An analysis of the physiological strain of submaximal exercise in patients with chronic obstructive bronchitis
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Thorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
Thorax (1975), 30, 415.
An analysis of the physiological strain of submaximal
exercise in patients with chronic obstructive bronchitis
S. G. SPIRO, H. L. HAHN, R. H. T. EDWARDS,
and N. B. PRIDE
Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital,
Du Cane Road, London W12 OHS
Spiro, S. G., Hahn, H. L., Edwards, R. H. T., and Pride, N. B. (1975). Thorax, 30, 415-425.
An analysis of the physiological strain of submaximal exercise in patients with chronic obstructive
bronchitis. An increasing work rate was performed by 40 patients with chronic obstructive
bronchitis, split into two groups according to FEV1 (group M, mean FEV, 1-45 1. and group
S, mean FEV1 0-62 1.), and by 20 normal, non-athletic men of similar age to the patients.
Values for cardiac frequency and ventilation were interpolated to standard oxygen uptakes
of 0 75, 1 0, and, where possible, 1-5 1 min-'. The tidal volume at a ventilation of 20 and 30
l min-' was also determined.
The cardiac frequencies at oxygen uptakes of 0 75 and 1 01 min-' were significantly higher
in the patient groups than in the normal men, and were highest in patient group S. The cardiac
output when related to the oxygen uptake was in the normal range in all three groups of
subjects, so that the patients had smaller stroke volumes than the normal men. Ventilation
at oxygen uptakes of 0 75 and 1 0 1 min-' was significantly higher in both patient groups
than in the normal subjects; there were no significant differences between the two patient
groups. Values for dead space/tidal volume ratio, alveolar-arterial oxygen gradient, and the
percent venous admixture measured during a constant work rate test were significantly greater
than normal in the patient groups.
Possible factors limiting exercise tolerance in these patients were assessed by extending the
increasing work rate test from submaximum to maximum exercise. Changes in blood gas
tensions and blood lactate concentrations from resting levels were small, and probably did
not limit exercise performance. Measurements at maximum exercise did not add appreciably
to the analysis of the disturbed cardiopulmonary function. This study has shown that major
disturbances in cardiopulmonary function can be demonstrated without the need for stressing
a patient to the limit of his effort tolerance.
INTRODUCTION trapolation of oxygen consumption to a theoretical
Although the working capacity of patients with maximum cardiac frequency (Shephard et al., 1968).
chronic obstructive bronchitis has been studied by However, this prediction does not take into account
many authors, no simple way of comparing the the curvilinearity of the relation between cardiac
capacity of these patients with that of normal frequency and oxygen consumption as maximum
subjects has been developed. Working capacity in values are approached and tends to underestimate
normal subjects is assessed by measuring maximum Vo2 max (Davies, 1968). Furthermore, the working
oxygen uptake (Vo2 max) (Robinson, 1938, Astrand, capacity of patients with chronic obstructive bron-
1952; Astrand, I, 1960) but this requires several chitis usually is limited by their impaired ventilatory
exercise tests carried to exhaustion and is obviously capacity so that their cardiac frequencies on exercise
impractical, and possibly hazardous, in clinical do not approach the expected maximum values for
practice. A simpler and less exhausting method is their age (Armstrong et al., 1966; Gabriel, 1973).
to predict V02 max from the relationship between Recently, because of these difficulties in obtaining
cardiac frequency and oxygen consumption during V02 max, Cotes et al. (1969) have suggested com-
progressive submaximal exercise by a linear ex- paring measurements obtained during submaximal
415Thorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
416 S. G. Spiro, H. L. Hahn, R. H. T. Edwards, and N. B. Pride
exercise at a standard oxygen uptake (Vo2). In body mass (LBM) calculated with the formulae of
normal populations they have used a Vo2 of 1-5 Durnin and Rahaman (1967) from the sum of four
l min-.1 This Vo2 is too high for older women and skinfold thicknesses measured over the triceps
for many patients; furthermore, values at a single and biceps muscles and in the subscapular and
V02 provide no information on the evolution of the suprailiac regions. A resting venous blood sample
exercise response or of the overall capacity for was taken from each subject for haemoglobin
exercise. For these reasons we have suggested an estimation. Vital capacity (VC) and FEV1 were
alternative approach in which measurements are measured with a waterless bellows spirometer
made throughout an increasing work rate test and the (McDermott, McDermott, and Collins, 1968)
results expressed, not only at suitable levels of Vo2 Three attempts were made and the highest value
(0 75, 1-0, and, where possible, 1-5 1 min-'), but was recorded. Lung volumes and specific airways
also in terms of the slope of the relationship of conductance were measured in the patients using a
cardiac frequency (fH) and ventilation (V) with V02. body plethysmograph (DuBois et al., 1956; DuBois,
From these slopes and a knowledge of the maximum Botelho, and Comroe, 1956). The transfer factor
ventilation and heart rate a measure of 'physiological for carbon monoxide (CO) was also measured in
strain' can be obtained, which can be applied to the patients using the single breath technique
both normal populations and patients (Spiro et al., (Ogilvie et al., 1957), and expressed as the ratio
1974). of CO transfer per litre alveolar lung volume STPD
In this paper we describe the changes in cardiac (Kco). The personal details of the subjects are
frequency and in ventilation in 40 patients with summarized in Table I.
chronic obstructive bronchitis and in 20 normal The subjects exercised while seated on an electric-
middle-aged men during a constant work rate ally braked cycle ergometer (ELEMA). They first
exercise test. Some additional measurements of gas performed an increasing work rate test. After
exchange and cardiac output were also made in all reaching a steady resting state, as judged by the
the subjects during a constant work rate test. continuous tracings of fH, V, and mixed expired
gas concentrations, exercise was begun at a power
SUBJECTS AND METHODS output of 100 kpm min-' (16-7 watts) and increased
Forty men (aged 47 to 72 years) attending the by 100 kpm min-' each minute. The patients were
Bronchitis Clinic at Hammersmith Hospital agreed encouraged to continue for as long as possible, and
to take part in the study. The criteria of chronic in every case exercise was stopped because of
obstructive bronchitis were the same as those of dyspnoea. The normal subjects were asked to stop,
Jones, Jones, and Edwards (1971). All the men had for safety reasons, when the cardiac frequency
been cigarette smokers and 25 were still smoking reached 85% of the maximum predicted for their
at the time of the study. None gave a history of age (Astrand, 1960). When it appeared that the
asthma or showed more than a 20 % increase in the patients were approaching their maximum exercise
forced expiratory volume in 1 second (FEV1) after capacity, blood samples were taken from a vaso-
bronchodilator. For analysis the patients were dilated ear lobe (Godfrey, et al., 1971) for measure-
divided into two groups according to their FEV1- ment of oxygen tension (Po2) and carbon dioxide
a group M, with moderate airways obstruction, tension (Pco2) during the last minute of exercise.
mean FEV1 145 1. (range 1- 02-2 1.), and a group In preliminary experiments we found no significant
S with severe airways obstruction, mean FEV1 differences in blood gas tensions in simultaneous
0-62 1. (range 0-2-0-9 1.). Bronchodilator therapy samples taken from the brachial artery and ear lobe
was omitted on the day of the study. All the subjects in 12 patients, so we have taken the blood gas
were in sinus rhythm and none was taking digoxin; tensions of capillary blood from the ear as equivalent
two had a previous history of oedema and four to the tensions in arterial blood (Pao2, Paco2).
had electrocardiographic evidence of right ventricular Measurement of blood gas tensions in 34 duplicate
hypertrophy. samples of ear lobe blood gave a coefficient of
Twenty normal, sedentary, middle-aged men variation of 2-7 % for Pao2 and 3 8 % for Paco2.
volunteered to take part in the study. A detailed A further sample for blood lactate concentration
medical history was taken on the day of the study. was taken from the ear lobe 5 minutes after the end
No subject had a history of abnormal exertional of exercise. Blood lactate concentration was mea-
dyspnoea, angina or any other systemic illness. sured from five drops of blood collected into a tube
Dyspnoea grade was assessed as set out by the Medical containing a weighed amount (0 5 ml) of 0-86 mol
Research Council (1965). 1-1 perchlorate solution. The tubes were shaken
Height and weight were measured, and the lean and stored before being analysed by an enzymaticThorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
Physiological strain of submaximal exercise in chronic obstructive bronchitis 417
TABLE I
PERSONAL DETAILS OF SUBJECTS (MEAN ± SEM SHOWN)
Normal Patients
Subjects Group M Group S
FEV, (range, 1.) 2-8-4-7 1-0-2-2 0 2-0 9
n 20 20 20
Age (years) 541±1I1 60*0±l10 62-0±1*7
Height (cm) 173-4±1 5 172-8±i14 166-4+1±3
Weight (kg) 76-2±2-3 72-9±2 8 68-6±2:9
Lean body mass (kg) 62-3±i16 60-2+1*8 56-6±2-0
FEV1 (1.) 3-44±0 1 145±0*1 0-62±0l1
VC (.) 4-48±0-1 2-92±0-1 2-01±0-1
FEV Y. normal1 115 0±2i8 49 2±229 24 0±1*7
Resting Pvco, (mmHg) 46-2±1-1 56-6±1-6
Dyspnoea grade' 2-2±0 2 3-0±0-2
Total lung capacity (L.) 758±0-2 7-72±0 4
Total lung capacity %/0 normal' 123 ±5 8 130±2-7
Residual volume (1.) 4-3±0-2 52±0'3
Kco (ml min-I mmHg-'I -l) 3 71±0 3 3-37±0 3
SGaw (sec- 1 cmH2O-') 0-071 ±0007 0 043 ±0-006
K0o = transfer factor for carbon monoxide per unit of alveolar volume (STPD).
SGaw = specific airways conductance.
'Normal value predicted from age and height according to Cotes (1968).
2MRC instructions for the use of the questionnaire on respiratory symptoms, Medical Research Council (1965).
method (Hohorst, 1957). The coefficient of variation which fH or V could potentially be increased during
for 40 analyses of duplicate samples was 8 '6 % over exercise (that is, the difference between resting
the range of 0 5-4 mmol l-1 (mean 1-4 mmol 1-1). and maximum values) was taken as the 'adaptation
Following a rest of at least 30 minutes the subjects capacity' (ACfH, ACV). Resting values for calcu-
performed a constant work rate test for 6 minutes. lating ACfH and ACV were obtained from measure-
The power output selected for the patients was ments made with the subject seated at rest on the
approximately 50% of the final work rate achieved cycle ergometer. In the normal subjects maximum
during the progressive exercise test, and for the ventilation was taken as the FEV1 x 35 (Gandevia
normal subjects was approximately 60% of their and Hugh-Jones, 1957). In the patients, because
final work rate. Duplicate resting ear lobe blood of the relatively poor accuracy of existing predictions,
samples were taken for measurement of Pao2, the actual ventilation reached at the end of the
Paco2, and blood lactate. Constant work rate exercise test was used. In all subjects the maximum
exercise then began and during the sixth minute a heart rate was predicted from their age using the
further ear lobe sample was taken for blood gas formula of Astrand (1960). By relating the absolute
tensions and lactate concentration. The mixed increase in ventilation or cardiac frequency (SV,
venous C02 tension (Pvco2) was measured at rest SfH) for a standard stress (an increase in V02 of 1
and at the end of the sixth minute of exercise by the 1 min-') to an estimate of the individual's capacity
rebreathing method of Jones et al. (1967). Cardiac to increase fH or V (ACfH, ACV), the 'physiological
frequency, ventilation, and oxygen uptake were strain' for ventilation or heart rate can be obtained
calculated from the Mingograf recordings in the (Spiro et al., 1974).
resting period and at the end of each minute of The pattern of breathing for each group was
exercise. The apparatus used, together with details assessed by plotting ventilation against tidal volume
of its accuracy, and the measurements made for the after the method of Hey et al. (1966). The sub-
calculation of gas exchange have been described maximal tidal volumes at a ventilation of 20 and
previously (Spiro et al., 1974). 30 1 'mmn-1 were interpolated from the individual
The slope of the relationship of cardiac frequency plots.
and oxygen uptake (SfH1) was measured from a The dead space/tidal volume ratio (VD/VT %) was
'least squares' regression line (fH against VO2) calculated using the Bohr equation, from which the
automatically calculated and drawn by an Eliott 4100 dead space (VD) was derived, allowing 60 ml for
digital computer. The slope for ventilation and oxy- the valve box dead space. Alveolar Po2 was derived
gen uptake (SV) was drawn by eye through the linear with the alveolar air equation, and the measured
(submaximal) range and did not include the inflexion Pao2 subtracted to obtain the alveolar-arterial Po2
that is often seen in normal subjects at high power gradient (PA-ao2). The cardiac output (4)) was
outputs (Cotes, 1968). The slopes (SfH, SV) were calculated by the indirect Fick equation for CO2,
expressed as the increases in fH or in V required for incorporating the 'downstream' correction (Jones
an increase in V02 of 1 I min-'. The range over etal., 1967). The percent venous admixture ((OS/OT %)Thorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
418 S. G. Spiro, H. L. Hahn, R. H. T. Edwards, and N. B. Pride
was estimated by use of the classical 'shunt' equation. uptake of 1-5 1 min-1 and these data have not been
Calculations were performed with the Eliott 4100 included. As half of the group M subjects exceeded
digital computer, using a programme based on the 1-5 1 VO2 min-', the mean value for this submaximal
manipulation of the indirect Fick principle (Godfrey, index was included. Only six subjects in group S
1970). failed to reach an oxygen uptake of 10 I min-'.
In the text and tables all gas volumes, except the The submaximal values for cardiac frequency were
Kco, are given corrected to BTPS, and values for significantly higher in both the patient groups than
VO2 are corrected to STPD. the normal men at 0 75 and 1 0 I min-' V02 (t =3-318;
P p>0 01). The dyspnoea grade (MRC, 1965) Ventilation at 075, 1 0, and 1 5 1 min-1 VO2 was
was significantly greater in patient group S than in higher in the patients than in the normal men
patient group M (t =2-63; 0-025>P>0-01). The (t =-277; 0-01 > p> 0 005), but there were no signifi-
mean total lung capacity was above the predicted cant differences in ventilation between group M and
value in both patient groups but there was no group S patients (Table III and Fig. 1). The slope of
significant difference between the two groups. The ventilation on oxygen uptake was slightly increased
residual volume was significantly greater in patient (compared to the normal subjects) in the group M
group S than in group M (t= 292; 0 01 >p>0 005). patients Q=2-03; 0 05>P>0 025) but there was
The transfer factor for CO related to alveolar volume no significant change in the severely obstructed
(Kco) was considerably lower in the patient groups, patients.
than for normal middle-aged men (van Ganse The ACV was significantly smaller in patient
Ferris, and Cotes, 1972). Specific airways con- group M than in the normal subjects (t=9-1;
ductance was significantly lower in patient group Pp> in patient group M (t=49; PP>0005). The
(Cotes, 1968). influence of differences of somatic muscle mass was
The interpolated responses of cardiac frequency corrected for by multiplying the physiological
at the submaximal levels of exercise (fH 0.75, fH 1.0, strain index by the LBM. This did not cause any
fH1.5) are summarized in Table II and in Figure 1. significant change in physiological strain for V or
Only two of the group S patients achieved an oxygen fH between any of the groups.
TABLE II
SUBMAXIMAL INDICES AND ESTIMATION OF ADAPTATION CAPACITY AND RELATED 'PHYSIOLOGICAL STRAIN'
FOR CARDIAC FREQUENCY (MEAN ± SEM SHOWN)
Normal Patients
Subjects Group M Group S
FEV, (I.) 2-84-7 10-2 2 0*2-0 9
n 20 20 20
fH rest (beats min- ') 81 4±3*5 85 9±2-9 85-0±2-6
fH,.,, (beats min-') 95 0±3*1 102*9±3t5 109*5i2±9
fH,.o (beatsmin-1) 105*6±3-1 113-2±3-5 120-1±3*8
fH,.5 (beats min-') 126-9±3-4 127.6±5.92
PredictedfH max (beats min- ') 175'1±0-8 171-0±0-7 169-8±1-1
Adaptation capacity forfH (ACf H; beats min- ') 93-6±3-5 85-2±3-3 84*9±2-6
'Slope' for fH(SfH; beats I Vo- ') 42 5±A19 40 9±2 1 43-3 ±4 9
Physiological strain' for
'Pysolgialstai' fH
orfH
SfH x 100
ACf H
463±2l1 49*1±2*9 52 1±6i9
'14 patienits.
210 patients.Thorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
Physiological strain of submaximal exercise in chronic obstructive bronchitis 419
TABLE III
SUBMAXIMAL INDICES AND ESTIMATIONS OF ADAPTATION CAPACITY AND RELATED 'PHYSIOLOGICAL STRAIN'
FOR VENTILATION (MEAN ± SEM SHOWN)
Normal Patients
Subjects Group M Group S
FEV5(LI) 2-8-4-7 1-02-2 02-0-9
n 20 20 20
V rest (1 min- 1) 13 9±i13 13-8±10 11-4±0-5
V,.7, (I min-1) 18q7±1 0 24*4±1*1 23-0±0*9
V1. (I min- 1) 25 0±1i0
32-0±1-4 29-5±1 21
V,, (Imin-') 43-3 ±2*4'
36-6±1 5
FEVL x 35 (1 min-') 121-1±3-9
50-8±2-9 21-9±16
Max observed ventilation (lmin-) 49 4±2448-6±2*1 30*0±2*1
Adaptation capacity for V (AVC; I min- 1) 108*0±4*1
34*8 ±2*63 19'0± 1 93
Slope for V (SV) 23X8±1431*5±1-8 25 6±P14
*SV xx 100 I 225i1497
225±4 2±i7'50' 152*7±:t18*7'
'Physiological strain' for V AC
114 patients.
210 patients.
'Adaptation capacity and physiological strain in patient groups calculated from the maximum observed ventilation.
180 60
:Predicted Maximum'
-.0.........
160 50
P-
0 E
140 1- aj 40
1-
120 _ 30
100 _- 20
. o Normal subjects
80 - A &Patient Group M
10
. oPatient Group S
-',
I I I ~ 0
0 0.5 1.0 1.5 2.0 0 0.5 1.0 1.5 2.0
COYGEN UPTAKE t STPD minm1 MYGEN UPTAKE tSTPD minm1
FIG. 1. Mean values for cardiac frequency and ventilation at rest and at the submaximal levels of J02 (O 75, 1 -0, and
1-5 1 min-') for all three groups of subjects (open symbols). The values during the last minute of constant work rate
exercise (closed symbols) are also shown. The submaximal indices for cardiac frequency are higher in the patient groups
than in the normal subjects and are higher in patientgroup S than group M. There is no increase in the submaximal ventilatory
indices in group S from group M.
Plots of VT against V (Hey et al., 1966) for 24 of The mean values of VT2o and VT30 were significantly
the patients and for half of the normal men who were smaller in both the patient groups than in the normal
selected at random are summarized in Figure 2a. men (t=3 5; PThorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
420 S. G. Spiro, H. L. Hahn, R. H. T. Edwards, and N. B. Pride
60
ICE
VI
a. NORMAL I NORMAL
I~- SUBJECTS SU BJECTS
go_
GROUP _i240 -
GROUP M
0
z vtGOUP S
20 -
z z
w
/ ,
1
0
I ,
-II.1
11
-1--II I -1a
0 -.
1-0 2.0 3.0 0 20 40 60
TIDAL VOLUME [l] TIDAL VOLUME %VITAL CAPACITY
FIG. 2(a). Mean relationships of exercise tidal volume and (b). Mean relationships between the tidal volume as a
ventilation illustrating the patterns in the two patient groups percentage of the vital capacity, and ventilation.
and the normal subjects. The maximum tidal volumes
reached are indicated by the inflexions.
TABLE IV
MEASUREMENTS DURING LAST MINUTE OF INCREASING WORK RATE TEST (MEAN ± SEM SHOWN)
Normal Patients
Subjects Group M Group S
FEV1 (1.) 2*8-4*7 1-0-2-2 0 2-0 9
n 20 20 20
Power output (kpm min 1) 900±54-7 595 ±32-8 385 ±33-5
Maximum V02 (ml min- 1) 2012±104 1511±83 1034±85
Maximum cardiac frequency (beats min- 1) 152-4±2-6 140-0±4 2 120-9±3 6
Maximum cardiac frequency as % predicted max fH(%) 86-7±19 82-0±2-4 71 0± 1 9
Maximum ventilation (I mnin l) 54-4±2 6 48 6±2-1 30 0±221
Maximum ventilation as °/ predicted MVV (°/) 455±2-1 99 0±4 7 146-0±10-6
Lactate rest (mmol 1-1) - 0*80±0*1 0-82±0-1
Lactate maximum (mmol I') - 3-63±0-3 2 56±0-2
Pao, (rest) mmHg 91 5±t17 76-3±21 69-7±A14
Pao, (last mnin of exercise) mmHg _ 76-2 ±30 60 9 ±2-3
Paco, (rest) mmHg 37-6±1*1 365±0 8 44-6±1-5
Paco2 (last min of exercise) mmHg 410±1-3 490+ 18
measurements became similar in all three groups p < 0)001). In the last minute of exercise, a significant
(Fig. 2b). Complete details of the mean and individual fall in Pao2 had occurred only in patient group S
data are available elsewhere (Spiro, 1975). (t=2.97; 0-005>P>0-001). The Paco2 showed a
The slope (m) of each Hey plot was similar in slight increase in both patient groups which was not
group M and the normal subjects but was signifi- significant.
cantly steeper in group S (t =2 15; 0 05 > p > 0 025). The resting Pao2 was found to correlate well with
The intercept (k) was similar in all three groups. the FEV1 (r =0-78; p < 0-001; Fig. 3). The maximum
Data relating to the last minute of the increasing ventilation reached during the last minute of exercise
work rate test are summarized in Table IV. The was significantly correlated with the measured
blood lactate concentration after exercise was V02 max (r=0'85; PThorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
Physiological strain of submaximal exercise in chronic obstructive bronchitis 421
1201 min-' (Davies, 1972) and even comparisons at a
.A standard heart rate of 130 bt min-' (Gabriel, 1973)
100 0
4 A
AA may be impossible in more severely affected patients.
a A.
A AL Detailed submaximal indices at lower levels of Vo2
ca 80- * *
AA0
A
a A
are therefore essential in order to allow direct
E
E
a
comparison between patient and normal populations.
osou a
CIRCULATORY RESPONSE TO EXERCISE Cardiac output
CL
40 was normal, but the heart rate was abnormally high
A Normal subjects on exercise in both patient groups S and M. Heart
20 o Patient group M rate in group S was higher than in group M; those
* Patient group S
patients in group M who achieved a Vo2 in excess
0 10 20 3.0 40 50 of 1P5 1 min-' had a normal response. The similar
FEV,L BTPS
FIG. 3. Relationship between the resting PaO2 and the 2-0 o Patientqroup M 0 0
FEVi for the two patient groups and the normal subjects. . Patient qroupS5 0 00
0 .0
were all significantly larger in both the patient 0
groups than in the normal men (t=4-0; PThorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
422 S. G. Spiro, H. L. Hahn, R. H. T. Edwards, and N. B. Pride
slope (SfH) in all three groups indicated that the reported for normal subjects (Spiro et al., 1974).
patients, despite a high resting cardiac frequency, The slopes (SfH, SV) indicate how much these
had their greatest increase at the start of exercise variables will increase in the course of everyday
(Fig. 1). While normal subjects commencing seated activities requiring an increase in energy expenditure
exercise increase their stroke volume by approxi- equivalent to 1 1 min-1 V02. The physiological
mately 30% (Astrand and Rodahl, 1970), Gabriel strain, however, depends on the overall physical
(1973) measured only an 800 increase in SV in a capacity of the individual to exercise, and in turn
group of subjects with chronic obstructive bronchitis requires accurate knowledge of maximum values
and a mean FEV1 similar to that of patient group M. of fH and V. fH max can be estimated from the age
Marcus et al. (1970) also found a low SV with no according to the well established formula of Astrand
change on exercise and a normal cardiac output in (1960)-for details see Spiro et al. (1974).
patients with chronic airways obstruction. Whether The prediction of maximum exercise ventilation
the impaired SV response is due to raised pulmonary is difficult, especially in patients with severe airways
artery pressure (Gabriel, 1973) or to features of left obstruction. Clark et al. (1969) showed that although
ventricular dysfunction (Baum et al., 1971) is the ventilatory capacity could be predicted from the
uncertain. FEV1, this was subject to considerable variation.
In the present study the opportunity was taken to
VENTILATORY RESPONSE TO EXERCISE Ventilation at re-examine the relation of FEV1 and exercise
a given oxygen uptake was greater in both patient ventilatory capacity. The relationship obtained in
groups than in the normal subjects. This enabled this part of the study agreed with that taken from
the less severely affected patients (group M) to the data of Raimondi et al. (1970) and Jones et al.
maintain an arterial Paco2 within normal limits (1971). By combining all three studies (performed
despite the increased dead space. However, there in the same laboratory), it has been possible to have
was no tendency for the more severely affected a more confident assessment of maximum exercise
patients (group S) to show larger increases in ventila- ventilation from the FEV1 (Fig. 5). It should be
tion than group M patients even though they had noted that the prediction of maximum exercise
more severe abnormalities in VD/VT% and in other ventilation as FEV1 x 35, though adequate in
indices of pulmonary gas exchange such as A-aPo2 normal subjects, considerably underestimates the
gradient, venous admixture (Table V), and Kco. exercise ventilation achieved by patients with an
We presume that patients with airflow obstruction FEV1Thorax: first published as 10.1136/thx.30.4.415 on 1 August 1975. Downloaded from http://thorax.bmj.com/ on October 27, 2021 by guest. Protected by copyright.
Physiological strain of submaximal exercise in chronic obstructive bronchitis 423
8Or
Ic ./
I 70k
-r /
0.
-
60k
z
0 50k
z 40h
-J
/ SOUPCE n F.E VI r PREDICTION
w
U)
30k I Gandevia and Y-FEVIx 35
13 x Hugh Jones
40 0.2-2.2 082 Y-(BQXFEV)+19.7
cc - 2 Present Study
'a
20k /
3 Jones et al 43 OA-2.4 0.69 Y-077 XFEV9)264
4 Ralmondi etd. 92 O02-2A 0.75 Y--97xFEVj)+2I.8
+ 2,3.
10k
I I I
0
0 05 1.0 1.5 2.5
FEVI L- BTPS.
FIG. 5. Summary of different predictors of maximum exercise ventilation in patients with chronic
obstructive bronchitis, and the FEVI. The solid lines are based on actual values, while the FEV1 x 35
(dashed line) considerably underestimates the exercise ventilation in subjects with FEV1 < 1 .
exercise levels were approached which is associated R.H.T.E. is indebted to the Wellcome Trust and H.L.H.
with a rising blood lactate concentration (Cotes, was in receipt of a British Council Scholarship.
1968), and it appears unlikely that the peak blood Full details of the individual data are available from S. G. Spiro.
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