Pulmonary Oedema is the accumulation of excess fluid in the lung tissue and alveoli, causing severe breathlessness and impaired gas exchange. Causes: Cardiogenic (most common - Left ventricular failure, increased pulmonary capillary pressure, fluid leaks into alveoli - cardiac asthma) and Non-cardiogenic ARDS (Direct lung injury, sepsis, aspiration, near-drowning). Symptoms: severe breathlessness (especially lying flat - orthopnoea), pink frothy sputum, cyanosis, crackling sounds (crepitations). Treatment: oxygen, diuretics (furosemide), morphine, vasodilators (cardiogenic); treat underlying cause.

Asbestosis is an occupational lung disease (pneumoconiosis) caused by prolonged inhalation of asbestos fibres, leading to progressive pulmonary fibrosis. Other pneumoconioses: Silicosis = inhalation of silica dust (miners, quarry workers, sandblasters - eggshell calcification of lymph nodes), Anthracosis (Coal workers' pneumoconiosis) = inhalation of coal dust (coal miners - black lung disease), Byssinosis = inhalation of cotton dust (textile workers - Monday fever), and Bagassosis = inhalation of sugarcane dust. Asbestos also causes mesothelioma (cancer of the pleura) - with a long latency period of 20-40 years.

Epistaxis is the medical term for a nosebleed - bleeding from the nasal cavity. The nose has a rich blood supply particularly at Kiesselbach's (Little's) area on the anterior nasal septum - the most common site of nosebleeds. Types: Anterior epistaxis (most common - 90% - from Kiesselbach's area; usually minor; controlled by pinching) and Posterior epistaxis (less common but more serious - from posterior nasal arteries; may require packing). Causes: dry air, trauma, hypertension, blood thinners, infections. First aid: lean forward, pinch the soft part of the nose for 10-15 minutes (NOT backward - to avoid swallowing blood).

Cheyne-Stokes Respiration is an abnormal breathing pattern characterised by a cyclic waxing and waning of breathing depth: Breathing gradually increases in depth (crescendo), then gradually decreases (decrescendo), followed by a period of apnoea (no breathing), then cycle repeats. Caused by: heart failure (delayed chemoreceptor feedback due to poor cardiac output), stroke/brain injury, altitude, opioid overdose. The cycle lasts about 30-90 seconds. Named after John Cheyne and William Stokes (19th century Irish physicians). Kussmaul breathing = deep, regular, rapid breathing seen in metabolic acidosis (DKA).

Tachypnoea is the medical term for an abnormally fast breathing rate - greater than 20 breaths per minute in adults. It is one of the earliest signs of respiratory distress or systemic illness. Causes include: pneumonia, asthma, COPD exacerbation, pulmonary embolism, sepsis, acidosis, anxiety, pain, fever. Compare with: Bradypnoea = rate <12/min (opioid overdose, brain injury, sleep), Eupnoea = normal breathing (12-20/min), Apnoea = no breathing, Hyperpnoea = increased depth (not necessarily rate), Kussmaul breathing = deep, rapid breathing in metabolic acidosis (diabetic ketoacidosis).

Pertussis (Whooping Cough) is a highly contagious respiratory disease caused by the bacterium Bordetella pertussis. It is characterised by severe paroxysmal (spasmodic) coughing fits followed by a characteristic high-pitched 'whoop' sound during the deep intake of breath after coughing. Three stages: Catarrhal (cold-like symptoms), Paroxysmal (severe coughing fits), and Convalescent (gradual recovery). Most dangerous in infants - can be fatal. Prevention: DPT/DTaP vaccine (Diphtheria, Pertussis, Tetanus). Treatment: erythromycin/azithromycin (antibiotics).

Anatomical Dead Space is the volume of air (~150 mL) that fills the conducting airways (nose, pharynx, larynx, trachea, bronchi, bronchioles) during each breath - these airways conduct air but do NOT participate in gas exchange. Of the normal tidal volume of 500 mL, only 350 mL reaches the alveoli for actual gas exchange. Physiological dead space includes anatomical dead space PLUS any non-functioning alveoli (alveoli that are ventilated but not perfused). In healthy individuals, physiological dead space = anatomical dead space.

The Eustachian (Auditory/Pharyngotympanic) Tube connects the middle ear to the nasopharynx and serves to equalise air pressure on both sides of the eardrum (tympanic membrane). When you swallow, yawn, or chew, the tube briefly opens allowing pressure equalisation - this is why ears pop during changes in altitude (flying, diving). Dysfunction: Otitis media (middle ear infection) is common in children due to a shorter, more horizontal Eustachian tube. Blockage causes ear fullness, pain, and muffled hearing during colds or allergies.

The Diaphragm is the most important (primary) muscle of inspiration, responsible for approximately 75% of the air movement during normal quiet breathing. During inspiration: the diaphragm contracts, domes flatten, thoracic cavity volume increases, pressure drops, air rushes in. It is innervated by the phrenic nerve (arising from C3, C4, C5 nerve roots). Mnemonic: C3, 4, 5 keeps the diaphragm alive. During forced inspiration (exercise, respiratory distress), accessory muscles assist: scalenes, sternocleidomastoid, pectoralis minor.

Important oxygen-related terms: Hypoxaemia = Low oxygen in the blood (PaO2 <80 mmHg or SpO2 45 mmHg) - CO2 retention. Cyanosis = Blue discolouration of skin/lips due to deoxygenated haemoglobin - appears when >5 g/dL of Hb is deoxygenated. Anaemia = Low haemoglobin - reduced O2 carrying capacity but PaO2 may be normal.