Reference values for lung function tests. II. Maximal ...

1 719 Braz J Med Biol Res 32(6) 1999 Muscle respiratory strength in healthy subjectsBrazilian Journal of Medical and Biological Research (1999) 32: 719-727 ISSN 0100-879 XReference values for lung functiontests. II. Maximal respiratorypressures and voluntary ventilation1 Department of Physiology, St. George s Hospital Medical School,University of London, London, UK2 Departamento de Medicina Preventiva e Social and3 Disciplina de Pneumologia, Departamento de Medicina,Escola Paulista de Medicina, Universidade Federal de S o Paulo,S o Paulo SP, Neder1,S. Andreoni2, Lerario2and Nery3 AbstractThe strength of the respiratory muscles can be evaluated from staticmeasurements ( Maximal inspiratory and expiratory pressures, MIPand MEP) or inferred from dynamic maneuvers ( Maximal voluntaryventilation, MVV). Although these data could be suitable for a num-ber of clinical and research applications, no previous studies haveprovided Reference values for such tests using a healthy, randomlyselected sample of the adult Brazilian population.

2 With this mainpurpose, we prospectively evaluated 100 non-smoking subjects (50males and 50 females), 20 to 80 years old, selected from more than8,000 individuals. Gender-specific linear prediction equations forMIP, MEP and MVV were developed by multiple regression analysis:age and, secondarily, anthropometric measurements explained up to56% of the variability of the dependent variables. The most citedprevious studies using either Caucasian or non-Caucasian samplessystematically underestimated the observed values of MIP (P< ).Interestingly, the self-reported level of regular physical activity andmaximum aerobic power correlates strongly with both respiratory andperipheral muscular strength (knee extensor peak torque) (P< ).Our results, therefore, provide a new frame of Reference to evaluate thenormalcy of some useful indexes of respiratory muscle strength inBrazilian males and females aged 20 to NeryDisciplina de PneumologiaEPM, UNIFESPRua Botucatu, 740, 3 andar04023-062 S o Paulo, SPBrasilFax: +55-11-570-2127E-mail: partially supported byCNPq and FAPESP.

3 Neder wasthe recipient of a post-doctoralfellowship from FAPESP(No. 95/9843-0).Received April 23, 1998 Accepted January 13, 1999 Key words respiratory muscle strength Maximal voluntaryventilation Pulmonary function testsIntroductionVentilation plays a key role in the ad-equacy of the external gas exchange, theultimate lung function . The appropriatenessof the ventilatory pump response to a givenmetabolic load, however, is intrinsicallylinked to the ability of the force-generatorunits ( , the respiratory muscles, RM) toprovide the required output. RM strength canbe directly measured using static pressures( Maximal inspiratory and expiratory pres-sures, MIP and MEP) or inferred from somedynamic maneuvers (such as the maximalvoluntary ventilation or MVV). MIP is thegreatest subatmospheric pressure that can begenerated during inspiration against an oc-cluded airway; MEP is the highest pressurethat can be developed during a forceful expi-ratory effort against an occluded airway, and720 Braz J Med Biol Res 32(6) Neder et is the largest volume that can be ven-tilated during a 10- to 15-s interval withvoluntary effort (1).

4 These relatively simple and inexpensivemeasurements, apart from having a role inthe diagnosis and prognosis of a number ofneuromuscular and pulmonary disorders,have been associated with health status,physical fitness and even post-surgical andgeneral morbidity-mortality (1-3). Referencevalues from these important measures, as formost biological variables, should ideally de-rive from a randomly selected, geographi-cally related population in an attempt toimprove both accuracy and predictive this, the interpretation of the testresults could be hampered and prone to mis-interpretation (4). To the best of our knowl-edge, however, there is no published sourceof Reference values for such variables whichhave been obtained from a sample of thegeneral population of Brazil. Therefore, thepurpose of this prospective study was toestablish a set of predictive equations forMIP, MEP and MVV for a randomizedsample of urban adult Brazilians.

5 In additionto the typical demographic and anthropo-metric variables, this study evaluated therelationship of physical fitness (aerobicpower and the level of regular physical activ-ity) with these indexes of respiratory and MethodsStudy design and subjectsThe exclusion criteria and the ethnic,demographic, anthropometric, spirometricand regular physical activity profile of thepopulation evaluated was previously de-scribed in detail (5).ProtocolThe subjects were submitted to the de-signed protocol in the morning of the sameday, and at least 3 h after the last meal and 12h after significant exertion, following thissequence: a) complete clinical, hematologicand cardiorespiratory evaluation at rest; b)evaluation of the regular physical activitypattern by a questionnaire (6); c) determina-tion of MIP and MEP and MVV; d) spirom-etry and static lung volume measurements;e) determination of the lung diffusion capac-ity for carbon monoxide (see Ref.

6 7), and f)cardiopulmonary exercise tests on a cycleergometer (a square-wave protocol at 25 Wfor subject familiarization and, after 1 h, amaximal ramp-incremental exercise test). Ona different day, g) total and regional bodycomposition was evaluated by dual energyX-ray absorptiometry (DEXA) and h) kneestrength measured by isokinetic dynamom-etry. A detailed description of the techniquescited in items a, b, d, f, g and h was previ-ously given (5).Before the tests , the procedures, includ-ing the known risks, were described in de-tail, and written informed consent (as ap-proved by the Institutional Medical EthicsCommittee) was obtained from all subjects did not receive voluntary ventilationMVV is the largest volume that can bebreathed into and out of the lungs during a10-15-s interval with Maximal voluntary ef-fort. In this study, the subjects wore noseclips and breathed deeply (with a volumegreater than the tidal volume but lower thanthe vital capacity) and rapidly for a 15-sinterval with flow measured by a Fleisch pneumotachograph.

7 After discarding thefirst three to five breaths, the subjects wereactively encouraged to maintain the samevolume and frequency by following an on-line display of the maneuver on a computerscreen, , the end-expiratory level remainedrelatively constant (1). At least two accept-able maneuvers (with no more than a 10%difference between them) were obtained and,721 Braz J Med Biol Res 32(6) 1999 Muscle respiratory strength in healthy subjectsafter flow integration, the highest value wasrecorded by extrapolating the 15-s accumu-lated volume to 1-min (l/min, body tempera-ture, ambient pressure, saturated with watervapor - BTPS). Maximal respiratory pressuresMaximal inspiratory pressure followedby Maximal expiratory pressure was obtainedfrom residual volume and total lung capac-ity, with the subjects seated wearing noseclips and with a rigid, plastic flanged mouth-piece in place. The subjects were connectedto a manual shutter apparatus with the maxi-mal pressures measured using a manometer,aneroid-type gauge ( 300 cmH2O)(Imebr s , S o Paulo, SP, Brazil).

8 The trans-ducer output was regularly compared withthat from the Valydine MP45-1 pressuretransducer using the mechanical recordingsystem of a Beckman R-414 polygraph. Asmall leak was introduced between the oc-clusion and the mouth in order to preventglottic closure and in addition the subjectsheld their cheeks with one hand during themaneuver. Inspiratory or expiratory effortwas sustained for at least 1 s. The measure-ments were made by two designated techni-cians who always first explained and dem-onstrated the correct maneuver. The subjectsperformed three to five acceptable and re-producible Maximal maneuvers ( , differ-ences of 10% or less between values ): therecorded value was the highest unless thiswas obtained from the last effort (1,2,4). Aninterval of about 1 min was allowed to elapsebetween analysisThe statistical approach used for dataanalysis (8-10) was also previously describedin detail (5).ResultsDescriptive statistics of the data are shownin Table 1: age-matched males presentedhigher values than females for all of thevariables studied and a significantly nega-tive effect of age was found (P< ) (Figure1).

9 On the other hand, height, weight, leanbody mass and regular level of physical ac-tivity showed a significant positive relation-ship (Table 2). When these variables wereconsidered in a multiple regression analysis,only gender and age continued to have anindependent predictive role for the three de-pendent variables (Table 3). In addition, inTable 1 - Maximal respiratory pressures and voluntary ventilation in males and females by age = Maximal inspiratory pressure; MEP = Maximal expiratory pressure; MVV = Maximal voluntary ventilation. Data are reported as mean SD.+Significant effect among age groups within sex (P< ); 20-29 age group vs 40-49, 60-69 and 70-80 groups. *Significant effect between sexgroups (P< ); males vs females by (years)Males (N = 50)Females (N = 50)MIPMEPMVVMIPMEPMVV(cmH2O)(cmH2O)(l)(c mH2O)(cmH2O)(l) +* +* +* + + + * * * * * * * * * * * * * * J Med Biol Res 32(6) Neder et male group, weight was also a predictorof MIP and height of MVV.

10 The other morecomplex measurements did not continue toshow independent predictive power for MIP,MEP and MVV when these simpler vari-ables were considered in the multiple regres-sion (Table 3).Direct comparison of equations from themost cited previous studies using both Cau-casian (11-13) and non-Caucasian samples(14) showed that they systematically under-estimated the observed values of MIP inboth sexes (P< ; Figure 2). Additionally,after application of the predicted residualsum of squares (PRESS) method to the lin-ear regression equations, we found only amild effect in the R and standard error of theestimate (SEE) original values (RPRESS rang-ing from units below original Rand SEEPRESS values being 3-6% higherthan the original SEE values (data not shown).Interestingly, we found a significant posi-tive linear association between both periph-eral (knee extensor peak torque) and respira-tory muscle strength (MIP, MEP, MVV) andthe physical activity score, independent ofgender or age (Figure 3).)