Day: May 30, 2024

The airways are also prone to being affected by hypersensitivity reactions – these are abnormal immune responses to normal stimuli. These are categorised into 4 different types.   Type 1 This is a rapid allergic reaction due to pre-formed IgE antibody to an exposed antigen. – It eventually leads to a large increase in histamine which can lead to anaphylactic shock.   Histamine is stored in mast cells and is released by calcium-dependent exocytosis: – IgE binds IgE receptor –> increases intracellular IP3 –> increases Calcium – Intracellular cAMP is an antagonist and works to block release of histamine Histamine

At the lungs, alveolar ventilation is matched with pulmonary blood flow to create a concentration gradient to exchange O2 and CO2 – Oxygen binds to haemoglobin and is transported in the blood. – The dissociation curve is sigmoidal, due to the cooperative binding of oxygen molecules. – This means that it is at first difficult to load the first oxygen molecule onto haemoglobin – However, once the first one binds, this causes a conformational shift which increases haemoglobin’s affinity for oxygen   It is then easier to bind the next oxygen molecules. This causes the steep rise in the oxygen dissociation

We can use spirometry to measure some key volumes of the lungs: Tidal volume = volume of air breathed in and out of the lungs during quiet breathing (500ml)   Inspiratory reserve volume = the maximal volume that can be inhaled from the end-inspiratory level   Expiratory reserve volume = describes the maximal volume of air that can be further exhaled subsequent to the volume achieved at the end of the exhalation phase of quiet breathing   Residual volume (RV) = the volume of air left in the lungs following expiration of the expiratory reserve volume i.e. the maximal exhalation capacity   Inspiratory capacity =

The breathing system relies on creating a pressure gradient between the inside and external environment, which needs an intimate relationship between the lungs and chest wall. – Lungs are lined by visceral and parietal pleura, which are separated by a thin layer of fluid.   The volume of thoracic cavity is determined by the outward recoil of chest wall + inward elastic recoil of lungs – These opposing forces are balanced by small negative pleural pressure. Breathing relies on increasing thoracic cage volume which then decreases intrapleural pressure i) At the end of expiration, alveolar pressure (PA) = 0 and

The thorax is divided by a transverse plane at the angle of Louis (T4/5) into the superior and inferior mediastinum. The latter can be subdivided into the anterior, middle and posterior compartments.   Ribs There are a total of 12 ribs: – Ribs 1 to 7 attached to sternum by costal cartilage – “true ribs” – Ribs 8 to 10 attached to the rib above by costal cartilage – “false ribs” – Ribs 11 and 12 are so-called “floating ribs,” as do not articulate with the sternum anteriorly   Airways The airway starts with the trachea which begins, beneath the

Obstructive Sleep Apnoea This is a condition where the walls of the airway briefly collapse during sleep. This obstructs the airway causing cessation of breathing during sleep (apnoea) followed by partial arousal to regain breath. The patient then falls asleep again and the cycle repeats itself. It can lead to pulmonary hypertension and type II respiratory failure. It is classically seen in middle-aged obese men who complain of loud snoring.   Risk factors Obesity Large tonsils Large tongue (macroglossia) Symptoms Loud snoring Lethargy with daytime napping Morning headache Decreased libido Hypertension Compensated respiratory acidosis   Key tests Epworth sleepiness scale

Acute Respiratory Distress Syndrome (ARDS) This refers to widespread inflammation at the alveolar-capillary interface, increasing the permeability of the alveolar capillaries. Fluid moves out of the permeable capillaries, resulting in non-cardiogenic pulmonary oedema that impairs ventilation. ARDS can progress to organ failure and carries a high morbidity and mortality risk. Causes Direct – this is due to direct lung injury (such as smoke inhalation) Indirect – due to conditions which cause inflammation (such as sepsis, shock and acute pancreatitis)   Symptoms Acute onset tachypnoea, dyspnoea Bilateral inspiratory crackles Low oxygen saturations and cyanosis with respiratory distress   Key tests ABG

This is a broad term which is most common cancer in the UK, which typically occurs in people of 60 years. It can be broken down into several types of specific types of cancers, which have different histology. Metastases are more common, typically arising from breast, prostate, colon, kidney and uterus. NICE Referral Guidelines   Carcinoma of the bronchus This type of carcinoma is generally divided into 2 main categories:   Small Cell Carcinoma This is a tumour which arises from neuro-endocrine cells in the lungs. It is named “small cell” because the cancerous cells look small when viewed under

These conditions are characterised by a restrictive pattern of spirometry. They occur due to inflammation which leads to fibrosis (irreversible scarring) of the lungs, meaning they cannot expand fully, reducing the vital capacity. Both the FVC and FEV1 are reduced in restrictive conditions. However, the FEV1/FVC ratio stays constant as both FEV1 and FVC decrease proportionally. Different conditions cause fibrosis predominantly in the upper or lower zones.   Upper Zone Fibrosis (BREASTS) Lower Zone Fibrosis (BRAINS) Berylliosis Bronchiectasis Radiation Rheumatoid Arthritis Extrinsic Allergic Alveolitis Asbestosis Ankylosing spondylitis Idiopathic Pulmonary Fibrosis Silicosis Nitrofurantoin (+ amiodarone, bleomycin, methotrexate) TB Scleroderma Sarcoidosis     Interstitial

Asthma Asthma is a disease that is characterised by reversible bronchoconstriction, bronchial hyper-responsiveness, and airway inflammation. Allergens induce a Th2 response which stimulates production of IgE and attracts eosinophils to the airways, leading to airway inflammation. This leads to the release of chemical mediators (such as histamine and leukotrienes) which leads to bronchoconstriction increasing airway resistance.   Risk factors Personal or family history of atopic conditions (allergic rhinitis, eczema) Air pollution Precipitants – cold air, allergens (ask about pets, carpet etc.) Drugs – e.g., aspirin intolerant asthma (usually features nasal polyps) Occupational (baking, factory work) – this classically causes reduced peak

Pneumonia This used to describe a lower respiratory tract infection which often occurs when normal defences are impaired It is a blanket term which can be subdivided into a number of types, with different causes and features:   Lobar pneumonia This is characterised by continuous consolidation of a lobe of the lung. It is most frequently due to a bacterial agent, e.g., Streptococcus pneumoniae, Klebsiella pneumoniae, Haemophilus influenzae and Moraxella catarrhalis.   Bronchopneumonia This is characterised by discontinuous areas of consolidation, often bilaterally in the basal lobes, with predominance around the bronchioles. It is usually caused by bacterial agents: Staph

Acute epiglottitis This refers to acute inflammation of the epiglottis, which is often caused by the bacteria Haemophilus influenzae type B. It needs to be recognised and treated quickly as it can lead to airway obstruction. It usually presents in children. However, due to the Haemophilus influenzae type B vaccination, its prevalence has decreased.   Symptoms Rapid onset high fever and malaise Drooling of saliva Muffled voice – due to very sore throat Inspiratory stridor (is a high-pitched sound due to turbulent air flow in the upper airway)   Key tests Usually clinical diagnosis, but fibre-optic laryngoscopy may be performed

Nasal polyp This is a benign, inflammatory proliferation of the lining of the nose, which usually occurs after recurrent colds (infective sinusitis).   Associations Eosinophilic granulomatosis with polyangiitis Conditions causing poor cilia motility, e.g., cystic fibrosis and primary ciliary dyskinesia (previously known as Kartagener’s syndrome) Samter’s triad – nasal polyps and asthma in conjunction with aspirin sensitivity Symptoms Nasal congestion Rhinorrhoea Changes to taste (ageusia) and smell (anosmia)   Management Steroid spray to reduce size of polyp If remains persistent, refer to ENT for examination and removal   Nasopharyngeal Carcinoma This is a malignant squamous cell tumour of the nasopharynx.