Respiratory Physiology II PDF

3 Mera Masalmeh Rawan Asrawi & Asma’a Abu-Qtaish Yanal Shafagoj Respiratory system Before we start our lecture today, we have to answer the doctor’s question at the end of the previous sheet: “Can the PDS be lesser than the ADS?” The answer: PDS can’t be less than ADS. PDS = ADS + WV ADS (constant =...

3 Mera Masalmeh Rawan Asrawi & Asma’a Abu-Qtaish Yanal Shafagoj Respiratory system Before we start our lecture today, we have to answer the doctor’s question at the end of the previous sheet: “Can the PDS be lesser than the ADS?” The answer: PDS can’t be less than ADS. PDS = ADS + WV ADS (constant =150mm), WV can be: 1) WV=0  PDS= ADS 2) WV>0  PDS will be higher than ADS In previous sheets, we focused on the pressure of air compositions in each part of the respiratory system. Now, let's consider mixed air. During expiration, the air you exhale first comes from the anatomical dead space (150 ml), followed by air from the alveoli (350 ml). Let's calculate the partial pressures of O2 and CO2 in mixed air situation. = = 15𝑂 𝑚𝑙 (𝑖𝑛 𝐴𝐷𝑆)×150 𝑚𝑚𝐻𝑔 (𝑃𝑂2)+350 (𝑖𝑛 𝐴𝑙𝑣𝑒𝑜𝑙𝑖) ×100 𝑚𝑚𝐻𝑔 (𝑃𝑂2) = 116 500 𝑚𝑙 150 𝑚𝑙 (𝑒𝑥ℎ𝑎𝑙𝑒)×𝑍𝑒𝑟𝑜 𝑚𝑚𝐻𝑔 (𝑃𝐶𝑂2 )+350 𝑚𝑙 (𝑖𝑛ℎ𝑎𝑙𝑒)×40 (𝑃𝐶𝑂2) 500 𝑚𝑙 -Past paper question! = 28 𝑚𝑚𝐻𝑔  mixed air expiration PO2 is highest in: A. Arterial blood B. Alveolar air C. Intersttal fuid D. Mixed expiraton air  Basic of the respiratory system - The respiratory tree is composed of 23 generations/divisions/branches. - Trachea is generation #0, Primary bronchi is generation #1, Secondary bronchi is generation #2 and so on. - You have to know the first two generations (trachea and Primary bronchi), generation #16 which is the terminal bronchiole, generation #17 which is the respiratory bronchiole and generation #23 which is the alveolus (closed bulb). 𝑚𝑚𝐻𝑔 - Generations #0  #16 are located in the conductive zone (no gas exchange occurs here). - Generations #17  #23 are located in the respiratory zone (the main sites for gas exchange) - Generations #0  #10 have cartilage which give them support and therefore they are not a collapsible structure unlike the rest generations (#11 #23) which are supported by smooth muscles, if the generation collapse the R will increase so we should increase ∆𝑃 to maintain the same flow.  The components of alveolus There are three types of cells: 1. Type1 alveolar: thin squamous because of its function (gas exchange), it occupies 95% of the alveolus. 2. Type2 alveolar: rounded and cuboidal epithelial cells containing microvilli, they secrete alveolar fluid which include surfactant (90% of its component is phospholipids), surfactant reduce surface tension, this type of cell occupies 5% of the alveolus. Immune cell: Alveolar macrophages Alveolar macrophage: Is the garbage man of the alveoli and thus clean the alveoli. - Alveolus diameter is 300 micrometer. - If the amount of the fluid in the interstitial space increase this will cause edema, therefore the thickness of the respiratory membrane will increase NOTE: the thickness is inversely related to the diffusion  𝐽𝑂2 ∝ 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎 𝑇ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠  Resistance - Flow (RMV: respiratory minute volume )= 6L/min The flow needs driving force (∆𝑃) to overcome R (if we have too much R, we will need high ∆𝑃) Flow = ∆𝑃 𝑅 But how we measure resistance? 𝑹 = 𝟖 𝜼𝑳 𝝅𝒓𝟒 →𝑹 ∝ 𝟏 𝒓𝟒 (We can’t calculate r4 to all respiratory structures, we express it by cross sectional area) 𝑨𝟐 = 𝝅𝒓𝟒 → 𝑹 ∝ 𝟏 𝒓𝟒 →𝑹 ∝ 𝟏 𝑨𝟐 Airway resistance is a vague expression (it’s difficult to be measured in direct ways), it’s ∆𝑷 ∆𝑷 measured indirectly. 𝑭 = 𝑹 → 𝑹 = 𝑭 - The opposite of resistance is permeability (K) and it’s inversely related to R  𝐾 ∝ 1 𝑅 - permeability is also a vague concept - Physiologically we have significant airway resistance which = 1 ,so we need pressure difference = 1 to keep the flow constant (6L/min). Flow = ∆𝑃⁄𝑅  R =1 ∆𝑃 = 1  R= 10 ∆𝑃 = 10 Now let’s compare the resistance between cardiovascular system and Respiratory one: Cardiovascular Respiratory CO=5L/min Flow =6L/min P1= 0 & P2= 100 → ∆𝑃 = 100 ∆𝑃 = 1 TPR=100 R=1 ✓ Airway resistance is small and negligible because we need very little ∆𝑃 to overcome R. ✓ Vascular resistance is 100 times more than airway resistance although their flow is almost the same. - Most of the airway resistance normally realized in large divisions, but why?! Because of the NET cross sectional area. - NET Cross sectional area in small generations is greater than the large ones ,so the R will be higher in large airways. We have bronchioles 12% or 200ml or more then the Asthma is reversable. Spirometry measurements are usually done before and after administration of a 2 agonists (salbutamol, dobutamine, albuterol, fenoterol, terbutaline…YOU don’t need to memorize those drugs). Reversibility with the use of a bronchodilator is defined as an increase in FEV 1 of 12% or 200 ml. Patients with severe asthma may need a short course of oral steroid therapy before they demonstrate reversibility THE END OF SHEET #3