Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle.
A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. A spirometer measures ventilation, the movement of air into and out of the lungs. The spirogram will identify two different types of abnormal ventilation patterns, obstructive and restrictive. There are various types of spirometers that use a number of different methods for measurement.
Exhalation is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing. This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles generate abdominal and thoracic pressure, which forces air out of the lungs.
Spirometry is the most common of the pulmonary function tests (PFTs). It measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is helpful in assessing breathing patterns that identify conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and COPD. It is also helpful as part of a system of health surveillance, in which breathing patterns are measured over time.
The peak expiratory flow (PEF), also called peak expiratory flow rate (PEFR) and peak flow measurement, is a person's maximum speed of expiration, as measured with a peak flow meter, a small, hand-held device used to monitor a person's ability to breathe out air. It measures the airflow through the bronchi and thus the degree of obstruction in the airways. Peak expiratory flow is typically measured in units of liters per minute (L/min).
A wheeze is a clinical symptom of a continuous, coarse, whistling sound produced in the respiratory airways during breathing. For wheezes to occur, part of the respiratory tree must be narrowed or obstructed, or airflow velocity within the respiratory tree must be heightened. Wheezing is commonly experienced by persons with a lung disease; the most common cause of recurrent wheezing is asthma, though it can also be a symptom of lung cancer, congestive heart failure, and certain types of heart diseases.
Functional residual capacity (FRC) is the volume of air present in the lungs at the end of passive expiration. At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm or other respiratory muscles.
An incentive spirometer is a handheld medical device used to help patients improve the functioning of their lungs. By training patients to take slow and deep breaths, this simplified spirometer facilitates lung expansion and strengthening. Patients inhale through a mouthpiece, which causes a piston inside the device to rise. This visual feedback helps them monitor their inspiratory effort. Incentive spirometers are commonly used after surgery or certain illnesses to prevent pulmonary complications.
Lung compliance, or pulmonary compliance, is a measure of the lung's ability to stretch and expand. In clinical practice it is separated into two different measurements, static compliance and dynamic compliance. Static lung compliance is the change in volume for any given applied pressure. Dynamic lung compliance is the compliance of the lung at any given time during actual movement of air.
Restrictive lung diseases are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation. Pulmonary function test demonstrates a decrease in the forced vital capacity.
Pulmonary function testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment. Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. PFTs are normally performed by a pulmonary function technologist, respiratory therapist, respiratory physiologist, physiotherapist, pulmonologist, or general practitioner.
The FEV1/FVC ratio, also called modified Tiffeneau-Pinelli index, is a calculated ratio used in the diagnosis of obstructive and restrictive lung disease. It represents the proportion of a person's vital capacity that they are able to expire in the first second of forced expiration (FEV1) to the full, forced vital capacity (FVC). FEV1/FVC ratio was first proposed by E.A. Haensler in 1950. The FEV1/FVC index should not be confused with the FEV1/VC index as they are different, although both are intended for diagnosing airway obstruction. Current recommendations for diagnosing pulmonary function recommend using the modified Tiffeneau-Pinelli index. This index is recommended to be represented as a decimal fraction with two digits after the decimal point.
Chlornaphazine, a derivative of 2-naphthylamine, is a nitrogen mustard that was developed in the 1950s for the treatment of polycythemia and Hodgkin's disease. However, a high incidence of bladder cancers in patients receiving treatment with chlornaphthazine led to use of the drug being discontinued.
A liquid ventilator is similar to a medical ventilator except that it should be able to ensure reliable total liquid ventilation with a breatheable liquid. Liquid ventilators are prototypes that may have been used for animal experimentations but experts recommend continued development of a liquid ventilator toward clinical applications.
Respiratory inductance plethysmography (RIP) is a method of evaluating pulmonary ventilation by measuring the movement of the chest and abdominal wall.
Heated humidified high-flow therapy, often simply called high flow therapy, is a type of respiratory support that delivers a flow of medical gas to a patient of up to 60 liters per minute and 100% oxygen through a large bore or high flow nasal cannula. Primarily studied in neonates, it has also been found effective in some adults to treat hypoxemia and work of breathing issues. The key components of it are a gas blender, heated humidifier, heated circuit, and cannula.
Modes of mechanical ventilation are one of the most important aspects of the usage of mechanical ventilation. The mode refers to the method of inspiratory support. In general, mode selection is based on clinician familiarity and institutional preferences, since there is a paucity of evidence indicating that the mode affects clinical outcome. The most frequently used forms of volume-limited mechanical ventilation are intermittent mandatory ventilation (IMV) and continuous mandatory ventilation (CMV). There have been substantial changes in the nomenclature of mechanical ventilation over the years, but more recently it has become standardized by many respirology and pulmonology groups. Writing a mode is most proper in all capital letters with a dash between the control variable and the strategy.
Inverse ratio ventilation (IRV) is not necessarily a mode of mechanical ventilation though it may be referred to as such. IRV is a strategy of ventilating the lungs in such a way that the amount of time the lungs are in inhalation is greater than the amount of time they are in exhalation, allowing for a constant inflation of the lungs, ensuring they remain "recruited". The primary goal for IRV is improved oxygenation by forcing inspiratory time to be greater than expiratory time increasing the mean airway pressure and potentially improving oxygenation. Normal I:E ratio is 5:6, so forcing the I:E to be 2:1, 3:1, 4:1, is the source of the term for the strategy.
Mean airway pressure typically refers to the mean pressure applied during positive-pressure mechanical ventilation. Mean airway pressure correlates with alveolar ventilation, arterial oxygenation, hemodynamic performance, and barotrauma. It can also match the alveolar pressure if there is no difference between inspiratory and expiratory resistance.
A respiratory pressure meter measures the maximum inspiratory and expiratory pressures that a patient can generate at either the mouth (MIP and MEP) or inspiratory pressure a patient can generate through their nose via a sniff maneuver (SNIP). These measurements require patient cooperation and are known as volitional tests of respiratory muscle strength. Handheld devices displaying the measurement achieved in centimetres of water pressure (cmH2O) and the pressure trace created, allow quick patient testing away from the traditional pulmonary laboratory and are useful for ward-based, out-patient and preoperative assessment, as well as for use by pulmonologists and physiotherapists.
