Breathing Function of Respiratory Tract The respiratory tract is a series of spaces and semirigid tubes designed to convey air into and out of the respiratory organs (lungs). Parts of the Respiratory Tract Structure of Respiratory Tract Upper Respiratory Tract ower Respiratory Tract Tubes: Nasal cavity Oral cavity Pharynx arynx Trachea Bronchi Extraction Organs: ungs 4 Physics of Breathing Tissues need oxygen Oxygen needs to be extracted from the air ungs are organs designed for gas exchange; they extract oxygen, remove carbon dioxide Respiratory System z The respiratory system is responsible for supplying oxygen to the blood and expelling waste gases (CO2) from the body. The upper structures of the respiratory system are combined with the sensory organs of smell and taste (in the nasal cavity and the mouth) and the digestive system (from the oral cavity to the pharynx). The larynx, or voicebox, is located at the head of the trachea, or windpipe. 1
The trachea extends down to the bronchi, which branch off at the tracheal bifurcation to enter the hilus of the left or right lung. The lungs contain the narrower passageways, or bronchioles, which carry air to the functional unit of the lungs, the alveoli. There, in the thousands of tiny alveolar chambers, oxygen is transferred through the membrane of the alveolar walls to the blood cells in the capillaries within. ikewise, waste gases diffuse out of the blood cells into the air in the alveoli, to be expelled upon exhalation. http://www.youtube.com/watch?v=d f3r0kiug&feature=related Physics of Breathing Problem: how to move air in and out of lungs? Solution: use Boyle s aw to design a container for the lungs Boyle s aw For a fixed amount of gas kept at a fixed temperature, pressure and volume are inversely proportional Physics of Breathing What we need to do is to: construct a container that can change its volume insert lungs into the container and seal them in place increase volume of the container, pressure between lungs and container will decrease, air will flow into lungs decrease volume of the container, pressure between lungs and container will increase, air will flow out of lungs Result: breathing!!! The Body s Respiratory Container The Thoracic Cage Pleura Bag within the Bony Container Membrane that covers inside of thoracic cage and covers the lungs Pleurae pleural cavities are lined by a serous membrane PEURA SAC lungs grow into the pleural sac, therefore are covered with ih pleura the space between the 2 layers of pleura is sealed within the thoracic cavity expansion of the thoracic cage will increase the volume of the intrapleural space 2
Volume Changes - Movement of Ribs Volume Changes - Movement of Sternum When the ribs are pulled up, the side to side diameter of the thoracic cavity increases Volume increases, intrathoracic pressure decreases When the ribs move up, they push the lower part of the breastbone forward Anteroposterior diameter increases Volume increases, intrathoracic pressure decreases Intercostal muscles Muscles Responsible for Inspiration 3 thin sheets of muscle run at an angle from one rib to another when muscle contracts, it pulls on the rib below result is like lifting a bucket handle lateral diameter increases; lifting the rib also pushes the attached sternum forward 1. Intercostals Muscles Responsible for Inspiration 2. Diaphragm Thoracic diaphragm muscle attached to margin of ribs and to vertebral bodies Separates the thoracic cavity from the abdominal cavity Contraction of the Diaphragm when the thoracic diaphragm contracts, it flattens out top to bottom diameter of thoracic cavity increases volume of the thoracic cavity increases, intrathoracic pressure decreases 3
Physics of Breathing: Summary Movement of ribs increases: side to side diameter front to back diameter Movement of diaphragm increases: top to bottom diameter Abdominal Cavity in Breathing abdominal cavity is the area below the diaphragm and above the pelvic cavity it is continuous with the pelvic cavity the true floor of the abdominal cavity is the pelvic floor the abdominal cavity contains viscera liver, spleen, stomach, pancreas, large and small intestines Role of Abdominal Muscles in Breathing Inspiration diaphragm descends and compresses viscera abdominal wall relaxes, to accommodate the movement of the viscera, minimizes increase in intraabdominal pressure Role of Abdominal Muscles in Breathing Expiration diaphragm relaxes and rebounds into the thoracic cavity abdominal muscles rebound and contract, decreasing the size of the abdominal cavity which increases intra-abdominal pressure intra-abdominal pressure pushes the diaphragm further upward, decreasing the size of the thoracic cavity, increasing intrathoracic pressure Diaphragm movement: http://www.youtube.com/watch?v=hp gcvw8pry&feature=related Respiration: http://www.youtube.com/watch?v=hit621prro0&feature=related Simpleanimation ofrespiration: http://www.youtube.com/watch?v=43jjgxudeps Respiration Physiology 4
RESPIRATORY VENTIATION: Sequence for Air Movement SEQUENCE FOR AIR MOVEMENT A. Pressure Development 1. Respiratory muscle contraction (or relaxation) 2. Transmission of pressure change through the intrapleural space ΔPalv = ΔPpl 3. Change in alveolar pressure Negative pressure (below atmospheric): Inspire Positive pressure (above atmospheric): Expire Spirometry 5.7 Ventilation Parameters ung Volumes 5.7 Capacities: combined volumes TC VC IC FRC I TV E 2.7 2.2 1.2 0 Tidal Volume (TV): Volume of gas exchanged each breath can change I as IC ventilation pattern changes and is about 0.5 liter. VC TC 2.7 Inspiratory Reserve Volume (I): maximum volume that can betvinspired 2.2 over and beyond the normal tidal volume and is about 3 liters in young male adult. E FRC 1.2 Expiratory Reserve Volume (E): maximum volume that can still be expired by forceful expiration after the end of a normal tidal expiration and 0 is about 1.1 litre in young male adult. Residual Volume (): volume remaining in the lungs and airways following a maximum expiratory effort and is about 1.2 litre in young male adult. lungs cannot empty completely because of 1- stiffness when compressed and 2- airway collapse and gas trapping at low lung volumes. Vital Capacity (VC): maximum volume of gas that can be exchanged in a single breath. VC = TV + I + E Total ung Capacity (TC): maximum volume of gas that the lungs (and airways) can contain. TC = VC + Functional Residual Capacity (FRC): volume of gas remaining in the lungs (and airways) at the end of expiratory position. FRC = + E Inspiratory Capacity (IC): maximum volume of gas that can be inspired from the of expiratory position IC = TV + I B. Air Movement, which depends on 1. Force of muscle contraction and Palv Plethysmography, Respirology ab, U of Manitoba 2. Elastic recoil of the lung and chest wall (compliance, C) C = ΔV/ ΔP or ΔV = C x ΔP 3. Resistance to rate of lung volume change (viscosity) Notation V' (flow or dv/dt) = Palv / Raw Raw = resistance of the airways to air movement and resistance of tissue to rapid shape change Palv = alveolar pressure; pressure within the alveoli; also called intrapulmonic or intrapulmonary pressure; measured by measuring pressure at mouth level when airflow is briefly occluded Ppl = intrapleural pressure; pressure within the pleural space; also called intrathoracic pressure; measured by injecting a small volume of air into the intrapleural space or swallowing an esophageal balloon Note: 1 mmhg = 1.36 cm H2O 5
ung Volume Measurement 1. The person sits in an upright chamber and breath normal (above FRC) 2. A shutter drops across the breathing tube, to increase the chest volume. The person starts like panting. 3. The chest volume increases the chamber s volume decreases Chamber s pressure increases. 4. We know the initial Chamber s volume and pressure and also the chamber s new pressure; hence, using Boyles aw: P1.V1=P2.V2 the new volume of the chamber is calculated. 5. V2 V1=ΔV of the person s chest volume change 6. et Vi = the initial lung volume (unknown), Pm=pressure at the mouth (known), Vins=the inspiratory volume of the chest (unknown) plus the change of the lung volume (calculated above), and Pm ins=the pressure at the mouth during inspiratory effort (known). Using Boyle s law again, we can compute the initial volume of the lung when the shutter was closed: ΔVPm ins Vi Pm = ( Vi ΔV ) Pm ins Vi = P P m m ins TC V ol u m e FRC 0 +10 20 30 40 Transpulmonary Pressure (cmh 2 0) Pressure-Volume hysteresis loop C FRC TC ung compliance versus lung volume Respiratory Model Nose Vocal tract Pharynx cavity Mechanical Model of the vocal tract f n nv =, n = 1,3,5,... 4 z Mouth Electrical Model Trachea ung R Z rad Muscle Force A more realistic model of an airway segment P = Pressure analogous to Voltage U = Volume flow (velocity) analogous to current R R The Acoustic R (viscosity loss): R = du G C R w w C w The Acoustic (Acoustic air mass): ρ = air density l = length of the pipe A = cross sectional area of the pipe u = particle velocity du F = m. a P. A = ρla dt ρl du du ρl P = = = A dt dt A Z rad 6
The Acoustic C (Compliance): V = Total Gas Volume η = a constant (=1.4 for air at normal condition) PV η = contant pηv 1 η dv η = = U P dt V dt V V U = = C Pη dt dt C = V Pη η 1 dv + V dt ΔV However,in pulmonary mechanicscis measured as ΔP η = 0 dt 7