Expiratory restriction

When reading a diagnosis, note whether the author states that a rib is in a position of inspiration [elevated] or restricted in inspiration [depressed]. An inspiration restriction denotes a rib that does not move into a position of inspiration but is held in a depressed or expiratory position. Inspiratory and expiratory restrictions are restrictions of motion of the rib on its respiratory axis Ihat is, during inspiration the anterior portion of the rib is elevated and during expiration the rib is depressed. 

If one rib stops moving before the other rib during exhalation, that rib has an expiratory restriction. 

The FVC, which represents the total amount of air than can be exhaled, can be expressed as a series of timed volumes. The forced expiratory volume in 1 second (FEVi) is the volume of air exhaled during the first second of the FVC maneuver. Although the FEVi is a volume, it conveys information on obstruction because it is measured over a known time interval. The EEVj depends on the volume of air within the lung and the effort during exhalation therefore, it can be diminished by a decrease in TLC or by a lack of effort. A more sensitive way to measure obstruction is to express the FEVi as a ratio of FVC. This ratio is independent of the patient s size or the TLC therefore, the FEVi/FVC is a specific measure of airway obstruction with or without restriction. Normally, this ratio is 75% or greater, and any value below 70% to 75% suggests obstruction. 

Spirometry is the most widely available and useful PFT. It takes only 15 to 20 minutes, carries no risks, and provides information about obstructive and restrictive disease. Spirometry allows for the measurement of aU lung volumes and capacities except RV, FRC, and TLC and allows assessment of FEVi and FEF25%-7s%. Spirometry measurements can be reported in two different formats—standard spirometry (Eig. 25-2) and the flow-volume loop (Fig. 25-3). In standard spirometry, the volumes are recorded on the vertical (y) axis and the time on the horizontal (x) axis. In flow-volume loops, volume is plotted on the horizontal (x) axis, and flow (derived from volume/time) is plotted on the vertical (y) axis. The shape of the flow-volume loop can be helpful in differentiating obstructive and restrictive defects and in the diagnosis of upper airway obstruction (Fig. 25 ). This curve gives a visual representation of obstruction because the expiratory descent becomes more concave with worsening obstruction. 

Coal Tar Products. In an industrial health survey of employees in four wood preservative plants in which coal tar creosote and coal tar were the main treatments used, decreased pulmonary function was noted (TOMA 1979). Restrictive deficits in pulmonary function, as indicated by decreases in FVC, were noted in 44 of 257 employees (10 of 47 nonsmokers). Obstructive deficits, as indicated by decreases in percentage forced expiratory volume in one second (FEV1) were noted in 19 of 257 employees (3 of 54 nonsmokers). Nevertheless, no clear relationship could be established because exposure routes in... 

A second way of looking at forced expiration is with a maximum expiratory flow-volume (MEFV) curve, which describes maximum flow as a function of lung volume during a forced expiration (Fig. 12). In healthy human subjects, flow rates or flow-volume curves reach a maximum and will not increase with additional effort after the lungs have emptied 20-30% of their volume (Fry and Hyatt, 1960). This phenomenon of flow limitation is due to airway compression over most of the lung volume. Thus, flow rate is independent of effort and is determined by the elastic recoil force of the lung and the resistance of the airways upstream of the collapse point. In obstructive diseases of the lung this curve is shifted to the left, whereas restrictive diseases shift the curve in the opposite direction (also shown in Fig. 12). 

Fic. 12. Comparison of the typical maximal expiratory flow-volume curve in healthy subjects and those with obstructive or restrictive diseases. 

Honeycomb change is most often associated with restriction and low DLco. whereas bronchial distortion is often associated with reduced expiratory flow rates (45). Airflow obstruction may be suggested on CT when bronchial mural thickening, small-airway narrowing, or patchy air trapping is present (46,74,75). Reticular shadows and thickened bronchovascular bundles on HRCT were independently associated with lower FEVi/FVC ratio (57). 

It is useful to define the disease category in order to predict the natural history and specific intervention. It is well known that patients with primarily restrictive disorders can have both inspiratory and expiratory muscle weakness, and apart from noninvasive ventilation (NIV), they also need cough assistance (4,5). On the other hand, patients with obstructive disorders rarely need mechanical expiratory aids except when they have a severe infectious exacerbation at which time difficulties in clearing copious secretions can occur (4,6,7). 

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