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By Dr. Nermine Mounir Lecturer of Chest Diseases Faculty of Medicine Ain shams University Respiratory system Neural generator pump Gas exchanger Ventilation→ mass movement Diffusion → exchange Perfusion→ pulmonary blood flow Blood gas transport→ carriage of gases Transfer→ exchange Cellular respiration→ intracellular metabolism DRG stimulates inspiratory muscles, 12-15 times / minute VRG active in forced breathing Pontine respiration centre: finetuning of breathing / inhibits DRG Marieb, Human Anatomy & Physiology, 7th edition Starting inspiration Increasing inspiration Medullary respiratory center neurons are continuously active Center receives stimulation from receptors and simulation from parts of brain concerned with voluntary respiratory movements and emotion Combined input from all sources causes action potentials to stimulate respiratory muscles More and more neurons are activated Stopping inspiration Neurons stimulating also responsible for stopping inspiration and receive input from pontine group and stretch receptors in lungs. Inhibitory neurons activated and relaxation of respiratory muscles results in expiration. Atmospheric pressure Intra-alveolar (intrapulmonary) pressure Intra-pleural pressure Transmural pressure→ across lung wall(transpulmonary pr.)& across thoracic wall Also called intra-alveolar pressure Is relative to Patm In relaxed breathing, the difference between Patm and intrapulmonary pressure is small: about —1 mm Hg on inhalation or +1 mm Hg on expiration Pressure in space between parietal and visceral pleura Averages —4 mm Hg Maximum of —18 mm Hg Remains below Patm throughout respiratory cycle Transpulmonary pressure = Alveolar pressure* – Pleural pressure *With no air movement and an open upper airway, mouth pressure equals alveolar pressure What is the cause of negativity of the intrapleural pressure ? Inhalation: always active Exhalation: active or passive Diaphragm: 1. contraction draws air into lungs 75% of normal air movement External intracostal muscles: 2. assist inhalation 25% of normal air movement Accessory muscles assist in elevating ribs: 3. sternocleidomastoid serratus anterior pectoralis minor scalene muscles Internal intercostal and transversus thoracis muscles: 1. depress the ribs Abdominal muscles: 2. compress the abdomen force diaphragm upward Boyle s law Active process – requires ATP for muscles contraction Passive process –muscles relax Work to overcome the elastic forces of the lung Work to overcome the viscosity of the lung and the chest wall structures. Work to overcome airway resistance. Normal respiration uses 3-5% of total work energy Heavy exercise can require 50 x more energy There are four volume subdivisions which: do not overlap. can not be further divided. when added together equal total lung capacity. Lung capacities are subdivisions of total volume that include two or more of the 4 basic lung volumes. Respiratory volumes Mechanical function Smoothing of blood gas fluctuations VC FEV1 FEV1/ FVC MMF 1- body size 2- age 3- sex 4- muscular training 5- diseases Mechanical properties Resistive elements Compliance Describes the stiffness of the lungs Change in volume over the change in pressure Elastic recoil The tendency of the lung to return to it’s resting state A lung that is fully stretched has more elastic recoil and thus larger maximal flows Determined by airway caliber Affected by Lung volume Bronchial smooth muscles Airway collapsibility Ruppel GL. Manual of Pulmonary Function Testing, 8th ed., Mosby 2003 Illustrates maximum expiratory and inspiratory flowvolume curves Useful to help characterize disease states (e.g. obstructive vs. restrictive) Spirometry Flow – Volume Loop (FVL) Variable extrathoracic Large airway obstruction Fixed Interpretation of % predicted: 80-120% 70-79% 50%-69% <50% Normal Mild reduction Moderate reduction Severe reduction Interpretation of % predicted: >70 60-69 50-59 35-49 <35 Mild Moderate Moderately severe obstruction Severe Very severe Interpretation of % predicted: >60% 40-60% 20-40% <10% Normal Mild obstruction Moderate obstruction Severe obstruction Limited Thoracic Expansion. Limited Diaphragmatic Descent. e.g. thoracic deformities (Kyphoscoliosis) and pleural fibrosis. e.g. ascites and pregnancy. Nerve or Muscle Dysfunction. Pain (surgery, rib fracture) Primary neuromuscular disease (e.g. Guillain-Barré Syndrome). Loss of Distensible Tissue Decreased Compliance. e.g. pneumonectomy, atelectasis. e.g. respiratory distress syndrome, alveolar edema, or infiltrative interstitial lung diseases. Increased Residual Volume. e.g. emphysema, asthma, or lung cysts. 1-Allows complete analysis of breathing mechanics of the respiratory system→ Specific airway resistance(sRaw) Intrathoracic gas volume (FRCpleth) Both →Airway resistance (Raw) 2-In combination with spirometry → Absolute volumes →RV-TLC Partial volumes → ERV-IRV Lung capacities → VC-IC 1- Insp. and exp. flow rate during the breathing cycle. 2-Air volume changes inside the cabinet 3 – Changes in air pressure at the subject mouth 1+2 →Determine sRaw 2+3 →Determine ITGV If temperature is constant: Pressure1 x Volume1 = Pressure2 x Volume2 P1 and V1 are the absolute pressure and volume before the manoeuvre while P2 and V2 are the pressure and volume after the manoeuvre. RV = FRCplet – ERV TLC = VC + RV sRtot → the points of max. volume shift on the loop. →high sensitivity down to the peripheral airways. sReff → derived from the area covered by the work of breathing. →high sensitivity within the central airways. Rtot= sRtot/(FRCplet +VT/2) Reff= sReff/(FRCplet +VT/2) Shape of the graphs resistance Raw =0.6-2.8 cm/L/sec sRaw =0.19-0.667 cm/L/sec pred./best < 80% Lung volumes FRC and RV65-135% TLC 80-120% RV/TLC% 20-35% VC 80-120% Volume Restrictive Air trapping Hyperinflation TLC ↓ N ↑ VC ↓ ↓ N FRC ↓ ↑ ↑ RV ↓ ↑ ↑ RV/TLC% N ↑ ↑
