Blood pressure reactivity and salt sensitivity in non-hypertensive adults

Matthews, Evan L.
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University of Delaware
The central goal of this project was to determine the relationship, if any, salt sensitivity (SS) status has with the autonomic nervous system control of blood pressure (BP) during rest and sympathoexcitation. This is important because SS is thought to be linked to the autonomic nervous system, yet very little human based research has been done on the topic. Additionally, individuals with high degrees of SS are more likely to develop hypertension and die of cardiovascular disease. We enrolled 50 non-hypertensive adults predetermined for SS status to undergo testing during rest, isometric handgrip exercise, post-exercise ischemia (PEI), venous distension, and a cold pressor test. We measured continuous BP, muscle sympathetic nervous activity (MSNA), and limb (femoral artery) blood flow. Additionally, sympathetic baroreflex sensitivity was assessed during rest and PEI. BP reactivity was not related to SS status during any of the sympathoexcitatory tests (all p>0.05). Furthermore, no relationship existed between SS status and the response of MSNA or limb resistance during PEI, venous distension, or the cold pressor test (all p>0.05). However, resting MSNA (burst frequency r=0.47, p=0.041; and burst incidence r=0.46, p=0.046) was directly related to SS status. During handgrip MSNA response was inversely related for all measures (all r<-0.50; p<0.05) except burst incidence (r=-0.37; p=0.129), as was limb resistance (r=-0.38; p=0.016). Conversely limb blood flow was positively related to SS status (r=0.33; p=0.036). This suggests that although the BP response was not related to SS status during handgrip, those with the greatest SS support the BP response with increased blood flow rather than increased sympathetic activity and resistance. Additionally, sympathetic baroreflex sensitivity did not relate SS status at rest or during PEI. Our findings suggest that resting sympathetic activity, but not sympathetic reactivity or sympathetic baroreflex sensitivity are related to salt sensitivity status in non-hypertensive adults. More research is needed to determine the cause and potential effects of these findings.