Key points Lung collapse occurs either from compression of lung tissue or by absorption of gas from lung units with occluded or severely narrowed airways. Many forms of interstitial lung disease exist, varying from purely inflammatory conditions (alveolitis) to those…
Key points Pulmonary oedema occurs when increases in pulmonary capillary pressure or the permeability of the alveolar/capillary membrane cause fluid to accumulate in the interstitial space and alveoli. Pulmonary embolism, with either thrombus or air, partially occludes the pulmonary circulation,…
Key points Whatever the cause, airway narrowing leads to expiratory flow limitation, gas trapping and hyperinflation of the lung, which manifests itself as breathlessness. Asthma involves intermittent, reversible airway obstruction caused by airway inflammation and bronchial smooth muscle contraction, both…
Key points Ventilatory failure occurs when alveolar ventilation becomes too low to maintain normal arterial blood gas partial pressures. There are many causes, involving the respiratory centre, the respiratory muscles or their nerve supply and abnormalities of the chest wall,…
Key points Breathing oxygen at increased atmospheric pressure achieves very high arterial P o 2 values, but venous P o 2 , and therefore minimum tissue P o 2 , only increases at 3 atm absolute pressure. Normal metabolic processes,…
Key points Anaemia has little effect on pulmonary gas exchange but decreases oxygen carriage in the arterial blood in direct proportion to the reduction in haemoglobin concentration. Mechanisms that compensate for the reduced oxygen delivery include increased cardiac output, increased…
Key points Intracellular acidosis from anaerobic metabolism occurs soon after the onset of cellular hypoxia and is worse when there is a plentiful supply of blood and glucose to the cell. Lack of high-energy substrates such as adenosine triphosphate (ATP)…
Key points Hypocapnia occurs when alveolar ventilation is excessive relative to carbon dioxide production, and usually results from hyperventilation because of hypoxia, acidosis or lung disease. Hypercapnia most commonly occurs because of inadequate alveolar ventilation from a multitude of causes,…
Key points All anaesthetic drugs reduce ventilation and impair the ventilatory response to both hypercapnia and hypoxia. Upper airway muscle function is inhibited by anaesthesia, leading to airway obstruction, usually at the level of the soft palate. Functional residual capacity…
Key points Although becoming less popular, one-fifth of the UK population still smokes tobacco, and worldwide, the number of smokers is increasing. Smoking involves the regular inhalation of a variety of toxic compounds that stimulate airway irritant receptors and activate…