Dr Lwiindi Respiratory System Physiology PDF

Lecture 1; Introduction and functional anatomy of Respiratory physiology Dr Lwiindi Lukubi Medical School 05/03/2015 1 Respiratory System Functions  Gas exchange: Oxygen enters blood and carbon dioxide leaves  Regulation of blood pH or acid – base balance: Al...

Lecture 1; Introduction and functional anatomy of Respiratory physiology Dr Lwiindi Lukubi Medical School 05/03/2015 1 Respiratory System Functions  Gas exchange: Oxygen enters blood and carbon dioxide leaves  Regulation of blood pH or acid – base balance: Altered by changing blood carbon dioxide levels  Voice production: Movement of air past vocal folds makes sound and speech  Olfaction: Smell occurs when airborne molecules drawn into nasal cavity  Protection: Against microorganisms by preventing entry and removing them 05/03/2015 2  Pulmonary ventilation Respiration, divided in two processes: external respiration, the absorption of O2 and removal of CO2 from the body as a whole; and internal respiration, the utilization of O2 and production of CO2 by cells and the gaseous exchanges between the cells and their fluid medium. 05/03/2015 3 Schematic View of Respiration External Respiration Internal Respiration 05/03/2015 4  Basics of the Respiratory System Respiration  What is respiration? ◦ Respiration = the series of exchanges that leads to the uptake of oxygen by the cells, and the release of carbon dioxide to the lungs Step 1 = ventilation  Inspiration & expiration Step 2 = exchange between alveoli (lungs) and pulmonary capillaries (blood)  Referred to as External Respiration Step 3 = transport of gases in blood Step 4 = exchange between blood and cells  Referred to as Internal Respiration ◦ Cellular respiration = use of oxygen in ATP synthesis 05/03/2015 5  Basics of the Respiratory System Functional Anatomy  What structural aspects must be considered in the process of respiration? ◦ The conduction portion ◦ The exchange portion ◦ The structures involved with ventilation  Skeletal & musculature  Pleural membranes  Neural pathways  All divided into ◦ Upper respiratory tract  Entrance to larynx ◦ Lower respiratory tract  Larynx to alveoli (trachea to lungs) 05/03/2015 6 05/03/2015 7  Basics of the Respiratory System Functional Anatomy  Bones, Muscles & Membranes 05/03/2015 8  Basics of the Respiratory System Functional Anatomy  Function of these Bones, Muscles & Membranes ◦ Create and transmit a pressure gradient  Relying on  the attachments of the muscles to the ribs (and overlying tissues)  The attachment of the diaphragm to the base of the lungs and associated pleural membranes  The cohesion of the parietal pleural membrane to the visceral pleural membrane  Expansion & recoil of the lung and therefore alveoli with the movement of the overlying structures 05/03/2015 9  Basics of the Respiratory System Functional Anatomy  Pleural Membrane Detail ◦ Cohesion between parietal and visceral layers is due to serous fluid in the pleural cavity  Fluid (30 ml of fluid) creates an attraction between the two sheets of membrane  As the parietal membrane expands due to expansion of the thoracic cavity it “pulls” the visceral membrane with it  And then pulls the underlying structures which expand as well  Disruption of the integrity of the pleural membrane will result in a rapid equalization of pressure and loss of ventilation function = collapsed lung or pneumothorax 05/03/2015 10 Pressures in the lungs ◦ Pleural pressure  negative pressure between parietal and visceral pleura that keeps lung inflated against chest wall  varies between -5 and -7.5 cmH2O (inspiration to expiration ◦ Alveolar pressure  subatmospheric during inspiration  supra-atmospheric during expiration ◦ Transpulmonary pressure  difference between alveolar P & pleural P  measure of the recoil tendency of the lung  peaks at the end of inspiration 05/03/2015 11 Pleural Pressure  Lungs have a natural tendency to collapse ◦ surface tension forces 2/3 ◦ elastic fibers 1/3  What keeps lungs against the chest wall? ◦ Held against the chest wall by negative pleural pressure “suction” 05/03/2015 12 Collapse of the lungs  If the pleural space communicates with the atmosphere, i.e. pleural P = atmospheric P the lung will collapse  Causes ◦ Puncture of the parietal pleura  Sucking chest wound ◦ Erosion of visceral pleura ◦ Also if a major airway is blocked the air trapped distal to the block will be absorbed by the blood and that segment of the lung will collapse 05/03/2015 13 Pneumothorax 05/03/2015 14  Basics of the Respiratory System Functional Anatomy  The Respiratory Tree ◦ connecting the external environment to the exchange portion of the lungs ◦ similar to the vascular component ◦ larger airway = higher air flow & velocity  small cross-sectional area ◦ smaller airway = lower air flow & velocity  large cross-sectional area 05/03/2015 15  Basics of the Respiratory System Functional Anatomy  The Respiratory Tree ◦ Upper respiratory tract is for all intensive purposes a single large conductive tube ◦ The lower respiratory tract starts after the larynx and divides again and again…and again to eventually get to the smallest regions which form the exchange membranes  Trachea  Primary bronchi  Secondary bronchi conductive portion  Tertiary bronchi  Bronchioles  Terminal bronchioles  Respiratory bronchioles with start of alveoli outpouches exchange portion  Alveolar ducts with outpouchings of alveoli 05/03/2015 16 05/03/2015 17 05/03/2015 18 05/03/2015 19 Alveolar Structure 05/03/2015 20  Alveoli are thin-walled, Inflatable, grapelike sacs at the terminal branches of conducting airways  Each contain single layer of epithelial cells  Epithelial cells are two types (a) Type I cells for gas exchange , large and occupy 95% of alveolar surface area (Pneumocyte type I ) (b) Type II cells Secrete surfactant for reducing surface tension ( small cells) (Pneumocyte type II )  Alveolar macrophages; function? 05/03/2015 21  Alveolocapillary membrane  Pulmonary Circulation gives off 280 billion capillaries, supplying 300 million alveoli. ◦ Surface area for gas exchange is about 70m2 equivalent to a tennis court for each lung!!!! 05/03/2015 22 Alveolocapillary membrane 23 05/03/2015  Basics of the Respiratory System Functional Anatomy  What is the function of the upper respiratory tract? Raises incoming air to 37 Celsius ◦ Warm Forms ◦ mucociliary Humidify Raises incoming escalator ◦ Filter air to 100% humidity ◦ Vocalize 05/03/2015 24  Basics of the Respiratory System Functional Anatomy  What is the function of the lower respiratory tract? ◦ Exchange of gases …. Due to  Huge surface area = 1x105 m2 of type I alveolar cells (simple squamous epithelium)  Associated network of pulmonary capillaries  80-90% of the space between alveoli is filled with blood in pulmonary capillary networks  Exchange distance is approx 1.0 um from alveoli to blood! ◦ Protection  Free alveolar macrophages (dust cells)  Surfactant produced by type II alveolar cells (septal cells) 05/03/2015 25  Basics of the Respiratory System Functional Anatomy  Characteristics of exchange membrane ◦ High volume of blood through huge capillary network results in  Fast circulation through lungs  Pulmonary circulation = 5L/min through lungs….  Systemic circulation = 5L/min through entire body!  Blood pressure is low…  Means  Filtration is not a main theme here, we do not want a net loss of fluid into the lungs as rapidly as the systemic tissues  Any excess fluid is still returned via lymphatic system 05/03/2015 26  Basics of the Respiratory System Functional Anatomy  Sum-up of functional anatomy ◦ Ventilation? ◦ Exchange? ◦ Vocalization? ◦ Protection? 05/03/2015 27  LAWS GOVERNING GASES IN ATMOSPHERE AND INSIDE BODY  Basic Atmospheric conditions ◦ Pressure is typically measured in mm Hg ◦ Atmospheric pressure is 760 mm Hg ◦ Atmospheric components  Nitrogen = 78% of our atmosphere  Oxygen = 21% of our atmosphere  Carbon Dioxide =.033% of our atmosphere  Water vapor, krypton, argon, …. Make up the rest  Laws to remember ◦ Dalton’s law ◦ Fick’s Laws of Diffusion ◦ Boyle’s Law ◦ Ideal Gas Law 05/03/2015 28  Respiratory Physiology Gas Laws  Dalton’s Law ◦ Law of Partial Pressures  “each gas in a mixture of gases will exert a pressure independent of other gases present” Or  The total pressure of a mixture of gases is equal to the sum of the individual gas pressures. ◦ What does this mean in practical application?  If we know the total atmospheric pressure (760 mm Hg) and the relative abundances of gases (% of gases)  We can calculate individual gas effects!  Patm x % of gas in atmosphere = Partial pressure of any atmospheric gas  PO2 = 760mmHg x 21% (.21) = 160 mm Hg  Now that we know the partial pressures we know the gradients that will drive diffusion! 05/03/2015 29  Respiratory Physiology Gas Laws  Fick’s Laws of Diffusion ◦ Things that affect rates of diffusion  Distance to diffuse   Gradient sizes  Diffusing molecule sizes   Temperature  ◦ What is constant & therefore out of our realm of concern?   So it all comes down to partial pressure gradients of gases… determined by Dalton’s Law! 05/03/2015 30  Respiratory Physiology Gas Laws  Boyle’s Law ◦ Describes the relationship between pressure and volume  “the pressure and volume of a gas in a system are inversely related”  P1V1 = P2V2 05/03/2015 31  Respiratory Physiology Gas Laws  How does Boyle’s Law work in us? ◦ As the thoracic cavity (container) expands the volume must up and pressure goes down  If it goes below 760 mm Hg what happens? ◦ As the thoracic cavity shrinks the volume must go down and pressure goes up  If it goes above 760 mm Hg what happens 05/03/2015 32  Respiratory Physiology Gas Laws  Can’t forget about poor Charles and his law or Henry and his law ◦ Aptly named … Charles’s Law & Henry’s Law As the temp goes up in a volume of gas the volume rises At a constant temperature, the amount of a given gas proportionately dissolved in a given type and volume of liquid is directly VT proportional to the partial pressure of that gas in equilibrium with that liquid. OR the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid. *also has a constant which is different for each gas 05/03/2015 33  Two Circulations in the Lungs  Pulmonary Circulation. ◦ Arises from Right Ventricle. ◦ Receives 100% of blood flow.  Bronchial Circulation. ◦ Arises from the aorta. ◦ Part of systemic circulation. ◦ Receives about 2% of left ventricular output. 05/03/2015 34 Pulmonary vs systemic circulation blood pressures 05/03/2015 35 Pulmonary and Bronchial Circulation 36 05/03/2015  Pulmonary and Bronchial Circulation  Pulmonary circulation has a lower 37 pressure than the systemic circulation  One third of pulmonary vessels are filled with blood at any given time  Pulmonary artery divides and enters the lung at the hilus  Each bronchus and bronchiole has an accompanying artery or arteriole 05/03/2015  Pulmonary and bronchial circulation  pulmonary circulation and the bronchial circulation contribute to blood flow in the lung.  In the pulmonary circulation, almost all the blood in the body passes via the pulmonary artery to the pulmonary capillary bed, where it is oxygenated and returned to the left atrium via the pulmonary veins.  The separate and much smaller bronchial circulation includes the bronchial arteries that come from systemic arteries. They form capillaries, which drain into bronchial veins or anastomose with pulmonary capillaries or veins. The bronchial veins drain into the azygos vein.  The bronchial circulation nourishes the trachea down to the terminal bronchioles and also supplies the pleura and hilar lymph nodes. It should be noted that lymphatic channels are more abundant in the lungs than in any other organ. 05/03/2015 38 05/03/2015 39  Pulmonary Circulation  Givesoff 280 billion capillaries, supplying 300 million alveoli. ◦ Surface area for gas exchange = 50 – 100 m2 equivalent to a tennis court for both lungs!!!! 05/03/2015 40 ◦ Formed by the shared alveolar and capillary 41 walls ◦ Thin membrane of alveolar epithelium, the alveolar basement membrane, interstitial space, the capillary basement membrane, and the capillary endothelium 05/03/2015 Alveolocapillary membrane 42 05/03/2015 05/03/2015 43  04/05/2015 LECTURE 2: SPIROMETRY, LUNG VOLUMES AND CAPACITIES, FEV1/FVC RATIO Dr Lukubi Lwiindi 1 Physiology Unit SPIROMETRY; USED TO MEASURE LUNG VOLUMES ON A SPIROGRAM IN PULMONARY FUNCTION TESTS 04/05/2015 2 SPIROMETRY 04/05/2015 3 PULMONARY FUNCTION TESTS 04/05/2015 Spirometry Body Plethysmography (Body Box) Body Box + Dlco Metacholine Challenge text(MCT) Cardiopulmonary Exercise Test (Ergospirometry) 4 WHAT INFORMATION DOES A SPIROMETER YIELD? 04/05/2015 A spirometer can be used to measure the following:  FVC and its derivatives (such as FEV1, FEF 25-75%)  Peak expiratory flow rate  Maximum voluntary ventilation (MVV)  Slow VC  IC, IRV, TV and ERV  Pre and post bronchodilator studies in assessing effective treatment in asthmatics 5 LUNG VOLUMES & CAPACITIES 04/05/2015 The amount of air that moves into the lungs with each inspiration (or the amount that moves out with each expiration) is called the tidal volume. The air inspired with a maximal inspiratory effort in excess of the tidal volume is the inspiratory reserve volume. The volume expelled by an active expiratory effort after passive expiration is the expiratory reserve volume, and the air left in the lungs after a maximal expiratory effort is the residual volume. The space in the conducting zone of the airways occupied by gas that does not exchange with blood in the pulmonary vessels is the respiratory dead space. The forced vital capacity (FVC), the largest amount of air that can be expired after a maximal inspiratory effort, is frequently measured clinically as an index of pulmonary function. It gives useful information about the strength of the respiratory muscles and other aspects of pulmonary function 6 LUNG VOLUMES AND CAPACITIES 04/05/2015 The fraction of the vital capacity expired during the first second of a forced expiration is referred to as FEV1 (formerly the timed vital capacity). The FEV1 to FVC ratio (FEV1/FVC) is a useful tool in the diagnosis of airway disease. The amount of air inspired per minute (pulmonary ventilation, respiratory minute volume) is normally about 6 L (500 mL/ breath x 12 breaths/min). The maximal voluntary ventilation (MVV) is the largest volume of gas that can be moved into and out of the lungs in 1 min by voluntary effort. The normal MVV is 125 to 180 L/min. 7 04/05/2015 8 SPIROMETER AND LUNG VOLUMES/ CAPACITIES 04/05/2015 9 MINUTE AND ALVEOLAR VENTILATION 04/05/2015 Minute ventilation: Total amount of air moved into and out of respiratory system per minute Respiratory rate or frequency: Number of breaths taken per minute Anatomic dead space: Part of respiratory system where gas exchange does not take place Alveolar ventilation: How much air per minute enters the parts of the respiratory system in which gas exchange takes place 10 RESPIRATORY DISEASES Restrictive Disease: 04/05/2015  Makes it more difficult to get air into the lungs because of ‘stiff lungs’  They “restrict” inspiration.  Decreased VC; Decreased TLC, RV, FRC  Includes: Fibrosis Sarcoidosis Muscular diseases Chest wall deformities 11 RESPIRATORY DISEASES 04/05/2015 Obstructive Diseases;  Make it more difficult to get air out of the lungs because of obstruction in airways.  Decrease VC; Increased TLC, RV, and FRC  Includes: Emphysema Chronic bronchitis Asthma 12  PFTS: FEV1, FVC AND THEIR RATIO 04/05/2015  Interpretationof Spirometry involves looking at the absolute values of FEV1, FVC, and FEV1/FVC.  Then comparing them with predicted values, and examining the shape of the spirograms.  Patientsshould complete three blows that are consistent and within 5% of each other—many electronic spirometers automatically provide this information. 13  FEV1/FVC RATIO 04/05/2015  The ratio of FEV1/FVC is normally between 0.7 and 0.8.  Values below 0.7 are a marker of airway obstruction, except in older adults where values 0.65–0.7 may be normal.  In people over 70 years old, the FEV1/FVC ratio may need to be lowered to 0.65 as a lower limit of normal.  Conversely, in people under 45, using a ratio of 0.7 may result in under-diagnosis of airway obstruction. 14  SPIROMETRY 04/05/2015 Forced Expiratory Volume (FEV1)  FEV1 is used in conjunction with FVC for: Simple screening Response to bronchodilator therapy Response to bronchoprovocation Detection of exercise-induced bronchospasm 15 FEV1/FVC 04/05/2015  FEV1% = FEV1/FVC x 100 Useful in distinguishing between obstructive and restrictive pulmonary disorders. 16  SPIROMETRY 04/05/2015 Forced Expiratory Volume Ratio (FEVT%)  Normal FEVT% Ratios for Health Adults FEV 0.5% = 50%-60% FEV 1% = 75%-85% FEV 2% = 90%-95% FEV 3% = 95%-98% FEV 6% = 98%-100%  Patients with obstructive pulmonary disease have reduced FEVT% for each interval 17 COPDS AND FEV1/FVC RATIO 04/05/2015 A decrease FEV1/FVC ratio is the “hallmark” of obstructive disease FEV1/FVC H2CO3 ---> H+ + HCO3 + Hb ---> HbCO + Hb --->HbH 2 HbO2 -----> Hb + O2 Red Blood Cell 38 CARBON DIOXIDE TRANSPORT IN THE BLOOD: AT THE LUNGS 04/30/2015 Alveolus Carbonic Anhydrase CO2 + H2O