Cardiovascular haemodynamics and the response of vasopressin, aldosterone, plasma renin activity and plasma catecholamines to head-up tilt in young and old healthy subjects

Carotid blood flow, cardiovascular and endocrine responses during head-up tilt in patients with acute cerebrovascular diseases

The purpose of this study was to define common carotid blood flow (CBF), cardiovascular and endocrine responses during head-up tilt (HUT) in patients with acute cerebrovascular diseases (CVD). In 31 male patients with acute CVD (damage of the supratentorial area) and 21 age-matched control male subjects, we measured CBF, mean blood pressure (MBP), heart rate, stroke volume and cardiac output responses before (baseline), during and after HUT. We also measured plasma levels of antidiuretic hormone, adrenaline, noradrenaline, aldosterone and plasma renin activity. After obtaining baseline measurements during 3-minutes horizontal position, HUT was performed for 5 minutes, followed by continuation of recording for 3 more minutes in the horizontal position. During HUT, CBF decreased significantly and equally in both groups. MBP did not change during HUT in both groups. The endocrine responses were also not different between the two groups. The results suggest that damage to the supratentorial area in patients with acute CVD do not alter the CBF, cardiovascular and endocrine responses. In other words, HUT does not predispose patients with acute CVD to serious falls in MBP and CBF at upright posture.

Influence of age and sex on signal intensities of the posterior lobe of the pituitary gland on T1-weighted images from 3 T MRI

PURPOSE

To elucidate the influence of age and sex on the signal intensity (SI) of the posterior lobe of the pituitary gland (PPG) on T1-weighted images (T1WI) from 3 T MRI.

MATERIALS AND METHODS

Sagittal T1WI acquired from three-dimensional fast spoiled gradient recalled acquisition in the steady state in 1,634 subjects without conditions affecting antidiuretic hormone were evaluated retrospectively. The presence or absence of a bright signal in the PPG was assessed qualitatively. The SI ratio of the PPG to the pons (SIR) was obtained from quantitative measurements. We statistically analyzed these data, creating 14 subject groups categorized according to age and sex, and applied a Poisson generalized linear model to the SIR data.

RESULTS

The characteristic bright signal was absent in 47 subjects (2.8 %), with no significant difference in incidence among the groups. The SIR was inversely related to age in both males (r > 0.7) and females (r > 0.9), and was significantly higher in females in the third to the eighth decades (p < 0.05). Analysis of the whole SIR dataset using a generalized linear model showed that the estimated SIR decreased by 1.7 % per decade and is higher in females.

CONCLUSION

Age and sex influence the SI of the PPG on T1WI. These findings may aid the recognition of PPG signal abnormalities on T1WI.

Aspects of control of the cardiovascular-respiratory system during orthostatic stress induced by lower body negative pressure

This paper considers a model developed to study the cardiovascular control system response to orthostatic stress as induced by two variations of lower body negative pressure (LBNP) experiments. This modeling approach has been previously applied to study control responses to transition from rest to aerobic exercise, to transition to non-REM sleep and to orthostatic stress as produced by the head up tilt (HUT) experiment. LBNP induces a blood volume shift because negative pressure changes the volume loading characteristics of the compartment which is subject to the negative pressure. This volume shift induces a fall in blood pressure which must be counteracted by a complicated control response involving a variety of mechanisms of the cardiovascular control system. There are a number of medical issues connected to these questions such as orthostatic intolerance in the elderly resulting in dizziness or fainting during the transition from sitting to standing. The model presented here is used to study the interaction of changes in systemic resistance, unstressed venous volume, venous compliance, heart rate, and contractility in the control of orthostatic stress. The overall short term response depends on a combination of these physiological reactions which may vary from individual to individual. There remain open questions about which factors have greater importance. The model simulations are compared to experimental data collected for LBNP exerted from the hips to feet and from ribs to feet.

Reliability of orthostatic responses in healthy men aged between 65 and 75 years

The purpose of this study was to investigate the short-, medium- and long-term reproducibility of cardiovascular responses during 90 degrees head-up tilt (HUT) in healthy older men. Twenty-eight healthy male subjects aged 69 (95% confidence intervals, 68-70) years participated in the study. Eight subjects underwent duplicate 90 degrees HUT tests on consecutive days, while 20 subjects underwent four 90 degrees HUT tests performed at baseline, and after 1 week, 1 month and 1 year. Following a 20-min supine resting period, each subject was rapidly tilted to the upright vertical position (90 degrees HUT) and remained in that position for 15 min. Beat-by-beat recordings of mean (MAP), systolic (SBP) and diastolic (DBP) pressures were made via Finapres, while heart rate (HR) was monitored continuously from an electrocardiogram. No significant test-retest differences (P > 0.05) were observed for the changes in HR, MAP, SBP or DBP during 90 degrees HUT. These measurements demonstrated high reproducibility (intraclass correlation coefficient, r = 0.91-0.99, P < 0.05). The supine resting and tilted HR, MAP, SBP and DBP over the 1-week, 1-month and 1-year period were not significantly different (P > 0.05) from baseline, and demonstrated high reproducibility (intraclass correlation coefficient, r = 0.82-0.98, P < 0.05). The results of this study demonstrate that in healthy older men, cardiovascular responses during orthostasis are highly reproducible, and this reproducibility is maintained over a 12-month period. These findings demonstrate that the 90 degrees HUT test offers a reproducible method of monitoring longitudinal orthostatic responses in healthy older men.

Neurocardiogenic syncope in children : current concepts in diagnosis and management

A wide variety of pharmacologic agents are currently used for the prevention of recurrent neurocardiogenic syncope in children and adolescents. Significant advances in the understanding of this syncopal disorder have occurred in the past decade, and the list of medications recommended has changed, reflecting the evolving understanding of the pathophysiology and development of agents with enhanced efficacy and fewer adverse effects. Clinicians have few randomized controlled trials available to guide their decisions about treating neurocardiogenic syncope, and even fewer when it comes to medications targeting the pediatric population. At the present time, beta-adrenergic receptor blockers, fludrocortisone, and also specific serotonin reuptake inhibitors and midodrine, appear to be favored treatment options. Ideally, specific therapy would be tailored to specific pathophysiologic mechanisms. Unfortunately, at present, specific treatments based on those abnormalities have not been identified.

Cerebral oxygenation responses to standing in elderly patients with predominantly diastolic dysfunction

Patients with left ventricular dysfunction may have different orthostatic responses of blood pressure (BP) and cerebral oxygenation than healthy elderly subjects. We investigated orthostatic changes in systemic haemodynamic variables and cerebral oxygenation in 21 elderly patients with heart failure New York Heart Association class I-III in stable condition (age 70-83 years) after withdrawal of furosemide and captopril for 2 weeks, and in 18 healthy elderly subjects (age 70-84 years). Frontal cortical concentration changes of oxyhaemoglobin ([O2Hb]) and deoxyhaemoglobin ([HHb]) were continuously measured by near-infrared spectrophotometry and BP changes by Finapres before and during 10 min of standing. Upon standing [O2Hb] reflecting blood flow, changed by -1.2 +/- 0.9 micromol L-1 (mean +/- SEM) in the patients, whereas it decreased by -4.5 +/- 0.6 micromol L-1 (P<0.01) in the healthy subjects after standing (P<0.05 between groups). [HHb] reflecting the sum of cerebral blood flow, arterial oxygen saturation and cerebral oxygen uptake, increased by 1.5 +/- 0.5 micromol L-1 (P<0.05) and 1.7 +/- 0.6 micromol L-1 (P<0.05), respectively. Compared with healthy elderly subjects, elderly patients with left ventricular dysfunction showed smaller orthostatic [O2Hb] decreases (P<0.01), in relation to higher orthostatic BP rises (P<0.05). These findings indicate that BP changes and an altered cardiovascular balance may influence orthostatic cortical haemodynamic responses in elderly subjects.

Autonomic function in elderly patients with chronic heart failure

AIMS

Autonomic function (AF) is attenuated by heart failure (HF). Reports have been based on studies of young patients with systolic heart failure (SHF). However, HF is a disease of older patients who are more likely to have diastolic heart failure (DHF). We investigated whether age alters AF in elderly HF patients and whether the haemodynamic type of HF influences AF.

METHOD AND RESULTS

Thirty-six elderly HF (Framingham criteria) patients (11 with SHF, 25 with DHF) and 21 matched healthy subjects underwent simple bedside AF tests. Compared with the reference values for healthy adults, the mean E:I ratios and the median 30:15 ratios standing were all essentially normal. The median 30:15 ratios tilt and the mean Valsalva ratios were all significantly below the reference value (P for all cases <<0.050). Comparing three groups, there were no significant differences for mean E:I ratio (P=0.111), 30:15 tilt (P=0.619) and 30:15 standing (P=0.167), whereas there were significant differences for the mean Valsalva ratios (P=0.001). The mean Valsalva ratio of the SHF patients was significantly lower than that for the DHF patients (P<0.001) which in turn was significantly lower than the result of the healthy subjects (P<0.001).

CONCLUSION

There is an age-related impairment in AF with further impairment occurring in patients with HF. However, the severity of autonomic dysfunction is less in patients with DHF compared with patients with SHF.

Reproducibility of orthostatic changes in cerebral oxygenation in healthy subjects aged 70 years or older

In the elderly, standing can frequently be accompanied by blood pressure (BP) changes and cerebral symptoms such as dizziness, fall, or even syncope, but this may vary from day-to-day. Therefore, we aimed to investigate the reproducibility of orthostatic responses of cerebral cortical oxygenation and systemic haemodynamics in elderly subjects. In 27 healthy elderly subjects (age 70-84 years), changes in systolic BP (SBP), diastolic BP (DBP), heart rate (HR) and stroke volume (SV) were continuously monitored by Finapres (Finger Arterial Pressure), and changes in oxyhaemoglobin ([O2Hb]) and deoxyhaemoglobin ([HHb]) concentrations were continuously measured over the right frontal cortex by near infrared spectroscopy (NIRS) during supine rest and 10 min of active standing on two separate occasions. SBP and DBP increased by 6.7 +/- 15.4 mmHg (P<0.05, mean +/- SD) and 8.2 +/- 6.4 mmHg (P<0.01), respectively, whereas HR increased by 9.5 +/- 5.0 bpm (P<0.01) and SV decreased by -8.3 +/- 7.4 ml (P<0.01) during standing on the first occasion. [O2Hb] decreased by -3.9 +/- 2.9 micromol l-1 (P<0.01), while [HHb] increased by 1.8 +/- 2.2 micromol l-1 (P<0.01). Group-averaged orthostatic changes in cortical oxygenation and systemic haemodynamics were very similar on the two occasions, although an intraindividual variation was found. Cortical oxygenation changes were not accompanied by severe cerebral symptoms. Active standing induced reproducible group-averaged frontal cortical oxygenation declines in healthy elderly subjects, although an intraindividual day-to-day variability was present, possibly related to the variability of orthostatic BP responses. These findings indicate that cerebral autoregulation fails to compensate completely for postural changes in elderly subjects, which might predispose elderly subjects to ischaemic cerebral symptoms.

Cerebral oxygenation declines in healthy elderly subjects in response to assuming the upright position

BACKGROUND AND PURPOSE

With increasing age, assuming the upright position is more often accompanied by symptoms such as dizziness and lightheadedness, possibly as a result of a diminished oxygen supply to the brain due to impaired cerebral autoregulation. We aimed to quantify postural changes in cerebral oxygenation and systemic hemodynamics in healthy elderly and young subjects.

METHODS

In 18 healthy elderly subjects (aged 70 to 83 years) and 10 healthy young subjects (aged 22 to 45 years), frontal cortical oxygenation and hemodynamic responses were continuously monitored by near infrared spectroscopy and Finapres, respectively, before and during 10 minutes of active standing.

RESULTS

-Cortical oxyhemoglobin concentration [O(2)Hb] decreased by -4.6+/-2.2 micromol/L (P<0.001) and cortical deoxyhemoglobin concentration increased by 1.5+/-2.4 micromol/L (P<0.05) in the elderly subjects after posture change, whereas these variables did not change significantly in the young subjects. The postural hemodynamic changes tended to be attenuated in the elderly subjects, except for the increases in systolic blood pressure (BP). Smaller postural increases in diastolic BP were related to larger [O(2)Hb] decreases (r=0.53, P<0.01, corrected for the age effect).

CONCLUSIONS

Assuming the upright position evokes an asymptomatic decrease in frontal cortical oxygenation in healthy elderly subjects but not in healthy young subjects. Cortical [O(2)Hb] changes are affected by diastolic BP changes. These findings may indicate that regulation of cerebral oxygenation alters with increasing age.

Age-related changes in vascular responses: a review

Normal aging is associated with different changes in the cardiovascular system that lead to an increase in pathological processes, such as hypertension, coronary artery disease, heart failure, and postural hypotension with enhancement of both morbidity and mortality. The vascular alterations consist of changes in the function and structure of the arteries, and increasing vascular stiffness, mainly when atherosclerosis is present, whose incidence is increased with age. The arteries accumulate lipids, collagen, and minerals. Cerebral perfusion may be reduced in the elderly, mainly regional cerebral blood flow, which leads to a deterioration of mental and physical functions. The degree of deterioration is increased when aging is associated with hypertension. Aging alters endothelial cells, which play an important role in vascular tone regulation. Such a process tends to reduce endothelium-dependent relaxations, and clearly reduces the vasodilation elicited by beta-adrenoceptor agonists. The contractions induced by different agents, such as 5-hydroxytryptamine, histamine, high potassium and angiotensin are barely affected with aging, whereas those elicited by noradrenaline or endothelin are usually reduced. However, plasma noradrenaline levels are increased with age, mainly due to a reduction in the sensitivity of presynaptic alpha 2-adrenoceptors and also of noradrenaline uptake. Sodium pump activity, that controls cellular ionic homeostasis, may be altered depending on animal species. Finally, vascular Ca2+ regulation appears to be altered and the extracellular Ca2+ dependence of contractile responses elicited by agonists is increased, which justifies the enhanced sensitivity to Ca2+ antagonists in senescence.

Effect of 6 months of exercise training on cardiovascular responses to head-up tilt in the elderly

The purpose of this investigation was to evaluate the effect of 6 months of exercise training on cardiovascular responses to 70 degrees head-up tilt (HUT) in the elderly. Forty-four elderly men and women (ages 60-82 years) were assigned to endurance training alone (n = 18), endurance training in combination with selected resistance exercises (n = 17), or to a non-exercising control group (n = 9). Head-up tilt testing at the start (T1) and end (T2) of 26 weeks of training consisted of 30 min of supine rest, 15 min of 70 degrees HUT, and 15 min of supine recovery. Endurance training consisted of uphill treadmill walking or stair climbing exercise 3 times per week, 30-45 min/day, at 75-85% of maximal heart rate reserve. In addition, the endurance/resistance group completed one set of 8-15 repetitions of biceps curl (BC), triceps extension (TE), and leg press, 3 times per week. After 26 weeks, increases in VO2max averaged 16.2% and 12.3% for endurance and endurance/resistance groups, respectively. In addition, the endurance/resistance group increased BC and TE strength by 25.3% and 26.1%, respectively. Results from the HUT test indicated that only the endurance group increased supine resting stroke volume (SV) and cardiac output (Q) from T1 to T2; however, SV and Q during HUT were not augmented as a result of training. Training did not affect heart rate, blood pressure, or peripheral resistance responses at rest or during HUT in any of the groups. These results suggest that 6 months of endurance training, alone or in combination with selected resistance exercises, is not detrimental to blood pressure controlling mechanisms to head-up tilt in the elderly.

Age and the renal blood supply: renal vascular responses to angiotensin converting enzyme inhibition in healthy humans

OBJECTIVE

To assess the relation between age, sodium intake, renal blood flow (RBF) and the renal vascular response to an angiotensin converting enzyme (ACE) inhibitor, captopril.

DESIGN

Blood flow studies were performed before and during the acute response to an oral 25-mg dose of captopril, selected to induce a maximal response, after 5 to 7 days on a metabolic ward, sufficient time to have achieved external balance on a fixed low-salt (10 mE/day) or high salt (200 mEq/day) diet. Blood flow was measured as radioxenon transit through the kidney.

SETTING

The study was performed on a metabolic ward, the Clinical Research Center, and in the Cardiovascular Radiology Laboratories of the Brigham and Women's Hospital in Boston.

PARTICIPANTS

The participants, all community dwellers, were potential kidney donors, in a renal transplant program. They were thought to be sufficiently healthy to consider donation of a kidney. The age range was 18 to 69 years.

RESULTS

Renal blood flow showed the anticipated decline with increasing age, whether the subjects were on a restricted or a liberal salt intake. Captopril induced an acute increase in RBF, averaging 88 +/- 7 mL/100 g/min in subjects on a high-salt diet, but no influence of age was identified on the renal vasodilator response on either diet. Increasing age did not limit the renal vasodilator response, although subjects beyond the sixth decade were not studied.

CONCLUSIONS

The limited renal vascular response to vasodilators we had documented in earlier studies does not extend to ACE inhibitors. Although ACE inhibitors lack the pharmacological specificity required to prove a role for angiotensin II (Ang II), the data are compatible with a contribution of Ang II to the maintenance of renal vascular tone that does not change with increasing age, at least to 70 years of age.

Aging and vasoconstrictor responses mediated by alpha 2-adrenoceptors and 5-HT1 and 5-HT2 receptors

The potencies of noradrenaline (NA) at producing alpha 2-adrenoceptor mediated contractions, and of 5-hydroxytryptamine (5-HT) at producing 5-HT1 and 5-HT2 receptor mediated contractions were investigated in rings of human saphenous vein obtained from varicose vein surgery. There was a significant negative correlation between agonist potency and age for NA at alpha 2-adrenoceptors (r = 0.52, n = 21, p < 0.05) and for 5-HT at both 5-HT1 (r = 0.47, n = 19, p < 0.05) and 5-HT2 (r = 0.54, n = 19, p < 0.05) receptors, so that both agonists were less potent with increasing age. This demonstrates an age-related decrease in alpha 2-adrenoceptor and 5-HT1 and 5HT2 mediated contractile responsiveness in the human saphenous vein.

Arginine vasopressin and osmolality in the elderly

OBJECTIVES

To evaluate the influence of age on plasma arginine vasopressin (AVP) concentrations and the relationship between plasma AVP and serum osmolality in younger and older subjects, and in the elderly, to assess the effect of gender on plasma AVP concentration and to determine the impact of prostaglandin blockade on renal responsiveness to AVP.

DESIGN

Cross-sectional study; randomized, double-blind, crossover, placebo-controlled study.

SETTING

The Renal Laboratory, Royal North Shore Hospital (younger adults) and Clinical Room, St Vincents Hospital (elderly subjects).

PARTICIPANTS

45 younger adults (35 +/- 9 years), and 41 elderly subjects (29 males, 12 females; 78 +/- 3 years). All subjects were healthy and non-institutionalized. The elderly subjects were screened to exclude significant pathology (clinical assessment, multiple investigations).

INTERVENTION

Blood samples were drawn from all younger and elderly subjects. The elderly subjects were randomly allocated indomethacin or placebo for 1 month. Following a 1 to 2-week washout, the alternative was administered for a further 1 month.

MAIN OUTCOME MEASURES

Plasma AVP and serum osmolality and plasma AVP, serum, and urine osmolality at baseline were measured on indomethacin and placebo.

RESULTS

In the elderly subjects, baseline plasma AVP concentration was significantly higher than in the younger subjects studied (4.7 +/- 0.7 vs 2.1 +/- 0.2 pg/mL respectively; P = 0.0003). Plasma AVP was strongly correlated with serum osmolality in the younger subjects (r = 0.76, P = 0.0001) but not in the elderly cohort (r = -0.18, P = 0.26). No difference was found between the sexes in plasma AVP (P = 0.89), and indomethacin treatment did not alter the plasma AVP/urine osmolality ratio (P = 0.85) in the elderly subjects. In addition, changes in plasma AVP with indomethacin therapy did not correlate with changes in serum osmolality (r = 0.16, P = 0.09).

CONCLUSIONS

Aging is accompanied by an increase in plasma AVP concentrations. In healthy, elderly subjects, plasma AVP is not dependent on serum osmolality and is not influenced by gender. Indomethacin has no effect on the renal responsiveness to plasma AVP.

Is there a relationship between supine systemic blood pressure and orthostatic hypotension in the elderly?

The relationship between blood pressure and orthostatic hypotension was studied in 48 elderly patients with orthostatic hypotension and 29 healthy age-matched controls. Individuals were designated as hypertensive (systolic > 160 and or diastolic > 90 mmHg) or normotensive on the basis of supine blood pressure levels. Systolic, diastolic and mean blood pressures, heart rate, stroke volume, cardiac output, cardiac index and total peripheral resistance were measured every 5 min before, during and after 10 min head-up tilt to 70 degrees. Eighteen orthostatic hypotension subjects and six controls were hypertensive, while 30 orthostatic hypotension subjects and 23 controls were normotensive. There were no differences between hypertensive and normotensive patients in mean age, weight, height or body surface area. Mean systolic blood pressure in orthostatic hypotension subjects was higher than in controls (148.8 +/- 3.6 vs. 137.5 +/- 3.34 mmHg). Mean diastolic pressure was not different (79.1 +/- 2.0 vs. 79.0 +/- 2.0 mmHg). There were no differences between patients with or without hypertension in the haemodynamic changes produced by head-up tilt. Heart rates in orthostatic hypotension subjects with hypertension were significantly lower throughout the study when compared with normotensive orthostatic hypotension patients. Further, the increases in heart rate on tilting were significantly smaller (8.4 +/- 1.9 vs. 14.5 +/- 1.8 beats/min). Control hypertensive subjects had significantly higher mean cardiac output and cardiac index compared with non-hypertensives from before and during tilt. We conclude that hypertension is not related to the development or the degree of orthostatic hypotension in the elderly.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of age on vascular content of calcitonin gene-related peptide and mesenteric vasodilator nerve activity in the rat

Effects of age on sensory nerve vasodilator activity and vascular calcitonin gene-related peptide (CGRP) levels were investigated in Fischer 344 rats, aged 6, 20 and 27 months. Increases in pressure to transmural nerve stimulation (TNS) of the isolated perfused mesentery were greater at 27 months compared to 6 or 20 at frequencies of 4 and 8 Hz. With guanethidine to block adrenergic nerves and methoxamine to increase smooth muscle tone, TNS-induced vasodilation of the perfused mesentery decreased with age, reaching statistical significance at a frequency of 4 Hz and 27 months. There were no significant differences with age in concentration-response curves to CGRP in the perfused mesentery, except for the oldest rats at low concentrations of CGRP which showed increased vasodilation. Levels of CGRP-like immunoreactivity (CGRP-LI) in mesenteric and femoral arteries at 27 months were significantly less compared with 6 and 20 months; in the renal artery CGRP-LI was significantly decreased by 20 months. This study suggests that decreased sensory nerve function in aging animals may contribute to age-related alterations in circulatory hemodynamics.

Effect of xamoterol in a patient with idiopathic autonomic failure

We report the effect of xamoterol on autonomic, humoral and haemodynamic function in a patient with idiopathic autonomic neuropathy. Xamoterol produced marked symptomatic improvement, slightly increased heart rates in the sitting, supine and upright tilt positions and higher blood pressures while seated and on recovery from upright tilt. There were, however, no differences in blood pressure responses following a meal or during head-up tilt. We suggest that before ascribing symptomatic benefit to xamoterol in this condition, objective haemodynamic improvement should be recorded. Further studies of treatment in idiopathic autonomic failure require to be placebo controlled.

Stress hormone and blood glucose response following acute stroke in the elderly

We studied the relation of reactive hyperglycemia, stress hormone response, and outcome in 23 consecutive elderly patients (median age 80 [range 75-92] years) following an acute first stroke. The median delay from the onset of the stroke to the first blood sample (day 0) was 9 (range 4-22) hours. Subsequent blood samples were taken, after fasting, for the determination of blood glucose, cortisol, catecholamine, insulin, C-peptide, glucagon, and lactate concentrations on days 1, 2, 3, 7, 14, 30, and 90. For all 23 patients, a significant relation was found between the blood glucose concentration and survival (p = 0.03) and the blood glucose concentration decreased with time (p less than 0.001). There was also a significant relation between blood glucose concentration and outcome (p = 0.02). For the 15 patients with complete data, the major determinants of the blood glucose concentration were the cortisol, insulin, and glucagon concentrations (all p less than 0.001), which accounted for 42% of the variance. When all the indexes were analyzed together by logistic regression, only the cortisol concentration was related to outcome (p = 0.02). Hyperglycemia following a stroke probably reflects the intensity of the stress hormone response. We have confirmed that hyperglycemia is a predictor of outcome in persons with stroke.

Subsensitivity to beta-adrenoceptor agonists in pacemakers isolated from senescent rats

1. The effects of aging on the responsiveness of the isolated pacemaker of the rat to the chronotropic effect of norepinephrine, isoproterenol and soterenol were studied. 2. Pacemakers isolated from senescent rats (22-24 months old) showed subsensitivity to norepinephrine, isoproterenol and soterenol, when compared with pacemakers isolated from young rats (3-4 months old). The maximum response to the partial agonist soterenol was reduced. 3. Determination of the pA2 value of metoprolol in pacemakers isolated from senescent and young rats showed that the chronotropic response is mediated by a homogeneous beta 1-adrenoceptor population. 4. Inhibition of extraneuronal uptake did not potentiate the chronotropic effect of isoproterenol in pacemakers isolated from senescent rats. Addition of cocaine shifted the concentration-effect curve for norepinephrine only 2.2-fold to the left in senescent rats. 5. It is concluded that, during aging, impairment of the extraneuronal and neuronal uptake mechanisms has an important role in the control of chronotropic responsiveness to catecholamines.

Haemodynamic and neurohumoral responses in elderly patients with postural hypotension

Haemodynamic and neurohumoral responses to head-up tilt were measured in 28 elderly patients with postural hypotension (EPPH) and 12 healthy elderly subjects (HE). There were no differences in catecholamines between the groups and only noradrenaline increased on tilt (P less than 0.001). Plasma renin activity and aldosterone were similar in HE and EPPH in the supine and tilt positions. In both groups vasopressin increases (P = 0.032), and plasma volume decreases were the same (P = 0.673). Supine EPPH had higher heart rates (P = 0.019) but similar cardiac indices (P = 0.621). Both had similar changes on tilting (P = 0.975 and P = 0.341). Stroke volume decrease was higher in HE (35%) than EPPH (23%; P less than 0.001). HE showed an increase in peripheral resistance on tilting with no change in EPPH (P = 0.005). EPPH had larger coefficients of variation for all variables. The differences in haemodynamic responses and the similarity of neurohumoral responses during tilting suggest end-organ failure in EPPH with individual variations. Postural hypotension in old age is not a single entity.