Respiratory system

Ventilation

The mechanical movement of gases in and out of the lungs.

Diffusion

The physical movement of oxygen and carbon dioxide across the alveolar-capillary membrane from an area of higher concentration to lower concentration.

Parietal Pleura

The serous membrane that lines the inner thoracic cavities.

Visceral Pleura

The serous membrane that covers and protects the external lung surfaces.

Angle of Louis (Manubriosternal Junction)

The bony ridge formed by the articulation of the manubrium and body of the sternum, located at the level of the 2nd rib and marking the tracheal bifurcation (carina).

Costal Angle

The angle formed by the intersection of the costal margins at the xiphoid process; expected to be $\le 90^\circ$ in a healthy adult.

Right Mainstem Bronchus

The shorter, wider, and more vertical main bronchus, which makes it the primary pathway for foreign body aspiration or misplaced endotracheal tubes.

Primary Muscles of Inspiration

The diaphragm (contracts downwards) and external intercostal muscles (elevate ribs), which create negative intrathoracic pressure.

Accessory Muscles

Muscles recruited during respiratory distress (such as the sternocleidomastoid, scalenes, pectoralis minor, and abdominal muscles).

Pack-Years

A quantitative measure of cigarette smoking calculated by multiplying the packs smoked per day by the total number of years smoked ($\text{PPD} \times \text{Years}$).

Orthopnea

Difficulty breathing when lying flat, typically quantified by the number of pillows a patient requires to sleep comfortably (e.g., "three-pillow orthopnea").

Paroxysmal Nocturnal Dyspnea (PND)

A sensation of shortness of breath that awakens the patient from sleep, forcing them to sit upright to catch their breath.

Hemoptysis

The coughing up of blood-streaked mucus or frank blood originating from the respiratory tract.

Pleuritic Chest Pain

Sharp, stabbing chest pain that worsens significantly on deep inspiration, often causing patient splinting and shallow breathing.

Eupnea

Normal, quiet, unlabored breathing at a rate of 12 to 20 breaths per minute in adults.

Tachypnea

An abnormally rapid respiratory rate exceeding 20 breaths per minute.

Bradypnea

An abnormally slow respiratory rate falling below 12 breaths per minute.

Kussmaul Respirations

A deep, rapid, and labored breathing pattern classically associated with metabolic acidosis or diabetic ketoacidosis (DKA).

Cheyne-Stokes Respirations

A breathing pattern characterized by regular alternating periods of deep, rapid breathing (waxing and waning) followed by regular periods of apnea.

Barrel Chest

An abnormal thoracic configuration where the anteroposterior-to-lateral diameter ratio approaches 1:1, caused by chronic air trapping in emphysema/COPD.

Clubbing

An increased nailbed angle ($\ge 180^\circ$) with loss of the normal diamond window, indicating chronic tissue hypoxia (seen in COPD, cystic fibrosis, and lung cancer).

Vesicular Breath Sounds

Low-pitched, soft, breezy breath sounds where inspiration is longer than expiration ($2.5:1$ ratio), heard normally over peripheral lung fields.

Bronchovesicular Breath Sounds

Moderate-pitched breath sounds where inspiration equals expiration ($1:1$ ratio), heard normally at the 1st and 2nd intercostal spaces anteriorly and between the scapulae posteriorly.

Bronchial Breath Sounds

High-pitched, loud, hollow breath sounds where expiration is longer than inspiration ($1:2$ ratio), heard normally only over the trachea.

Crackles (Rales)

Discontinuous, popping adventitious breath sounds caused by fluid or secretions in the alveoli (pneumonia, heart failure); not cleared by coughing.

Wheezes

High-pitched, musical, continuous squeaking sounds caused by narrowed small airways (asthma, bronchospasm).

Rhonchi

Low-pitched, coarse, snoring or moaning adventitious sounds caused by mucus obstruction in large airways; may clear with coughing.

Stridor

A harsh, high-pitched inspiratory sound caused by upper airway or tracheal obstruction (croup, foreign body). Medical emergency.

Pleural Friction Rub

A superficial, grating adventitious sound caused by inflamed pleural surfaces rubbing together.

Tactile (Vocal) Fremitus

Palpable chest wall vibrations felt while the patient recites "ninety-nine"; increased in consolidation, decreased or absent in fluid/air barriers.

Crepitus

A coarse, crackling sensation palpated under the skin caused by subcutaneous air leakage.

Resonance

The normal, hollow percussion tone heard over healthy adult lung tissue.

Hyperresonance

A booming, hyperinflated percussion tone heard when air is trapped (emphysema, pneumothorax).

Dullness

A thud-like, dense percussion tone heard over solid tissue or fluid accumulation (atelectasis, pleural effusion, pneumonia).

Bronchophony

A vocal resonance test where the patient speaks "ninety-nine"; normal is muffled, but consolidation makes it clear and loud.

Egophony

A vocal resonance test where the patient says "E-E-E"; normal sounds like "E", but consolidation causes it to sound like a nasal "A-A-A".

Whispered Pectoriloquy

A vocal resonance test where the patient whispers "one-two-three"; normal is faint/inaudible, but consolidation makes it clear and distinct.

Pneumonia

Terminal bronchiole/alveolar infection characterized by fever, productive yellow/green sputum, dullness, increased fremitus, and crackles.

Tuberculosis (TB)

A contagious bacterial infection causing night sweats, weight loss, fever, and classic rust-colored sputum.

Asthma

Hyperreactive airway disease causing bronchoconstriction, expiratory wheezing, dyspnea, and prolonged expiration.

Emphysema

A form of COPD involving destruction of alveolar walls leading to permanent air trapping, barrel chest, hyperresonance, and pursed-lip breathing.

Chronic Bronchitis

A form of COPD defined by hypersecretion of mucus with a productive cough for $\ge 3$ months in 2 consecutive years, manifesting with rhonchi and cyanosis.

Pneumothorax

Presence of air in the pleural space causing lung collapse, pleuritic pain, hyperresonance, and absent breath sounds.

Tension Pneumothorax

A life-threatening emergency pneumothorax causing tracheal deviation away from the affected side, hypotension, and mediastinal shift.

Pleural Effusion

Accumulation of serous fluid in the pleural space causing dullness, decreased fremitus, and absent breath sounds.

Atelectasis

Alveolar collapse resulting in dullness on percussion, decreased fremitus, and diminished or absent breath sounds (common postoperatively).

Croup Syndrome

A pediatric upper airway infection causing a barking cough and inspiratory stridor; strictly avoid invasive throat/oral exams with tongue depressors if epiglottitis is suspected to prevent total laryngospasm.