第五章 呼吸
2011-06-08 18:15:52   来源：   作者：  评论：0 点击：

（中南大学湘雅医学院 管茶香）
Summary
Respiration is an important sign of life with the function of gas exchange between the body and the environment. It includes three processes: external respiration (pulmonary ventilation and gas exchange in lungs), gas transport in the blood and internal respiration.
Pulmonary ventilation is the gas exchange between the alveolus and the environment. The rhythmic contraction and relaxation of the respiratory muscles lead to the expansion or reduction of the chest cavity, which results in the expansion or reduction of the alveoli to change the alveolar pressure. During inspiration, alveolar pressure is lower than the atmospheric pressure so air flows into the lung (inhalation). During expiration, opposite changes occur, the alveolar pressure is greater than the atmospheric pressure so air flows out of the lung (exhalation). Therefore the original impetus of pulmonary ventilation is respiration movement and the direct impetus is the pressure difference between alveolar pressure and atmospheric pressure.
The intrapleural pressure(IP) is mean the pleural space and made of two factors: alveolar pressure (AP) acting on alveolar cell wall(namely visceral pleura ) and recoil force(RF) of lung. It can be expressed as follows: IP＝AP－RF. Hence, although the intrapleural pressure is a slightly negative pressure it has a very important role in the process of pulmonary ventilation. The physiological significance of negative pressure in pleural space is required to hold the lungs expansion and enhance venous return and lymphatic return.
During the process of pulmonary ventilation, only when the driving force overcomes the resistance, can ventilation go along. There are two kinds of resistance of pulmonary ventilation .One is the elastic resistance of pulmonary ventilation and the other is the non-elastic resistance of pulmonary ventilation.
The elastic resistance of pulmonary ventilation can be classified into two categories: alveolar surface tension and elastic recoil of the lung; alveolar surface tension is more important. The common index to reflect the elastic resistance of the lung is the compliance of lung, which is the inverse of elastic resistance. Type II alveolar epithelial cells synthesize and secrete pulmonary surfactant (PS). The physiological functions of PS are to reduce the alveolar surface tension thereby allowing easier lung expansion, stabilize the different size alveoli in lungs, prevent alveolar collapse and prevent the infiltration of fluid into the alveoli.
The non-elastic resistance of pulmonary ventilation includes airway resistance, inertia resistance and tissue viscosity resistance. The airway resistance is the major element of non-elastic resistance. Many factors can lead to the contraction of bronchial smooth muscle and the reduction of the bronchi radius. These changes can place a premium on asthma.
Many indexes can be used to evaluate the function of pulmonary ventilation. Timed vital capacity and alveolar minute volume are good indexes for the function of pulmonary ventilation and the efficiency of pulmonary ventilation respectively. Some indexes also can be used to differentiate obstructive between restrictive pulmonary ventilation dysfunction.
The gas exchange between the alveolar gas and blood in the capillary vessel is called pulmonary gas exchange. The diffusion constant is in direct proportion to the difference in gas partial pressure, temperature, the solubility of the gas and alveoli area, whereas in inverse proportion to the respiratory membrane thickness and the square root of the molecular weight. Ventilation-perfusion is another important factor affecting gas exchange.
In the body, the exchange within histocyte must be carried out through blood transportation which has two transport forms (physical dissolved form and chemical combined form included) to maintain homostasis. The physical dissolved form is an obligatory form for oxygen (O2) and carbon dioxide (CO2) in and out of the blood; whereas the chemical combined form is the major form of transportation for Oxygen and carbon dioxide. O2 is mainly transported in combination with hemoglobin and CO2 is mainly transported as bicarbonate.
Respiration movement is a rhythmical movement regulated by respiratory center and reflection. It is reported that the respiratory center locates in the area from cerebellum to spinal, and the basic respiratory center that the Pre-Botzing complex is the rhythm pacemaker locates in the medulla. The cooperation of medulla and pons can form the normal breathing rhythm.
Respiration movement is regulated by mechanical reflection and chemical reflection. Mechanical reflection mainly includes pulmonary stretch reflex (pulmonary stretch reflex includes inflation reflex and deflation reflex and it prevents overexpansion of the lungs during strenuous exercise) and respiratory reflex of respiratory muscle . There are two types of chemoreceptor: peripheral chemoreceptor which located in the carotid and aortic bodies and central chemoreceptor which located near the ventral surface of the medulla. The peripheral chemoreceptors are sensitive to a decrease in arterial Po2 or pH and an increase in Pco2. When the blood Pco2 rises, CO2 will also rapidly penetrate the blood-brain barrier and enter the cerebrospinal fluid. Subsequently CO2 will promptly be hydrated to produce H2CO3, H＋ will dissociate from H2CO3. So the local H＋ will stimulate central chemoreceptors in the end. The control center responds to both sets of chemoreceptors by sending signals to regulate the rate and depth of respiration to maintain the homeostasis of Pco2、Po2 and H＋.

参考文献
1.贺石林，李俊成、秦晓群主编. 2001. 临床生理学. 北京：科学出版社.
2.姚泰主编，2000. 生理学（五版）.北京:人民卫生出版社，
3.姚泰主编，2001. 人体生理学（三版）.北京:人民卫生出版社，
4.范少光、汤浩、潘伟丰主编. 2000.人体生理学（二版）。北京：北京医科大学出版社，
5.William F. Ganong. 2001. Review of Medical Physiology.20th ed. New York, McGraw-Hill.
6.Lingappa VR and Farey K. 2001. Physiological Medicine-A Clinical Approach to Basic Medical Physiology. 5th ed. New York, McGraw-Hill.
7. Rekling JC, Feldman JL. 1998. PreBotzinger complex and pacemaker neurons: Hypothesized site and kernel for respiratory rhythm generation. Ann Rev Physiol.;60:385～405.
8.Smith JC , Ellenberger HH, Ballanyi K ,et al. 1991. Pre-Botzinger complex ：a brainstem region that may generate respiratory rhythm in mammals. Science, 254:726～729.
9.Solway J and Fredberg JJ. 1997. Perhaps airway smooth muscle dysfunction contributes to asthmatic bronchial hyperresponsiveness after all. Am J Respir cell Mol Biol., 17:144～146.
10. Balaban, CD, McGee DM, Zhou JM, el al. 2002. Responses of Primate Caudal Parabrachial Nucleus and K?lliker-Fuse Nucleus Neurons to Whole Body Rotation , J. Neurophysiol. 88:3175～3193.
11.Chiba H, Pattanajitvilai S, Mitsuzawa H ,et al. 2003. Pulmonary surfactant proteins A and D recognize lipid ligands on mycoplasma pneumoniae and markedly augment the innate immune response to the organism. Chest 123(3 suppl):426s.

复习思考题
1． 述肺表面活性物质的成分、来源、生理作用及其临床意义。
2． 试述评价肺通气功能的主要指标。
3． 增大无效腔，呼吸有何改变，为什么？
4． 试述CO2浓度变化对呼吸的影响。
5． 简述气道上皮的生理作用。
6． 为什么临床上易出现缺O2,而CO2潴留不明显?
7． 29岁男性患者，因右下肺肺炎入院。血气分析显示，动脉O2分压（PaO2）49mmHg（正常值100mmHg）PaCO2 38mmHg（正常40mmHg），pH7.42；每分通气量12 L/分。第二天因右肺炎症加重，呼吸增加到30次/分，虽吸入100%，但PaO2 仍只有63mmHg，PaCO2分压反而降至32mmHg。
（1）请解释该患者PaO2和PaCO2 同时降低的原因。
（2）你认为患者处于何种体位有利于改善患者呼吸功能？