Respiratory system Points * Ventilation * Diffusion * Perfusion Function * The main role of the respiratory system is to work closely with the heart and blood to extract oxygen from the external environment and dispose of waste gases, principally carbon dioxide. * This requires the lungs to function as an efficient bellows, expelling used air, bringing fresh air in and mixing it efficiently with the air remaining in the lungs. * The lungs have to provide a large surface area for gas exchange and the alveoli walls have to present minimal resistance to gas diffusion. This means the lungs have to present a large area to the environment and this can be damaged by dusts, gases and infective agents. * Host defence is therefore a key priority for the lung and is achieved by a combination of structural and immunological defences. Of the first seven divisions, the bronchi have: * * walls consisting of cartilage and smooth muscle * epithelial lining with cilia and goblet cells * submucosal mucus-secreting glands * endocrine cells - Kulchitsky or APUD (amine precursor and uptake decarboxylation) containing 5-hydroxytryptamine * In the next 16-18 divisions the bronchioles have: * no cartilage and a muscular layer that progressively becomes thinner * a single layer of ciliated cells but very few goblet cells * granulated Clara cells that produce a surfactant-like substance. * The ciliated epithelium S25798-14-f02 S25798-14-f03 S25798-14-f04 Breathing * Lung ventilation can be considered in two parts: * the mechanical process of inspiration and expiration * the control of respiration to a level appropriate for the metabolic needs. * S25798-14-f07 Airway resistance * From the trachea to the periphery, the airways become smaller in size (although greater in number). The cross-sectional area available for airflow increases as the total number of airways increases. The flow of air is greatest in the trachea and slows progressively towards the periphery (as the velocity of airflow depends on the ratio of flow to cross-sectional area). In the terminal airways, gas flow occurs solely by diffusion. * The resistance to airflow is very low (0.1-0.2 kPa/L in a normal tracheobronchial tree), steadily increasing from the small to the large airways. Airways expand as lung volume is increased, and at full inspiration (total lung capacity, TLC) they are 30-40% larger in calibre than at full expiration (residual volume, RV). In chronic obstructive pulmonary disease (COPD) the small airways are narrowed and this can be partially compensated by breathing at a larger lung volume. Control of airway tone * This is under the control of the autonomic nervous system. Bronchomotor tone is maintained by vagal efferent nerves. Many adrenoceptors on the surface of bronchial muscles respond to circulating catecholamines; sympathetic nerves do not directly innervate them. * Airway tone shows a circadian rhythm, which is greatest at 04.00 and lowest in the mid-afternoon. Tone can be increased briefly by inhaled stimuli acting on epithelial nerve endings, which trigger reflex bronchoconstriction via the vagus. These stimuli include cigarette smoke, inert dust and cold air; airway responsiveness to these increases following respiratory tract infections even in healthy subjects. In asthma, the airways are very irritable and as the circadian rhythm remains the same, asthmatic symptoms are usually worst in the early morning. S25798-14-f08 Static spirometry * parameters independent on time Lung Volume Measurements * Measured by dilutional techniques (helium dilution or nitrogen washout) or by displacement techniques in a body box * The FRC is measured and then the other measurements are determined: * TLC = inspiratory capacity + FRC * RV= FRC – ERV (expiratory reserve volume) Dynamic spirometry • –Forced Vital Capacity – FVC –Forced Expiratory Volume in One Second - FEV1 –Peak respiratory flow - PEF –Forced Expiratory Volume in One Second Expressed as a Percentage of the Forced Vital Capacity - FEV1/FVC % –- Mean Forced Expiratory Flow during the Middle Half of the Forced Vital Capacity –FEF 25-75% Ventilatory dysfunction * Obstructive: airways collaps during exspiration, air-trapping phenomenon • * Restrictive: difficulties in inspiration, lung tissue scarring, infiltration or weak muscles, lung volumes decrease * * Combined Lung Volume Patterns * Obstructive Disease: Characterized by hyperinflation and gas trapping (decreased PEF, FEV1/FVC, increased TLC and RV/TLC) * Restrictive Disease: Characterized by generalized reduction in lung volume (decreased TLC, RV and FRC) Types of spirometers f3p8 Mild Obstruction Flow Volume Mild Obstruction Volume Time Curve Graphs Volume-time Flow-volume Expiration Inspiration FEV1 Flow-volume loops * The relationship between maximal flow rates on expiration and inspiration is demonstrated by the maximal flow-volume (MFV) loops. * In subjects with healthy lungs the clinical importance of flow limitation will not be apparent, since maximal flow rates are rarely achieved even during vigorous exercise. * In patients with severe COPD, limitation of expiratory flow occurs even during tidal breathing at rest.To increase ventilation these patients have to breathe at higher lung volumes and also allow more time for expiration by increasing flow rates during inspiration, where there is relatively less flow limitation. Thus patients with severe airflow limitation have a prolonged expiratory phase to their respiration. Flow-volume graphs Normal Restrictive Obstructive S25798-14-f09 FVC • Note changes in lung volume and ê in flow in COPD and é relative flow in restrictive disease fv_NOR Severe Obstruction Flow Volume Severe obstruction Flow-volume loops * The measure of the volume that can be forced in from RV in 1 second (FIV1) will always be greater than that which can be forced out from TLC in 1 second (FEV1). Thus, the ratio of FEV1 to FIV1 is below 1. * The only exception to this occurs when there is significant obstruction to the airways outside the thorax, such as with a tumour mass in the upper part of the trachea. Under these circumstances expiratory airway narrowing is prevented by the tracheal resistance (a situation similar to pursing the lips) and expiratory airflow becomes more effort-dependent. During forced inspiration this same resistance causes such negative intraluminal pressure that the trachea is compressed by the surrounding atmospheric pressure. Inspiratory flow thus becomes less effort-dependent, and the ratio of FEV1 to FIV1 becomes greater than 1. This phenomenon, and the characteristic flow-volume loop, is used to diagnose extrathoracic airways obstruction. When obstruction occurs in large airways within the thorax (lower end of trachea and main bronchi), expiratory flow is impaired more than inspiratory flow but a characteristic plateau to expiratory flow is seen. Pk flo 1 Pk Flo 2 Unacceptable Curves Delayed expiration Suboptimal initial blow Unacceptable curves * Cough Pk Flo 3 Pk Flo 5 Pk flo 4 * Premature termination –(volume-time curve shown) * * Variable effort flowvol1 Scale effort Obstructive and restrictive diseases obstructive bronchial asthma (alergic, non-alergic), chron. bronchitis, emphysema, COPD restrictive idiopatic pulmonary fibrosis, sarcoidosis, professional intersticial diseases, pleural diseases, pneumothorax, scoliosis, neuromuscular disorders, pneumonia Scales of obstruction Scales of restrictive disorders 22 –year-old patient * Pre-bronchodilator * FVC 4.0(80%) * FEV1 2.0 (66%) * FEV1/FVC 50% * MVV 70L (665) * Post-bronchodilator * FVC 4.2 * FEV1 3.0 (100%) * FEV1/FVC 73% * MVV 105 L Arterial Blood Gases * Measurement of pH, pCO2 and pO2 on room air is often done along with spiro, lung volumes and diffusing capacity to help characterize the severity of disease Ventilation-perfusion * For efficient gas exchange it is important that there is a match between ventilation of the alveoli ([Vdot]A) and their perfusion ([Qdot]). * There is a wide variation in the [Vdot]A/[Qdot] ratio throughout both normal and diseased lung. In the normal lung the extreme relationships between alveolar ventilation and perfusion are: * ventilation with reduced perfusion (physiological deadspace) * perfusion with reduced ventilation (physiological shunting). * In normal lungs there is a tendency for ventilation not to be matched by perfusion towards the apices, with the reverse occurring at the bases. http://studentblogs.med.ed.ac.uk/2014-ssc2a-d9/wp-content/uploads/sites/39/2014/11/Untitled-1.png Physiological shunt and dead space http://www.meddean.luc.edu/lumen/MedEd/medicine/pulmonar/IMAGES/phys/physi15.jpg http://intranet.tdmu.edu.ua/data/kafedra/internal/normal_phiz/classes_stud/en/nurse/Bacchaour%20of% 20sciences%20in%20nurses/ADN/13_Ventilation_of_lungs.files/image026.jpg Shunt and dead space S25798-14-f23 Pathological features of chronic bronchitis and emphysema. Respiratory insufficiency * Partial –Isolated hypoxia (the saturation of Hb may be lower, than in global insufficiency) –When only a part of lung is affected, the hypercapnia may be compensated by unaffected alveoli (this results from CO2 dissociation curve) –On the other hand, the saturation by O2 in a blod flowing out of healthy alveoli is almost 100% (97-99%), the hypoxia in one pulmonary segment can‘t be compensated by another * Global –Hypoxia with hypercapnia –When whole respiretory system is affected, both O2 and CO2 exchange is affected http://flylib.com/books/3/98/1/html/2/007_files/da1db2c7ff7.png Chronic obstructive pulmonary disease * Pink puffers –emphysema predominance –collapse of bronchioli and alveolar septa –↑ dead space –respiratory insufficiency occur only in late stages, but high respiratory effort to overcome the dead space is necessary –α1-antitrypsin deficiency (hereditary or acquired - smoking) * Blue bloaters –chronic bronchitis predominance –obstruction of bronchioli –↑ shunt –partial, later global respiratory insufficiency –hypercapnia occur only in later stages – respiratory effort does not occur –severe hypoxia– increased deoxyHb –mostly smokers pink puffers vs. blue bloaters