Airway flow

In another accidental exposure of five chlorine plant workers and 13 nonworkers, rales, dyspnea, and cyanosis were observed in the most heavily exposed and cough was present in nearly all the patients. Pulmonary function tests 24—48 hours after exposure showed airway obstruction and hypoxemia these conditions cleared within 3 months except in four of the chlorine workers, who still showed reduced airway flow and mild hypoxemia after 12-14 months. ... 

Peak expiratory flow (PEF) - to support spirometry in monitoring changes in airway flow as a result of infection/inflammation (however use for COPD not supported by British Thoracic Society guidelines). 

Topical anesthesia of the airways is commonly used to facilitate endoscopy and sometimes manipulation of the airways. This can result in an increase in airway flow resistance, possibly due to laryngeal dysfunction (21). Lidocaine spray 10%, used for upper airways anesthesia for fiberoptic intubation in a grossly obese patient, caused acute airway obstruction. The patient went on to have a percutaneous tracheotomy, and it was postulated that the local anesthetic had abolished laryngeal receptors responsible for airway maintenance, or that laryngospasm and reduced muscle tone due to the lidocaine might have been the cause (SEDA-22,140). 

Pressure for airway flow resistance, Peak flow rate x R (cm H2O)... 

As a part of the sustainable pressure must be used to overcome normal airway flow resistance and elastic recoil of lung and chest, the amount of pressure (Pa) allowed to be used to overcome abnormal airway blockage, such as plastic film blockage, is smaller and can be found by... 

In utero exposure to maternal smoking was associated with reduced peak expiratory flow rate, mean mid-expiratory flow, and forced expiratory flow, but not FEVi. In utero exposure to maternal smoking was found to be independently associated with decreased lung function in children of school age, especially for small airway flow rates [274(IIa)]. 

AIRWAY FLOW, DYNAMICS, AND STABILITY 4.11 REFERENCES 4.12 BIBUOGRAPHY 4.14... 

Airways flow has a boundary condition of diffusion only at the terminal level within the alveolar sacs. While air is moved in and out in the upper respiratory system, diffusion is die means by which material is shifted near the lung-blood interfaces. A flow model of the lower respiratory system should be such that air does not physically move in and out of the alveolar sacs. 

Fig. 3 Schematic diagrams of the different types of plethysmographs. (a) Headout with volume displacement, (b) head-out with constant volimie, (c) whole body, (d) Pennock -style dualchamber plethysmograph to measure both airway flow and thoracic volume changes...

Three anatomic patterns of TBA exist, each with distinct pulmonary function test characteristics (i) proximal trachea, ii) mainstem bronchi, and (Hi) distal airways. Proximal disease limits expiratory airflows, producing flow-volume loop changes consistent with extrathoracic upper airway obstruction. Mainstem bronchial disease affects large airways flow, decreasing FEVl/FWC ratio. In contrast, distal airway involvement results in decreased small airway or FEF 25 to 75 flows (56). Bronchoscopically, TBA appears as submucosal plaques or diffuse infiltration in 44% cases, nodular disease in 28%, and circumferential lesions in 28% (58). 

Experimental methods for determining the potential of materials to produce hypersensitivity reactions by inhalation use procedures to detect hyperreactivity of the airways as demonstrated by marked changes in resistance to air flow, and the detection of antibodies in blood semm (93). 

Note chat turbulent flow (Reynolds number > 3000 is predicted only m the extrathoracic airways at flow races < 30 IVmin. 

Forced expiration is commonly used to assess pulmonary function in both healthy and impaired individuals. Static measures of lung volumes (TLC, Vj, FRC) fail to detect dynamic changes in pulmonary function that are attributable to disease (e.g., asthmatic airway constriction). Obtaining maximum expiratory flow-volume (MEFV) curves (Fig. 5.21) permits derivation of key parameters in detecting changes in lung function. 

Forced vital capacity (FVC) quantifies the maximum air volume expired following a maximal inspiration and is one of the basic measures of analyzing flow changes such as reduced airway patency observed in asthma. To measure FVC, an individual inhales maximally and then exhales as rapidly and completely as possible. FVC primarily reflects the elastic properties of the respiratory tract. The gas volume forcibly expired within a given time interval, FEV (where t is typically one second, FEVj q)... 

Mean airstream velocity diminishes as inspiratory flow moves toward the lung parenchyma because of the rapid increase in total cross-sectional area. The largest increases in area occur in the distal bronchioles and pulmonary airways, causing u to approach zero because... 

Airway wall fibrosis, thickening + Flow limitation... 

Continuous, coarse, whistling sound produced in the respiratory airways during breathing when air flow becomes accelerated through narrowed or obstructed airways. 

Patients receiving bronchodilators or antiasthma drugs otten need to monitor their lung function at home with a peak flow meter. Doing so provides the patient and the physidan with valuable information about the status of the patient s condition and the effectiveness of therapy. Otten, trends in the readings can detect changes in the patient s airway and airflow even before any signs and symptoms are experienced. This allows possible intervention before a major problem arises. 

When cyanosis occurs, oxygen should be supplemented by a facemask or by an oropharyngeal airway with a flow rate of about 7 liters/min. When indicated or when there is a ventilatory insufficiency, intubation should be performed to support breathing. Patients who are vomiting should be positioned adequately in order to avoid aspiration (table 1). 

---