EXERCISE HEART RATE DURING TREADMILL TEST IS RELATED TO RENAL FUNCTIONAL RESERVE IN ESSENTIAL HYPERTENSIVE PATIENTS: A NOVEL LINK BETWEEN THE HEART AND THE KIDNEYS

Objective: Renal functional reserve (RFR) refers to the capacity of the kidney to augment its level of function under the influence of certain stimuli and it constitutes a valuable diagnostic tool for recognizing high risk patients for acute kidney injury and chronic kidney disease. The aim of our study was to assess the relation of RFR with diverse clinical parameters in patients with essential hypertension and glomerular filtration rate (GFR) > 60 ml/min/1.73m2. Design and method: 15 hypertensive subjects [mean age = 57 years, body mass index = 28.5 kg/m2, office systolic/diastolic blood pressure (BP) = 148/90 mmHg] were included and underwent exercise treadmill stress test, 24-hour ambulatory BP and echocardiographic examination. All subjects were fasted for 8 hours and then baseline hydration status was recorded using bioimpedance analysis. Basal GFR was measured after hydration and stress GFR was achieved after ingestion of oral protein 1 g/kg as cooked meal. Basal and Stress GFR were determined by Creatinine Clearance = Urine Creatinine/Serum Creatinine x Urine Volume/time x 1.73/body surface area. RFR was calculated as Stress GFR – Basal GFR. Results: Patients with a history of hypertension greater than 10 years, had lower RFR values (-14.59 ± 43.26vs 21.35 ± 28.19 ml/min/1.73m2, p < 0.001). There was no correlation of RFR values with respect to age, family history, smoking, dipping status and office BP. In contrast, a statistically significant positive correlation was found between RFR and maximum heart rate during treadmill test (r = 0.880, p = 0.009). Hypertensives with high RFR were also characterized by higher maximum HR during treadmill test (157 ± 22 vs 142 ± 20 bpm, p < 0.05). Conclusions: RFR is related to treadmill exercise heart rate in essential hypertension, suggesting a link between the dynamic regulation of renal function and sympathetic overdrive's influence on the heart rate. These findings suggest that treadmill test may be used to identify hypertensive patients with unfavorable RFR, thus more susceptible to kidney damage.