site of gas exchange.

Alveolar Anatomy and Gas Exchange

• Alveoli: primary site for gas exchange with pulmonary capillaries.
• Pores of Kohn: interconnections between alveoli that allow air passage and can enable bacterial spread.
• Surfactant: lipoprotein secreted by alveoli when stretched; reduces surface tension to prevent alveolar collapse. A sigh (~every 5–6 breaths) stretches alveoli and promotes surfactant secretion.
• Atelectasis: collapsed alveoli (e.g., due to anesthesia, ARDS).

Blood Supply to the Respiratory System

• Pulmonary circulation: gas exchange occurs here.
  • Artery: deoxygenated blood from right ventricle to lungs.
  • Capillaries: site of gas exchange at the alveoli.
  • Veins: return oxygenated blood to the left atrium.
• Bronchial circulation: supplies oxygen to bronchi and lung tissues.
• Azygos vein: drains deoxygenated blood to superior vena cava.

Chest Wall and Pleura

• Chest wall components: Ribs (24 total) and sternum; Thoracic cage protects lungs and heart.
• Mediastinum: contains heart, aorta, esophagus.
• Pleura: Parietal pleura lines chest cavity; Visceral pleura covers lungs.
• Intrapleural space normally contains 10–20 mL of fluid, providing lubrication and facilitating expansion.
• Empyema: bacterial infection of the pleural space.

Diaphragm and Respiratory Muscles

• Diaphragm: major muscle of respiration.
  • Inspiration: contracts downward toward the abdomen, increasing intrathoracic volume.
  • Works with intercostal and scalene muscles.
  • Nerve supply: phrenic nerves (right and left) from cervical vertebrae C3–C5.
• Spinal cord injury above C3 can cause diaphragm paralysis, resulting in dependence on mechanical ventilation.

Physiology of Respiration

• Oxygenation: delivery of O₂ from atmosphere to organs and tissues.
  • Oxygen dissolved in plasma: $PaO<em>2$ in arterial blood; normal range $PaO</em>2 = 80\text{ to }100\text{ mmHg}.$
  • Oxygen bound to hemoglobin: arterial oxygen saturation $SaO<em>2$; normal SaO2 > 95\%.
• Diffusion: movement of O₂ and CO₂ across the alveolar-capillary membrane from high to low concentration until equilibrium.

Ventilation and Lung Mechanics

• Ventilation: inspiration and expiration driven by intrathoracic pressure changes and muscle action.
• Dyspnea triggers additional muscle recruitment to aid breathing.
• Expiration: generally passive.
• Elastic recoil: lungs return to original size after expansion.
• Compliance: ease of lung expansion; decreased compliance makes inflation harder to achieve; increased compliance makes recoil harder to restore.
• Resistance: air flow impeded during inspiration and/or expiration due to narrowed airways or secretions.

Control of Respiration

• Medulla: respiratory center located in the brainstem; responds to chemical and mechanical signals; sends impulses to respiratory muscles via spinal cord and phrenic nerves.
• Chemoreceptors:
  • Central chemoreceptors (medulla): respond to changes in H⁺ concentration in CSF.
  • Peripheral chemoreceptors (carotid bodies and aortic bodies): respond to changes in PaO₂, pH, and PaCO₂.
• Central chemoreceptor responses:
  • Increased H⁺ concentration (acidosis) → increased respiratory rate (RR) and tidal volume (VT).
  • Decreased H⁺ concentration (alkalosis) → increased RR and VT.
  • Increased PaCO₂ → increased H₂CO₃ → decreased pH of CSF → increased RR.
  • Decreased PaCO₂ → decreased H₂CO₃ → increased pH of CSF → decreased RR.
• Peripheral chemoreceptors:
  • Trigger increased RR in response to hypoxemia or acidosis or hypercapnia.
  • In COPD, chronically elevated PaCO₂ can blunt the respiratory drive (hypoxic drive).
• Mechanical receptors:
  • Located in conducting upper airways, chest wall, diaphragm, and alveolar capillaries.
  • Types: irritant, stretch (Hering–Breuer reflex), J-receptors (juxtacapillary).

Respiratory Defense Mechanisms

• Filtration of air and sedimentation to remove particles (1–5 μm).
• Mucociliary clearance system (mucociliary escalator).
• Cough reflex and reflex bronchoconstriction.
• Alveolar macrophages.

Gerontologic Considerations (Aging Effects)

• Structural changes: reduced chest expansion and fewer functional alveoli.
• Defense mechanisms: reduced immune function.
• Respiratory control: slower responses to changes in O₂ and CO₂ levels.

Assessment of the Respiratory System — Subjective Data

• Health history and initial view: assess degree of respiratory distress.
• Important health information: history of respiratory or allergic conditions; consider other body systems.
• Genetic risk alert: family history of respiratory problems (e.g., CF, COPD, asthma).
• Medications: prescription, OTC, illicit, oxygen.
• Surgical history and other treatments: nebulizer, humidifier, airway clearance modalities, high-frequency chest wall oscillation, postural drainage, percussion.

Functional Health Patterns (Nursing Assessment Framework)

• Health Perception–Health Management:
  • Smoking history or exposure to smoke.
  • Changes in respiratory status; characteristics of cough and sputum; travel history.
  • Hemoptysis vs. hematemesis.
  • Risk for TB; immunizations status.
• Nutritional–Metabolic pattern: weight changes, fluid intake.
• Elimination pattern: incontinence; constipation.
• Activity–Exercise pattern: dyspnea limitations; positional effects on breathing; activities of daily living (ADLs).
• Sleep–Rest pattern: nocturnal symptoms; apnea; night sweats; head-of-bed (HOB) elevation.
• Cognitive–Perceptual pattern: neurologic changes (apprehension, restlessness, irritability, memory) related to cerebral oxygenation; ability to cooperate with treatment; pain with breathing (location, severity, factors).
• Self-Perception–Self-Concept: body image, self-esteem, social interactions.
• Role–Relationship: family, work, social life; occupational exposures (fumes, asbestos, coal, fibers, silica).
• Sexuality–Reproductive: changes in sexual activity or positions.
• Coping–Stress Tolerance: anxiety–dyspnea cycle; support group or pulmonary rehab referral.
• Value–Belief: adherence to treatment and constraints.

Objective Data Examination

• Physical examination components:
  • Vital signs with pulse oximetry.
  • Nose: patency, inflammation, deformity, symmetry, discharge.
  • Mouth and pharynx: color, lesions, masses, gums, dentition, bleeding.
  • Neck: symmetry, tenderness, swollen nodes.
  • Thorax and lungs: inspection, palpation, percussion, auscultation; use imaginary lines to describe locations of abnormalities.

Technique of Assessment (Exam Procedure)

• Expose chest in well-lit room with privacy.
• Begin on the posterior chest; ask patient to lean forward with arms folded.
• Complete all maneuvers rather than repeatedly switching sides (anterior/posterior).
• Position: patient sit upright or supine with HOB at 30° (semi-Fowler’s) to assess the anterior chest.
• Patient may lean on table for support during breathing.

Inspection of the Chest and Lungs

• Assess appearance and signs of respiratory distress.
• Evaluate shape, symmetry, and movement.
• Normal anteroposterior diameter (AP ratio) is 1:2.
• Look for sternal abnormalities: pectus carinatum (pigeon chest) or pectus excavatum.
• Respiratory rate, depth, and rhythm; normal rate is RR = 12$-$20 ext{ breaths/min} with an inspiratory-to-expiratory (I:E) ratio of $1:2$.
• Look for abnormal breathing patterns: Kussmaul, Cheyne–Stokes, Biot’s.
• Assess skin and nails for cyanosis and clubbing.

Palpation

• Tracheal position: displacement may indicate tension pneumothorax or other pathology.
• Tracheal deviation toward side of pneumonectomy or away from tension pneumothorax.
• Expansion: normal expansion is about $1''$ (2.5 cm) of chest wall symmetry.
• Fremitus: palpable vibration through the chest during voice transmission (to be evaluated in exam).

Percussion

• Used to assess density or aeration of the lungs.
• Technique: start above the clavicles and percuss downward, intercostal space by intercostal space, with patient semi-sitting or supine.
• For posterior chest, have patient sit leaning forward with arms folded.

Auscultation

• Sequence of examination: systematic listening to lung fields.
• Normal breath sounds and their locations.
• Abnormal/adventitious breath sounds:
  • Crackles (rales) — fine or coarse
  • Wheezes
  • Stridor
  • Pleural friction rub
• Abnormal voice sounds:
  • Egophony
  • Bronchophony
  • Whispered pectoriloquy

Diagnostic Studies for Respiratory System

• Assessing for hypoxia:
  • Oximetry
  • Arterial blood gases (ABG)
  • Evaluate SaO₂ or PaO₂ with adequate cardiac function
  • CO₂ monitoring for hypercapnia
  • Evaluate venous O₂ saturation if impaired cardiac output or hemodynamic instability

Oximetry

• Measurement of blood O₂ saturation; can be performed invasively or noninvasively.
• Arterial O₂ saturation (SaO₂) and pulse oximetry (SpO₂): noninvasive, continuous monitoring.
• Common measurement sites: finger, toe, ear, forehead, nasal bridge.
• Relationship: SpO₂ ≈ SaO₂; represents how much O₂ hemoglobin (Hb) is carrying relative to its maximum capacity.
• Normal SpO₂ values: > $95\%$.
• Note on accuracy: if in doubt, obtain ABGs; oximetry may be less accurate at SpO₂ < 70% and can be affected by various factors.

Venous Oximetry and Central Venous Measurements

• Venous pulse oximetry is invasive and helps determine tissue oxygenation.
• Central venous O₂ saturation (ScvO₂) typically obtained from the superior vena cava (SVC).
• Mixed venous O₂ saturation (SvO₂) comes from the pulmonary artery.
• Normal values at rest: 60\% \, \leq\SvO2, ScvO2\leq 80\%.
• Decreased values (< 60%) suggest insufficient O₂ delivery or increased consumption; signs include altered mental status, decreased strength, weak pulses, poor capillary refill, reduced urine output, pale/cool skin.
• Increased values may indicate clinical improvement or problems such as sepsis (excess O₂ delivery or reduced extraction).

Arterial Blood Gases (ABGs)

• ABG analysis provides:
  • Oxygenation: $PaO<em>2$, $SaO</em>2$
  • Ventilation: $PaCO_2$
  • Acid-base: pH, $HCO_3^-$
• Normal arterial values depend on age and altitude; typical discussion includes oxygenation and acid-base balance.

CO₂ Monitoring and Capnography

• Capnography provides continuous measurement and display of exhaled CO₂:
  • Transcutaneous CO₂ (PtCO₂) electrode on the skin.
  • End-tidal CO₂ (PetCO₂) sensor analyzes exhaled air.
• Usually presented as a graph of expiratory CO₂ vs. time.

Sputum Studies and Skin Tests

• Sputum studies:
  • Evaluate color, volume, viscosity, presence of blood.
  • Specimens obtained via expectoration, suctioning, or bronchoscopy.
  • Induction by patient inhaling an irritating aerosol may be used.
• Skin tests:
  • Intradermal injection of an antigen to assess allergies or exposure to TB bacilli or fungi.
  • Results interpretation:
  • Positive = exposure to antigen; Negative = no exposure or depression of cell-mediated immunity (e.g., HIV).

Skin Tests: Nursing Considerations

• Prevention of false-negative reactions:
  • Administer intradermally (not subcutaneously).
  • Circle the site and instruct the patient not to rub the area.
• Documentation: draw and label a diagram of the test site in the health record.
• Reading results:
  • Ensure good lighting.
  • Measure induration in millimeters (mm); do not measure reddened, flat areas.

Summary: Key Measurements and Landmarks

• PaO₂ normal: $80\le PaO_2 \le 100\ \text{mmHg}$
• SaO₂ normal: SaO_2 > 95\%
• Intrapleural fluid: $10\text{ to }20\ \text{mL}$
• Respiratory rate: $RR = 12\text{ to }20\ \text{breaths/min}$; I:E ratio $1:2$
• AP chest diameter:AP:lateral ratio = $1:2$
• Trachea: approximately $5''\text{ long} \times 1''\text{ wide}$
• Normal SpO₂: > $95\%$
• Normal ScvO₂/SvO₂ at rest: $60\% \leq SvO<em>2, ScvO</em>2 \leq 80\%$
• Diaphragm innervation: phrenic nerves from C3–C5; injury above C3 can cause diaphragm paralysis
• Key anatomy terms: Carina, Angle of Louis, Pores of Kohn, Hering–Breuer reflex, Egophony/Bronchophony/Whispered pectoriloquy