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Forefoot transcutaneous oxygen tension at different leg positions in patients with peripheral vascular disease
Eurl VascSurg 4, 185-189 (1990)
Forefoot Transcutaneous Oxygen Tension at D i f f e r e n t Leg Positions in Patients W i t h Peripheral Vascular Disease Jens F r o m h o l t Larsen, Bente V e b e r Jensen, Knud Stenild Christensen and Klas Egeblad Department of Thoracic and Vascular Surgery, Aalborg Sygehus, Denmark Transcutaneous oxygen tension ( TcPo2) was measured on the forefoot of 150 limbs of 128 patients with different stages of peripheral vascular disease (PVD) and on 36 limbs of 18 healthy subjects in the sitting and supine position. The diagnostic value of TcPo2 measurements was tested and compared with indirect toe pressure measurements, TcPo2 measured in the supine position gives the best diagnostic discrimination between healthy controls and patients with PVD and between patients with different degrees of PVD. The median TcPo2 in patients with PVD and rest pain (severe PVD), patients with PVD without rest pain (moderate PVD) and control subjects was 12 mmHg (range 0-61), 50 mmHg (range 0-86), and 60 mmHg (range 35-78), respectively. In the supine position, 95% of the patients with severe PVD had TcPo2 values below 40 mmHg, as opposed to 28% of the patients with moderate PVD and 8% of the control subjects. TcPo2 below 40 mmHg measured on the forefoot in the supine position suggests severe ischaemia. The diagnostic value of TcPo2 measurement is comparable with that of toe systolic pressure measurement. As a diagnostic and quantitative non-invasive method of evaluating patients suspected of PVD, TcPo2 measurement is ideal as it is easy to perform, and does not cause discomfort. Key Words: Transcutaneous oxygen tension; Positional change; Peripheral vascular disease.
Introduction In the management of patients with peripheral vascular disease (PVD) it is important to be able to quantify objectively the severity of the disease by means of a noninvasive technique. Transcutaneous oxygen tension (TcP02) which reflects local blood flow 1 has been introduced as a noninvasive method for the diagnosis and assessment of PVD, and for the preoperative, perioperative, and postoperative monitoring of patients undergoing vascular surgery. 2 6 There is, however, a considerable overlap of TcP02 values measured at rest in patients with moderate PVD and in healthy subjects. 5 To increase the accuracy of TcP02 measurements in the quantification of the severity of PVD different methods have been suggested, e.g. continuous TcP02 measurements during exercise, s measurements of transcutaneous oxygen recovery half-time after temporPlease address all correspondenceand reprint requests to: lens Fromholt Larsen, The Department of Surgery and Gastroenterology, Aalborg Sygehus, 5YDDK-9000, Aalborg,Denmark. 0950-821X/90/020185+05 $03.00/0 © 1990Grune&StrattonLtd
ary ischaemia, 7 and measurements of TcPo2 at various leg positions. Of these, the latter has proven to be a reliable method for the discrimination between different degrees of vascular disease. 8 This paper presents the results of transcutaneous oxygen tension measured at rest on the forefoot in the sitting and supine positions of control subjects and patients with various degrees of PVD. The ability of the method to discriminate between healthy subjects and patients with different clinical stages of PVD was tested and was compared to that of indirect pressure measurements.
M a t e r i a l and M e t h o d s Patients
One-hundred and fifty limbs were studied in ] 2 8 patients with different stages of PVD. Median age was 64 years (25 percentile: 57 yrs, 75 percentile: 72 yrs). All of the
186
Jens F r o m h o l t Larsen e t al.
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100
E E
90
80 ~'
70
g o, >,
"F O 3_
T O
T
3_
60 .L
T T
50 =
T
0
40
3_
o= 30
O
m
.L
o
T
T
3_
3_
20 o
10 3-
0 N=36 Controls
N=89 Patients without symptoms a t r e s t
N:24 Patients with r e s t pain w i t h o u t chr, u l c e r a t i o n s
N= 29 P a t i e n t s with r e s t pain and chr. u l c e r a t i o n s
N=8 P a t i e n t s with d i a b e t e s r e s t pain and chr. u l c e r a t i o n s
Fig.!. MedianforefootTcPo2measured in sitting and supine position. O = sitting position; *= supine position; T = 75% percentile; ± = 25% percentile.
patients were classified into four clinical groups according to Toennesen et al.: 9 (1) patients with ischaemic pain only during exercise; (2) patients with ischaemic rest pain but without chronic ulceration; (3) patients with ischaemic rest pain and with ulceration; (4) diabetics with rest pain and with ulceration.
the supine position, and the probe was placed on the dorsum of the foot 2 cm proximal to the space between the first and second toes. The electrodes w~ere allowed to equilibrate until stable values had been achieved.
Statistic
Indirect pressure measurements were performed by a strain gauge technique with the patient supine.
The analysis included paired rank sum test (Wilcoxon's test), and two-sample rank sum test (Mann-Whitney test).
Controls
Results
Eighteen healthy subjects, with a median age of 49 years (25 percentile: 42 yrs, 75 percentile: 60 yrs) were studied as control subjects.
It appears from Figure 1 that the TcP02 measured on the forefoot of patients in the sitting and in the supine position decreases with the severity of symptoms. In the sitting and supine position, a significant difference (P < 0.001) was found between the control group and the various clinical PVD groups. Both in the sitting and in the supine position significant differences in TcP02 values were found between the patient group without symptoms at rest and the patient group with rest pain but without chronic ulceration (P<0.O01), patients with rest pain and chronic ulceration ( P < 0 . 0 0 1 ) , and patients with diabetes and rest pain ( P < 0 . 0 0 1 ) . Within the three groups of patients with rest pain, significant differences could not be demonstrated in either the sitting or in the supine position. Thus, the patients could be classified into three groups by TcPo2 meusurements:
Transcutaneous oxygen measurements
TcPo2 was measured with a commercially available Clark type oxygen sensor (E 5242) and a TCM2 oxygen monitor (Radiometer). The principle (E 5242) and technique of TcPo2 measurement have been described in details elsewhere. 10 The probe temperature was thermostatically controlled at 45°C and all measurements were made at a room temperature of 23 ° (+2°)C. The TcPo2 measurements were made with the patient in the sitting and in EurJ VascSurg Vol 4, April 1990
Forefoot Transcutaneous Oxygen Tension
187
IOO
I00
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90
9O
80
80
T
70
70
60
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50
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40
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j.
/
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T 20-
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o
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_L
0
J-
.L
[0-
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c o., 40 g. 30
T 0
0
50
0 .L
I0 0
o
N=36 Controls
N=89 Patients without symptoms at rest
N=24 Patients with rest p a i n w i t h o u t
N=29 Patients with r e s t p a i n and
N=8 Patients with diabetes rest pain and
chr. ulcerations
chr. u l c e r a t i o n s
chr. u l c e r a t i o n s
Fig. 2. AbsoluteTcPo2changes from sitting to supine position measured in mmHg and relative changes expressedas percentage of sitting TcPo2. © = median absolute change; *= median relative change; T = 75% percentile; J_= 25% percentile.
Patients with rest pain (severe PVD) The median values in the sitting and in the supine positions were 40 m m H g (range 0 - 7 0 ) and 12 m m H g (range 0-61), respectively. In the sitting position, 67% of the patients had TcPo2 values below 60 mmHg. In the supine position, 95% had TcPo2 values below 40 mmHg.
Patients without symptoms at rest (moderate PVD) The median values in the sitting and in the supine positions were 67 m m H g (range 0 - 9 6 ) and 50 m m H g (range 0-86), respectively. In the sitting position, 20% of the patients had TcPo2 values below 60 mmHg. In the supine position, 28% of the patients had a TcPo2 below 40 mmHg.
Control subjects The median values in the sitting and in the supine positions were 8 3 m m H g (range 6 4 - 9 5 ) and 6 0 m m H g (range 35-78), respectively. In the sitting position, none of the control subjects had TcPo2 values below 60 mmHg. In the supine position, 8% of the patients had TcPo2 values below 40 mmHg. The decrease in TcPo2 from the sitting to the supine positions was highly significant in all groups (P < 0.001). The median, absolute decrease in TcPo2 of the control
subjects and of the patients with moderate PVD was almost identical, namely 19 m m H g (range 7-37) and 1 8 m m H g (range 0-96), respectively. The decrease in TcPo2 of patients with severe PVD was 26 m m H g (range 0 - 6 7 ) and was significantly ( P < 0.05) different from that of the control subjects, although the overlap was considerable, Figure 2. The relative change in TcPo2 of the control subjects and of the patients with moderate PVD was 25% (range 1 0 - 5 0 ) and 27% (range 0-100), respectively, and no significant difference was found ( P = 0.35). The relative change in TcPo2 of patients with severe PVD was 62% (range 12-100), which was significantly different from that of control subjects and patients with moderate PVD (P
-
-
-
It appeared that supine TcPo2 measurements and toe sysEurJ Vasc Surg Vol 4, April 1990
188
Jens
Fromholt
etal.
Larsen
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oxygen
tension supine
o o
2o
"£ .o_
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x x x
8°°
N=29
Patients with rest painwithout chr. ulcerations
pressure
o
xxxx
N=24
Patients without symptoms at rest
3o
o x
xx
x
o
40
o
o
I0 E_
° o
Ooo
o o
'g
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P a t i e n t s with r e s t p a i n and chr. ulcerations
xxx
O
N=8
Patients with diabetes rest pain and chr. u l c e r a t i o n s
supine position position
Fig. 3. Forefoot TcPo2 and arterial systolic pressure measured in supine position. © = transcutaneous oxygen tension measured on the forefoot; × = arterial systolic pressure measured on the first toe.
Table 1. The diagnostic value of TcPo2 measurements in patients with severe PVD and in control subjects TcPo2 measurements
Specificity
Sensitivity
Sitting
1.00
0.77
Supine
0.96
0.92
Relative change
0.90
0.84
Table 2. Diagnostic value of TcPo2 measurements and of indirect toe systolic pressure measurements in patients with severe and moderate PVD Measurement
Specificity
Sensitivity
Sitting TcPo2
O. 63
0.85
Supine TcPo2
0.64
0.95
Relative change TcPo2
0.60
0.91
Toe systolic pressure
0.64
0.93
tolic pressure were equally suitable for discrimination between the various PDV stages.
Discussion
Our study demonstrates that TcPo2 values at rest both in the sitting and in the supine positions of patients with PVD were significantly reduced compared with those of healthy subjects. Also, a relationship could be demonstrated between the TcPo2 measurements and the severity of PVD. Our results correspond with those of previous studies where TcPo2 was measured on the foot at rest in the supine position in healthy subjects ( 5 9 - 7 0 mmHg), in patients with PVD but without rest pain ( 4 5 - 5 5 mmHg), and in patients with rest pain ( 3 - 3 6 m m H g ) . 3,n-13 In agreement with other investigations it was not possible to discriminate between healthy subjects and patients with E u r J Vasc Surg Vol 4, April 1 9 9 0
only moderate degrees of PVD because of the considerable overlap of TcP02 values at rest. s' 14 In contrast, based on TcP02 measurements, it was possible to distinguish between healthy subjects and patients with severe PVD, particularly w h e n TcP02 was measured in the supine position. When TcP02 values of 60 mmHg and 40 mmHg were chosen as the critical limits in the sitting position and in the supine position, respectively, we found the best discrimination between the PVD groups in the supine position. When TcP02 measurements were compared with toe systolic pressure measurements, we found the same specificity and sensitivity. Consequently, TcP02 measurements and indirect toe systolic pressure measurements seem equally suitable for the diagnosis of the different clinical stages of PVD. These results correspond with those of other methods, e.g. continuous 24 hour record-
Forefoot Transcutaneous Oxygen Tension
ing of subcutaneous adipose tissue flow by means of the 13 3-xenon wash-out method. ~s The positional absolute changes in TcP02 measurements differed only slightly between healthy subjects and patients with various degrees of PVD. The changes, however, tended to increase with increased severity of ischaemia. Absolute positional changes in TcP02 yielded no further information concerning the distinction between healthy subjects and patients with PVD or patients with different stages of PVD. The relative changes (change in TcPo2/sitting TcP02), however, rendered the same specificities and sensitivities as TcP02 measurements in the supine position. In a previous paper 16 it was demonstrated that normal blood flow regulation is abolished in the heated tissue under the Po2-electrode. As blood flow is determined by the perfusion pressure and the local peripheral resistance, a change in the perfusion pressure or in the resistance will result in a change in TcP02. During limb lowering, perfusion pressure remains constant in healthy subjects, is W h e n the skin is heated or during reactive hyperaemia the normal compensatory vaso-reactions can be inactivated, making the vessels react passively to changes in transmural pressure. 1'17 By lowering the limb, the increased transmural pressure dilates the resistance vessels in the ischaemic vascular bed. 17 Moreover, even the perfusion pressure m a y increase during lowering of the ischaemic leg. ~8 Those mechanisms result in an increased flow and therefore an increased TcP02 and m a y explain our finding of the additional increase in TcP02 in patients with severe PVD compared with healthy subjects and patients with mild PVD (Fig. 2).
Conclusion TcPo2 measured in the supine position gives a good discrimination between healthy control subjects and patients with PVD and different degrees of PVD. The diagnostic value of TcP02 measurements is comparable with that of indirect systolic pressure measurements. TcPo2 below 40 m m H g measured at rest on the forefoot of subjects in the supine position suggests severe ischaemia. As seen with other noninvasive methods, e.g. indirect systolic pressure and Xe- 13 3 wash-out measurements, there is an appreciable overlap in TcPo2 values obtained in patients with different stages of PVD. This reflects the continuous spectrum of the arteriosclerotic disease rather than the accuracy of the methods.
189
TcPo2 m e a s u r e m e n t is well suited as a diagnostic and quantitative method for the evaluation of patients clinically suspected of PVD. It is non-invasive, easy to perform, and without any discomfort to the patient.
References 1 EmI
Accepted 20 December 1988
Eur ] Vasc Surg Vol 4, April 1990
Forefoot Transcutaneous Oxygen Tension at D i f f e r e n t Leg Positions in Patients W i t h Peripheral Vascular Disease Jens F r o m h o l t Larsen, Bente V e b e r Jensen, Knud Stenild Christensen and Klas Egeblad Department of Thoracic and Vascular Surgery, Aalborg Sygehus, Denmark Transcutaneous oxygen tension ( TcPo2) was measured on the forefoot of 150 limbs of 128 patients with different stages of peripheral vascular disease (PVD) and on 36 limbs of 18 healthy subjects in the sitting and supine position. The diagnostic value of TcPo2 measurements was tested and compared with indirect toe pressure measurements, TcPo2 measured in the supine position gives the best diagnostic discrimination between healthy controls and patients with PVD and between patients with different degrees of PVD. The median TcPo2 in patients with PVD and rest pain (severe PVD), patients with PVD without rest pain (moderate PVD) and control subjects was 12 mmHg (range 0-61), 50 mmHg (range 0-86), and 60 mmHg (range 35-78), respectively. In the supine position, 95% of the patients with severe PVD had TcPo2 values below 40 mmHg, as opposed to 28% of the patients with moderate PVD and 8% of the control subjects. TcPo2 below 40 mmHg measured on the forefoot in the supine position suggests severe ischaemia. The diagnostic value of TcPo2 measurement is comparable with that of toe systolic pressure measurement. As a diagnostic and quantitative non-invasive method of evaluating patients suspected of PVD, TcPo2 measurement is ideal as it is easy to perform, and does not cause discomfort. Key Words: Transcutaneous oxygen tension; Positional change; Peripheral vascular disease.
Introduction In the management of patients with peripheral vascular disease (PVD) it is important to be able to quantify objectively the severity of the disease by means of a noninvasive technique. Transcutaneous oxygen tension (TcP02) which reflects local blood flow 1 has been introduced as a noninvasive method for the diagnosis and assessment of PVD, and for the preoperative, perioperative, and postoperative monitoring of patients undergoing vascular surgery. 2 6 There is, however, a considerable overlap of TcP02 values measured at rest in patients with moderate PVD and in healthy subjects. 5 To increase the accuracy of TcP02 measurements in the quantification of the severity of PVD different methods have been suggested, e.g. continuous TcP02 measurements during exercise, s measurements of transcutaneous oxygen recovery half-time after temporPlease address all correspondenceand reprint requests to: lens Fromholt Larsen, The Department of Surgery and Gastroenterology, Aalborg Sygehus, 5YDDK-9000, Aalborg,Denmark. 0950-821X/90/020185+05 $03.00/0 © 1990Grune&StrattonLtd
ary ischaemia, 7 and measurements of TcPo2 at various leg positions. Of these, the latter has proven to be a reliable method for the discrimination between different degrees of vascular disease. 8 This paper presents the results of transcutaneous oxygen tension measured at rest on the forefoot in the sitting and supine positions of control subjects and patients with various degrees of PVD. The ability of the method to discriminate between healthy subjects and patients with different clinical stages of PVD was tested and was compared to that of indirect pressure measurements.
M a t e r i a l and M e t h o d s Patients
One-hundred and fifty limbs were studied in ] 2 8 patients with different stages of PVD. Median age was 64 years (25 percentile: 57 yrs, 75 percentile: 72 yrs). All of the
186
Jens F r o m h o l t Larsen e t al.
o, ::E
100
E E
90
80 ~'
70
g o, >,
"F O 3_
T O
T
3_
60 .L
T T
50 =
T
0
40
3_
o= 30
O
m
.L
o
T
T
3_
3_
20 o
10 3-
0 N=36 Controls
N=89 Patients without symptoms a t r e s t
N:24 Patients with r e s t pain w i t h o u t chr, u l c e r a t i o n s
N= 29 P a t i e n t s with r e s t pain and chr. u l c e r a t i o n s
N=8 P a t i e n t s with d i a b e t e s r e s t pain and chr. u l c e r a t i o n s
Fig.!. MedianforefootTcPo2measured in sitting and supine position. O = sitting position; *= supine position; T = 75% percentile; ± = 25% percentile.
patients were classified into four clinical groups according to Toennesen et al.: 9 (1) patients with ischaemic pain only during exercise; (2) patients with ischaemic rest pain but without chronic ulceration; (3) patients with ischaemic rest pain and with ulceration; (4) diabetics with rest pain and with ulceration.
the supine position, and the probe was placed on the dorsum of the foot 2 cm proximal to the space between the first and second toes. The electrodes w~ere allowed to equilibrate until stable values had been achieved.
Statistic
Indirect pressure measurements were performed by a strain gauge technique with the patient supine.
The analysis included paired rank sum test (Wilcoxon's test), and two-sample rank sum test (Mann-Whitney test).
Controls
Results
Eighteen healthy subjects, with a median age of 49 years (25 percentile: 42 yrs, 75 percentile: 60 yrs) were studied as control subjects.
It appears from Figure 1 that the TcP02 measured on the forefoot of patients in the sitting and in the supine position decreases with the severity of symptoms. In the sitting and supine position, a significant difference (P < 0.001) was found between the control group and the various clinical PVD groups. Both in the sitting and in the supine position significant differences in TcP02 values were found between the patient group without symptoms at rest and the patient group with rest pain but without chronic ulceration (P<0.O01), patients with rest pain and chronic ulceration ( P < 0 . 0 0 1 ) , and patients with diabetes and rest pain ( P < 0 . 0 0 1 ) . Within the three groups of patients with rest pain, significant differences could not be demonstrated in either the sitting or in the supine position. Thus, the patients could be classified into three groups by TcPo2 meusurements:
Transcutaneous oxygen measurements
TcPo2 was measured with a commercially available Clark type oxygen sensor (E 5242) and a TCM2 oxygen monitor (Radiometer). The principle (E 5242) and technique of TcPo2 measurement have been described in details elsewhere. 10 The probe temperature was thermostatically controlled at 45°C and all measurements were made at a room temperature of 23 ° (+2°)C. The TcPo2 measurements were made with the patient in the sitting and in EurJ VascSurg Vol 4, April 1990
Forefoot Transcutaneous Oxygen Tension
187
IOO
I00
E E
90
9O
80
80
T
70
70
60
SO
50
J.
40
T
j.
/
T T
50~
T 20-
g
o
0 3.
T *
T
_L
0
J-
.L
[0-
20
J..L
c o., 40 g. 30
T 0
0
50
0 .L
I0 0
o
N=36 Controls
N=89 Patients without symptoms at rest
N=24 Patients with rest p a i n w i t h o u t
N=29 Patients with r e s t p a i n and
N=8 Patients with diabetes rest pain and
chr. ulcerations
chr. u l c e r a t i o n s
chr. u l c e r a t i o n s
Fig. 2. AbsoluteTcPo2changes from sitting to supine position measured in mmHg and relative changes expressedas percentage of sitting TcPo2. © = median absolute change; *= median relative change; T = 75% percentile; J_= 25% percentile.
Patients with rest pain (severe PVD) The median values in the sitting and in the supine positions were 40 m m H g (range 0 - 7 0 ) and 12 m m H g (range 0-61), respectively. In the sitting position, 67% of the patients had TcPo2 values below 60 mmHg. In the supine position, 95% had TcPo2 values below 40 mmHg.
Patients without symptoms at rest (moderate PVD) The median values in the sitting and in the supine positions were 67 m m H g (range 0 - 9 6 ) and 50 m m H g (range 0-86), respectively. In the sitting position, 20% of the patients had TcPo2 values below 60 mmHg. In the supine position, 28% of the patients had a TcPo2 below 40 mmHg.
Control subjects The median values in the sitting and in the supine positions were 8 3 m m H g (range 6 4 - 9 5 ) and 6 0 m m H g (range 35-78), respectively. In the sitting position, none of the control subjects had TcPo2 values below 60 mmHg. In the supine position, 8% of the patients had TcPo2 values below 40 mmHg. The decrease in TcPo2 from the sitting to the supine positions was highly significant in all groups (P < 0.001). The median, absolute decrease in TcPo2 of the control
subjects and of the patients with moderate PVD was almost identical, namely 19 m m H g (range 7-37) and 1 8 m m H g (range 0-96), respectively. The decrease in TcPo2 of patients with severe PVD was 26 m m H g (range 0 - 6 7 ) and was significantly ( P < 0.05) different from that of the control subjects, although the overlap was considerable, Figure 2. The relative change in TcPo2 of the control subjects and of the patients with moderate PVD was 25% (range 1 0 - 5 0 ) and 27% (range 0-100), respectively, and no significant difference was found ( P = 0.35). The relative change in TcPo2 of patients with severe PVD was 62% (range 12-100), which was significantly different from that of control subjects and patients with moderate PVD (P
-
-
-
It appeared that supine TcPo2 measurements and toe sysEurJ Vasc Surg Vol 4, April 1990
188
Jens
Fromholt
etal.
Larsen
x
~ !
xxx
IOO
I00
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~ o
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xxxx xxx
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xxxxxxx
oxygen
tension supine
o o
2o
"£ .o_
~
~,
x x x
8°°
N=29
Patients with rest painwithout chr. ulcerations
pressure
o
xxxx
N=24
Patients without symptoms at rest
3o
o x
xx
x
o
40
o
o
I0 E_
° o
Ooo
o o
'g
x
XllXllXllX
P a t i e n t s with r e s t p a i n and chr. ulcerations
xxx
O
N=8
Patients with diabetes rest pain and chr. u l c e r a t i o n s
supine position position
Fig. 3. Forefoot TcPo2 and arterial systolic pressure measured in supine position. © = transcutaneous oxygen tension measured on the forefoot; × = arterial systolic pressure measured on the first toe.
Table 1. The diagnostic value of TcPo2 measurements in patients with severe PVD and in control subjects TcPo2 measurements
Specificity
Sensitivity
Sitting
1.00
0.77
Supine
0.96
0.92
Relative change
0.90
0.84
Table 2. Diagnostic value of TcPo2 measurements and of indirect toe systolic pressure measurements in patients with severe and moderate PVD Measurement
Specificity
Sensitivity
Sitting TcPo2
O. 63
0.85
Supine TcPo2
0.64
0.95
Relative change TcPo2
0.60
0.91
Toe systolic pressure
0.64
0.93
tolic pressure were equally suitable for discrimination between the various PDV stages.
Discussion
Our study demonstrates that TcPo2 values at rest both in the sitting and in the supine positions of patients with PVD were significantly reduced compared with those of healthy subjects. Also, a relationship could be demonstrated between the TcPo2 measurements and the severity of PVD. Our results correspond with those of previous studies where TcPo2 was measured on the foot at rest in the supine position in healthy subjects ( 5 9 - 7 0 mmHg), in patients with PVD but without rest pain ( 4 5 - 5 5 mmHg), and in patients with rest pain ( 3 - 3 6 m m H g ) . 3,n-13 In agreement with other investigations it was not possible to discriminate between healthy subjects and patients with E u r J Vasc Surg Vol 4, April 1 9 9 0
only moderate degrees of PVD because of the considerable overlap of TcP02 values at rest. s' 14 In contrast, based on TcP02 measurements, it was possible to distinguish between healthy subjects and patients with severe PVD, particularly w h e n TcP02 was measured in the supine position. When TcP02 values of 60 mmHg and 40 mmHg were chosen as the critical limits in the sitting position and in the supine position, respectively, we found the best discrimination between the PVD groups in the supine position. When TcP02 measurements were compared with toe systolic pressure measurements, we found the same specificity and sensitivity. Consequently, TcP02 measurements and indirect toe systolic pressure measurements seem equally suitable for the diagnosis of the different clinical stages of PVD. These results correspond with those of other methods, e.g. continuous 24 hour record-
Forefoot Transcutaneous Oxygen Tension
ing of subcutaneous adipose tissue flow by means of the 13 3-xenon wash-out method. ~s The positional absolute changes in TcP02 measurements differed only slightly between healthy subjects and patients with various degrees of PVD. The changes, however, tended to increase with increased severity of ischaemia. Absolute positional changes in TcP02 yielded no further information concerning the distinction between healthy subjects and patients with PVD or patients with different stages of PVD. The relative changes (change in TcPo2/sitting TcP02), however, rendered the same specificities and sensitivities as TcP02 measurements in the supine position. In a previous paper 16 it was demonstrated that normal blood flow regulation is abolished in the heated tissue under the Po2-electrode. As blood flow is determined by the perfusion pressure and the local peripheral resistance, a change in the perfusion pressure or in the resistance will result in a change in TcP02. During limb lowering, perfusion pressure remains constant in healthy subjects, is W h e n the skin is heated or during reactive hyperaemia the normal compensatory vaso-reactions can be inactivated, making the vessels react passively to changes in transmural pressure. 1'17 By lowering the limb, the increased transmural pressure dilates the resistance vessels in the ischaemic vascular bed. 17 Moreover, even the perfusion pressure m a y increase during lowering of the ischaemic leg. ~8 Those mechanisms result in an increased flow and therefore an increased TcP02 and m a y explain our finding of the additional increase in TcP02 in patients with severe PVD compared with healthy subjects and patients with mild PVD (Fig. 2).
Conclusion TcPo2 measured in the supine position gives a good discrimination between healthy control subjects and patients with PVD and different degrees of PVD. The diagnostic value of TcP02 measurements is comparable with that of indirect systolic pressure measurements. TcPo2 below 40 m m H g measured at rest on the forefoot of subjects in the supine position suggests severe ischaemia. As seen with other noninvasive methods, e.g. indirect systolic pressure and Xe- 13 3 wash-out measurements, there is an appreciable overlap in TcPo2 values obtained in patients with different stages of PVD. This reflects the continuous spectrum of the arteriosclerotic disease rather than the accuracy of the methods.
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TcPo2 m e a s u r e m e n t is well suited as a diagnostic and quantitative method for the evaluation of patients clinically suspected of PVD. It is non-invasive, easy to perform, and without any discomfort to the patient.
References 1 EmI
Accepted 20 December 1988
Eur ] Vasc Surg Vol 4, April 1990