PULMONARY MECHANICS GAS TRANSPORT I. PULMONARY MECHANICS • RESPIRATORY MUSCLES • LUNGS ELASTICITY • COMPLIANCE • WORK OF BREATHING II. TRANSPORT OF GASES • O2 • CO2 FORCES PARTICIPATING IN RESPIRATION 1 QUIET RESPIRATION EXPIRATION - passive (elastic) forces only INSPIRATION - active forces of inspiratory muscles prevail PASSIVE FORCES represented by: ACTIVE FORCES performed by respiratory muscles lungs elasticity chest elasticity I. PULMONARY MECHANICS • RESPIRATORY MUSCLES • LUNGS ELASTICITY • COMPLIANCE • WORK OF BREATHING II. TRANSPORT OF GASES • O2 • CO2 obr 2a cut RESPIRATORY MUSCLES accessory muscles external intercostals diaphragm internal intercostals abdominal muscles EXPIRATORY INSPIRATORY 2a INSPIRATORY muscles QUIET breathing diaphragm (≥ 80 % ) external intercostals (≤ 20 % ) accessory inspiratory muscles (scalene muscles, …) FORCED breathing 2b EXPIRATORY muscles internal intercostals muscles of the anterior abdominal wall (abdominal recti, …) Only at FORCED breathing I. PULMONARY MECHANICS • RESPIRATORY MUSCLES • LUNGS ELASTICITY • COMPLIANCE • WORK OF BREATHING II. TRANSPORT OF GASES • O2 • CO2 1 kPa = 7.5 mm Hg LUNGS ELASTICITY 3 obr 3 přech 200 150 100 50 0 0.4 INTRAPULMONARY PRESSURE (kPa) 0.8 1.2 1.6 2.0 HYSTERESIS LOOP INFLATION DEFLATION opening pressure AIR LUNGS ELASTICITY INHERENT TISSUE ELASTICITY (elastin and collagen fibres) SURFACE TENSION FORCES (physical properties of air-liquid interface) SALINE 4 P distending pressure (transmural DP) r radius T surface tension LAW OF LAPLACE spherical structures BULLOUS EMPHYSEMA EXPANSION OF ALVEOLI P1 > P2 P1 P2 COLLAPSE OF ALVEOLI P r T r T P 2 = ATELECTASIS ? PATHOLOGY INFANT RESPIRATORY DISTRESS SYNDROME 5a PATCHY ATELECTASIS AFTER CARDIAC SURGERY SURFACTANT SURFACE TENSION LOWERING AGENT obr 5 přech ALVEOLAR EPITHELIAL CELLS macrofage fatty acids, choline, glycerol, amino acids, etc.) surfactant surfactant cycle exocytosis of lamellar bodies PHOSPHOLIPID dipalmitoyl fosfatidyl cholin TYPE II specialized granular epithelial cells PRODUCTION OF SURFACTANT EFFECT MAINLY IN THE EXPIRED POSITION TYPE I thin epithelial cells DIFFUSION OF GASSES 200 150 100 50 0 0.4 ALVEOLAR PRESSURE (kPa) 0.8 1.2 1.6 2.0 HYSTERESIS LOOP INFLATION DEFLATION opening pressure AIR SALINE Factors involved in HYSTERESIS LOOP 5b LAPLACE LAW (opening pressure of alveoli) Dynamic changes in the DENSITY OF SURFACTANT MOLECULES during inspiration and expiration I. PULMONARY MECHANICS • RESPIRATORY MUSCLES • LUNGS ELASTICITY • COMPLIANCE • WORK OF BREATHING II. TRANSPORT OF GASES • O2 • CO2 obr 6 přech b cut COMPLIANCE (VOLUME STRETCHABILITY) alveolar pressure DPA (mm Hg) 0 100 50 150 200 -50 -100 0 +1 -1 +2 +3 -2 VC RV FRC relaxation volume 18 relaxation pressure curve STATIC MEASUREMENT IN CLOSED SYSTEM V P DP DV compliance is increased ¯ stiffness of the tissue compliance is decreased stiffness of the tissue P V C D D = end of quiet expiration Valsalva´s maneuver Müller´s maneuver TOTAL RESPIRATORY SYSTEM (lungs and chest) I. PULMONARY MECHANICS • RESPIRATORY MUSCLES • LUNGS ELASTICITY • COMPLIANCE • WORK OF BREATHING II. TRANSPORT OF GASES • O2 • CO2 obr 7 přech cut ELASTIC (STATIC) WORK CLOSED SYSTEM 0 0 -15 pressure ΔP (mm Hg) 1 2 +15 PPL PA PTP 7 TV 500 ml elastic force of the chest is zero (PA-PPL) relaxation pressure curve CHEST relaxation pressure curve LUNGS expiratory reserve volume ? elastic forces of the chest and lungs act in the same direction relaxation pressure curve TOTAL SYSTEM WELAST (J) TOTAL SYSTEM intrapulmonary pressure PA LUNGS transpulmonary pressure PTP = PA - PPL CHEST intrapleural pressure PPL elastic forces of the chest and lungs are in equilibrium WTOTAL ELASTIC insp = WLUNG + (-WCHEST) STRETCHING against elastic forces of the lungs ELASTIC RECOIL of the chest 8a TOTAL ELASTIC (STATIC) WORK OF INSPIRATORY MUSCLES AT QUIET INSPIRATION (V ~ 500 ml) ELASTIC FORCES OF THE CHEST HELP inspiratory muscles to increase thoracic cavity ACTIVE AND PASSIVE (ELASTIC) FORCES IN RESPIRATORY SYSTEM PA Felast-lungs PPL STATES OF BALANCE RESPIRATORY SYSTEM (LUNGS and CHEST) RESPIRATORY SYSTEM: elastic forces of lungs and chest are balanced 8b VT VT tidal volume at quiet inspiration (~500 ml) Fmuscle INSPIRATION CHEST CHEST: elastic force of the chest alone is zero at ΔV~ 1 l LUNGS LUNGS: elastic force of the lungs is zero only when PPL = PATM ( pneumothorax ) 0 0 PATM air ways Felast-chest ELASTIC (STATIC) WORK to overcome the elastic forces of the lungs and chest DYNAMIC WORK to overcome the resistance of air passages during the air movement – AERODYNAMIC RESISTANCE (~ 28%) to overcome the friction during the mutual movement of inelastic tissues – VISCOUS RESISTANCE (~ 7%) 9a (total work of respiratory muscles) TOTAL WORK OF BREATHING (65%) (35%) RESISTANCE OF AIR PASSAGES HAGEN-POISEUILLE´S LAW (laminar flow Q) 9b LAMINAR FLOW TURBULENT FLOW REYNOLDS NUMBER Re < 2000 < Re Ohm´s law l … length r … radius η … viscosity r … radius v … velocity ρ … density η … viscosity Critical velocity TOTAL WORK OF RESPIRATORY MUSCLES [J] DURING RESPIRATORY CYCLE AT QUIET BREATHING 1.5 3.0 WDYN is finally transformed into heat energy (loss of energy) WDYN WDYN = WDYN insp + WDYN expir WINSPIR = WELAST + WDYN insp ±WELAST WEXPIR = -WELAST + WDYN expir change in pressure ΔP (mm Hg) WINSPIR = WELAST + WDYN insp WEXPIR = -WELAST +WDYN expir 0 500 DYNAMIC WORK WDYN is done to overcome aerodynamic resistance frictional (viscose) resistance 10 DYNAMIC PRESSURE-VOLUME DIAGRAM 1 kPa = 7.5 mm Hg obr 11 a cut 0 1 0.5 change in pressure (kPa) 0.6 0.4 0.2 I E 11 NORMAL LUNGS elastic work INCREASED RESISTANCE OF AIR PASSAGES OBSTRUCTIVE LUNG DISEASE (asthma bronchial) changes in pressure (kPa) 1 0 0.6 0.4 0.2 additional work of expiratory muscles I E CLINICAL IMPLICATION Expiratory muscles are active to overcome the resistance of air passages I. PULMONARY MECHANICS • RESPIRATORY MUSCLES • LUNGS ELASTICITY • COMPLIANCE • WORK OF BREATHING II. TRANSPORT OF GASES • O2 • CO2 obr 17 přech b cut obr 17 přech a cut HAEMOGLOBIN α α β β 1 nm Fe Fe N N N N N N N N DEOXY OXY N N N polypeptide chain polypeptide chain O2 Fe3+ (methaemoglobin) oxidation Hb4 + 4 O2 ↔ Hb4O8 oxygenation 12 fetal Hb γ γ Fe2+ tetramer porfyrin O2–HAEMOGLOBIN DISSOCIATION CURVE 100 50 PO2 (mm Hg) deoxyHb- + H+→ H-Hb CO Hb 13 myoglobin fetal Hb BOHR EFFECT (↓pH, ↑CO2) 50 0 50 100 0 plateau area steep portion pH, CO2 ↑BPG (2,3-bisphosphoglycerate) ↑temperature physically dissolved O2 (1.4%) methaemoglobin physiological range v a P50 PCO (mm Hg) I. PULMONARY MECHANICS • RESPIRATORY MUSCLES • LUNGS ELASTICITY • COMPLIANCE • WORK OF BREATHING II. TRANSPORT OF GASES • O2 • CO2 obr 19 přech cut TRANSPORT OF CO2 HAMBURGER CHLORIDE SHIFT H2 CO3 CO2 + H2O CA CA – carbonic anhydrase H2O 14 HCO3- H+ + H+ + deoxyHb- H-deoxyHb Cl- HCO3- Cl- CO2 obr 20 přech b cut obr 20 přech a cut HbO2 CO2 O2 15 CO2 CO2 CO2 physically dissolved (~5.3%) CO2 O2 H2O Cl- HCO3- NaHCO3 Na+ K+ KHCO3 CO2+ H2O HCO3- + H+ CO2 + H 2O HCO3- + H+ (~89.3%) Hb.CO2 CO2 + Hb-NH2 Hb.NH-COO- (carbamino-Hb) (~5.3%) ~60% in plasma, ~29% in red blood cell obr 21 přech copy HALDANE EFFECT CO2 DISSOCIATION CURVE deoxygenated blood 5 10 15 20 25 30 10 20 30 40 50 60 70 PCO2 (mm Hg) physically dissolved CO2 a v oxygenated blood 16 deoxygenated blood in peripheral tissues oxygenated blood in the lungs CO2 + H2O H2CO3 H+ + HCO3- Hb- + H+ HHb TISSUES: DEOXY-Hb binds H+ more readily (weaker acid) Þ ↑ amount of chemically bound CO2 ? physiological values in arterial and venous blood Hb.NH.COO- 1 Hb- + H+ HHb 2 LUNGS: H+ is released from OXY-Hb Þ ↓ amount of chemically bound CO2 DEOXY-Hb PROCESSES UNDERLYING TRANSPORT O2 AND CO2 FACILITATE EACH OTHER 17 BOHR´s AND HALDANE´s EFFECTS uptake of CO2 by blood release of O2 from Hb TISSUES binding of O2 to Hb release of CO2 from blood LUNGS OCCUR SIMULTANEOUSLY IN RED BLOOD CELLS END