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The Maximal Expiratory Flow-Volume Curve in Normal Subjects in India
The Maximal Expiratory Flow-Volume Curve in Normal Subjects in India* F. E. Udwadia, M.D., F.C.C.P.;t ]. D. Sunavala, M.D., F.C.C.P.;*
V. M. Shetye, B.Sc.;§ and Praveen K. Jain, M.D.11
Data on pulmonary function, with particular reference to Bow-volumes, were obtained in 760 normal healthy Indians in Bombay, who had never smoked and who had no symptom or history of eardiorespiratory disease. Prediction equations were derived for spirometric parameters and for muimal espintory Bows. 1be muimal expiratory Oow-
volume curves showed considerable intersubject variability. Both Oow and volume decreased with advancing age, with the &ow-volume curve appearing increasingly convex towards the volume uis in its second halfwith increase in age. 1he maximal expiratory Oows in our study were significantly lower compared to values reported by workers in the West.
maximal expiratory flow-volume curve as a test T ofhepulmonary function proposed by Hyatt and
familiar with the instrument and the technique of testing. The
was
associates1 in 1958. The present study is directed towards determining the nature of the maximal expiratory flow-wlume curve and deriving prediction equations from these data in normal Indians in the large congested metropolitan city of Bombay, India. MATERIALS AND METHODS Pulmonary function tests which included maximal expiratory flowvolume curves were obtained and studied at the Breach Candy Hospital in 760 healthy nonsmoken between 15 and 65 years of age. The subjects studied were volunteen (without any type of inducement) who, besides being nonsmoken and riever having smoked in the past, bad no symptom of cardiorespiratory disease as judged from answen to an elaborate questionnaire modelled on the American Thoracic Societys questionnaire. The questionnaire considered symptoms such as cough, production of sputum, hemoptysis, dyspnea, eflOrt tolerance, wheeze, Cewr, nasal allergy, other evidence of atopy, and other features of common respiratory diseases. The answen to all of these questions in relation to abnormal respiratory symptoms were negative in the subjects studied. There was also no history of significant respiratory problems in childhood (eg, asthma, sinusitis, or recurrent chest infection) or at any time in the past The &ndings from a clinical examination (which included an s-ray esaminatiml of the chest in most patients) were perfectly normal in each of the 760 subjects. The subjects included manual worken; clerks; hospital staff; relatives of patients admitted to the hospital; executives of engineering, pharmaceutical, and other companies; and students and teachen from schools, colleges, and the university.
•From Breach Candy Hospital and Research Centre, Bombay, India. tConsultant Physician, Breach Candy Hospital, and Honorary Consultant Physician, J. J. Hospital and P. G. Hospital, Bombay. *Consultant Physician, Intensive Care Unit, Breach Candy Hospital, and Honorary Assistant Physician, P. G. Hospital, Bombay. §Senior 'lechniciaii. UMedical Hegistrar. Manuscript receiwd February 18; revision ~ted November 4.
&print reqtlUfa: Dr. UdwadlO, Breach Candy Hoapltal, Bhulabhai Daal lload, Bombay, India 4000'J6
812
The test was carried out by a trained technician thoroughly
measurements of flow and volume were made in the upright (straight-backed) sitting position with a nose clip obstructing the nares. The subject to be tested was first made thoroughly familiar with the machine and the technique ofthe test The instrument used fur measuring and recording the flow-volume curve was a pulmonary calculator system (Hewlett-Packard 47804 S). This is a computeri7.ed machine with a printer. This system includes a Fleisch-type size No. 3 pneumotachograph and a flow transducer to measure flow which is integrated by computer to volume. The pneumotachograph in the Hewlett-Packard system measures linearized flow rates up to 12.5 Usec, minimizing resistance and nonlinearity when measuring high flows. The system plots a point-to-point flow-volume curve and has no special device to smooth these curves. The computer system obtains the flow-volume curve by the trape7.0idal rule of integration of flow data samples to get volume. The very fint piece of data is taken at the 10-msec interval, and the second right up to the nth data (end ofthe test) were taken at 50-msec intervals. All ofthese data are stored in the memory and plotted by the 98TI printer after the end of the test. Befi>re testing each subject, the pneumotachograph was calibrated fur accuracy using a 1.5-L syringe. The syringe was discharged through the pneumotachograph smoothly and evenly, and the procedure was repeated until a consistent volume of 1.5 L was obtained. The pneumotachograph was then checked at various flow rates. The readings at different flow rates were within ± 3 percent of the recommended limit. The test recording the maximal expiratory flow-volume curve was carried out by asking the patient to take a muimal inspiration fullowecl by a furced maximal expiration through the mouthpiece into the machine; this was again immediately fullowecl by a furced muimal inspiration. The computer system analyzed perfi>rmances to give furced vital capacity (FVC), furced expiratory volume in the first second (FEVJ, peak expiratory flow, (PEF), mean furced expiratory flow during the middle half of the FVC (FEnS-75'1>; muimal midexpiratory flow) and maximal expiratory flow at 50 and 75 percent of the FVC (\Tm~ and Vmu25,.). Three constant readings were obtained, and the single best test which had the largest sum of FVC and FEV1 was selected fur analysis. All parameten reported herein were calculated from this single best test in each study subject. Our method and in particular the instrumentation involwd in our system have been tested fur accuracy and reliability and have been accepted as oonfi>rming to the standards of the American Thoracic Society.• MEFV Cl.IW In Normal SUbjedll In Inda (Udwadla et el)
4
}
FEV1 ~-----·-··--...
-- ---~-
FVC
~
I
2
•-;E~t- :._
-------
-~
•----
MALE
-------...}FtllALE
--·-··•--·--·-·•
area. These indices or variables did not contribute further when compared to the standard indices of age and height The results of our analysis of FVC and FEV1 are given in Tu.hie l, from which prediction equations may be obtained in the fullowing manner: y = C +(age in
years x age coefficient)+ (standing height in cm X height coefficient).
FEV/FVC and Expiratory Flow Rates
0o
t5-19
20-19 50-39 AIE (YEARS)
40-49
I0-59
FIGURE 1. Changes in mean FVC and FEV1 with age in normal male and female subjects.
REsuCTS
FVC andFEVi We used the best of three consecutive tests to analyze our data. It was observed that the FVC and FEV1 increased with age up to 30 years in both men and women and then decreased with increasing age. The age-related changes of FVC and FEV1 are depicted in Figure 1 fur male and female subjects in the normal populations. On the basis of this observation, separate prediction equations were derived fur male and female subjects below 30 years of age and above 30 years of age, incorporating age and height as independent variables. We did not observe any advantage in an analysis using five-year or ten-year groups in both male and female subjects as compared to the previously specified composite analysis. Multiple regression and co~ relation analyses were perfurmed on each parameter (FVC; FEVJ fur the fuur age-sex groups previously described, using height, weight, and body surface
The FEV/FVC, the PEF, the FEF2.5-75%, the Vmax50%, and the Vmax75%, each showed a consistent decline with increasing age. An analysis of each of these values together with prediction equations (using age and height as independent variables) for all age groups in male and female subjects are presented in Tu.hie 2.
Maximal Expiratory Flow-Volume Curves Mean absolute values of maximal flow at 25 percent, 50 percent, and 75 percent of the FVC were used to plot maximal expiratory flow-volume curves fur each sex according to the age group. Mean maximal expiratory flow-volume curves were constructed fur male and female subjects between 15and19 years of age and fur each decade between 20 and 60 years. Since there were only seven subjects between 60 and 65 years, they were not included in this analysis (Fig 2). The variability of our data around the calculated regression lines is indicated by the column labelled Sy.x in Tu.hies 1 and 2. These values cannot be totally relied upon to give the range of"normal" subjects at all ages and at all heights, particularly fur Vmax. We have circumvented the difficulty of dealing with occasional "below normal" distribution of data in some subjects by determining in all age groups (male and female) the percentage of predicted values above which 95 percent of the "normal" subjects fall. These values were then
Table 1-Analyaia tfFVC and FEV, in 760 Normal Subjecta and Predicted Value.* Coefficient Group and Data
n
Male subjects<30 yr FEV1 162 FVC 162 Male subjects;;i.30 yr FEV1 310 FVC 310 Female suhjects<30 yr FEV1 147 FVC 147 Female subjects;;i.30 yr FEV1 141 FVC 141
Mean
SD
a•
c
Age (yr)
Height (cm)
Sy.x
3.064 3.681
0.495 0.664
0.371 0.422
-3.266 -6.058
-0.010 0.019
0.039 0.055
0.392 0.505
2.603 3.296
0.452 0.601
0.473 0.409
-2.650 -4.832
-0.022 -0.018
0.037 0.054
0.328 0.462
2.184 2.580
0.373 0.418
0.166 0.187
-1.424 -2.284
-0.011 0.006
0.025 0.030
0.341 0.377
1.923 2.394
0.389 0.444
0.367 0.412
-2.580 -3.755
-0.012 -0.010
0.032 0.043
0.309 0.341
•R1, Coefficient of determination; C, constant in regression equation; and Sy.x, standard deviation around regression line. CHEST I 89 I 8 I JUNE, 11188
853
Table 2-Analyaia and Prediction Equationa for AU Age Groups* Coefficient Group and Data Male subjects FEV{FVC'JJ PEF FEF25-75'JJ Vmax.5()'JJ Vmu:75'JJ Female subjects FEV{FVC'JJ PEF FEF25-75'JJ Vmax.5()'JJ Vmu:75'JJ
n
Mean
SD
RI
c
Age (yr)
Height (cm)
Sy.x
472 472 472 472 472
80.93 7.26 3.00 3.63 1.38
8.3258 1.4570 0.9963 1.1353 0.6841
0.1355 0.1967 0.2592 0.1720 0.2974
119.3640 -6.2083 1.6108 1.7383 1.0402
-0.2457 -0.0187 -0.0407 -0.0365 -0.0301
-0.1756 0.08.50 0.0173 0.0195 0.0088
7.7411 1.3059 00.8575 1.0331 0.5734
288 288 288 288 288
82.61 4.95 2.56 3.05 1.30
11.2569 1.0305 0.8052 0.8812 0.6348
0.0449 0.0882 0.2762 0.1793 0.2853
94.8867 -2.7154 -0.1399 -0.2704 0.5012
-0.2146 -0.0018 -0.0336 -0.0279 -0.0288
-0.0334 0.0497 0.0245 0.0272 0.0113
11.0011 0.9840 0.6850 0.7983 0.5367
*R'. Coefficient of determination; C, constant in regression equation; and Sy.x, standard deviation around regression line.
the lower limit of normal, so that 5 percent of the total studied group of nonsymptomatic clinically normal subjects would be considered as falling below the "normal range." This lower 5-percentile value is the same as the mean less 1. 98 SD (1able 3). DISCUSSION
Our prediction equations for Vmax50% and Vmax75% fill a serious lacuna in an important aspect of ventilatory functions in Indians, since a similar large study (with a direct recording offl.ow-volume loops) has not been reported as yet &om India. We have three major points of observation in relation to our maximal expiratory flow-volume curves. lnteraulJject Variability
A significant variability in Vmax was observed in our healthy nonsmoking Indian subjects. This variability has also been found in Western studies and has been discussed at length by Knudson et al, 3 and by Cherniack and Raber. 4 Our study, like the studies of Green et al, 11 Black et al,' and Knudson et al, 3 failed to improve intersubject variability when flows were corrected to pulmonary size.
Maximal Expiratory Flow-Volume Curoes and Age It was observed that (a) flow and volume decrease with increasing age (Fig 2) and (b) the maximal expiratory flow-volume curves appear increasingly convex towards the volume axis in the second half of the curve (Fig 2). Green et al11 noted a similar increased convexity to the volume axis of the latter half of the maximal expiratory flow-volume curve with age in adults to 55 years ofage. Age-related changes observed in the maximal expiratory flow-volume curves could well be related to loss of elastic recoil in the lungs with advancing age. In fact, a loss of elastic recoil with increasing age has been demonstrated by Turner et al. 7
Maximal Expiratory Flow-Volume Curoes in Indians A striking feature of the maximal expiratory flowvolume curves in our study of healthy Indian subjects is low values of Vmax50% and Vmax75% compared to values reported by many workers in the West. Thus, our Vmax readings in all age groups in both male and female subjects are much lower (p<0.01) than those reported by Knudson et al3 and by Cherniack and Raber. 4 The readings are also low in most age groups (p<0.01 to p<0.05) when compared to values given by Black et al, 8 Bass, 8 Schoenberg et al, 9 and Knudson et al. 10 Values for Vmax75% in black female subjects as reported by Schoenberg et al, 9 form important exceptions, in that these values are not significantly higher compared to those in Indian female subjects. A comparison of linear regression equations for Vmax in our study with linear regression equations in the comprehensive Western study of Knudson et al10 shows that the coefficient for height (age and height being the two variables frequently used in prediction equations) is significantly greater in the Western study. 10 Thus, height influences prediction equations to a greater extent in Western subjects compared to Indian subjects. As an illustrative example, the age and height coefficients for Vmax50% in the recent study of Knudson et al10 for men aged 25 years and older are - 0.0368 and + 0.0684, respectively, compared to our values of - 0. 036l5 and + 0. 0195. Knudson et al10 found Table 3-Normal Bonge
n
Lower 95th Percentile
472 472
>64.5 >56.8
288 288
>71.9 >58.2
MEFV CuMt In Normal Subjects In India (Udwtldla et Ill)
'f·r · · · · · · . .
·r ·\·. . ,.r. . .·. i·r . . . . . . .. . . . . . ,
..
'I\
·r · ·-,. .
'L ·. ·-. ,,_
I
I
0
0
t--IL-~
'•,
~·~·~~.
.......
FDaE
MALE
'j
'r · . .
tll-11
••22
'r · · ·. . . ..
'f
•
·.
····....
..
I~f ··.. j "···.··.......
·r1 o
·-·-.. .. . . .,
.____,_____,.....::::.___.
t
I
--IL-.1
I
4
FIGURE 2. Mean maximal expiratory flow-volume curves in normal male and female subjects in various age groups. Flow is absolute flow in liters per second. Volume is mean FVC for each sex-age group, expressed as volume expired from total lung capacity. Data points on center curve in each age group represent mean flow at peak flow and 25, 50, and 75 percent of actual expired FVC. Limits shown for each curve constitute 90 percent of data between 5th and 95th percentiles.
that age and height coefficients fur Vmax75% in men aged 25 years and older were -0.0230 and +0.0310, respectively, compared to our values of -0.012 and +0.0085. We also observed that the prediction power of the regression equations is consistently higher in the study of Knudson et al. 10 Unquestionably, other factors besides age and height signi&cantly influence Vmax in our study, and it would be important to determine what these factors are and why our values are lower than those reported in Western studies.
The lower Vmax in healthy Indians could theoretically be related either to a decrease in elastic recoil or to an increase in airway resistance during furced expiration. There are no data on either of these values in normal Indians. An increase in airway resistance could conceivably b'e related to a genetically determined smaller intrinsic size of the airways in Indians or to other factors governing distensibility of the airways, particularly airway compliance, bronchomotor tone, and transbronchial pressure difference. A possible CHEST I 89 I 6 I JUNE, 1966
&
increase in "collapsibility" of the smaller airways during the furced expiratory maneuver in Indians may al$o be an important factor in producing lower Vmax vis-a-vis Western subjects. Finally, the role of pollution in Bombay in the production of silent disease of the small airways (and therefure lower Vmax) also needs to be considered. Studies of maximal expiratory flow-volume curves from other parts of India and from lµ'eas in the country which are comparatively unpolluted would unquestionably be helpful in a more clear assessment of Indian values.
4
5 6
7 8
REFERENCES 1 Hyatt RE, Schilder DP, Fry DL. Relationship between maximum expiratory Bow and degree of lung inflation. J Appl Physiol 1958; 13:331-36 2 Gardner RM, Hanlcinson JL, West BJ. Evaluating commercially available spirometers. Am Rev Respir Dis 1980; 121:73-82 3 Knudson RJ, Slatin RC, Lebowitz MD, Burrows B. The maximal
9
10
expiratory flow volume curve. Am Rev Respir Dis 1976; 113:587-600 Cherniaclc RM, Raber MB. Normal standards fur ventilatory function usiJJg an automated wedge spirometer. Am Rev Respir Dis 1972; 106:38-46 Green M, Mead J, Turner JM. Variability of maximum "'1>iratory Bow volume curves. J Appl Physiol 1974; 37:67-74 Black LF, Offord K, Hyatt RE. Variability in the maximal expiratory Bow volume curve in asymptomatic smokers and nonsmokers. Am Rev Respir Dis 1974; 110:282-92 Turner JM, Mead J, Wohl ME. Jl:lasticity of human lungs in relation to age. J Appl Physiol 1968; 25:664-71 Bass H. The Bow volume loop: normal standard and abnormalities in chronic obstructive pulmonary disease. Chest 1973; 63:171-76 Schoenberg JB, Beck GJ, Bouhuys A. Growth and decay of pulmonary function in healthy blacks and whites. Respir Physiol . 1978; 33:367-93 Knudson RJ, Lebowitz MD, Holberg CJ, Burrows B. Changes in the normal maximal expiratory Bow volume curve with growth and aging. Am Rev Respir Dis 1983; 127:725-34
34th Annual James J. Waring Chest Conference The Colorado 'Ihldeau Society will present this 34th annual conference in Estes Park, August 28-30. For intOrmation, contact Ms. Shirley Lindquist, Colorado 'Ihldeau Society, PO Box 921, Loveland 80539 (303:667-5198).
-
MEFV Curw In Normal Subjects In India (UdwrJdla at al)
V. M. Shetye, B.Sc.;§ and Praveen K. Jain, M.D.11
Data on pulmonary function, with particular reference to Bow-volumes, were obtained in 760 normal healthy Indians in Bombay, who had never smoked and who had no symptom or history of eardiorespiratory disease. Prediction equations were derived for spirometric parameters and for muimal espintory Bows. 1be muimal expiratory Oow-
volume curves showed considerable intersubject variability. Both Oow and volume decreased with advancing age, with the &ow-volume curve appearing increasingly convex towards the volume uis in its second halfwith increase in age. 1he maximal expiratory Oows in our study were significantly lower compared to values reported by workers in the West.
maximal expiratory flow-volume curve as a test T ofhepulmonary function proposed by Hyatt and
familiar with the instrument and the technique of testing. The
was
associates1 in 1958. The present study is directed towards determining the nature of the maximal expiratory flow-wlume curve and deriving prediction equations from these data in normal Indians in the large congested metropolitan city of Bombay, India. MATERIALS AND METHODS Pulmonary function tests which included maximal expiratory flowvolume curves were obtained and studied at the Breach Candy Hospital in 760 healthy nonsmoken between 15 and 65 years of age. The subjects studied were volunteen (without any type of inducement) who, besides being nonsmoken and riever having smoked in the past, bad no symptom of cardiorespiratory disease as judged from answen to an elaborate questionnaire modelled on the American Thoracic Societys questionnaire. The questionnaire considered symptoms such as cough, production of sputum, hemoptysis, dyspnea, eflOrt tolerance, wheeze, Cewr, nasal allergy, other evidence of atopy, and other features of common respiratory diseases. The answen to all of these questions in relation to abnormal respiratory symptoms were negative in the subjects studied. There was also no history of significant respiratory problems in childhood (eg, asthma, sinusitis, or recurrent chest infection) or at any time in the past The &ndings from a clinical examination (which included an s-ray esaminatiml of the chest in most patients) were perfectly normal in each of the 760 subjects. The subjects included manual worken; clerks; hospital staff; relatives of patients admitted to the hospital; executives of engineering, pharmaceutical, and other companies; and students and teachen from schools, colleges, and the university.
•From Breach Candy Hospital and Research Centre, Bombay, India. tConsultant Physician, Breach Candy Hospital, and Honorary Consultant Physician, J. J. Hospital and P. G. Hospital, Bombay. *Consultant Physician, Intensive Care Unit, Breach Candy Hospital, and Honorary Assistant Physician, P. G. Hospital, Bombay. §Senior 'lechniciaii. UMedical Hegistrar. Manuscript receiwd February 18; revision ~ted November 4.
&print reqtlUfa: Dr. UdwadlO, Breach Candy Hoapltal, Bhulabhai Daal lload, Bombay, India 4000'J6
812
The test was carried out by a trained technician thoroughly
measurements of flow and volume were made in the upright (straight-backed) sitting position with a nose clip obstructing the nares. The subject to be tested was first made thoroughly familiar with the machine and the technique ofthe test The instrument used fur measuring and recording the flow-volume curve was a pulmonary calculator system (Hewlett-Packard 47804 S). This is a computeri7.ed machine with a printer. This system includes a Fleisch-type size No. 3 pneumotachograph and a flow transducer to measure flow which is integrated by computer to volume. The pneumotachograph in the Hewlett-Packard system measures linearized flow rates up to 12.5 Usec, minimizing resistance and nonlinearity when measuring high flows. The system plots a point-to-point flow-volume curve and has no special device to smooth these curves. The computer system obtains the flow-volume curve by the trape7.0idal rule of integration of flow data samples to get volume. The very fint piece of data is taken at the 10-msec interval, and the second right up to the nth data (end ofthe test) were taken at 50-msec intervals. All ofthese data are stored in the memory and plotted by the 98TI printer after the end of the test. Befi>re testing each subject, the pneumotachograph was calibrated fur accuracy using a 1.5-L syringe. The syringe was discharged through the pneumotachograph smoothly and evenly, and the procedure was repeated until a consistent volume of 1.5 L was obtained. The pneumotachograph was then checked at various flow rates. The readings at different flow rates were within ± 3 percent of the recommended limit. The test recording the maximal expiratory flow-volume curve was carried out by asking the patient to take a muimal inspiration fullowecl by a furced maximal expiration through the mouthpiece into the machine; this was again immediately fullowecl by a furced muimal inspiration. The computer system analyzed perfi>rmances to give furced vital capacity (FVC), furced expiratory volume in the first second (FEVJ, peak expiratory flow, (PEF), mean furced expiratory flow during the middle half of the FVC (FEnS-75'1>; muimal midexpiratory flow) and maximal expiratory flow at 50 and 75 percent of the FVC (\Tm~ and Vmu25,.). Three constant readings were obtained, and the single best test which had the largest sum of FVC and FEV1 was selected fur analysis. All parameten reported herein were calculated from this single best test in each study subject. Our method and in particular the instrumentation involwd in our system have been tested fur accuracy and reliability and have been accepted as oonfi>rming to the standards of the American Thoracic Society.• MEFV Cl.IW In Normal SUbjedll In Inda (Udwadla et el)
4
}
FEV1 ~-----·-··--...
-- ---~-
FVC
~
I
2
•-;E~t- :._
-------
-~
•----
MALE
-------...}FtllALE
--·-··•--·--·-·•
area. These indices or variables did not contribute further when compared to the standard indices of age and height The results of our analysis of FVC and FEV1 are given in Tu.hie l, from which prediction equations may be obtained in the fullowing manner: y = C +(age in
years x age coefficient)+ (standing height in cm X height coefficient).
FEV/FVC and Expiratory Flow Rates
0o
t5-19
20-19 50-39 AIE (YEARS)
40-49
I0-59
FIGURE 1. Changes in mean FVC and FEV1 with age in normal male and female subjects.
REsuCTS
FVC andFEVi We used the best of three consecutive tests to analyze our data. It was observed that the FVC and FEV1 increased with age up to 30 years in both men and women and then decreased with increasing age. The age-related changes of FVC and FEV1 are depicted in Figure 1 fur male and female subjects in the normal populations. On the basis of this observation, separate prediction equations were derived fur male and female subjects below 30 years of age and above 30 years of age, incorporating age and height as independent variables. We did not observe any advantage in an analysis using five-year or ten-year groups in both male and female subjects as compared to the previously specified composite analysis. Multiple regression and co~ relation analyses were perfurmed on each parameter (FVC; FEVJ fur the fuur age-sex groups previously described, using height, weight, and body surface
The FEV/FVC, the PEF, the FEF2.5-75%, the Vmax50%, and the Vmax75%, each showed a consistent decline with increasing age. An analysis of each of these values together with prediction equations (using age and height as independent variables) for all age groups in male and female subjects are presented in Tu.hie 2.
Maximal Expiratory Flow-Volume Curves Mean absolute values of maximal flow at 25 percent, 50 percent, and 75 percent of the FVC were used to plot maximal expiratory flow-volume curves fur each sex according to the age group. Mean maximal expiratory flow-volume curves were constructed fur male and female subjects between 15and19 years of age and fur each decade between 20 and 60 years. Since there were only seven subjects between 60 and 65 years, they were not included in this analysis (Fig 2). The variability of our data around the calculated regression lines is indicated by the column labelled Sy.x in Tu.hies 1 and 2. These values cannot be totally relied upon to give the range of"normal" subjects at all ages and at all heights, particularly fur Vmax. We have circumvented the difficulty of dealing with occasional "below normal" distribution of data in some subjects by determining in all age groups (male and female) the percentage of predicted values above which 95 percent of the "normal" subjects fall. These values were then
Table 1-Analyaia tfFVC and FEV, in 760 Normal Subjecta and Predicted Value.* Coefficient Group and Data
n
Male subjects<30 yr FEV1 162 FVC 162 Male subjects;;i.30 yr FEV1 310 FVC 310 Female suhjects<30 yr FEV1 147 FVC 147 Female subjects;;i.30 yr FEV1 141 FVC 141
Mean
SD
a•
c
Age (yr)
Height (cm)
Sy.x
3.064 3.681
0.495 0.664
0.371 0.422
-3.266 -6.058
-0.010 0.019
0.039 0.055
0.392 0.505
2.603 3.296
0.452 0.601
0.473 0.409
-2.650 -4.832
-0.022 -0.018
0.037 0.054
0.328 0.462
2.184 2.580
0.373 0.418
0.166 0.187
-1.424 -2.284
-0.011 0.006
0.025 0.030
0.341 0.377
1.923 2.394
0.389 0.444
0.367 0.412
-2.580 -3.755
-0.012 -0.010
0.032 0.043
0.309 0.341
•R1, Coefficient of determination; C, constant in regression equation; and Sy.x, standard deviation around regression line. CHEST I 89 I 8 I JUNE, 11188
853
Table 2-Analyaia and Prediction Equationa for AU Age Groups* Coefficient Group and Data Male subjects FEV{FVC'JJ PEF FEF25-75'JJ Vmax.5()'JJ Vmu:75'JJ Female subjects FEV{FVC'JJ PEF FEF25-75'JJ Vmax.5()'JJ Vmu:75'JJ
n
Mean
SD
RI
c
Age (yr)
Height (cm)
Sy.x
472 472 472 472 472
80.93 7.26 3.00 3.63 1.38
8.3258 1.4570 0.9963 1.1353 0.6841
0.1355 0.1967 0.2592 0.1720 0.2974
119.3640 -6.2083 1.6108 1.7383 1.0402
-0.2457 -0.0187 -0.0407 -0.0365 -0.0301
-0.1756 0.08.50 0.0173 0.0195 0.0088
7.7411 1.3059 00.8575 1.0331 0.5734
288 288 288 288 288
82.61 4.95 2.56 3.05 1.30
11.2569 1.0305 0.8052 0.8812 0.6348
0.0449 0.0882 0.2762 0.1793 0.2853
94.8867 -2.7154 -0.1399 -0.2704 0.5012
-0.2146 -0.0018 -0.0336 -0.0279 -0.0288
-0.0334 0.0497 0.0245 0.0272 0.0113
11.0011 0.9840 0.6850 0.7983 0.5367
*R'. Coefficient of determination; C, constant in regression equation; and Sy.x, standard deviation around regression line.
the lower limit of normal, so that 5 percent of the total studied group of nonsymptomatic clinically normal subjects would be considered as falling below the "normal range." This lower 5-percentile value is the same as the mean less 1. 98 SD (1able 3). DISCUSSION
Our prediction equations for Vmax50% and Vmax75% fill a serious lacuna in an important aspect of ventilatory functions in Indians, since a similar large study (with a direct recording offl.ow-volume loops) has not been reported as yet &om India. We have three major points of observation in relation to our maximal expiratory flow-volume curves. lnteraulJject Variability
A significant variability in Vmax was observed in our healthy nonsmoking Indian subjects. This variability has also been found in Western studies and has been discussed at length by Knudson et al, 3 and by Cherniack and Raber. 4 Our study, like the studies of Green et al, 11 Black et al,' and Knudson et al, 3 failed to improve intersubject variability when flows were corrected to pulmonary size.
Maximal Expiratory Flow-Volume Curoes and Age It was observed that (a) flow and volume decrease with increasing age (Fig 2) and (b) the maximal expiratory flow-volume curves appear increasingly convex towards the volume axis in the second half of the curve (Fig 2). Green et al11 noted a similar increased convexity to the volume axis of the latter half of the maximal expiratory flow-volume curve with age in adults to 55 years ofage. Age-related changes observed in the maximal expiratory flow-volume curves could well be related to loss of elastic recoil in the lungs with advancing age. In fact, a loss of elastic recoil with increasing age has been demonstrated by Turner et al. 7
Maximal Expiratory Flow-Volume Curoes in Indians A striking feature of the maximal expiratory flowvolume curves in our study of healthy Indian subjects is low values of Vmax50% and Vmax75% compared to values reported by many workers in the West. Thus, our Vmax readings in all age groups in both male and female subjects are much lower (p<0.01) than those reported by Knudson et al3 and by Cherniack and Raber. 4 The readings are also low in most age groups (p<0.01 to p<0.05) when compared to values given by Black et al, 8 Bass, 8 Schoenberg et al, 9 and Knudson et al. 10 Values for Vmax75% in black female subjects as reported by Schoenberg et al, 9 form important exceptions, in that these values are not significantly higher compared to those in Indian female subjects. A comparison of linear regression equations for Vmax in our study with linear regression equations in the comprehensive Western study of Knudson et al10 shows that the coefficient for height (age and height being the two variables frequently used in prediction equations) is significantly greater in the Western study. 10 Thus, height influences prediction equations to a greater extent in Western subjects compared to Indian subjects. As an illustrative example, the age and height coefficients for Vmax50% in the recent study of Knudson et al10 for men aged 25 years and older are - 0.0368 and + 0.0684, respectively, compared to our values of - 0. 036l5 and + 0. 0195. Knudson et al10 found Table 3-Normal Bonge
n
Lower 95th Percentile
472 472
>64.5 >56.8
288 288
>71.9 >58.2
MEFV CuMt In Normal Subjects In India (Udwtldla et Ill)
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FIGURE 2. Mean maximal expiratory flow-volume curves in normal male and female subjects in various age groups. Flow is absolute flow in liters per second. Volume is mean FVC for each sex-age group, expressed as volume expired from total lung capacity. Data points on center curve in each age group represent mean flow at peak flow and 25, 50, and 75 percent of actual expired FVC. Limits shown for each curve constitute 90 percent of data between 5th and 95th percentiles.
that age and height coefficients fur Vmax75% in men aged 25 years and older were -0.0230 and +0.0310, respectively, compared to our values of -0.012 and +0.0085. We also observed that the prediction power of the regression equations is consistently higher in the study of Knudson et al. 10 Unquestionably, other factors besides age and height signi&cantly influence Vmax in our study, and it would be important to determine what these factors are and why our values are lower than those reported in Western studies.
The lower Vmax in healthy Indians could theoretically be related either to a decrease in elastic recoil or to an increase in airway resistance during furced expiration. There are no data on either of these values in normal Indians. An increase in airway resistance could conceivably b'e related to a genetically determined smaller intrinsic size of the airways in Indians or to other factors governing distensibility of the airways, particularly airway compliance, bronchomotor tone, and transbronchial pressure difference. A possible CHEST I 89 I 6 I JUNE, 1966
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increase in "collapsibility" of the smaller airways during the furced expiratory maneuver in Indians may al$o be an important factor in producing lower Vmax vis-a-vis Western subjects. Finally, the role of pollution in Bombay in the production of silent disease of the small airways (and therefure lower Vmax) also needs to be considered. Studies of maximal expiratory flow-volume curves from other parts of India and from lµ'eas in the country which are comparatively unpolluted would unquestionably be helpful in a more clear assessment of Indian values.
4
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REFERENCES 1 Hyatt RE, Schilder DP, Fry DL. Relationship between maximum expiratory Bow and degree of lung inflation. J Appl Physiol 1958; 13:331-36 2 Gardner RM, Hanlcinson JL, West BJ. Evaluating commercially available spirometers. Am Rev Respir Dis 1980; 121:73-82 3 Knudson RJ, Slatin RC, Lebowitz MD, Burrows B. The maximal
9
10
expiratory flow volume curve. Am Rev Respir Dis 1976; 113:587-600 Cherniaclc RM, Raber MB. Normal standards fur ventilatory function usiJJg an automated wedge spirometer. Am Rev Respir Dis 1972; 106:38-46 Green M, Mead J, Turner JM. Variability of maximum "'1>iratory Bow volume curves. J Appl Physiol 1974; 37:67-74 Black LF, Offord K, Hyatt RE. Variability in the maximal expiratory Bow volume curve in asymptomatic smokers and nonsmokers. Am Rev Respir Dis 1974; 110:282-92 Turner JM, Mead J, Wohl ME. Jl:lasticity of human lungs in relation to age. J Appl Physiol 1968; 25:664-71 Bass H. The Bow volume loop: normal standard and abnormalities in chronic obstructive pulmonary disease. Chest 1973; 63:171-76 Schoenberg JB, Beck GJ, Bouhuys A. Growth and decay of pulmonary function in healthy blacks and whites. Respir Physiol . 1978; 33:367-93 Knudson RJ, Lebowitz MD, Holberg CJ, Burrows B. Changes in the normal maximal expiratory Bow volume curve with growth and aging. Am Rev Respir Dis 1983; 127:725-34
34th Annual James J. Waring Chest Conference The Colorado 'Ihldeau Society will present this 34th annual conference in Estes Park, August 28-30. For intOrmation, contact Ms. Shirley Lindquist, Colorado 'Ihldeau Society, PO Box 921, Loveland 80539 (303:667-5198).
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MEFV Curw In Normal Subjects In India (UdwrJdla at al)