Ventilatory Mechanics PDF

Batna University 2 Faculty of Medicine Department of Medicine Ventilatory mechanics Presentation Dr. B.Kermiche  Plan I. Introduction General Concepts and definitions II. Presentation of the Ventilation System 1. Passive system (parietal structures...

Batna University 2 Faculty of Medicine Department of Medicine Ventilatory mechanics Presentation Dr. B.Kermiche  Plan I. Introduction General Concepts and definitions II. Presentation of the Ventilation System 1. Passive system (parietal structures, pulmonary parenchyma and airways) 2. Active system (inspiratory and expiratory muscles) III. Metrological Data 1. Pressure Study - pleural - alveolar 2. Study of Deformations - Flow - Volume IV. Ventilatory cycle V. Mechanical Properties of the Respiratory System A. In static conditions: P=EV
Pulmonary Volumes 1- Mobilizable 2- Not mobilizable
Compliance Study 1 - Applied to the lung 2 - Applied to the thoracopulmonary system 3 - Origin of pulmonary elasticity + Histological Factor + Physicochemical factor
Concept of Surfactant - Law of LA PLACE B. In dynamic conditions + Resistances + The Flow Rates  I. Introduction General Breathing :corresponds to gas exchanges between the external environment and the organism (supply of O₂ to the tissues and rejection of CO₂, etc.) There are 4 steps: - pulmonary ventilation. - alveolar-capillary diffusion. - blood transport - cell diffusion Pulmonary ventilation: is an air flow that takes between atmospheric air and alveolar air. Role: renew the alveolar air to maintain its stable composition Pulmonary ventilation is a phenomenon cyclic, Inspiratory and expiratory  Concepts and definitions Ventilatory mechanics:Study of the forces which enable or which opposes the renewal of alveolar air. Its aim is to determine the physical properties of the thoraco-abdominal and pulmonary structures In static conditions: volumes +++ (absence of movement) In dynamic conditions: Flow rates +++ (resistances, flow rates, etc.) secondary to the forces (constraints) applied by the respiratory muscles
Constraint: it is a force applied per unit of surface expressed in terms of pressure ∆p: pressure difference measured on either side of a structure.
Deformation: in static conditions it is characterized by a variation in volume, in dynamic conditions it results in variation in flow rate and acceleration II. Presentation of the ventilation system 1. Passive system Figure: Airway branching 2. Active system  Inspiratory muscles:The diaphragm and external intercostal muscles Muscle activity during inspiration (Human Physiology SHERWOOD 2th2009 edition) Expiratory muscles:Internal and abdominal intercostals Muscle activity during expiration(Human Physiology SHERWOOD 2 2009 edition) th  III. Metrological Data 1. Pressure study: Pleural pressure: or intra-pleural always negative due to passive retractive tendencies lower than 4 mm H₂O at rest = 756 mm Hg. Alveolar pressure: variation induced by the contraction of the respiratory muscles and variation in the volume of the lung- thoracic cage. Atmospheric pressure: barometric or peri- thoracic external pressure = 760 mm Hg. Pressure gradient: Transpulmonary pressure: Pᴛᴘ= Palv - Ppl Transthoracic pressure: Ptt= Pрl - Patm Transthoracopulmonary pressure: Pttr= Palv- Patm 2. Study of deformations
Speed: according to Poiseuille's law: the flow rate is proportional to the ∆P = P₁- P₂ which exists on either side of a conduit And SO
volumes: - Mobilizable volumes + Vt: current volume + VRI: Inspiratory reserve volume + VRE:Expiratory reserve volume - Non-mobilizable volumes +VR: Residual volume + CRF: Functional residual capacity + CPT: Total lung capacity  IV. Ventilatory cycle Inspiratory phase  500ml, Tidal volume (Vc) Contraction of m. insp. (Diaphragm + Intercostal ext.) If forced inspiration: Scalenes, SCM, pectorals  Rib cage volume  Lung volume  intraalveolar pressure (palveolar< pATM) Air flow from the zones from htes p (env) to low zone p (lungs) Expiratory phase  passive phenomenon Relaxation of the inspiratory muscles Unless forced expiration: Abdominals, Intercostals Int Alveolar volume (lung elasticity)  intrapulmonary pressure(alveolar p > patm) Flow of air out of the lungs V. Mechanical properties of the respiratory system A. In static conditions: comparing the respiratory system to a bellows Pmus ΔV Pmus bellows Normal breathing Full breath Static, elastic Dynamic, E: elasticity of the respiratory system component resistive (rigidity of the respiratory system) component ΔV: inspiratory volume A: airway resistance -Pmus= E.ΔV + R. V᾿ V᾿: inspiratory flow At rest in a normal subject in the absence of respiratory movements, Newton's equation simplifies to Normal breathing Static, elastic component -Pmus= E.ΔV Only inspiration is active, expiration is passive thanks to the elastic factors of the respiratory system which then cause it to leave its equilibrium volume and which always tends to find this again, sheltered from any external force in the absence of contractions of the respiratory muscles.  Lung volumes Bell Spirometer  IRV VC TLC Vt ERV CRF RV Mobilizable and non-mobilizable static lung volumes  Lung volumes 1. mobilizable volumes: determined by spirometry or pneumotachography -Vᵼ:Tidal volume is the volume of air mobilized during a ventilation cycle ≈0.5l - IRV: inspiratory reserve volume (volume of air mobilized during a maximum inspiration after a calm inspiration ≈2500 ml). - ERV: expiratory reserve volume (volume of air mobilized after a forced expiratory breath following a calm expiration ≈1200ml). - VC: Vital capacity CV = VRI + Vᵼ + VRE (volume of air mobilized by a forced expiration following a forced inspiration ≈4200ml). 2. Volumes of non-mobilizable capacities: - RV: residual volume (volume of air remaining in the airways at the end of a forced expiration ≈ 1000 ml). - FRC: functional residual capacity (volume of air remaining in the lung after a quiet expiration VRE+VR). - TLC: total lung capacity (volume of air that the respiratory system can contain at the end of a forced inspiration ≈ 6000 ml)   Compliance Study
Compliance: it is the ease with which a structure (or system) can be stretched by a constraint applied to it. For an elastic system -At rest: L₀ -After applying a force F: length L₁ -∆L= L₁ - L₀ -Compliance = ∆ L/∆F For the lung -Compliance = distensibility -C = ∆V/∆P -C pulm =200ml/cmH₂O
Elastance= Retractability: resistance to distension - E = 1/C = ∆P /∆ V  A very distended lung will have its Compliance increased (Emphysema).  A slightly distended lung will have low Compliance (Fibrosis)  1. Compliance applied to the lung  Lung pressure/volume relationship -Let's make the lung communicate with the atmosphere, it retracts until it reaches its relaxation volume for which the transpulmonary pressure: Pᴛᴘ= Palv – Ppl=0 -In an anatomical situation, even at the end of forced expiration, the retraction pressure is not zero and the retraction volume is not reached. Cage thoracic (CT)   Thorax pressure/volume relationship -The relaxation volume of the thorax is high located ≈ 60% of the CV. - Beyond this point, the wall exerts a retraction pressure which goes in the same direction as that of the lung. - Below this volume the wall exerts a distension pressure and the thorax tends to fill. 2. Applied to the thoracopulmonary system  3. Origin of pulmonary elasticity Histological factors - Elastin and collagen fibers of the interstitium and bronchial tree - All the elastic elements of the lung (Vx, Bronchi, etc.). - The liquid content. The elastic forces of lung tissue represent ≈ 50%. Physiological factors - represented by the gas-liquid interface giving rise to a surface tension. Respiratory Physiology Course 2 AM  Surfactant T P At an air-liquid interface, the surface tensionTis the superficial force of contraction which tends to bring the alveolar walls closer together Collapse According to Laplace's law -P: distension pressure -r: radius of the sphere Without Surfactant: tensionTis identical in all small- caliber alveoli (r) - Therefore, Palv is higher in small-caliber alveoli (r) Air movement from small alveoli to large alveoli Collapse of small alveoli and distension of large alveoli Surfactant The surfactant lines the alveolar wall (air/liquid interface) Synthesized by pneumocytes II Surfactant - Decrease in alveolar surface tension, energy gain, favorable condition for the ventilatory muscles (inspiration) - The surfactantadapts surface tension to alveolar sizeso that the Palv is identical in all the alveoli whatever their caliber stabilization of the alveoli of different caliber (antiatelectatic role). Increases Compliance (C = ∆V/∆P). Action against alveolar flooding (barrier). Lubrication and mucus flow  Hyaline membranes (surfactant deficiency), poor Normal infant gas exchange (respiratory distress) r = 25 μ r = 50 μ T =25 dyn/cm T = 5 dyn/cm P = 2 x 25 / 25 P = 2 x 5 / 50 dyn/cm² dyn/cm² P = 2 cm H2O P = 20 cm H2O P=2xT/r B. In dynamic conditions  The resistances: Total pulmonary resistances Resistance of lung parenchyma: 20% VA resistance: 80% Rubbing of lung tissue VAS resistance: 50% VAI resistance:50% Trachea + large bronchi: 40% Small VAI:10% The bronchial tree in physiology   The flow rates Flow = ∆ P/R a. Average flow rates or volume/time relationship: -FEV1(maximum expiratory volume per second). -D25-75%(DEM), this is the time needed to exhale a fixed volume (25 to 75% of CV). - FEV1/VCsaid report oftiffeneau(if it is < 70% DVO) b. Instantaneous flow rates or flow/volume relationship By convention, during forced expiration, the flow rates at 75%, 50% and 25% of the CV are measured, as well as the maximum flow rate DEP (point flow rate).