The impact of obesity on the relationship between pulse-wave velocity and 24-hour urinary electrolyte excretion

Date
2020
Authors
Nkosi, Brian Godfrey
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Abstract
An upsurge in overweight or obesity in South Africa is largely implicated as a contributing factor in the rise of cardiovascular diseases. Hypertension and arterial stiffness are largely promoted by dietary habits including high salt and low potassium consumption. This is especially of greater concern in a salt-sensitive population with a high incidence of obesity such as this. Since the high incidence of obesity in this population and previous reports of obesity masking the relationship between urinary sodium excretion and blood pressure, the role of obesity in modifying the relationship between urinary electrolytes and pulse wave velocity was investigated. One-hundred-and-fifty South African individuals of African ancestry were randomly recruited in and around Johannesburg. The participants were divided into two groups according to BMI, namely normal weight (BMI<25 but > than 18) and overweight/ obese (BMI≥25) individuals. Blood pressure was measured using 24-hour ambulatory BP monitoring, while electrolyte excretion was assessed by the collection of 24-hour urine samples. Arterial stiffness was indexed by use of carotid-femoral pulse wave velocity (PWV) measurement. Urinary daytime K+ excretion was directly associated with 24-hour systolic BP (P=0.019) and daytime systolic BP (P=0.024). Night-time Na+:K+ ratio was directly associated with 24-hour systolic BP in the overweight/ obese group (P= 0.034). Night-time Na+:K+ ratio was directly associated with systolic (P= 0.006) and diastolic BP (P= 0.040) in the overweight/ obese group. Twenty-four-hour Na+:K+ ratio was significantly associated with night-time systolic BP (P= 0.021). Pulse wave velocity was directly associated with BMI (P<0.001), and WC (P<0.001). No relationship was observed between PWV and 24-hour urinary electrolytes. Overweight/ obesity diminishes arterial compliance and reduces arterial compliance thus leading to increases in BP. However, obesity does not influence the relationship between urinary electrolyte excretion and PWV
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A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Medicine, 2020
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