Sequential hemodynamic changes in end-stage renal disease and the anephric state during volume expansion

Sodium and water handling during hemodialysis: new pathophysiologic insights and management approaches for improving outcomes in end-stage kidney disease

Space medicine and new technology such as magnetic resonance imaging of tissue sodium stores (²³NaMRI) have changed our understanding of human sodium homeostasis and pathophysiology. It has become evident that body sodium comprises 3 main components. Two compartments have been traditionally recognized, namely one that is circulating and systemically active via its osmotic action, and one slowly exchangeable pool located in the bones. The third, recently described pool represents sodium stored in skin and muscle interstitium, and it is implicated in cell and biologic activities via local hypertonicity and sodium clearance mechanisms. This in-depth review provides a comprehensive view on the pathophysiology and existing knowledge gaps of systemic hemodynamic and tissue sodium accumulation in dialysis patients. Furthermore, we discuss how the combination of novel technologies to quantitate tissue salt accumulation (e.g., ²³NaMRI) with devices to facilitate the precise attainment of a prescribed hemodialytic sodium mass balance (e.g., sodium and water balancing modules) will improve our therapeutic approach to sodium management in dialysis patients. While prospective studies are required, we think that these new diagnostic and sodium balancing tools will enhance our ability to pursue more personalized therapeutic interventions on sodium and water management, with the eventual goal of improving dialysis patient outcomes.

Role of the kidney in the pathogenesis of hypertension: time for a neo-Guytonian paradigm or a paradigm shift?

The "Guytonian paradigm" places the direct effect of arterial pressure, on renal excretion of salt and water, at the center of long-term control of blood pressure, and thus the pathogenesis of hypertension. It originated in the sixties and remains influential within the field of hypertension research. However, the concept of one central long-term feedback loop, through which arterial pressure is maintained by its influence on renal function, has been questioned. Furthermore, some concepts in the paradigm are undermined by experimental observations. For example, volume retention and increased cardiac output induced by high salt intake do not necessarily lead to increased arterial pressure. Indeed, in multiple models of salt-sensitive hypertension the major abnormality appears to be failure of the vasodilator response to increased cardiac output, seen in salt-resistant animals, rather than an increase in cardiac output itself. There is also evidence that renal control of extracellular fluid volume is driven chiefly by volume-dependent neurohumoral control mechanisms rather than through direct or indirect effects of changes in arterial pressure, compatible with the concept that renal sodium excretion is controlled by parallel actions of different feedback systems, including hormones, reflexes, and renal arterial pressure. Moreover, we still do not fully understand the sequence of events underlying the phenomenon of "whole body autoregulation." Thus the events by which volume retention may develop to hypertension characterized by increased peripheral resistance remain enigmatic. Finally, by definition, animal models of hypertension are not "essential hypertension;" progress in our understanding of essential hypertension depends on new results on system functions in patients.

Residual renal function and arterial stiffness mediated the blood pressure change during interdialytic weight gain in hemodialysis patients

Volume overload is thought to be the main cause of hypertension in dialysis patients. However, the effect of interdialytic weight gain (IDWG) in hemodialysis (HD) patients, which was considered as an increase in extracellular water (ECW), on blood pressure (BP) change, was controversial. Our aim was to examine the changes in hemodynamics and arterial stiffness during IDWG in HD patients and attempt to explore the possible mechanism of diverse BP change. Thirty prevalent patients on HD were enrolled. The height, weight, BP, blood chemistry, volume status assessed by bioelectrical impedance analysis, hemodynamic parameters obtained by echocardiography, and pulse wave velocity (PWV) were collected within 1 hour postdialysis and again just before the next dialysis session. Meanwhile, blood samples were drawn to analyze vasoactive hormones, including renin, angiotensin II, catecholamine, and endothelin. The patients' weights and ECWs during the next predialysis were significantly higher than those during the postdialysis. The BP showed no difference between postdialysis and the next predialysis. There was an obvious increase in cardiac output and decrease in total peripheral resistance as a whole during the next predialysis than that during postdialysis. When patients were divided into the BP increase group (BPI group, 13 patients) and BP decrease group (BPD group, 11 patients) according to the change in systolic BP higher than 10 mmHg, both groups displayed a significant increase in weight, ECW, cardiac output, and a decrease in total peripheral resistance. As compared with the BPI group, patients in the BPD group had significantly lower IDWG, shorter time on dialysis treatment, and higher residual renal function. A decrease in catecholamine and endothelin in the next predialysis was obvious in the BPD group. There was a significant decrease in PWV at the next predialysis in the BPD group while the PWV did not change significantly in the BPI group. Our results showed that the diverse BP change during IDWG was significantly affected by residual renal function, PWV, and vasoactive substances.

Impacts of Measurement Protocols on Blood Pressure Tracking From Childhood Into Adulthood

The best approach for blood pressure (BP) measurement in children remains controversial, specifically regarding the choice of Korotkoff phase 4 versus Korotkoff phase 5 for diastolic BP (DBP) and the use of automated devices. To examine the impacts of different BP measurement protocols on BP tracking from childhood into adulthood, we conducted a meta-analysis of 50 related studies published between 1970 and 2006 identified based on a systematic search of PubMed. These studies provided 617 data points (tracking correlation coefficient, our outcome variable) for systolic BP and 547 data points for DBP for our meta-analysis. The explanatory variables included the use of Korotkoff phase 4/Korotkoff phase 5, BP device, and number of BP measurements per visit. Analyses were adjusted for potential confounders, including sex, baseline age, follow-up length, publication year, and study country. Tracking correlation coefficients for DBP measured using Korotkoff phase 4 was higher than that of Korotkoff phase 5 by 0.035 but not significant. DBP tracking assessed by automated device was higher than that of Korotkoff phase 5 by 0.152 ( P =0.024) and higher than the mercury manometer by 0.223 ( P =0.005). BP tracking was slightly higher with multiple BP measurements per visit, but measurements of ≥3 times did not improve the tracking further compared with 2 measurements. Although policy-making bodies currently recommend the use of Korotkoff phase 5 to assess DBP in children, our metaregression analysis did not support the recommendation. In general, Korotkoff phase 4 seems to be different from Korotkoff phase 5, and automated device is a promising approach for BP assessment in childhood.

Why is there significant overlap in volume status between hypertensive and normotensive patients on dialysis?

BACKGROUND/AIM

Volume overload is believed to play a pivotal role in the pathogenesis of hypertension in dialysis patients. Although the extracellular water (ECW) content in hypertensive dialysis patients was significantly higher than in normotensive dialysis patients on the whole, there was considerable overlap in ECW between the two groups. Little is known about the hemodynamic characteristics in subgroups of patients with normotension but a high volume (HV) status or with hypertension but a normal volume (NV) status. We investigate the overlap in ECW between controlled and uncontrolled hypertension in dialysis patients.

METHODS

Fifty-two patients (mean age 62 years, 26 males and 26 females) on peritoneal dialysis were enrolled into this study. The ECW was assessed by bioimpedance analysis and normalized by individual height in meters (NECW). The mean value of NECW in both sexes was arbitrarily set to define NV status (lower than mean value) or HV status (higher than mean value). All patients were thus divided into four subgroups: controlled hypertension with NV (CHT-NV), controlled hypertension with HV (CHT-HV), uncontrolled hypertension with NV (UHT-NV) and uncontrolled hypertension with HV (UHT-HV). The stroke volume, cardiac output and total peripheral resistance were echocardiographically measured and their respective indices were calculated.

RESULTS

There were 12 (23%), 8 (15%), 14 (27%) and 18 (35%) patients in the CHT-NV, CHT-HV, UHT-NV and UHT-HV subgroups, respectively. The four subgroups were matched for sex, diabetes and age. The NECW in the CHT-HV group was higher than that in CHT-NV and UHT-NV groups (p < 0.01), but was comparable with that in the UHT-HV group. The stroke volume and cardiac output indices in the CHT-HV group were not significantly different from those in the CHT-NV and UHT-NV groups. The total peripheral resistance index in the CHT-HV group was lower than that in UHT-NV and CHT-NV groups (p < 0.05), but was comparable to that in the UHT-HV group. There was no difference in heart rate among the four groups.

CONCLUSIONS

The overlap in ECW between controlled hypertension and uncontrolled hypertension in dialysis patients was related to a significant difference in total peripheral resistance index, but not to significant differences in stroke volume and cardiac output indices. The CHT-HV patients were characterized by lower total peripheral resistance indices.

Origins of the "black/white" difference in blood pressure: roles of birth weight, postnatal growth, early blood pressure, and adolescent body size: the Bogalusa heart study

BACKGROUND

The determinants of differences in blood pressure that emerge in adolescence between black Americans of predominantly African descent and white Americans of predominantly European descent are unknown. One hypothesis is related to intrauterine and early childhood growth. The role of early blood pressure itself is also unclear. We tested whether differences in birth weight and in carefully standardized subsequent measures of weight, height, and blood pressure from 0 to 4 or 5 years were related to black/white differences in blood pressure in adolescence.

METHODS AND RESULTS

Two Bogalusa cohorts who had complete follow-up data on birth weights and early childhood and adolescent anthropometric and blood pressure measures were pooled. One hundred eighty-five children (48 black and 47 white boys and 41 black and 49 white girls) were followed up and studied after 15 to 17 years. Birth weights were a mean 443 and 282 g lower in black boys and girls, respectively, than in whites (P<0.001). Blood pressures in adolescence were 3.4/1.9 and 1.7/0.6 mm Hg higher, respectively, and tracked from early childhood. In regression analyses, birth weight accounted for the ethnic difference in adolescent blood pressure, which was also independently predicted, in decreasing impact order, by adolescent height, adolescent body mass index, and systolic blood pressure at 4 to 5 years and inversely by growth from 0 to 4 to 5 years.

CONCLUSIONS

If these results can be replicated in larger and independent samples, they suggest that efforts to improve intrauterine growth in black infants as well as lessen weight gain in adolescence might substantially reduce excess high blood pressure/hypertension in this ethnic group.

The heterogeneous and delayed course of blood pressure normalization in hypertensive patients after bilateral nephrectomy with and without subsequent renal transplantation

BACKGROUND

Controversy exists about the time course of blood pressure normalization following bilateral nephrectomy. We sought to evaluate the time course of blood pressure normalization following bilateral nephrectomy and after subsequent kidney transplantation.

METHODS AND RESULTS

Clinical data from 14 hypertensive patients were retrospectively assessed. Baseline blood pressure was 175 +/- 33/109 +/- 9 mmHg. Ten patients firstly underwent unilateral nephrectomy, which resulted in a slight increase of blood pressure (185 +/- 22/110 +/- 5 mmHg). One month following bilateral nephrectomy, blood pressure was 167 +/- 23/104 +/- 17 mmHg, at 3 months 159 +/- 42/104 +/- 25 mmHg, and at 6 months 149 +/- 41/96 +/- 30 mmHg. Antihypertensive medication was necessary in 9/14 patients at a 2 year follow-up. Eight patients remained anephric (group I), 6 patients had subsequent kidney transplantation (group II). In group I, blood pressure was 159 +/- 42/93 +/- 17 mmHg and 129 +/- 34/75 +/- 14 mmHg at 3 and 6 months, respectively (p< 0.05 vs. baseline). In group II, blood pressure decreased from 188 +/- 42/ 128 +/- 46 mmHg to 167 +/- 48/113 +/- 32 mmHg at 3 months, but increased after transplantation to 186 +/- 39/118 +/- 33 mmHg. Antihypertensive medication was still necessary in 5 transplanted patients (83%) and in 3 anephric patients (38%).

CONCLUSION

Adaptation of the blood pressure response following bilateral nephrectomy is a time requiring process, and long-term antihypertensive medication may still be necessary.

Hypertension in end-stage renal disease

Patients with moderate to severe renal disease have a very high incidence of hypertension. In end-stage renal disease (ESRD) this is true regardless of the nature of the underlying renal disease. Nevertheless, patients with glomerular diseases and autosomal dominant polycystic kidney disease are particularly vulnerable. Evidence is presented that ESRD hypertension is the result of extracellular volume expansion, increased or inappropriate response of the renin-angiotensin system and overactivity of the sympathetic system. In addition, the role of endothelin-1, nitric oxide and other vasodilators, and abnormal ion channels in generating high blood pressure, is considered.

Role of increased oxygen free radical activity in the pathogenesis of uremic hypertension

Earlier studies have demonstrated increased oxygen free radical (OFR) activity, diminished antioxidant capacity and reduced OFR-inactivating enzymes in chronic renal failure (CRF). Via inactivation of nitric oxide (NO), oxidation of arachidonic acid and a direct vasoconstrictive action, OFR can potentially raise blood pressure (BP). This study was designed to test the hypothesis that increased OFR activity may contribute to CRF hypertension. Four weeks after 5/6 nephrectomy rats were treated for two weeks with either lazaroid, a potent antioxidant and lipid peroxidation inhibitor (CRF-LZ group), or vehicle alone (CRF group) by daily gastric gavage. The control group was sham operated and placebo treated. The CRF group exhibited significant increases in BP and plasma lipid peroxidation product, malondialdehyde (MDA), indicating enhanced OFR activity. This was accompanied by decreased urinary nitrate/nitrite (NOx) excretion suggesting depressed NO production. LZ therapy normalized plasma MDA and significantly ameliorated CRF-induced hypertension. Both MDA and blood pressure (BP) rose to values seen in the untreated CRF group within two weeks after termination of LZ therapy. Intravenous administration of the hydroxyl radical scavenger, dimethylthiourea (DMTU), significantly lowered BP and raised urinary NOx excretion. However, no discernible effects were found with either superoxide dismutase or catalase (superoxide and H2O2 quenchers). The results suggest that increased OFR activity is, in part, responsible for CRF-associated HTN. The study further points to hydroxyl radicals as the major source of OFR in CRF animals. If substantiated in humans, antioxidant therapy becomes a logical adjunct in the management of CRF.

The effect of interdialytic weight gain on predialysis blood pressure

Interdialytic weight gain is believed to influence predialysis blood pressure. Since interdialytic weight gains vary among treatments for individual patients, blood pressure and weight gain data could be examined to determine how weight variations correlate with differences in blood pressure. Therefore, the quantitative effect on prehemodialysis blood pressure of typical interdialytic weight gains was prospectively studied in 19 nondiabetic patients on chronic hemodialysis. Over a mean of 23.6 treatments (range 17-25), the slope of each patient's prehemodialysis blood pressure versus excess weight (prehemodialysis weight minus baseline dry weight) was determined. The mean slope of the prehemodialysis mean blood pressure/excess weight regression line was 1.2 mm Hg/lb excess weight. No significant correlation was found between individual prehemodialysis blood pressure/excess weight slopes and patient age (r = 0.20), months on dialysis (r = 0.33), dry weight (r = 0.05), or mean excess weight (r = 0.19). Slopes did not differ for 3-day versus 2-day interdialytic intervals, hypertension-treated versus untreated patients, or men versus women. In 5 patients, individual prehemodialysis mean blood pressure/excess weight slopes were significantly greater than 0, averaging 2.4 mm Hg/lb excess weight (vs. 0.8 mm Hg/lb in the remaining patients). These 5 volume-responsive patients did not differ clinically from the 14 volume-resistant patients. The weight gains commonly observed in patients undergoing chronic hemodialysis have only a modest effect on prehemodialysis blood pressure in the majority of patients.

Body fluid spaces and blood pressure in hemodialysis patients during amelioration of anemia with erythropoietin

Blood pressure (BP) may increase in hemodialysis patients during treatment of anemia with recombinant human erythropoietin (r-HuEPO). Since fluid volume is a determinant of BP in dialysis patients, changes in body fluid spaces during r-HuEPO therapy could affect BP. Thus, 51Cr-labeled red blood cell (RBC) volume, inulin extracellular fluid (ECF) volume, and urea total body water (TBW), as well as cardiac output, plasma renin activity (PRA), and plasma aldosterone concentration were determined postdialysis before and after r-HuEPO therapy in patients in whom changes in BP could be managed by ultrafiltration alone. Eleven patients entered the study: one had a renal transplant and two required addition of antihypertensive drug therapy and were excluded; eight, of whom two required antihypertensive drug therapy following the study, were included in the analyses. Results revealed an increase in predialysis hemoglobin from 67 to 113 g/L (6.7 to 11.3 g/dL) (P = 0.001) during 18 +/- 6 weeks of therapy. Predialysis diastolic BP increased from 80 to 85 mm Hg (P = 0.07), while postdialysis diastolic BP was unchanged at 73 mm Hg. 51Cr-RBC volume increased, from 0.7 to 1.3 L (P = 0.004). ECF tended to decrease, from 13.7 to 10.8 L (P = 0.064), while TBW decreased to a similar extent, but not significantly, 34.3 to 31.2 L (P = 0.16). Postdialysis ECF volume was positively correlated with mean arterial BP at baseline (r = 0.89, P = 0.007) and after therapy (r = 0.74, P = 0.035). However, the regression lines for this relationship were different (P = 0.022) before and after therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of the baroreflex afferent nerves to the production of vasoconstricted hypertension in volume-expanded dogs

Dextran in lactated Ringer's solution (20 ml/kg) was infused for 1 hour into anesthetized dogs with sinoaortic denervation and vagotomy (deafferentation; n = 10) and dogs treated with hexamethonium (de-efferentation; n = 13) to compare with our previous observation in dogs with an intact autonomic nervous system (control, n = 34). During the infusion, increase in blood pressure associated with increase in cardiac output was observed in all three groups. The increases in blood pressure were larger in the two groups with an impaired autonomic nervous system. In the recovery period, the control dogs and the hexamethonium-treated dogs showed gradual increases in total peripheral resistance and in vasoconstricted hypertension 3 hours after stopping the infusion. In contrast, the dogs with sinoaortic denervation and vagotomy did not show any increase in total peripheral resistance. The vasoconstricted groups showed peaks of natriuresis soon after the infusion, not 3 hours after the infusion when vasoconstriction was observed, although the dogs with deafferentation did not show a significant increase in natriuresis. Norepinephrine (0.5 micrograms/kg) was administered intravenously before and after volume expansion, and the pressor responses in the three groups after volume expansion were enhanced similarly (143%, 128%, and 136%, respectively). These results indicate that the afferent signals from peripheral vessels to the brain contribute to the production of vasoconstricted hypertension after acute volume expansion and that the vasoconstriction is independent of pressor hypersensitivity and is dissociated in time from the natriuresis.

Effect of ouabain on hemodynamics in acute volume expanded hypertensive dogs

To evaluate possible roles of endogenous Na+-K+-ATPase inhibitors in vasoconstricted blood pressure elevation produced by acute volume expansion, we administered ouabain (Na+-K+-ATPase inhibitor) intravenously (30 micrograms/kg) for 10 min to dogs, 3 h after volume expansion with dextran in lactated Ringer's solution (20 ml/kg, for 1 h). Acute volume expansion resulted in the elevation of blood pressure associated with an increase in cardiac output. In some dogs the blood pressure remained elevated with gradual increase in total peripheral resistance (Group I) or with sustained high cardiac output (Group II), and in other dogs (Group III) it returned to the control level. Ouabain administration elevated the blood pressure and total peripheral resistance in these groups and sham dogs which did not have volume expansion. And these effects of ouabain were not correlated with the degree of blood pressure or vasoconstriction produced by volume expansion. Thus, it is not likely that endogenous Na+-K+-ATPase inhibitors increased to produce vasoconstricted hypertension after acute volume expansion.

Effect of volume expansion on hemodynamic variables in nephrectomized dogs

We have previously demonstrated that blood pressure elevation by acute blood volume expansion is volume-dependent during the infusion period and resistance-dependent in the post-infusion period in normal anesthetized dogs, and that such an increase in blood pressure is associated with a potentiation of the pressor response to norepinephrine. To evaluate the possible renal contribution to these hemodynamic changes, blood volume expansion was performed for 1 h with dextran dissolved in lactated Ringer's solution (20 ml/kg) in 15 nephrectomized dogs. The mean blood pressure, cardiac output and total peripheral resistance at the end of infusion were 126%, 225% and 60%, respectively; 3 h after volume expansion they were 126%, 151%, and 92% respectively. However, in 4 dogs, there was an increase in mean blood pressure (138%) 3 h after volume expansion. This was thought to result from an increase in the total peripheral resistance (133%) associated with the recovery of cardiac output (106%). The pressor response to norepinephrine (0.5 microgram/kg) was potentiated after volume expansion. These results indicate that the handling of volume by the kidney contributed to the maintenance of an elevated level of cardiac output. However, nephrectomy did not seem to interfere with the hemodynamic switching of the causative factor for blood pressure elevation from increased cardiac output to increased total peripheral resistance. Neither was the potentiation of pressor response to norepinephrine affected.

Vasoconstriction and hypersensitivity to vasoactive substances after acute volume expansion in dogs

In a search for factors contributing to the sustained blood pressure (BP) elevation in acutely volume-loaded animals, dextran dissolved in lactated Ringer's solution (20 ml/kg) was infused into 34 mongrel dogs over a period of 1 hour under pentobarbital anesthesia and changes in hemodynamic and humoral variables were monitored during its infusion and for 3 hours after its infusion. BP elevation during volume loading (from 114 +/- 3 to 128 +/- 3 [SEM] mm Hg) was attributed to an increase in cardiac output. After volume loading, some dogs maintained BP elevation whereas others did not. The former group showed an increase in total peripheral resistance, demonstrating a transformation of cardiac output to total peripheral resistance as a responsible factor in maintenance of the elevated BP. The plasma levels of norepinephrine, vasopressin, and plasma renin activity were not elevated, indicating that these vasoactive factors were not responsible for elevation of the BP or total peripheral resistance. The changes in the hematocrit, atrial natriuretic factor, urine volume, and urinary sodium excretion were identical in the two groups, and natriuresis was not prominent when total peripheral resistance was high. Pressor responses to norepinephrine and angiotensin II were potentiated 3 hours after stopping infusion in both groups, but this potentiation was not correlated with the increase in total peripheral resistance or mean BP. Thus, acute volume expansion produced resistance-dependent hypertension following the initial volume-dependent hypertension. It is unlikely that a vascular sensitizing natriuretic factor plays a role in the resistance-dependent BP elevation. The mechanism and physiological importance of hypersensitivity to vasoactive substances remain to be elucidated.

'Sodium sensitivity' in man

Increased cell membrane permeability to sodium is proposed as the initial event leading to high blood pressure in susceptible subjects when sodium intake is increased. All cells, including circulating cells, would be affected, but a key role for endothelial cells in the pathophysiology of the diastolic blood pressure elevation is proposed. Involvement of capillary endothelium could increase capillary permeability to proteins, and thereby would contribute to the altered fluid distribution on the high sodium diet which has been observed. If movement of fluid into the interstitium raised interstitial fluid pressure, venous capacitance would fall and right atrial pressure would rise. Several mechanisms would cause vascular smooth muscle tone to increase. Altered fluid distribution correlates with the rise in diastolic blood pressure from reduced sodium to high sodium diet, but arteriolar constriction would reduce capillary flow so altered fluid distribution occurs first. Arteriolar constriction could serve as a negative feedback to the raised atrial filling pressure by reducing raised capillary flow, which would decrease both altered fluid distribution and interstitial fluid pressure rise. Consequently, diastolic blood pressure would be chronically raised in 'sodium sensitive' subjects taking increased amounts of sodium in the diet. The relationship of the findings to "essential" hypertension and to premorbid cardiovascular sequelae, and the key role of capillary endothelium in the development of "essential" hypertension is discussed.

Contribution of elevated peripheral resistance to acute volume loaded hypertension in dogs

The role of peripheral resistance in volume loaded hypertension was examined by measuring changes in hemodynamic and humoral factors during dextran infusion for one hour, and for three hours after stopping the infusion in 30 anesthetized dogs. The mean blood pressure was elevated significantly (118%, p less than 0.01), accompanied by increased cardiac output (170%, p less than 0.01) during volume loading. In the recovery period, cardiac output returned to the basal level while the total peripheral resistance gradually increased (118%, p less than 0.01) contributing to the maintenance of high blood pressure (108%, p less than 0.01). There was no significant correlation between the hematocrit change and the increase in peripheral resistance in the recovery period. The levels of plasma norepinephrine, epinephrine, renin activity and vasopressin were suppressed by volume loading. These results demonstrated the importance of increase in peripheral resistance for maintaining high blood pressure in this acute volume excess model. The participation of the renin-angiotensin system, the sympathetic nervous system and vasopressin were all excluded and vascular structural changes were most unlikely to be involved in this acute experiment. It remains unknown whether this conversion is attributable to the summation of local autoregulation or to some other factors.

Evidence for altered vascular reactivity in sodium-sensitive young subjects with borderline hypertension

To assess mechanisms associated with the pressor effects of a high sodium diet in susceptible individuals, the hemodynamic and hormonal effects of sodium depletion and repletion were studied in 33 normal subjects and 30 subjects with borderline hypertension. The hypertensive group had significantly higher mean arterial pressure, weight, hematocrit, and upright plasma renin activity. Forearm hemodynamics were measured during periods of ad lib diet, 10 mEq, and 200 mEq sodium diet. The fall in forearm resistance during reactive hyperemia was inversely related to mean arterial pressure at rest (R = .400, p less than .005) and rose significantly in hypertensive subjects during salt depletion, 39 +/- 3.6 to 61 +/- 6.1 mmHg/ml/min/100 g (p less than .05). Sodium sensitivity in either normotensive or borderline hypertensive subjects was defined as an increase in mean blood pressure of more than 5% when sodium repleted. The individuals who were sodium sensitive had a higher forearm vascular resistance during sodium depletion than those who were sodium resistant, 67 +/- 10.5 versus 45 +/- 4.1 mm/ml/min/100 g (p less than .03). We conclude that young individuals with borderline hypertension already have alterations in vascular reactivity. This trait is shared by normotensive individuals whose blood pressure rises in response to sodium.

Hemodynamic mechanisms of adaptation to chronic high sodium intake in normal humans

The long-term hemodynamic effects of a high dietary sodium intake were studied in 10 young normal subjects. After a 4-day diet of 10mEq of sodium and 60 mEq of potassium per day the mean arterial blood pressure (MAP) was 82.3 +/- 15.1 mmHg, the cardiac index (CI) was 2.32 +/- 0.69 liter/min/m2, and total peripheral resistance (TPR) was 1778 +/- 947 dyne sec cm-5. After 4 to 6 days of 200 mEq of sodium and 60 mEq of potassium per day, MAP was 84.3 +/- 20.9 mm Hg, CI had risen to 2.53 +/- 0.61 liter/min/m2, and TPR fell to 1437 +/- 328 dyne sec cm-5. After 6 months of unrestricted sodium intake, urinary sodium excretion (UNa) was 144.1 +/- 51.9 mEq/24 hrs (p less than 0.001), MAP remained at 83.1 +/- 13.8 mm Hg, CI had risen to 3.11 +/- 1.01 liter/min/m2 (p less than 0.05) and TPR was 1268 +/- 444 dyne sec cm-5. After 12 months, UNa had risen to 171.5 +/- 97.6 mEq/24 hrs (p less than 0.005), while MAP remained at 82.4 +/- 17.9 mm Hg, CI at 3.08 +/- 1.16 liter/min/m2 (p less than 0.05), and TPR at 1282 +/- 500 dyne/sec/cm-5. Thus, cardiac index rises significantly with sodium intake in normal subjects and remains at a higher level for as long as 12 months. Blood pressure does not rise because TRP falls proportionately.

Effect of salt loading on the cardiovascular response to stress in adolescents

This study investigated, in normotensive adolescents, three accepted risk factors for essential hypertension (EH): stress, dietary salt, and parental history (genetic risk). The cardiovascular response to mental stress was evaluated before and after salt loading in eight subjects without, and in seven with, a family history (FH) of EH. The effect of salt loading on the FH positive group was to increase significantly the stress-induced systolic and diastolic pressure while the heart rate response decreased. Salt loading resulted in no change in cardiovascular response to stress in the FH negative group.

Whole-body venous capacity and effective total tissue compliance in SHR

Whole-body venous capacity was examined in conscious 4-month-old male spontaneously hypertensive rats (SHR) and Wistar-Kyoto normotensive (WKY) rats by determining mean circulatory filling pressure (MCFP) and blood volume. The MCFP was determined in conscious animals after briefly arresting the circulation by inflating an indwelling balloon in the right atrium. Blood volume was determined by dilution of 125I-albumin and 51Cr-red cells. Although blood volume was not significantly different between SHR (60.9 +/- 0.7 ml/kg, SE) and WKY (59.6 +/- 0.8 ml/kg), MCFP was slightly, but significantly elevated in the SHR (9.5 +/- 0.3 vs 8.5 +/- 0.2 mm Hg, mean +/- SE, p less than 0.05). Increased MCFP with normal blood volume suggests decreased venous capacity in the SHR. In addition, effective total tissue compliance (ETTC) was measured in conscious 5-month-old female SHR and WKY. A decrease in tissue fluid volume was induced by i.v. infusion of hyperoncotic albumin solution. Changes in interstitial fluid pressure were monitored continuously with implanted tissue capsules. Changes in tissue fluid volume were estimated from changes in plasma volume and urine volume. In SHR 3 hours postinfusion, tissue fluid volume decreased by 38.7 +/- 2.7 ml/kg and interstitial fluid pressure decreased from -1.4 +/- 0.3 to -6.6 +/- 1.5 mm Hg. In WKY, tissue fluid volume decreased by 32.5 +/- 2.7 ml/kg and interstitial fluid pressure decreased from -1.4 +/- 0.4 to -3.9 +/- 0.5 mm Hg. The linear regression line for delta interstitial fluid pressure and delta fluid volume was estimated for each rat and the inverse of this slope represented ETTC, which averaged 7.4 +/- 1.0 and 9.6 +/- 2.1 ml/kg/mm Hg (p greater than 0.3) in SHR and WKY respectively. Thus, there were no significant differences in interstitial fluid pressure or ETTC between female SHR and WKY. The results of this study confirm a decreased venous capacity in male SHR with established hypertension and provide new information indicating no measurable abnormalities in interstitial fluid pressure or effective total tissue compliance in adult female SHR as compared with WKY.

Recent pathogenic aspects in essential hypertension and hypertension associated with diabetes mellitus

The sympathetic system, the body sodium-fluid volume state, the renin-angiotensin system, functional and structural characteristics of the heart and blood vessels, and some other components are important complementary factors in blood pressure regulation. A deviation from the normal equilibrium among these components, with a persisting non-physiologic increase in pressor factor(s) or in the basal vascular tone and/or cardiovascular reactivity to pressor factors, leads to hypertension. This review discusses recent observations and concepts regarding the pathogenesis of essential hypertension and hypertension associated with diabetes mellitus. It focuses on the roles of various pressor factors as well as cardiovascular pressor responsiveness in the genesis of high blood pressure and in the antihypertensive mechanism of diuretic treatment.