Eur J VascSurg 6, 642-646 (1992)
Co-variation Between Walking Ability and Circulatory Alterations in Patients with Intermittent Claudication Berndt Arfvidsson, Ake Wennmalm, Johan Gelin, Ann-Gret Dahll6f, Birgitta H~illgren and Kent Lundholm Departments of Surgery, Clinical Physiology and Medical Rehabilitation, University of GSteborg, Sahlgrenska Hospital, GSteborg, Sweden Unselected patients (n = 183) with subjective symptoms of intermittent claudication were examined clinically and by various circulatory tests (calf blood-flow, ankle, toe pressures). The aims of the present study were to evaluate to what extent the central or peripheral circulation is limiting in unselected patients with subjective symptoms of intermittent claudication, to determine the co-variation between the maximum walking capacity and traditional haemodynamical measures mentioned above and to evaluate to what extent a traditional bicycle ergometer exercise test and treadmill walking test give similar information regarding maximum performance. Eighty-five per cent of all patients were or had been smokers and 16% were diabetics. The mean ankle/brachiaI blood pressure index was 0.58 + 0.02 and the average post-ischemic maximum calf bloodflow was 13.3 + 0.6 ml/min/lOO ml tissue. Leg arterial insufficiency was the limiting factor of walking capacity in 90% of all patients at 87 + 2 W corresponding to a walking distance of 282 + 13 m, while leg exhaustion was the limiting factor in 80% of the patients during test on the bicycle ergometer at maximum 84 + 2 W. The mean maximum walking capacity for all patients was 86 ++_3 Wand the mean maximum capacity on the bicycle ergometer was 87 + 2 W. The ankle/brachial index showed only a weak correlation (r = 0.30, p < 0.002) to walking capacity. Our results demonstrate that the maximum walking capacity on a treadmill agrees with mean values of maximum exercise capacity on a bicycle ergometer. The results re-emphasise that conventional leg circulatory measures (ankle, toe pressure, post-ischaemic maximal calf blood flow) are not useful to predict walking disability in patients with intermittent claudication. Key Words: Intermittent claudication; Circulatory; Haemodynamics.
Introduction
degrees of walking disability. 1"4'5 Therefore, we have now adopted a walking test on a treadmill with a The severity of leg arterial insufficiency is generally step-wise increasing slope, which allowed us to described objectively by segmental pressure determine the maximum walking capacity in watts measurements along the extremity. 14'15 Blood press- (W) for each individual. 7 This method measures the ure gradients, however, do not give full information, whole body integrated circulatory capacity which particularly in patients with primarily stenotic lesions should be the most important evaluation in patients in large vessels. In such cases the pressure gradient suffering from intermittent claudication who genermay be insignificant at rest while the increase in ally also have coronary lesions leading to a lowered blood flow in response to exercise may be severely performance. 18 hampered. ~°'16 Previously, we used standardised The aim of the present study was three-fold: walking ability on a horizontal treadmill with con- first, to evaluate to what extent the central or periphstant speed to determine the maximum walking dis- eral circulation is limiting in unselected patients with tance in evaluation of efficacy in treatment before and subjective symptoms of intermittent claudication; after surgical intervention. However, this method did secondly to evaluate to what extent a traditional not discriminate patients with intermediate and low bicycle ergometer exercise test and treadmill walking test give similar information regarding maximum performance; and thirdly, to determine the co-variation Please address all correspondenceto: KentLundholm,Department between the maximum walking capacity and traof Surgery, SahlgrenskaHospital, S-41345 G6teborg, Sweden. ditional haemodynamical measures (brachial, ankle, 0950-821X/92/060642+05 $08.00/0© 1992Grune& StrattonLtd.
Patients with Intermittent Claudication
toe pressures, m a x i m u m post-ischaemic calf blood
643
Results
f l o w ) . 2 , 6, 8, 11, 12, 17, 19
Clinical and h a e m o d y n a m i c a l variables and blood chemistry test results are p r e s e n t e d in Table 1 for the Material and Methods
Experimental protocol
Table 1. Clinicial and laboratory test results in the patient material. Proportion of patients and m e a n + s.E.
Number of patients More than 200 consecutive outpatients with symptoms of intermittent claudication for more than 6 m o n t h s were referred to our vascular unit d u r i n g a 2 year period for consultation of a specialist in vascular surgery. One h u n d r e d and eighty three of these patients were invited to take part in this investigation. The protocol included physical examination, blood chemical tests, vascular laboratory tests including systemic, ankle and toe blood pressures, postischaemic calf blood flow m e a s u r e m e n t , d y n a m i c spirometry and bicycle e r g o m e t r y with simultaneous ECG recordings. The walking capacity was assessed by a treadmill operated at a speed of l m / s with a step-wise (1 ° min -1) increasing slope thus providing a gradually increasing work-load. The result of this walking test was given as the m a x i m u m w o r k performance in watts and as the m a x i m u m walking distance in meters. The m a x i m u m calf blood flow after ischaemic exercise was m e a s u r e d with standard strain gauge p l e t h y s m o g r a p h y . Dynamic s p i r o m e t r y and bicycle e r g o m e t r y with ECG recording were m e a s u r e d according to conventional routine procedures in our hospital. Blood pressures were m e a s u r e d with a non-invasive Doppler based technique. There were no restrictions of patient inclusion criteria for age and subjective walking ability. Patients with s y m p t o m s of more severe arterial insufficiency such as rest pain, ischaemic ulcer or gangrene were all excluded. Patients with concomitant disease contraindicating the possibility of future surgery and patients with mental disorders indicating that follow-up could not be properly p e r f o r m e d or unwillingness to give informed consent were also excluded. The s t u d y was a p p r o v e d b y the Committee for Ethics at the Medical Faculty, University of G6teborg, Sweden.
Statistics Results are given as m e a n values and standard error of the mean. The significance of regressions were tested b y analysis of variance.
183
Age (years)
67 + 1
Males/females
119/64
65%/35%
Smokers/ex-smokers/non-smokers
92/63/28 50%/35%/ 15%
Diabetes/non-diabetes
30/153
16%/84%
High/low arterial stenosis
99/84
54%/46%
Serum cholesterol (~*mol/1)
6.8 _+0.1
Serum triglycerides 0*mol/1)
2.2 _+0.2
Serum creatinine (b~mol/1)
99 + 2
Haemoglobin concentration (g/l)
145 + 1
Dynamic spirometry (normal/ pathological)
150/33
Systemic systolic blood pressure (mmHg)
152 _+2
Arterial ankle pressure (mmHg)
84 _+2
Arterial toe pressure (mmHg)
53 + 2
Maximum post-ischaemic calf bloodflow (ml/min/100ml of tissue)
13.3 _+0.6
Maximum walking capacity (W)
86 + 3
Maximum bicycle ergometer capacity (W)
87 + 2
82%/18%
total patient material. Mean plasma cholesterol was within normal values, while the m e a n blood triglyceride value was increased with borderline significance. Fifty per cent of all patients were smokers and 35% h a d recently s t o p p e d smoking. The m e a n anklePorachial blood pressure index was 0.58 + 0.02 in the entire material, of which 14% of the patients had an index lower than 0.4. Fifty-four per cent of the patients had aorto-iliac obliterations of significance based on a w e a k femoral pulse. Leg arterial insufficiency was the limiting factor for walking ability o n the treadmill in 164 individuals (90%), w h o s t o p p e d at a m a x i m u m work-load of 87 + 3W. The rest of the patients (10%) s t o p p e d due to angina pectoris (6%) or general fatigue (4%). Patients Eur J Vasc Surg Vol 6, November 1992
644
B. Arfvidsson et al.
with angina pectoris as the limiting factor stopped walking after a work-load of 68 + 7W. Leg exhaustion was the limiting factor in 147 individuals (80%), when bicycle ergometry exercise was performed at a maximum work-load of 84 + 2 W, while 36 patients (20%) stopped due to angina pectoris or general exhaustion at 104 + 4W. The relationship between maximum walking ability and maximum bicycle ergometry is shown in Fig. 1. There was no correlation 25O 225
0 0 0
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o
175
o o
o
o e8° 0
150
ol/o
125 o
IO0
75 5O 25 0
I
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i
I
40
l
I
60
80
I
I
i
I
l
I 0 0 120 mox. BCE
I
i
140
I
160
i
180
Fig. 1. The relationship b e t w e e n m e a s u r e m e n t s of the m a x i m u m exercise capacity p e r f o r m e d on a bicycle e r g o m e t e r (max. BCE) in w a t t s a n d the m a x i m u m w a l k i n g capacity p e r f o r m e d o n a treadmill (walking max.) in watts. The p o l y n o m i a l function (y = 4.2x 0.037x 2 + 1.26 x 10 4 X 3 - - 81.48); r = 0.61, p < 0.0001) h a d the best fit w h e n applied on observations for all patients.
between objective walking capacity and patients' own estimation of their walking ability estimated as the walking distance on a flat ground at spontaneous speed. There was only a weak correlation between the ankle/brachial index and the walking ability (r = 0.30, p < 0.002, Fig. 2) and this relationship was not strengthened when only patients with ankle/brachial index below 0.5 were analysed. These patients had a maximum walking capacity of 73 + 5 W. The 220 0
20O
O
0 180
0
,~ 160
140
0 0
80
0
0
--C
40 20 O.
%~
0
0
0
0
0
0
0
0 0
~
0
_.,
VO0
o
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OoO o o
0000%°~"
S
Ol I I 00, I I I 0.5 0.4 0.5 0.6 0.7 0.8 0.9 Ankle index
I 1.0
I I.I
1.2
Fig. 2. The relationship between ankleYorachial index and maxim u m w a l k i n g capacity (W), y = 71.7x + 42.9, r = 0.30, p < 0.002.
Eur J Vasc Surg Voi 6, N o v e m b e r 1992
mean subjective walking distance was 780 _+ 60 (range 100-1500) m and the mean objective walking distance before they had to stop due to leg pain on the non-horizontal treadmill was 282 + 13 m. A correlation matrix (not shown) was constructed including potentially interesting variables associated with walking and exercise ability. Statistical calculations indicated that correlation coefficients above 0.45 were highly statistically significant and should be of some clinical importance in a material of this size. The maximum walking capacity on the treadmill had an intermediately high correlation to maximum exercise performance on the bicycle ergometer (0.61), which are measures provided by two independent methods. This correlation did not increase when the calculation was performed only on patients with leg insufficiency as the limiting factor in both the walking test and the bicycle ergometer test. In addition, this correlation was independent of whether the calculation was performed on the total patient material or on patients with mainly aorto-iliac obliterations. The correlation between maximum walking distance (m) and maximum walking performance (W) measured simultaneously on the treadmill was 0.88, which thus represents a within-method correlation. The maximum walking capacity did not correlate significantly to either ankle pressure, toe pressure or maximum post-ischaemic calf blood flow. However, local leg circulatory variables correlated to each other with correlations coefficients as: ankle/toe pressure, 0.68; ankle pressure/calf blood flow, 0.49; toe/calf blood flow, 0.62. There was no simple relationship between haemoglobin concentration and the maximum walking capacity on the treadmill. Multiple regression analyses were performed with either maximum walking capacity (W) or maxim u m bicycle ergometer capacity (W) as dependent variables. Independent variables were chosen on clinical grounds and were: post-ischaemic calf blood flow, ankle/toe blood pressure, haemoglobin concentration, pulse rate during maximal work and systemic blood pressure during a maximum work-load. These calculations demonstrated that calf blood flow, ankle and tow pressures did not explain the variability in walking capacity to any statistically significant extent. When haemoglobin concentration, pulse rate and systemic blood pressure during a maximum workload were included, it was found that these variables explained 18% all together of the variability in maximum walking capacity. When the corresponding analysis was performed on variables obtained during bicycle ergometry, it was found that 40% of the variability in maximum exercise capacity was explained by all the six variables of which pulse rate during maxi-
Patients with Intermittent Claudication
m u m exercise and haemoglobin concentration were the only individual variables of statistical significance (not shown).
Discussion
In the clinical setting, there is a need for objective criteria to evaluate performance status in patients with combined central and peripheral arterial insufficiency. ~8 It is often not clear to what extent older patients will benefit from arterial reconstructions, since their handicap, including walking disability, may be multifactorial. 4 Therefore, vascular surgeons need a simple, reliable and reproducible tool for evaluating the overall performance, particularly walking ability, both as a clinical preoperative tool and for follow-up studies. In many circumstances, only subjective information provided by the patient is available, sometimes combined with ankle/brachial pressure measurements. Although informative, resting pressures cannot be expected to provide integrated information predicting work performance. 16 The importance of this limitation regarding pressure information may be serious in evaluation of operative indications. The present investigation demonstrates that the mean walking performance capacity was low in unselected patients with intermittent claudication, irrespective of whether tested on a treadmill or a bicycle ergometer. Interestingly, these two rather different principles gave almost the same mean maximum performance, although it cannot be concluded that the two methods are entirely dependent on the same limiting factors during a work-load. The relationship between walking capacity on the treadmill and on the bicycle ergometer was highly significant, although it may not have been proportional throughout the investigated work-load interval (Fig. 1). Multiple regression analysis also demonstrated that individual systemic variables like blood haemoglobin concentration, maximum pulse rate and blood pressure, as well as local leg circulatory variables such as postischaemic maximum calf blood flow, ankle and toe pressure, explained less than 15-20% of the variability of the walking performance. Although the overall contribution of these variables were statistically significant, no individual variable could be demonstrated to be of particular importance. In bicycle ergometer exercise, the same variables explained around 40% of the variability in performance ability, again without any particular variable being most important. Thus, other factors such as motivation, experience
645
and joint stiffness etc., may be additional factors that explain the variations in walking ability both during the examination procedure as well as during spontaneous walking. Calculations of simple correlation coefficients between walking capacity and the leg circulatory measurements confirmed poor co-variation, again suggesting that no isolated circulatory variable was useful in prediction of walking disability or walking capacity. B'9,10,13 However, the various leg circulatory variables correlated significantly to each other, as expected. Thus, it is warranted to include objective assessment of walking ability in pre- and postoperative evaluations in patients with intermittent claudication. In conclusion, this study demonstrates that the maximum walking capacity measured on a treadmill agrees with maximum exercise capacity measured on a bicycle ergometer, although the two methods may not be dependent on the same limiting circulatory and muscular-related factors. Our results confirm previous findings that leg circulatory measures like maximum calf blood-flow, brachial, ankle and toe pressures are not appropriate to predict hampered walking performance in patients with intermittent claudication. This fact must be better considered in future evaluations of functional results following vascular surgery.
Acknowledgements Supported in parts by grants from the Swedish Medical Research Council (B89-17X-00536-25A, B89-17K-08712-01A), Tore Nilson Foundation, Swedish and G6teborg Medical Societies and the Medical Faculty, University of G6teborg, Sweden.
References 1 BONDE-PETERSENF. The effects of varying walking speeds when measuring the claudication distance on horizontal and sloping levels. Acta Chir Scand 1967; 133: 627-630. 2 BONDE-PETERSENF, SIGGAARD-ANDERSENJ.Physicalperformance capacity in patients with dysbasia arteriosclerotica. Scand J Rehab Med 1974; 6: 31-35. 3 CARTER SA, HAMEL ER, PATERSONJM, SNOW CJ, MYMIN D. Walking ability and ankle systolic pressures: observations in patients with intermittent claudication in a short-term walking exercise program. J Vasc Surg 1989; 10: 642-649. 4 CLEMENTDL. Diagnostic work-up of patients with intermittent claudication. Acta Cardiologica 1979; XXXIV: 141-151. 5 CLYNECAC, TRIPOLITISA, JAMIESONCW, GUSTAVER, STUARTF. The reproducibility of the treadmill walking test for claudication. Surg Gynecol Obstet 1979; 149: 727-728. 6 DAHLLOFAG, HOLM J, SCHERSTI~NT, SIVERTSSONR. Peripheral arterial insufficiency. Scand J Rehab Med 1976; 8: 19-26. 7 GARDNERAW, SKINNERJS, CANTWELLBW, SMITHLK. ProgressEur J Vasc Surg Vol 6, November 1992
646
8 9 10 11
12 13 14
B. Arfvidsson et aL
ive vs single-stage treadmill tests for evaluation of claudication. Med Sci Sports Exer 1991; 23: 402-408. HILLESTADLK. The peripheral blood flow in intermittent claudication IV. The significance of the claudication distance. Acta Med Scand 1963; 173: 467-478. JACOBSS, REICH T. Calf blood flow in intermittent claudication. Arch Surg 1975; 110: 1465-1468. JONASONT, RINGQVISTI. Changes in peripheral blood pressures after five years of follow-up in non-operated patients with intermittent claudication. Acta Med Scand 1986; 220: 127-132. KALLEROKS, E~ICSSONBF, BERG~NTZSE. The diagnosis intermittent claudication. The value of walking test, ankle pressure index and calf plethysmography in relation to the clinical findings. Acta Chir Scand 1983; 149: 377-382. LORENTSEN E. Blood pressure and flow in the calf in relation to claudication distance. Scand J Clin Lab Invest 1973; 31: 141-146. LUNDGREN F, DAHLLOF AG, LUNDHOLM K, SCHERSTI~N T, VOLKMANN R. Intermittent claudication--surgical reconstruction or physical training? Ann Surg 1989; 209: 346-355. O'RIORDAIN DS, O'DONNELL JA. Realistic expectations for the
Eur J Vasc Surg Vol 6, November 1992
15 16 17 18
19
patient with intermittent claudication. Br J Surg 1991; 78: 861863. ROSENBLOOM MS, FLANIGAN DP, SCHULER JJ, et al. Risk factors affecting the natural history of intermittent claudication. Arch Surg 1988; 123: 867-870. STRANDNESSDE. Evaluation of the patient for vascular surgery. Surg Clin North Am 1974; 54: 13-22. SUMNER DS, STRANDNESS DE. The relationship between calf blood flow and ankle blood pressure in patients with intermittent claudication. Surgery 1969; 65: 763-771. WEINER DA, RYAN TJ, McCABE CH, et al. Correlations among history of angina, ST-segment response and prevalence of coronary-artery disease in the coronary artery surgery study (CASS). N Engl J Med 1979; 301: 230-235. YAo ST. A comparative study of strain-gauge pletysmography and Doppler ultrasound in the assessment of occlusive arterial disease of the lower extremities. Surgery 1972; 71: 4-9.
Accepted 3 July 1992
Co-variation Between Walking Ability and Circulatory Alterations in Patients with Intermittent Claudication Berndt Arfvidsson, Ake Wennmalm, Johan Gelin, Ann-Gret Dahll6f, Birgitta H~illgren and Kent Lundholm Departments of Surgery, Clinical Physiology and Medical Rehabilitation, University of GSteborg, Sahlgrenska Hospital, GSteborg, Sweden Unselected patients (n = 183) with subjective symptoms of intermittent claudication were examined clinically and by various circulatory tests (calf blood-flow, ankle, toe pressures). The aims of the present study were to evaluate to what extent the central or peripheral circulation is limiting in unselected patients with subjective symptoms of intermittent claudication, to determine the co-variation between the maximum walking capacity and traditional haemodynamical measures mentioned above and to evaluate to what extent a traditional bicycle ergometer exercise test and treadmill walking test give similar information regarding maximum performance. Eighty-five per cent of all patients were or had been smokers and 16% were diabetics. The mean ankle/brachiaI blood pressure index was 0.58 + 0.02 and the average post-ischemic maximum calf bloodflow was 13.3 + 0.6 ml/min/lOO ml tissue. Leg arterial insufficiency was the limiting factor of walking capacity in 90% of all patients at 87 + 2 W corresponding to a walking distance of 282 + 13 m, while leg exhaustion was the limiting factor in 80% of the patients during test on the bicycle ergometer at maximum 84 + 2 W. The mean maximum walking capacity for all patients was 86 ++_3 Wand the mean maximum capacity on the bicycle ergometer was 87 + 2 W. The ankle/brachial index showed only a weak correlation (r = 0.30, p < 0.002) to walking capacity. Our results demonstrate that the maximum walking capacity on a treadmill agrees with mean values of maximum exercise capacity on a bicycle ergometer. The results re-emphasise that conventional leg circulatory measures (ankle, toe pressure, post-ischaemic maximal calf blood flow) are not useful to predict walking disability in patients with intermittent claudication. Key Words: Intermittent claudication; Circulatory; Haemodynamics.
Introduction
degrees of walking disability. 1"4'5 Therefore, we have now adopted a walking test on a treadmill with a The severity of leg arterial insufficiency is generally step-wise increasing slope, which allowed us to described objectively by segmental pressure determine the maximum walking capacity in watts measurements along the extremity. 14'15 Blood press- (W) for each individual. 7 This method measures the ure gradients, however, do not give full information, whole body integrated circulatory capacity which particularly in patients with primarily stenotic lesions should be the most important evaluation in patients in large vessels. In such cases the pressure gradient suffering from intermittent claudication who genermay be insignificant at rest while the increase in ally also have coronary lesions leading to a lowered blood flow in response to exercise may be severely performance. 18 hampered. ~°'16 Previously, we used standardised The aim of the present study was three-fold: walking ability on a horizontal treadmill with con- first, to evaluate to what extent the central or periphstant speed to determine the maximum walking dis- eral circulation is limiting in unselected patients with tance in evaluation of efficacy in treatment before and subjective symptoms of intermittent claudication; after surgical intervention. However, this method did secondly to evaluate to what extent a traditional not discriminate patients with intermediate and low bicycle ergometer exercise test and treadmill walking test give similar information regarding maximum performance; and thirdly, to determine the co-variation Please address all correspondenceto: KentLundholm,Department between the maximum walking capacity and traof Surgery, SahlgrenskaHospital, S-41345 G6teborg, Sweden. ditional haemodynamical measures (brachial, ankle, 0950-821X/92/060642+05 $08.00/0© 1992Grune& StrattonLtd.
Patients with Intermittent Claudication
toe pressures, m a x i m u m post-ischaemic calf blood
643
Results
f l o w ) . 2 , 6, 8, 11, 12, 17, 19
Clinical and h a e m o d y n a m i c a l variables and blood chemistry test results are p r e s e n t e d in Table 1 for the Material and Methods
Experimental protocol
Table 1. Clinicial and laboratory test results in the patient material. Proportion of patients and m e a n + s.E.
Number of patients More than 200 consecutive outpatients with symptoms of intermittent claudication for more than 6 m o n t h s were referred to our vascular unit d u r i n g a 2 year period for consultation of a specialist in vascular surgery. One h u n d r e d and eighty three of these patients were invited to take part in this investigation. The protocol included physical examination, blood chemical tests, vascular laboratory tests including systemic, ankle and toe blood pressures, postischaemic calf blood flow m e a s u r e m e n t , d y n a m i c spirometry and bicycle e r g o m e t r y with simultaneous ECG recordings. The walking capacity was assessed by a treadmill operated at a speed of l m / s with a step-wise (1 ° min -1) increasing slope thus providing a gradually increasing work-load. The result of this walking test was given as the m a x i m u m w o r k performance in watts and as the m a x i m u m walking distance in meters. The m a x i m u m calf blood flow after ischaemic exercise was m e a s u r e d with standard strain gauge p l e t h y s m o g r a p h y . Dynamic s p i r o m e t r y and bicycle e r g o m e t r y with ECG recording were m e a s u r e d according to conventional routine procedures in our hospital. Blood pressures were m e a s u r e d with a non-invasive Doppler based technique. There were no restrictions of patient inclusion criteria for age and subjective walking ability. Patients with s y m p t o m s of more severe arterial insufficiency such as rest pain, ischaemic ulcer or gangrene were all excluded. Patients with concomitant disease contraindicating the possibility of future surgery and patients with mental disorders indicating that follow-up could not be properly p e r f o r m e d or unwillingness to give informed consent were also excluded. The s t u d y was a p p r o v e d b y the Committee for Ethics at the Medical Faculty, University of G6teborg, Sweden.
Statistics Results are given as m e a n values and standard error of the mean. The significance of regressions were tested b y analysis of variance.
183
Age (years)
67 + 1
Males/females
119/64
65%/35%
Smokers/ex-smokers/non-smokers
92/63/28 50%/35%/ 15%
Diabetes/non-diabetes
30/153
16%/84%
High/low arterial stenosis
99/84
54%/46%
Serum cholesterol (~*mol/1)
6.8 _+0.1
Serum triglycerides 0*mol/1)
2.2 _+0.2
Serum creatinine (b~mol/1)
99 + 2
Haemoglobin concentration (g/l)
145 + 1
Dynamic spirometry (normal/ pathological)
150/33
Systemic systolic blood pressure (mmHg)
152 _+2
Arterial ankle pressure (mmHg)
84 _+2
Arterial toe pressure (mmHg)
53 + 2
Maximum post-ischaemic calf bloodflow (ml/min/100ml of tissue)
13.3 _+0.6
Maximum walking capacity (W)
86 + 3
Maximum bicycle ergometer capacity (W)
87 + 2
82%/18%
total patient material. Mean plasma cholesterol was within normal values, while the m e a n blood triglyceride value was increased with borderline significance. Fifty per cent of all patients were smokers and 35% h a d recently s t o p p e d smoking. The m e a n anklePorachial blood pressure index was 0.58 + 0.02 in the entire material, of which 14% of the patients had an index lower than 0.4. Fifty-four per cent of the patients had aorto-iliac obliterations of significance based on a w e a k femoral pulse. Leg arterial insufficiency was the limiting factor for walking ability o n the treadmill in 164 individuals (90%), w h o s t o p p e d at a m a x i m u m work-load of 87 + 3W. The rest of the patients (10%) s t o p p e d due to angina pectoris (6%) or general fatigue (4%). Patients Eur J Vasc Surg Vol 6, November 1992
644
B. Arfvidsson et al.
with angina pectoris as the limiting factor stopped walking after a work-load of 68 + 7W. Leg exhaustion was the limiting factor in 147 individuals (80%), when bicycle ergometry exercise was performed at a maximum work-load of 84 + 2 W, while 36 patients (20%) stopped due to angina pectoris or general exhaustion at 104 + 4W. The relationship between maximum walking ability and maximum bicycle ergometry is shown in Fig. 1. There was no correlation 25O 225
0 0 0
2OO
o
175
o o
o
o e8° 0
150
ol/o
125 o
IO0
75 5O 25 0
I
2O
i
I
40
l
I
60
80
I
I
i
I
l
I 0 0 120 mox. BCE
I
i
140
I
160
i
180
Fig. 1. The relationship b e t w e e n m e a s u r e m e n t s of the m a x i m u m exercise capacity p e r f o r m e d on a bicycle e r g o m e t e r (max. BCE) in w a t t s a n d the m a x i m u m w a l k i n g capacity p e r f o r m e d o n a treadmill (walking max.) in watts. The p o l y n o m i a l function (y = 4.2x 0.037x 2 + 1.26 x 10 4 X 3 - - 81.48); r = 0.61, p < 0.0001) h a d the best fit w h e n applied on observations for all patients.
between objective walking capacity and patients' own estimation of their walking ability estimated as the walking distance on a flat ground at spontaneous speed. There was only a weak correlation between the ankle/brachial index and the walking ability (r = 0.30, p < 0.002, Fig. 2) and this relationship was not strengthened when only patients with ankle/brachial index below 0.5 were analysed. These patients had a maximum walking capacity of 73 + 5 W. The 220 0
20O
O
0 180
0
,~ 160
140
0 0
80
0
0
--C
40 20 O.
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0
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0
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~
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S
Ol I I 00, I I I 0.5 0.4 0.5 0.6 0.7 0.8 0.9 Ankle index
I 1.0
I I.I
1.2
Fig. 2. The relationship between ankleYorachial index and maxim u m w a l k i n g capacity (W), y = 71.7x + 42.9, r = 0.30, p < 0.002.
Eur J Vasc Surg Voi 6, N o v e m b e r 1992
mean subjective walking distance was 780 _+ 60 (range 100-1500) m and the mean objective walking distance before they had to stop due to leg pain on the non-horizontal treadmill was 282 + 13 m. A correlation matrix (not shown) was constructed including potentially interesting variables associated with walking and exercise ability. Statistical calculations indicated that correlation coefficients above 0.45 were highly statistically significant and should be of some clinical importance in a material of this size. The maximum walking capacity on the treadmill had an intermediately high correlation to maximum exercise performance on the bicycle ergometer (0.61), which are measures provided by two independent methods. This correlation did not increase when the calculation was performed only on patients with leg insufficiency as the limiting factor in both the walking test and the bicycle ergometer test. In addition, this correlation was independent of whether the calculation was performed on the total patient material or on patients with mainly aorto-iliac obliterations. The correlation between maximum walking distance (m) and maximum walking performance (W) measured simultaneously on the treadmill was 0.88, which thus represents a within-method correlation. The maximum walking capacity did not correlate significantly to either ankle pressure, toe pressure or maximum post-ischaemic calf blood flow. However, local leg circulatory variables correlated to each other with correlations coefficients as: ankle/toe pressure, 0.68; ankle pressure/calf blood flow, 0.49; toe/calf blood flow, 0.62. There was no simple relationship between haemoglobin concentration and the maximum walking capacity on the treadmill. Multiple regression analyses were performed with either maximum walking capacity (W) or maxim u m bicycle ergometer capacity (W) as dependent variables. Independent variables were chosen on clinical grounds and were: post-ischaemic calf blood flow, ankle/toe blood pressure, haemoglobin concentration, pulse rate during maximal work and systemic blood pressure during a maximum work-load. These calculations demonstrated that calf blood flow, ankle and tow pressures did not explain the variability in walking capacity to any statistically significant extent. When haemoglobin concentration, pulse rate and systemic blood pressure during a maximum workload were included, it was found that these variables explained 18% all together of the variability in maximum walking capacity. When the corresponding analysis was performed on variables obtained during bicycle ergometry, it was found that 40% of the variability in maximum exercise capacity was explained by all the six variables of which pulse rate during maxi-
Patients with Intermittent Claudication
m u m exercise and haemoglobin concentration were the only individual variables of statistical significance (not shown).
Discussion
In the clinical setting, there is a need for objective criteria to evaluate performance status in patients with combined central and peripheral arterial insufficiency. ~8 It is often not clear to what extent older patients will benefit from arterial reconstructions, since their handicap, including walking disability, may be multifactorial. 4 Therefore, vascular surgeons need a simple, reliable and reproducible tool for evaluating the overall performance, particularly walking ability, both as a clinical preoperative tool and for follow-up studies. In many circumstances, only subjective information provided by the patient is available, sometimes combined with ankle/brachial pressure measurements. Although informative, resting pressures cannot be expected to provide integrated information predicting work performance. 16 The importance of this limitation regarding pressure information may be serious in evaluation of operative indications. The present investigation demonstrates that the mean walking performance capacity was low in unselected patients with intermittent claudication, irrespective of whether tested on a treadmill or a bicycle ergometer. Interestingly, these two rather different principles gave almost the same mean maximum performance, although it cannot be concluded that the two methods are entirely dependent on the same limiting factors during a work-load. The relationship between walking capacity on the treadmill and on the bicycle ergometer was highly significant, although it may not have been proportional throughout the investigated work-load interval (Fig. 1). Multiple regression analysis also demonstrated that individual systemic variables like blood haemoglobin concentration, maximum pulse rate and blood pressure, as well as local leg circulatory variables such as postischaemic maximum calf blood flow, ankle and toe pressure, explained less than 15-20% of the variability of the walking performance. Although the overall contribution of these variables were statistically significant, no individual variable could be demonstrated to be of particular importance. In bicycle ergometer exercise, the same variables explained around 40% of the variability in performance ability, again without any particular variable being most important. Thus, other factors such as motivation, experience
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and joint stiffness etc., may be additional factors that explain the variations in walking ability both during the examination procedure as well as during spontaneous walking. Calculations of simple correlation coefficients between walking capacity and the leg circulatory measurements confirmed poor co-variation, again suggesting that no isolated circulatory variable was useful in prediction of walking disability or walking capacity. B'9,10,13 However, the various leg circulatory variables correlated significantly to each other, as expected. Thus, it is warranted to include objective assessment of walking ability in pre- and postoperative evaluations in patients with intermittent claudication. In conclusion, this study demonstrates that the maximum walking capacity measured on a treadmill agrees with maximum exercise capacity measured on a bicycle ergometer, although the two methods may not be dependent on the same limiting circulatory and muscular-related factors. Our results confirm previous findings that leg circulatory measures like maximum calf blood-flow, brachial, ankle and toe pressures are not appropriate to predict hampered walking performance in patients with intermittent claudication. This fact must be better considered in future evaluations of functional results following vascular surgery.
Acknowledgements Supported in parts by grants from the Swedish Medical Research Council (B89-17X-00536-25A, B89-17K-08712-01A), Tore Nilson Foundation, Swedish and G6teborg Medical Societies and the Medical Faculty, University of G6teborg, Sweden.
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Accepted 3 July 1992
