Gravitational Lorentz Force and the Description of the Gravitational Interaction

In the context of a gauge theory for the translation group, we have obtained, for a spinless particle, a gravitational analog of the Lorentz force. Then, we have shown that this force equation can be rewritten in terms of magnitudes related to either the teleparallel or the riemannian structures induced in spacetime by the presence of the gravitational field. In the first case, it gives a force equation, with torsion playing the role of force. In the second, it gives the usual geodesic equation of General Relativity. The main conclusion is that scalar matter is able to feel anyone of the above spacetime geometries, the teleparallel and the metric ones. Furthermore, both descriptions are found to be completely equivalent in the sense that they give the same physical trajectory for a spinless particle in a gravitational field.Comment: Equations (44)-(47) correcte

Sympathetic and hemodynamic responses to exercise in heart failure with preserved ejection fraction

Excessive sympathetic activity during exercise causes heightened peripheral vasoconstriction, which can reduce oxygen delivery to active muscles, resulting in exercise intolerance. Although both patients suffering from heart failure with preserved and reduced ejection fraction (HFpEF and HFrEF, respectively) exhibit reduced exercise capacity, accumulating evidence suggests that the underlying pathophysiology may be different between these two conditions. Unlike HFrEF, which is characterized by cardiac dysfunction with lower peak oxygen uptake, exercise intolerance in HFpEF appears to be predominantly attributed to peripheral limitations involving inadequate vasoconstriction rather than cardiac limitations. However, the relationship between systemic hemodynamics and the sympathetic neural response during exercise in HFpEF is less clear. This mini review summarizes the current knowledge on the sympathetic (i.e., muscle sympathetic nerve activity, plasma norepinephrine concentration) and hemodynamic (i.e., blood pressure, limb blood flow) responses to dynamic and static exercise in HFpEF compared to HFrEF, as well as non-HF controls. We also discuss the potential of a relationship between sympathetic over-activation and vasoconstriction leading to exercise intolerance in HFpEF. The limited body of literature indicates that higher peripheral vascular resistance, perhaps secondary to excessive sympathetically mediated vasoconstrictor discharge compared to non-HF and HFrEF, drives exercise in HFpEF. Excessive vasoconstriction also may primarily account for over elevations in blood pressure and concomitant limitations in skeletal muscle blood flow during dynamic exercise, resulting in exercise intolerance. Conversely, during static exercise, HFpEF exhibit relatively normal sympathetic neural reactivity compared to non-HF, suggesting that other mechanisms beyond sympathetic vasoconstriction dictate exercise intolerance in HFpEF

Evolving Discourses on Water Resource Management and Climate Change in the Equatorial Nile Basin

Transboundary water resources management in the Equatorial Nile Basin (EQNB) is a politically contested issue. There is a growing body of literature examining water-related discourses which identifies the ability of powerful actors and institutions to influence policy. Concern about the effects of future climate change has featured strongly in research on the Nile River for several decades. It is therefore timely to consider whether and how these concerns are reflected in regional policy documents and policy discourse. This study analyzes discourse framings of water resources management and climate change in policy documents (27, published between 2001 and 2013) and as elicited in interviews (38) with water managers in the EQNB. Three main discursive framings are identified which are present in the discourses on both subjects: a problem-oriented environmental risk frame and two solution-oriented frames, on governance and infrastructure development. Climate change discourse only emerges as a common topic around 2007. The framings found in the water resources management discourse and the climate change discourse are almost identical, suggesting that discursive framings were adopted from the former for use in the latter. We infer that the climate change discourse may have offered a less politically sensitive route to circumvent political sensitivities around water allocation and distribution between riparian countries in the EQNB. However, the climate change discourse does not offer a lasting solution to the more fundamental political dispute over water allocation. Moreover, in cases where the climate change discourse is subsumed within a water resources management discourse, there are dangers that it will not fully address the needs of effective adaptation

Magnitude of the Morning Surge in Blood Pressure is Associated with Sympathetic but not Cardiac Baroreflex Sensitivity

The ability of the arterial baroreflex to regulate blood pressure may influence the magnitude of the morning surge in blood pressure. The aim was to investigate the relationships between sympathetic and cardiac baroreflex sensitivity (BRS) and the morning surge. Twenty-four hour ambulatory blood pressure was recorded in 14 young individuals. The morning surge was defined via the pre-awakening method, which is calculated as the difference between mean blood pressure values two hours before and two hours after rising from sleep. The mean systolic morning surge, diastolic morning surge and morning surge in mean arterial pressures were 15 ± 2 mmHg, 13 ± 1 mmHg and 11 ± 1 mmHg respectively. During the laboratory protocol, continuous measurements of blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) were made over a 10-min period of rest. Sympathetic BRS was quantified by plotting MSNA burst incidence against diastolic pressure (sympathetic BRSinc), and by plotting total MSNA against diastolic pressure (sympathetic BRStotal). Cardiac BRS was quantified using the sequence method. The mean values for sympathetic BRSinc, sympathetic BRStotal and cardiac BRS were -1.26 ± 0.26 bursts/100hb/mmHg, -1.60 ± 0.37 AU/beat/mmHg and 13.1 ± 1.5 ms/mmHg respectively. Significant relationships were identified between sympathetic BRSinc and the diastolic morning surge (r =0.62, p =0.02) and the morning surge in mean arterial pressure (r =0.57, p =0.03). Low sympathetic BRS was associated with a larger morning surge in mean arterial and diastolic blood pressure. Trends for relationships were identified between sympathetic BRStotal and the diastolic morning surge (r =0.52, p =0.066) and the morning surge in mean arterial pressure (r =0.48, p =0.095) but these did not reach significance. There were no significant relationships between cardiac BRS and the morning surge. These findings indicate that the ability of the baroreflex to buffer increases in blood pressure via reflexive changes in MSNA may play a role in determining the magnitude of the morning surge in blood pressure

The effects of biological sex and oral contraception on the sympathetic neurocirculatory adjustments to static handgrip exercise in humans.

Biological sex affects the neurocirculatory adjustments to fatiguing exercise. However, the effects of sex and oral contraceptive pills (OCPs) on sympathetic action potential (AP) emission patterns and the transduction of AP discharge into vasoconstriction during static handgrip (SHG) exercise remains unknown. We tested the hypothesis that males, and females using OCPs, would demonstrate larger increases in sympathetic activation and sympathetic vascular transduction compared to naturally menstruating females during SHG and post-exercise circulatory occlusion (PECO). Young males (n=14, 25[5] yr), females using OCPs (n=16, 24[6] yr), and naturally menstruating females (n=18, 26[4] yr) underwent assessments of multi-unit muscle sympathetic nerve activity (MSNA)/AP discharge patterns (microneurography), and femoral artery blood flow (ultrasound) during fatiguing SHG at 40% maximum voluntary contraction and 2-min PECO. Sympathetic vascular transduction was determined as the quotient of the change in leg vascular conductance (LVC) and MSNA/AP discharge. Males demonstrated greater increases in APs/burst (P=0.028) and total AP clusters (P=0.008) compared to naturally menstruating females only, but not those using OCPs during exercise. Sympathetic vascular transduction of MSNA burst amplitude, APs/burst, and total AP clusters was greater in males and females using OCPs compared to naturally menstruating females (range: P=0.004-0.044). In contrast, no group differences in AP discharge were observed during PECO (range: P=0.510-0.872), and AP discharge was not related to LVC during PECO (range: P=0.08-0.949). These data indicate that biological sex and OCP use impact the central generation of efferent AP discharge, as well as the transduction of these neuronal messages into peripheral vasoconstriction during static exercise

Relationship between spontaneous sympathetic baroreflex sensitivity and cardiac baroreflex sensitivity in healthy young individuals

Low baroreflex sensitivity (BRS) is associated with elevated cardiovascular risk. However, the evidence is based primarily on measurements of cardiac BRS. It cannot be assumed that cardiac or sympathetic BRS alone represent a true reflection of baroreflex control of blood pressure. The aim of this study was to examine the relationship between spontaneous sympathetic and cardiac BRS in healthy, young individuals. Continuous measurements of blood pressure, heart rate, and muscle sympathetic nerve activity (MSNA) were made under resting conditions in 50 healthy individuals (18–28 years). Sympathetic BRS was quantified by plotting MSNA burst incidence against diastolic pressure (sympathetic BRSinc), and by plotting total MSNA against diastolic pressure (sympathetic BRStotal). Cardiac BRS was quantified by plotting R‐R interval against systolic pressure using the sequence method. Significant sympathetic BRSinc and cardiac BRS slopes were obtained for 42 participants. A significant positive correlation was found between sympathetic BRSinc and cardiac BRS (r = 0.31, P = 0.049). Among this group, significant sympathetic baroreflex slopes were obtained for 39 participants when plotting total MSNA against diastolic pressure. In this subset, a significant positive correlation was observed between sympathetic BRStotal and cardiac BRS (r = 0.40, P = 0.012). When males and females were assessed separately, these modest relationships only remained significant in females. Analysis by gender revealed correlations in the females between sympathetic BRSinc and cardiac BRS (r = 0.49, P = 0.062), and between sympathetic BRStotal and cardiac BRS (r = 0.57, P = 0.025). These findings suggest that gender interactions exist in baroreflex control of blood pressure, and that cardiac BRS is not appropriate for estimating overall baroreflex function in healthy, young populations. This relationship warrants investigation in aging and clinical populations

Age- and sex-specific differences in sympathetic vascular transduction and neuro-hemodynamic balance in humans.

Bursts of muscle sympathetic nerve activity (MSNA) and the ensuing vasoconstriction are pivotal determinants of beat-by-beat blood pressure regulation. Although age and sex impact blood pressure regulation, how these factors affect the central and peripheral arcs of the baroreflex remains unclear. In 27 young (25[3] years) males (YM; n=14) and females (YF; n=13) and 23 older (71[5] years) males (OM; n=11) and females (OF; n=12) femoral artery blood flow, blood pressure and MSNA were recorded for 10 minutes of supine rest. Sympathetic baroreflex sensitivity (i.e., central arc) was quantified as the relationship between diastolic blood pressure and MSNA burst incidence. Signal averaging was used to determine sympathetic vascular transduction into leg vascular conductance (LVC) for 12 cardiac cycles following MSNA bursts (i.e., peripheral arc). Older adults demonstrated attenuated sympathetic transduction into LVC (both PP=0.004-0.032). YM (r2=0.36; P=0.032) and OM (r2=0.51; P=0.014) exhibited an inverse relationship between the central and peripheral arcs of the baroreflex, whereas females did not (YF: r2=0.03; P=0.621, OF: r2=0.06; P=0.445). MSNA burst incidence was inversely related with sympathetic transduction in YM and OF (range: P=0.03-0.046), but not in YF or OM (range: P=0.360-0.603). These data indicate that age is associated with attenuated sympathetic vascular transduction whereas age- and sex-specific changes are present in the relationship between the central and peripheral arcs of the baroreflex regulation of blood pressure