Jasperse JL, Shoemaker JK, Gray EJ, Clifford PS. Positional differences in reactive hyperemia provide insight into initial phase of exercise hyperemia. J Appl Physiol 119: 569 -575, 2015. First published July 2, 2015; doi:10.1152/japplphysiol.01253.2013.-Studies have reported a greater blood flow response to muscle contractions when the limb is below the heart compared with above the heart, and these results have been interpreted as evidence for a skeletal muscle pump contribution to exercise hyperemia. If limb position affects the blood flow response to other vascular challenges such as reactive hyperemia, this interpretation may not be correct. We hypothesized that the magnitude of reactive hyperemia would be greater with the limb below the heart. Brachial artery blood flow (Doppler ultrasound) and blood pressure (finger-cuff plethysmography) were measured in 10 healthy volunteers. Subjects lay supine with one arm supported in two different positions: above or below the heart. Reactive hyperemia was produced by occlusion of arterial inflow for varying durations: 0.5 min, 1 min, 2 min, or 5 min in randomized order. Peak increases in blood flow were 77 Ϯ 11, 178 Ϯ 24, 291 Ϯ 25, and 398 Ϯ 33 ml/min above the heart and 96 Ϯ 19, 279 Ϯ 62, 550 Ϯ 60, and 711 Ϯ 69 ml/min below the heart (P Ͻ 0.05). Thus a standard stimulus (vascular occlusion) elicited different responses depending on limb position. To determine whether these differences were due to mechanisms intrinsic to the arterial wall, a second set of experiments was performed in which acute intraluminal pressure reduction for 0.5 min, 1 min, 2 min, or 5 min was performed in isolated rat soleus feed arteries (n ϭ 12). The magnitude of dilation upon pressure restoration was greater when acute pressure reduction occurred from 85 mmHg (mimicking pressure in the arm below the heart; 28.3 Ϯ 7.9, 37.5 Ϯ 5.9, 55.1 Ϯ 9.9, and 68.9 Ϯ 8.6% dilation) than from 48 mmHg (mimicking pressure in the arm above the heart; 20.8 Ϯ 4.8, 22.6 Ϯ 4.4, 31.2 Ϯ 5.8, and 49.2 Ϯ 7.1% dilation). These data support the hypothesis that arm position differences in reactive hyperemia are at least partially mediated by mechanisms intrinsic to the arterial wall. Overall, these results suggest the need to reevaluate studies employing positional changes to examine muscle pump influences on exercise hyperemia. muscle blood flow; muscle contraction; skeletal muscle pump; functional hyperemia AT THE ONSET OF DYNAMIC EXERCISE, there is a rapid increase in blood flow [30,31,41, and see Fig. 2 in Clifford and Hellsten (5)]. In fact, even a single muscle contraction produces a prompt increase in blood flow (1,7,14,26,36,39). There has been a debate over the last few decades about whether this rapid hyperemia is due to the muscle pump mechanism or to rapid vasodilation (5, 35).The muscle pump, as described by Laughlin (20), depends on an increased pressure gradient across the skeletal muscle vascular bed. Muscle contraction compresses the veins within the contracting muscle, expelling blood from the veins. ...
Cancer therapy-induced complications in the bowel and mesentery are fairly common. It is important for clinicians to be aware of these complications and the agents most frequently implicated. Cancer therapy is rapidly evolving and often encompasses both classic cytotoxic drugs and newer molecular targeted agents. Drugs from both broad classes can have numerous adverse effects on the bowel and mesentery that can be detected on imaging. These adverse effects include ileus, various forms of enterocolitis, gastrointestinal perforation, pneumatosis intestinalis, secretory diarrhea, and sclerosing mesenteritis. These complications are diverse and range from relatively benign to life threatening. The management is also variable, but many of these conditions are easily controlled and reversed with supportive care and cessation of the particular cancer therapy. The objective of this pictorial essay is to demonstrate some of the more common cancer therapy-induced complications of the bowel and mesentery, with a focus on the radiographic findings.
BACKGROUND AND PURPOSE:One feature that patients with steno-occlusive cerebrovascular disease have in common is the presence of white matter (WM) lesions on MRI. The purpose of this study was to evaluate the effect of direct surgical revascularization on impaired WM cerebrovascular reactivity in patients with steno-occlusive disease. MATERIALS AND METHODS:We recruited 35 patients with steno-occlusive disease, Moyamoya disease (n ϭ 24), Moyamoya syndrome (n ϭ 3), atherosclerosis (n ϭ 6), vasculitis (n ϭ 1), and idiopathic stenosis (n ϭ 1), who underwent unilateral brain revascularization using a direct superficial temporal artery-to-MCA bypass (19 women; mean age, 45.8 Ϯ 16.5 years). WM cerebrovascular reactivity was measured preoperatively and postoperatively using blood oxygen level-dependent (BOLD) MR imaging during iso-oxic hypercapnic changes in end-tidal carbon dioxide and was expressed as %⌬ BOLD MR signal intensity per millimeter end-tidal partial pressure of CO 2 .RESULTS: WM cerebrovascular reactivity significantly improved after direct unilateral superficial temporal artery-to-middle cerebral artery (STA-MCA) bypass in the revascularized hemisphere in the MCA territory (mean Ϯ SD, Ϫ0.0005 Ϯ 0.053 to 0.053 Ϯ 0.046 %BOLD/mm Hg; P Ͻ .0001) and in the anterior cerebral artery territory (mean, 0.0015 Ϯ 0.059 to 0.021 Ϯ 0.052 %BOLD/mm Hg; P ϭ .005). There was no difference in WM cerebrovascular reactivity in the ipsilateral posterior cerebral artery territory nor in the vascular territories of the nonrevascularized hemisphere (P Ͻ .05). CONCLUSIONS:Cerebral revascularization surgery is an effective treatment for reversing preoperative cerebrovascular reactivity deficits in WM. In addition, direct-STA-MCA bypass may prevent recurrence of preoperative symptoms. ABBREVIATIONS:ACA ϭ anterior cerebral artery; BOLD ϭ blood oxygen level-dependent; CVR ϭ cerebrovascular reactivity; MMD ϭ Moyamoya disease; PCA ϭ posterior cerebral artery; P ET CO 2 ϭ end-tidal partial pressure of CO 2 ; STA ϭ superficial temporal artery
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