Maximal Inspiratory and Expiratory Pressures in Adolescents

Maximal Inspiratory and Expiratory Pressures in Adolescents· Normal Values Robert]. Smyth, M.Sc.; Kenneth R. Chapman, M.D., F.C.C.P.;t and Anthony S. Rebuck, M.D., F.C.C.P.

The measurement of maximal inspiratory and expiratory pressures at the mouth (MIP and MEP, respectively) provides a noninvasive clinical method for evaluating the strength of respiratory muscles. In an attempt to reconcile the widely divergent normal values reported in the literature for healthy adolescents, we have measured, using simple manometry, MIP and MEP in 112 white subjects, 76 adolescents and 36 healthy adults. For female adolescents the values for MIP and MEP were 76 ± 25 and 86 ± 22 cm HIO, respectively, and were significantly less than those for male adolescents (p
107 ± 26 and ll4 ± 35 cm HIO, respectively. Mean values for adolescents were comparable to values measured in adult control subjects, and for both adolescents and adults, mean values approximated the lower end of the previously reported ranges of normal values in healthy subjects. Thus, MIP and MEP in healthy adolescents are significantly greater in male subjects than female subjects, but are comparable to those of healthy adults of the same sex. FUrthermore, these studies suggest that the choice of normal values for MIP and MEP must take into account significant methodologic differences among laboratories.

The measurement of maximal inspiratory and expiratory pressures generated at the mouth (MIP and ME~ respectively) is an accepted noninvasive clinical method for evaluating the strength of respiratory muscles; however, the choice of normal values for this measurement is made difficult by the wide variation in normal values reported in the literature. In studies of healthy adult male subjects, mean values ranging from 89 to 146 em H 20 have been reported for MI~1.2 Published values for MEP in adult male subjects are even more discrepant, ranging from 130 to 247 em H 20. 1.2 We have recently encountered a similar problem in choosing a range of normal values for MIP and MEP in adolescent subjects. While normal data have been published for healthy children aged seven to 13 years, 3 there have been few studies in the adolescent age group, and reported mean values vary widely, in particular for maximal expiratory pressures. Leech et al' have reported a mean value for MEP in male adolescents of 131 cm H 20 , whereas Cook et al" reported a mean value of 198 cm H 20, a difference of more than 50 percent. In an attempt to reconcile these apparent discrepancies, we wish to report inspiratory and expiratory pressures in a large group of healthy male and female adolescents (aged 13 to 18 years).

MATERIALS AND METHODS

*From the Divisions of Respiratory and Rehabilitation Medicine, Toronto Western Hospital, Toronto, Canada. tSupported by a fellowship from the Medical Research Council of Canada. Manuscript received December 13; revision accepted April 4. Reprint requests: Dr. Chapman, Suite 201 Edith Cavell Wing, Toronto Western Hospital, Toronto, Ontario, Canada M5T 2S8

588

One hundred and twelve white subjects participated in the study. Seventy-six were adolescents (36 male and 40 female subjects) who were examined after parental consent was obtained. All subjects denied any respiratory problem and were not receiving medical therapy. Each subject was examined by a physiotherapist and a public health nurse for the presence of scoliosis, and those with a curve of greater than 10° were omitted from the study. Measurements of standing height and weight were obtained, and chronologie age was recorded. Spirometric measurements were made using a diaphragm spirometer (Breon model 24(0). Duplicate measurements of forced vital capacity (FVC) and forced expired volume in one second (FEV J were obtained in the standing posture. If necessary, a third measurement was made if there was more than a 10 percent difference between the first two values of FVC. All volumes were corrected to body temperature and pressure saturated (BTPS), and the predictive equations of Weng and Levison" were used to calculate the obtained percent of predicted FVC. In addition, 21 healthy adults aged 23 to 43 years (six men and 15 women) were studied using the same protocol. A further 15 adult subjects (10men and five women) were studied separately using a rapidly responding pressure transducer to validate the protocol employed.

Normal Values Values of MIP and MEP were obtained using a mercury-filled

V-tube and a rubber scuba-type mouthpiece reinforced to prevent

collapse (internal diameter, 3.1 em), Each subject was instructed to exhale to residual volume (RV) or inhale to total lung capacity (TLC), before attempting to inhale/exhale maximally into the mouthpiece for measurement of MIP and ME~ respectively. The subject was also instructed to avoid collapsing the cheeks during the measurement of MI~ a precaution designed to prevent the generation of negative pressure by the upper airway muscles with glottis closed.F' If close inspection revealed air leakage around the lips during the maneuver, the measurement was repeated until technically satisfactory. The value was recorded as the level of mercury which was sustained for two to three seconds. Each measurement was made twice, and the higher value was recorded and expressed in centimeters of water.

Maximal Inspiratoryand ExpiratoryPressures in Adolescents(Smyth, Chapman, Rebuck)

Table I-Physical Characteristics and Spirometric Data of Adolescents· Data No. of subjects Age, yr Height, em Weight, kg Percent of predieted FVC FEV/FVC%

Male Subjects

Female Subjects

Total

30 15±1 168±8 63.7±14.4

37 15±2 162±7 54.3±8.4

67 15±1 164±8 58.4± 12.3

105± 11 87.7±7.8

106± 17 89.4±6.3

106± 15 89.3±6.0

*Values are expressed as means ± SD.

Validation of Protocol In 15 adult volunteers, we examined the nature of pressure transients induced by the maneuvers described and the effect of a deliberate mouthpiece leak, as described by earlier investigators, on the values measured. Subjects were asked to perform the respiratory maneuvers described in the protocol as pressure was monitored by a pressure transducer (Validyne MP 45-32) calibrated against a mercury manometer. The analog transducer output was recorded by a strip-chart recorder (Hewlett-Packard 7404A) at a paper speed of 50 mm/min. Measurements were performed in random sequence using both the standard mouthpiece described earlier and the same mouthpiece with a leak produced by insertion of an 18-gauge needle. Five of these subjects were also asked to generate maximal inspiratory and expiratory pressures using sharp, nonsustained inspiration and expiration at RV and TLC, respectively. Results are expressed as the mean ± SD. Means were compared using the unpaired and paired t-tests where appropriate. Regression analysis was performed separately on MIP and MEP for male and female subjects using the following independent variables: age; height; weight; FVC; FEV l ; and percent of predicted FVC. RESULTS

Seven of the adolescent subjects (9 percent; five male and two female subjects) had measurements of FVC which were below the 95 percent confidence limit for their height, and two of the subjects (3 percent; one male and one female subject) had values for FEV/FVC which were more than 2 SD below the mean for the group. In order to ensure that all results were from a normal healthy population, the data for these subjects were not included in the analysis. The characteristics of the remaining subjects are recorded in Table 1.

Normal Values The mean values for respiratory pressures for male and female adolescents are presented in Table 2. 3 ,4.8 The female subjects showed a larger difference between MIP and MEP (13.2 percent; MEP>MIP) than the male subjects (6.5 percent); however, both respiratory pressures were Significantly higher for the male subjects (for both, p
Validation of Protocol Examination of the pressure tracings produced by the maximal inspiratory and expiratory maneuvers revealed frequent transient peaks of mouth pressure at the onset of such maneuvers before pressure fell to a plateau sustained for one to three seconds. Such transients were present in approximately half of the records. The use of a small leak in the mouthpiece did not prevent the generation of these pressure transients. Peak inspiratory pressures were 22 ± 22 percent greater than plateau inspiratory pressure when a needle leak was employed, with the largest difference being 69 ern H 20 (72 percent) in one subject. High transients were less noticeable during expiratory maneuvers; mean peak expiratory pressure exceeded mean plateau expiratory pressure by 10 ± 8 percent. In the five subjects asked to make sharp, nonsustained maximal maneuvers, peak inspiratory and expiratory pressures were obtained which exceeded significantly

Table 2-Valuesfrom Literature for Respiratory Pressures in Healthy Adolescents·

Reference Leech et al4 Cook et al5 Jones et al8 Present study

Male Subjects

No. of Subjects

Female Subjects

Age, yr

Male

Female

cm H 2O

ern H 2O

ern H 2O

cm H 2O

13-17 11-15 13-16 13-17 13-18

46 0 10 0 29

68 10 0 27 37

111±34

131±30

132±26

198±36

85±28 103±21

95±29 145±28

107±26

114±35

73±25 76±25

98±21 86±22

MI~

ME~

MI~

ME~

*Values are expressed as means ± SD. CHEST / 86 / 4 / OCTOBER. 1984

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45 55 85 75 85 95105115125135145155185175185185 38 53 88 83 98 113 128143 168 173 188 203 218

MEP

(cmH 20)

FIGURE 1. Frequency distributions of MIP and MEP for male and female subjects separately. A (upper left), MIP in female subjects; B (upper right), MEP in female subjects; C (lower left), MIP in male subjects; and D (lower right), MEP in male subjects.

the plateau pressures measured earlier; This difference

was more marked for expiratory maneuvers. Mean

nonsustained expiratory pressure was 157 ± 35 cm HIO. and mean sustained expiratory pressure was 129±26 em H 20 (p
Creation of a needle leak in the mouthpiece, suggested as a method for preventing glottic closure and ardfactually high maximal inspiratory pressures, was without effect on MIP in this study. Mean MIP with a leak (118 ± 33 cm H 20 ) was not significantly different from mean MIP measured without a leak (li5 ± 37 em H20 ) (p>O.05). DISCUSSION

In the present study, we measured MIP and MEP in a group of healthy adolescents in order to define a

range of normal values. The reported mean values for MIP in female adolescents have ranged from mean values of73 to 103cm H 20 and for MEP from 95 to 145 em H 20 .4•5•8 In the present large group of subjects of comparable height and weight, the measured values closely approximate the lower end of this range (Table 2). The reported mean values ofMIP and MEP in male adolescents are based on only two studies with markedly different results: for MI~ ill and 132em H 20 ; and for ME~ 131 and 198 em H 20 . Similar to female adolescents, our results from adolescent males more closely approximate the lower end of the previously reported range. To verify that these low values were not a consequence of poor motivation in our adolescent subjects, we measured MIP and MEP in a group of highly motivated laboratory and hospital staff. In these control adult subjects the mean values (for men, MIP=100 cmH 20 , and MEP=112 em H 20 ; for women, MIP=72 em H 20 , and MEP=95 em H 20 )

MaximalInspiratory and Expiratory Pressures in Adolescents (Smyth, Chapmen, Rebuck)

Table 3-Valuesfrom Uterature for Respiratory Preuura in Healthy Adulta*

Age, Reference Hutchinson' Ringqvist2 Leech et al4 Cook et als Black and Hyate Jones et al8 Gilbert et ali Cross" Rahn et al 11 Shilling lJ Cripps" Schneider" DiMarco et al lS

Men

No. of Subjects MI~

Women ME~

MI~

yr

Men

Women

cmH.O

cmH.O

Adult 18-29 21-35 18-32 18-47 20-54 18-23 20-54 15-54 Adult Adult Adult Adult Adult

1,061 37 108 0 12 60 0 53 30 31 419 950 123 11

0 33 81 9 0 60 24 42 0 0

89 146±26 114

130 247±41 160

133±39 124±22

237±45 233±42

119 109 109

0 0

0 0

108±6

162 158 155 181 167

ME~

cmH.O

cmH.O

113±24 67 l00± 19

170±29 94 146±34

63±24 82

101±38

*Values are expressed as means ± SD.

were also at the lower end of the previously reported range of normal values for adults (Table 3).1.2,4,5,7-15 We have also found that measured values are not altered significantly by the simple expedient of creating a small deliberate leak in the mouthpiece of the apparatus. Clausen" has recently drawn attention to his observation that MIP and MEP measured in the clinical laboratory frequently fall at or below the quoted range of normal values. Our own data support this observation. Several factors may contribute to the wide range of values described for adults and adolescents in previous studies. The first concerns the temporal course of the pressures generated. Although Rahn et al" first reported that the maximum expiratory pressure that can be sustained voluntarily is about 160 cm H20 , Mills" later showed that values over 260 em H 20 could be obtained transiently by sudden voluntary efforts. This latter value is closer to that reported by some laboratories as a normal MEP for male adults. Thus, measurements of MIP and MEP may vary markedly with the speed of maneuver, the response characteristics of the pressure measuring device, and the decision of the observer to record either peak or sustained maximal pressure. To support this contention, we have observed in our own subjects, whether or not a deliberate leak was created in the instrument's mouthpiece, pressure transients which exceeded the plateau pressures we sought to measure. In a small number of subjects studied, sudden voluntary effort produced marked pressure transients, particularly on expiration. Secondly, air leaks at the nose and mouth can produce inaccuracy during forced expiratory maneuvers. In the majority of our subjects, detectable air leaks were clearly apparent during initial trial studies, but were readily corrected with careful instruction. Thirdly, forced respiratory maneuvers are notoriously influ-

enced by motivation. Our control subjects were highly motivated laboratory staff familiar with respiratory measurements, whose obtained values were similar to those reported in previous studies.1.8-11,15 Finally, the number of trials used to measure MIP and MEP may affect the maximal pressure recorded. It has been shown that maximal values recorded may increase over ten attempts. Thus, Ringqvist," using ten or more trials, reported higher maximal pressures than Black and Hyatt' or Leech et al," who used two and three trials, respectively, to determine their normal values. Normal values based on a small number of trials may be a more appropriate choice for the clinical laboratory, where repeated trials may be impractical or impossible in patients. While maximal mouth pressures generated are highly dependent on the pulmonary volumes at which they are measured, most studies have stated that measurements were made at or near RV and TLC for MIP and ME~ respectively. Thus, it seems unlikely that differences among laboratories in the pulmonary volumes chosen for these respiratory maneuvers account for the wide variability in reported values. It has long been recognized that highly negative inspiratory pressures can be generated by the cheek muscles alone against a closed glottis." In an attempt to avoid this artifact, Bmgqvist" and later investigators advocated the use of a small leak at the mouthpiece to prevent glottic closure. Our own data suggest that this procedure is insufficient to prevent negative pressure transients. Our data do not show excessively high values for MI~ suggesting that careful instruction and observation of the subject may be more valuable than reliance on a small leak in the mouthpiece to prevent an artifact from glottic closure. A review of reported normal values for MIP and MEP in healthy adolescents (Table 2) shows substantial variations, most probably a consequence of one or CHEST I 88 I .. I OClOBER, 1984

571

more of the factors outlined previously. When assessed by a one-way analysis of variance, these differences are seen to be not only clinically but statistically significant: for MEP in both male and female subjects, pp>O.05, approaching conventional levels of statistical significance. These significant contrasts suggest differences which are greater than can be accounted for by chance alone and may be attributed to unresolved differences in methodology. Thus, normal values from the literature should be used for comparison with caution, if they are to be used at all. H normal values must be selected from the literature, care must be taken to use values measured in the same fashion as that to be used for clinical testing. More appropriately, when data on MIP and MEP are reported in future studies, control values from the same laboratory should be used for comparison, rather than arbitrarily selecting from the available range in the literature, at least until procedural differences among laboratories are resolved. ACKNOWLEDGMENT: We thank Ms. C. MacHattie for her technical assistance, and Ms. M. 1: Berk for her assistance in preparation of the manuscript.

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4 Leech ]A, Ghezzo H, Stevens D, Becklake MR. Respiratory pressures and function in young adults. Am Rev Respir Dis 1983; 128:17-23 5 Cook CD, Mead J, Orzalesi MM. Static volume-pressure characteristics of the respiratory system during maximal efforts. J Appl Physiol 1964; 19:1016-22 6 Weng T-R, Levison H. Standards of pulmonary function in children. Am Rev Respir Dis 1969; 99:879-94 7 Black LF, Hyatt RE. Maximal respiratory pressures: normal values and relationship to age and sex. Am Rev Respir Dis 1969; 99:696-702 8 Jones RS, Kennedy JD, Hasham F, Owen R, Taylor RF: Mechanical inefficiency of the thoracic cage in scoliosis. Thorax 1981; 36:456-61

9 Gilbert R, Auchincloss H, Bleb S. Measurement of maximum inspiratory pressure during routine spirometry. Lung 1978; 155:23-32 10 Gross D. Investigations concerning vital capacity. Am Heart J 1943; 25:335-43 11 Hahn H, Otis AB, Chadwick LE, Fenn WOo The pressurevolume diagram of the thorax and lung. Am J Physiol 1946; 146:161-78 12 Shilling CWo Expiratory force as related to submarine escape training. US Naval Med Bull 1963; 18:386 13 Cripps LD. The application of the air force physical efficiency tests to men and women. Med Res Counc Spec Rep Ser 1924; 84 14 Schneider EC. A record of experience with certain physical efficiency and low oxygen tests. Am J Med Sci 1921; 161:395 15 DiMarco AF, Kelsen SG, Cherniack NS, Gothe B. Occlusion pressure and breathing pattern in patients with interstitial lung disease. Am Rev Respir Dis 1983; 127:425-30 16 Clausen JL. Maximal inspiratory and expiratory pressures. In: Clausen JL, ed. Pulmonary function testing guidelines and controversies. New York: Academic Press, Inc, 1982:187-91 17 Mills IN. The pressures developed in abdomen and thorax during the Flack tests. J Physiol (Lond) 1950; 111:368-75

Maximal Inspiratory and Expiratory PressuresIn Adolescents (Smyth, Chapman, Rebuck)