Postural changes in cardiac volumes in men in relation to adult age

Cardiac changes associated with vascular aging

Cardiovascular aging is a complex process of adaptive structural and functional changes over time. With advancing age, the arterial tree thickens and decreases in compliance, resulting in increased pulse wave velocity, systolic blood pressure, and left ventricular afterload. In response to these arterial changes, the myocardium remodels to maintain systolic function and diastolic filling. These adaptive mechanisms are not necessarily pathologic but increase the susceptibility for myocardial ischemia and heart failure in the presence of common age-associated comorbidities. This article reviews the pathophysiology of cardiovascular aging and discusses therapeutic interventions that may ameliorate these processes.

Positional Changes in Arterial Oxygen Saturation and End-Tidal Carbon Dioxide at High Altitude: Medex 2015

Background: Body position alters aspects of pulmonary function in health and disease. Although studies have assessed positional effects on the heart and lungs, little is known about positional changes in gas exchange parameters at high altitude. We hypothesized that following ascent, supine positioning would cause lower oxygen saturation than sitting, partially due to decreased ventilation and increased partial pressure of end-tidal carbon dioxide (Petco₂). Materials and Methods: Twenty-eight healthy subjects were studied at sea level and following gradual ascent to 5150 m. After 10 minutes of sitting rest, subjects were studied for 5 minutes each in the sitting, supine, and prone positions with the order randomly assigned. Pulse oximeter oxygen saturation (SpO₂), minute ventilation (V_E), end-tidal O₂ (Peto₂) and Petco₂, oxygen consumption, and CO₂ production were continuously measured. Alveolar ventilation (V_A) was calculated from the measured parameters. Results: At high altitude, V_E was not affected by body position (12.96 ± 3.09 and 11.54 ± 3.45 L/min in the sitting and supine positions, respectively, p = 0.255). Petco₂ increased from sitting to supine (22.8 ± 3.1 to 23.5 ± 3.3 mm Hg, p < 0.005), but V_E and Petco₂ were not different between the supine and prone positions. Calculated V_A was not significantly affected by body position at either sea level or high altitude. SpO₂ decreased from 81.3% ± 4.4% sitting to 78.8% ± 6.0% supine (p = 0.025), with a mean positional SpO₂ difference of 2.5% ± 4.9% (95% confidence interval 0.6%-4.4%). SpO₂ was not different between the supine and prone positions. Twenty-two of 28 subjects had lower SpO₂ supine compared with sitting. Conclusions: These results extend earlier low-altitude studies and demonstrate the importance of postural regulation in different environments. As 79% of subjects had lower SpO₂ while supine than sitting, control of body position is necessary for SpO₂ comparisons at altitude to be meaningful.

Modeling arterial pulse waves in healthy aging: a database for in silico evaluation of hemodynamics and pulse wave indexes

The arterial pulse wave (PW) is a rich source of information on cardiovascular (CV) health. It is widely measured by both consumer and clinical devices. However, the physical determinants of the PW are not yet fully understood, and the development of PW analysis algorithms is limited by a lack of PW data sets containing reference CV measurements. Our aim was to create a database of PWs simulated by a computer to span a range of CV conditions, representative of a sample of healthy adults. The typical CV properties of 25-75 yr olds were identified through a literature review. These were used as inputs to a computational model to simulate PWs for subjects of each age decade. Pressure, flow velocity, luminal area, and photoplethysmographic PWs were simulated at common measurement sites, and PW indexes were extracted. The database, containing PWs from 4,374 virtual subjects, was verified by comparing the simulated PWs and derived indexes with corresponding in vivo data. Good agreement was observed, with well-reproduced age-related changes in hemodynamic parameters and PW morphology. The utility of the database was demonstrated through case studies providing novel hemodynamic insights, in silico assessment of PW algorithms, and pilot data to inform the design of clinical PW algorithm assessments. In conclusion, the publicly available PW database is a valuable resource for understanding CV determinants of PWs and for the development and preclinical assessment of PW analysis algorithms. It is particularly useful because the exact CV properties that generated each PW are known.NEW & NOTEWORTHY First, a comprehensive literature review of changes in cardiovascular properties with age was performed. Second, an approach for simulating pulse waves (PWs) at different ages was designed and verified against in vivo data. Third, a PW database was created, and its utility was illustrated through three case studies investigating the determinants of PW indexes. Fourth, the database and tools for creating the database, analyzing PWs, and replicating the case studies are freely available.

Evaluation of inert gas rebreathing for determination of cardiac output: influence of age, gender and body size

The aim of this study was to evaluate an inert gas rebreathing method (Innocor) for measurement of cardiac output and related haemodynamic variables and to provide robust normative data describing the influence of age, gender and body size on these variables. Four separate studies were conducted: measurement repeatability (study 1, n = 45); postural change (study 2, n = 40); response to submaximal cycling exercise (study 3, n = 20); and the influence of age, gender and body size (study 4, n = 1400). Repeated measurements of cardiac output, stroke volume and heart rate were similar, with low mean (±SD) differences (0.26 ± 0.53 L/min, 0 ± 11 mL and 2 ± 6beats/min, respectively). In addition, cardiac output and stroke volume both declined progressively from supine to seated and standing positions (P < 0.001 for both) and there was a stepwise increase in both parameters moving from rest to submaximal exercise (P < 0.001 for both). In study 4, there was a significant age-related decline in cardiac output and stroke volume in males and females, which remained significant after adjusting for body surface area (BSA, P < 0.001 for all comparisons). Both parameters were also significantly higher in those with high body mass index (BMI; P < 0.01 versus those with normal BMI for all comparisons), although indexing cardiac output and stroke volume to BSA reversed these trends. Inert gas rebreathing using the Innocor device provides repeatable measurements of cardiac output and related indices, which are sensitive to the effects of acute physiological manoeuvres. Moreover, inert gas rebreathing is a suitable technique for examining chronic influences such as age, gender and body size on key haemodynamic components of the arterial blood pressure.

Orthostatic Hypotension and Risk of Clinical and Subclinical Cardiovascular Disease in Middle-Aged Adults

Background

Although orthostatic hypotension (OH) is a well‐recognized manifestation of neuropathy and hypovolemia, its contribution to cardiovascular disease (CVD) risk is controversial.

Methods and Results

Participants with OH, defined as a decrease in blood pressure (systolic ≥20 mm Hg or diastolic ≥10 mm Hg) from the supine to standing position, were identified during the first visit of the ARIC (Atherosclerosis Risk in Communities) Study (1987–1989) within 2 minutes of standing. All participants were followed up for the development of myocardial infarction, heart failure, stroke, fatal coronary heart disease (CHD), any CHD (combination of silent, nonfatal, and fatal CHD or cardiac procedures), and all‐cause mortality. Participants were assessed for carotid intimal thickness and plaque during the first visit. Detectable high‐sensitivity troponin T (≥5 ng/L) and elevated NT‐proBNP (N‐terminal pro‐B‐type natriuretic peptide; ≥100 pg/mL) were determined in blood collected during the second visit (1990–1992). All associations were adjusted for known CVD risk factors. In 9139 participants (57% women; 23% black; mean age, 54±5.7 years), 3% had OH. During follow‐up (median, 26 years), OH was associated with myocardial infarction (hazard ratio [HR], 1.88; 95% confidence interval [CI], 1.44–2.46), congestive heart failure (HR, 1.65; 95% CI, 1.34–2.04), stroke (HR, 1.83; 95% CI, 1.35–2.48), fatal CHD (HR, 2.77; 95% CI, 1.93–3.98), any CHD (HR, 2.00; 95% CI, 1.64–2.44), and all‐cause mortality (HR, 1.68; 95% CI, 1.45–1.95). OH was also associated with carotid intimal thickness (β, 0.05 mm; 95% CI, 0.04–0.07 mm), carotid plaque (odds ratio, 1.51; 95% CI, 1.18–1.93), detectable high‐sensitivity troponin T (odds ratio, 1.49; 95% CI, 1.16–1.93), and elevated NT‐proBNP (odds ratio, 1.92; 95% CI, 1.48–2.49).

Conclusions

OH identified in community‐dwelling middle‐aged adults was associated with future CVD events and subclinical CVD. Further research is necessary to establish a causal role for OH in the pathogenesis of CVD.

Age-associated abnormalities of intrinsic automaticity of sinoatrial nodal cells are linked to deficient cAMP-PKA-Ca(2+) signaling

A reduced sinoatrial node (SAN) functional reserve underlies the age-associated decline in heart rate acceleration in response to stress. SAN cell function involves an oscillatory coupled-clock system: the sarcoplasmic reticulum (SR), a Ca(2+) clock, and the electrogenic-sarcolemmal membrane clock. Ca(2+)-activated-calmodulin-adenylyl cyclase/CaMKII-cAMP/PKA-Ca(2+) signaling regulated by phosphodiesterase activity drives SAN cells automaticity. SR-generated local calcium releases (LCRs) activate Na(+)/Ca(2+) exchanger in the membrane clock, which initiates the action potential (AP). We hypothesize that SAN cell dysfunctions accumulate with age. We found a reduction in single SAN cell AP firing in aged (20-24 mo) vs. adult (3-4 mo) mice. The sensitivity of the SAN beating rate responses to both muscarinic and adrenergic receptor activation becomes decreased in advanced age. Additionally, age-associated coincident dysfunctions occur stemming from compromised clock functions, including a reduced SR Ca(2+) load and a reduced size, number, and duration of spontaneous LCRs. Moreover, the sensitivity of SAN beating rate to a cAMP stress induced by phosphodiesterase inhibitor is reduced, as are the LCR size, amplitude, and number in SAN cells from aged vs. adult mice. These functional changes coincide with decreased expression of crucial SR Ca(2+)-cycling proteins, including SR Ca(2+)-ATPase pump, ryanodine receptors, and Na(+)/Ca(2+) exchanger. Thus a deterioration in intrinsic Ca(2+) clock kinetics in aged SAN cells, due to deficits in intrinsic SR Ca(2+) cycling and its response to a cAMP-dependent pathway activation, is involved in the age-associated reduction in intrinsic resting AP firing rate, and in the reduction in the acceleration of heart rate during exercise.

The ageing cardiovascular system

The increase in the ageing population has generated much interest and research into what constitutes normal ageing. By identifying normal ageing processes it is hoped it will be possible to distinguish risk factors for the development of abnormal or premature ageing.

This review discusses biological, structural and mechanical changes in the cardiovascular system with ageing that are thought to increase the risk of cardiovascular disease with ageing. Contributory factors are thought to be genetic and lifestyle related. Measurements of biological as opposed to chronological ageing such as vascular stiffness are explored as a possible useful predictor of cardiovascular morbidity and mortality, indicating its possible utilization as a non-invasive screening tool in older people.

The identification of those at risk of cardiovascular disease and modification of risk factors may minimize interactions of the ageing process and therefore reduce the incidence of cardiovascular disease within the UK population.

Postural differences in hemodynamics and diastolic function in healthy older men

The shift from upright to supine posture increases stroke volume in healthy young adults, primarily through increased end-diastolic volume. Aging is associated with increased ventricular stiffness and impaired diastolic function. The purpose of this study was to determine whether the stroke volume change between the upright and supine posture was blunted in healthy older men and whether the early mitral inflow response to this postural change was reduced by aging. Pulsed Doppler echocardiography and tissue Doppler imaging were used to assess stroke volume and left ventricular function during upright and supine posture in 10 young and 12 older healthy men. Cardiac output was greater in the supine versus upright condition in both groups. In young men supine posture was associated with a large increment in stroke volume (63.1 +/- 7.2 upright to 98.6 +/- 11.7 ml supine; P < 0.05) and a decrease in heart rate. In older men, the stroke volume increment was smaller (63.9 +/- 3.6 upright to 82.0 +/- 5.7 ml supine; P < 0.05) and heart rate decreased less than young men when comparing upright to supine posture. Increased stroke volume was associated with higher peak early diastolic filling velocity (E) in young men and higher peak late diastolic filling velocity (A) in older men. These findings indicate that healthy aging attenuates the increase in early filling associated with moving from an upright to a supine posture. Furthermore, healthy older men are more dependent upon atrial diastolic filling to augment end-diastolic and stroke volume, which may be due to age-associated increases in left ventricular filling pressure and impaired compliance.

Assessment of age-related changes in left ventricular structure and function by freehand three-dimensional echocardiography

To determine age-related changes in left ventricular (LV) structure and function, the authors used freehand three-dimensional echocardiography, a previously validated tomographic technique, to measure LV mass, volumes, and derived parameters in 94 sedentary, but ambulatory and clinically healthy, adult male and female volunteers aged 20-94. LV volumes and mass were significantly greater in men than in women (p<0.001) and remained greater after adjustment for body surface area and height (p<0.05). Declines in end-diastolic and stroke volumes with age were reduced or absent after accounting for body size. By multivariate analysis, age accounted for only about 6%-11% of the variance among LV volumes and mass, in comparison with body surface area and gender, which accounted jointly for about 46%-77% of the variance. In conclusion, changes occur in LV structure and function with normal aging, but these changes are relatively minor when body size and gender are taken into account.

Age and cardiac output during cycle exercise in thermoneutral and warm environments

To determine whether chronological age, independent of changes in aerobic capacity, alters cardiac output (Qc), the central hemodynamic responses to intermittent incremental cycle exercise were studied in two groups of men. Qc was measured at rest and during exercise at 35%, 60%, 75%, and 85% peak aerobic capacity (VO2peak) using a CO2 rebreathing method in seven trained older (65 +/- 2 yr) and eight normally active but untrained young men (26 +/- 1 yr) matched for VO2peak and anthropometric measures. Subjects were tested in both a thermoneutral (22 degrees C) and a warm (36 degrees C) environment to investigate possible differential cardiovascular responses to exercise in the heat. Only subjects with no history of pulmonary, cardiac, neuromuscular, or endocrine disease and a normal electrocardiogram were studied. The older men had significantly lower (P < 0.05) Qc relative to the younger men at intensities greater than 60% VO2peak in both environmental conditions. At these higher intensities, the older men had a significantly higher stroke volume (SV) and lower heart rate (HR) (P < 0.05). A higher arteriovenous oxygen difference ((a-v)O2)) compared with their younger counterparts enabled the older men to exercise at the same absolute intensity, most likely because of training induced changes in left-ventricular performance and oxygen extraction. The addition of an exogenous heat source did not alter the Qc response in either group of men; however, a higher HR (P < 0.05) and smaller SV (P > 0.05) were observed in the young men during exercise in the heat. This may reflect previously reported differences in the skin blood flow response of VO2peak-matched young and older men during exercise. It is suggested that endurance trained older men can enhance left-ventricular performance to augment SV, but not sufficiently to maintain Qc in light of an attenuated HR response during exercise at intensities above 60% VO2peak.

Cardiovascular responses to exercise. Effects of aging and exercise training in healthy men

BACKGROUND

Cardiac aging alters many of the acute responses to exercise stress, but the extent to which chronic exercise (ie, training) can alter or improve the effects of aging in humans is largely unknown.

METHODS AND RESULTS

Cardiovascular responses to graded supine exercise stress (beginning at 200 kpm and increasing by 200 kpm every 3 minutes till exhaustion) were assessed using radionuclide ventriculography in 13 older (age, 60 to 82 years) and 11 young (age, 24 to 32 years) rigorously screened healthy men before and after 6 months of endurance training. Repeated-measures ANOVA was used to test significance. During exercise, the old group had a lesser increase in heart rate (+105% old versus +166% young), a greater increase in mean blood pressure (+35% old versus +22% young), lesser increases in ejection fraction (+3 ejection fraction units old versus +11 units young) and peak ejection rate (+62% old versus +119% young), a greater increase in end-diastolic volume index (+8% old versus -10% young), a lesser fall in end-systolic volume index (-0% old versus -32% young), and a lesser increase in cardiac index (+135% old versus +189% young) (all P < .01 young/old versus exercise stage). Stroke volume index response to exercise was not different with aging (+14% old versus +6% young, P = NS). Exercise training increased maximal oxygen intake by 21% in the older group (28.9 +/- 4.6 to 35.1 +/- 3.8 mL.kg-1.min-1, P < .001) and by 17% in the young (44.5 +/- 5.1 to 52.1 +/- 6.3 mL.kg-1.min-1, P < .001) and increased peak workload by 24% in the old and 28% in the young. Exercise training had no differential effects on old versus young men. Among all subjects, training significantly reduced the resting heart rate by 12% (-8 beats per minute) and increased resting end-diastolic volume index by 13% (+9 mL/M2) and resting stroke volume index by 18% (+7 mL/M2) (all P < .01). At peak exercise, cardiac index increased by 16% (+1.07 L.M-2.min-1) compared with before training, which was the result of an increase in stroke volume of 18% (+7 mL/M2) (P < .001); peak heart rate was unchanged. The increase in stroke volume index at peak exercise was the result of both a 12% increase in end-diastolic volume index (+8 mL/M2) (P < .01) and an increase in ejection fraction (+3 ejection fraction units) (P < .05) at peak exercise. The increased ejection fraction at peak exercise occurred despite a 9% increase in systolic blood pressure (+18 mm Hg) (P < .01), suggesting an increase in contractility. Thus, both the young and old increased peak exercise cardiac output by use of the Frank-Starling mechanism (ie, cardiac dilatation) as well as an increase in ejection fraction.

CONCLUSIONS

We conclude that there is an age-associated decline in heart rate, ejection fraction, and cardiac output responses to supine exercise in healthy men. Although the stroke volume responses of the young and old are similar, the old tend to augment stroke volume during exercise more through cardiac dilatation, with an increase in end-diastolic volume (+8%) but without much change in ejection fraction (+3 ejection fraction units), whereas the young rely more on an increase in the ejection fraction (+11 ejection fraction units) with no cardiac dilatation (-10%). Despite the significant cardiovascular changes that occur in the response to a single bout of exercise with aging, adaptations to chronic exercise training were not different with aging and included improvements in maximal workload and increases in ejection fraction, stroke volume index, and cardiac index at peak exercise.

Venous plasma noradrenaline increases with age: correlation to total blood volume and long-term smoking habits

Venous plasma noradrenaline (NA), cardiac index, total blood volume, and other haemodynamic parameters were measured in 12 young (median age of 29, range 21-37 years) and 10 elderly (median age of 68, range 55-85 years) healthy male subjects in the resting supine and sitting positions. Cardiac index was equal in the two groups and did not correlate to plasma NA. Plasma NA was significantly elevated in the elderly subjects in the sitting position (2.47 +/- 0.28 vs. 1.80 +/- 0.13 nmol l-1, P = 0.038). Elevated plasma NA levels were confined to elderly long-term smokers. Sitting plasma NA was significantly correlated to total blood volume corrected for body weight, r = -0.720, P = 0.0002, but with no difference in blood volume between smokers and non-smokers. It is concluded, that long-term smoking may result in elevated plasma NA levels seen in elderly subjects. It is suggested, that this is a compensatory mechanism to vascular dilation induced by chronic smoking.

Effect of postural stress on left ventricular performance using the continuous-wave Doppler technique

To evaluate the effect of postural shifts on continuous-wave Doppler indices of left ventricular performance in normal man, we recorded Doppler signals suprasternally in 69 healthy volunteers, ranging in age from 20 to 86 years, in the supine position and 2 min after assumption of sitting and standing postures. All indices decreased progressively with increasing orthostasis: peak acceleration (PKA): 15.6 +/- 4.5 m/s2 to 14.0 +/- 4.0 m/s2 to 13.6 +/- 4.6 m/s2; peak velocity (PKV): 0.64 +/- 0.18 m/s to 0.58 +/- 0.17 m/s to 0.56 +/- 0.17 m/s; stroke distance (SD): 11.4 +/- 3.7 cm to 9.8 +/- 3.4 cm to 8.0 +/- 2.8 cm; SD x heart rate (VIH): 717 +/- 272 cm to 655 +/- 268 cm to 572 +/- 217 cm, from supine to sitting to standing, respectively (p less than 0.001). In contrast heart rate increased modestly from 62.4 +/- 10.0 bpm supine, to 66.9 +/- 12.4 bpm sitting, to 71.3 +/- 9.9 bpm standing (p less than .001). Similar postural changes in Doppler variables were seen in all three age groups (20 to 44 years; 45 to 64 years; and 65 to 86 years). Thus, orthostasis in normal subjects is accompanied by a reduction in all continuous-wave Doppler indices of left ventricular performance, regardless of age.

Comparison of differences in the hemodynamic response to passive postural stress in healthy subjects greater than 70 years and less than 30 years of age

To test the hypothesis that age-related increases in arterial pressure alter the cardiovascular response to physiologic stress, 9 healthy elderly volunteers (74 +/- 2 years) and 7 young subjects (27 +/- 3 years) were subjected to a standard 60 degrees upright tilt. Cardiac volumes were measured with patients in the supine position and 5 minutes after they assumed an upright posture using radionuclide ventriculography, while heart rate, blood pressure and forearm cutaneous flow were recorded continuously and simultaneously. Only the expected age-related increase in mean arterial pressure (young subjects, 79 +/- 1 mm Hg; elderly subjects, 99 +/- 3 mm Hg; p less than 0.001) distinguished the 2 groups at baseline. However, during upright tilt, elderly subjects had significant decreases in stroke volume (supine [108 +/- 9 ml] vs upright [78 +/- 9 ml]; p less than 0.01) and cardiac index (supine [3.4 +/- 0.2 liters/min/m2] vs upright [2.8 +/- 0.2 liters/min/m2]; p less than 0.05) because of an inability to reduce end-systolic volume (supine, 44 +/- 6 ml; upright, 51 +/- 7 ml); however, mean arterial pressure was maintained through an increase in peripheral resistance. In contrast, the young relied solely on cardiac adaptations to postural stress by decreasing end-systolic volume (supine, 62 +/- 5 ml; upright, 39 +/- 5 ml; p less than 0.01) and increasing heart rate (57 +/- 2 min-1 to 71 +/- 3 min-1, p less than 0.01), whereby cardiac output and mean arterial pressure were maintained during tilt.(ABSTRACT TRUNCATED AT 250 WORDS)

The age-associated decline in glomerular filtration in healthy normotensive volunteers. Lack of relationship to cardiovascular performance

Whether the well-documented age-associated decline in the glomerular filtration rate, manifest as a decline in creatinine clearance, is secondary to an age-related change in cardiovascular performance is at present unknown. To answer this question, we measured arterial blood pressure, 24-hour creatinine clearance, and cardiac output determined from gated cardiac blood pool scans in the sitting position in healthy normotensive men (n = 75) and women (n = 42) (ages 25 to 82 years), from the Baltimore Longitudinal Study on Aging. These subjects were selected for the absence of cardiovascular disease, renal disease, and confounding medications. By linear regression analysis, creatinine clearance, expressed in mL/min/m2, declined cross-sectionally with age (creatinine clearance = 90 -0.33[age], r = .31, P less than .001), whereas systolic blood pressure in mm Hg increased with age (systolic blood pressure = 111 + 0.27[age], r = .30, P less than .001); cardiac output in L/min/m2 did not vary with age (r = .03, P = .74). In stepwise multiple regression analysis with age, cardiac index, and systolic blood pressure as independent variables and creatinine clearance as the dependent variable, only age was a significant predictor of creatinine clearance. (F = 11.31, DF + 116, r = .30, P less than .001). Thus, the age-associated decline in creatinine clearance is not modulated by changes in cardiac index or systolic blood pressure in healthy normotensive subjects.

Reduced supine cardiac volumes and diastolic filling rates in elderly patients with chronic medical conditions. Implications for postural blood pressure homeostasis

Very elderly individuals with multiple chronic illnesses are at high risk of orthostatic hypotension, falls, and associated morbidity and mortality. Alterations in cardiac volumes and filling characteristics may contribute in part to an increased prevalence of orthostatic hypotension and falls in these people. In this study cardiac function was evaluated with gated radionuclide ventriculography in eight healthy young subjects (19-38 years) and 25 elderly persons with stable chronic illnesses (73-96 years), 14 of whom had a history of recurrent falls. Blood pressure was measured supine during the radionuclide ventriculography, then after one minute of standing. Supine stroke volume index, end diastolic volume index, cardiac index, and peak filling rates were significantly lower in elderly subjects compared to young, and ejection fraction and end systolic volume index (measures of systolic function) were the same in young and old. Compared to the young, elderly subjects had a reduction in ventricular filling during the first third of diastole, but an augmentation in the last third, during atrial contraction. Within the group of elderly subjects, the directional change in systolic blood pressure during orthostasis was significantly correlated with basal supine systolic blood pressure (R = 0.81, P less than .0001) and supine cardiac index (R = 0.66, P = .002). Thus, very old people representative of those seen in clinical practice have reduced cardiac volumes and impaired early diastolic filling, a result possibly related to elevations in systolic blood pressure. These changes in cardiac structure and function may contribute, in part, to orthostatic hypotension in advanced age.