I. Lung Volume Measurement Definition of the Components of Lung Volume The volume of gas in the lungs is changed due to the movement of the respiratory muscles with the expansion and contraction of the thorax; when breathing calmly, the amplitude of the thoracic movement is small, so the change in the volume of gas in the lungs is also small; when inhaling deeply, the lungs expand more, and thus inhale more gas. The total gas volume of the lungs can be categorized into the following 4 base volumes: Tidal volume (VT): the volume of gas exhaled or inhaled each time during calm breathing. Inspiratory Reinspiratory Volume (IRV): The volume of gas that can be inhaled at the end of a calm inhalation with a maximum deep inhalation. Expiratory Volume (ERV): The volume of gas that can be exhaled by a maximum deep expiration at the end of a calm expiration. Residual Volume (RV): The volume of air that remains in the lungs at the end of maximal expiration. The following 4 lung volumes are composed of 2 or more base volumes. Inhalation Capacity (IC): the volume of air that can be inhaled at the end of a calm expiration by performing a maximal deep inhalation, consisting of tidal volume and make-up inhalation volume. Vital Capacity (VC): the volume of air that can be exhaled by maximal deep expiration at the end of maximal inspiration (equal to the volume of deep inspiration plus the volume of compensatory expiration), and the volume of air that can be inhaled by maximal deep inspiration at the end of maximal expiration can also be determined, the former is also known as expiratory vital capacity, and the latter is also known as inspiratory vital capacity. Functional Residual Capacity (FRC): The volume of air contained in the lungs at the end of calm expiration, consisting of expiratory and residual volumes. Total Lung Capacity (TLC): the volume of air contained in the lungs after maximal inspiration, equal to spirometry plus residual air volume. Lung volume is related to age, sex and height, and the size of lung volume has an effect on gas exchange. Measurement methods Tidal volume, deep inspiration volume, expiratory volume and lung capacity can be measured directly by spirometry, while residual air volume should be measured by gas dilution method or body volume tracing method. The gas dilution method includes nitrogen flushing and helium dilution, while the body volume tracing method adopts Boyle’s law, which is measured in an airtight chamber. Clinical application The measurement of lung volume usually reflects the activity of the thorax and the elastic changes of the lungs and thorax. Therefore, changes in respiratory physiologic mechanisms caused by thoracic and pulmonary diseases are often reflected as changes in lung volume. Lung volume represents the respiratory amplitude of maximum expansion and contraction of the lungs, and in any clinical situation where this respiratory amplitude is restricted, lung volume decreases, which can be seen in extra-thoracic, pleural and intrapulmonary lesions. Examples include thoracic deformities, pneumothorax, pleural effusion, pleurisy, pulmonary stromal disease, and intrapulmonary space-occupying lesions. Increased residual air volume and functional residual air volume indicate hyperinflation of the lungs and are seen mainly in emphysema and partial bronchial obstruction and thoracic deformities. Total lung volume is the sum of lung volume and residual air volume. An increase in total lung volume is mainly seen in emphysema; a decrease in total lung volume is seen in some pneumothoracic restrictive diseases and extensive lung disorders, such as pulmonary edema, pulmonary congestion, pulmonary atelectasis, lung tumors and so on. Second, ventilation function measurement ventilation refers to the lungs to inhale fresh air with high oxygen content from the outside world, and at the same time, the gas with low oxygen content and high CO2 in the alveoli will be discharged from the body. It is an important part of the process of gas exchange between the body and the outside world. Resting Ventilation The so-called resting ventilation (VE) is the resting state, the sum of the volume of air exhaled per minute, that is, to maintain the metabolism of the resting state of the volume of ventilation per minute, which is equal to the tidal volume multiplied by the respiratory rate. It is usually about 10L for normal men and 9L for women. Because of the large reserve of ventilatory function, resting ventilation is usually not abnormal unless there is a severe ventilatory disorder. An increase in resting ventilation is considered hyperventilation and can cause respiratory alkalosis; a decrease in resting ventilation is considered hypoventilation and can cause respiratory acidosis. Maximal Ventilation Maximal Ventilation Volume (MVV) is the volume of ventilation obtained by taking a deep, rapid breath with maximum force per unit of time. It reflects the dynamic function of respiration and is one of the more meaningful indicators in the measurement of ventilatory function, which is used to measure the elasticity of lung tissues, airway resistance, thoracic elasticity and the strength of respiratory muscles, and reflects the reserve function and the size of the compensatory capacity of the lungs to ventilate. The method of measurement is to do deep and fast breathing within a limited time (12s or 15s), and multiply the measured expiratory volume by 5 or 4, that is, the value of the maximum independent ventilation per minute. Normal maximum voluntary ventilation depends on the following factors: (1) the integrity of the thorax and normal respiratory muscles; (2) the smoothness of the trachea and bronchi; (3) the soundness and normal elasticity of the lung tissue. Any clinical conditions or pathological changes that can affect the above three factors can cause a decrease in the maximum voluntary ventilation, the common ones are as follows: 1, limited lung activity, such as interstitial fibrosis, massive pleural effusion, pulmonary edema and lung parenchymal lesions. 2, increased airway resistance, such as chest integrity and normal respiratory muscles; ② tracheal and bronchial patency; ③ sound and normal elasticity of lung tissue. 2, increased airway resistance, such as chronic obstructive pulmonary disease, asthma, bronchial tumors and upper airway stenosis, obstruction. Weakening or loss of respiratory muscle strength, such as poliomyelitis and myasthenia gravis. 4, Thoracic deformities such as scoliosis. Maximum voluntary ventilation is considered to be an important predictor of the risk of pulmonary comorbidity before thoracic surgery. It has been noted that mortality in patients undergoing thoracic surgery is related to MVV, with 50% of those who die having an MVV <50% of the predicted value, and to this day, MVV is still used by clinical surgeons as a primary indicator of the ability to perform thoracic surgery in patients with COPD. Forceful lung volume and first second forceful lung volume Forceful lung volume (FVC) refers to the volume of air that can be exhaled with maximum force and speed after maximum inhalation to the total lung volume position and exhalation to the residual airway position, of which first second forceful lung volume (FEV1) is a commonly used index to determine the presence or absence of airway obstruction, and the first second forceful lung volume of most normal people can reach 70% to 80% of FVC, which is generally expressed by FEV1/FVC. FEV1/FVC is commonly used. Its clinical significance is mainly to reflect the presence or absence of bronchial obstruction, FEV1/FVC decrease indicates airway obstruction. Normal people can exhale almost all the lung volume in 3s, while patients with obstructive ventilation disorders need 5-6s or even longer time to exhale all. In addition to determining the presence or absence of bronchial obstruction, FEV1/FVC can also provide corroboration for determining the presence or absence of restrictive ventilation disorders. For example, in certain diseases in which alveolar expansion is restricted, the decrease in respiratory amplitude allows the expiration of the entire exerted lung volume in 1 to 2 s, and in some cases, even all of the lung volume can be exhaled within 1 s, resulting in an FEV1/FVC of 100 %. In reversible bronchial obstruction, such as bronchial asthma, the application of bronchodilators leads to an improvement in FEVl/FVC and allows FEV1 values to increase. The mid-expiratory flow rate (FEF25% to 75% or MMEF) is obtained by dividing the FVC into four equal portions, dividing it into four equal parts, dividing it into two portions at the beginning and two portions at the end, determining the middle 50% of the lung volume and calculating the ratio of it to the time taken to exhale this portion of the lung volume, i.e., the FEF25% to 75%. the FEF25% to 75% is mainly dependent on the non-exertion-dependent portion of the FVC, as at the beginning of the exhalation, the expiratory flow rate can reach a peak very quickly. The expiratory flow rate can peak very quickly, when the flow rate is related to the magnitude of the exertion; however, when expiration is continued with exertion, the flow rate begins to decrease and decreases with the decrease in intra-volume until the flow rate is zero. The flow rate in this segment of the lung volume is independent of exertion. Measurement of mid-expiratory flow velocity is useful for early detection of small airway obstruction. Peak expiratory flow rate (PEF) Peak expiratory flow rate refers to the instantaneous flow rate at which the expiratory flow rate is the fastest during exertion spirometry, which is mainly used to reflect the strength of the respiratory muscles and the presence or absence of airway obstruction. In normal people, PEF values may vary slightly at different time points within a day, but generally do not exceed 20%. Asthma patients, the difference can be significantly increased, if the difference between different time points within 1 day PEF, value is greater than 30%, can be used as the main basis for the diagnosis of atypical asthma. Patients with asthma should be monitored for long-term changes in PEF, and if a significant decrease in PEF, or an increase in the variation of PEF within one day is found, it suggests that the condition is aggravated and must be treated accordingly. There are three types of ventilation dysfunction: 1. Restrictive pulmonary ventilation dysfunction, which is ventilation dysfunction caused by the restriction of alveolar expansion. Commonly found in: ① interstitial lung diseases, such as stromal pneumonia, pulmonary fibrosis, pulmonary edema, silicosis, etc.; ② occupational lesions in the lungs or after lobectomy, such as lung tumors, lung cysts, etc.; ③ pleural diseases, such as pleural effusion, pneumothorax, pleural tumors, etc.; ④ spinal diseases of the chest wall, such as spondylolisthesis, ankylosing spondylitis, thoracoplasty and so on; ⑤ other, such as obesity, ascites, pregnancy and neuromuscular diseases. 2. Obstructive pulmonary ventilation dysfunction refers to pulmonary ventilation dysfunction caused by airway narrowing or blockage. Common causes are: ① tracheal and bronchial diseases, such as tracheal tumors, stenosis, bronchial asthma, chronic bronchitis, etc.; ② emphysema, pulmonary herpes; ③ upper respiratory tract diseases, such as pharyngeal infections, tumors and so on. 3, mixed pulmonary ventilation dysfunction, that is, obstructive ventilation dysfunction and restrictive ventilation dysfunction at the same time. Different types of ventilation dysfunction of pulmonary function test indexes are summarized in Table 3-47-1. small bronchial tubes. As the airway resistance and the cross-sectional area of the trachea is inversely proportional to the total cross-sectional area of the small airways is much larger than the total cross-sectional area of the airways with a diameter of more than 2mm, therefore, the small airway resistance only accounts for 10% to 20% of the total airway resistance, and its abnormal changes are not easy to detect for the conventional lung function measurement methods. 1, closed volume (CV), because the determination method is complicated, is now less used, so omitted. 2, maximum expiratory flow a volume curve (V-V curve) of the low lung capacity section of the expiratory flow has nothing to do with exertion, but mainly by the caliber of the small airways and alveolar elastic retraction force. The indexes used to measure small airway function are usually FEF50% and F'EF75%. If these two indexes are less than 80% of the normal value, it can be considered that this flow is reduced, which suggests that there is obstruction in the small airways. By observing the shape of the slope of the descending branch of the MEFV line is also of great significance in determining small airway function. Lung diffusion function measurement Principle Diffusion refers to the movement of molecules from the high-concentration area to the low-concentration area, which is a passive process that does not require the consumption of energy. Lung diffusion is the process of gas exchange between oxygen and carbon dioxide in the alveolar gas and oxygen and carbon dioxide in the alveolar wall capillaries, through the alveolar wall capillary membrane. Factors affecting diffusion through alveolar capillaries are: diffusion area, diffusion distance, and the difference in partial pressure of oxygen between the alveoli and capillaries. The diffusion volume is the amount of gas that can pass through the alveoli per unit time (1min) and per unit pressure difference of 0.133kPa (1mmHg). Clinically, diffusion function refers to oxygen. Carbon monoxide gas is usually used for this measurement. Measurement Methods There are three methods of measuring diffusion: the single breath method, the constant state method, and the repetitive breath method. The single-breath method is the more commonly used clinical method. The subject inhales a gas mixture of 0.3% CO, 10% He, and 20% O2 (with N2 as the equilibrium gas) into the total lung volume at the residual gas level, and exhales to the residual gas level after holding the breath for 10s. The concentrations of CO and He were continuously measured during this process, and then the lung diffusion volume was calculated (the concentrations and proportions of the gas mixtures used varied between instruments). Lung diffusion volume correlates with age, gender, body position, and stature, with males being greater than females and young people being greater than the elderly. Clinical significance 1. A diffusion volume less than 80% of the normal expected value suggests diffusion dysfunction. Diffusion volume decrease is common in: ① diffusion distance increase, such as interstitial fibrosis, asbestosis, etc.; ② alveolar capillary volume decrease, such as emphysema, tuberculosis, pneumothorax, lung infection, pulmonary edema, etc.; ③ circulatory system disorders, such as congenital heart disease, rheumatic heart disease, anemia. 2, the diffusion amount can be increased in erythrocytosis (due to increased CO uptake by erythrocytes), pulmonary hemorrhage (extravascular blood hemoglobin can take up a certain amount of CO) and so on. V. Lung Compliance Measurement Principle Compliance is the change in volume caused by a change in unit pressure, which reflects the elasticity of the lung tissue, and usually includes lung compliance, chest wall compliance and total compliance. Lung volume change ΔV Lung compliance CL = transpulmonary pressure in L/kPa. Measurement method Lung compliance can be categorized into static and dynamic compliance. Static compliance refers to the pulmonary compliance measured when airflow is briefly blocked during the respiratory cycle, while dynamic compliance is the pulmonary compliance measured when airflow is not blocked during the respiratory cycle. While static compliance reflects the elasticity of lung tissue, dynamic compliance is also affected by airway resistance. The pressure required to keep the lungs at a certain volume is called the elastic retraction force; an increase in elastic retraction force decreases compliance, and vice versa. Clinical significance (a) Diseases in which the total lung volume is increased 1, emphysema emphysema patients have increased static compliance and decreased dynamic compliance. 2.Bronchial asthma is sometimes characterized by a decrease in static compliance. 3, acromegaly with increased lung volume, static compliance increased proportionally, while the lung elastic retraction pressure is normal. (ii) Diseases in which the total lung volume decreases (restrictive lung diseases) 1, pulmonary resection, pulmonary atelectasis lung volume decreases, lung compliance decreases. 2, diffuse interstitial pulmonary fibrosis static and dynamic compliance are reduced. 3, Extrapulmonary diseases such as poliomyelitis, spinal deformity, etc., decreased pulmonary compliance and chest wall compliance. 4.ARDS, pulmonary edema, etc. Due to the reduction of normal alveolar air spaces, the lung volume is reduced and the lung compliance is reduced. (iii) Frequency dependence of small airway disorders In small airway disorders, pulmonary compliance is affected by respiratory rate, and when respiratory rate increases, compliance decreases, which is called frequency dependence of dynamic compliance. (D) Application in mechanical ventilation and respiratory failure monitoring Helps to determine the optimal PEEP level, the PEEP pressure that produces maximum compliance is the best. PEEP pressure. Sixth, airway resistance measurement Principle and method of measurement The friction generated by the flow of gas within the lungs in the airway during quiet breathing is usually expressed in terms of the pressure difference required to generate a unit flow rate. Airway resistance is usually measured by volumetric tracing or forced impulse oscillation. Airway resistance = pressure difference/flow rate (kPa?s/L) Clinical application Because airway resistance is inversely proportional to the fourth power of the radius of the airway, and because the total cross-sectional area of a small airway is significantly larger than that of a large airway, more than 80% of the airway resistance comes from that of the large airway. (A) airway resistance increases in the following disorders 1, bronchial asthma, asthma attack airway resistance increases, remission airway resistance can be normal. Increased airway resistance during an asthma attack can be relieved by bronchodilators. 2.Emphysema Airway atrophy during expiration can cause an increase in airway resistance; or excessive intrathoracic pressure during expiration, compression of the airway, resulting in an increase in airway resistance. 3.Obstructive ventilation dysfunction, slow branch, tumor, and other causes of obstructive ventilation disorders, can also increase airway resistance. 4.Medical airway resistance increases such as tracheal intubation or tracheotomy. (ii) Relationship between airway resistance and other ventilatory functions Increased airway resistance can cause decreases in forceful expiratory flow rate, inspiratory flow rate, and MVV. VII.EXERCISE LUNG FUNCTION TESTS Principle Exercise lung function tests examine the dynamic changes in lung function during exercise and are clinically useful in understanding physiologic and pathologic conditions that cannot be demonstrated in the resting condition. Exercise decreases the dead space ventilation/tidal volume ratio, increases ventilation, accelerates carbon dioxide excretion, increases oxygen uptake and consumption, and of course increases cardiovascular burden. Exercise Pulmonary Function Tests Exercise Pulmonary Function Tests are usually performed using a flat treadmill, i.e. walking on a movable flat surface with a certain incline and rotational speed, while also monitoring electrocardiogram and blood pressure changes. A modified Bruce protocol is used for the exercise program. The exercise test generally takes the subject reaching the sub-extreme heart rate as the endpoint of the test, and after reaching the sub-extreme heart rate, the subject still continues to walk slowly and gradually returns to the basal heart rate. The test should be stopped if significant dyspnea, myocardial ischemia, arrhythmia, or increased or decreased blood pressure occurs during the test. Preparation Before starting the exercise test, it is necessary to explain clearly to the subject the precautions to be taken in each step of the whole exercise process, and to ask the subject to relax as much as possible, not to be nervous, and at the same time prepare first aid medicines and oxygen, etc., in order to prevent accidents from occurring. Common Test Indicators Maximum Oxygen Uptake or Oxygen Consumption (VO2 max): VO2 max is a major indicator of the level of cardiorespiratory function of the human body during extreme exercise. It represents the sum of the capacity of the oxygen transport system. Respiratory exchange rate (RER): the ratio of CO2 expired per minute to O2 uptake per minute in the lungs. The ratio of maximal ventilation (MVV) to maximal ventilation during exercise VEmax (VEmax/MVV) is the dyspnea index, which is an objective index to determine the severity of dyspnea. Anaerobic threshold: the exercise intensity corresponding to the starting point of the sharp increase in blood lactate during the incremental increase in exercise load, which is used to reflect the anaerobic metabolic capacity. When the anaerobic threshold is exceeded, continued increase in exercise intensity will lead to metabolic acidosis. Metabolic equivalent: a practical indicator of energy expenditure, a metabolic equivalent is equivalent to 3.5 ml of oxygen uptake per minute, per kilogram of body weight, is an important indicator of exercise intensity when the anaerobic threshold is not reached. Clinical application The human heart and lung function has a large reserve capacity. In the resting state some of the function is not easy to show a reduction, only in the function of a serious obstacle will show clinical symptoms. Therefore, the exercise test can detect the pathophysiological mechanisms that can not be detected at rest, and can find out the pattern from the factors limiting the amount of exercise, the symptoms that appear during exercise, and early detection of cardiopulmonary function abnormalities. 1.Exercise induced asthma Exercise FEV l is positive if it is reduced by 10% compared with that before exercise, which is an important indicator for the diagnosis of exercise asthma. 2.Predicting the risk of complications after thoracic surgery If VO2 max is significantly reduced, the risk of postoperative comorbidities is higher. 3.Application in cardiovascular disease In the state of exercise load can understand myocardial blood supply and heart rhythm changes, which can help diagnose coronary heart disease and arrhythmia. 4, through the observation of anaerobic threshold can be expected to human exercise endurance. 5.It can be used for differential diagnosis of chest tightness, shortness of breath and dyspnea. Contraindications 1, heart disease, hypertension and so on. 2, Lung function has been impaired, such as FEVl less than 70% of the expected value. 3, Asthma attack period. 4, Elderly, frail and mobility impaired.