PFT Part 1 By Dr Nermine Mounir Lecturer

PFT (Part 1) By Dr. Nermine Mounir Lecturer of Chest Diseases Faculty of Medicine Ain shams University

Respiratory system Neural generator pump Gas exchanger

Steps of respiration � Ventilation→ mass movement � Diffusion → exchange � Perfusion→ pulmonary blood flow � Blood gas transport→ carriage of gases � Transfer→ exchange � Cellular respiration→ intracellular metabolism

Respiratory Structures in Brainstem

Regulation of breathing � � � 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, 7 th edition

Rhythmic Ventilation � 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

Intrapulmonary Pressure � � � 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

Intrapleural Pressure � � 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 Transpulmonary pressure = Alveolar pressure* – Pleural pressure *With no air movement and an open upper airway, mouth pressure equals alveolar pressure

Pulmonary Pressures

� What is the cause of negativity of the intrapleural pressure ?

The Mechanics of Breathing � Inhalation: � always � active Exhalation: � active or passive

3 Muscle Groups of Inhalation 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 �

Muscles of Active Exhalation 1. Internal intercostal and transversus thoracis muscles: � 2. depress the ribs Abdominal muscles: compress the abdomen � force diaphragm upward �

� Boyle s law

Alveolar Pressure Changes

Inspiration Active process – requires ATP for muscles contraction

Expiration Passive process –muscles relax

Work of breathing � 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

Volumes Versus Capacities. � 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.

Spirometer and Lung Volumes/Capacities

Respiratory volumes

Significance of FRC � � Mechanical function Smoothing of blood gas fluctuations

Important parameters � � VC FEV 1/ FVC MMF

Factors affecting lung volumes � � � 1 - body size 2 - age 3 - sex 4 - muscular training 5 - diseases

Lung Factors Affecting Spirometry � � Mechanical properties Resistive elements

Mechanical Properties � 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

Resistive Properties � � Determined by airway caliber Affected by � Lung volume � Bronchial smooth muscles � Airway collapsibility

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

Breathing

Airway Function Tests � Spirometry � Flow – Volume Loop (FVL)

Variable extrathoracic Large airway obstruction Fixed

FVC � Interpretation of % predicted: � 80 -120% � 70 -79% � 50%-69% � <50% Normal Mild reduction Moderate reduction Severe reduction

FEV 1 � Interpretation of % predicted: � >70 � 60 -69 � 50 -59 � 35 -49 � <35 Mild Moderately severe obstruction Severe Very severe

FEF 25 -75 � Interpretation of % predicted: � >60% � 40 -60% � 20 -40% � <10% Normal Mild obstruction Moderate obstruction Severe obstruction

Extrapulmonary Factors Can Reduce Vital Capacity � 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).

Pulmonary Factors Can Reduce Vital Capacity � 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.

Volume-constant body plethysmograph

Functions of body box 1 -Allows complete analysis of breathing mechanics of the respiratory system→ Specific airway resistance(s. Raw) 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 �

Three types of measurments: � 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 s. Raw � 2+3 →Determine ITGV

Boyle’s Law If temperature is constant: Pressure 1 x Volume 1 = Pressure 2 x Volume 2 P 1 and V 1 are the absolute pressure and volume before the manoeuvre while P 2 and V 2 are the pressure and volume after the manoeuvre.

Body - Measurement

Calculated parameters � RV = FRCplet – ERV � TLC = VC + RV

Important resistance parameters s. Rtot → the points of max. volume shift on the loop. →high sensitivity down to the peripheral airways. s. Reff → derived from the area covered by the work of breathing. →high sensitivity within the central airways. Rtot= s. Rtot/(FRCplet +VT/2) Reff= s. Reff/(FRCplet +VT/2)

Interpretation � � � Shape of the graphs resistance Raw =0. 6 -2. 8 cm/L/sec s. Raw =0. 19 -0. 667 cm/L/sec pred. /best < 80% Lung volumes FRC and RV 65 -135% TLC 80 -120% RV/TLC% 20 -35% VC 80 -120%

Lung volumes Volume Restrictive Air trapping Hyperinflation TLC ↓ N ↑ VC ↓ ↓ N FRC ↓ ↑ ↑ RV/TLC% N ↑ ↑