Pressure Control Mechanisms Research Articles

유연 플래퍼와 연계한 압전 밸브 모듈레이터의 동적 모델링 및 압력 제어

This paper proposes a novel type of pressure control mechanism which can apply to vehicle ABS (anti-lock braking system) utilizing the piezoactuator based valve system associated with the pressure modulator. As a first step, a flapper-nozzle of a pneumatic valve system is devised by integrating the piezoacuator to the flexible beam structure. The dynamic modeling of the valve system is then undertaken and subsequently the governing equation of pressure control is derived considering the pressure modulator. A sliding mode controller is designed in order to achieve accurate pressure tracking control in the presence of actuator uncertainty as well as input pressure variation. It is shown through computer simulation that an accurate pressure tracking for sinusoidal motion whose magnitude is 40 bar is achieved by utilizing the proposed pressure control mechanism.

Long-Term Reprogramming of Cardiovascular Function in Infants of Active Smokers

Newborn infants of smokers show symptoms of cardiovascular stress hyperreactivity. Persistent hyperreactivity could increase the risk of short- and/or long-term complications, such as hypertension. Here we determined whether incipient dysfunction in a smoker's infant persists or worsens with age, by comparing cardiovascular reflex function of control and tobacco-exposed infants longitudinally from birth to 1 year. We compared infants born at term to nonsmoking couples (controls; n=19) and mothers who smoked moderately (average consumption=15 cigarettes per day; n=17). All were tested at 1 to 3 weeks, 3 months, and 1 year during sleep. We recorded blood pressure and heart rate noninvasively during passive repositioning (60 degrees head-up tilt). Tilting control infants raised blood pressure slightly above baseline at 1 week (+2%) and much more at 1 year (+10%). This trend was reversed in the tobacco-exposed cohort (+10% at 1 week but only +4% at 1 year). At 3 months and 1 year, the heart rate response of tobacco-exposed infants to tilt was also abnormal (highly exaggerated). Our study reveals that maternal smoking leads to long-lasting "reprogramming" of infant blood pressure control mechanisms. The underlying dysfunction in a smoker's infant could plausibly be a precursor or early marker of long-term susceptibility to complications, such as raised blood pressure.

Cardiovascular Outcomes and Angiotensin Converting Enzyme Inhibitors: Beyond Blood Pressure Control

Atherosclerosis and its complications, stroke, coronary artery disease and peripheral arterial disease, remain the leading cause of mortality and morbidity and are increasing in incidence in the developing world [1]. Multiple mechanisms are associated with the development of atherosclerosis but since the discovery of renin by Tigerstedt and Bergman [2] more that 100 years ago, the renin–angiotensin system (RAS) has been focus of intensive investigative efforts. Although our understanding of the RAS and the development of atherosclerosis has grown increasingly complex, inhibition of the RAS with an angiotensinconverting enzyme inhibitor (ACE-I) has become a firmly established therapeutic approach for reducing morbidity and the risk of death across a broad spectrum of cardiovascular diseases based on multiple, well-conducted, randomized clinical outcome trials (RCT) [3–6]. The benefits of ACE-I on clinical outcomes are due in part to blood pressure control but other mechanisms beyond blood pressure lowering, such as their anti-atherosclerotic properties has been postulated in recent clinical trials [7]. These clinical trials have broadened our knowledge of management of cardiovascular risk The Heart Outcome Prevention and Evaluation (HOPE) study [8] demonstrated the benefits of ACE-I on clinical outcomes in patients with established atherosclerosis or diabetes. The HOPE study by excluding patients with left ventricular systolic dysfunction and heart failure made obvious that the ACE-I ramipril not only reduced cardiovascular mortality, but also significantly reduced incidence of myocardial infarction and stroke. Similarly, the European Reduction of Cardiac Events with Perindopril in Stable Coronary Artery Disease (EUROPA) [9] study demonstrated that inhibition of the RAS with an ACE-I perindopril will result in secondary prevention of coronary events in a much broader population, patients with stable coronary disease irrespective of risk profile. The ACE-I perindopril in EUROPA [9] significantly reduced the combined endpoint of cardiovascular death, non-fatal myocardial infarction, and resuscitated sudden cardiac death by 20%. However studies such as PEACE [10] failed to replicate the results of EUROPA and HOPE. In the PEACE trial, patients with coronary artery disease and with preserved left ventricular systolic function treated with ACE-I trandolapril in a dose of 4 mg for several years did not show any reduction in cardiovascular outcomes. The lack of benefits of trandolapril in PEACE may be due to a lower cardiovascular risk population included in the trial and that patients were optimally treated with other evidence based treatments such as statins, beta blockers, antiplatelets and revascularization therefore they do not benefit with additional ACE-I. Cardiovasc Drugs Ther (2009) 23:109–111 DOI 10.1007/s10557-008-6152-5

Structural Insight on the Activity of Type 1 Angiotensin II Peptide Antagonists Using MD Simulations

Angiotensin II (AngII) is an octapeptide hormone, which plays a very important role in the blood pressure control mechanism. The excess production of this hormone is one of the main causes of hypertension illness. The antagonists for AngII At1 receptor constitute some of the most effective antihypertension drugs. In this work, both tested type1 AngII antagonists as well as new modeled antagonists (obtained by substitution of nonspecific amino acids by noncode residues (Sarcosine (Sar) and several Calpha, Calpha-dialkylglycines)) were simulated in dimethyl sulfoxide (DMSO) using molecular dynamics (MD). A number of common structural characteristics were identified on the active (and potentially active) simulated analogs, which seem to be correlated with their antagonistic activity. Two of the designed analogs were proposed as possible antagonists.

Effect of Hyperosmolality on Vasopressin Secretion in Intradialytic Hypotension: A Mechanistic Study

Administration of a small volume of hypertonic solution has been used as an effective treatment for patients with intradialytic hypotension. Hypertonic solutions have been considered to act as plasma volume expanders. This clinical study examines whether arginine vasopressin (AVP) is involved in this mechanism of blood pressure control. Nonrandomized trial. 42 patients on long-term hemodialysis therapy at a single hospital. Effects of intravenous infusions of 20 mL of 10% saline, 20 mL of 50% glucose, 200 mL of 0.9% saline, or physiological doses of AVP were examined during intradialytic hypotension. Changes in plasma AVP levels, osmolality, plasma volume, and blood pressure were analyzed. Hypertonic saline infusion increased plasma osmolality (mean, 292.7 to 302.3 mOsm/kg H(2)O; P < 0.001), plasma AVP levels (3.9 to 7.8 pg/mL; P = 0.03), and mean arterial pressure (66.6 to 71.8 mm Hg; P = 0.01). The increase in plasma volume (2.3%; P = 0.03) was too small to increase blood pressure because of volume alone. Hypertonic glucose infusion yielded similar results. Isotonic saline infusion increased blood pressure with an abrupt increase in plasma volume (12.7%; P < 0.001). AVP infusion increased blood pressure and plasma AVP to levels similar to those induced by the hypertonic solutions. There are limitations in accurately measuring changes in plasma volume during hemodialysis. Results strongly suggest that the osmotic stimulation of AVP secretion by hypertonic solutions has an important role in increasing blood pressure in patients with intradialytic hypotension. Manipulating plasma AVP appropriately may help correct and prevent intradialytic hypotension.

Weight Loss and Blood Pressure Control (Pro)

Overweight is an increasingly prevalent condition throughout the world. Current estimates, which are probably conservative, indicate that at least 500 000 000 people worldwide are overweight as defined by a body mass index (BMI) of between 25.0 and 29.9 and an additional 250 000 000 are obese with a BMI of 30.0 or higher.1 In the United States, recent data indicate that as much as 66% of the adult population is overweight or obese.2 Overweight and obesity are established risk factors for cardiovascular disease (CVD), stroke, noninsulin dependent diabetes (NIDDM), certain cancers, and numerous other disorders.3,4,5,6,7 It is also a risk factor for hypertension.8 Hypertension, defined as a systolic blood pressure in excess of 140 mm Hg or a diastolic blood pressure higher than 90 mm Hg, is also a globally increasing public health concern. Roughly 1 billion individuals worldwide are estimated to exhibit clinically significant elevated blood pressure with about 50 million of those residing in the United States.8 Hypertension, in turn, is associated with increased risk for CVD, stroke, renal disease, and all-cause mortality.9,10,11,12 The JNC VII report defines Stage 1 hypertension as blood pressure levels between 140 and 159 mm Hg systolic and 90 and 99 diastolic. Additionally, the report establishes a category of Prehypertension (Systolic blood pressure between 120 and 140 mm Hg or diastolic between 80 and 89 mm Hg). These 2 blood pressure classifications are deemed to be appropriate primary targets for lifestyle modification interventions, including weight loss. Higher levels of blood pressure, or stage 1 hypertension that is maintained over a long period, should be addressed primarily with medications or other physician directed treatments. There is a positive relationship between overweight or obesity and blood pressure and risk for hypertension. As early as the 1920s, a significant …

Activator of G Protein Signaling 3 Null Mice: I. Unexpected Alterations in Metabolic and Cardiovascular Function

Activator of G protein signaling (AGS)-3 plays functional roles in cell division, synaptic plasticity, addictive behavior, and neuronal development. As part of a broad effort to define the extent of functional diversity of AGS3-regulated-events in vivo, we generated AGS3 null mice. Surprisingly, AGS3 null adult mice exhibited unexpected alterations in cardiovascular and metabolic functions without any obvious changes in motor skills, basic behavioral traits, and brain morphology. AGS3 null mice exhibited a lean phenotype, reduced fat mass, and increased nocturnal energy expenditure. AGS3 null mice also exhibited altered blood pressure control mechanisms. These studies expand the functional repertoire for AGS3 and other G protein regulatory proteins providing unexpected mechanisms by which G protein systems may be targeted to influence obesity and cardiovascular function.

2P1-B17 建設作業機の機械インピーダンス調節のための油圧システム設計(建設・解体ロボット・メカトロニクス)

In this paper, hydraulic system for mechanical impedance adjustment of construction machinery was designed. This system is composed by model reference adaptive control (MRAC) and pressure control mechanism which applied accumulator and direction control valve. It gives passive compliance by using accumulator and adjusts the compliance characteristics by PWM control of pressure control mechanism. However, the dynamic characteristics influence the control so that hydraulic system behaves nonlinear. Therefore, it was adopted MRAC that did not depend on dynamic characteristics. The system applied front structure of hydraulic excavator, and it was shown to be able to adjust mechanical impedance.

IDENTIFICATION OF BLOOD PRESSURE CONTROL MECHANISMS BY POWER SPECTRAL ANALYSIS

1. Blood pressure and organ perfusion are controlled by a variety of cardiovascular control systems, such as the baroreceptor reflex and the renin-angiotensin system (RAS), and by local vascular mechanisms, such as shear stress-induced release of nitric oxide (NO) from the endothelium and the myogenic vascular response. Deviations in arterial blood pressure from its set point activate these mechanisms in an attempt to restore blood pressure and/or secure organ perfusion. However, the response times at which different cardiovascular mechanisms operate differ considerably (e.g. blood pressure control by the RAS is slower than blood pressure control via the baroreceptor reflex). 2. Owing to these different response times, some cardiovascular control systems affect blood pressure more rapidly and others more slowly. Thus, identifying the frequency components of blood pressure variability (BPV) by power spectral analysis can potentially provide important information on individual blood pressure control mechanisms. 3. Evidence is presented that the RAS, catecholamines, endothelial-derived NO and myogenic vascular function affect BPV at very low frequencies (0.02-0.2 Hz) and that low-frequency (LF) BPV (0.2-0.6 Hz) is affected by sympathetic modulation of vascular tone and endothelial-derived NO in rats. In humans, LF BPV (0.075-0.15 Hz) is affected by sympathetic modulation of vascular tone and myogenic vascular function. The impact of the RAS and endothelial-derived NO on BPV in humans requires further investigation. 4. In conclusion, power spectral analysis is a powerful diagnostic tool that allows identification of pathophysiological mechanisms contributing to cardiovascular diseases, such as hypertension, heart failure and stroke, because it can separate slow from fast cardiovascular control mechanisms. The limitation that some cardiovascular control mechanisms affect the same frequency components of BPV requires the combination of blood pressure spectral analysis with other techniques.

Opioid Analgesia in Persons at Risk for Hypertension

Acute pain sensitivity is reduced in clinical hypertension, but the precise relationship between pain perception and altered blood pressure control is not well-characterized. A negative correlation between resting blood pressure and pain sensitivity is observed throughout the normotensive range, suggesting links between basic mechanisms of blood pressure control and pain regulation. The opioid peptides are important endogenous analgesic mechanisms, but their role in the hypoalgesia of blood pressure elevations has not been well-established. The current study sought to examine the effects of endogenous opioids on blood pressure-associated hypoalgesia in young adults at risk for hypertension development. The effects of the opioid receptor antagonist, naltrexone, on cold pressor pain sensitivity were assessed in young adult men (n = 49) and women (n = 76) with mildly elevated casual blood pressure. Results indicate interactions between hypertension risk and the effects of opioid blockade on pain sensitivity. These findings suggest exaggerated opioid analgesia in persons at enhanced risk for hypertension and point to important links between altered neuropeptide regulation of pain and altered blood pressure control mechanisms in the early stages of hypertension.

New Insights into the Structural Organization of the Plant Polymer Lignin

The organizational features of lignin structure and the mechanism of its synthesis have significant implications for the response of the plant to stress. It was unknown whether the enzymic formation of lignin in the cell wall is an uncontrolled process or finely regulated in time and space. In vitro scanning tunneling microscopy (STM), atomic force microscopies (AFM), near-field scanning optical microscopy (NSOM). and the novel environmental scanning electron microscopy (ESEM) imaging studies of the lignin model compounds have directly shown its highly ordered structure and elucidated its modular and fractal organization. Direct evidence was presented for the existence of strong intermolecular forces responsible for holding lignin globules together in highly ordered structures. Fractal analysis was applied as a theoretical approach, to show regularity and modular organization of lignin. Surface chemistry studies of the lignin monolayer reveal intrinsic properties that may be a key to osmotic pressure and cell size control mechanism in the higher plant cells. The obtained data contribute to the explanation of the mechanisms of cell wall synthesis in vivo.

Multiple gene approaches to delineate the role of the renin-angiotensin-aldosterone system in nephropathy

Multiple gene approaches to delineate the role of the renin-angiotensin-aldosterone system in nephropathy

Plasma volume and blood pressure regulation in hypertensive pregnancy.

Pre-eclampsia is a multisystem disorder, peculiar to and frequent in human pregnancy. It remains a leading cause of maternal and neonatal morbidity and mortality. Hemodynamic disturbances are the most prominent features of the syndrome. To provide an overview of plasma volume regulation and blood pressure control mechanisms outside pregnancy, and of the changes in normal pregnancies and in pregnancies complicated by hypertensive disorders. Furthermore, to discuss the rationale of several hemodynamic interventions. In normal pregnancy, large cardiovascular changes take place. A generalized fall in vascular tone by systemic vasorelaxation causes increased blood volume, heart rate and cardiac output. In the preclinical phase, differences have been observed between normal and hypertensive pregnancies in the function of the autonomic nervous system, cardiac output and plasma volume, the volume remaining at the non-pregnant level. In the clinical phase of pre-eclampsia the typical case picture is one of a vasoconstrictive state with low plasma volume and cardiac output, high blood pressure and systemic vascular resistance in combination with signs of organ damage [proteinuria, hemolysis elevated liver enzymes low platelets (HELLP) syndrome]. Hemodynamic management is necessary in severe disease to prevent maternal complications. Management primarily focuses on pharmacological treatment of blood pressure. Clinicians make educated choices from a limited array of available drugs: beta-receptor antagonists, nifedipine, dihydralazine, methyldopa or ketanserine. Other drugs have restricted use in pregnancy. Management of low circulating volume with plasma expanders remains a subject of controversy.

Functional magnetic resonance imaging during hypotension in the developing animal.

Hypotension in adult animals recruits brain sites extending from cerebellar cortex to the midbrain and forebrain, suggesting a range of motor and endocrine reactions to maintain perfusion. We hypothesized that comparable neural actions during development rely more extensively on localized medullary processes. We used functional MRI to assess neural responses during sodium nitroprusside challenges in 14 isoflurane-anesthetized kittens, aged 14-25 days, and seven adult cats. Baseline arterial pressure increased with age in kittens, and basal heart rates were higher. The magnitude of depressor responses increased with age, while baroreceptor reflex sensitivity initially increased over those of adults. In contrast to a decline in adult cats, functional MRI signal intensity increased significantly in dorsal and ventrolateral medullary regions and the midline raphe in the kittens during the hypotensive challenges. In addition, significant signal intensity differences emerged in cerebellar cortex and deep nuclei, dorsolateral pons, midbrain tectum, hippocampus, thalamus, and insular cortex. The altered neural responses in medullary baroreceptor reflex sites may have resulted from disinhibitory or facilitatory influences from cerebellar and more rostral structures as a result of inadequately developed myelination or other neural processes. A comparable immaturity of blood pressure control mechanisms in humans would have significant clinical implications.

Effect of chronic stress on the cardiac baroreflex in the post-weanling rat

There is increasing evidence that early life stressors may program blood pressure control mechanisms such that the risk for cardiovascular disease in later life is increased. In the present investigation, the effect of repeated restraint/heat stress during the two-week period immediately after weaning on baroreflex function was determined and the contribution of brain angiotensin II (ANG II) to the changes was assessed in young, conscious, freely moving Sprague Dawley rats. In rats two weeks post weaning, basal MAP was significantly higher and basal HR significantly lower than rats tested immediately after weaning. This change in the operating point of HR was not accompanied by any changes in baroreflex function. Treatment with chronic icv infusion of losartan, an AT1 receptor antagonist, during the two-week period prevented the changes in basal MAP and HR. Chronic stress during the two weeks post weaning, whether due to surgical implantation of icv cannulae or due to restraint/heat stress, significantly shifted the set-point of the baroreflex function to a higher pressure. Chronic icv infusion of losartan during the period prevented these effects (at least in the case of stress due to the presence of icv cannulae) suggesting a role for brain ANG II in the change. Changes in the expression of CRH mRNA in the paraventricular nucleus could not explain the stress-related change in baroreflex function. If the rightward shift in the baroreflex persists into adulthood, it could increase the susceptibility to cardiovascular diseases such as hypertension.

Effect of a perinatal high-salt diet on blood pressure control mechanisms in young Sprague-Dawley rats.

In the present investigation we sought to determine if a perinatal high-salt treatment affects blood pressure at an early age (30 days), and if so, to determine the mechanisms responsible for the hypertension. Pregnant dams were given an 8% NaCl diet [high-salt (HS) rats] during the final one-third of gestation and throughout the suckling period. After weaning, the pups continued to receive the high-salt diet until testing at age 30 days. Control groups received a normal-salt diet (NS rats). In HS rats, mean arterial pressure (MAP) was significantly increased (110 +/- 5 vs. 96 +/- 3 mmHg) compared with NS rats. Blockade of brain AT(1) receptors with intracerebroventricular losartan decreased MAP in HS but not NS rats. Blockade of alpha-adrenergic receptors with intravenous phentolamine or ganglionic transmission with intravenous chlorisondamine produced a greater decrease in MAP in HS rats. Baroreflex control of heart rate was assessed using a four-parameter logistics function. The mid-range MAP (p3) was significantly increased in the HS rats. No other baroreflex parameters were affected. Specific binding of (125)I-[Sa (1),Ile(8)]ANG II to AT(1) receptors was increased in the subfornical organ (SFO) of the HS rats. Expression of AT(1a) receptor mRNA was greater in both SFO and PVN of the HS rats. These data suggest that even at an early age, Sprague-Dawley rats treated with a perinatal high-salt diet are hypertensive. The elevated blood pressure appears to be caused by increased sympathetic nervous activity, resulting, in part, from increased brain AT(1) receptor activation.

Disruption of the type 2 dopamine receptor gene causes a sodium-dependent increase in blood pressure in mice

BackgroundDopamine D2 receptors (D2Rs) are expressed in the kidney. It has not been determined whether D2Rs are involved in the mechanism of sodium handling and blood pressure (BP) control. MethodsThe function of D2Rs was investigated in mice disrupted with D2R gene (D2KO mice). Six-week-old male D2KO mice and wild-type (WT) mice were fed high-salt (4% NaCl) or low-salt (0.01% NaCl) diets for 8 weeks. ResultsBefore starting the metabolic diet, there were no significant differences in body weight, food consumption, and 24-h urine excretions of creatinine, sodium and potassium. The high-salt diet caused a significant elevation in systolic BP in D2KO mice but not in WT mice. Calculation of sodium and potassium balances revealed a significantly high level of sodium retention in D2KO mice placed on the high-salt diet. Twenty-four-hour urine norepinephrine excretions and heart rates, indicators of sympathetic activity, were not different in D2KO and WT mice on the high-salt diet. Administration of nemonapride, a specific D2-like receptor antagonist, to WT mice given 0.9% NaCl in drinking water caused suppression of urinary sodium excretion but had no effect in mice without salt loading. ConclusionsThese results suggest that D2 receptors promote sodium excretion during a period of high salt intake. A defect in this mechanism may result in sodium-dependent BP elevation.

Heart rate variability and autonomic activity at rest and during exercise in various physiological conditions.

The rhythmic components of heart rate variability (HRV) can be separated and quantitatively assessed by means of power spectral analysis. The powers of high frequency (HF) and low frequency (LF) components of HRV have been shown to estimate cardiac vagal and sympathetic activities. The reliability of these spectral indices, as well as that of LF/HF ratio as a marker of autonomic interaction at rest and during exercise, is briefly reviewed. Modifications in autonomic activities induced by different physiological conditions, e.g. hypoxia exposure, training, and water immersion, have been found in HRV power spectra at rest. The changes in HF and LF powers and in LF/HF ratio observed during exercise have been shown not to reflect the decrease in vagal activity and the activation of sympathetic system occurring at increasing loads. HF peak was recognised in power spectra in the entire range of relative intensity, being responsible for the most part of HR variability at maximal load. LF power did not change during low intensity exercise and decreased to negligible values at medium-high intensity, where sympathetic activity was enhanced. There was no influence from factors such as fitness level, age, hypoxia, and blood distribution. In contrast, a dramatic effect of body position has been suggested by the observation that LF power increased at medium-high intensities when exercising in the supine position. The increased respiratory activity due to exercise would be responsible of HF modulation of HR via a direct mechanical effect. The changes in LF power observed at medium-high intensity might be the expression of the modifications in arterial pressure control mechanisms occurring with exercise. The finding of opposite trends for LF rhythm in supine and sitting exercises suggests that different readjustments might have occurred in relation to different muscular inputs in the two positions.

Volume control and blood pressure management in patients undergoing quotidian hemodialysis

Background: Hypertension and interdialytic weight gain are associated with left ventricular hypertrophy (LVH), an important predictor of cardiovascular mortality in hemodialysis (HD) patients. Methods: In the London Daily/Nocturnal Hemodialysis Study, a group of patients receiving quotidian HD, either short daily (n = 11) or long nocturnal (n = 12), were followed for up to 18 months. Patients were assessed for effects of quotidian HD therapy on blood pressure, interdialytic weight gain, extracellular fluid volume (ECFV), intensity of antihypertensive therapy, and homocysteine levels. Results: Significant reductions in predialysis mean arterial blood pressure were observed in the daily HD group at 6 months ( P < 0.04) and in the nocturnal HD group at 9 months ( P < 0.03); these improvements persisted throughout the study period. The daily HD group had a 60% reduction in mean number of antihypertensive tablets per day at 1 month and an 8.8-fold reduction by 18 months. Nocturnal HD patients experienced a 3.3-fold reduction, and control patients, a 1.4-fold increase in mean number of tablets per day by 18 months. By 3 months, the daily HD group showed a significant decrease in interdialytic weight gain ( P < 0.0005) and lower ECFV than controls ( P < 0.05). The nocturnal HD group had a transient, but significant, increase in interdialytic weight gain at 6 and 15 months ( P < 0.05) and no difference in ECFV compared with controls, suggesting a different mechanism of blood pressure control. Homocysteine levels were significantly lower for both quotidian HD groups compared with conventional HD patients. Conclusion: Quotidian HD is a promising therapy with potent antihypertensive effects, resulting in improved blood pressure control. This, together with improved homocysteine levels, may be beneficial in the long term with regard to cardiovascular mortality.

Social Isolation and Health, with an Emphasis on Underlying Mechanisms

Social isolation is a potent but little understood risk factor for morbidity and mortality, and its negative consequences are most profound among the elderly, the poor, and minorities, some of the fastest growing segments of the U.S. population. A steadily increasing number of people are living alone and are therefore more likely to experience social isolation. We discuss four mechanisms--attractiveness, health behavior, stress, and repair and maintenance--by which perceived social isolation might affect health. Our studies show that neither attractiveness nor health behaviors differ as a function of social isolation, but stress and repair and maintenance do seem to be factors. While socially isolated young adults did not report more frequent everyday stressors, they rated everyday events as more intensely stressful. They were also more likely to report passively coping with stressors, and to show greater vascular resistance, a mechanism of blood pressure control previously associated with passive coping and a risk factor for hypertension. Finally, they exhibited less efficacious repair and maintenance of physiological functioning, including slower wound healing and poorer sleep efficiency. These mechanisms have implications for designing appropriate interventions. We advocate a national health care plan that promotes preventive medicine, recognizes the significance of stress-related disorders, and supports the maintenance of social connections across the life span.