Lung Function_1

gas exchange metabolism of some compounds filtering of toxic substances reservoir for blood

Fick's Law of diffusionamount of gas that moves across a sheet of tissue is proportional to the area of the sheet, but inversely proportional to its thicknessLung area 50-100m2

Airway - Conducting airways - trachea- R & L main bronchi-lobar bronchi - segmental bronchi --- terminal bronchioles -  respiratory zone - respiratory bronchioles and alveolar ducts and alveoli lobule/acinus - portion of lung distal to terminal bronchiole

Air Movement by flow down to about terminal bronchioles by diffusion  in respiratory zone  ( CSA of airways vv large - velocity slows to almost 0) - rapid diffusion, short distances - equilibrate within 1 sec In consequence - dust particles fall out in terminal bronchiole diaphragmatic descension + intercostal lifting 500mL breath requires 3cm H2O, (balloon requires 30cm H20 for 500L)

Blood Vessels and Flow Arteries veins and bronchi run together until towards periphery, where arterioles and bronchi travel together in centre of acini, while venules travel between capillary diameter 10microm, just big enough for RBC capillary segments are so short they almost form continuous sheet Pulmonary artery pressure of 20cmH2O required for 6L/min flow each RBC spends around 3/4sec in capillary network - almost complete equilibration separate bronchial circulation supplies conducting airways, fraction of supply, transplanted lung functions adequately without it

ALVEOLAR STABILITYsurfactant lowers surface tension of alveolar lining layer

REMOVAL OF INHALED PARTICLES large particles - nose conducting airways - mucociliary elevator (mucus from goblet cells and mucous glands) alveoli - macrophages - then removed via lymphatics or bloodstream leukocytes also defend against foreign material

VOLUMESTidal Volume - 500mLAnatomical dead space 150mLAlveolar gas 3,000mLPulmonary Capillary blood 70mL

FLOWSTotal ventilation 7,500mL/minfrequency 15 breaths /minAlveolar ventilation 5,250mL/minPulmonary Blood flow 5,000mL/min

LUNG VOLUMESTotal lung capacityVital Capacity (TLC -residual volume)Tidal volumeFunctional residual capacityResidual volume

SPIROMETER  measuresVital capacitytidal volume

GAS DILUTION (Helium)used to calculate total volumemeasures only communicating airways

BODY PLETHYSMOGRAPHYuses Boyles law Pressure x volume is a constant at constant temperaturemeasures total volume of gas in lung, even that trapped behind closed airways

TOTAL VENTILATION = tidal volume x breaths per minuteALVEOLAR VENTILATION = total excludes anatomical deadspace  = volume of air available for gas exchangeboth measured at exhalationCan estimate dead space, or calculate from the fractional concentration of CO2

Lung Function and anatomy

Ventilation