Raul De Miguel

Transtubular potassium concentration gradient: comparison between healthy old people and chronic renal failure patients.

Transtubular potassium concentration gradient (TTKG) is an index of potassium secretory activity in the distal tubule. Since water reabsorption takes place in the distal tubule as well, urine potassium concentration is a less accurate index evaluating distal K+ secretion because the effect of water is not taken into account on urine potassium concentrations. Potassium secretion and water reabsorption are strongly related to age and renal function. As a consequence, TTKG would be altered in both elderly individuals, as well as in patients with chronic renal failure (CRF). The aim of this study was to assess and compare TTKG in these two groups.Patients & MethodsA total of 55 individuals were studied, 12 of them were patients with CRF and 43 healthy elderly subjects with normal renal function. Informed consent was obtained from all patients. Patients with diabetes mellitus, cardiac failure, cirrhosis, obstructive uropathy, hyperkalemia, hypokalemia, or taking any medication that could alter the potassium balance were excluded from the study. All subjects were on a diet containing 50xa0mmol of potassium intake daily (documented by a three-day dietary record). Plasma potassium, creatinine, urea, glucose and osmolality were measured in all as well. 24xa0h creatinine clearance (CrCl ) and TTKG were calculated. Statistical analysis was made using Student’s t-test.ResultsTTKG was significantly lower in the elderly group (4.2±1.9 vs 6.2±1.8 , P 0.005)Both groups had a significantly lower TTKG when compared to healthy young people (8±2). Plasma and urine potassium levels, as well as plasma osmolality were similar in the two groups. Only urine osmolality was lower in the CRF group (382±141 vs. 514±180, P=0.01)ConclusionBoth old age and renal impairment lead to a reduced TTKG in comparison with young healthy people. Furthermore, TTKG is significantly lower in elderly healthy subjects compared to patients with CRF.

Fractional excretion of K, Na and Cl following furosemide infusion in healthy, young and very old people.

Furosemide test is a simple and useful test of renal physiology used to evaluate the capability of the collecting ducts to secrete potassium under the effect of serum aldosterone. Its behaviour pattern has been established in children and young adults but not described in very old healthy people, which we explored in this study.Material and methodsTwenty-six healthy volunteers on a standard Western diet (50xa0mmol of K/day) were studied: 20 of them were young (between 17 and 40xa0years old) and the rest were very old (between 75 and 85xa0years old). They suffered from no diseases and were not on any medication. Before, during the test and 180xa0min after a single dose of intravenous furosemide (1xa0mg/kg), urine and blood samples were obtained for creatinine and electrolytes levels. From these data we calculated fractional excretion (FE) of electrolytes; serum aldosterone was measured pre and post furosemide infusion. Statistical analysis was performed by applying Student’s t-test.ResultsThere was no significant difference regarding pre-furosemide (basal) FE of potassium between the very old and young group. Post-furosemide average FE of potassium was significantly lower in the very old group (27.4xa0±xa02%) compared with the young group (35.4xa0±xa09%) (Pxa0=xa00.04). Even though there was no significant difference in post-furosemide peak FE of potassium value, it was reached later in the very old (120xa0min) compared with the young (30xa0min). Serum aldosterone levels were significantly higher post furosemide in both groups: 18.3xa0±xa012.2xa0ng/dl (pre) versus 32.5xa0±xa018.6xa0ng/dl (post) in the young (Pxa0=xa00.007) and 69.8xa0±xa013.7xa0ng/dl (pre) versus 113.3xa0±xa054.8xa0ng/dl (post) in the very old (Pxa0=xa00.04). Furthermore, all serum aldosterone values (pre and post furosemide) were significantly higher in very old people compared with young people (Pxa0<xa00.001). Basal fractional excretion of sodium and chloride were slightly higher in the very old group compared with the young group (Pxa0=xa00.05). Average post-furosemide FE of sodium and chloride were slightly and significantly lower in the very old (Pxa0=xa00.05 and Pxa0=xa00.03), respectively. However, there was no significant difference in peak post-furosemide FE of sodium and chloride values, which were reached later in the very old (120xa0min) compared with the young (30xa0min).ConclusionFurosemide test showed a significantly lower average post-furosemide FE of potassium value, delayed post-furosemide peak FE of Na, K and Cl and a hormonal pattern of aldosterone resistance in very old people.

Renal physiology in elderly persons with severe immobility syndrome

ObjectiveThe immobility syndrome (IS) is a common condition in the elderly and consists of a reduction in the capacity to perform daily activities because of motor function deterioration. This syndrome leads to characteristic structural and physiological changes in the body, but renal physiology studies have not been conducted on this population. For this reason, we decided to study prospectively changes in renal function in these individuals.Material and methodsWe enrolled into this study 17 volunteers over 64xa0years of age, all of whom lived in the same nursing home. The patients were divided into two groups: nine healthy mobile persons and eight others who suffered from severe IS. Exclusion criteria were the presence of any disease or use of any drug that could induce water and electrolytes alteration. Blood and urine samples were drawn to measure sodium, potassium, creatinine, urea, calcium, phosphorus, magnesium, and uric acid in order to obtain their fractional excretion. Plasma osmolality and vasopressin were also measured. Total body water and lean body mass were obtained by bioelectrical impedance analysis. Statistical analysis was performed applying Student’s t-test (Pxa0=xa00.01) and Pearson’s correlation test.ResultsA significant difference in body water composition was found between the groups. Thus in the IS group plasma sodium level was slightly lower and total water content was significantly higher than in the mobile subjects: 140xa0±xa05 vs. 143xa0±xa01xa0mmol/l (Pxa0=xa00.01); 61xa0±xa08% vs. 50xa0±xa010% (Pxa0<xa00.001), respectively. Despite these differences, plasma osmolality and vasopressin values were within the normal range in both groups. However, there was a good positive correlation between these two variables in the mobile group only: R 0.9 (mobile) vs. R −0.2 (immobile). We found no significant difference in plasma creatinine or fractional excretion of sodium, potassium, calcium, phosphorus, magnesium, urea, and uric acid between the groups.ConclusionTotal body water content was significantly higher in the elderly who suffered from severe immobility syndrome than in healthy mobile elderly. In contrast with the mobile group, for which there was a good positive correlation between plasma osmolality and plasma vasopressin, for individuals with IS there was no correlation between plasma osmolality and plasma vasopressin.

Furosemide test in stage III-chronic kidney disease and kidney transplant patients on tacrolimus

AimFurosemide test is a simple and useful test of renal physiology usually used for evaluating the capability of the collecting ducts to secrete potassium under the effect of this drug. Its behaviour pattern has already been established in healthy children, young, and old people, as well as in stage III-chronic kidney disease (III-CKD) patients. However, its behaviour has not been described in kidney transplant patients yet, which we explored in this study.Materials and methodsTwenty young volunteers on a standard western diet (50xa0mmol of potassium/day) were studied: Ten were III-CKD and the rest were kidney transplant (KT) patients on FK. Before, while the test was being carried out, and 180xa0min after a single dose of intravenous furosemide (1xa0mg/kg), urine and blood samples were obtained, for creatinine and potassium levels. From these data, we calculated fractional excretion of potassium (FEK). Statistical analysis was performed applying Wilcoxon test.ResultsThere was a significant difference regarding pre-furosemide (basal) FE of potassium between the III-CKD and KT groups 16xa0±xa05 (III-CKD) versus 7xa0±xa05 (KT), pxa0=xa00.008. Regarding the post-furosemide, peak FEK was significantly lower in the KT group (15xa0±xa011xa0%) compared to the III-CKD ones (49.8xa0±xa09xa0%, pxa0=xa00.01). In both groups, the peak FEK post-furosemide was reached later (120xa0min) compared to the conventional test (30xa0min).ConclusionFurosemide test showed significantly lower basal and post-furosemide peak FEK values in KT patients on tacrolimus compared with stage III-chronic renal disease.