Mechanics of Breathing
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Created by:
ojames03 Plus on February 9, 2012
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Math / Symbols | English |
|---|---|
 General Features of Pressure | -->Pressure is caused by gas mol. striking a container -->" is related to the VOLUME of the container -->If larger volume: 1)Gas mol. strike the walls less frequently 2)Mol exert less pressure -->If small volume 1)Gas mol. strike the walls more frequently 2)Mol. exert more pressure ***Seen in Boyle's Law |
| Boyle's Law | -->The pressure of a gas is inversely proportional to the volume of its container (↑ in pressure, leads to a ↓ in pressure) |
| Changes in Thorax & Muscles Involved during inspiration (↑Intrathoracic Volume; ↓Intrathoracic Pressure) | -->Diaphram contracts & pushes abdominal contents downward -->Downward movment pushes the rib cage OUTWARD & UPWARD -->Muscles involved (External Intercostal & SCM contracts & pulls the ribs outward) |
| Changes in the Thorz & Muscles Involved During Forced Expiration | -->Diaphram relaxes & returns to its dome shape -->Upward movement pushes the rib cage INWARD & DOWNWARD -->Muscles involved (Abdominal & Internal Intercostal Muscles contract & pull ribs INWARD |
| Mechanism of Inspiration | -->An incr. in thoracic volume leads to an incr. in lung volume -->The incr in lung volume causes lung pressure to DECREASE, leading to the pressure in the alveoli being LESS than atmospheric pressure 1)This allows air to flow down its pressure gradient & enter the lungs, which initiates INSPIRATION -->Inspiration ends when **Palv = Patm** |
| 2 Rib movements that incr. the thoracic diameters | 1)Pump Handle Movement (↑ in the antero-posterior diameter of rib cage -->Ribs move upwards & forwards 2)Bucket Handle Movment (↑ in the lateral diameter of rib cage) -->Ribs move upwards & outwards |
| Exoiration | -->Is normal a PASSIVE PROCESS b/c both the lung & chest wall are ELASTIC STRUCTURES which return back to their resting conditions after inspiration -->Muscles are only used for expiration mainly (i)during exeercise, or (ii) during lung disease (*Bronchial Asthma**) -->***See slide for more details |
| Additional ways to think about Functional Residual Ca | (1)The capcity or volume from which you end up when TV is passively expired -->Ex. If you turn off your muscle, your body can passively reach FRC (2)The capacity/volume of the lung where the OUTWARD recoil tendency of the chest wall is EQUAL & OPPOSITE IN SIGN to the inward recoil tendency of the lung |
| Interpleural Space | -->The space btwn the visceral pleura around the lungs & the parietal pleura around the chest wall -->Is considered "Air Tight" b/c no air can get in or out unless their is a pathology (Ex. Pneumothrorax) -->Under normal conditions it has ***Negative Intrapleual Pressure, caused by 2 opposiing forces: 1)The lung tendency to recoil 2The Chest wall tendency to spring outward -->Negative Interpleural Pressure is Subatmospheric at -5cm H20 |
| 4 Important Pressure | 1)Atmospheric Pressure (Patm) -->Is the Pressure exerted by the air surrounding the body -->**Total atmospheric pressure is ZERO** 2)Intrapulmonary /Intra-alveolar pressure (Palv) -->the pressure within the alveoli of the lungs --> Rises & Falls during breathing, but always equalizes with the atmospheric pressue 3)Intrapleural Pressure (Pip) -->Pressure within the pleural cavity -->***ESOPHAGEAL PRESSURE is an index of intrapleural pressure -->Under NORMAL conditions, it should always be LOWER than both Palv & Patm pressures |
| Condition where no air flows out of the lung ("FRC") | --> When the atmospheric pressure = intra-alveolar pressure (Patm = Palv) |
| Condition where Air flows into the lung ("Inspiration") | -->When atmospheric pressure is GREATER than intra-alveolar pressure (Patm > Palv) -->The chest wall will DECR. its tendency to want to expand, while the lung wall will INCREASE its tendency to want to collapse ("inward recoil") |
| Condition where Air flows out of the lung ("Expiration") | -->When the atmopheric pressure is LESS than the intra-alveolar pressure (Patm < Palv) -->The lung wall will DECR its tendency to want to want to collapse, while the chest wall will INCR its tendency to want to expand |
| Characteristic of Individual Pressures | (1)P(alv) -->Is NEGATIVE during inspiration -->Is POSITIVE during expiration -->Is 0 at any lung volumes as long as there is NO AIR FLOW (2)Pip -->At rest it is -5 cm H20 -->Becomes a lesser value (i.e. more negative;; Ex -8 cm H20) during inspiration -->Becomes a greater value (i.e. less negative; Ex. -6 cm H20) during expiration -->It can only become + if you proved POSITIVE PRESSURE OF FORCED EXPIRATION (Ex. Coughing, Sneezing, Inflatting a ballon) (3)Transmural Pressure (Transalveolar pressure; collapsing pressure of the lung) -->Is +5 cm H20 at rest -->Becomes MORE POSITIVE (LESS) during Inspiration (Expiration) -->Will be the most POSITIVE at Total Lung Capacity (where you have the most volume) -->***Can be ZERO at pneumothorax, when the lung is completly deflated -->**Can NEVER BE NEGATIVE** |
| Transmural Pressure | -->Refers to the pressure across a structure, which is the diff. btwn the intra-alveolar pressur & intrapleural pressue btwn the lung & chest wall -->When it is +: 1)Lung wall has an incr. tendency to want to collapse during inspiration 2)Chest wall has a decr. tendency to want to expand during inspiration -->When it is -: 1)Lung wall has a decr. tendency to want to collapse during expiration 2)Chest wall has a incr tendency to want to expan during expiration |
| Characteristics at equilibrium | -->Intrapleural Pressure is NEGATIVE (at subatmospheric pressure) b/c the INTRAPLEURAL FLUID in btwn the lungs firmly pushes the lung to the chest wall (~ to a suction cup) -->The 2 opposing forces of the lung & chest wall are equal & oppostit |
| Characteristics of Inspiration | *See pwerpt notes** |
| Characteristics at the end of inspiration | -->Lung expands until the recoil force incr. to = intapleural pressure -->***Alveolar pressure returns back to ZERO -->Intrapleural pressure is more - than its original value of -5 cm H20 -->Lung volume increases by ONE TIDAL VOLUME, at a point where the recoil force of the lung & the chest wall is at a MAXIMUM (***FRC + TV) |
| ***Graphs of intra-alveolar pressure & intrapleural pressure | -->**See your notes** |
| General Differences btwn obstructive & restrictive disorders of the lung | -->Obstructive Disorders: Disorders that decr. the inspiratory work of breathing 1)Ex. Emphysema or Asthma 2)Requires more energy (↑resistance) to force air out of the lungs during expiration -->Restrictive Disorder: Disorders: Disorders that incr. the inspiratory work of breathing 1)Ex. Fibrosis 2)Requires less energy (↓resistance) to force air out of the lung during expiration |
| Features of COPD | -->See Notes for Details -->Forced expiration may cause the airways to COLLAPSE due to loss of elastic fibers -->Intrapleural pressure is raised to the SAME VALUE as a normal person 1)Problem is that IA pressure & airway pressure have DECREASED relative to a normal person -->Transmural pressure remains + across the alveoli, but is - above them, which lead to the COLLAPSE of the airway in the conduction portion of respiratory system -->Consequence of collapse is: 1)↑ in resistance to airflow 2)Incr. difficulty to expire 3)Leads to incr in **FRC & RV*, known as *AIR TRAPPING** in the alveoli 4)↑ in AP diameter relative to the transverse diameter of the chest of affected patient |
| Pursed Lip Treatment of in patients with COPD | -->Patients learn to expire slowly in order to RAISE the airway prssure, which prevents the REVERSAL OF THE TRANSMURAL PRESSURE, which: 1)Prevents the reversal of the transmural pressure gradient across large airways, and PREVENTS their collapse |
| Valsalva Manuver | -->The process of expiring against a CLOSED GLOTTIS (Tongue), which creates positive pressure in the thoracic cavity due the contraction of expiratory muscles -->Results in an incr. in intrapleural pressure, which creates a + alveolar pressure -->Intra-alveolar pressure will be + |
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