Salt sensitivity of blood pressure is accompanied by slow respiratory rate: results of a clinical feeding study

Drug treatment of hypertension in older patients with diabetes mellitus

INTRODUCTION

Hypertension is more prevalent in the elderly (age>65 years) diabetic population than in the general population and shows an increasing prevalence with advancing age. Both diabetes mellitus (DM) and hypertension are independent risk factors for cardiovascular (CV) related morbidity and mortality. Optimal BP targets were not identified in elderly patients with DM and hypertension.

AREAS COVERED

In this review article, the authors briefly discuss the pathophysiology of hypertension in elderly diabetics, present evidence with various antihypertensive drug classes supporting the treatment of hypertension to reduce CV events in older diabetics, and then discuss the optimal target BP goals in these patients.

EXPERT OPINION

Clinicians should have a BP goal of less than 130/80 mm in all elderly patients with hypertension and DM, especially in those with high CV-risk. When medications are required for optimal BP control in addition to lifestyle measures, either thiazide diuretics, angiotensin-converting-enzyme inhibitors, angiotensin receptor blockers, or calcium channel blockers should be considered as initial therapy. Combinations of medications are usually required in these patients because BP control is more difficult to achieve in diabetics than those without DM.

Effect of Salt Intake on Plasma and Urinary Uric Acid Levels in Chinese Adults: An Interventional Trial

Uric acid (UA) has been proposed as an important risk factor for cardiovascular and renal morbidity. We conducted an interventional trial to assess effects of altered salt intake on plasma and urine UA levels and the relationship between UA levels and salt sensitivity in humans. Ninety subjects (18–65 years old) were sequentially maintained on a normal diet for 3 days at baseline, a low-salt diet for 7 days (3.0 g/day, NaCl), and a high-salt diet for an additional 7 days (18.0 g/day of NaCl). Plasma UA levels significantly increased from baseline to low-salt diet and decreased from low-salt to high-salt diet. By contrast, daily urinary levels of UA significantly decreased from baseline to low-salt diet and increased from low-salt to high-salt diet. The 24 h urinary sodium excretions showed inverse correlation with plasma UA and positive correlation with urinary UA excretions. Additionally, salt-sensitive subjects presented significantly higher plasma UA changes in comparison to salt-resistant subjects, and a negative correlation was observed between degree of salt sensitivity and plasma UA difference. The present study indicates that variations in dietary salt intake affect plasma and urine UA levels, and plasma UA may be involved in pathophysiological process of salt sensitivity.

Opposing effects of sodium intake on uric acid and blood pressure and their causal implication

Reducing uric acid is hypothesized to lower blood pressure, although evidence is inconsistent. In this ancillary of the DASH-Sodium trial, we examined whether sodium-induced changes in serum uric acid (SUA) were associated with changes in blood pressure. One hundred and three adults with prestage or stage 1 hypertension were randomly assigned to receive either the DASH diet or a control diet (typical of the average American diet) and were fed each of the three sodium levels (low, medium, and high) for 30 days in random order. Body weight was kept constant. SUA was measured at baseline and following each feeding period. Participants were 55% women and 75% black. Mean age was 52 (SD, 10) years, and mean SUA at baseline was 5.0 (SD, 1.3) mg/dL. Increasing sodium intake from low to high reduced SUA (-0.4 mg/dL; P < .001) but increased systolic (4.3 mm Hg; P < .001) and diastolic blood pressure (2.3 mm Hg; P < .001). Furthermore, changes in SUA were independent of changes in systolic (P = .15) and diastolic (P = .63) blood pressure, regardless of baseline blood pressure, baseline SUA, and randomized diet, as well as sodium sensitivity. Although both SUA and blood pressure were influenced by sodium, a common environmental factor, their effects were in opposite directions and were unrelated to each other. These findings do not support a consistent causal relationship between SUA and BP.

Risk Factors in Adolescent Hypertension

Hypertension is a complex and multifaceted disease, with many contributing factors. While diet and nutrition are important influences, the confounding effects of overweight and obesity, metabolic and genetic factors, racial and ethnic predispositions, socioeconomic status, cultural influences, growth rate, and pubertal stage have even more influence and make diagnosis quite challenging. The prevalence of hypertension in adolescents far exceeds the numbers who have been diagnosed; studies have found that 75% or more go undiagnosed. This literature review summarizes the challenges of blood pressure classification in adolescents, discusses the impact of these confounding influences, and identifies actions that will improve diagnosis and treatment outcomes.

Device-guided slow-breathing effects on end-tidal CO(2) and heart-rate variability

Previous studies have reported that regular practice of a device-guided slow-breathing (DGB) exercise decreases resting blood pressure (BP) in hypertensive patients. The performance of DGB is associated with acute decreases in sympathetic vascular tone, and it has been suggested that the decreases in resting BP produced by regular practice of DGB over periods of weeks are due to chronic decreases in sympathetic nervous system activity. However, the kidneys respond to sympathetically mediated changes in BP by readjusting blood volume levels within a few days. Thus, the mechanism by which DGB could produce long-term BP changes remains to be clarified. Previous research with laboratory animals and human subjects has shown that slow, shallow breathing that increases pCO(2) potentiates BP sensitivity to high sodium intake. These findings raise the possibility that deeper breathing during DGB that decreases BP might involve opposite changes in pCO(2). The present study tested the hypothesis that performance of DGB acutely decreases a marker of pCO(2), end-tidal CO(2) (PetCO(2)). Breathing rate, tidal volume, and PetCO(2) were monitored before, during, and after a 15-min session of DGB by patients with elevated BP. BP, heart rate, and heart-rate variability (HRV) were also measured under these conditions. A control group was also studied before, during, and after a 15-min session of spontaneous breathing (SB). The DGB group, but not the SB group, showed progressive and substantial increases in tidal volume and low-frequency HRV and decreases in PetCO(2) and systolic BP. The PetCO(2) effects persisted into the posttask, rest period. The findings are consistent with the hypothesis that habitual changes in breathing patterns of the kind observed during DGB could potentiate an antihypertensive adaptation via effects on pCO(2) and its role in cardiovascular homeostasis.

Breathing variability at rest is positively associated with 24-h blood pressure level

BACKGROUND

Previous research has reported that inhibition of breathing can be observed in hypertensive patients at rest during the daytime, as well as in sleep at night. The present study hypothesized that the variability of breathing and end-tidal CO(2) (PetCO(2)) in seated women at rest is positively associated with their 24-h blood pressure level.

METHODS

Breath-to-breath measures of breathing rate and tidal volume were recorded via inductive plethysmography in each of 54 women during two 20-min sessions of seated rest, and in 32 women during night time sleep. PetCO(2) was also recorded during these sessions via a respiratory gas monitor. Ambulatory blood pressure was recorded for 24 h between the two clinic sessions via oscillometry.

RESULTS

Breath pauses >10 s were observed significantly more often in women in the upper than the lower tertile of 24-h systolic blood pressure. Breath-to-breath variability in breathing rate, tidal volume, and minute ventilation were greater in the higher blood pressure tertile women. Variability in PetCO(2) was also greater in high blood pressure tertile. These associations were independent of age, weight, and body surface area (BSA). Breathing variability was inversely correlated with heart rate variability (HRV).

CONCLUSION

Greater variability in breathing at rest that is independent of metabolic activity characterizes women with elevated blood pressure. The linear association of breathing variability with 24-h blood pressure level is consistent with the hypothesis that intermittent breathing inhibition may predispose to the development of some forms of hypertension.

Endogenous sodium pump inhibitors and age-associated increases in salt sensitivity of blood pressure in normotensives

Factors that mediate increases in salt sensitivity of blood pressure with age remain to be clarified. The present study investigated 1) the effects of high-NaCl intake on two Na pump inhibitors, endogenous ouabain (EO) and marinobufagenin (MBG), in middle-aged and older normotensive Caucasian women; and 2) whether individual differences in EO and MBG are linked to variations in sodium excretion or salt sensitivity. A change from 6 days of a lower (0.7 mmol.kg(-1).day(-1))- to 6 days of a higher (4 mmol.kg(-1).day(-1))-NaCl diet elicited a sustained increase in MBG excretion that directly correlated with an increase in the fractional Na excretion and was inversely related to age and to an age-dependent increase in salt sensitivity. In contrast, EO excretion increased only transiently in response to NaCl loading and did not vary with age or correlate with fractional Na excretion or salt sensitivity. A positive correlation of both plasma and urine levels of EO and MBG during salt loading may indicate a casual link between two Na pump inhibitors in response to NaCl loading, as observed in animal models. A linear mixed-effects model demonstrated that age, dietary NaCl, renal MBG excretion, and body mass index were each independently associated with systolic blood pressure. Thus, a sustained increase in MBG in response to acutely elevated dietary NaCl is inversely linked to salt sensitivity in normotensive middle-aged and older women, and a relative failure of MBG elaboration by these older persons may be involved in the increased salt sensitivity with advancing age.