Chapter 6 Gas exchange

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1 Chapter 6 Gas Exchange between Air and Blood: Diffusion Department of Pathophysiology, the School of Medicine, Shandong University Zhongrui Yuan( 袁中瑞 ), Ph.D. zhongruiyuan@sdu.edu.cn

2 Why do we need a respiratory system? food O 2 ATP CO 2

3 人体基础代谢的氧气消耗大约 250 ml/min 产生 CO 2 200ml/min 呼吸商 (Respirator y quotient, RQ ) 一定时间内, 机体呼出的二氧化碳与摄入氧的体积之比 RQ=0.8

4 Introduction :The path from air to tissue Air: PCO 2 0.3mmHg PO 2 159mmHg

5 Gas exchange between air and blood 气体分子不停地进行着非定向运动, 在不同的区域间, 从分压高处向分压低处发生净转移的过程, 为气体弥散 ( 或扩散,Diffusion)

6 Partial Pressure Gradients Gases diffuse down pressure gradients in the lungs and other organs Diffusion of a gas depends on differences in a quantity called partial pressure A gas diffuses from a region of higher partial pressure to a region of lower partial pressure In the lungs and tissues, O 2 and CO 2 diffuse from where their partial pressures are higher to where they are lower

7 Gas Composition in the Normal Alveolar Space Air: PCO 2 = 760mmHg 0.04% = 0.3 mmhg PO 2 = 760mmHg 21% = 159 mmhg Trachea: partial pressure of CO 2 is approximately 0 PiO 2 = (barometric pressure-h 2 O vapor pressure)xfio2 = (760 47) x 0.21 =150 mmhg In the alveolar space, oxygen diffuses into the blood and CO 2 diffuses into the alveolus from the blood.

8 Alveolar Gas Equation PAO 2 = (PiO 2 ) (PaCO 2 /R). PaCO 2 approximates PACO 2 due to the rapid diffusion of CO 2 RQ = Respiratory Quotient (V CO2 /V O2 ) = 0.8 Respiratory exchange ratio In a normal individual breathing room air: PAO 2 = /0.8 = 100 mmhg

9 Gas Composition in the Normal Alveolar Space Air: PCO 2 = 760mmHg 0.04% = 0.3 mmhg PO 2 = 760mmHg 21% = 159 mmhg Trachea: partial pressure of CO 2 is approximately 0 PiO 2 = (barometric pressure-h 2 O vapor pressure)xfio2 = (760 47) x 0.21 =150 mmhg In the alveolar space, oxygen diffuses into the blood and CO 2 diffuses into the alveolus from the blood. Pulmonary Gas exchange :O 2 & CO 2 exchange between alveoli & blood

10 气体扩散速率 : 单位时间内气体的扩散量 Rate of Diffusion = P T A S / d MW Fick s Law of Diffusion 扩散系数 : 气体分子本身的特征 Diffusion Coefficient = S/ MW Solubility in plasma :O 2-0.3ml/100ml CO 2 24 times MW: O 2 32, CO 2 44 平方根之比为 0.85 The ratio of the diffusion coefficient: 20:1. So, CO 2 20 times more ready than O 2 to diffuse at the same pressure gradient

11 Lungs Total surface area in humans alveoli is m 2 Gas exchange across thin epithelium of millions of alveoli

12 Respiratory membrane, R-M air-blood barrier R-M is extremely thin (average 600nm; some places merely 200nm) and is permeable to molecular O 2, CO 2, NO and other gases.

13 Oxygenation of Blood 0.25 s for O 2

Time in the capillaries mm Hg 100 45 40 0.13s Alveolus Blood capillary Time for exchange 0.25s P O2 Saturated very quickly Reserve diffusive Capacity of the lung 1) Thansit time less than 0.

14 Time in the capillaries mm Hg s Alveolus Blood capillary Time for exchange 0.25s P O2 Saturated very quickly Reserve diffusive Capacity of the lung 1) Thansit time less than 0.25 s do not allow sufficient time for equilibration 2) During heavy exercise, CO and transit time 3) At altitude the PO 2 of air 4) It is usually O 2 that is first affected by diffusional difficulties P CO2 0 Time 0.75 sec (at rest) 0.34s (in exercise)

15 Although there are situations when the lung can be so damaged as to restrict the diffusion of CO 2, it is usually O 2 that is first affected by diffusional difficulties. The rate of removal of CO 2 is governed primarily by alveolar ventilation

16 PaCO 2 and Alveolar Ventilation PaCO 2 is: directly related to CO 2 production (tissue metabolism). Inversely related to alveolar ventilation. V CO 2 PaCO =K 2 V A Increased PaCO 2 (hypercarbia) is always a reflection of inadequate alveolar ventilation (V A ).

17 Diffusion in the blood plasma RBCs are about the same diameter as pulmonary capillaries. There is very little plasma between the RBC and the capillary wall for gas to diffuse through. The doughnut shape of RBC and the kneading of RBC aid diffusion.

Reaction with Hb Oxygen is carried in the blood in 2 forms: 1. Dissolved O 2 (~1.5% of total O 2 content) 0.3ml/100ml 2. O 2 bound to hemoglobin (~98.5 % of total O 2 content) CO 2 max: 1.

18 Reaction with Hb Oxygen is carried in the blood in 2 forms: 1. Dissolved O 2 (~1.5% of total O 2 content) 0.3ml/100ml 2. O 2 bound to hemoglobin (~98.5 % of total O 2 content) CO 2 max: 1.34ml/g 15gHb/100ml=20ml/100ml CaO 2 :19ml/100ml the rate at which O 2 can be taken up or released by hemoglobin (Hb) in the RBC acts as a rate-limiting step of its overall rate of thansfer.

19 Diffusion Capacity of lung ( D L, 肺扩散容量 ) 在单位分压下, 每分钟通过呼吸膜进行扩散的气体毫升数. D L = V/(P A P C ) V is the volume of a gas that diffuses through the membrane each minute(ml/min) P A is the average partial pressure of a gas in the air of alveoli, P C is the average partial pressure of a gas in the blood of pulmonary capillary. D L for O 2 :20ml/(min 1 mmhg) ; D L for CO 2 : 20 times Factors Affecting the D L : Exercise, Body posture (Body posture: horizontal position pulm. perfusion improved V/Q D L verse up-right position); Pulmonary diseases

20 Measuring D L CO binds Hb 250 times more strongly than O 2, there is almost no CO in plasma (P CO =0 mmhg). CO is uptaken continuously. The diffusion of CO is influenced by R-M, not by blood flow. So CO is used to measure diffusion capacity of lung.

Diffusion impairment 1) Area of R-M: Normal adult R-M: 70-100 m 2 At

), pulmonary consolidation( 肺实变 ),lobar resection( 肺叶切除 ),

21 Diffusion impairment 1) Area of R-M: Normal adult R-M: m 2 At rest, used R-M:35~40 m 2 In exercise: Area of R-M : atelectasis( 肺不张 ), pulmonary consolidation( 肺实变 ),lobar resection( 肺叶切除 ), emphysema( 肺气肿 ) 2) Thickness of R-M : pulmonary edema, fibrosis PaO 2, hypoxia

22 发绀 (cyanosis) 毛细血管中脱氧血红蛋白 5 g/dl, 使皮肤粘膜呈青紫色. (normally only 2.6 g/dl) 2.6g/dl HHb 5g/dl HbO 2 正常缺氧

23 Cardiogenic acute pulmonary edema Cardiogenic acute pulmonary edema is caused due to the increase pulmonary capillary pressure from 8-12 mm Hg (normal) to over 18 mm Hg.

24 Pulmonary interstitial fibrosis Hamman-Rich Disease 蜂窝肺 Hamman-Rich 氏病多种名称, 如特发性肺纤维化弥漫性间质性肺纤维化和弥漫性进行性间质性肺纤维化等病因不明, 可能同炎症自体免疫或变态反应等因素有关.

25 4. Treating Diffusion impairment Thickening of R-M (fibrosis) or loss of surface area (emphysema) are usually irreversible: PiO 2 O 2 therapy:21% O 2 30% O 2 PiO 2 = (barometric pressure-h 2 O vapor pressure)xfio2 = (760 47) x 0.21 = 150 mmhg = (760 47) x 0.30 = 214 mmhg

26 Homework Case of Fibrosing alveolitis: clinical features, the diagnosis and treatment

28 我们正常的肺就像一块海绵, 海绵里面的小孔就好比是我们的肺泡, 这些孔与孔之间的部分就是肺间质, 因为肺间质部分的正常作用, 健康的肺就像一块海绵一样, 有很好的弹性, 肺泡能够储存大量的氧气, 保证我们的呼吸自如, 得了肺间质纤维化的肺会变成一个什么样子呢? 就像干硬的丝瓜瓤, 尽管中间也有很多孔, 但是孔与孔之间的肺间质已经变成纤维组织, 导致肺不能够有弹性地收放, 已经失去弹性了, 这就是纤维化了的肺由于失去弹性, 肺泡无法完成气体的交换, 于是人就会出现气短, 胸闷, 咳嗽等这样一些症状, 最终的结果就是无法呼吸, 憋死肺间质纤维化还有一个更为形象的名字叫做蜂窝肺, 它目前是一个世界性的难题, 患者生存率非常的低,5 年生存率不到 50%,10 年生存率只有不到 10% 间质性肺炎大多由于病毒所致, 主要为腺病毒呼吸道合胞病毒, 流感病毒副流感病毒麻疹病毒等其中以腺病毒和流感病毒引起的间质性肺炎较多见, 也较严重, 常形成坏死性支气管炎及支气管肺炎, 病程迁延易演变为慢性肺炎肺炎支原体也能引起间质性肺炎支原体经呼吸道侵入后, 主要侵犯细支气管和支气管周围组织, 由于无破坏性病变, 故能完全恢复过敏性肺炎, 是由于吸入含有真菌孢子细菌产物动物蛋白质或有机物尘埃所引起的非哮喘性变应性肺疾患, 以弥漫性肺间质炎为病理特征, 能痊愈, 不留后遗症比较少见的, 如肺炎链球菌肺炎, 金黄色葡萄球菌肺炎的并发症, 化脓性炎症扩展到间质组织, 引起化脓性间质性肺炎若炎症继续发展可发生肺脓肿脓胸等 ; 若病变停止发展, 则转向恢复痊愈, 但也可形成慢性间质性肺炎病理 : 间质性肺炎是肺的间质组织发生炎症, 炎症主要侵犯支气管壁肺泡壁, 特别是支气管周围血管, 周围小叶间和肺泡间隔的结缔组织, 而且, 多呈坏死性病变间质性肺炎, 又叫间质性肺疾病弥漫性肺疾病等, 作为病名, 只有十多年的历史, 顾名思义它是肺间质的病变间质性肺炎不是一个单一的疾病, 而是一大类疾病的总称, 约有百余种, 已知一小部分病因已明, 如尘肺药物性肺炎放射性肺炎等 ; 但有相当一部分病因不明, 如特发性肺纤维化结节病等间质性肺炎虽然称为肺炎, 但主要不是由细菌病毒等微生物感染而成 ; 特发性肺纤维化 (idiopathic pulmonary fibrosis,ipf) 是一种原因不明以弥漫性肺泡炎和肺泡结构紊乱最终导致肺间质纤维化为特征的疾病按病程有急性亚急性和慢性之分, 所谓 Hamman- Rich 综合征属急性型, 临床更多见的则是亚急性和慢性型欧洲学者多称本病为隐源性致纤维性肺泡炎 (cryptogenicfibrosingalveolitis,cfa) 美国习用 IPF 我国一度盛行 CFA 的名称, 近来却多用 IPF 本病多为散发, 估计发病率 3~5/10 万, 占所有间质性肺病的 65% 左右见于各年龄组, 而症状 : 时有呼吸困难, 干咳此后常因感冒急性呼吸道感染而诱发和加重, 且呈进行性加重逐渐出现呼吸增快但无喘鸣, 刺激性咳嗽或有咳痰, 少数有发烧咯血或胸痛严重后出现动则气喘, 心慌出虚汗, 全身乏力, 体重减轻, 唇甲紫绀及杵状指 ( 趾 ) 作体检时在下肺野可听到湿罗音在并发肺原性心脏病时有肺动脉第二音亢进, 颈静脉努张, 肝肿大和下肢浮肿

1269 malondialdehyde (MDA) were significantly decreased, while oxygen partial pressure (PaO 2 ), ph value, superoxide dismutase (SOD) and glutathione

1269 malondialdehyde (MDA) were significantly decreased, while oxygen partial pressure (PaO 2 ), ph value, superoxide dismutase (SOD) and glutathione 1268 维生素 A 联合牛肺表面活性物质治疗新生儿呼吸窘迫综合征的临床研究朱琼 1, 陈小利 2, 叶华 2 1. 重庆市合川区妇幼保健计划生育服务中心儿科, 重庆 401520 2. 重庆市合川区妇幼保健计划生育服务中心内儿科, 重庆 401520