Lung volume
During respiratory exercise o varying respiratory amplitude can cause changes in the volume of air held in the lungs.
Basal volume of the lungs Tidal volume (VT). During calm breathing o The volume of air inhaled or exhaled per breath. Replacement inspiratory volume (IRV). The maximum volume of air that can be inhaled after a calm inspiration. Expiratory volume (ERV). The maximum volume of air that can continue to be exhaled after a calm exhalation. Residual Volume (RV) The amount of residual air that cannot be exhaled from the lungs after compensatory exhalation.
The four volumes of the lungs:Deep inspiratory volume (IC). The maximum volume of air that can be inhaled after a calm exhalation. Consists of tidal volume and compensatory inspiratory volume. Lung volume (VC). The maximum volume of air that can be exhaled after maximum inspiration. Consists of deep inspiratory volume and compensatory expiratory volume. Functional residual volume (FRC). The volume of air contained in the lungs after a calm exhalation. Consists of the compensatory expiratory volume and the residual volume. Total lung volume (TLC). The total volume of air contained in the lungs after a deep inspiration. Consists of lung volume and residual air volume. Tidal volume p deep inspiratory volume p compensatory expiratory volume and lung volume can be measured directly with a spirometer. o Functional residual volume and residual volume cannot be measured directly with a spirometer. o Only indirect methods can be used. Total lung volume can be determined by summing spirometry and residual air volume.
Decreased spirometry is seen in thorax, restricted lung expansion, lung tissue damage, airway obstruction, and changes in functional residual air volume often coexist with changes in residual air volume. Residual air volume is increased in obstructive lung diseases such as bronchial asthma and emphysema. Restrictive lung disorders such as diffuse interstitial lung fibrosis, pulmonary occupational disease, and post-pneumonectomy lung tissue compression reduce residual air volume. Residual air volume/total lung volume is used as a clinical assessment index.
Pulmonary ventilation
Pulmonary ventilation function is measured as the volume of air inhaled or exhaled by the lungs per unit time.
Resting ventilation per minute is the product of tidal volume and respiratory rate. o The number of breaths per minute in a normal adult at rest is about 15. o The tidal volume is 500 mlo and its ventilation is 7.5 L/min. 140 ml of gas in the tidal volume is retained in the airway without gas exchange. o It is called anatomical dead space. o Therefore, the alveolar ventilation is only 5.5 L/min.
If the breathing is shallow and fast, the anatomical dead space ventilation is relatively higher o affect the alveolar ventilation. The amount of gas entering the alveoli can be due to insufficient local blood flow resulting in gas exchange with the blood. This part of the gas is called the alveolar dead space volume. The alveolar dead volume plus the anatomical dead volume together is called the physiological dead volume. Alveolar ventilation = (tidal volume – physiologic dead space volume) × respiratory rate. Insufficient alveolar ventilation volume o is commonly seen in emphysema r increased alveolar ventilation volume is seen in hyperventilation syndrome.
Maximum ventilation volume (MVV) The amount of ventilation obtained by breathing as fast and as deeply as possible per unit time. The patient is usually asked to breathe deeply and rapidly for 12 seconds. o The resulting ventilation is multiplied by 5 to obtain the maximum ventilation per minute. It is a simple stress test that measures the patency of the airway, the elasticity of the lungs and thorax, and the strength of the respiratory muscles. It is commonly used as an indicator of the ability to perform thoracic surgery.
Force spirometry (FVC) The expiratory spirometry done at the fastest possible speed. From this, the ratio of the volume exhaled in the first second and the volume exhaled in the first second to the force spirometry can be calculated. Force spirometry is the best current measurement o reflect the expiratory resistance of the larger airways. It can be used as an aid in the diagnosis of chronic bronchitis p bronchial asthma and emphysema. o It can also assess the efficacy of bronchodilators.
Peak expiratory flow rate (PEFR) In the total lung volume position o blow hard and fast to the highest expiratory flow meter o observe the highest expiratory flow rate. The measurement method is simple p easy to perform. It is widely used in epidemiological investigation of respiratory diseases. It is especially useful for the determination of bronchial asthma disease and its efficacy. During 24-hour dynamic observation of the condition of asthma patients o it was found that the lowest value of their peak expiratory flow rate often occurs at 0~5 am.
Pulmonary ventilation blood flow ratio Inhaled air exchanges oxygen and carbon dioxide with the blood in the alveolar capillaries after reaching the alveoli. Lung tissue and blood flow are affected by gravity so that ventilation and blood flow are not perfectly uniform in all parts of the upper and lower lungs. If pulmonary ventilation and blood flow per minute can be maintained at a certain ratio (4s5) on average, o gas exchange can be performed normally.
Pulmonary function measurements reflecting uneven gas distribution are nitrogen cleaning rate and phase III slope rate. In normal subjects, the alveolar nitrogen concentration is less than 2.5% after a 7-minute washout of pure oxygen. The III-phase slope is the average nitrogen concentration increased by the gas at the residual gas position after inhalation of pure oxygen up to the total lung volume o exhalation of 750 ml and 1250 ml does not exceed 1.5%. Impaired small airway function p Long-term smokers or patients with emphysema can cause uneven gas distribution.
If pulmonary ventilation is normal p Decreased or obstructed pulmonary capillary blood flow o Increased alveolar dead space o Increased ventilation/blood flow ratio r If pulmonary fine bronchial obstruction o Inadequate oxygenation of local blood flow o Formation of physiological shunts o Decreased ventilation/blood flow ratio. Pulmonary function tests that reflect the ventilation/flow ratio are physiologic dead space measurement p alveolar arterial oxygen partial pressure difference measurement p physiologic shunt measurement. Increased physiologic dead space is seen in diseases such as red emphysema or pulmonary embolism. Increased physiological fractional flow is seen in disorders such as cyanotic bloated emphysema or adult respiratory distress syndrome.
Small airway ventilation function in the inspiratory state of fine bronchi with an inner diameter of Q2 mm is called small airway o Small airway resistance accounts for only 20% of the total airway resistance. It is difficult to detect with conventional pulmonary function measurements that reflect large airway resistance. Small airway resistance has been measured at low lung volume levels. r Small airway lesions are reversible in the early stages. There are 2 commonly used methods of examining small airway function. The maximum expiratory flow-volume curve (MEFR) looks at the expiratory flow at each instant during the period from expiration at the total lung volume level to the residual air volume. Flow is affected in small airways with impaired function o more than 50% of the exhaled lung volume o especially when 75% of the exhaled lung volume is present.
Closure volume (CV) measures the volume of air that can continue to be exhaled when the small airways at the base of the lung begin to close when the total lung volume is reached near the residual airspace. An increase in closure volume/spirometry % indicates early closure of the small airways at the base of the lungs. It can be caused by small airway pathology or by a decrease in the elastic retraction of the lung.
Impairment of small airway function is common in patients exposed to atmospheric pollution p long-term heavy smokers o long-term exposure to volatile chemicals o early pneumoconiosis p fine bronchial virus infection p asthma in remission p early emphysema p interstitial pulmonary fibrosis, etc.
Respiratory mechanics
Respiratory movements are analyzed from the mechanical point of view.
Compliance: the change in unit volume caused by a change in unit pressure. o It is a common property of all elastic objects. Respiratory system compliance can be divided into total compliance, chest wall compliance and lung compliance according to its components. Total compliance is the change in lung volume caused by the difference in pressure between the alveoli and the atmosphere r Chest wall compliance is the change in lung volume caused by the difference in pressure between the chest cavity and the atmosphere r Lung compliance is the change in lung volume caused by the difference in pressure between the alveoli and the chest cavity. Pulmonary compliance can be further divided into static compliance and dynamic compliance. The lung compliance measured during the respiratory cycle o when airflow is temporarily blocked is static lung compliance. o The lung compliance measured during the respiratory cycle o when airflow is not blocked is dynamic lung compliance. The former reflects the elasticity of the lung tissue o while the latter is also influenced by airway resistance. Reduced pulmonary compliance is mainly seen in pulmonary fibrosis p pulmonary edema p pulmonary atelectasis and pneumonia and other lung disorders that limit lung expansion. In emphysema o pulmonary compliance is increased due to the loss of elastic fibers in the alveolar wall and thus the pressure change required to expand the lung volume to a certain level is lower than in normal lungs.
Another clinical application of pulmonary compliance measurement is the measurement of dynamic pulmonary compliance in the presence of increased respiratory rate (typically 30 and 60 breaths/min or faster). o This measurement can be used as an indicator of small airway dysfunction. The lung compliance is reduced when the respiratory rate increases due to obstruction of the diseased small airways. This change in compliance is influenced by the respiratory rate and is referred to as frequency-dependent compliance.
Airway resistance The difference in pressure required per unit of flow rate. This is generally expressed as the pressure difference (in centimeters of column) at a ventilation rate of 1 liter per second. Increased airway resistance is seen in chronic bronchitis p acute exacerbation of bronchial asthma p swollen cancer p scar tissue or other causes of obstructive ventilatory disorders. In emphysema, the airway resistance increases due to the weakening of the elasticity of the lung to the circumferential pulling force of the bronchus o making the bronchus easily trapped during expiration.
Respiratory work The energy expended to overcome the resistance of the lungs, chest wall and abdominal organs when air enters and leaves the airway. The resistance of the lungs and chest wall includes elastic and inelastic resistance. The work done by the contraction of the respiratory muscles during calm breathing is basically used during inspiration, while the elastic retraction of the lungs during exhalation is sufficient to overcome the inelastic resistance of the air and tissues during exhalation. During calm breathing, the total oxygen consumption of normal human body is 200~300ml/mino and the oxygen consumption of respiratory organs accounts for less than 5% of the total oxygen consumption. The oxygen consumption of respiratory organs as a percentage of total oxygen consumption increases when the volume of ventilation per minute increases.
Diffusion function The main function of the lungs is gas exchange, i.e., the exchange of oxygen and carbon dioxide. The site of gas exchange in the lungs is in the alveoli and follows the principle of diffusion o i.e. gas molecules diffuse from high partial pressure through the alveolar capillary membrane (blood-gas barrier) to low partial pressure o until the pressure equilibrium between the two sides of the membrane is reached. Partial pressure is the percentage of the total pressure of a gas in a gas mixture o the pressure of a particular gas. The partial pressure of oxygen in the alveolar gas is higher than the partial pressure of oxygen in the capillaries of the alveolar membrane. o Therefore, oxygen diffuses from the alveoli through the alveolar membrane into the capillaries and binds to hemoglobin in the red blood cells. The partial pressure of blood carbon dioxide is higher than that of the gas in the alveoli. o Therefore, carbon dioxide diffuses from the blood into the alveoli. Since the diffusion capacity of carbon dioxide is 20 times greater than that of oxygen, once diffusion impairment occurs, it is mainly an impairment of oxygen diffusion. Reduced diffusion is mainly seen in interstitial lung diseases such as diffuse interstitial fibrosis, and in other cases such as emphysema, due to destruction of the alveolar wall and reduced diffusion area, or in anemia, due to reduced hemoglobin, which can reduce pulmonary diffusion.
Blood gas transport
Includes transport of oxygen and carbon dioxide.
Oxygen transport. Oxygen is transported in the blood in two forms o i.e. physical dissolution and binding to hemoglobin Oxygen combines with hemoglobin to form oxyhemoglobin This is the main form of oxygen presence and transport in the blood. The percentage of oxygenated hemoglobin to hemoglobin is called oxygen saturation. Physically dissolved oxygen accounts for only 1.5% of the oxygen content of arterial blood, but oxygen saturation is largely dependent on changes in the partial pressure of physically dissolved oxygen in the blood, which is not a linear relationship but an S-shaped curve. From this curve, we can see that when the partial pressure is 90~100mmHg, the oxygen saturation of arterial blood can reach 95%. When the partial pressure drops to 60mHg, the oxygen saturation can still reach 90%. The oxygen supply to the body tissues is mainly dependent on the oxygen saturation of the blood.
Carbon dioxide transport. There are three main forms of carbon dioxide transport in the blood s physically dissolved carbon dioxide accounts for only about 5% of the total carbon dioxide in the whole blood o but plays an important role in respiratory regulation and acid-base balance in the body. Bicarbonate accounts for about 88-90% of total arterial blood carbon dioxide o About 25% of this is present in the red blood cells o 75% is present in the plasma and is the most important form of carbon dioxide transport in the blood. A small fraction of the carbon dioxide entering the erythrocytes can bind to the alpha amino group of hemoglobin to form hemoglobin carbamate. o It accounts for 5-7% of the total carbon dioxide in the blood and acts more slowly than bicarbonate.
The control and regulation of respiratory movements occurs through three pathways.
Central control and regulation of respiration Human respiration is both random and involuntary (i.e., autonomous). The random respiratory movements are mainly controlled by the cerebral cortex. o Autonomic rhythmic respiration originates in some neural structures of the medulla oblongata.
Neuroreflex regulation of respiration The central nervous system receives impulses from various receptors to regulate respiration. The lungs expand or contract and cause a reflex change in breathing called the tensor reflex, also known as the Herring-Broil II reflex, which inhibits inspiration and keeps it from being too deep and too long.
Respiratory chemoregulation The chemoreceptors associated with respiration can be divided into two categories: central and peripheral, according to their location. The central chemoreceptors are located in the ventral guillotine on the surface of the medulla oblongata and are sensitive to carbon dioxide. When the concentration of carbon dioxide in the blood increases, the chemoreceptors are stimulated to deepen and speed up breathing. Peripheral chemoreceptors are located in the carotid and aortic bodies and are mainly sensitive to hypoxia.
Abnormalities in respiratory rhythm can be caused by impaired respiratory control and regulation.
Exercise test
Changes in cardiopulmonary function are observed through a certain amount of exercise load. The human respiratory and circulatory organs have a large functional reserve, so there can be impairment of cardiopulmonary function before symptoms appear. Exercise tests can be more sensitive in showing early changes in pulmonary function. Shortness of breath is a common symptom and the exercise test can identify whether the shortness of breath is due to cardiopulmonary disorders or to psychological factors. The former can cause changes in cardiopulmonary function through exercise testing, while the latter shows no significant changes. Workforce identification of occupational diseases such as silicosis is also an important objective indicator, in addition to history, signs and chest X-rays, pulmonary function tests or exercise tests in the early stages of the disease. Exercise tests can cause the appearance of cardiopulmonary dysfunction or symptoms in some patients called provocation tests. Some asthmatic patients may have reduced pulmonary ventilation through exercise provocation tests o or even asthma attacks. Early stage coronary artery disease patients can induce ECG changes or angina attacks and other symptoms through exercise provocation test.
Clinical applications
Can assist in clinical diagnosis o Determine the presence of pulmonary dysfunction and the nature and extent of the dysfunction. It is an early diagnostic tool for some pulmonary disorders such as interstitial lung disorders early manifestations can be reduced diffusion function. Abnormal small airway function can be an early manifestation of pulmonary dysfunction in chronic obstructive pulmonary disorders such as chronic bronchitis. It can guide clinical treatment such as bronchial asthma patients after the application of bronchodilators pulmonary function tests can be used as an important indicator of efficacy. It can be used in clinical research such as airway allergy measurement of allergic diseases and sleep respiratory physiology research. Pre-surgical pulmonary function measurements in thoracic surgery patients can help determine the completeness of surgery. The role in the field of labor health and occupational diseases can be