Kevin D. Monahan

Age-predicted maximal heart rate revisited

OBJECTIVES We sought to determine a generalized equation for predicting maximal heart rate (HRmax) in healthy adults. BACKGROUND The age-predicted HRmax equation (i.e., 220 - age) is commonly used as a basis for prescribing exercise programs, as a criterion for achieving maximal exertion and as a clinical guide during diagnostic exercise testing. Despite its importance and widespread use, the validity of the HRmax equation has never been established in a sample that included a sufficient number of older adults. METHODS First, a meta-analytic approach was used to collect group mean HRmax values from 351 studies involving 492 groups and 18,712 subjects. Subsequently, the new equation was cross-validated in a well-controlled, laboratory-based study in which HRmax was measured in 514 healthy subjects. RESULTS In the meta-analysis, HRmax was strongly related to age (r = -0.90), using the equation of 208 - 0.7 x age. The regression equation obtained in the laboratory-based study (209 - 0.7 x age) was virtually identical to that obtained from the meta-analysis. The regression line was not different between men and women, nor was it influenced by wide variations in habitual physical activity levels. CONCLUSIONS 1) A regression equation to predict HRmax is 208 - 0.7 x age in healthy adults. 2) HRmax is predicted, to a large extent, by age alone and is independent of gender and habitual physical activity status. Our findings suggest that the currently used equation underestimates HRmax in older adults. This would have the effect of underestimating the true level of physical stress imposed during exercise testing and the appropriate intensity of prescribed exercise programs.

Aging, Habitual Exercise, and Dynamic Arterial Compliance

BackgroundA reduction in compliance of the large-sized cardiothoracic (central) arteries is an independent risk factor for the development of cardiovascular disease with advancing age. Methods and ResultsWe determined the role of habitual exercise on the age-related decrease in central arterial compliance by using both cross-sectional and interventional approaches. First, we studied 151 healthy men aged 18 to 77 years: 54 were sedentary, 45 were recreationally active, and 53 were endurance exercise–trained. Central arterial compliance (simultaneous B-mode ultrasound and arterial applanation tonometry on the common carotid artery) was lower (P <0.05) in middle-aged and older men than in young men in all 3 groups. There were no significant differences between sedentary and recreationally active men at any age. However, arterial compliance in the endurance-trained middle-aged and older men was 20% to 35% higher than in the 2 less active groups (P <0.01). As such, age-related differences in central arterial compliance were smaller in the endurance-trained men than in the sedentary and recreationally active men. Second, we studied 20 middle-aged and older (53±2 years) sedentary healthy men before and after a 3-month aerobic exercise intervention (primarily walking). Regular exercise increased central arterial compliance (P <0.01) to levels similar to those of the middle-aged and older endurance-trained men. These effects were independent of changes in body mass, adiposity, arterial blood pressure, or maximal oxygen consumption. ConclusionsRegular aerobic-endurance exercise attenuates age-related reductions in central arterial compliance and restores levels in previously sedentary healthy middle-aged and older men. This may be one mechanism by which habitual exercise lowers the risk of cardiovascular disease in this population.

Regular Aerobic Exercise Prevents and Restores Age-Related Declines in Endothelium-Dependent Vasodilation in Healthy Men

BackgroundIn sedentary humans endothelium-dependent vasodilation is impaired with advancing age contributing to their increased cardiovascular risk, whereas endurance-trained adults demonstrate lower age-related risk. We determined the influence of regular aerobic exercise on the age-related decline in endothelium-dependent vasodilation. Methods and ResultsIn a cross-sectional study, 68 healthy men 22 to 35 or 50 to 76 years of age who were either sedentary or endurance exercise–trained were studied. Forearm blood flow (FBF) responses to intra-arterial infusions of acetylcholine and sodium nitroprusside were measured by strain-gauge plethysmography. Among the sedentary men, the maximum FBF response to acetylcholine was 25% lower in the middle aged and older compared with the young group (P <0.01). In contrast, there was no age-related difference in the vasodilatory response to acetylcholine among the endurance-trained men. FBF at the highest acetylcholine dose was almost identical in the middle aged and older (17.3±1.3 mL/100 mL tissue per minute) and young (17.7±1.4 mL/100 mL tissue per minute) endurance-trained groups. There were no differences in the FBF responses to sodium nitroprusside among the sedentary and endurance- trained groups. In an exercise intervention study, 13 previously sedentary middle aged and older healthy men completed a 3-month, home-based aerobic exercise intervention (primarily walking). After the exercise intervention, acetylcholine-mediated vasodilation increased ≈30% (P <0.01) to levels similar to those in young adults and middle aged and older endurance-trained men. ConclusionsOur results indicate that regular aerobic exercise can prevent the age-associated loss in endothelium-dependent vasodilation and restore levels in previously sedentary middle aged and older healthy men. This may represent an important mechanism by which regular aerobic exercise lowers the risk of cardiovascular disease in this population.

Effect of acute and chronic ascorbic acid on flow-mediated dilatation with sedentary and physically active human ageing.

Peripheral conduit artery flow‐mediated dilatation decreases with ageing in humans. The underlying mechanisms and efficacy of preventive strategies are unknown. Brachial artery flow‐mediated dilatation was determined at baseline and after ascorbic acid (vitamin C) intravenous infusion and chronic supplementation (500 mg day−1 for 30 days) in three groups of healthy men: young sedentary (n= 11; 25 ± 1 years, mean ±s.e.m.), older sedentary (n= 9; 64 ± 2), and older endurance‐exercise trained (n= 9; 64 ± 2). At baseline, flow‐mediated dilatation (normalized for the hyperaemic stimulus) was ∼45% lower in the older (0.015 ± 0.001) versus young (0.028 ± 0.004) sedentary men (P < 0.01), but was preserved in older exercising men (0.028 ± 0.004). Ascorbic acid infusion increased plasma concentrations > 15‐fold in all groups and restored flow‐mediated dilatation in the sedentary older men (to 0.023 ± 0.002; P > 0.1 versus other groups), with no effects in the other two groups. Oral ascorbic acid supplementation did not affect flow‐mediated dilatation in any group. Brachial artery endothelium‐independent dilatation (sublingual nitroglycerin) did not differ among the groups at baseline nor change with ascorbic acid administration. These results provide the first evidence for an important role of oxidative stress in both the impairment in peripheral conduit artery flow‐mediated dilatation with sedentary human ageing and the preservation of flow‐mediated dilatation with physically active ageing.

Regular endurance exercise induces expansive arterial remodelling in the trained limbs of healthy men

1 In experimental animals chronic elevations in arterial blood flow increase the lumen diameter and reduce the intima‐media thickness (IMT) of the arterial segment involved. We determined whether intermittent elevations in active muscle blood flow associated with regular aerobic leg exercise induced such expansive arterial remodelling in the common femoral artery of humans. 2 In the cross‐sectional study 53 sedentary (47 ± 2 years) and 55 endurance exercise‐trained (47 ± 2 years) men were studied. Common femoral artery lumen diameter (B‐mode ultrasound) was 7 % greater (9.62 ± 0.12 vs. 9.03 ± 0.13 mm), and femoral IMT (0.46 ± 0.02 vs. 0.55 ± 0.02 mm) and IMT/lumen ratio were 16‐21 % smaller in the endurance‐trained men (all P < 0.001). Basal femoral artery blood flow (duplex ultrasound) was not different, shear stress tended to be lower (P = 0.08), and mean femoral tangential wall stress was 30 % higher in the endurance‐trained men (P < 0.001). 3 In the intervention study 22 men (51 ± 2 years) were studied before and after 3 months of regular aerobic leg exercise (primarily walking). After training, the femoral diameter increased by 9 % (8.82 ± 0.18 vs. 9.60 ± 0.20 mm), and IMT (0.65 ± 0.05 vs. 0.56 ± 0.05 mm) and the IMT/lumen ratio were ≈15‐20 % smaller (all P < 0.001). Basal femoral blood flow and shear stress were not different after training, whereas the mean femoral tangential wall stress increased by 31 %. The changes in arterial structure were not related to changes in risk factors for atherosclerosis. 4 Our results are consistent with the concept that regular aerobic leg exercise induces expansive arterial remodelling in the femoral artery of healthy men. This adaptive process is produced by even a moderate training stimulus, is not obviously dependent on corresponding improvements in risk factors for atherosclerosis, and is robust, occurring in healthy men of different ages.

Blood pressure reductions with exercise and sodium restriction in postmenopausal women with elevated systolic pressure: Role of arterial stiffness

OBJECTIVES This study determined the relative efficacy of aerobic exercise (daily walking) and moderate dietary sodium restriction (sodium intake <100 mmol/day) for reducing systolic blood pressure (SBP) and pulse pressure (PP) in postmenopausal women with elevated initial levels, and the potential role of reductions in large artery stiffness in these changes. BACKGROUND Lifestyle behaviors are recommended for lowering blood pressure (BP) in adults with elevated baseline levels, but there is little information as to the relative efficacy of different interventions or the mechanisms underlying their potential beneficial effects. METHODS After baseline measurements and random assignment, 35 nonmedicated healthy postmenopausal women with SBP between 130 and 159 mm Hg completed three months of either aerobic (walking) exercise (n = 18; 62 +/- 9 years, mean +/- SD) or moderate dietary sodium restriction (SR) (n = 17; 65 +/- 10 years, mean +/- SD). RESULTS Body mass and composition, plasma volume, and fasting concentrations of metabolic coronary risk factors did not differ between the groups at baseline or change with intervention. Systolic BP and PP at rest decreased with both exercise and SR (p < 0.05); however, the reductions were three- to fourfold greater with SR (p < 0.05). Sodium restriction, but not exercise, also reduced 24-h SBP and PP (p < 0.05). Aortic pulse wave velocity (PWV) and carotid augmentation index were reduced only with SR (p < 0.05). Changes in SBP and PP at rest and over 24 h correlated with the corresponding changes in aortic PWV (r = 0.53 to 0.61, p < 0.01). CONCLUSIONS Moderate SR lowers SBP and PP in postmenopausal women with elevated baseline levels more than does daily walking. The greater blood pressure reductions with SR may be mediated in part by a decrease in the stiffness of the large elastic arteries.

Regular aerobic exercise modulates age‐associated declines in cardiovagal baroreflex sensitivity in healthy men

1 Cardiovagal baroreflex sensitivity (BRS), the arterial baroreflex‐mediated change in the R‐R interval per unit change in systolic blood pressure, decreases with advancing age in sedentary adult humans. We determined the effects of regular aerobic exercise on the age‐related decline in cardiovagal BRS. 2 In the cross‐sectional study, 133 healthy men 18‐79 years of age who were either sedentary, performing moderate aerobic exercise, or endurance exercise trained were studied. Among the sedentary men, cardiovagal BRS (phase IV of Valsalvas manoeuvre) was progressively lower (P < 0·05) in the middle‐aged (≈33 %) and older (≈60 %) groups compared with the young group. In contrast, cardiovagal BRS was similar in the young and middle‐aged men in the moderate exercise and endurance‐trained groups. Cardiovagal BRS was lower (P < 0·05) in the older exercising men, but the magnitude of decline across age (≈30 %) was only half as great as that in sedentary men. Cardiovagal BRS was 40‐75 % greater (P < 0·05) in middle‐aged and older men who exercised regularly compared with their sedentary peers. 3 In the intervention study, a 3 month aerobic exercise intervention (primarily walking) increased cardiovagal BRS by an average of 25 % (P < 0·05) in 13 previously sedentary middle‐aged and older (56 ± 1 years) healthy men. 4 Our results demonstrate for the first time that regular aerobic exercise: (1) attenuates the age‐associated decline in cardiovagal BRS; and (2) partially restores the loss of cardiovagal BRS in previously sedentary middle‐aged and older healthy men.

Entrainment/Mapping Criteria for the Prediction of Termination of Ventricular Tachycardia by Single Radiofrequency Lesion in Patients With Coronary Artery Disease

BACKGROUND A variety of mapping criteria have been proposed to localize critical sites at which radiofrequency (RF) can predictably terminate reentrant ventricular tachycardia (VT) caused by coronary artery disease. The purpose of this study was to determine the accuracy of using a combination of 3 mapping criteria in predicting termination of VT by a single RF lesion. METHODS AND RESULTS Fifteen consecutive patients with coronary artery disease and recurrent sustained VT underwent an attempted RF ablation of 20 monomorphic VTs. Successful termination of VT by a single RF lesion was predicted if all the following mapping criteria were met: (1) an exact QRS match in the 12-lead ECG during entrainment; (2) a return cycle length </=10 ms of the VT cycle length; (3) presystolic potentials (<70% of VT cycle length) with an activation time to the QRS within 10 ms of the stimulus to QRS. Inability to meet these 3 criteria was considered to predict failure of VT termination by RF energy at that site. RF ablation was applied to 44 left ventricular sites in 20 VTs at which at least 1 of the mapping criteria was met. VT was terminated with a single RF lesion in 19 of 19 sites meeting all criteria; RF failed to terminate VT at 24 of 25 sites at which all 3 criteria were not met (P<0.0005). CONCLUSIONS To maximize success and minimize the number of RF lesions in patients with infarct-related VT, all the above 3 mapping criteria should be met before the application of RF energy.

Carotid Artery Wall Hypertrophy With Age Is Related to Local Systolic Blood Pressure in Healthy Men

Abstract—Carotid artery intima-media thickness (IMT) increases with advancing age in humans. The underlying mechanism of this increase is unknown, but data from animal studies suggest that a chronic increase in local distending pressure can act as a stimulus. To test this hypothesis, we studied a total of 129 healthy normotensive, nonobese, nonsmoking men aged 18 to 77 years. Brachial systolic blood pressure (SBP) was unchanged, but carotid SBP increased progressively with age (P <0.05). Carotid IMT and the ratio of carotid IMT to lumen (ultrasonography) increased progressively with age (P <0.05). Carotid IMT was ≈50% greater in the older compared with the young men. Carotid SBP was positively related to carotid IMT (r =0.55, P <0.001). After carotid SBP was taken into account (ANCOVA), the age-related difference in carotid IMT was no longer statistically significant (P =0.22). We conclude that carotid IMT increases with age in healthy men in the absence of elevations in peripheral SBP. Carotid SBP increases progressively with advancing age in this population and is significantly related to the corresponding carotid wall hypertrophy. These results support the hypothesis that chronic increases in local distending pressure may be an important mechanism in the wall thickening that occurs with human aging in central elastic arteries.

Aging affects the cardiovascular responses to cold stress in humans.

Cardiovascular-related mortality peaks during cold winter months, particularly in older adults. Acute physiological responses, such as increases in blood pressure, in response to cold exposure may contribute to these associations. To determine whether the blood pressure-raising effect (pressor response) of non-internal body temperature-reducing cold stress is greater with age, we measured physiological responses to 20 min of superficial skin cooling, via water-perfused suit, in 12 younger [25 +/- 1 (SE) yr old] and 12 older (65 +/- 2 yr old) adults. We found that superficial skin cooling elicited an increase in blood pressure from resting levels (pressor response; P < 0.05) in younger and older adults. However, the magnitude of this pressor response (systolic and mean blood pressure) was more than twofold higher in older adults (P < 0.05 vs. younger adults). The magnitude of the pressor response was similar at peripheral (brachial) and central (estimated in the aorta) measurement sites. Regression analysis revealed that aortic pulse wave velocity, a measure of central arterial stiffness obtained before cooling, was the best predictor of the increased pressor response to superficial skin cooling in older adults, explaining approximately 63% of its variability. These results indicate that there is a greater pressor response to non-internal body temperature-reducing cold stress with age in humans that may be mediated by increased levels of central arterial stiffness.