School of Dentistry SUNYAB PGY452 Respiratory Lectures March 10 2015 Daniel D Swartz Ph D Lecture 3 PulmonaryMechanics Reading Assignment Berne Levy chapter 21 pages 430 443 Respiratory System Mechanics 1 Lung 2 Chest wall 3 Respiratory System RS lung chest wall Respiratory System Mechanics PA airflow direction and velocity Pleural pressure can be measured with an esophageal balloon Figure 17 11 Chest Wall and Lung Interaction PL is the distending pressure Pel is the pressure tending to collapse the lung PA Pel Ppl PL Pel At FRC PB PA PPL 5 cm H2O Pel Pcw are equal and opposite PL Sequence of Events Leading to Inspiration Inspiratory Muscles Contract Chest Wall Expands Ppl Becomes More Subatmospheric Lung Expands PA Becomes Sub atmospheric Air Flows into Alveoli Lung Collapse with Pneumothorax Also pneumothorax can occur from inside of lung tumor infection or over expansion Pressure volume curve of the Lung Chest Wall and Respiratory System What structures limit RV and TLC Chest wall at neutral point Fig 21 7 B L Pressure Volume Curve of Respiratory System Surface Tension Compliance and Elastance C V P CL V Ppl Normal 0 2L cm H2O less distensible at high volumes Compliance ability of the lung to stretch effects work of breathing Restrictive lung disease reduces compliance of the lung Fibrotic Lung Disease inelastic scar tissue in lung Respiratory Distress Syndrome lack of surfactant in the lung TLC Compliance V P V VITAL CAPACITY L Emphysema High Compliance RDS and Fibrosis Low Compliance P Translung Pressure cm H2O Elastance ability of the lung to recoil back to resting volume Emphysema reduces elastance of the lung Specific compliance corrects for the decreased compliance at higher volumes Type II Alveolar Cells Secrete Surfactant Surfactant Secreted by Type II alveolar cells 85 90 Phospholipids DPPC PG 10 15 Proteins SP A SP B SP C SP D regulate surfactant turnover immune regulation formation of tubular myelin Decreases surface tension Secretion of surfactant type II epithelial cells exocytosis of lamellar bodies adrenergic agonist activators of PKC leukotrienes purinergic agonist Clearance of surfactant reuptake by type II cells absorption into lymphatics clearance by alveolar macrophages Surfactant Function Law of LaPlace Without Surfactant Without surfactant the lower lung volumes would require a greater transmural pressure to keep the lung expanded With Surfactant Interdependence prevents alveoli from collapsing atelectasis Pressure Volume Curve of the Lung Deflation P V curve compare 1 to 2 normal 0 2 L cm H2O Compliance decreases with increase in volume V P FRC to 1 L CL Fig 21 4 B L Non compressible Airway Resistance Poiseuille s Law R L r4 Length Viscosity Radius Table 17 3 Airway Resistance Resistance in Series R total R1 R2 R3 R4 upper airway Resistance in Parallel R total 1 R1 1 R2 1 R3 1 R4 distal airway Resistance to airflow decreases as lung volume increase negative pleural pressure of inhalation pulls open airways Other Factors that increase airway resistance mucus edema contraction of bronchial smooth muscle increase air density scuba diving Airway Resistance in Small vs Large Airw 1 In small airways laminar flow predominates and resistances are No breath primarily in parallel Both resultsounds in low silent airway resistance 2 In large airways turbulent flow predominates and resistances are both in series and in parallel Both result in Breath higher airway resistance sounds Re Reynolds number r radius of airway v airflow velocity d air density n air viscosity If Re is 2000 then laminar flow predominates and airflow for a given pressure will increase If Re is 2000 then turbulent flow predominates Turbulence increases when airflow velocity and or airway radius increase Thus for a given airflow a higher airway pressure is required to support turbulent versus laminar airflow What happens to airway resistance in laminar versus turbulent airflow v Laminar flow In small airways v Turbulent flow in large airways VE Expired or minute ventilation how much air you breathe out each minute VT Tidal Volume F breathing frequency how many times you breathe each minute Work of Breathing ventilatio n f BPM emphysema normal pulmonary fibrosis Factors that influence the rate of airflow through the airways 1 Laminar versus turbulent airflow Re Reynolds number 2 Airflow resistances in series and in parallel 3 Flow limitation and the Equal Pressure Point Effect of Airway Branching on Airway Resistance RAW Increasing lung volume Inc radius of airway Dec resistance to airway Increase airway resistance Mucus Edema Contraction of SMC Inspired gas density and viscosity FIG 21 10 B L Flow Limitation and the Equal Pressure Point Flow Limitation and the Equal Pressure Point Expiration effort dependent Peak expiratory flow rate Expiratio n Maximum Inspiratory 1 Inspiratory muscle effort Flow 2 3 increases w volume increase Recoil of lung increases w volume increase Airway resistance decreases w increase in volume Fig 21 12 B L Inspiration Flow Limitations PEFR effort dependent flow limitation Fig 21 13 B L Effects of Lung Disease on Airflow Measurements FIG 28 9 Asthma emphyse ma Asthma emphysema Fig 21 14 B L Compression of airways Pressure inside the airway Pressure outside the airway In Disease Greater resistive drop in pressure Equal pressure point is closer to alveoli in noncartilage airway Increase lung volume to offset airway resistance Airway resistance continues to increase crackles and rales on inspiration Transpulmonary Pressure PL PA Ppl 30 Transairway Pressure Pta PairwayPpl 30 1 Expiratory airflow resistance decreases 2 Gas velocity increases which decreases pressure Equal pressure point Negative Transairway pressure beyond this point Airway compression beyond this point Pta becomes negative
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