Peripheral Blood Biomarkers Associated With Improved Functional Outcome in Patients With Chronic Left Ventricular Dysfunction: A Biorepository Evaluation of the FOCUS-CCTRN Trial.

Cell therapy trials for heart failure (HF) have shown modest improvement; however, the mechanisms underlying improvement in some patients but not others are not well understood. Although immune cells are important in the course of HF, our understanding of the immune processes in HF is limited. The objective of this study was to evaluate associations between temporal changes in peripheral blood (PB) cell subpopulations and improved outcome in patients with chronic ischemic cardiomyopathy after bone marrow-derived mononuclear cell therapy or placebo in the FOCUS-CCTRN trial. Peripheral blood was collected at days 0, 1, 30, 90, and 180 from consented participants. We used flow cytometry to compare PB populations in patients with the best (cohort 1) or worst functional outcome (cohort 2) in three primary endpoints: left ventricular (LV) ejection fraction, LV end-systolic volume, and maximal oxygen consumption (VO2 max). A linear mixed model was used to assess changes over time in 32 cell populations. The difference between each time point and baseline was calculated as linear contrast. Compared with cohort 2, patients who improved (cohort 1) had a higher frequency of CD45+CD19+ B cells at days 0, 1, 90, and 180. CD11B+ cells increased over baseline at day 1 in both cohorts and remained higher in cohort 2 until day 30. CD45+CD133+ progenitor cells decreased over baseline at day 30 in cohort 1. We identified specific cell subpopulations associated with improved cardiac function in patients with chronic LV dysfunction. These findings may improve patient selection and prediction of outcomes in cell therapy trials.

Evaluation of Cell Therapy on Exercise Performance and Limb Perfusion in Peripheral Artery Disease: The CCTRN PACE Trial (Patients With Intermittent Claudication Injected With ALDH Bright Cells).

BACKGROUND: Atherosclerotic peripheral artery disease affects 8% to 12% of Americans >65 years of age and is associated with a major decline in functional status, increased myocardial infarction and stroke rates, and increased risk of ischemic amputation. Current treatment strategies for claudication have limitations. PACE (Patients With Intermittent Claudication Injected With ALDH Bright Cells) is a National Heart, Lung, and Blood Institute-sponsored, randomized, double-blind, placebo-controlled, phase 2 exploratory clinical trial designed to assess the safety and efficacy of autologous bone marrow-derived aldehyde dehydrogenase bright (ALDHbr) cells in patients with peripheral artery disease and to explore associated claudication physiological mechanisms. METHODS: All participants, randomized 1:1 to receive ALDHbr cells or placebo, underwent bone marrow aspiration and isolation of ALDHbr cells, followed by 10 injections into the thigh and calf of the index leg. The coprimary end points were change from baseline to 6 months in peak walking time (PWT), collateral count, peak hyperemic popliteal flow, and capillary perfusion measured by magnetic resonance imaging, as well as safety. RESULTS: A total of 82 patients with claudication and infrainguinal peripheral artery disease were randomized at 9 sites, of whom 78 had analyzable data (57 male, 21 female patients; mean age, 66±9 years). The mean±SEM differences in the change over 6 months between study groups for PWT (0.9±0.8 minutes; 95% confidence interval [CI] -0.6 to 2.5; P=0.238), collateral count (0.9±0.6 arteries; 95% CI, -0.2 to 2.1; P=0.116), peak hyperemic popliteal flow (0.0±0.4 mL/s; 95% CI, -0.8 to 0.8; P=0.978), and capillary perfusion (-0.2±0.6%; 95% CI, -1.3 to 0.9; P=0.752) were not significant. In addition, there were no significant differences for the secondary end points, including quality-of-life measures. There were no adverse safety outcomes. Correlative relationships between magnetic resonance imaging measures and PWT were not significant. A post hoc exploratory analysis suggested that ALDHbr cell administration might be associated with an increase in the number of collateral arteries (1.5±0.7; 95% CI, 0.1-2.9; P=0.047) in participants with completely occluded femoral arteries. CONCLUSIONS: ALDHbr cell administration did not improve PWT or magnetic resonance outcomes, and the changes in PWT were not associated with the anatomic or physiological magnetic resonance imaging end points. Future peripheral artery disease cell therapy investigational trial design may be informed by new anatomic and perfusion insights. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01774097.

Method for sectioning and sampling hearts for histologic evaluation after delivery of biological agents by transendocardial injection.

The use of transendocardial (TE) injection as a validated method for delivering therapeutic agents to the diseased heart is increasing. Of the catheter systems currently available, TE injections guided by electromechanical mapping are attractive due to their minimal use of fluoroscopy and three-dimensional reconstruction capabilities that allow precise targeting of injections. We propose a method of cardiac sampling that takes advantage of the spatial accuracy of this system. Our preclinical experience with this methodology has yielded encouraging results, allowing a thorough examination of the injected areas through limited sampling.

Comparison of scanning electron microscopy and optical coherence tomography for imaging of coronary bifurcation stents.

BACKGROUND: Optical coherence tomography (OCT) is a new intracoronary imaging modality that has excellent resolution and image quality and has been used to image neointimal coverage after stent implantation. OCT has been compared to histologic, intravascular ultrasound, and scanning electron microscopy (SEM) studies. However, OCT has not been compared with SEM for imaging stent coverage over side branches. OBJECTIVE: The aim of this study was to compare OCT with SEM in imaging neointimal coverage over stent struts bridging coronary side-branch ostia. METHODS: Using a balloon-overstretch in-stent restenosis model, we deployed 38 everolimus-eluting stents across coronary bifurcations in nine pigs. We performed OCT immediately after stenting and 4 weeks later; SEM was performed after euthanizing the pigs. OCT images of each stent were compared to the corresponding SEM image. RESULTS: We analyzed OCT frames (n=111) for strut-level neointimal coverage and compared them to corresponding SEM images. The concordance correlation coefficient was 0.809 (95%CI; 0.734-0.864) and 0.951 (95%CI; 0.930-0.966) for covered and uncovered struts, respectively. CONCLUSIONS: In a non-atherosclerotic pig model, we showed strong agreement between OCT and SEM in imaging coverage of stent struts bridging side-branch ostia.

Rationale and design for PACE: patients with intermittent claudication injected with ALDH bright cells.

Peripheral artery disease (PAD) is recognized as a public health issue because of its prevalence, functional limitations, and increased risk of systemic ischemic events. Current treatments for claudication, the primary symptom in patients with PAD, have limitations. Cells identified using cytosolic enzyme aldehyde dehydrogenase (ALDH) may benefit patients with severe PAD but has not been studied in patients with claudication. PACE is a randomized, double-blind, placebo-controlled clinical trial conducted by the Cardiovascular Cell Therapy Research Network to assess the safety and efficacy of autologous bone marrow-derived ALDH(br) cells delivered by direct intramuscular injections in 80 patients with symptom-limiting intermittent claudication. Eligible patients will have a significant stenosis or occlusion of infrainguinal arteries and a resting ankle-brachial index less than 0.90 and will be randomized 1:1 to cell or placebo treatment with a 1-year follow-up. The primary end points are the change in peak walking time and leg collateral arterial anatomy, calf muscle blood flow, and tissue perfusion as determined by magnetic resonance imaging at 6 months compared with baseline. The latter 3 measurements are new physiologic lower extremity tissue perfusion and PAD imaging-based end points that may help to quantify the biologic and mechanistic effects of cell therapy. This trial will collect important mechanistic and clinical information on the safety and efficacy of ALDH(br) cells in patients with claudication and provide valuable insight into the utility of advanced magnetic resonance imaging end points.

Xenotransplantation of human unrestricted somatic stem cells in a pig model of acute myocardial infarction.

BACKGROUND: Stem cell therapy may help restore cardiac function after acute myocardial infarction (AMI), but the optimal therapeutic cell type has not been identified. METHODS: We examined the effects of CD34-/CD45- human unrestricted somatic stem cells (USSCs) in pigs (n = 30) with an AMI created by a 90-min occlusion of the left anterior descending coronary artery. Pigs were randomly assigned to receive either USSCs (302 ± 23 × 10(6) cells) or phosphate-buffered saline via 15 NOGA-guided transendocardial injections 10 days after AMI. Cyclosporine A (10 mg/kg orally, twice a day) was started in all pigs 3 days before control or cell treatment. Cardiac function was assessed by echocardiography before injection and at 4 and 8 weeks after treatment. Serum titers for pig IgG antibodies against USSCs were also measured at these time points and before AMI. RESULTS: Compared with control pigs, USSC-treated pigs showed no significant differences in any of the functional parameters examined. USSC-treated pigs showed variable increases in anti-USSC IgG antibody titers in the blood and chronic inflammatory infiltrates at the cell injection sites. Immunohistochemical studies of the injection sites using human anti-mitochondrial antibodies failed to detect implanted USSCs. CONCLUSIONS: We conclude that human USSCs did not improve cardiac function in a pig model of AMI. Cell transplantation in a xenogeneic setting may obscure the benefits of stem cell therapy.

Carotid artery stenting versus endarterectomy: a systematic review.

For about 2 decades, investigators have been comparing carotid endarterectomy with carotid artery stenting in regard to their effectiveness and safety in treating carotid artery stenosis. We conducted a systematic review to summarize and appraise the available evidence provided by randomized trials, meta-analyses, and registries comparing the clinical outcomes of the 2 procedures. We searched the MEDLINE, SciVerse Scopus, and Cochrane databases and the bibliographies of pertinent textbooks and articles to identify these studies. The results of clinical trials and, consequently, the meta-analyses of those trials produced conflicting results regarding the comparative effectiveness and safety of carotid endarterectomy and carotid stenting. These conflicting results arose because of differences in patient population, trial design, outcome measures, and variability among centers in the endovascular devices used and in operator skills. Careful appraisal of the trials and meta-analyses, particularly the most recent and largest National Institutes of Health-sponsored trial (the Carotid Revascularization Endarterectomy vs Stenting Trial [CREST]), showed that carotid stenting and endarterectomy were associated with similar rates of death and disabling stroke. Within the 30-day periprocedural period, carotid stenting was associated with higher risks of stroke, especially for patients aged >70 years, whereas carotid endarterectomy was associated with a higher risk of myocardial infarction. The slightly higher cost of stenting compared with endarterectomy was within an acceptable range by cost-effectiveness standards. We conclude that carotid artery stenting is an equivalent alternative to carotid endarterectomy when patient age and anatomy, surgical risk, and operator experience are considered in the choice of treatment approach.

Randomized, double-blind pilot study of transendocardial injection of autologous aldehyde dehydrogenase-bright stem cells in patients with ischemic heart failure.

BACKGROUND: The optimal type of stem cell for use in patients with ischemic heart disease has not been determined. A primitive population of bone marrow-derived hematopoietic cells has been isolated by the presence of the enzyme aldehyde dehydrogenase and comprises a multilineage mix of stem and progenitor cells. Aldehyde dehydrogenase-bright (ALDH(br)) cells have shown promise in promoting angiogenesis and providing perfusion benefits in preclinical ischemia studies. We hypothesize that ALDH(br) cells may be beneficial in treating ischemic heart disease and thus conducted the first randomized, controlled, double-blind study to assess the safety of the transendocardial injection of autologous ALDH(br) cells isolated from the bone marrow in patients with advanced ischemic heart failure. METHODS: Aldehyde dehydrogenase-bright cells were isolated from patients' bone marrow on the basis of the expression of a functional (aldehyde dehydrogenase) marker. We enrolled 20 patients (treatment, n = 10; control, n = 10). Safety (primary end point) and efficacy (secondary end point) were assessed at 6 months. RESULTS: No major adverse cardiovascular or cerebrovascular events occurred in ALDH(br)-treated patients in the periprocedural period (up to 1 month); electromechanical mapping-related ventricular tachycardia (n = 2) and fibrillation (n = 1) occurred in control patients. Aldehyde dehydrogenase-bright-treated patients showed a significant decrease in left ventricular end-systolic volume at 6 months (P = .04) and a trend toward improved maximal oxygen consumption. The single photon emission computed tomography delta analysis showed a trend toward significant improvement in reversibility in cell-treated patients (P = .053). CONCLUSIONS: We provide preliminary evidence that treatment with the novel cell population, ALDH(br) cells, is safe and may provide perfusion and functional benefits in patients with chronic myocardial ischemia.

Flat-panel versus 64-channel computed tomography for in vivo quantitative characterization of aortic atherosclerotic plaques.

BACKGROUND: Flat-panel computed tomography (FpCT) provides better spatial resolution than 64-channel CT (64-CT) and may improve in vivo quantitative assessment of atherosclerotic plaques. METHODS AND RESULTS: Lesions in 184 aortic histology sections from 6 Watanabe heritable hyperlipidemic rabbits were quantitatively compared with 64-CT (image thickness, 0.625 mm) and FpCT (image thickness, 0.150 mm) images. Images were re-oriented perpendicular to the vessel centerline. For detecting plaque, FpCT and 64-CT were not significantly different (sensitivity, 76% vs 66%; P=NS). Although FpCT was significantly more sensitive (42% vs 0%; P=<0.001) for detecting eccentric lesions, the area under the curve (AUC) for FpCT (0.6) was not significantly different from that for 64-CT (0.45; P=NS). In detecting plaques with ≤ 10% lipid (low attenuation foci), FpCT was significantly more sensitive than 64-CT (24% vs 0.7%; P<0.00) and had a significantly greater AUC (0.6 vs 0.5; P<0.006). Additionally, FpCT was more sensitive (65% vs 0%; P<0.00) in detecting plaques with ≤ 5% calcium (high attenuation foci) but not in detecting branch points. Both FpCT and histology allowed us to detect low-attenuation foci as small as 0.3mm in diameter, whereas 64-CT allowed us to detect only low-attenuation foci ≥ 1.5mm in diameter. CONCLUSIONS: Flat-panel CT seemed to have more potential for quantitatively screening low-risk small atherosclerotic lesions, whereas 64-CT was apparently more useful when imaging established, well-characterized lesions, particularly when measuring the vascular wall thickness in a rabbit model of atherosclerosis.

Imaging long-term fate of intramyocardially implanted mesenchymal stem cells in a porcine myocardial infarction model.

The long-term fate of stem cells after intramyocardial delivery is unknown. We used noninvasive, repetitive PET/CT imaging with [(18)F]FEAU to monitor the long-term (up to 5 months) spatial-temporal dynamics of MSCs retrovirally transduced with the sr39HSV1-tk gene (sr39HSV1-tk-MSC) and implanted intramyocardially in pigs with induced acute myocardial infarction. Repetitive [(18)F]FEAU PET/CT revealed a biphasic pattern of sr39HSV1-tk-MSC dynamics; cell proliferation peaked at 33-35 days after injection, in periinfarct regions and the major cardiac lymphatic vessels and lymph nodes. The sr39HSV1-tk-MSC-associated [(18)F]FEAU signals gradually decreased thereafter. Cardiac lymphography studies using PG-Gd-NIRF813 contrast for MRI and near-infrared fluorescence imaging showed rapid clearance of the contrast from the site of intramyocardial injection through the subepicardial lymphatic network into the lymphatic vessels and periaortic lymph nodes. Immunohistochemical analysis of cardiac tissue obtained at 35 and 150 days demonstrated several types of sr39HSV1-tk expressing cells, including fibro-myoblasts, lymphovascular cells, and microvascular and arterial endothelium. In summary, this study demonstrated the feasibility and sensitivity of [(18)F]FEAU PET/CT imaging for long-term, in-vivo monitoring (up to 5 months) of the fate of intramyocardially injected sr39HSV1-tk-MSC cells. Intramyocardially transplanted MSCs appear to integrate into the lymphatic endothelium and may help improve myocardial lymphatic system function after MI.

Synthesis and evaluation of an anti-MLC1 × anti-CD90 bispecific antibody for targeting and retaining bone-marrow-derived multipotent stromal cells in infarcted myocardium.

A key issue regarding the use of stem cells in cardiovascular regenerative medicine is their retention in target tissues. Here, we have generated and assessed a bispecific antibody heterodimer designed to improve the retention of bone-marrow-derived multipotent stromal cells (BMMSC) in cardiac tissue damaged by myocardial infarction. The heterodimer comprises an anti-human CD90 monoclonal antibody (mAb) (clone 5E10) and an anti-myosin light chain 1 (MLC1) mAb (clone MLM508) covalently cross-linked by a bis-arylhydrazone. We modified the anti-CD90 antibody with a pegylated-4-formylbenzamide moiety to a molar substitution ratio (MSR) of 2.6 and the anti-MLC1 antibody with a 6-hydrazinonicotinamide moiety to a MSR of 0.9. The covalent modifications had no significant deleterious effect on mAb epitope binding. Furthermore, the binding of anti-CD90 antibody to BMMSCs did not prevent their differentiation into adipo-, chondro-, or osteogenic lineages. Modified antibodies were combined under mild conditions (room temperature, pH 6, 1 h) in the presence of a catalyst (aniline) to allow for rapid generation of the covalent bis-arylhydrazone, which was monitored at A(354). We evaluated epitope immunoreactivity for each mAb in the construct. Flow cytometry demonstrated binding of the bispecific construct to BMMSCs that was competed by free anti-CD90 mAb, verifying that modification and cross-linking were not detrimental to the anti-CD90 complementarity-determining region. Similarly, ELISA-based assays demonstrated bispecific antibody binding to plastic-immobilized recombinant MLC1. Excess anti-MLC1 mAb competed for bispecific antibody binding. Finally, the anti-CD90 × anti-MLC1 bispecific antibody construct induced BMMSC adhesion to plastic-immobilized MLC1 that was resistant to shear stress, as measured in parallel-plate flow chamber assays. We used mAbs that bind both human antigens and the respective pig homologues. Thus, the anti-CD90 × anti-MLC1 bispecific antibody may be used in large animal studies of acute myocardial infarction and may provide a starting point for clinical studies.

Human hepatocyte growth factor (VM202) gene therapy via transendocardial injection in a pig model of chronic myocardial ischemia.

BACKGROUND: Hepatocyte growth factor (HGF) may stimulate angiogenesis. We examined the safety and therapeutic potential of the HGF plasmid (VM202) in pigs with chronic myocardial ischemia. METHODS AND RESULTS: We delivered VM202 or vehicle transendocardially to 4 groups of pigs: vehicle control (n = 9); high-dose VM202 (n = 9); low-dose VM202 (n = 3); and normal control (no ischemia; n = 1). Pigs were killed 3, 30, and 60 days after injection. No adverse events were associated with VM202 treatment or delivery. Quantitative polymerase chain reaction indicated that heart injection sites had the highest levels of VM202 (day 3), which became almost undetectable by 30-60 days. Most nontarget tissues showed clearance of VM202 plasmid by day 30. Control and VM202-treated pigs did not differ in global functional data. Dobutamine-stressed myocardial-contrast echocardiogram suggested that VM202 may help preserve microvascular perfusion at 30 days; reperfusion velocity in ischemic myocardium decreased significantly in control (baseline to follow-up, 5.1 ± 1.9 to 2.7 ± 1.0; P = .031) but not in VM202 groups (high-dose: 3.1 ± 1.1 vs 3.1 ± 1.5 [P = .511]; low-dose: 3.8 ± 1.1 vs 3.9 ± 1.5 [P = .559]). Linear local shortening increased significantly from day 0 to 30 in VM202-treated versus control pigs (5.0 ± 4.7% vs 9.2 ± 7.5% vs 0.9 ± 5.8% [high-dose, low-dose, control, respectively]; P = .021). CONCLUSIONS: Transendocardial delivery of VM202 was safe and may help to preserve microcirculatory perfusion and improve wall motion.

A randomized study of transendocardial injection of autologous bone marrow mononuclear cells and cell function analysis in ischemic heart failure (FOCUS-HF).

BACKGROUND: Autologous bone marrow mononuclear cell (ABMMNC) therapy has shown promise in patients with heart failure (HF). Cell function analysis may be important in interpreting trial results. METHODS: In this prospective study, we evaluated the safety and efficacy of the transendocardial delivery of ABMMNCs in no-option patients with chronic HF. Efficacy was assessed by maximal myocardial oxygen consumption, single photon emission computed tomography, 2-dimensional echocardiography, and quality-of-life assessment (Minnesota Living with Heart Failure and Short Form 36). We also characterized patients' bone marrow cells by flow cytometry, colony-forming unit, and proliferative assays. RESULTS: Cell-treated (n = 20) and control patients (n = 10) were similar at baseline. The procedure was safe; adverse events were similar in both groups. Canadian Cardiovascular Society angina score improved significantly (P = .001) in cell-treated patients, but function was not affected. Quality-of-life scores improved significantly at 6 months (P = .009 Minnesota Living with Heart Failure and P = .002 physical component of Short Form 36) over baseline in cell-treated but not control patients. Single photon emission computed tomography data suggested a trend toward improved perfusion in cell-treated patients. The proportion of fixed defects significantly increased in control (P = .02) but not in treated patients (P = .16). Function of patients' bone marrow mononuclear cells was severely impaired. Stratifying cell results by age showed that younger patients (≤60 years) had significantly more mesenchymal progenitor cells (colony-forming unit fibroblasts) than patients >60 years (20.16 ± 14.6 vs 10.92 ± 7.8, P = .04). Furthermore, cell-treated younger patients had significantly improved maximal myocardial oxygen consumption (15 ± 5.8, 18.6 ± 2.7, and 17 ± 3.7 mL/kg per minute at baseline, 3 months, and 6 months, respectively) compared with similarly aged control patients (14.3 ± 2.5, 13.7 ± 3.7, and 14.6 ± 4.7 mL/kg per minute, P = .04). CONCLUSIONS: ABMMNC therapy is safe and improves symptoms, quality of life, and possibly perfusion in patients with chronic HF.

A randomized, controlled study of autologous therapy with bone marrow-derived aldehyde dehydrogenase bright cells in patients with critical limb ischemia.

OBJECTIVES: The safety and efficacy of direct intramuscular injections of aldehyde dehydrogenase bright (ALDH(br)) cells isolated from autologous bone marrow mononuclear cells (ABMMNCs) and ABMMNCs were studied in patients with critical limb ischemia (CLI) who were not eligible for percutaneous or surgical revascularization. BACKGROUND: Many CLI patients are not candidates for current revascularization procedures, and amputation rates are high in these patients. Cell therapy may be a viable option for CLI patients. METHODS: Safety was the primary objective and was evaluated by occurrence of adverse events. Efficacy, the secondary objective, was evaluated by assessment of Rutherford category, ankle-brachial index (ABI), transcutaneous partial pressure of oxygen (TcPO(2)), quality of life, and pain. RESULTS: ALDH(br) cells and ABMMNCs were successfully administered to all patients. No therapy-related serious adverse events occurred. Patients treated with ALDH(br) cells (n = 11) showed significant improvements in Rutherford category from baseline to 12 weeks (mean, 4.09 ± 0.30 to 3.46 ± 1.04; P = 0.05) and in ABI at 6 (mean, 0.22 ± 0.19 to 0.30 ± 0.24; P = 0.02), and 12 weeks (mean, 0.36 ± 0.18; P = 0.03) compared with baseline. Patients in the ABMMNC group (n = 10) showed no significant improvements at 6 or 12 weeks in Rutherford category but did show improvement in ABI from baseline to 12 weeks (0.38 ± 0.06 to 0.52 ± 0.16; P = 0.03). No significant changes from baseline were noted in ischemic ulcer grade or TcPO(2) in either group. CONCLUSIONS: Administration of autologous ALDH(br) cells appears to be safe and warrants further study in patients with CLI.

Coronary blood flow responses to physiological stress in humans.

Animal reports suggest that reflex activation of cardiac sympathetic nerves can evoke coronary vasoconstriction. Conversely, physiological stress may induce coronary vasodilation to meet an increased metabolic demand. Whether the sympathetic nervous system can modulate coronary vasomotor tone in response to stress in humans is unclear. Coronary blood velocity (CBV), an index of coronary blood flow, can be measured in humans by noninvasive duplex ultrasound. We studied 11 healthy volunteers and measured beat-by-beat changes in CBV, blood pressure, and heart rate during 1) static handgrip for 20 s at 10% and 70% of maximal voluntary contraction; 2) lower body negative pressure at -10 and -30 mmHg for 3 min each; 3) cold pressor test for 90 s; and 4) hypoxia (10% O(2)), hyperoxia (100% O(2)), and hypercapnia (5% CO(2)) for 5 min each. At the higher level of handgrip, mean blood pressure increased (P < 0.001), whereas CBV did not change [P = not significant (NS)]. In addition, during lower body negative pressure, CBV decreased (P < 0.02; and P < 0.01, for -10 and -30 mmHg, respectively), whereas blood pressure did not change (P = NS). The dissociation between the responses of CBV and blood pressure to handgrip and lower body negative pressure is consistent with coronary vasoconstriction. During hypoxia, CBV increased (P < 0.02) and decreased during hyperoxia (P < 0.01), although blood pressure did not change (P = NS), suggesting coronary vasodilation during hypoxia and vasoconstriction during hyperoxia. In contrast, concordant increases in CBV and blood pressure were noted during the cold pressor test, and hypercapnia had no effects on either parameter. Thus the physiological stress known to be associated with sympathetic activation can produce coronary vasoconstriction in humans. Contrasting responses were noted during systemic hypoxia and hyperoxia where mechanisms independent of autonomic influences appear to dominate the vascular end-organ effects.

Vasoconstriction seen in coronary bypass grafts during handgrip in humans.

In animal studies, sympathetically mediated coronary vasoconstriction has been demonstrated during exercise. Human studies examining coronary artery dynamics during exercise are technically difficult to perform. Recently, noninvasive transthoracic Duplex ultrasound studies demonstrated that 1) patients with left internal mammary artery (LIMA) grafts to the left anterior descending artery can be imaged and 2) the LIMA blood flow patterns are similar to those seen in normal coronary arteries. Accordingly, subjects with LIMA to the left anterior descending artery were studied during handgrip protocols as blood flow velocity in the LIMA was determined. Beat-by-beat analysis of changes in diastolic coronary blood flow velocity (CBV) was performed in six male clinically stable volunteers (60 +/- 2 yr) during two handgrip protocols. Arterial blood pressure (BP) and heart rate (HR) were also measured, and an index of coronary vascular resistance (CVR) was calculated as diastolic BP/CBV. Fatiguing handgrip performed at [40% of maximal voluntary contraction (MVC)] followed by circulatory arrest did not evoke an increase in CVR (P = not significant). In protocol 2, short bouts of handgrip (15 s) led to increases in CVR (18 +/- 3% at 50% MVC and 20 +/- 8% at 70% MVC). BP was also increased during handgrip. Our results reveal that in conscious humans, coronary vasoconstriction occurs within 15 s of onset of static handgrip at intensities at or greater than 50% MVC. These responses are likely to be due to sympathetic vasoconstriction of the coronary circulation.

Renal vasoconstrictor responses to static exercise during orthostatic stress in humans: effects of the muscle mechano- and the baroreflexes.

Renal circulatory adjustments to stress contribute to blood pressure and volume regulation. Both handgrip (HG) and disengagement of baroreflexes with lower body negative pressure (LBNP) can engage the sympathetic nervous system (SNS). However, the effect of simultaneous HG and LBNP on the renal circulation in humans is not known. Eighteen young healthy volunteers were studied. Beat-to-beat changes in renal blood flow velocity (RBV; Duplex Ultrasound), mean arterial pressure (MAP; Finapres) and heart rate (ECG) were monitored during (a) 15 s HG at 30% maximum voluntary contraction (MVC); (b) LBNP at -10 and -30 mmHg (each level for 5 min); and (c) 15 s HG (at 30% MVC) during LBNP at both levels. Renal vascular resistance index (RVR units) was calculated by dividing MAP by RBV. The increases in RVR during HG alone (12 +/- 6%) were not different from the responses noted during combined HG and LBNP (17 +/- 6% at -10 mmHg and 25 +/- 8% at -30 mmHg). These results suggest occlusion occurs between a neural circuit engaged during 15 s of HG (central command and/or the muscle mechanoreflex) and a circuit activated by LBNP. In additional experiments (n = 6), similar non-algebraic summation of RVR was seen during 15 s involuntary biceps contractions (engages only muscle reflexes) and LBNP. With respect to RVR, neural occlusion occurs between baroreflexes and the muscle mechanoreflex. Muscle mechanoreflex mediated renal vasoconstriction during short bouts of HG is not influenced by baroreflex disengagement.