Cough Tests

Scientific basis. Measurement of pressure during cough is of interest because the main expiratory muscles, the abdominal muscles, are also those used in cough. Reduced cough pressure is of clinical importance because it may predispose to chest infections. Also, in some patients technical difficulties preclude measurement of mouth pressure during a static maximal expiratory maneuver (Pemax); in these patients measurement of maximal cough pressures is an alternative measurement technique.

A normal cough consists of four phases: inspiratory, compressive, expulsive, and relaxation (70). For cough to be a measurement of expiratory muscle strength, two aspects re-

TABLE 3. TRANSDIAPHRAGMATIC PRESSURES DURING MAXIMAL STATIC RESPIRATORY EFFORTS AND MAXIMAL SNIFFS

(cm H2O)

(cm H2O)

Mean

SD

Range

Mean

SD

Range

Men

37

108

30

52-164

148

24

112-204

Women

27

65

31

16-40

121

25

82-182

All

64

90

37

16-164

137

28

82-204

Definition of abbreviations: Pi,di,max = maximum static transdiaphragmatic pressure; Pdi,sn = transdiaphragmatic pressure during sniff. Reprinted by permission from Reference 61.

Definition of abbreviations: Pi,di,max = maximum static transdiaphragmatic pressure; Pdi,sn = transdiaphragmatic pressure during sniff. Reprinted by permission from Reference 61.

quire consideration: how standard is the maneuver and what should be measured.

Expiratory muscle strength is influenced by lung volume (71). it is normal to take a deep breath before a maximal cough. Thus, although no instructions are given concerning the magnitude of inspiration, the actual lung volume is probably relatively constant for a given individual during serial measurements. Compression requires a functional glottis; in some disorders, for example bulbar type amyotrophic lateral sclerosis, this may not be present (72). A glottis that does not open immediately causes an uncomfortable choking sensation and makes measurement of mouth pressure (during either a PEmax maneuver or a cough) difficult, but would not exclude obtaining useful measurements from a gastric or esophageal balloon (73).

Theoretically, the peak cough pressure could be measured at the mouth, esophagus, or stomach, but measurements at the mouth have not been reported. Pdi is generated during cough (74) and forced expiration (75) so that Pes,co is always less than Pga,co (76). This Pdi can be substantial in a few subjects (76); it may be due to active contraction of the diaphragm, or passive stretching. in general, gastric pressure can be viewed as a reasonable measure of abdominal muscle strength. The surface EMG from abdominal muscle also varies with cough intensity (77), but difficulties in standardizing it between measurements make this relatively impractical as a measurement of strength.

Methodology. After passage and positioning of appropriate balloon catheters the subject is asked to cough as forcefully as possible. Visual feedback seems to be helpful, as with the diaphragm (53). Peak pressures are measured between the baseline at relaxed end-expiratory lung volume, and peak pressure (Figure 8).

Voluntary coughs are usually initiated from above FRC. Lung volume may need to be controlled or measured, although this may not be necessary for clinical measurements.

it would, theoretically, be possible to measure the pressure generation during an induced (e.g., with citric acid) cough in patients unable to cough voluntarily, for example, those in intensive care units.

Cough pressures can be large, so it is necessary to have an adequate volume of air in the balloon, to avoid compression of the gas bubble in the balloon and its displacement into the catheter-transducer system.

Normal ranges. No normal data exist from large studies. Black and Hyatt (78) found PEmax and cough esophageal pressures comparable in a subgroup of their subjects. Other authors have found lower values in patients with COPD (79). The mean maximal Pga,co in a small group of normal subjects 20-75 years of age was 230 cm H2O for men and 166 cm H2O for women, with lower limits of 160 cm H2O for men and 120 cm H2O for women (76).

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  • Tapio
    How to measure peak cough pressure?
    6 years ago

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