Effect of advancing age on cardiopulmonary baroreceptor function in hypertensive men

Cardiopulmonary baroreceptors modify pain intensity in patients with chronic back pain

Objective

Baroreceptors play a significant role in nociceptive pain. However, the extent to which baroreceptors modulate nociception in patients with chronic pain is unclear. We tested the hypothesis that cardiopulmonary baroreceptor unloading via LBNP would significantly increase pressure pain threshold and habituation to heat pain among patients with chronic back pain.

Methods

Mechanical pressure pain threshold at the upper trapezius (hand-held algometer) and habituation to heat pain at the forearm were performed during sitting and supine position, and during baroreceptor unloading via lower body negative pressure (LBNP) of -10 mmHg in 12 patients with chronic back pain (54 ± 11 years of age). To determine whether pain reduction is normal during LBNP, studies were repeated in 7 young, healthy participants (23 ± 7).

Results

Mechanical pressure pain threshold (P < 0.01) and habituation to heat pain (P = 0.04) were significantly reduced during supine compared with sitting. Conversely, baroreceptor unloading via LBNP significantly increased pressure pain threshold (P = 0.03) and heat pain habituation (P < 0.01) compared with supine. In young healthy controls, pressure pain threshold was similarly affected when comparing sitting and supine (P = 0.01) and during LBNP (P < 0.01), whereas habituation to heat pain was unaltered when comparing sitting and supine (P = 0.93) and during LBNP (P = 0.90). Total peripheral resistance was increased during LBNP (P = 0.01) but not among young, healthy controls (P = 0.71).

Conclusions

The findings demonstrate cardiopulmonary baroreceptor modulation of nociceptive pain in patients with chronic pain. Interestingly, habituation to heat pain appears more readily modified by cardiopulmonary baroreceptors in patients with chronic back pain compared with young, healthy individuals.

Age-Associated Differences in Central Artery Responsiveness to Sympathoexcitatory Stimuli

BACKGROUND

Age-associated arterial stiffening may be the result of greater tonic sympathetic nerve activity. However, age-associated changes in central artery responsiveness to sympathoexcitatory stimuli are understudied. Therefore, we examined changes in central artery stiffness and wave reflection in response to sympathoexcitatory stimuli in young and older adults.

METHODS

Fourteen young (25 ± 4 years) and 15 older (68 ± 4 years) subjects completed 3 minutes of the cold pressor test (CPT) and lower-body negative pressure (LBNP) separated by 15 minutes. Carotid-femoral pulse wave velocity (cfPWV), central augmentation pressure (cAP), and augmentation index (AIx) were measured in duplicate during rest and the final minute of each perturbation.

RESULTS

Young subjects had lower baseline cfPWV, cAP, and AIx than older subjects (P < 0.05 for all). During the CPT mean arterial pressure (MAP), cfPWV, cAP, and AIx increased in both groups (P < 0.05 for all); however, changes (Δ) in MAP (18 ± 7 vs. 9 ± 5 mm Hg), cfPWV (1.3 ± 0.7 vs. 0.6 ± 0.9 m/s), cAP (4 ± 2 vs. 6 ± 3 mm Hg), and AIx (18 ± 9% vs. 7 ± 4%) were greater in young vs. older subjects, respectively (P < 0.05 for all). With MAP as a covariate, cfPWV, cAP, and AIx responses to the CPT were no longer significantly different between groups. During LBNP, changes in MAP (-1 ± 3 vs. -3 ± 5 mm Hg), cfPWV (0.5 ± 0.3 vs. 0.5 ± 0.7 m/s), cAP (-2 ± 2 vs. -2 ± 3 mm Hg), and AIx (-7 ± 7% vs. -3 ± 6%) were similar between young and older groups, respectively (P > 0.05 for all).

CONCLUSIONS

Collectively, our data suggest the sympathetic nervous system may directly modulate central hemodynamics and that age-associated differences in central artery responsiveness to sympathoexcitatory stimuli are largely attributable to differential blood pressure responses.

Hypertension in the Elderly

Hypertension is predictive of a wide variety of subsequent adverse events in elderly patients, at least up to the age of 80 years. Treatment can reduce these adverse outcomes, although the benefits in the very elderly remain somewhat unclear. In the very elderly, there appears to be a reduction in cardiovascular events, but this reduction is perhaps at the expense of an increase in overall mortality. Target BPs in the elderly remain controversial. Among patients who have not had previous stroke or significant cardiovascular or renal disease, the benefits of reducing the SBP below 159 mm Hg are well documented. There is some evidence to suggest, however, that if doing so increases the day-night difference in BP by more than 20% or is associated with a decline in DBP below 65 mm Hg, then the benefits of treatment may be attenuated or lost. In addition, there is some suggestion that reducing SBP consistently below 135 mm Hg may accelerate cognitive decline. There appears to be a role for sodium restriction in those who can comply without otherwise compromising nutrient intake. Likewise, exercise may be beneficial and have benefits beyond simply lowering BP. Weight loss in those who are overweight may also help in lowering the BP. For most patients, low-dose thiazides such as hydrochlorothiazide are likely to be the appropriate first-line therapy (even in patients who have diabetes) unless they exacerbate or precipitate urinary incontinence or gout or complicate concomitant drug therapy (eg, lithium treatment of bipolar disorder). In very elderly patients, the apparent beneficial effects on strokes, major cardiovascular events, and heart failure rates may justify treating despite lack of benefit on overall mortality.

Hypertension, hormones, and aging

The most rapidly growing segment of the United States population is the geriatric group, especially those above 75 years of age. Hypertension, diabetes mellitus, and dyslipidemia increase with advancing years in Westernized, industrialized societies such as the United States. These disorders contribute significantly to strokes and myocardial infarctions and associated morbidity and mortality in our elderly population. The increase in these chronic disease processes with aging is related, in part, to increasing obesity, reductions in physical activity, and medications that predispose to these conditions (ie, nonsteroidal inflammatory agents and hypertension). Hypertension in the elderly is characterized by high peripheral vascular resistance/reduced cardiac output, impaired baroflex sensitivity, relatively greater systolic pressures, increased blood pressure variability, and a propensity to salt sensitivity. Type 2 diabetes in the elderly is related to alterations in body composition (ie, increased central adiposity and decreased lean body mass) and to reduced physical activity. There is an increasing body of evidence that aggressive treatment of hypertension and dyslipidemia in the elderly results in comparable, if not greater, reductions in cardiovascular morbidity and mortality in the elderly as in younger counterparts.

Autonomic and cardiovascular function in the geriatric patient

The elderly patient is at an increased risk for hemodynamic instability during anesthesia. The underlying mechanisms are primarily a decrease in the beta-receptor response to stimulation, stiffening of the connective tissue throughout the cardiovascular system, and increased vascular resistance during surgical stress and an increased dependency on cardiac filling. Unfortunately, the ability to maintain a steady preload diminishes with age and in general, changes in blood volume are buffered less effectively. Anesthetic management requires closer monitoring of blood pressure and a greater emphasis on vasomotor tone than on fluid administration when treating hypotension.

Estrogen replacement, vascular distensibility, and blood pressures in postmenopausal women

The pathogenesis of blood pressure (BP) rise in aging women remains unexplained, and one of the many incriminating factors may include abnormalities in arteriolar resistance vessels. The aim of this study was to determine the effects of unopposed estrogen on arteriolar distensibility, baroreceptor sensitivity (BRS), BP changes, and rate-pressure product (RPP). We tested the hypotheses that estrogen replacement therapy (ERT) enhances arteriolar distensibility and ameliorates BRS, which leads to decreases in BP and RPP. Postmenopausal women participated in a single-blind crossover study; the participants of this study, after baseline measurements, were randomly assigned to receive estrogen (ERT) or a drug-free treatment with a 6-wk washout period between treatments. The single-blind design was instituted because subjects become unblinded due to physiological changes (i.e., fluid shifts, weight gain, and secretory changes) associated with estrogen intake. However, investigators and technicians involved in data collection and analyses remained blind. After each treatment, subjects performed identical autonomic tests, during which electrocardiograms, beat-by-beat BPs, and respiration were recorded. The area under the dicrotic notch of the BP wave was used as an index of arteriolar distensibility. The magnitude of the reflex bradycardia after a precipitous rise in BP was used to determine BRS. Power spectral analysis of heart rate variability was used to assess autonomic activity. BPs were recorded from resistance vessels in the finger using a beat-by-beat photoplethysmographic device. RPP, a noninvasive marker of myocardial oxygen consumption, was calculated. Repeated-measures analyses of variance revealed a significantly enhanced arteriolar distensibility and BRS after ERT (P < 0.05). A trend of a lower sympathovagal balance at rest was observed after ERT, however, this trend did not reach statistical significance (P = 0.061) compared with the other treatments. The above autonomic changes produced significantly lower systolic and diastolic BP changes and RPPs (P < 0.05) at rest and during isometric exercise. We conclude that short-term unopposed ERT favorably enhances arteriolar distensibility, BRS, and hemodynamic parameters in postmenopausal women. These findings have clinical implications in the goals for treating cardiovascular risk factors in aging women.

Heart rate variability and aerobic fitness

Heart rate variability, a noninvasive marker of parasympathetic activity, diminishes with aging and is augmented after exercise training. Whether habitual exercise over time can attenuate this loss is unknown. This cross-sectional investigation compared 72 male runners, aged 15 to 83 to 72 age- and weight-matched sedentary control subjects for the amplitude of their heart rate variability. Heart rate variability was assessed during rest while subjects were breathing at a rate of 6 breaths per minute and at an augmented tidal volume (tidal volume = 30% of vital capacity). Fitness levels were assessed with on-line, open-circuit spirometry while subjects were performing an incremental stress test. Overall results between the two groups showed that the physically active group had significantly higher fitness levels (p < 0.001), which were associated with significantly higher levels of heart rate variability, when compared with their sedentary counterparts (p < 0.001). These findings provide suggestive evidence for habitual aerobic exercise as a beneficial modulator of heart rate variability in an aging population.

Age-related modifications in neural cardiovascular control

Integrated cardiovascular responses to a range of different stimuli, as well as the overall, spontaneously occurring variability in blood pressure and heart rate, undergo complex changes with aging. A general trend is that homeostatic control mechanisms lose part of their ability to modulate heart rate and to buffer the concomitant blood pressure variations; the two phenomena are possibly linked by a cause-effect relationship. A detailed analysis of the age-related changes in the major reflex systems reveals a clear-cut impairment in arterial baroreceptor control of the heart rate, but much less pronounced changes in its control of blood pressure, on the other hand, both the hemodynamic and humoral components of the cardiopulmonary reflex appear to be markedly attenuated. The experimental evidence of the mechanisms underlying these changes is still largely incomplete, and it appears that the gaps will have to be filled by a systematic, detailed analysis, i.e., that no generalizations or extrapolations will be possible. Indeed, the data available so far indicate that the age-related alterations are highly non-uniform, some functions undergoing a definite impairment but others being much better preserved and some being even enhanced; thus aging is by no means associated with a generalized decline in cardiovascular functions and should instead be viewed as a complex, highly selective process. These peculiar biological features of the aging phenomena merit further investigation in both the cardiovascular and the other organ systems, in order to verify the possibility that currently unrecognized homeostatic potentials in the elderly subject may be exploited to advance his/her clinical management in health and disease.

Effect of nifedipine tablets on ambulatory blood pressure in patients aged less than 60 and greater than 65 years with systemic hypertension

To evaluate the effect of age on the pattern of circadian blood pressure after nifedipine tablets, ambulatory blood pressure after administration of low and high doses of nifedipine, taken twice daily, was measured over a 24-hour period in 10 elderly and 8 young hypertensive patients. After a 2-week control period without antihypertensive drug, 10 mg of nifedipine was administered twice daily for 2 weeks (low-dose period), followed by 2 weeks of 20 mg (high-dose period). At the end of each period, ambulatory BP monitoring was conducted every 30 minutes for 24 hours, using an ABPM 630 (Nippon-Colin, Komaki, Japan). In both groups, averages of systolic and diastolic BP for the entire day decreased significantly from the control to the low-dose periods. However, after the high-dose period, only the elderly group had further significant reduction of systolic BP, whereas no further reduction was seen in the young group. Separate analysis of whole-day data into daytime and nighttime values revealed that a further decrease in systolic BP after the high-dose period in the elderly group was a reflection of nighttime decline. It was suggested that circadian BP patterns after administration of nifedipine tablets in the elderly differed from those in young hypertensive patients, especially after administration of the high-dose.

Impact of age, race, and obesity on hypertensive mechanisms and therapy

Despite the demonstrated efficacy of traditional antihypertensive therapy in reducing blood pressure, hypertension continues to be a major cause of cardiovascular disease morbidity and mortality. Stepped-care therapy is a nonphysiologic approach that, due to potential metabolic derangements and stimulation of undesirable reflex responses, may not substantially reduce the cardiovascular and renal complications associated with hypertension or improve long-term survival in many hypertensive patients. Because of fundamental hemodynamic differences related to the age, race, and weight of hypertensive patients, drug treatment often elicits varying responses. Certain classes of drugs are not only more effective but also more appropriate from a physiologic standpoint in specific types of patients. Therapy selection based in part on hemodynamic mechanisms and demographic patterns is a more rational approach to patient management and may contribute to a better overall outcome than has been observed with conventional treatment.

Pressor hormones in elderly hypertensive persons. Racial differences

The purpose of this study was to examine pressor hormones and platelet alpha 2-adrenergic receptors in elderly unmedicated free-living subjects. Eighty-seven subjects, 70 +/- 5 years old (mean +/- SD), hypertensive or normotensive (blood pressure less than 160/90 mm Hg) were recruited for measurement of blood levels of norepinephrine, epinephrine, and vasopressin, as well as density and affinity of alpha 2-adrenergic receptors from platelet membranes, assessed by maximal binding (Bmax) and dissociation constant (Kd) of rauwolscine. They were separated into white hypertensive (n = 22) or normotensive (n = 41), and black hypertensive (n = 11) or normotensive (n = 13) groups, with similar age distribution throughout and similar blood pressure levels in the hypertensive and normotensive groups. Vasopressin was higher in the black hypertensive than white hypertensive group (1.5 +/- 1.0 vs. 0.7 +/- 0.5 pg/ml, respectively, p less than 0.005), whereas epinephrine correlated inversely with diastolic blood pressure (r = -0.7, p less than 0.02, in the black hypertensive group). Kd was higher in the black normotensive group than in the other groups (1.6 +/- 0.6 vs. 1.0 +/- 0.2, 1.1 +/- 0.3, or 1.0 +/- 0.3 nM in the white normotensive, black hypertensive, or white hypertensive group, respectively, p less than 0.002). Bmax was no different among groups but was significantly correlated with vasopressin levels for the whole group (r = 0.4, p less than 0.0004) although no such correlation existed within the black hypertensive group. The data suggest that various vasoconstrictor systems participate to different extents in the mechanisms generating and sustaining hypertension in elderly white and black subjects.

Baroreceptor reflex in elderly essential hypertensives: effect of chronic inhibition of angiotensin converting enzyme

Baroreflex function and plasma angiotensin II (Ang II) were examined in five elderly and five young or middle-aged essential hypertensive patients before and after enalapril treatment. Baroreflex sensitivity (BS) during blood pressure (BP) elevation by phenylephrine (PE) but not during BP reduction by sodium nitroprusside (SNP) was significantly attenuated in the elderly compared with the younger group, while plasma Ang II concentration was not different between the two groups. Enalapril treatment reduced BP without significant changes in heart rate and plasma norepinephrine in both groups, suggesting a leftward shift of barofunction curve. It also increased the BS in some cases in each group. However, plasma Ang II was not significantly reduced during enalapril treatment. The changes in BS did not correlate with changes in plasma Ang II. These results suggest that BS may be attenuated with increasing age independent of plasma Ang II and that ACE inhibitor influences the set point of the barofunction curve and BS by different mechanisms.

Norepinephrine and forearm vascular resistance responses to tilt and cold pressor test in essential hypertension: effects of aging

Heart rate, blood pressure, forearm vascular resistance (FVR), and catecholamine and renin responses to head-up tilt at 80 degrees and cold pressor test were investigated in 15 hypertensive men aged less than fifty-five (mean 44 +/- 7 years; M +/- SD) and 13 similarly hypertensive men aged more than fifty-five (mean 62 +/- 4 years; M +/- SD). Baseline plasma norepinephrine levels, as well as norepinephrine responses to tilt and cold pressor stress, were similar in the two groups, suggesting a lack of age-related increase in plasma norepinephrine (NE) responses in patients with essential hypertension. Normalized FVR responses (% change) to tilting (28 +/- 21 vs 95 +/- 36; M +/- SE) and cold pressor test (33 +/- 12 vs 64 +/- 21; M +/- SE) were significantly less (p less than 0.01) in older hypertensives. These results, but not the plasma NE responses to reflex sympathetic activation by tilt and cold pressor testing in older hypertensives, suggest an impaired forearm vasoconstriction.

Low dose of nitroglycerin failed to improve splanchnic hemodynamics in patients with cirrhosis: evidence for an impaired cardiopulmonary baroreflex function

High doses of nitroglycerin may decrease portal pressure in patients with cirrhosis with untoward effects such as arterial hypotension and a decrease in systemic O2 uptake. In the present study, low doses of nitroglycerin (7 to 15 micrograms per min, i.v.) were administered in 11 patients with cirrhosis in order to unload cardiopulmonary baroreceptor--one of the possible mechanisms by which nitroglycerin may improve splanchnic hemodynamics--and moreover to avoid deleterious systemic effects. Nitroglycerin significantly decreased right atrial pressure (-35%) and pulmonary wedged pressure (-27%) with significant increase in plasma norepinephrine concentration (+23%), which indicated that cardiopulmonary baroreceptor unloading was achieved. Changes in systemic hemodynamics were slight, although significant, with a decrease in arterial pressure (-8%) and an increase in heart rate (+8%); this indicates a minimal effect on high-pressure baroreflexes. In contrast, no significant change was observed in hepatic venous pressure gradient, hepatic blood flow and azygos blood flow. However, the fraction of cardiac output reaching the azygos system significantly increased by 18%. Plasma renin activity did not change significantly. Moreover, O2 transport and uptake were significantly decreased. These findings show that low doses of nitroglycerin failed to improve splanchnic hemodynamics in patients with cirrhosis. These results suggest an impaired cardiopulmonary baroreflex function which is probably located on the efferent arch.

Hypertension and diabetes

Diabetes mellitus and hypertension are both common diseases, especially with an increasingly aged population. Hypertension accelerates the development of diabetic retinopathy, nephropathy, and peripheral vascular disease in the diabetic patient. Diabetes represents a type of premature aging and hypertension in the diabetic patient is characterized by many of the same pathophysiologic properties seen in the elderly hypertensive patient.

Physiologic and hemodynamic considerations in blood pressure control while maintaining organ perfusion

Essential hypertension remains a significant contributor to mortality, despite treatments effective in decreasing blood pressure. A major reason mortality remains high may be that the conventional stepped-care approach does not always reduce blood pressure in a physiologic manner, which may result in metabolic derangements and elicitation of undesirable reflex mechanisms. Use of the stepped-care approach does not take into account fundamental hemodynamic differences associated with a hypertensive patient's age, race and weight. A nonphysiologic approach in the use of antihypertensive agents may be associated with progression of left ventricular hypertrophy, metabolic derangements, arrhythmias, sudden death, and increased atherosclerotic and nephrosclerotic complications. Considerations of the alterations in cardiovascular structure that can occur in light of the activity of the renin-angiotensin system, the sympathetic nervous system and transcellular calcium flux are discussed as to how they affect long-term survival.

Systemic hypertension in diabetes mellitus

Hypertension occurs more frequently in diabetics and markedly exacerbates the vascular morbidity and mortality resulting from this metabolic disorder. However, the etiology of hypertension in diabetics remains poorly understood. Like aging persons, diabetics have increased systemic resistance and a probable reduction in baroreceptor sensitivity. They also have an expanded total body sodium pool and a tendency to lower levels of plasma renin activity. Some of these factors suggest that a subtle calcium deficiency could also be of etiologic importance.

Salt sensitivity and systemic hypertension in the elderly

Aging in industrialized societies is accompanied by increases in the incidence and prevalence of hypertension, with a disproportionately greater increase occurring among aging blacks than among aging whites. This geriatric hypertension is generally of a salt-sensitive nature with a disproportionate frequency of isolated systolic hypertension. Although salt-taste acuity declines with age, salt sensitivity among the elderly does not appear to result from a compensatory increase in salt intake. Rather, age-related increases in salt sensitivity result, in part, from a reduced ability to appropriately excrete a salt load, which is due to a decline in renal function and to a reduced generation of natriuretic substances such as prostaglandin E2 and dopamine. Age-associated declines in the activity of membrane sodium/potassium-adenosine triphosphatase (Na/K-ATPase) may also contribute to geriatric hypertension because this results in increased intracellular sodium that may cause reduced sodium-calcium exchange and thereby increase intracellular calcium and vascular resistance. Reductions in cellular calcium efflux due to reduced calcium-ATPase activity may similarly cause an increase in intracellular calcium and vascular resistance. Increasing dietary calcium intake may represent an effective nonpharmacologic treatment for some salt-sensitive persons because it appears to reduce intracellular calcium by (1) suppressing parathyroid hormone-mediated calcium influx, (2) increasing Na/K-ATPase activity, and (3) reducing intravascular volume due to calcium-induced natriuresis.