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Variability and reversibility of the slow and forced vital capacity in chronic airflow obstruction
Br. J. Dis. Chest (1987) 81, 182
VARIABILITY AND REVERSIBILITY OF THE SLOW AND FORCED VITAL CAPACITY IN CHRONIC AIRFLOW OBSTRUCTION R. I. GOVE*, J. SHEPHERD AND P. S. BURGE Department of Thoracic Medicine, East Birmingham Hospital, Birmingham B9 ST
Summary
The variability of the forced (FVC) and slow vital capacity (SVC) manoeuvres were compared in 33 adult patients with chronic airflow obstruction. The reversibility of the two manoeuvres to nebulized salbutamol were compared in 18 of the patients. Both manoeuvres had equally small variances both before and after bronchodilator. The degree of reversibility of the FVC was however significantly greater (P
GOVE,
SHEPHERD,
BURGE:
CHRONIC
AIRFLOW
OBSTRUCTION
183
obtained from 33 patients (six female) with a mean age (years+sn) of 57+14. All except two were current or ex-smokers (mean pack year&so, 35f17) and all had a history of more than 5 years’ symptoms of CAO. Both PVC and SVC were measured on a dry bellows spirometer (Vitalograph) with the patient standing and wearing a nose-clip. The patients rested for 20 minutes between the two VC manoeuvres. Five blows were performed by each method, and the first two of each discarded. The next three blows which were within 10% of each other after 5 secondswere used for analysis. All blows followed a maximum inspiration and patients were actively encouraged to continue the expiratory manoeuvre for as long as possible. Patients were left to recover as long as they felt was necessary in between blows. Eighteen patients repeated the procedure 15 minutes after receiving 5 mg of nebulized salbutamol in 2 ml physiological saline administered from an Inspiron Mini nebulizer. The PVC was always performed before the SVC and all patients had abstained from using their usual bronchodilator aerosols for 8 hours before coming to the laboratory. All patients attended the laboratory for a second visit when their lung volumes were measured by a 20 minute helium dilution test and their transfer factor measured by single breath carbon monoxide uptake. The total variance was calculated from the total sum of squares divided by (n- l)N, where n=the number of observations, and N the number of patients. The reversibility data were analysed by comparing the change shown in the two measurements using a paired t-test. The correlations between the subdivisions of lung volume and the individual variances were calculated by Kendall’s rank correlation.
RESULTS The mean pre- and post-bronchodilator FVC and SVC values are given in Table I. The other mean physiological variables given as a percentage of the predicted value (*SD) are FEV, 47.6220.5, residual volume (RV) 179.9k29.4, total lung capacity (TLC) 123.2f17.8, transfer factor corrected for lung volumes (Kco) 69.2f33.5. The baseline variances for FVC and SVC were very similar (Table II). Although the post-bronchodilator SVC variance (0.0264) was less than the FVC variance (0.0344) the Table I. Mean values for PVC and SVC at the baseline (n=33) and
before and after salbutamol in 18 patients
Baseline (litres) Prebronchodilator Post-bronchodilator (litres)
WC
svc
2.97 (f0.88) 3.00 (f0.85) 3.50 (k0.92)
3.38 (f0.88) 3.40 (20.89) 3.70 (20.91)
The figures in parentheses represent one standard deviation. Table ZZ. Variance for PVC and SVC and resulting F-value at
baseline (n=33) and after nebulized salbutamol in 18 patients
Baseline variance Post-bronchodilator variance
WC
svc
F-value
0.0276
0.0274
1.005
0.0344
0.0264
1.3
The F-values are not significant.
184
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J. DIS.
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81 NO.
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difference was again not significant (Table II). The mean of the individuals’ SVC was greater than the corresponding FVC in all except two patients (SVC-FVC (litres), median and range: 0.31, -0.07 to 1.43). Reversibility was significantly (P< 0.05) greater in FVC than SVC (see Table I) and as a result the SVC-FVC difference decreased in these 18 patients (SVC-FVC (litres) median and range: 0.33, -0.07 to 1.43 prebronchodilator; 0.06, -0.18 to 0.88 postbronchodilator). No correlation between the variance of either technique or the difference between FVC and SVC and any other parameter of lung function measured (FEV,, RV, TLC, Kco) was demonstrated. DISCUSSION Both FVC and SVC are equally reproducible measurements of the VC. Patients who were variable in one measurement tended to be equally variable in the other. The selection of blows that were within 10% of each other at 5 seconds would minimize the variability, but this is standard practice in the laboratory where the tests were conducted. In most patients all blows are within 10% of each other at this point. The reasons for the difference in FVC and SVC in CA0 probably relate to the degree of lung destruction. Loss of supporting tissue to the small airways may result in more pressure dependent collapse during a forced manoeuvre. The significantly greater degree of FVC reversibility may support this suggestion, since dilation of the small airways would minimize pressure dependent collapse and have the effect of moving the theoretical ‘equal pressure point’ (3) proximally into larger airways. The lack of any correlation between the variance of either technique or the SVC-FVC difference and any other physiological parameter suggest that neither technique is influenced by increasing airflow obstruction or a falling Kco. Reversibility was significantly more marked in FVC and if 15% is taken as being indicative of a ‘significant’ response to bronchodilators this would have been missed in eight patients (44%) using SVC alone. There is evidence that an increased FVC correlates better with improved exercise performance than FEV, (4) and that bronchodilatation can cause improvements in FVC without changes in flow (5, 6). Failure to measure the reversibility of FVC as well as FEV, may therefore result in a patient being incorrectly labelled as unresponsive to bronchodilators. FVC and SVC are thus equally reproducible parameters in the assessment of CAO, although they are not the same measurement. If reversibility is to be measured, however, the FVC is likely to show a greater response and this may be clinically relevant. For the routine assessment of pulmonary function in CAO, should reversibility measurements be desired, measurement of the FVC alone rather than both parameters would be simpler. Technicians should be aware, however, of the importance of true SVC manoeuvres during the measurement of lung volumes in order not to overestimate RV. REFERENCES 1. Hyatt RE. Dynamic lung volumes. In: Fenn DO, Rahn H, eds. Handbook Washington: American Physiological Society, 1965:1394.
of physiology.
GOVE,
SHEPHERD,
BURGE:
CHRONIC
AIRFLOW
OBSTRUCTION
185
2. Bubis MJ, Sigurdson RN, McCarthy DS, Anthonisen NR. Differences between slow and fast vital capacities in patients with obstructive disease. Chest 1980;77:626-31. 3. Mead J, Turner JM, Macklem PT, Little JB. Significance of the relationship between lung recoil and maximum expiratory flow. J Appf Physiol 1967;22:95-108. 4. Williams IP, McGavin CR. Corticosteroids in chronic airways obstruction: can the patient’s assessmentbe ignored? Br J Dis Chest 1980;74:142-8. 5. Ramsdell JW, Tisi GM. Determination of bronchodilatation in the clinical pulmonary function laboratory. Chest 1979;76:622-8. 6. Girard WM, Light RW. Should the FVC be considered in calculating response to bronchodilator? Chest 1983; 84:87-9.
Date accepted 20 June I986
VARIABILITY AND REVERSIBILITY OF THE SLOW AND FORCED VITAL CAPACITY IN CHRONIC AIRFLOW OBSTRUCTION R. I. GOVE*, J. SHEPHERD AND P. S. BURGE Department of Thoracic Medicine, East Birmingham Hospital, Birmingham B9 ST
Summary
The variability of the forced (FVC) and slow vital capacity (SVC) manoeuvres were compared in 33 adult patients with chronic airflow obstruction. The reversibility of the two manoeuvres to nebulized salbutamol were compared in 18 of the patients. Both manoeuvres had equally small variances both before and after bronchodilator. The degree of reversibility of the FVC was however significantly greater (P
GOVE,
SHEPHERD,
BURGE:
CHRONIC
AIRFLOW
OBSTRUCTION
183
obtained from 33 patients (six female) with a mean age (years+sn) of 57+14. All except two were current or ex-smokers (mean pack year&so, 35f17) and all had a history of more than 5 years’ symptoms of CAO. Both PVC and SVC were measured on a dry bellows spirometer (Vitalograph) with the patient standing and wearing a nose-clip. The patients rested for 20 minutes between the two VC manoeuvres. Five blows were performed by each method, and the first two of each discarded. The next three blows which were within 10% of each other after 5 secondswere used for analysis. All blows followed a maximum inspiration and patients were actively encouraged to continue the expiratory manoeuvre for as long as possible. Patients were left to recover as long as they felt was necessary in between blows. Eighteen patients repeated the procedure 15 minutes after receiving 5 mg of nebulized salbutamol in 2 ml physiological saline administered from an Inspiron Mini nebulizer. The PVC was always performed before the SVC and all patients had abstained from using their usual bronchodilator aerosols for 8 hours before coming to the laboratory. All patients attended the laboratory for a second visit when their lung volumes were measured by a 20 minute helium dilution test and their transfer factor measured by single breath carbon monoxide uptake. The total variance was calculated from the total sum of squares divided by (n- l)N, where n=the number of observations, and N the number of patients. The reversibility data were analysed by comparing the change shown in the two measurements using a paired t-test. The correlations between the subdivisions of lung volume and the individual variances were calculated by Kendall’s rank correlation.
RESULTS The mean pre- and post-bronchodilator FVC and SVC values are given in Table I. The other mean physiological variables given as a percentage of the predicted value (*SD) are FEV, 47.6220.5, residual volume (RV) 179.9k29.4, total lung capacity (TLC) 123.2f17.8, transfer factor corrected for lung volumes (Kco) 69.2f33.5. The baseline variances for FVC and SVC were very similar (Table II). Although the post-bronchodilator SVC variance (0.0264) was less than the FVC variance (0.0344) the Table I. Mean values for PVC and SVC at the baseline (n=33) and
before and after salbutamol in 18 patients
Baseline (litres) Prebronchodilator Post-bronchodilator (litres)
WC
svc
2.97 (f0.88) 3.00 (f0.85) 3.50 (k0.92)
3.38 (f0.88) 3.40 (20.89) 3.70 (20.91)
The figures in parentheses represent one standard deviation. Table ZZ. Variance for PVC and SVC and resulting F-value at
baseline (n=33) and after nebulized salbutamol in 18 patients
Baseline variance Post-bronchodilator variance
WC
svc
F-value
0.0276
0.0274
1.005
0.0344
0.0264
1.3
The F-values are not significant.
184
BR.
J. DIS.
CHEST:
VOL.
81 NO.
2
difference was again not significant (Table II). The mean of the individuals’ SVC was greater than the corresponding FVC in all except two patients (SVC-FVC (litres), median and range: 0.31, -0.07 to 1.43). Reversibility was significantly (P< 0.05) greater in FVC than SVC (see Table I) and as a result the SVC-FVC difference decreased in these 18 patients (SVC-FVC (litres) median and range: 0.33, -0.07 to 1.43 prebronchodilator; 0.06, -0.18 to 0.88 postbronchodilator). No correlation between the variance of either technique or the difference between FVC and SVC and any other parameter of lung function measured (FEV,, RV, TLC, Kco) was demonstrated. DISCUSSION Both FVC and SVC are equally reproducible measurements of the VC. Patients who were variable in one measurement tended to be equally variable in the other. The selection of blows that were within 10% of each other at 5 seconds would minimize the variability, but this is standard practice in the laboratory where the tests were conducted. In most patients all blows are within 10% of each other at this point. The reasons for the difference in FVC and SVC in CA0 probably relate to the degree of lung destruction. Loss of supporting tissue to the small airways may result in more pressure dependent collapse during a forced manoeuvre. The significantly greater degree of FVC reversibility may support this suggestion, since dilation of the small airways would minimize pressure dependent collapse and have the effect of moving the theoretical ‘equal pressure point’ (3) proximally into larger airways. The lack of any correlation between the variance of either technique or the SVC-FVC difference and any other physiological parameter suggest that neither technique is influenced by increasing airflow obstruction or a falling Kco. Reversibility was significantly more marked in FVC and if 15% is taken as being indicative of a ‘significant’ response to bronchodilators this would have been missed in eight patients (44%) using SVC alone. There is evidence that an increased FVC correlates better with improved exercise performance than FEV, (4) and that bronchodilatation can cause improvements in FVC without changes in flow (5, 6). Failure to measure the reversibility of FVC as well as FEV, may therefore result in a patient being incorrectly labelled as unresponsive to bronchodilators. FVC and SVC are thus equally reproducible parameters in the assessment of CAO, although they are not the same measurement. If reversibility is to be measured, however, the FVC is likely to show a greater response and this may be clinically relevant. For the routine assessment of pulmonary function in CAO, should reversibility measurements be desired, measurement of the FVC alone rather than both parameters would be simpler. Technicians should be aware, however, of the importance of true SVC manoeuvres during the measurement of lung volumes in order not to overestimate RV. REFERENCES 1. Hyatt RE. Dynamic lung volumes. In: Fenn DO, Rahn H, eds. Handbook Washington: American Physiological Society, 1965:1394.
of physiology.
GOVE,
SHEPHERD,
BURGE:
CHRONIC
AIRFLOW
OBSTRUCTION
185
2. Bubis MJ, Sigurdson RN, McCarthy DS, Anthonisen NR. Differences between slow and fast vital capacities in patients with obstructive disease. Chest 1980;77:626-31. 3. Mead J, Turner JM, Macklem PT, Little JB. Significance of the relationship between lung recoil and maximum expiratory flow. J Appf Physiol 1967;22:95-108. 4. Williams IP, McGavin CR. Corticosteroids in chronic airways obstruction: can the patient’s assessmentbe ignored? Br J Dis Chest 1980;74:142-8. 5. Ramsdell JW, Tisi GM. Determination of bronchodilatation in the clinical pulmonary function laboratory. Chest 1979;76:622-8. 6. Girard WM, Light RW. Should the FVC be considered in calculating response to bronchodilator? Chest 1983; 84:87-9.
Date accepted 20 June I986