Prevalence and factors associated with masked hypertension in chronic kidney disease

OBJECTIVES

Optimal blood pressure (BP) control is key to prevent cardiovascular complications in patients with chronic kidney disease (CKD). We described the prevalence and factors associated with masked hypertension in CKD.

METHODS

We analyzed 1113 ambulatory 24-h BP monitoring (ABPM) records of 632 patients referred for kidney function evaluation. Masked hypertension was defined as office BP less than 140/90 mmHg but daytime BP at least 135/85 mmHg or nighttime BP at least 120/70 mmHg. Factors associated with masked hypertension were assessed with mixed logistic regression models.

RESULTS

At inclusion, 424 patients (67%) had controlled office BP, of whom 56% had masked hypertension. In multivariable analysis conducted in all visits with controlled office BP ( n  = 782), masked hypertension was positively associated with male sex [adjusted OR (95% confidence interval) 1.91 (1.16-3.27)], sub-Saharan African origin [2.51 (1.32-4.63)], BMI [1.11 (1.01-1.17) per 1 kg/m 2 ], and albuminuria [1.29 [1.12 - 1.47] per 1 log unit), and was negatively associated with plasma potassium (0.42 [0.29 - 0.71] per 1 mmol/L) and 24-h urinary potassium excretion (0.91 [0.82 - 0.99] per 10 mmol/24 h) as well as the use of renin-angiotensin-aldosterone (RAAS) blockers (0.56 [0.31 - 0.97]) and diuretics (0.41 [0.27 - 0.72]).

CONCLUSION

Our findings support the routine use of ABPM in CKD, as more than half of the patients with controlled office BP had masked hypertension. Weight control, higher potassium intake (with caution in advanced CKD), correction of hypokalemia, and larger use of diuretics and RAAS blockers could be potential levers for better out-of-office BP control.

Diminished antiproteinuric effect of the angiotensin receptor blocker losartan during high potassium intake in patients with CKD

Background

Angiotensin II type 1 receptor blockers (ARBs) lower blood pressure (BP) and proteinuria and reduce renal disease progression in many-but not all-patients. Reduction of dietary sodium intake improves these effects of ARBs. Dietary potassium intake affects BP and proteinuria. We set out to address the effect of potassium intake on BP and proteinuria response to losartan in non-diabetic proteinuric chronic kidney disease (CKD) patients.

Methods

We performed a post hoc analysis of a placebo-controlled interventional cross-over study in 33 non-diabetic proteinuric patients (baseline mean arterial pressure and proteinuria: 105 mmHg and 3.8 g/day, respectively). Patients were treated for 6 weeks with placebo, losartan and losartan/hydrochlorothiazide (HCT), combined with a habitual (∼200 mmol/day) and low-sodium (LS) diet (<100 mmol/day), in randomized order. To analyse the effects of potassium intake, we categorized patients based on median split of 24-h urinary potassium excretion, reflecting potassium intake.

Results

Mean potassium intake was stable during all six treatment periods. Losartan and losartan/HCT lowered BP and proteinuria in all treatment groups. Patients with high potassium intake showed no difference in the BP effects compared with patients with low potassium intake. The antiproteinuric response to losartan monotherapy and losartan combined with HCT during the habitual sodium diet was significantly diminished in patients with high potassium intake (20% versus 41%, P = 0.011; and 48% versus 64%, P = 0.036). These differences in antiproteinuric response abolished when shifting to the LS diet.

Conclusions

In proteinuric CKD patients, the proteinuria, but not BP-lowering response to losartan during a habitual high-sodium diet was hampered during high potassium intake. Differences disappeared after sodium status change by LS diet.

Dietary potassium and the kidney: lifesaving physiology

Potassium often has a negative connotation in Nephrology as patients with chronic kidney disease (CKD) are prone to develop hyperkalaemia. Approaches to the management of chronic hyperkalaemia include a low potassium diet or potassium binders. Yet, emerging data indicate that dietary potassium may be beneficial for patients with CKD. Epidemiological studies have shown that a higher urinary potassium excretion (as proxy for higher dietary potassium intake) is associated with lower blood pressure (BP) and lower cardiovascular risk, as well as better kidney outcomes. Considering that the composition of our current diet is characterized by a high sodium and low potassium content, increasing dietary potassium may be equally important as reducing sodium. Recent studies have revealed that dietary potassium modulates the activity of the thiazide-sensitive sodium-chloride cotransporter in the distal convoluted tubule (DCT). The DCT acts as a potassium sensor to control the delivery of sodium to the collecting duct, the potassium-secreting portion of the kidney. Physiologically, this allows immediate kaliuresis after a potassium load, and conservation of potassium during potassium deficiency. Clinically, it provides a novel explanation for the inverse relationship between dietary potassium and BP. Moreover, increasing dietary potassium intake can exert BP-independent effects on the kidney by relieving the deleterious effects of a low potassium diet (inflammation, oxidative stress and fibrosis). The aim of this comprehensive review is to link physiology with clinical medicine by proposing that the same mechanisms that allow us to excrete an acute potassium load also protect us from hypertension, cardiovascular disease and CKD.

Regulation of the Renal NaCl Cotransporter and Its Role in Potassium Homeostasis

Daily dietary potassium (K+) intake may be as large as the extracellular K+ pool. To avoid acute hyperkalemia, rapid removal of K+ from the extracellular space is essential. This is achieved by translocating K+ into cells and increasing urinary K+ excretion. Emerging data now indicate that the renal thiazide-sensitive NaCl cotransporter (NCC) is critically involved in this homeostatic kaliuretic response. This suggests that the early distal convoluted tubule (DCT) is a K+ sensor that can modify sodium (Na+) delivery to downstream segments to promote or limit K+ secretion. K+ sensing is mediated by the basolateral K+ channels Kir4.1/5.1, a capacity that the DCT likely shares with other nephron segments. Thus, next to K+-induced aldosterone secretion, K+ sensing by renal epithelial cells represents a second feedback mechanism to control K+ balance. NCC’s role in K+ homeostasis has both physiological and pathophysiological implications. During hypovolemia, NCC activation by the renin-angiotensin system stimulates Na+ reabsorption while preventing K+ secretion. Conversely, NCC inactivation by high dietary K+ intake maximizes kaliuresis and limits Na+ retention, despite high aldosterone levels. NCC activation by a low-K+ diet contributes to salt-sensitive hypertension. K+-induced natriuresis through NCC offers a novel explanation for the antihypertensive effects of a high-K+ diet. A possible role for K+ in chronic kidney disease is also emerging, as epidemiological data reveal associations between higher urinary K+ excretion and improved renal outcomes. This comprehensive review will embed these novel insights on NCC regulation into existing concepts of K+ homeostasis in health and disease.