The mechanism of calf claudication: studies of simultaneous clearance of 99Tcm from the calf and thigh

Skeletal muscle metabolic changes in peripheral arterial disease contribute to exercise intolerance: a point-counterpoint discussion

Patients with claudication have a marked impairment in exercise performance. Several factors contribute to this limitation, including reductions in large vessel blood flow and oxygen delivery as well as metabolic abnormalities in skeletal muscle. The relative contribution of these factors and their role in the pathophysiology of the exercise limitation is discussed using a point-counterpoint approach. Future directions for research conclude the discussion.

Effect of type 2 diabetes mellitus on exercise intolerance and the physiological responses to exercise in peripheral arterial disease

AIMS/HYPOTHESIS

There are conflicting data about the effect of type 2 diabetes mellitus on exercise tolerance in peripheral arterial disease. To elucidate this problem, we compared the tolerance and physiological responses to treadmill and cycle exercise in 31 patients with peripheral arterial disease and intermittent claudication.

MATERIALS AND METHODS

One group of these patients had type 2 diabetes (n = 12) and its members were matched for sex and age with a group of patients who did not have diabetes (n = 12). Since BMI and body weight were greater in the diabetic group (28.4 +/- 3.7 vs 25.2 +/- 2.4 kg/m(2); 84.0 +/- 14.6 vs 73.8 +/- 8.0 kg), we also studied a third, 'heavy' group of non-diabetic patients with claudication of similar age (n = 7; BMI = 30.9 +/- 5.3 kg/m(2); body weight = 85.2 +/- 8.2 kg).

RESULTS

Compared with the 'light' non-diabetic group, maximum treadmill times were shorter for the diabetic and heavy non-diabetic groups (1,448 vs 845 and 915 s; ANOVA p = 0.01); maximum cycle time also tended to be shorter (ANOVA, p = 0.08) in the diabetic and heavy non-diabetic groups (median = 1,231 vs 730 and 797 s). The majority of physiological responses assessed were not different between the groups, although the time constant of oxygen uptake during submaximal treadmill and cycle exercise was significantly larger (ANOVA p < 0.05) for the diabetic group.

CONCLUSIONS/INTERPRETATION

These data demonstrate that exercise tolerance is lower in diabetic than non-diabetic patients with claudication, but that this difference is due to obesity rather than diabetes itself.

Post-exercise Hyperemia after Ischemic and Non-ischemic Isometric Handgrip Exercise

Post-exercise related time course of muscle oxygenation during recovery provides valuable information on peripheral vascular disease. The purpose of the present study was to examine post-exercise hyperemia (forearm blood flow; FBF, Doppler ultrasound) assessed by peak FBF, excess FBF and the time constant for FBF (FBF(Tc)) following isometric handgrip exercise (IHE). Post-exercise hyperemia was assessed in an ischemic and non-ischemic state at different exercise intensities and durations. Peak FBF and excess FBF were defined as the maximum FBF during recovery, and the total amount of FBF volume, respectively. FBF(Tc) represents the time to reach approximately 37% of the change in FBF between peak FBF and resting FBF (delta peak FBF). Ten subjects performed IHE at "10% and 30% maximum voluntary contraction (MVC)" for 2 min with or without arterial occlusion (AO), followed by 2 min of AO alone (Study I). In Study II, six subjects performed 30%MVC-IHE with AO for "100%, 66%, 33% and 10% of the exhausted exercise duration" (time to exhaustion). In Study I, although peak FBF and excess FBF were significantly higher in ischemic than non-ischemic IHE for both 10% and 30%MVC (p<0.05), FBF(Tc) was similar in the ischemic and non-ischemic conditions. The peak FBF, excess FBF and FBF(Tc) were all significantly higher at 30% than at 10%MVC (p<0.05). In Study II, the peak FBF and excess FBF increased linearly compared to the absolute and relative exercise durations for ischemic IHE. FBF(Tc) increased exponentially when compared to the absolute and relative exercise durations. These data suggest the ischemic exercise has a larger hyperemic response compared to the non-ischemic exercise. In conclusion, the peak FBF, excess FBF and FBF(Tc) seen during post-exercise hyperemia are closely correlated with exercise intensity and duration, not only in non-ischemic, but also in the ischemic exercise. In combination with the ischemic exercise, these parameters could potentially prove to be valuable indicators of peripheral vascular disease.

Haemodynamic limitations and exercise performance in peripheral arterial disease

It has been frequently argued that haemodynamic limitations are poor predictors of exercise performance in people with peripheral arterial disease (PAD) and intermittent claudication. This review has tried to address this argument through a review of published data that appears to support or counterbalance it, brief consideration of some of the methodological limitations associated with these data, as well as some other considerations. The main argument rests primarily upon data about the resting ankle-brachial index (ABI) and/or blood flow after calf exercise or an ischaemic challenge; whereas the counter argument rests mainly on data about blood flow during walking or cyding exercise. Consideration of the limitations of all methods suggests that the measurement of blood flow during exercise has the greatest value in explaining differences in exercise performance amongst claudicants; whereas the other methods are relatively limited in their explanatory value. This strengthens the counter argument and undermines the main argument proposed by others. Consequently, asserting that haemodynamic limitations are poor predictors of exercise performance in claudicants is not justified in light of available evidence.

Muscle contraction-induced steal model in the anesthetized cat

The current study describes a model in the anesthetized cat which may be used to investigate pharmacological interventions for the treatment of vascular "steal" during muscle contraction. An artificial stenosis was placed around both the descending abdominal aorta and the left external iliac artery. Arterial blood flow was measured in the right and left external iliac and right femoral arteries. Contraction of the left hindquarters, induced by electrical stimulation of the left sciatic and femoral nerves, resulted in an increase of left iliac artery blood flow from 14.7+/-2.0 to 30.5+/-2.8 ml min-1 (p<0.001). A simultaneous reduction of blood flow measured at the level of the right femoral artery (6.7+/-0.1 to 4.5+/-0.7 ml min(-1), p<0.01) was observed in the noncontracting hindlimb (y = 7.76 - 0.10x, correlation coefficient = -0.865). The magnitude of each response was reproducible within the same animal. Administration of 8-phenyltheophylline, a nonselective antagonist of adenosine receptors, reduced the functional hyperemia response within the left external iliac artery by 32% and reduced the "steal" from the vascular bed perfused by the right femoral artery by 21%.

Ischaemic skeletal muscle hyperaemia in the anaesthetized cat: no contribution of A2A adenosine receptors

1. The present study investigated the contribution of the A2A adenosine receptor subtype to the functional hyperaemia response evoked by muscle contraction in anaesthetized cats when muscle blood flow was limited. 2. Application of a stenosis reduced the hindlimb blood flow at rest from 9.67 +/- 1.80 to 5.53 +/- 0.91 ml min(-1) (kg body mass)(-1) and during muscle contraction from 36.80 +/- 2.55 to 11.11 +/- 1.19 ml min(-1) (kg body mass)(-1) (P < 0.001). The force produced by the extensor digitorum longus and tibialis anterior (EDL-TA) muscle groups was also reduced, from 9.66 +/- 0.56 to 4.10 +/- 0.4 N (kg muscle mass)(-1) (P < 0.01). 3. The selective A2A adenosine receptor antagonist ZM241385 (3 mg kg(-1), I.V.) had no effect upon the hindlimb vascular conductance or muscle contraction responses in the presence of the flow-limiting stenosis. 4. In contrast, in the absence of the flow restriction the vascular conductance response was reduced by 27.5 +/- 5.0% (P < 0.05), whilst the isometric force produced by the EDL-TA muscle group was unaffected (pre- vs. post-contraction, 5.8 +/- 0.8 vs. 4.6 +/- 1.0 N (kg muscle mass)(-1) contraction). Oxygen consumption by the contracting hindlimb muscles was maintained (1.71 +/- 0.25 vs. 1.69 +/- 0.26 ml min(-1) (kg body mass)(-1)) by an increase in the oxygen extraction (51.9 +/- 4.9 vs. 66.2 +/- 6.1%; P< 0.01). 5. These results confirm previous data showing that adenosine, acting at the A2A receptor subtype, can contribute up to 30% of the functional hyperaemia response in the hindlimb of anaesthetized cats under free flow conditions. However, when blood flow is limited by a stenosis, antagonism of the A2A adenosine receptor does not affect functional hyperaemia.

Metabolic responses of canine gracilis muscle during contraction with partial ischemia

The metabolic effects of partial ischemia on canine skeletal muscle were examined during 20 min of isometric contraction. A reduction in blood flow of approximately 75% resulted in an approximate 40% reduction in contractile function. Muscle lactate accumulation and phosphocreatine (PCr) hydrolysis were greater during ischemia, indicating a greater reliance on anaerobic ATP regeneration. Pyruvate dehydrogenase transformation to its active form (PDCa) during contraction was not affected by ischemia, such that PDCa did not appear to be a determinant of skeletal muscle fatigue. Acetylcarnitine concentration was greater during ischemic contraction and inversely correlated with PCr concentration (r = -0.79, P<0.01). Furthermore, acetylcarnitine accumulation and PCr degradation correlated with the degree of skeletal muscle fatigue (r = 0.56, P<0.05 and r = 0.70, P<0.01, respectively). Thus the greater the acetyl group oxidation, the lesser the contribution from anaerobic ATP provision and, subsequently, the smaller the degree of muscle fatigue observed. The metabolic characteristics of this model of ischemic muscle contraction are indistinguishable from the normal metabolic responses observed with increasing contractile intensity.

Postocclusive hyperaemic duplex scan: a new method of aortoiliac assessment

Aortoiliac duplex scanning, while accurate, is time-consuming and technically demanding. This study aimed to develop a fast, non-invasive screening test for aortoiliac disease. Colour duplex scanning was used to record common femoral Doppler ultrasonographic waveforms following 3 min of arterial occlusion using a thigh cuff in 25 patients with normal aortoiliac segments and 25 patients with significant aortoiliac disease. The latter patients had a prolonged period of postocclusive hyperaemic flow compared with the former. End diastolic velocity, 70 s after cuff release, was a significant discriminant between the two groups (sensitivity of 88 per cent, accuracy of 92 per cent). The postocclusive hyperaemic duplex (PHD) test performed well when used prospectively in a further 50 limbs (sensitivity of 86 per cent, accuracy of 84 per cent). The test was more sensitive than femoral pulse palpation and compared favourably with arteriography. The PHD test provides a simple, noninvasive assessment for aortoiliac disease that can be performed on the initial outpatient clinic visit.

Isotope limb blood flow measurement in patients undergoing peripheral laser angioplasty

A technique of isotope limb blood flow (ILBF) measurement employing Technetium-labelled human albumin and a gamma camera, was used to assess limb perfusion in 19 patients undergoing percutaneous laser angioplasty, both before and one month after treatment. Twenty-three limbs with femoro-popliteal occlusions ranging in length from 3-35 cm (median 8 cm) were recanalized using an Nd-YAG laser and sapphire tipped optical fibre. Primary angiographic success was achieved in 19 lesions of which 6 re-occluded within the first month, and 13 remained patent with relief of symptoms. Clinically successful procedures were associated with a large increase in ILBF. However, normal blood flow was restored in only 54% of limbs. There was a slight decrease in limb perfusion after failed laser angioplasty but this was not statistically significant in this small series. Furthermore, there was no clinically apparent circulatory compromise, or need for urgent surgical bypass in failed cases. We conclude that ILBF is a useful means of assessing patients undergoing laser angioplasty, particularly for detecting small flow changes in patients who are unable to complete a standard exercise test. Its use can be recommended for assessing blood flow changes following other forms of limb revascularization.

Common femoral artery volume flow in peripheral vascular disease

Common femoral artery volume flow was measured at rest and during postocclusive reactive hyperaemia in 80 normal subjects and 67 patients with radiological evidence of occlusive peripheral vascular disease. At rest, means(s.d.) common femoral artery volume flow in normal subjects (344(135) ml/min) and all patients with peripheral vascular disease (401(168) ml/min) was not significantly different. During postocclusive reactive hyperaemia, mean(s.d.) peak flow was significantly higher in normal subjects (1951(438) ml/min) than in patients with peripheral vascular disease (996(457) ml/min) (P less than 0.01). Common femoral artery volume flow in patients with critical ischaemia and intermittent claudication did not differ at rest but mean(s.d.) peak flow in patients with critical ischaemia (697(276) ml/min) was significantly lower than in claudicants (1131(447) ml/min) (P less than 0.01). Mean(s.d.) resting common femoral artery volume flow in limbs with femoropopliteal disease (457(185) ml/min) was significantly greater than that in limbs with occlusion of the aortoiliac segment (308(130) ml/min) (P less than 0.01). However, this difference did not persist during postocclusive reactive hyperaemia. A hyperaemic index, calculated from the hyperaemic responses to below knee and whole limb ischaemia, was used to quantify segmental perfusion during postocclusive reactive hyperaemia. The mean(s.d.) value in normal subjects, 46(9) per cent, and in those with aortoiliac disease, 52(12) per cent, indicated approximately equal perfusion of the above and below knee limb segments. In those with femoropopliteal disease the mean(s.d.) hyperaemic index was 17(13) per cent, revealing relative hypoperfusion of the below knee segment.

Effect of oral pentoxifylline therapy on venous lower extremity ulcers due to deep venous incompetence

The effect of oral pentoxifylline, administered 1,200 mg/day (400 mg slow-release tablets tid) through six weeks, was studied in 10 patients with established deep venous incompetence and persisting venous ulcers. The following parameters were used for verification of the therapeutic result: venous patency (VP) and valvular competence (VC) assessed by means of Doppler ultrasound; venous refilling time (VRT) assessed by photoplethysmography; skin blood flow (SBF) at rest and after tiptoeing exercise, as well as skin perfusion pressure (SPP), both assessed by means of 99mtechnetium clearance technique. Finally, photo documentation of the tissue lesion was obtained, using a two-dimensional (max and min diameter = Dmax, Dmin) metered scale photo. There was an overall good response to the treatment, the studied parameters showing the following changes: VP and VC remained unchanged; VRT improved in 8 patients, SBF increased in 10; SPP slightly improved in 5; and Dmax and Dmin in all 10 patients. Removal or substantial diminution of the ulcers was obtained in 8 patients. These findings indicate that oral administration of pentoxifylline over a period of six weeks supports the conservative treatment and improves considerably the condition of patients with persisting venous ulcers.

A reliable and readily available method of measuring limb blood flow in intermittent claudication

To evaluate isotope limb blood flow measurement in intermittent claudication we have assessed 58 non-diabetic patients comparing our new method with treadmill testing and Doppler assessment. Limb blood flow was applicable to all 58 patients; 25 patients were unable to walk on a treadmill and of the 33 who could 12 failed to walk for one minute, making a standard one minute exercise test inappropriate. In those patients who could perform exercise tests there was a significant correlation between maximum walking distance and limb blood flow (r = 0.35, P = 0.02). Resting, post-exercise and post-hyperaemic ankle-brachial systolic pressure indices bore no relationship to the maximum walking distance. Isotope limb blood flow measurement is reproducible (r = 0.97), can be applied to those patients who cannot walk on a treadmill and provides information about both legs. It correlated significantly with all the other tests and can be recommended for the minimally invasive assessment of intermittent claudication.

Continuous infusion treatment with pentoxifylline in patients with severe peripheral vascular occlusive disease

The effect of continuous i.v. infusion of pentoxifylline, administering 1,200 mg/24 hours through 15 days, was studied in 22 patients (19 m, 3 f) with arteriographically confirmed extensive occlusion in the femoro-popliteal segment, associated with marked intermittent claudication and rest pain of varying severity. The following parameters were used for the verification of the therapeutic response: Flow resistance factor (RF), pressure indices at rest (RPI) and after exercise (PPI) and recovery time (RT) assessed by means of ultrasonic Doppler technique; muscle and skin blood flow at rest and after exercise using 99m Technetium Clearance Technique (TC); toe skin temperature (TST) by electric thermometer; painfree walking distance (WD) assessed on treadmill (horizontal, 4 km/h); rest pain (RP) was assessed by a 4-step-relief-scale. There was an overall good response to treatment, the studied parameters showing the following changes: RF improved in 12/17 patients (= 70%); RT decreased in 14/22 patients (= 63%) RPI and PPI showed no change; TC (muscle) increased after exercise in 17/22 patients (= 77%); TC (skin) increased after exercise in 20/22 patients (= 90%); WD increased on average by 80% (from 115 m to 206 m); TS increased in 16 limbs; RP showed an overall relief. The results of this study indicate that the continuous infusion of pentoxifylline is safe and effective in improving the condition of patients with severe peripheral vascular disease.

The measurement of limb blood flow using technetium-labelled red blood cells

A method for measuring blood flow below the knee during reactive hyperaemia induced by 3 min of arterial occlusion has been developed. Subjects are positioned with lower limbs within the field of view of a gamma camera and pneumatic cuffs are placed below the knees to isolate the blood and induce a hyperaemic response. The remaining blood pool is labelled with 99Tcm-labelled red cells. Blood flows have been derived from the initial gradients of time-activity curves and from equilibrium blood sampling. The technique has been validated using a tissue-equivalent leg phantom and peristaltic pump. The method has been applied to a small group of patients with peripheral vascular disease and to normal controls. The mean value (+/- SD) of limb perfusion for normal controls was found to be 16.4 +/- 3.0 ml/100 ml/min and for patients with intermittent claudication was 5.1 +/- 2.6 ml/100 ml/min. Flow measurements are found to correlate with clinical findings and with symptoms. Reproducibility (established by repeated measurements) is high. The method is well tolerated even by patients suffering from rest pain.

Method of assessing the contribution of components of an anastomosing vascular network to total vascular impedance

The cerebral circulation has extensive communications between its four feeder arteries, their tributaries, and the extracerebral arteries. A theoretically derived method and its experimental verification is described by which the various impedances in a network can be quantified. It involved serial observations of pulsatile pressure, flow, and input impedance, in response to a pattern of input vessel occlusions. Fourier analysis permitted the response of the network to be studied for the component frequencies, so that linear and phasor algebra could be used to obtain a solution. Possible errors introduced by assumptions in the original model are minimal, and do not invalidate the method in practice.

Isolated profunda femoris artery occlusion: the mechanism of thigh claudication studied by 99mTc muscle clearance from the thigh and calf

99mTc muscle clearance from the gastrocnemius and quadriceps and ankle pressure measurements have been studied in 5 limbs of 5 patients with an isolated profunda femoris artery occlusion shown on the aortogram. The changes of flow and pressure which occurred after exercise may explain the hemodynamics of thigh claudication which is the consequence of thigh deprivation in favour of calf flow.

Simultaneous isotope clearance from the muscles of the calf and thigh

There has been no end to the attempts made to determine the site and severity of arterial lesions in claudicants by the use of non-invasive methods but, so far, their diagnostic value has been limited. A method whose diagnostic accuracy in determining the site and functional severity of the lesions approaches that of arteriography is discussed. The hyperaemic index, which is the ratio of the total excess of blood supply during post-exercise hyperaemia over the maximum hyperaemic flow, has been determined in the thigh and calf simultaneously, by measuring the 99Tcm muscle clearance in 30 limbs of 20 healthy volunteers and 139 limbs of 145 patients with claudication. Lumbar arteriography classified the lesions in all patients as 0-10 per cent, 10-40 per cent, 40-70 per cent and more than 70 per cent stenosis. A bivariate analysis of the hyperamic indices of the thigh and calf determined the site and whether single lesions consisted of a stenosis greater or less than 70 per cent. In limbs with combined aorto-iliac and superficial femoral lesions the values of the hyperaemic indices could determine which of the two lesions was the more severe in addition to whether lesions consisted of a stenosis greater or less than 70 per cent. These findings have been confirmed in a further blind prospective study of 47 limbs in which determination of the site and severity of lesions preceded aortography.