1 / 55

Mechanics of respiration

Mechanics of respiration. By Dr. M.B.Bhat. Mechanics of Respiration. Ventilation –Breathing in & out of air from lungs Inspiration –Taking in of air –Active process Expiration –Given out of air –Passive process (normally) –Active process in forced expiration Normal respiration by

hoper
Download Presentation

Mechanics of respiration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mechanics of respiration By Dr. M.B.Bhat.

  2. Mechanics of Respiration • Ventilation –Breathing in & out of air from lungs • Inspiration –Taking in of air –Active process • Expiration –Given out of air –Passive process (normally) –Active process in forced expiration • Normal respiration by • Negative pressure breathing – • Advantage –increase venous return

  3. Normal Respiration • During inspiration – • By operation of respiratory pump (Muscle Force)—Thorax expand –along with Lungs also expand– • Decreases pressure in thoracic cavity • By over-coming resistance • Rushing of air from atmosphere through the respiratory tract into lungs • Till intra-pulmonary & atmospheric pressure equals

  4. During expiration – (cessation of inspiratory activity) By elastic recoiling – Thorax assumes its original position –Lungs get compressed – Thoracic cavity pressure rises – Air goes out (through the same routes) –till the air pressure between intra-pulmonary & atmospheric are equal Hence normal expiration is apassive process

  5. Mechanism of respiration • Involves 3 processes • Creation ofForce (for operation of respiratory pump) –by respiratory muscles • Pressure changes (in the thoracic cavities) • Resistance to over come (for air movements)

  6. Respiratory muscles –Inspiratory & Expiratory muscles • Inspiratory muscles – • Chief inspiratory muscles (operate during quite respiration) –Diaphragm & External inter-costal muscles • Expiratory muscles –(operate only during forceful expiration) –Internal inter-costal muscles; Abdominal muscles • Accessory respiratory muscles (operate only in forceful respiration) –Scaleni, Sternocledo-mastoid, Anterior Serati, Extensor muscles of vertebral columns

  7. Diaphragm –Chief inspiratory muscle

  8. Nerve supply –Phrenic nerve (C3,4&5) Contraction of diaphragm flatten it towards abdomen by 1.5cm (during quite respiration) & up to 7cm (during forceful respiration) Result –increase in vertical dimension of thoracic cavity Account for 75% change in intrathoracic volume during quite respiration (2/3rd of Tidal volume) Though important for respiration not absolute necessity

  9. External inter-costalmuscles • Origin –From the lower border of one rib to -- • Insertion— upper border of the rib below • Course –From origin pass obliquely forwards & downwards to the lower rib • Nerve supply –Nerve to inter-costal muscles (T1 to T12) • Contraction –leads to upward & forward movements of ribs

  10. Thoracic cavity • Thoracic lid –made up of 1st pair of ribs jointed between vertebral column & manubrium sterni –moves very little (in hyperpnea manubrium moves upwards –thereby increase antero-posterior diameter) • Upper costal area –2nd to 6th ribs –slope obliquely downward & forward from posterior to anterior • Lower costal area –7th to 10th ribs –swing outward & upwards

  11. As Thoracic lid is immovable – Contraction external inter-costal muscles pull the lower ribs causing upward & outward movements Upward movements push manubrium upwards –increase antero-posterior diameter –Pump-handle movement Outward movements –by virtue of the bowed mid-part of ribs –increase transversediameter –Bucket-handle movement

  12. By the contraction of diaphragm— Vertical dimension of thoracic cavity increases – to about 1.5cm during quite respiration & 7cm during forceful respiration By the action of inter-costal muscles & accessory muscles – Circumference of chest increases by – 1cm in quite respiration 5 to 11cm in forced respiration

  13. Expiration isa quiet passivemotion Cessation of inspiratory muscle activity – Due to elastic recoiling tendency of lungs & chest –expiration takes place For forceful expiration – Internal inter-costal muscles (arrangement of which is quiet opposite to external inter-costal muscles) draws the ribs inwards & downwards Abdominal muscles –increase intra abdominal pressure and abdominal contents push diaphragm upwards; & draws the lower ribs downwards & medially thereby decrease thoracic dimension

  14. Pressures of the thoracic cage • Two types of pressures • Intra-Pleural pressure (Or) Intra-Thoracic pressure (Pressure between two pleura) 2Intra-Alveolar pressure (Or) Intra-Pulmonary pressure (Pressure in the lungs –alveoli)

  15. Pressures in the thoracic cage

  16. Intra pleural pressure (or) Intra thoracic pressure – • Normal value—During quite respiration • At the beginning of inspiration= –3 cm H2O (–2mm Hg) • At the end of inspiration= –7.5 cm H2O (–6mmg) • Max. in forced inspiration = –20 mm Hg • Ma. In forced expiration = +40 mm Hg

  17. Measurement of intra pleural pressure • Direct-- • Indirect– Principle --pressure at lower 3rd of esophagus beneath the lungs is same as intra thoracic pressure –as esophagus also present in the thoracic cavity. • Procedure - Catheter tipped with a balloon is swallowed & kept at lower 3rd of esophagus and inflate & connect the catheter with manometer. • Reasons for negative pressure (explain)

  18. Significance of intra pleural pressure • Always negative (sub-atmospheric) in normal respiration • Prevents collapse of alveoli • Prevents collapse of small air ways • Aids in venous return (Respiratory pump) • In Pneumothorax it becomes equal to atmospheric pressure –alveoli collapse

  19. Intra alveolar pressure (or) Intra pulmonary pressure • At the beginning of inspiration & at the end of expiration –it is zero • During inspiration= minus 1to 4 mm Hg • During expiration – Plus 1to 4 mm Hg • During forced inspiration – minus 20 mm Hg • During forced expiration – plus 40 mm Hg • Measurement – “Mouth pressure”

  20. Trans-pulmonary pressure • Difference between intra thoracic pressure & intra pulmonary pressure • Pressure operating inner & outer wall of the alveoli • Measure the elastic forces in the lungs

  21. Resistances • Elastic resistance & • Non-elastic resistances –are; • Air-way resistance • Non-elastic tissue resistance

  22. Elastic resistance • Resistance due to elastic nature of lungs & thoracic cage • Reciprocal of elastic resistance is compliance

  23. Compliance • Compliance is the measure of stretch ability or elasticity • StaCompliance is change in volume by unit change in pressure (∆V/∆P) – L/cm H2O • Specific compliance –Compliance/FRC (in L per cm H2O per L)

  24. Types of compliances • As both lungs & thoracic cage has elastic nature –in the respiratory system the various compliances are; • Lung compliance (L.C) • Thoracic compliance (Th.C) • Total compliance (T.C) -- (both L.C & Th.C) • Compliance is measured in static condition

  25. Lung compliance • Volume of lung expansion for each unit increase in intra pleural pressure • Normal value –0.22L / cm H2O • (range – 0.09 to 0.26 / cm H2O) • In infant – 0.005 / cm H2O

  26. Factors affecting lung compliance • Size • Phases of Respiratory cycle – Deflation & Inflation • Gravity –less at apices • Factors Compliance -- • Emphysema & Old age • Factors Compliance -- • Pul. Congestion, Pul. edema & fibrosis --

  27. Total compliance • Normal value – 0.11L / Cm H2O • Measurement -- ∆V / ∆P (Airway pressure –Intra pulmonary Pressure)

  28. Thoracic compliance • Is due to Sterno-costal joints • Normal value – 0.22L / cm H2O • Cannot measure directly • Calculate by using the equation-

  29. Factors determining lung compliance • Elastic nature of pulmonary tissue (contribute 1/3rd) • Surface tension (contribute 2/3rd)

  30. Elastic nature of pulmonary tissue • Inter woven of elastin & collagen fibers like nylon stocking arrangement • In emphysema –degradation of elastin & collagen frame work –leads to increase distensiblity • In old age –change in physico-chemical properties of elastin & collagen –increase distensibility • In pul.fibrosis –increase in interstitial tissue –stiffness – distensibility

  31. Surface tension • Of pure water =70dynes/cm • Of Alveolar fluid without surfactant =50dynes/cm • Of Alveolar fluid with surfactant =5 dynes/cm • Laplace law – P = 2T/r

  32. Average size alveoli (100µm) – the collapsing pressure Or distending pressure (P)-- • with surfactant; P= 4cm H2O (3 mm Hg) • Without surfactant; P = 18cm H2O

  33. Surfactant • Surface tension lowering agent • Secreted from Type II cells • Contains – • Dipalmitoyl phosphatidyl choline (DPPC) (Dipalmitoyl lecithin) – 62% • Phosphatidly glycerol –5% • Other phospholipids –10% • Neutral lipids –13% • Protein – 8% • Carbohydrate – 2% • And calcium ions

  34. Mechanism of action of Surfactant • Surfactant consist of mainly of–Phospholipids • Phospholipids have hydrophilic (phosphate portion) & hydrophobic (lipid portion) ends • The hydrophilic end dissolves into the alveolar fluid; while the hydrophobic end facing the exterior. • As the hydrophobic portion (lipid) has attraction towards gas, the inward attraction of the molecules of the surface area can be minimized & thereby lowering the surface tension.

  35. Significance of surfactant • Surface tension (by 1/12th –1/2) • Compliance • Respiratory work load is • Helps in stability of alveoli of unequal size • Prevent collapse of alveoli during expiration • Prevent bursting of alveoli during inspiration • Keeps the alveoli dry (prevent pul. Congestion)

  36. Factors affecting surfactant • Factors surfactant – • Occlusion of main bronchus • Occlusion of pulmonary artery • Long-term inhalation of 100% O2 • Cutting of both vagi • Cigarette smoking Factors surfactant – • Thyroid hormone -- production • Glucocorticoids – accelerate maturation

  37. Clinical significance of surfactant • (Infant) Respiratory distress syndrome (IRDS) or • Hyaline membrane disease (due to deficiency of surfactant in fetal life)

  38. Pulmonary Resistance • Non-elastic tissue resistance (Viscous resistance) • Air-way resistance Resistance are measured during dynamic condition R = ∆P/ V (flow) in liter/sec

  39. Pulmonary resistance (Total resistance) • Air way resistance + viscous resistance • Obtained by using intra pleural pressure • 3.5cm H2O per liter per second

  40. Air way resistance • Due to friction between molecules of flowing gas & also with walls of the tube • Raw = (Pmouth – Palv) / V in L/sec • Normal value = 0.6 to 2.4 cm H2O per Liter per second • LFTs used in determine Raw are – • PEFR; MVV; FEV • Raw --Increases in obstructive type respiratory diseases

  41. Factors determining air way resistance Factors air wayresistance Decrease lung volume Decrease in diameter Total cross sectional area Increase in Density & viscosity Types of flow -- Dynamic compression of air ways

  42. Non-elastic tissue resistance • Resistance offered by the non-elastic tissue of the thoracic cavity –Lungs, rib-cage, diaphragm & abdominal content • Responsible for the Hysteresis (closed loop) type of pressure-volume relation of respiratory cycle • Account for 20% of total pulmonary resistance • Itis increased greatly in Emphysema

  43. Thoracic resistance • Pulmonary resistance (Airway resistance + viscous resistance) + chest wall resistance • Thoracic cage resistance –no measurement developed so far

  44. Work done of breathing • Work done = Pressure x volume • Normal value of total work done = 0.3 to 0.8 kg m/min • Elastic work –65% • Non-elastic work –35%; out of this • Airway resistance work –28% • Viscous resistance work (Inertia work)–7% • Work of breathing increases in – • Emphysema, asthma, congestive cardiac failure with dyspnea & orthopnea

More Related