Respiratory Physiology PDF

LESSON 5. THE RESPIRATORY PHYSIOLOGY. Mechanics of pulmonary ventilation. Lung volumes and capacities. 1. PULMONARY VENTILATION 1.1. Pressure Changes During Pulmonary Ventilation 1.1.1. Inhalation 1.1.2. Exhalation 1.2. Surface Tension of Alveolar Fluid 1.3. Co...

LESSON 5. THE RESPIRATORY PHYSIOLOGY. Mechanics of pulmonary ventilation. Lung volumes and capacities. 1. PULMONARY VENTILATION 1.1. Pressure Changes During Pulmonary Ventilation 1.1.1. Inhalation 1.1.2. Exhalation 1.2. Surface Tension of Alveolar Fluid 1.3. Compliance of the Lungs 1.4. Airway Resistance 2. LUNG VOLUMES AND CAPACITIES 1. PULMONARY VENTILATION Respiration = process of gas exchange in the body. 3 basic steps: 1. Pulmonary ventilation (breathing) = the inhalation (inflow) and exhalation (outflow) of air. Involves the exchange of air between the atmosphere and the alveoli of the lungs. 2. External (pulmonary) respiration = exchange of gases between the alveoli of the lungs and the blood in pulmonary capillaries. Pulmonary capillary blood gains O2 and loses CO2. 3. Internal (tissue) respiration = exchange of gases between blood in systemic capillaries and tissue cells. Blood loses O2 and gains CO2. Cellular respiration = metabolic reactions that consume O2 and give off CO2 during the production of ATP.  In pulmonary ventilation, air flows between the atmosphere and the alveoli of the lungs because of alternating pressure differences created by contraction and relaxation of respiratory muscles. 1 The rate of airflow and the amount of effort needed for breathing is also influenced by OTHER FACTORS: – alveolar surface tension 2 – compliance of the lungs 3 – airway resistance. 4 1.1. Pressure Changes During Pulmonary Ventilation Air moves into the lungs when the air pressure inside the lungs is less than the air pressure in the atmosphere. Air moves out of the lungs when the air pressure inside the lungs is greater than the air pressure in the atmosphere. 1.1.1. Inhalation = Breathing in = inspiration. Just before each inhalation, the air pressure inside the lungs is equal to the air pressure of the atmosphere. For air to flow into the lungs, the pressure inside the alveoli must become lower than the atmospheric pressure: increasing the size of the lungs. The diaphragm and external intercostals contract and the overall size of the thoracic cavity increases, the volume of the pleural cavity also increases, which causes intrapleural pressure to decrease.  1. Diaphragm: Contraction of the diaphragm causes it to flatten, lowering its dome. This increases the vertical diameter of the thoracic cavity. Contraction of the diaphragm is responsible for about 75% of the air that enters the lungs during quiet breathing. 2. External intercostals. When these muscles contract, they elevate the ribs. There is an increase in the anteroposterior and lateral diameters of the chest cavity. Contraction of the external intercostals is responsible for about 25% of the air that enters the lungs during normal quiet breathing.  During deep, forceful inhalations, accessory muscles of inspiration also participate in increasing the size of the thoracic cavity: – sternocleidomastoid muscles, which elevate the sternum; – the scalene muscles, which elevate the first two ribs; – the pectoralis minor muscles, which elevate the third through fifth ribs.  1.1.2. Exhalation= Breathing out =expiration. The pressure in the lungs is > than the pressure of the atmosphere. Normal exhalation during quiet breathing is a passive process. No muscular contractions are involved. Exhalation results from elastic recoil of the chest wall and lungs. Two forces contribute to elastic recoil: (1) the recoil of elastic fibers that were stretched during inhalation an (2) the inward pull of surface tension due to the film of alveolar fluid. Exhalation starts when the inspiratory muscles relax: decrease the vertical, lateral, and anteroposterior diameters of the thoracic cavity: decreases lung volume. Alveolar pressure increases. Air flows from the area of > pressure in the alveoli to the area of < pressure in the atmosphere. Exhalation becomes active only during forceful breathing (playing a wind instrument or during exercise): muscles of exhalation (the abdominals and internal intercostals) contract. 1.2 Surface Tension of Alveolar Fluid A thin layer of alveolar fluid coats the surface of alveoli and exerts a force known as surface tension. Surface tension causes the alveoli to assume the smallest possible diameter. During breathing, surface tension must be overcome to expand the lungs during each inhalation. The surfactant (a mixture of phospholipids and lipoproteins) present in alveolar fluid reduces its surface tension. A deficiency of surfactant in premature infants causes respiratory distress syndrome, in which the surface tension of alveolar fluid is greatly increased, so that many alveoli collapse at the end of each exhalation. Great effort is then needed at the next inhalation to reopen the collapsed alveoli. 1.3. Compliance of the Lungs Compliance refers to how much effort is required to stretch the lungs and chest wall. High compliance means that the lungs and chest wall expand easily; low compliance means that they resist expansion. Decreased compliance is a common feature in pulmonary conditions that: – (1) scar lung tissue (for example, tuberculosis) – (2) cause lung tissue to become filled with fluid (pulmonary edema) – (3) produce a deficiency in surfactant – (4) impede lung expansion in any way (for example, paralysis of the intercostal muscles). 1.4. Airway Resistance The rate of airflow through the airways depends on the pressure difference and the resistance. The walls of the bronchioles offer resistance to the flow of air into and out of the lungs. As the lungs expand during inhalation, the bronchioles enlarge. Larger diameter airways have decreased resistance. Airway resistance increases during exhalation as the diameter of bronchioles decreases. Airway diameter is also regulated by the degree of contraction or relaxation of smooth muscle in the walls of the airways. Signals from the SNS cause relaxation of this muscle: bronchodilation and decreased resistance. The hallmark of asthma or chronic obstructive pulmonary disease (COPD)—emphysema or chronic bronchitis—is increased airway resistance due to obstruction or collapse of airways. 2. LUNG VOLUMES AND CAPACITIES At rest, a healthy adult averages 12 breaths a minute, with each inhalation and exhalation moving 500 mL of air. The volume of one breath is called the tidal volume (VT). The minute ventilation (MV) (the total volume of air inhaled and exhaled each minute) is respiratory rate multiplied by tidal volume: MV = 12 breaths/min x 500 mL/breath = 6 liters/min Spirometer = apparatus used to measure the volume of air exchanged during breathing and the respiratory rate. The record is called a spirogram. Inhalation is recorded as an upward deflection, and exhalation is recorded as a downward deflection.  In a typical adult, about 70% of the tidal volume (350 mL) reaches the respiratory zone of the respiratory system (the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli). The other 30% (150 mL) remains in the conducting airways of the nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. The alveolar ventilation rate = volume of air per min that reaches the respiratory zone. Ex: 350 mL/breath x 12 breaths/min = 4200 mL/min. In general, these volumes are larger in males, taller individuals, and younger adults, and smaller in females, shorter individuals, and the elderly. The values given here are averages for young adults. By taking a very deep breath, you can inhale more than 500 mL. This additional inhaled air, called the inspiratory reserve volume, is about 3100 mL in an average adult male and 1900 mL in an average adult female.  If you inhale normally and then exhale as forcibly as possible, you should be able to push out considerably more air in addition to the 500 mL of tidal volume. The extra 1200 mL in males and 700 mL in females is called the expiratory reserve volume. The FEV1.0 = forced expiratory volume in 1 second, the volume of air that can be exhaled from the lungs in 1 second with maximal effort following a maximal inhalation. Chronic obstructive pulmonary disease (COPD) greatly reduces FEV1.0 because COPD increases airway resistance. Even after the expiratory reserve volume is exhaled, considerable air remains in the lungs. This volume, which cannot be measured by spirometry, is called the residual volume and amounts to about 1200 mL in males and 1100 mL in females.  Lung capacities are combinations of specific lung volumes. Inspiratory capacity is the sum of tidal volume and inspiratory reserve volume (500 mL + 3100 mL = 3600 Ml in males and 500 mL + 1900 mL = 2400 mL in females). Functional residual capacity is the sum of residual volume and expiratory reserve volume (1200 mL + 1200 mL = 2400 mL in males and 1100 mL + 700 mL = 1800 mL in females). Vital capacity is the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume (4800 mL in males and 3100 mL in females). Total lung capacity is the sum of vital capacity and residual volume (4800 mL + 1200 mL = 6000 mL in males and 3100 mL + 1100 mL = 4200 mL in females). https://www.youtube.com/watch?v=BP-uPD92DMk https://www.youtube.com/watch?v=jSkwBoed6Tw 1. External (pulmonary) respiration is: a. Exchange of gases between the alveoli of the lungs and the blood in pulmonary capillaries b. The inhalation (inflow) and exhalation (outflow) of air c. The exchange of gases between blood in systemic capillaries and tissue cells d. None of the previous answers is true. 2. Spirometry can be used to accurately measure all of the following except a. Residual volume b. Expiratory reserve volumen c. Inspiratory reserve volume d. Tidal volume 3. The hallmark of asthma or chronic obstructive pulmonary disease is: a. Increased airway resistance due to obstruction or collapse of airways b. Decreased compliance c. A deficiency of surfactant d. None of the previous answers is true