Reactivity In Blacks Research Articles

Comparison of Platelet Reactivity in Black Versus White Patients With Acute Coronary Syndromes After Treatment With Ticagrelor

Ticagrelor, a potent platelet inhibitor, has primarily been studied in white patients. Platelet reactivity among black patients with acute coronary syndrome (ACS) on ticagrelor, however, is unknown. Our objective was to compare platelet reactivity in black versus white patients with ACS treated with ticagrelor. We conducted a prospective, pharmacodynamic study of 29 black patients with ACS treated with ticagrelor. Platelet reactivity was assessed at 1, 4, and 8hours after a loading dose of ticagrelor 180mg and at 30days on a maintenance dose of ticagrelor 90mg twice daily. Assays included light transmission aggregometry, VerifyNow P2Y12, and vasodilator-stimulated phosphoprotein. We provided comparison with a historical white cohort. Platelet reactivity among blacks with ACS on ticagrelor was similar to that in whites, except that blacks had lower values at 4hours, 8hours, and on maintenance therapy for light transmission aggregometry with 20μmol/L adenosine diphosphate. Among blacks, high-on-treatment platelet reactivity for all 3 assays was uncommon at 1hour and nonexistent at 4hours, 8hours, and while on maintenance therapy. Blacks preloaded with clopidogrel (n= 17) had significantly lower results of VerifyNow (64 ± 65 vs 198 ± 86, p <0.001) and vasodilator-stimulated phosphoprotein (12.8 ± 21.6 vs 58.9 ± 19.9, p <0.001) at 1hour compared with those with no clopidogrel preload. In conclusion, among patients with ACS receiving ticagrelor, levels of platelet reactivity in blacks are similar to that in whites. This suggests that the cardiovascular benefits of ticagrelor observed in the platelet inhibition and patient outcomes (PLATO) trial are likely to be observed in blacks and whites.

Study of sodium manganese fluorides as positive electrodes for Na-ion batteries

Na2MnF5 and NaMnF3 were prepared in aqueous media using Mn2O3 and NaMnO4·H2O as Mn precursors and characterized by XRPD, ATR-IR and ICP-OES/ICP-MS. Additionally, a new metastable hydrated oxyfluoride was prepared, with a diffraction pattern (neutron and SXRPD data) consistent with an orthorhombic cell with a=4.07559Å, b=9.04090Å and c=6.77290Å and Cccm space group which yielded NaMnF4 upon dehydration. The feasibility of Na+ deintercalation was experimentally tested in electrochemical cells against sodium metal counter electrodes under different conditions, and also investigated by first principles methods. Experimental results were confronted to blank experiments performed with electrodes containing only carbon black and allowed to conclude that the redox processes observed were not related to active materials but to electrolyte/carbon black reactivity. DFT results point at the electrochemical activity of such compounds taking place at high potential values, in some cases well outside the electrolyte stability window. In the case of NaMnF3, for which he calculated density of states predicts a bang gap of 2.7eV, its insulating character induces significant cell polarization thus electrochemical activity cannot not practically reached with the available electrolytes.

Subjective Stress and Coping Resources Interact to Predict Blood Pressure Reactivity in Black College Students

This study examined the effects of subjective stress and coping resources on blood pressure reactivity. Sixty-nine Black college students (mean age = 23.58 years) completed the Life Experiences and Stress Scale to explore the subjective stressfulness associated with life events, the Coping Orientations to Problems Experienced Scale to measure usual ways of coping, and a standardized serial addition laboratory challenge during which blood pressure was assessed. Multiple regression analyses revealed that the interactive effects of subjective stress and coping resources predicted diastolic blood pressure reactivity (both p &lt; .025) but not systolic blood pressure reactivity (both p &gt; .10). These significant interaction effects indicated that higher levels of problem-focused coping were related to more marked diastolic blood pressure changes under conditions of high subjective stress and that emotion-focused coping was associated with less exaggerated diastolic blood pressure changes under conditions of low subjective stress. These findings highlight the potential contribution of psychosocial factors to blood pressure reactivity in Blacks.

Parental History of Hypertension and Coping Responses Predict Blood Pressure Changes in Black College Volunteers Undergoing a Speaking Task About Perceptions of Racism

This investigation explored the relationship of coping responses and parental history of hypertension to task-induced blood pressure changes. The sample consisted of 215 black college student volunteers (median age = 25.95 y). During the speaking task, participants responded to standardized questions about perceptions of intra-ethnic and inter-ethnic group racism. Systolic blood pressure and diastolic blood pressure were measured via an automated blood pressure monitor. Usual ways of coping with intra-ethnic group racism were assessed with the COPE Scale, and parental history of hypertension (PHH) was self-reported by participants. Findings from the final step of hierarchical general linear models indicated that the main effect of emotion-focused coping was negatively associated with diastolic blood pressure (p = 0.02) and systolic blood pressure (p = 0.002) changes. Further, these analyses revealed that PHH interacted: (1) with the coping responses of planning (p = 0.007) and denial (p = 0.002) to predict changes in systolic blood pressure and (2) with the planning coping response to predict diastolic blood pressure changes (p = 0.02). The direction of these effects indicated that among participants who were high in these coping responses, participants who also had a positive PHH had larger blood pressure changes. Regression analyses also revealed that PHH interacted with the cognitive coping response (p = 0.01) to predict changes in systolic blood pressure. The direction of this effect indicated that among participants who were low in this coping response, participants who also had a positive PHH had larger systolic blood pressure changes. This study highlights the importance of examining the joint contribution of biological and psychosocial parameters to blood pressure reactivity in blacks.

Self-reported racism and social support predict blood pressure reactivity in Blacks.

This study explored the effects of perceived racism and social support (quantity and quality) on blood pressure reactivity. In a college sample of 64 Blacks (M age = 22.69 years, SD =6.60), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were assessed before and during a standardized serial subtraction task. Perceptions of racism and the quantity and quality of social support were measured by self-report. Separate multiple regression analyses revealed that perceived racism and social support (neither quantity nor quality) were not independent predictors of SBP or DBP changes (ps >.05). These analyses did indicate that perceived racism interacted with the quantity of social support (p <.002, partial R2 =.175) and with the quality of social support (p <.0007, partial R2 =.195) to predict DBP changes. Perceived racism also interacted with the quantity of social support to predict changes in SBP (p <.02, partial R2 =.11). In general, whereas high social support was related to less marked blood pressure changes under conditions of low perceived racism, high social support was associated with exaggerated blood pressure changes under conditions of high perceived racism. These significant interaction effects persisted after statistically controlling for potential confounders. The findings highlight the importance of examining the joint contribution of real-world experiences and coping resources to blood pressure reactivity in Blacks.

Sympathetic vascular transduction is augmented in young normotensive blacks.

The purpose of the present study was to determine sympathetic vascular transduction in young normotensive black and white adults. We hypothesized that blacks would demonstrate augmented transduction of muscle sympathetic nerve activity (MSNA) into vascular resistance. To test this hypothesis, MSNA, forearm blood flow, heart rate, and arterial blood pressure were measured during lower body negative pressure (LBNP). At rest, no differences existed in arterial blood pressure, heart rate, forearm blood flow, and forearm vascular resistance (FVR). Likewise, LBNP elicited comparable responses of these variables for blacks and whites. Baseline MSNA did not differ between blacks and whites, but whites demonstrated greater increases during LBNP (28 +/- 7 vs. 55 +/- 18%, 81 +/- 21 vs. 137 +/- 42%, 174 +/- 81 vs. 556 +/- 98% for -5, -15, and -40 mmHg LBNP, respectively; P < 0.001). Consistent with smaller increases in MSNA but similar FVR responses during LBNP, blacks demonstrated greater sympathetic vascular transduction (%FVR/%MSNA) than whites (0.95 +/- 0.07 vs. 0.82 +/- 0.07 U; 0.82 +/- 0.11 vs. 0.64 +/- 0.09 U; 0.95 +/- 0.37 vs. 0.35 +/- 0.09 U; P < 0.01). In summary, young whites demonstrate greater increases in MSNA during baroreceptor unloading than age-matched normotensive blacks. However, more importantly, for a given increase in MSNA, blacks demonstrate greater forearm vasoconstriction than whites. This finding may contribute to augmented blood pressure reactivity in blacks.

Racial Differences in Hemodynamic Responses to Environmental Thermal Stress Among Adolescents

Previous studies by our laboratory and others have shown that blood pressure (BP) responses to many short-term laboratory stressors are greater in black than in white children. We sought to determine the cardiac and vascular contributions to these differences in BP reactivity and whether racial differences in vascular reactivity involve excessive vasoconstriction or deficient vasodilation. We evaluated BP, heart rate, and impedance cardiographic measures of preejection period (PEP) and total peripheral resistance (TPR) in healthy black (n=76) and white (n=60) adolescents (mean age, 14.8 years) during passive exposure to a vasoconstrictive cold chamber (8 degrees C to 10 degrees C) and a vasodilatory heat chamber (40 degrees C to 42 degrees C). Results indicated greater decreases in PEP and increases in TPR in blacks than whites during cold exposure (P<0.05) but no group differences during heat exposure. Covariance analyses indicated that the racial differences during cold exposure probably reflected greater beta-adrenergic cardiac reactivity and alpha-adrenergic vasoconstrictive reactivity in blacks than whites. Blacks and whites exhibited comparable myocardial and vasodilatory responses to heat stress, but blacks exhibited heightened myocardial and vasoconstrictive reactivity to cold stress. These results suggest that the locus of racial differences in vascular reactivity involves vasoconstrictive rather than vasodilatory function. The pattern of racial differences during cold stress raises the possibility that both myocardial and vasoconstrictive mechanisms may contribute to the increased risk of hypertension in blacks.

Manifest Hostility may Affect Habituation of Cardiovascular Reactivity in Blacks

In a study of cardiovascular reactivity to dietary manipulation of sodium and calcium, we pretested 30 young black normotensive males who were equally divided by positive and negative parental histories of hypertension with a 12-item anger questionnaire we devised and the Cook-Medley Hostility, Manifest Hostility, Overcontrolled Hostility, and Inhibited Hostility scales of the Minnesota Multiphasic Personality Inventory. Contrary to expectations, we found no correlation of resting blood pressure or cardiovascular reactivity to repeated mental demands with the two measures of inhibited hostility. We did, however, find resistance to habituation of cardiovascular reactivity in subjects with high Manifest Hostility and positive family histories of essential hypertension. Our findings suggest that vulnerability to hypertension may be revealed by the perseveration of blood pressure reactivity to repeated mental challenge. We propose that the perseveration of blood pressure reactivity is a disinhibitory phenomenon caused by a difficulty in the management of multiple inhibitory demands that disrupts the natural course of habituation and could be an important etiologic factor in essential hypertension.

Psychophysiological reactivity to mental arithmetic stress in black and white normotensive men.

Racial differences in physiological responses to a behavioral stressor were examined. Thirty-four Black and 42 White male normotensives 34 to 55 years old (mean age = 43.01 years) performed a mental arithmetic task while blood pressure, heart rate, and skin conductance were recorded. Compared to Whites, Blacks had significantly higher baseline diastolic blood pressure (77.93 mm Hg vs. 73.11 mm Hg) and lower skin conductance levels (11.08 microS vs. 12.25 microS). These effects persisted during performance of the mental arithmetic task. However, when baseline differences were covaried, there were no significant physiological effects associated with the task. Analysis of changes in response levels from baseline revealed a nonsignificant trend for Whites to show greater increases in systolic blood pressure than Blacks. There were no significant race or family history effects. Further, task performance did not influence the outcome. Failure to demonstrate greater cardiovascular reactivity in Blacks and all men with a positive family history of hypertension is discussed with regard to possible "survivor effects" and methodologic limitations.