Cherniack R M
University of Colorado, National Jewish Center for Immunology and Respiratory Medicine, Denver.
Dis Mon. 1992 Jul;38(7):505-76. doi: 10.1016/0011-5029(92)90025-k.
From a conceptual standpoint, the tests of pulmonary function can be divided into those that assess the ventilatory function of the lungs and those concerned with gas exchange. Tests of ventilatory function reflect alterations of the elastic resistance and flow resistance of the respiratory apparatus. The elastic properties of the lungs are assessed by determining the position and shape of the curve representing the relationship between the pressure across the lungs and absolute lung volume. When there is reduced distensibility of either the lungs or the chest wall, the volume-pressure curve is shifted down and to the right. The slope of the curve is reduced in the patient with pulmonary fibrosis, while it is normal in the patient with obesity. In asthma (or chronic bronchitis) and emphysema, the volume-pressure curve is shifted up and to the left. In emphysema, the slope of the curve is increased, while it is normal in patients with asthma or bronchitis. In practice, lung volume is used as an index of alterations of the volume-pressure characteristics of the lungs and/or chest wall. The vital capacity is often used as a surrogate for the TLC but it is lower than expected in both restrictive and obstructive disorders. The FEV1.0 reflects the degree of expiratory flow limitation. In a restrictive disorder, lung volume and the FEV1.0 are reduced, but the FEV1.0/FVC ratio is normal. In airflow limitation, lung volume, the FEV1.0, and the FEV1.0/FVC ratio are lower than expected. In airflow limitation, the reversibility with inhaled bronchodilator should be determined. Tests of airway responsiveness are indicated when evaluating patients with unexplained chronic cough, chest tightness, or wheezing, particularly if other lung function tests are normal. The adequacy of gas exchange is assessed by determining the arterial blood gas tensions--PaO2 and PaCO2--and the alveoloarterial pO2 gradient--P(A-a)O2. A lower-than-expected PaO2 can result from several different physiologic disturbances. When alveolar hypoventilation is the sole disturbance, the oxygen in the alveoli and in the blood perfusing them virtually comes into equilibrium, so that the P(A-a)O2 is normal. An elevated P(A-a)O2 is caused by either mismatching of ventilation and perfusion, true venous admixture, a diffusion abnormality, or a combination of these disturbances. Because dyspnea on exertion is a cardinal symptom of respiratory disease, exercise tolerance should be assessed. A reduced exercise tolerance may result from ventilatory limitation, impaired gas exchange, cardiac impairment, impaired delivery of the oxygen to the working muscles, or an inability to use the energy.
从概念上讲，肺功能测试可分为评估肺通气功能的测试和与气体交换相关的测试。通气功能测试反映了呼吸装置弹性阻力和气流阻力的改变。通过确定代表肺跨压与绝对肺容积之间关系的曲线的位置和形状来评估肺的弹性特性。当肺或胸壁的扩张性降低时，容积 - 压力曲线向下并向右移动。肺纤维化患者曲线的斜率降低，而肥胖患者曲线斜率正常。在哮喘（或慢性支气管炎）和肺气肿中，容积 - 压力曲线向上并向左移动。在肺气肿中，曲线斜率增加，而哮喘或支气管炎患者曲线斜率正常。在实际应用中，肺容积被用作肺和/或胸壁容积 - 压力特征改变的指标。肺活量常被用作肺总量的替代指标，但在限制性和阻塞性疾病中它都低于预期值。第一秒用力呼气容积（FEV1.0）反映呼气气流受限的程度。在限制性疾病中，肺容积和FEV1.0降低，但FEV1.0/用力肺活量（FVC）比值正常。在气流受限情况下，肺容积、FEV1.0以及FEV1.0/FVC比值均低于预期。在气流受限情况下，应确定吸入支气管扩张剂后的可逆性。当评估原因不明的慢性咳嗽、胸闷或喘息患者时，特别是其他肺功能测试正常时，需要进行气道反应性测试。通过测定动脉血气张力——动脉血氧分压（PaO2）和动脉血二氧化碳分压（PaCO2）——以及肺泡 - 动脉氧分压差——P（A - a）O2来评估气体交换是否充分。低于预期的PaO2可能由几种不同生理紊乱导致。当肺泡通气不足是唯一的紊乱时，肺泡内和灌注它们的血液中的氧气实际上达到平衡，因此P（A - a）O2正常。P（A - a）O2升高是由通气与灌注不匹配、真性静脉血掺杂、弥散异常或这些紊乱的组合引起的。由于劳力性呼吸困难是呼吸系统疾病的主要症状，应评估运动耐力。运动耐力降低可能是由于通气受限、气体交换受损、心脏功能受损、向工作肌肉输送氧气受损或无法利用能量所致。
