Hemodynamics and its regulation in old age

Environmental triggers of COPD symptoms: a case cross-over study

INTRODUCTION

This study investigated the hypothesis that common environmental chemical exposures with known irritant or sensitising properties trigger exacerbations for patients with chronic obstructive pulmonary disease (COPD).

METHODS

We conducted a case cross-over study in 168 patients with COPD who were members of a disease management group in central Massachusetts. Participants completed a baseline health survey and several short exposure surveys. Exposure surveys were administered by a nurse when a participant telephoned to report an exacerbation (case periods) and at a maximum of three randomly identified control periods when they were not experiencing an exacerbation. We compared exposures in the week preceding an exacerbation with exposures in normal (non-exacerbation) weeks. The questionnaire assessed short-term (1 week) home, community and workplace activities and exposures that may be associated with COPD exacerbation.

RESULTS

Self-reported exercise was negatively associated with exacerbation (OR=0.59, 95% CI: 0.35 to 1.00). Among the environmental chemical exposures, car and truck exhaust (OR=4.36, 95% CI: 1.76 to 10.80) and use of scented laundry products (OR=2.69, 95% CI: 1.31 to 5.52) showed strong positive effects. Self-reported respiratory infections were strongly associated with exacerbation (OR=7.90, 95% CI 4.29 to 14.50). Variations in outdoor temperature were associated with COPD exacerbation risk (moderate versus cold temperature OR=1.95, 95% CI 1.09 to 3.49 and warm versus cold OR=0.43, 95% CI: 0.26 to 0.70).

CONCLUSIONS

These results suggest that some environmental chemical exposures may play a role in triggering COPD exacerbations. If confirmed, they may provide useful guidance for patients with COPD to better manage their disease.

Young borderline hypertensives are hyperreactive to mental arithmetic stress: spectral analysis of R-R intervals

To investigate whether sympathetic tone and its reactivity to stress are increased in borderline hypertension, we compared pressor and autonomic nervous responses to mental arithmetic stress in male borderline hypertensives (BH) and normotensive volunteers (NT). Three age groups, 30, 40 and 50-year-old groups, which included 30 to 39, 40 to 49 and 50 to 59-year-old subjects, were studied. Fractional LF (%LF), fractional HF (%HF) and L/H, obtained from the power spectrum of R-R intervals, were used as indices of autonomic nervous function. Baseline autonomic nervous indices did not differ between NT and BH of any age group. Blood pressure rose higher during mental arithmetic stress in 50 than in 30-year-old NT but not in comparable age groups of BH. Pressor responses were augmented in BH compared to NT only in the 30-year-old group. However, the differences were not significant when pressor responses were expressed as percent increases in blood pressure. Both %L and L/H increased during arithmetic stress. The increase in %L did not differ between NT and BH but that in L/H (% delta L/H) was larger in 50 than in 30-year-old NT. % delta L/H was larger in BH than in NT only in the 30-year-old group. These findings suggest that both pressor and autonomic nervous responses to metal arithmetic stress were altered by aging and augmented in BH compared to NT in the 30-year-old group.

Reduction of endothelial function with age in the mesenteric arterial bed of the normotensive rat

1. Age-related changes in endothelial vasodilator function were studied in an in vitro preparation of the mesenteric arterial bed removed from male, normotensive, Wistar rats. 2. Animals were killed at 2, 12 or 22 months of age, the superior mesenteric artery was cannulated and the gut removed. The mesenteric arterial bed was perfused at a constant flow rate of 4 ml min-1 and perfusion pressure was taken as an index of arteriolar tone. 3. The muscarinic agonist, carbachol, antagonized noradrenaline-induced vasoconstriction in the presence, but not in the absence, of endothelium. This cholinoceptor agonist-induced release of endothelial-derived relaxing factor (EDRF) was impaired in 22 month old rats. 4. Noradrenaline-induced vasoconstriction increased following removal of endothelium suggesting that agonist-induced release of EDRF attenuates vasoconstrictor responses to noradrenaline measured in the presence of endothelium. 5. Removal of endothelium had less effect on noradrenaline-induced vasoconstriction in old rats suggesting once again that agonist-induced release of EDRF is impaired in old rats. 6. The noradrenaline dose-response curve established in the presence of endothelium was shifted to the left in 22 month old rats. 7. In conclusion, aging in the rat appears to lead to a reduction in endothelial vasodilator function in a resistance vessel.

Aging escalates baroreceptor reflex suppression by the posterior hypothalamus in rats

To examine whether baroreceptor reflex regulation by the posterior hypothalamus becomes modified with age, we compared baroreceptor reflex sensitivity and hypothalamic responsiveness in 2- and 10-month-old rats anesthetized with urethane-chloralose. Hypothalamic regulation of baroreceptor reflex sensitivity was assessed by recording responses to intravenously infused phenylephrine and afferent aortic nerve stimulation after sham operation or electrolytic destruction of the posterior hypothalamus. Regardless of age, reflex bradycardia and sympathoinhibition elicited during pressor responses to phenylephrine, as well as all cardiovascular and sympathetic nerve responses to afferent aortic nerve stimulation, were stronger in rats with bilateral hypothalamic lesions than in age-matched, sham-operated controls. Distinctively, because baroreceptor reflex sensitivity differed with age only in sham-operated controls but not in lesioned rats, we concluded that age-related differences in baroreceptor reflex sensitivity had been abolished by posterior hypothalamic lesions. Other experiments were then performed to compare responses to graded electrical stimulation of the posterior hypothalamus in baroreceptor-intact rats. Pressor and sympathoexcitatory responses to hypothalamic stimulation were larger, and stimulus thresholds were lower at 10 than at 2 months of age thereby suggesting that hypothalamic responsiveness had increased with age. Our results are in accord with the interpretation that aging exacerbates the baroreceptor reflex suppression normally exerted by the posterior hypothalamus.

Age-induced decreases in the messenger RNA coding for the sarcoplasmic reticulum Ca2(+)-ATPase of the rat heart

Age-associated slowing of cardiac relaxation related to the decline in the Ca2+ pump function of cardiac sarcoplasmic reticulum (SR) has been previously described. It is unclear if the decreased Ca2+ pump function results from a lower amount of Ca2(+)-ATPase protein or a decreased pumping activity of the enzyme. To determine if these alterations could be mediated by changes in the amount of the protein itself, the level of the messenger RNA (mRNA) coding for the Ca2(+)-ATPase of the SR of Fischer rat hearts (4- and 30-month-old rats) were quantitated with a Northern blotting technique. We observed that the levels of SR Ca2(+)-ATPase mRNA were 60% lower in old rats as compared with young rats, suggesting that a quantitative reduction in the levels of the corresponding protein could occur during aging to explain the delayed diastolic relaxation documented in old animals as opposed to a change in the specific activity of this enzyme. The thyroid hormone responsiveness of SR Ca2(+)-ATPase mRNA has been previously established. We have found in this study that the thyroxine levels were consistently lower in old rats; however, this difference was relatively small (4.3 +/- 0.7 and 3.1 +/- 0.8 micrograms/dl [mean +/- SD), respectively, in young and old rats). In addition, no age-induced decrease in 3,5,3'-triiodothyronine levels was observed, suggesting that the aging process itself may be responsible for the changes in SR Ca2(+)-ATPase mRNA levels.

Comparison of arterial wall properties in young and old racing greyhounds

Arteries were obtained from several sites in young (YGH) and old racing greyhounds (OGH). Segments were used for the determination of arterial wall mechanics under conditions of active (norepinephrine) and passive (Ca2+ free and 2 mM EGTA) smooth muscle. Contiguous segments were used for the chemical analysis of connective tissue, water and electrolyte content. The passive stiffness of arteries from OGH was consistently greater than that of the YGH. Collagen content and the collagen-elastin ratio were larger at all sites in the OGH. However, the connective tissue changes were not considered to be of sufficient magnitude to explain the changes in passive mechanics. Maximum values of active stress development were generally lower in arteries from the OGH as was their relative cell content. Active stress development normalized to smooth muscle cell cross-section was not uniformly changed in arteries from OGH. In spite of the lower active stress development in some arteries, the ability of smooth muscle to constrict lumen diameter was not different between OGH and YGH at transmural pressures in the physiological range. While a number of changes occur in arteries of purebred greyhounds with aging, they appear to occur in such a fashion that normal function is not grossly altered.

Comparison of ATP-dependent calcium transport and calcium-activated ATPase activities of cardiac sarcoplasmic reticulum and sarcolemma from rats of various ages

Age-associated decline in the Ca2+ pump function of cardiac sarcoplasmic reticulum (SR), and increase in the Ca2+ pump activity of sarcolemma (SL) were suggested by my previous study which compared the ATP-energized in vitro Ca2+ transport activities of these membranes from young (3-4-month-old) and aged (24-25-month-old) rat myocardium (Biochim. Biophys. Acta, 678 (1981) 442-459). In the present study, ATP-dependent Ca2+ transport and Ca2+ sensitive ATPase activities of SR and SL derived from the myocardium of rats aged 3 (young), 6 (young adult), 12 (adult), 18 (aging) and 24 (aged) months were determined so as to further characterize age-related changes in the Ca2+ transport function of these membranes. The rates of ATP-dependent Ca2+ accumulation by SR from 3- and 6-month-old rats were virtually similar whereas the rates of Ca2+ accumulation by this membrane from 12-, 18- and 24-month-old rats were significantly lower when compared to 3- or 6-month-old rats; the magnitude of this age-related decline amounted to approx. 18, 45 and 50%, respectively, for SR from 12-, 18- and 24-month-old animals. In contrast to the above findings with SR, SL from 18- and 24-month-old rats displayed substantially higher rates (approx. 45 and 80% increase, respectively, at 18 and 24 months of age) of ATP-dependent Ca2+ accumulation than SL preparations from 3-, 6- and 12-month-old rats; no significant age-related difference was evident between the latter three age groups. The divergent age-related changes in the Ca2+ accumulating activities of SR and SL were seen at varying Ca2+ concentrations (0.54-25.2 microM). With either membrane, kinetic analysis showed that the velocity of Ca2+ transport, but not the apparent affinity of the transport system for Ca2+ underwent age-related changes. The Ca2+-stimulated ATPase activities of SR and SL were not altered significantly with increasing age from 3 to 24 months. Comparison of the 'combined Ca2+ transport activity' of SR and SL from rats of various ages showed a significant overall age-related decline in the rates of Ca2+ transport via the ATP-driven membrane Ca2+ pumps; this decrement in membrane function was moderate at 12 months of age (approx. 16%) and became pronounced with advancing age thereafter (approx. 35 and 38%, respectively, at 18 and 24 months of age). Similar progressive age-related decline was observed in the ATP-dependent Ca2+ sequestering activity of cardiac homogenates.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensitivity to noradrenaline and electrical stimulation decreases with age in the rat tail artery

We have studied vasoconstrictor responses to noradrenaline and electrical field stimulation in the isolated perfused/superfused tail arteries of rats of 6-7, 16-17 and 30-31 months of age. Maximal vasoconstrictor responses to noradrenaline were the same at all three ages. Sensitivity to noradrenaline and to electrical stimulation were reduced in the 16-17 and 30-31 month old rats. The noradrenaline content of the arteries of the two latter age groups was reduced. We conclude that aging in this resistance vessel is accompanied by a decrease in the arterial noradrenaline content and in the sensitivity of the artery to noradrenaline.

Aging and atrial electrophysiologic properties in man

In order to assess the influence of age on atrial electrophysiologic properties, we studied 17 normal subjects, whose ages were homogeneously distributed between 17 and 78 years, measuring in each of them effective (ERP) and functional (FRP) refractory periods at 3 sites of the right atrium (high, middle and low in the lateral wall) at the same driven frequency (120/min). Twice threshold stimuli of 2 msec duration were applied. Dispersion of atrial refractoriness was measured as the longest minus the shortest refractory period. A significant direct correlation was observed between age and dispersion of atrial refractoriness (of ERP: r = 0.75, P less than 0.001; of FRP: r = 0.82, P less than 0.001). Moreover, age showed a significant direct correlation with refractoriness at high right atrium (ERP: r = 0.66, P less than 0.01; FRP: r = 0.76, P less than 0.001), but did not correlate with that at the other two sites. We suggest that ageing modifies atrial refractoriness in a non-uniform manner inducing a progressive increment of dispersion of atrial refractoriness. The impression is that a slow but continuous process takes place from juvenility to old age.

Mechanisms of neurohumoral regulation of heart function in aging

Changes in hemodynamics and myocardial contractile capacity following the stimulation of extracardial nerves and administration of various doses of acetylcholine, norepinephrine, propranolol, phentolamin, atropine, serpasil and benzohexonium were studied in albino rats, rabbits and cats of various age. The shifts in cardiac acetylcholine and norepinephrine content and the activity of some enzymes of their catabolism were determined as well. Functional changes were compared with the structural shifts in intramural nervous system. In old animals there was a rise in threshold of voltage, which induced threshold reaction at stimulation of n. vagus and n. sympaticus and there was a change in heart sensitivity to acetycholine and norepinephrine, propranolol, atropine, serpasil and benzohexonium. A relationship was shown between age changes in nervous regulation of heart and transmitter metabolism. The intensity of acetylcholine and norepinephrine synthesis was decreased in old age, the transmitter metabolism in various parts of the heart was not uniformly altered, the sensitivity of epicardial chemoreceptors to nicotine, veratrum, acetylcholine was increased. The reflexes from cardiac mechanoreceptors were diminished.

Central neurotransmitter substances and aging: a review

Available evidence suggests that age is an important determinant of the levels of neurotransmitters and their associated enzymes and metabolites in some regions of the brain. Alterations at the synaptic level, or selective cell death in the brain, or both, may be implicated in progressive loss of function, behavioral changes and the onset of age-related diseases. Stimulation of hypothalamic neuroendocrine transducer cells by agents that alter neurotransmitter metabolism might provide some measure of control of the process of aging.