**2. Negative expiratory pressure technique (NEP) – Methodology**

In the last 2 decades, expiratory flow limitation (EFL) in patients with various respiratory disorders has been studied extensively using the negative expiratory pressure technique (NEP). This method does not require performance of forced expiratory maneuvers or the body plethysmograph (D'Angelo et al., 1993; Koulouris et al., 1995; Valta et al., 1994). It con‐ sists of applying a small negative pressure (3–10 cm H2O, depending on the circumstances)

at the onset of tidal expiration and comparing the ensuing expiration flow-volume curve with that of the preceding control expiration (Figures 1-3).

**Figure 3.** Schema of the control and NEP tidal flow-volume curves and how measurements of EFL% and AUC% were

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As the driving pressure at the airway opening increases with application of NEP, expiratory

**Figure 4.** Tracings of the control and NEP tidal curves in a healthy subject. Note increase in expiratory flow with appli‐

flow should increase if the individual is not flow-limited (Figure 4).

obtained.

cation of NEP.

**Figure 1.** Schema of negative expiratory pressure (NEP) setup to assess expiratory flow limitation (EFL).

**Figure 2.** Tracings of airway pressure, volume and flow during quiet breathing. Application of negative expiratory pressure at the onset of expiration is indicated by NEP.

at the onset of tidal expiration and comparing the ensuing expiration flow-volume curve

**Figure 1.** Schema of negative expiratory pressure (NEP) setup to assess expiratory flow limitation (EFL).

**Figure 2.** Tracings of airway pressure, volume and flow during quiet breathing. Application of negative expiratory

pressure at the onset of expiration is indicated by NEP.

with that of the preceding control expiration (Figures 1-3).

124 Oncogenesis, Inflammatory and Parasitic Tropical Diseases of the Lung

**Figure 3.** Schema of the control and NEP tidal flow-volume curves and how measurements of EFL% and AUC% were obtained.

As the driving pressure at the airway opening increases with application of NEP, expiratory flow should increase if the individual is not flow-limited (Figure 4).

**Figure 4.** Tracings of the control and NEP tidal curves in a healthy subject. Note increase in expiratory flow with appli‐ cation of NEP.

By contrast, intrathoracic EFL is demonstrated by a sustained absence in increase in flow during application of NEP (as occurs in COPD) (Figure 5). That is, in these individuals the control and NEP-generated tidal expiratory are superimposed on each other.

**Figure 6.** Tracings of control and NEP tidal flow-volume curves in a patient with a chest wall disorder, in this case amyotrophic lateral sclerosis with bulbar involvement (but without obstructive sleep apnea). Note the decrease in ex‐

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**Figure 7.** Tracings of control and NEP curves in a patient with severe obstructive sleep apnea. Note the sustained de‐

crease of flow during application of NEP below the control expiratory tidal flow.

piratory flow below the control tidal expiration with application of NEP.

In obese individuals, some patients with restrictive respiratory disorders (Figure 6, individ‐ ual with amyotrophic lateral sclerosis) and some subjects free of cardiorespiratory disease, application results in a reduction in the increase in flow or transient decrease below the con‐ trol expiration. This finding is prevalent in patients with documented obstructive sleep ap‐ nea (Figure 7).

The NEP test is simple, noninvasive, practical and accurate. It has been validated by simul‐ taneous determination of isovolume flow-pressure relationships (Valta et al., 1994).

By contrast, intrathoracic EFL is demonstrated by a sustained absence in increase in flow during application of NEP (as occurs in COPD) (Figure 5). That is, in these individuals the

**Figure 5.** Tracings of control and NEP tidal curves in a patient with chronic obstructive pulmonary disease. Note ab‐

In obese individuals, some patients with restrictive respiratory disorders (Figure 6, individ‐ ual with amyotrophic lateral sclerosis) and some subjects free of cardiorespiratory disease, application results in a reduction in the increase in flow or transient decrease below the con‐ trol expiration. This finding is prevalent in patients with documented obstructive sleep ap‐

The NEP test is simple, noninvasive, practical and accurate. It has been validated by simul‐

taneous determination of isovolume flow-pressure relationships (Valta et al., 1994).

sence of change in expiratory flow with application of NEP.

nea (Figure 7).

control and NEP-generated tidal expiratory are superimposed on each other.

126 Oncogenesis, Inflammatory and Parasitic Tropical Diseases of the Lung

**Figure 6.** Tracings of control and NEP tidal flow-volume curves in a patient with a chest wall disorder, in this case amyotrophic lateral sclerosis with bulbar involvement (but without obstructive sleep apnea). Note the decrease in ex‐ piratory flow below the control tidal expiration with application of NEP.

**Figure 7.** Tracings of control and NEP curves in a patient with severe obstructive sleep apnea. Note the sustained de‐ crease of flow during application of NEP below the control expiratory tidal flow.
