By Dr. Nermine Mounir Lecturer of Chest Diseases Faculty of Medicine Ain shams University

 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, times / minute  VRG active in forced breathing  Pontine respiration centre: finetuning of breathing / inhibits DRG Marieb, Human Anatomy & Physiology, 7 th edition

 Starting 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  Increasing inspiration  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 P atm  In relaxed breathing, the difference between P atm 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 P atm 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

1. Diaphragm:  contraction draws air into lungs  75% of normal air movement 2. External intracostal muscles:  assist inhalation  25% of normal air movement 3. Accessory muscles assist in elevating ribs:  sternocleidomastoid  serratus anterior  pectoralis minor  scalene muscles

1. Internal intercostal and transversus thoracis muscles:  depress the ribs 2. Abdominal muscles:  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

 Illustrates maximum expiratory and inspiratory flow- volume curves  Useful to help characterize disease states (e.g. obstructive vs. restrictive) Ruppel GL. Manual of Pulmonary Function Testing, 8 th ed., Mosby 2003

Airway Function Tests  Spirometry  Flow – Volume Loop (FVL)

Variable extrathoracic Fixed Large airway obstruction

 Interpretation of % predicted:  %Normal  70-79%Mild reduction  50%-69%Moderate reduction  <50%Severe reduction

 Interpretation of % predicted:  >70Mild  60-69Moderate  50-59Moderately severe obstruction  35-49Severe  <35Very severe

 Interpretation of % predicted:  >60%Normal  40-60%Mild obstruction  20-40%Moderate obstruction  <10%Severe obstruction

 Limited Thoracic Expansion.  e.g. thoracic deformities (Kyphoscoliosis) and pleural fibrosis.  Limited Diaphragmatic Descent.  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  e.g. pneumonectomy, atelectasis.  Decreased Compliance.  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

Boyle ’ s Law If temperature is constant: Pressure 1 x Volume 1 = Pressure 2 x Volume 2 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 = cm/L/sec sRaw = cm/L/sec pred./best < 80%  Lung volumes  FRC and RV  % TLC  % RV/TLC%  20-35% VC  %

VolumeRestrictive Air trapping HyperinflationTLC↓N↑ VC↓↓N FRC↓↑↑ RV↓↑↑ RV/TLC%N↑↑