Expiratory flow

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. 

Classification of asthma severity is based on daytime and nighttime symptoms, physical activity, lung function, variability in peak expiratory flow (PEF), and use of reliever medications. 

FEV, forced expiratory volume in 1 second PEF, peak expiratory flow MDI, metered-dose inhaler DPI, dry powder inhaler. 

FIGURE 11-2. Home management of acute asthma exacerbation. Patients at risk for asthma-related death should receive immediate clinical attention after initial treatment. PEF, peak expiratory flow. 

FIGURE 11-3. Emergency department and hospital-based management of asthma exacerbation. FEV-, forced expiratory volume in 1 second Pco2, partial arterial pressure of carbon dioxide PEF, peak expiratory flow 02, oxygen. (From Kelly HW, Sorkness CA. Asthma. In DiPiro JT, Talbert RL, Yee GC, et al, (eds.) Pharmacotherapy A Pathophysiologic Approach. 6th ed. New York McGraw-Hill 2005 517, with permission.)... 

FEF Forced expiratory flow rate HH Hiatal hernia... 

PEFR Peak expiratory flow rate QS Quantity sufficient... 

Peak expiratory flow The maximum flow rate of air leaving the lungs upon forced exhalation. 

Pulmonary function tests Decreased vital capacity Prolonged expiratory flow... 

Peak expiratory flow (PEF) and FEVj are less than 50% of normal predicted values. Pulse oximetry reveals decreased arterial oxygen and 02 saturations. The best predictor of outcome is early response to treatment as measured by improvement in FEVj at 30 minutes after inhaled /12-agonists. 

FIGURE 80-2. Home management of acute asthma exacerbation. Patients at risk of asthma-related death should receive immediate clinical attention after initial treatment. Additional therapy may be required. (MDI, metered-dose inhaler PEF, peak expiratory flow.) (Adapted from NHLBI, National Asthma Education and Prevention Program, Expert Panel Report 2. Guidelines for the Diagnosis and Management of Asthma. NIH Publication No. 97-4051. Bethesda, MD U.S. Department of Health and Human Services, 1997.)... 

Peak expiratory flow measurements are not adequate for diagnosis of COPD because of low specificity and a high degree of effort dependence. However, a low peak expiratory flow is consistent with COPD. 

Respiratory problems are diagnosed using a spirometer. The patient exhales as hard and as fast as possible into the device. The spirometer measures (1) the total volume exhaled, called the forced vital capacity (FVC), with units in liters (2) the forced expired volume measured at 1 second (FEV,), with units in liters per second (3) forced expiratory flow in the middle range of the vital capacity (FEV 25-75%), measured in liters per second and (4) the ratio of the observed FEVj to FVC X 100 (FEVj/FVC%). 

Atmospheres were within a few percent of nominal concentrations the mean oxygen concentration was approximately 20.5%. No significant or consistent differences were found between air exposure and test chemical exposure for clinical observations, blood pressure, heart rate, peak expiratory flow, or EKG recordings. During blood sampling and blood pressure measurements, all subjects showed sinus arrhythmia before and after exposure. 

Effects No effects on tested parameters of blood pressure, heart rate, electrocardiogram (EKG) rhythms, or lung peak expiratory flow. 

Obstructive disease reduces peak expiratory flow rate (PEFR) and increases RV via gas trapping. The TLC may also be higher although this is difficult to demonstrate without values on the x axis. The important point to demonstrate is reduced flow rates during all of expiration, with increased concavity of the expiratory limb owing to airway obstruction. The inspiratory limb is less affected and can be drawn as for the normal curve but with slightly lower flow rates. 

This curve is seen where a large airway has a fixed orifice through which gas is able to flow, such as may be seen in patients with tracheal stenosis. The peak inspiratory and expiratory flow rates are, therefore, dependent on the diameter of the orifice rather than effort. The curves should be drawn almost symmetrical as above, with both limbs demonstrating markedly reduced flow. The TLC and RV are generally unaffected. 

Respiratory Respiration rate, inspiratory and expiratory times, tidal volume, minute volume, peak inspiratory, and expiratory flows Whole body piety smography Rat McMahon et al.185... 

Laboratory exposure to dust clouds and dust extract aerosols results in chest tightness, dyspnea and decreases in both expiratory flow and dynamic lung compliance (4). Bouhuys et al. showed that aerosols of cotton dust extract inhaled by man produced reversible small-airway obstruction within 10 minutes O) the same effects were noted in cardroom workers exposed to dust on Mondays, i.e. decreased maximum expiratory flow rates and increased airway resistance ( ). These changes are compatible with narrowing of small airways as the principal effect of acute dust exposure. 

Clinical studies of cotton mill workers who had previously demonstrated a decreased expiratory flow measured by flow volume curves and FEV during cotton dust exposure showed an increase in WBC to 25.5% after 4 hours of exposure. Segmented neutrophils increased most (33%), while eosinophil mean counts did not change. The ratio of segmented neutrophils to epithelial cells from nasal mucosal swabs increased from 0.56 before to 1.84 after 4 hours of exposure. Peripheral blood and PMN counts increased upon exposure to cotton dust, and PMN were recruited to the nasal mucosa. Chest tightness and decreased flow were temporarily correlated with leukocyte recruitment following cotton dust exposure (2). 

Figure 2. Maximum (MEFV thin lines) and partial (PEFV heavy lines) expiratory flow-volume curves by a healthy 25 year old female subject.

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