Maximum Inspiratory and Expiratory Pressures

Rationale. Mouth Pi,max and PE,max measurements are used to study respiratory muscle strength.

Methods. Accurate mouth Pi,max and PE,max measurements can be obtained at approximately 6-7 years of age.

Children must be well instructed before the test. Pressures are measured with the child seated and wearing a noseclip. A cylindrical mouthpiece is recommended, as PE,max has been shown to be significantly lower when a scuba-type mouthpiece is used instead of a cylindrical one (41). A small leak, created by placement of a needle (1 mm in diameter by 15 cm long) in the mouthpiece, is recommended to eliminate glottic closure and artificially high Pi,max (13, 42). Each effort should be maintained for at least 1 second. Simultaneous measurement of the lung volume at which maximal pressure is generated is recommended, using either a body plethysmograph or a spirom-eter. Pi,max measurements at residual volume (RV) and pE,max measurements at total lung capacity (TLC) require two successive cooperation-dependent maneuvers. However, Pi,max or PE,max at the end of a normal expiration, i.e., at FRC, requires only one cooperation-dependent maneuver, thereby limiting the potential for fatigue.

Advantages. Maximum inspiratory and expiratory measurements in children are simple and noninvasive.

Disadvantages. The disadvantages of Pi,max and PE,max measurements in children are their variability and a learning effect. When fewer than five maneuvers were performed, the coefficient of variation (CV) was found to be 9% and was independent of maneuver, age, and sex (13). Studies in healthy children and in children with various respiratory disorders have shown a learning effect (43, 44). With multiple Pi,max and PE,max determinations, i.e., more than 20 attempts, pressures were significantly higher than with a short Pi,max and PE,max method, i.e., fewer than five attempts (43, 44). in routine practice, it is recommended to perform five measurements or more until two reproducible maximal values are obtained. in healthy children tested seated, Pi,max and PE,max have been shown to be independent of the thoracoabdominal configuration assumed during the maneuver (45).

Normal values. Table 2 shows normal values of Pi,max and PE,max in children and adolescents (13, 41, 42, 46, 47). in a number of studies the level of lung volume has not been controlled during the test. Only one study provides normal values for Pi,max at FRC. Maximum inspiratory and expiratory pressures increase with age in children (15, 43), and are lower in girls than in boys even before puberty. However, the increase in Pi,max and PE,max with age underestimates the increase in

TABLE 1. NORMAL VALUES OF CHEST WALL COMPLIANCE WITH AGE

First Reference Age Range -

TABLE 1. NORMAL VALUES OF CHEST WALL COMPLIANCE WITH AGE

First Reference Age Range -

Author

No.

(yr)

ml/cm H2O

ml/cm H2O/kg

Ccw/CL

Gerhardt

32

Preterm

5.7 ± 1.4

(3-10)

Papastamelos

33

Infancy

17.4 ± 6.7

(2-5)

(3-6)

2.8 ± 0.87

(1-2)

1-3

20.1 ± 7.7

(1-3)

2.0 ± 0.51

(1-2)

Sharp

37

5-16

5

78

4

8

106

4

12

156

4

16

184

3

Mittman

38

Adulthood

20-29

350

5

2

30-39

250

3.5

1.2

40-49

250

3.5

1

50-59

250

3.5

0.8

60-69

136

2

0.7

70-79

210

3

0.7

Definition of abbreviations: Ccw = chest wall compliance; Cl = lung compliance. Values are means or means ± SD. Values in parentheses are ranges.

Definition of abbreviations: Ccw = chest wall compliance; Cl = lung compliance. Values are means or means ± SD. Values in parentheses are ranges.

net muscle force, i.e., the product of pressure and surface area over which the pressure is applied (13).

Clinical application. Measurements of Pi,max and PE,max are useful in children and/or adolescents with neuromuscular disorders (48-50), with cystic fibrosis (51-55), and with chronic obstructive pulmonary disease (16). in the case of hyperinflation, Pi,max and PE,max values have to be corrected for the absolute volume at which measurements were made (16, 53). Pi,max and PE,max measurements may be useful in malnourished children (53). Maximum inspiratory pressure at FRC provides an assessment of the inspiratory maximal reserve of the respiratory muscles during quiet breathing in children (16, 55, 56). it has been proposed that inspiratory muscle strength be assessed by the measurement of the maximal pressure obtained while breathing 5% CO2 at the time of weaning from MV in infants and children (57).

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