Effect of intra-arterially induced alpha-receptor blockade upon resistance in collateral arteries in patients with occlusion of the superficial femoral artery

Risk factors for poor collateral development in claudication

The objective of this retrospective, cross-sectional study was to determine risk factors for poor collateral development in patients with claudication. The authors listed all patients with calf claudication who had undergone angiography in this hospital between 1999 and 2001 and extracted those with superficial femoral artery (SFA) occlusion, a popliteal artery without major lesions, and at least 1 patent calf artery. Forty-five patients met the criteria, and concomitant disease and claudication characteristics, ankle/brachial index (ABI) and number of outflow vessels were recorded. Three blinded observers calculated the number of collaterals on the angiograms, and the collateral count was related to the other factors by use of regression analysis. The mean patient age was 69 years (SD 11), and 62% were women. Their walking distance was 90 m (77) and ABI 0.47 (0.15). Thirty-three percent had diabetes and 50% had duration of symptoms longer than 5 years. The mean number of collaterals bypassing the occlusion was 15.1 (SD 4.8). Univariate regression analysis indicated an association (p <0.08) between few collateral vessels and diabetes, short duration of symptoms, current smoking habits, and old age. In the multivariate analysis only diabetes and short duration of symptoms were related to having few collaterals. In patients with claudication and SFA occlusion, few collaterals from the deep femoral artery appear to be associated with having diabetes and a short duration of symptoms.

Placebo-controlled comparison of captopril, atenolol, labetalol, and pindolol in hypertension complicated by intermittent claudication

In a six month placebo-controlled cross-over trial twenty patients with hypertension and peripheral arterial disease were randomised to captopril 25 mg twice daily, atenolol 100 mg once daily, labetalol 200 mg twice daily, or pindolol 10 mg twice daily for one month. Although all treatments were equally effective at lowering blood pressure, pain-free and maximum walking distances on a treadmill were decreased by atenolol, labetalol, and pindolol, but not by captopril. Post-exercise calf blood flow availability was impaired by atenolol, labetalol, and pindolol, but not by captopril. Despite ancillary characteristics of cardioselectivity, intrinsic sympathomimetic activity, or combination with alpha-blockade, beta-blockers seem to impair the lower limb circulation in such patients, whereas captopril seems to preserve it, possibly by maintaining the collateral blood supply.

Sympathetic reflex control of skeletal muscle blood flow in patients with congestive heart failure: evidence for beta-adrenergic circulatory control

Mechanisms controlling forearm muscle vascular resistance (FMVR) during postural changes were investigated in seven patients with severe congestive heart failure (CHF) and in seven control subjects with unimpaired left ventricular function. Relative brachioradial muscle blood flow was determined by the local 133Xe-washout technique. Unloading of baroreceptors with use of 45 degree upright tilt was comparably obtained in the patients with CHF and control subjects. Control subjects had substantially increased FMVR and heart rate to maintain arterial pressure whereas patients with CHF had decreased FMVR by 51 +/- 11% (mean +/- SEM, p less than .02) and had no increase in heart rate despite a fall in arterial pressure during upright tilt. The autoregulatory and local vasoconstrictor reflex responsiveness during postural changes in forearm vascular pressures were intact in both groups. Further investigations were carried out in the patients with CHF. The left axillary nerve plexus was blocked by local anesthesia in the seven patients. No alterations in forearm vascular pressures were observed. This blockade preserved the local regulation of FMVR but reversed the vasodilator response to upright tilt as FMVR increased by 30 +/- 7% (p less than .02). Blockade of central neural impulses to this limb combined with brachial arterial infusions of phentolamine completely abolished the humoral vasoconstriction in the tilted position. Infusions of propranolol to the contralateral brachial artery that did not affect baseline values of heart rate, arterial pressure, or the local reflex regulation of FMVR reversed the abnormal vasodilator response to upright tilt as FMVR increased by 42 +/- 12% (p less than .02). Despite augmented baseline values, forearm venous but not arterial plasma levels of epinephrine increased in the tilted position, as did arterial rather than venous plasma concentrations of norepinephrine in these patients. The results suggest a beta-adrenergic reflex mechanism elicited by spinal or supraspinal neural impulses and probably modulating a cotransmitter release in the patients with CHF.

Forefoot capillary filtration rate measured during lowering in normal subjects and in patients with occlusive arterial disease before and after arterial reconstruction

Capillary filtration rate (CFR) was measured by a mercury-in-silastic strain-gauge around the forefoot when the forefoot was lowered 40 cm below heart level. In seven normal limbs, CFR was 0.061 (0.049-0.086) ml (100 g min)-1 against 0.049 (0.016-0.071) ml (100 g min)-1 in 24 limbs with occlusive arterial disease (P = 0.01). About 8 days after arterial reconstruction CFR decreased to 0.039 (0.018-0.071) ml (100 g min)-1, but before 3 months after reconstruction CFR increased to normal values 0.061 (0.037-0.071) ml (100 g min)-1. The explanation offered for the reduced CFR before and immediately after arterial reconstruction is temporary thrombosis in the smallest distributing arteries and in the arterioles resulting in heterogeneous flow distribution and decreased fluid filtration in poorly perfused segments of the capillary bed. The results speak against increased capillary filtration as the aetiology of the post-reconstructive oedema.

Contribution of local blood flow regulation mechanisms to the maintenance of arterial pressure in upright position during epidural blockade

The contribution of local blood flow regulation mechanisms to the maintenance of arterial pressure in upright position was studied in 5 normal subjects. Central sympathetic blockade was induced by epidural anesthesia. Blood flow in anterior tibial muscle in both legs and in brachioradial muscle in one arm was measured by the local 133Xe washout technique. Arterial blood pressure was recorded directly from the radial artery. Slow head-up tilt (about 30 degrees) caused a decrease in blood flow of about 36% in the dependent legs and in arm remaining at heart level. Arterial pressure decreased by about 10%. Blockade of the local sympathetic veno-arteriolar "axon reflex" in one leg by injection of phentolamine into the common femoral artery caused a vasodilatation in the ipsilateral muscle, while muscle blood flow did not change in the other leg or arm. Within 20 s after the injection of phentolamine arterial pressure decreased by about 7%. This cannot be explained by a "systemic" effect because injection of phentolamine into the femoral vein did not effect arterial pressure within the first 40 s. Vasoconstriction due to blood-borne factors is ruled out since preventing the increase in vascular transmural pressure in the leg by inducing counterpressure locally, abolished the vasoconstriction. Thus, the results suggest that the local veno-arteriolar "axon reflex" together with myogenic mechanisms contribute to the maintenance of arterial pressure in the upright position.

Effect of propranolol on the tone of collateral arteries in patients with occlusion of the superficial femoral artery

The effect of administration of 0.5 mg propranolol into the femoral artery in eight patients with lower limb ischaemia and superficial femoral artery occlusion on collateral arterial resistance was studied in supine and tilted head-up position. Mean blood pressures were recorded directly from the femoral and popliteal artery and femoral blood flow was measured by an indicator dilution technique. After beta-receptor blockade in the supine position the collateral arterial resistance increased by 7 +/- 2%, femoral blood flow decreased 10 +/- 4%, and popliteal artery pressure increased by 4 mmHg (8 +/- 3%). During head-up tilt there was no change in femoral blood flow and collateral arterial resistance after propranolol. The peripheral vasoconstrictor effect of propranolol, therefore, seems not to be harmful to patients with vascular disease.