Physiology of the Healthy Aging Kidney

Changes in renal function after catheter ablation of atrial fibrillation are associated with CHADS2and CHA2DS2-VASc scores and arrhythmia recurrences

“…The average eGFR decline is about 0.8 mL/min/1.73 m 2 every year after the age of 30 years and acceleration of the eGFR decline occurs after the age of 65 years 24. However, creatinine clearance decreases over time at a rate of up to 8 mL/min/year and is considered as significant worsening in renal function 25…”

Renal Functional Reserve and Renal Recovery after Acute Kidney Injury

“…GFR is remarkably stable over years, although it may change from day to day. There is an age-related decline in GFR physiologically by 0.8 ml/min/1.73 m 2 /year, after the age of 30 years [2,3,4]. It was found that the rates of decline in GFR were lower in healthy males than healthy females [5]; however, in chronic kidney disease (CKD), these rates are similar [5].…”

Creatinine, urea, uric acid, water and electrolytes renal handling in the healthy oldest old

“…On one hand, it has been documented that fractional excretion of urea, in volume contraction as well as in volume expansion, was significantly higher than the one reached by the young: 40% vs 24% (P = 0.017) and 65% vs 53% (P = 0.04) respectively [14][15][16] . Due to the fact that a reduction in the number of urea channels (UT1) has been documented in the collecting tubules of very old rats, it could be suggested that the senile increase in urea excretion may be the consequence of a lower reabsorption of urea at the distal tubules [17] . Clinical consequences: This increase in the urea urinary excretion, as well as the low protein diet that aged people usually have, both explain the normal serum urea value characteristically found in the elderly, despite of their reduced glomerular filtration rate [17] .…”

“…Due to the fact that a reduction in the number of urea channels (UT1) has been documented in the collecting tubules of very old rats, it could be suggested that the senile increase in urea excretion may be the consequence of a lower reabsorption of urea at the distal tubules [17] . Clinical consequences: This increase in the urea urinary excretion, as well as the low protein diet that aged people usually have, both explain the normal serum urea value characteristically found in the elderly, despite of their reduced glomerular filtration rate [17] . Additionally, the high urea urinary excretion documented in the very old could be one of the factors which explains the senile medullar hypotonicity (reduced urea medullar content) and the nocturia (urea osmotic diuresis) usually found in the very old patients [15,16] .…”

“…The information obtained by means of the furosemide test (senile hyposecretion of potassium) explains why the tubular handling of potassium (measured as FEK and transtubular potassium gradient: TTKG) in basal situation, does not show any significant difference between the very old group and the young one, despite the existence of lower glomerular filtration in the very old, which ultimately accounts for the relatively reduced cation excretion in the very old, since it is known that the potassium excretion tends to increase paralelly to the reduction of glomerular filtration: FEK: 10% (young) vs 8% (very old); TTKG: 4 (young) vs 4 (very old), P = NS [25] . Clinical consequences: the reduced potassium secretion capability usually found in very old people explains how easy it is for this aged group to develop hyperkalemia when administered drugs which promotes potassium saving, such as converting enzyme inhibitors and/or angiotensin Ⅱ receptor blockers [17,25] .…”