1 Respiratory system.. mechanics of breathing and PFTs….L2 Faisal I. Mohammed, MD, PhD Yanal A. Shafagoj MD, PhD University of Jordan

Mechanics of Breathing Airflow is governed by the basic flow equation, which relates flow to driving force (pressure) & airways resistance. Always remember Ohm’s law: Flow = pressure difference / resistance =  P/R 1. By positive Pressure Breathing: resuscitator: P at the nose or mouth is made higher than the alveolar pressure (P alv ). This is artificial type of breathing 2. By negative Pressure Breathing: P alv is made less than P atm. This is normal pattern of breathing It is the pressure difference between the two opposite ends of the airways: (P alv – P atm ) If R is large then  P must be large too to keep flow constant. Boyle’s law: The pressure and the volume of a gas are inversely related if the temperature is kept constant.

3 Inhalation Inhalation is active – Contraction of:  Diaphragm – most important muscle of inhalation Flattens, lowering dome when contracted Responsible for 75% of air entering lungs during normal quiet breathing  External intercostal muscles: Contraction elevates ribs 25% of air entering lungs during normal quiet breathing  Accessory muscles for deep, forceful inhalation When thorax expands, parietal and visceral pleurae adhere tightly due to subatmospheric pressure and surface tension – pulled along with expanding thorax As lung volume increases, alveolar (intrapulmonic) pressure drops University of Jordan

4 Exhalation/ expiration  Pressure in lungs greater than atmospheric pressure  Normally passive – muscle relax instead of contract Based on elastic recoil of chest wall and lungs from elastic fibers and surface tension of alveolar fluid Diaphragm relaxes and become dome shaped External intercostals relax and ribs drop down  Exhalation only active during forceful breathing University of Jordan

5 Inhalation/ inspiration  Pressure inside alveoli becomes lower than atmospheric pressure for air to flow into lungs 760 millimeters of mercury (mmHg) or 1 atmosphere (1 atm)  Achieved by increasing size of lungs Boyle’s Law – pressure of a gas in a closed container is inversely proportional to the volume of the container  Inhalation – lungs must expand, increasing lung volume, decreasing pressure below atmospheric pressure… the inflated lung drives air in, it is not the air which inflate the lung University of Jordan

6 Boyle’s Law University of Jordan

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Diaphragm is the main muscle of inspiration Dome-shaped

Inspiration

Expiration

12 University of Jordan

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Lung Diseases and Pulmonary function Tests Prevalence of lung disease depends on the population, but in general obstructive is 70%, restrictive is 20-25% and vascular is 5-10%

Pulmonary Pathology Obstructive Diseases  Increased resistance to flow Restrictive Diseases  Decreased expansion of the lungs

About Pulmonary Function Tests Spirometry provides an objective assessment of airflow obstruction and is important in staging asthma severity. It should be done on initial diagnosis of asthma, after treatment is started and symptoms have stabilized, and every 1 to 2 years afterward. Spirometry is used to measure the rate of airflow during maximal expiratory effort after maximal inhalation. It can be useful in differentiating between obstructive and restrictive lung disorders. In asthma (an obstructive lung disorder) the forced expiratory volume in 1 second (FEV1) is usually decreased, the forced vital capacity (FVC) is usually normal and the ratio FEV1/FVC is decreased. In restrictive disorders the FEV1 and FVC are both decreased, leaving a normal FEV1/FVC. Spirometry measurements are usually done before and after administration of a  2 agonists (salbutamol, dobutamine, albuterol, fenoterol, terbutaline).. Reversibility with the use of a bronchodilator is defined as an increase in FEV 1 of 12% or 200 ml. Patients with severe asthma may need a short course of oral steroid therapy before they demonstrate reversibility.

Terms Used to Describe Lung Volumes and Capacities

19 Lung volumes and capacities Minute ventilation (MV) = total volume of air inhaled and exhaled each minute Normal healthy adult averages 12 breaths per minute moving about 500 ml of air in and out of lungs (tidal volume) MV = 12 breaths/min x 500 ml/ breath = 6 liters/ min Alveolar ventilation = (tidal volume – dead space)* respiratory rate e.g Alveolar ventilation = ( )*12= 4.2 liters/min University of Jordan

20 Spirometer

Lung volumes and capacities Spirometer - measurement of lung volumes - measurement of the oxygen consumption

22 Spirogram of Lung Volumes and Capacities University of Jordan

23 Lung Volumes Only about 70% of tidal volume reaches respiratory zone Other 30% remains in conducting zone Anatomic (respiratory) dead space – conducting airways with air that does not undergo respiratory gas exchange Alveolar ventilation rate – volume of air per minute that actually reaches respiratory zone Inspiratory reserve volume – taking a very deep breath University of Jordan

24 Lung Volumes Expiratory reserve volume – inhale normally and exhale forcefully Residual volume – air remaining after expiratory reserve volume exhaled Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume Total lung capacity = vital capacity + residual volume University of Jordan

Minute and Alveolar Ventilation Minute ventilation: Total amount of air moved into and out of respiratory system per minute Respiratory rate or frequency RR: Number of breaths taken per minute Anatomic dead space: Part of respiratory system where gas exchange does not take place ≈ 150 ml in an adult (2 ml/kg)  Physiological dead space=ADS + alveolar wasted volume Alveolar ventilation: How much air per minute enters the parts of the respiratory system in which gas exchange takes place

The lungs, if alone, (outside the body) or in open-chest surgery, it will collapse up to 150 ml air = minimal volume. This volume is used for medico legal purposes…also known as unstressed volume

Lung Volumes End of normal inspiration End of normal expiration Volume Time TV IRV RV ERV

Lung Capacities Lung capacity is the sum of two or more lung volumes V T : Tidal Volume IRV: Inspiratory Reserve Volume ERV: Expiratory Reserve Volume RV: Residual Volume Volume Time TV IRV RV ERV

Lung Capacities: Inspiratory Capacity (IC) IC: the maximum amount of air that can be inspired following a normal expiration IC = V T + IRV Volume Time TV IRV RV ERV

Lung Capacities: Vital Capacity (VC) VC: the maximum amount of air that can be expired following a maximal inspiration VC = IRV + V T + ERV Volume Time TV IRV RV ERV

Lung Capacities: Functional Residual Capacity (FRC) FRC: the amount of air remaining in the lungs following a normal expiration. FRC = ERV + RV Volume Time TV IRV RV ERV

Lung Capacities: Total Lung Capacity (TLC) TLC: the amount of air in the lungs at the end of a maximal inspiration. TLC = IRV + V T + ERV + RV Volume Time TV IRV RV ERV

VAVA VTVT F I F E F A VDVD Expired air has alveolar and dead space air Copyright © 2011 by Saunders, an imprint of Elsevier Inc.

DEAD SPACE ANATOMICAL: Anatomical dead space is the volume of air that does not participate in gas exchange  150 ml (2 ml/Kg body weight) PHYSIOLOGICAL  Depends on ventilation-perfusion ratio  Physiologic Dead Space = Anatomic Dead Space + alveolar dead space

Anatomic Dead Space Low Blood Flow Physiologic Dead Space

Anatomic Dead Space Low Blood Flow Physiologic Dead Space Copyright © 2011 by Saunders, an imprint of Elsevier Inc.

Forced Expiratory Vital Capacity Figure 42-3

Chronic Obstructive Pulmonary Disease 60% - 79% predicted: MILD COPD 40% - 59% predicted: MODERATE COPD Less than 40% predicted: SEVERE COPD FEV 1 values (expressed as a percentage of predicted) may classify the severity of the COPD

ABG An arterial blood gas (ABG) is a blood test that is primarily performed using blood from an artery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery or other sites are used. The blood can also be drawn from an arterial catheter.

The test is used to determine the pH of the blood, the partial pressure of carbon dioxide and oxygen, and the bicarbonate level. Many blood gas analyzers will also report concentrations of lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxyhemoglobin.

Components of the Arterial Blood Gas The arterial blood gas provides the following values: pH Measurement of acidity or alkalinity, based on the hydrogen (H+) ions present. The normal range is 7.35 to 7.45 PaO2 The partial pressure of oxygen that is dissolved in arterial blood. The normal range is 80 to 100 mm Hg. SaO2 The arterial oxygen saturation. The normal range is 95% to 100%.

PaCO2 The amount of carbon dioxide dissolved in arterial blood. The normal range is 35 to 45 mm Hg. HCO3 The calculated value of the amount of bicarbonate in the bloodstream. The normal range is 22 to 26 mEq/liter B.E. The base excess indicates the amount of excess or insufficient level of bicarbonate in the system. The normal range is –2 to +2 mEq/liter. (A negative base excess indicates a base deficit in the blood.)

Control of Bronchiolar Diameter Nervous  Sympathetics  2 receptors dilate (salbutamol, dobutamine, albuterol, fenoterol, terbutaline).  Parasympathetics Acetylcholine constrict Humoral  Histamine, acetylcholine >> Constrict  Adrenergic (  agonists) >> Relax

44 Airflow Air pressure differences drive airflow 3 other factors affect rate of airflow and ease of pulmonary ventilation  Surface tension of alveolar fluid Causes alveoli to assume smallest possible diameter Accounts for 2/3 of lung elastic recoil Prevents collapse of alveoli at exhalation  Lung compliance High compliance means lungs and chest wall expand easily Related to elasticity and surface tension  Airway resistance Larger diameter airway has less resistance Regulated by diameter of bronchioles & smooth muscle tone University of Jordan

Surfactant Complex mixture of phospholipids, proteins, ions Produced by type II alveolar epithelial cells It reduces surface tension forces by forming a monomolecular layer between aqueous fluid lining alveoli and air, preventing a air/water interface Function  Reduces surface tension  Prevents alveolar collapse  Increases compliance  Reduces work of breathing  Other functions as well

46 However, the high surface tension and collapse of the alveoli is prevented by surfactant.

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Compliance Distensibility (stretchability):  Ease with which the lungs can expand. Change in lung volume per change in transpulmonary pressure. DV/DP 100 x more distensible than a balloon.  Compliance is reduced by factors that produce resistance to distension.

49 Thank You University of Jordan