Glossary

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Glossary Entries
Word(s)	Definition	Image	Caption	Link	Source
COPD	Chronic Obstructive Pulmonary Disease usually involves both chronic bronchitis and emphysema, the proportions of which can vary from patient-to-patient and is dependent on the cause. Ninety percent of COPD is caused by tobacco use. Related Glossary Terms: Chronic Bronchitis, Emphysema
Conducting zone	The conducting zone is comprised of upper and early stages of the bronchial tree; trachea, primary to tertiary bronchi and the terminal bronchioles. Related Glossary Terms: Alveolar Ventilation, Anatomical Deadspace, Respiratory Zone
Anatomical Deadspace	Initial airways of the bronchial tree that do not perform gas exchange. The role of these airways is to conduct air rather than perform gas exchange. Anatomical deadspace has a volume of approximately 150 mls and must be considered when calculating alveolar ventilation. Related Glossary Terms: Alveolar Ventilation, Conducting zone, Minute Ventilation, Respiratory Zone
Bronchoconstriction	Inappropriate (pathological) contraction of airway smooth muscle that leads to airway narrowing and increased airway resistance. Bronchoconstriction (sometimes referred to as bronchospasm) is a major component of asthma (the other being accompanying airway inflammation).
Alveolus	A balloon like structure constructed of squamous Type 1 and Type 2 cells found at the end of the respiratory ducts. Collectively the alveoli provide the colossal surface area and airspace needed for effective gas exchange. Related Glossary Terms: Ascinus
Alveolar Ventilation	The amount of air (liters per minute) that reaches the gas exchange surface (respiratory zone). Alveolar ventilation is calculated by subtracting dead space ventilation from minute ventilation. Related Glossary Terms: Anatomical Deadspace, Conducting zone, Minute Ventilation, Respiratory Zone
Chloride shift	TBA
Bohr effect (shift)	The rightward shift of the oxygen saturation curve associated with elevated PCO₂. The consequence of this shift is that hemoglobin releases O₂ more readily when in a high PCO₂ environment, such as in tissue with a high metabolic rate (and therefore high O₂ demand). Related Glossary Terms
Boyle’s Law	Boyle’s law states that the pressure of a gas is inversely proportionate to the volume it occupies. In terms of pulmonary physiology and mechanics, this means as the lung expands (volume increases) the pressure in the lung falls. Conversely, as the lung relaxes (volume decreases) the pressure rises.
Chronic Bronchitis	Chronic bronchitis involves long-term or repeated inflammation of the airway walls that leads to their narrowing and eventually remodeling. It is associated with a productive cough as chronic inflammation leads to the hyperplasia and hypertrophy of mucus glands and consequently over-production of thicker mucus that has to be removed by the cough. Mucus can also lead to airway narrowing and even complete blockage (plugging). Because of its tendency to narrow airway (through inflamed walls or mucus), Chronic Bronchitis is a major component of COPD. Related Glossary Terms: COPD, Emphysema
Ascinus	The functional unit of the lung comprised of the respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli. Related Glossary Terms: Alveolus, Respiratory Zone
Laplace’s Law	Laplace’s Law describes the relationship between the radius and wall tension of a cylinder or sphere required to oppose internal pressure. In terms of pulmonary mechanics, Laplace’s Law states that the surface tension generated by fluid on the internal surface of an alveolus will have a more effective collapsing force the smaller the alveolus becomes, i.e. the smaller the radius, the more surface tension tends to collapse an alveolus.
Inspiratory Reserve Volume	The volume that can be inhaled after a normal tidal inhalation is complete. (Abbreviation = IRV and Units = mls). Related Glossary Terms: Inspiratory Capacity
Accessory muscles	A group of thoracic muscles (sternocleidomastoids, scalenes and pectoralis minor) that extent the expansion of the thoracic cage to increase tidal volume during periods of high ventilatory drive. Use of these muscles to breathe is a useful clinical sign and indicative of a significant problem when observed when the patient is at rest. Related Glossary Terms: Tidal volume, Ventilatory drive
Wakeful drive to breathe	The neural activity of higher brain centers that influences breathing independently of brainstem chemoreflexes. The wakeful drive is excitatory, and hence its removal during sleep causes breathing to decline and arterial PCO ₂ to rise 2-4mmHg above wakeful levels. Related Glossary Terms: Ventilatory drive
Vital Capacity	The volume that can be expelled from the lung after an inspiration to Total Lung Capacity (TLC). This differs to TLC as TLC includes Residual Volume. When a complete expiration is perform forcefully, as in some lung function tests, the volume is referred to as Forced Vital Capacity (FVC). (Abbreviation = VC and Units = ml). Related Glossary Terms: Residual Volume, Total Lung Capacity
Visceral pleura	The membrane lining surround the external surface of the lungs that forms the internal boundary of the pleural space. Related Glossary Terms: Intra-pleural pressure, Parietal pleura, Pleural Space
Ventilatory drive	A term used to encompass the neural activity deployed to achieve respiratory muscle activation and alveolar ventilation. Ventilatory drive can be affected by chemoreflexes, intra-pulmonary receptors and higher brain centers. Related Glossary Terms: Accessory muscles, Tidal breathing, Wakeful drive to breathe
wakeful drive	The neural activity of higher brain centers that influences breathing independently of brainstem chemoreflexes. The wakeful drive is excitatory, and hence its removal during sleep causes breathing to decline and arterial PCO₂ to rise 2-4mmHg above wakeful levels.
Total Lung Capacity	The total volume that a lung holds after a maximal inspiration. This differs to Vital capacity as it includes residual volume. (Abbreviation = TLC and Units = ml). Related Glossary Terms: Residual Volume, Vital Capacity
Tidal breathing	Sometimes referred to as resting breathing, with normal 'tidal volume' generating sufficient exchange of air to maintain blood gas homeostasis. Related Glossary Terms: Tidal volume, Ventilatory drive
Tidal volume	The amount of air exchanged from the lungs during a normal breath. Can sometimes sub-divided into inhaled tidal volume and exhaled tidal volume. (Abbreviation = VT and Units = ml). Related Glossary Terms: Accessory muscles, Inspiratory Capacity, Tidal breathing
Respiratory rate	The number of breaths performed in 1 minute. Abbreviation = RR (nb. sometimes fR) Units = breaths per minute (bpm)
Respiratory Zone	Regions of the lung capable of performing gas exchange through having close proximity to pulmonary capillaries and thin structural walls. The respiratory zone is comprised of the respiratory bronchioles, respiratory ducts and alveoli. Related Glossary Terms: Alveolar Ventilation, Anatomical Deadspace, Ascinus, Conducting zone
Spirometer	A device to measure the volume of air that flows to and from the mouth and is common in pulmonary function test labs.
Residual Volume	The volume remaining in the lung after a complete expiratory effort. Not passing through the airways this volume cannot be measured by spirometry, but can be measured with more sophisticated techniques such as whole-body plethysmography. Abbreviation = RV
Pleural Space	The fluid filled space between the visceral pleural membrane that surrounds the lungs and the parietal pleural membrane that lines the thoracic cavity. Sometimes referred to as the intra-pleural space. Related Glossary Terms: Intra-pleural pressure, Parietal pleura, Visceral pleura
Radial Traction	The effect of lung parenchymal fibers pulling open alveoli, small airways and blood vessels during expansion of the lung. Sometimes referred to as ‘Parenchymal traction’.
Minute Ventilation	The amount of air (liters per minute) exchanged in the lung and airways in one minute. Minute ventilation is measured at the mouth, so includes air from anatomical deadspace and that reaching the respiratory zone. Related Glossary Terms: Alveolar Ventilation, Anatomical Deadspace
Intra-pleural pressure	The pressure within the intra-pleural space. This is usually negative because of the lungs recoil inward and the chest-walls tendency to spring outward. During inspiration the intra-pleural pressure becomes more negative, and less negative during expiration. During forceful (active expiration) the pleural membranes can be compressed together by the action of the expiratory muscles and intra-pleural pressure can become positive. Related Glossary Terms: Parietal pleura, Pleural Space, Visceral pleura
Lung Compliance	A measure of the distensibility of the lung determined by the volume change achieved by a particular change in airway pressure.
Mucocilary Escalator	A term describing the action of airway ciliated epithelium moving mucus secretion away from the gas exchange surfaces. Airway remodeling and some lung diseases can impair the efficiency of the mucocilary escalator and impede expulsion of particulates and pathogens causing airway irritation and infection.
Parietal pleura	The membrane lining the inside of the thoracic cage that forms the external boundary of the pleural space. Related Glossary Terms: Intra-pleural pressure, Pleural Space, Visceral pleura
Emphysema	Emphysema involves abnormal and permanent enlargement of the airspaces distal to the terminal bronchioles that is accompanied by destruction of the air-space walls, without obvious fibrosis. Concurrent lose of elastic parenchymal tissue leads poor lung recoil and more collapsable airways (loss of radial traction). The consequent active exhalation (positive intra-pleural pressure) exacerbates airway collapse leading to obstruction. Because of this, emphysema is an obstructive disorder and a common component of COPD. Related Glossary Terms: Chronic Bronchitis , COPD
Expiratory Reserve Volume	The amount of lung volume that can be exhaled after a normal expiration. (Abbreviation = ERV and Units = ml)
Haldane Effect
Inspiratory Capacity	The volume that can be inhaled after a normal tidal expiration. Clinically useful as a diminished inspiratory capacity is indicative of hyperinflation. (Abbreviation = IC and Units = mls). Related Glossary Terms: Inspiratory Reserve Volume, Tidal volume