Cardiovascular risk factors and graded treadmill exercise endurance in healthy adults: The Framingham Offspring Study

Cigarette smoking impairs Na+-K+-ATPase activity in the human coronary microcirculation

The extracellular K(+) concentration ([K(+)](o)) has been proposed to link cardiac metabolism with coronary perfusion and arrhythmogenesis, particularly during ischemia. Several animal studies have also supported K(+) as an EDHF that activates Na(+)-K(+)-ATPase and/or inwardly rectifying K(+) (K(ir)) channels. Therefore, we examined the vascular reactivity of human coronary arterioles (HCAs) to small elevations in [K(+)](o), the influence of risk factors for coronary disease, and the role of K(+) as an EDHF. Changes in the internal diameter of HCAs were recorded with videomicroscopy. Most vessels dilated to increases in [K(+)](o) with a maximal dilation of 55 ± 6% primarily at 12.5-20.0 mM KCl (n = 38, average: 16 ± 1 mM). Ouabain, a Na(+)-K(+)-ATPase inhibitor, alone reduced the dilation, and the addition of Ba(2+), a K(ir) channel blocker, abolished the remaining dilation, whereas neither endothelial denudation nor Ba(2+) alone reduced the dilation. Multivariate analysis revealed that cigarette smoking was the only risk factor associated with impaired dilation to K(+). Ouabain significantly reduced the vasodilation in HCAs from subjects without cigarette smoking but not in those with smoking. Cigarette smoking downregulated the expression of the Na(+)-K(+)-ATPase catalytic α(1)-subunit but not Kir2.1 in the vessels. Ouabain abolished the dilation in endothelium-denuded vessels to a same extent to that with the combination of ouabain and Ba(2+) in endothelium-intact vessels, whereas neither ouabain nor ouabain plus Ba(2+) reduced EDHF-mediated dilations to bradykinin and ADP. A rise in [K(+)](o) dilates HCAs primarily via the activation of Na(+)-K(+)-ATPase in vascular smooth muscle cells with a considerable contribution of K(ir) channels in the endothelium, indicating that [K(+)](o) may modify coronary microvascular resistance in humans. Na(+)-K(+)-ATPase activity is impaired in subjects who smoke, possibly contributing to dysregulation of the coronary microcirculation, excess ischemia, and arrhythmogenesis in those subjects. K(+) does not likely serve as an EDHF in the human coronary arteriolar dilation to bradykinin and ADP.

Prevalence and predictors of abnormal cardiovascular responses to exercise testing among individuals with type 2 diabetes: the Look AHEAD (Action for Health in Diabetes) study

OBJECTIVE

We examined maximal graded exercise test (GXT) results in 5,783 overweight/obese men and women, aged 45-76 years, with type 2 diabetes, who were entering the Look AHEAD (Action for Health in Diabetes) study, to determine the prevalence and correlates of exercise-induced cardiac abnormalities.

RESEARCH DESIGN AND METHODS

Participants underwent symptom-limited maximal GXTs. Questionnaires and physical examinations were used to determine demographic, anthropometric, metabolic, and health status predictors of abnormal GXT results, which were defined as an ST segment depression > or =1.0 mm, ventricular arrhythmia, angina pectoris, poor postexercise heart rate recovery (<22 bpm reduction 2 min after exercise), or maximal exercise capacity less than 5.0 METs. Systolic blood pressure response to exercise was examined as a continuous variable, without a threshold to define abnormality.

RESULTS

Exercise-induced abnormalities were present in 1,303 (22.5%) participants, of which 693 (12.0%) consisted of impaired exercise capacity. ST segment depression occurred in 440 (7.6%), abnormal heart rate recovery in 206 (5.0%), angina in 63 (1.1%), and arrhythmia in 41 (0.7%). Of potential predictors, only greater age was associated with increased prevalence of all abnormalities. Other predictors were associated with some, but not all, abnormalities. Systolic blood pressure response decreased with greater age, duration of diabetes, and history of cardiovascular disease.

CONCLUSIONS

We found a high rate of abnormal GXT results despite careful screening for cardiovascular disease symptoms. In this cohort of overweight and obese individuals with type 2 diabetes, greater age most consistently predicted abnormal GXT. Long-term follow-up of these participants will show whether these abnormalities are clinically significant.

Hypercholesterolemia impairs exercise capacity in mice

We previously reported an attenuation of both exercise hyperemia and measures of aerobic capacity in hypercholesterolemic mice. In this study, we expanded upon the previous findings by examining the temporal and quantitative relationship of hypercholesterolemia to aerobic and anaerobic capacity and by exploring several potential mechanisms of dysfunction. Eight-week-old wild type (n = 123) and apoE knockout (n = 79) C57BL/6J mice were divided into groups with distinct cholesterol levels by feeding with regular or high-fat diets. At various ages, the mice underwent treadmill ergospirometry. To explore mechanisms, aortic ring vasodilator function and nitrate (NO(x)) activity, urinary excretion of NO(x), running muscle microvascular density and citrate synthase activity, as well as myocardial mass and histologic evidence of ischemia were measured. At 8 weeks of age, all mice had similar measures of exercise capacity. All indices of aerobic exercise capacity progressively declined at 12 and 20 weeks of age in the hypercholesterolemic mice as cholesterol levels increased while indices of anaerobic capacity remained unaffected. Across the four cholesterol groups, the degree of aerobic dysfunction was related to serum cholesterol levels; a relationship that was maintained after correcting for confounding factors. Associated with the deterioration in exercise capacity was a decline in measures of nitric oxide-mediated vascular function while there was no evidence of aberrations in functional or oxidative capacities or in other components of transport capacity. In conclusion, aerobic exercise dysfunction is observed in murine models of genetic and diet-induced hypercholesterolemia and is associated with a reduction in vascular nitric oxide production.

Associations of Muscle Strength and Fitness with Metabolic Syndrome in Men

PURPOSE

To examine the associations for muscular strength and cardiorespiratory fitness with the prevalence of metabolic syndrome among men.

METHODS

Participants were 8570 men (20-75 yr) for whom an age-specific muscular strength score was computed by combining the body weight adjusted one-repetition maximum measures for the leg press and the bench press. Cardiorespiratory fitness was quantified by age-specific maximal treadmill exercise test time.

RESULTS

Separate age and smoking adjusted logistic regression models revealed a graded inverse association for metabolic syndrome prevalence with muscular strength (beta = -0.37, P < 0.0001) and cardiorespiratory fitness (beta = -1.2, P < 0.0001). The association between strength and metabolic syndrome was attenuated (beta = -0.08, P < 0.01) when further adjusted for cardiorespiratory fitness. The association between cardiorespiratory fitness and metabolic syndrome was unchanged (beta = -1.2, P < 0.0001) after adjusting for strength. Muscular strength added to the protective effect of fitness among men with low (P trend = 0.0002) and moderate (P trend < 0.0001) fitness levels. Among normal weight (BMI < 25), overweight (BMI 25-30), and obese (BMI >or= 30) men, respectively, being strong and fit was associated with lower odds (73%, 69%, and 62% respectively, P < 0.0001) of having prevalent metabolic syndrome.

CONCLUSIONS

Muscular strength and cardiorespiratory fitness have independent and joint inverse associations with metabolic syndrome prevalence.

Metabolic risk factors for coronary heart disease: current and future prospects

In this review, data are reviewed concerning various metabolic risk factors that have been associated with coronary heart disease, drawing upon the experience of observational studies and clinical trials. Topics include lipids, glycemia, secular trends, hematologic factors, homocysteine, estrogen replacement, and familial and genetic factors. Using combinations of these types of factors in multivariate risk profiles is discussed, along with the opportunity to incorporate some of these factors into the prediction of coronary heart disease in the future.

Coronary heart disease risk indicators, aerobic power, and physical activity in men with spinal cord injuries

OBJECTIVE

To compare the lipid and (apo-)lipoprotein profile and blood pressure of men with long-standing spinal cord injuries (SCI) to those of an age-matched able-bodied (AB) population, and to assess the most important determinants of this profile and blood pressure.

DESIGN

A cross-sectional study of persons with chronic SCI residing in the community.

SETTING

Tests were performed in a university research laboratory.

SUBJECTS

Thirty-seven men (age 37.4 +/- 12.0 yrs) with longstanding (14.7 +/- 8.6 yrs) SCI ranging from level C4/5 to L5 volunteered to participate. Comparisons were made with published data from 3,498 AB men, age 20 to 59 yrs, from the same country.

MAIN OUTCOME MEASURES

Lipid and lipoprotein profile (total cholesterol [TC], high-, low-, and very low-density lipoprotein cholesterol [HDL-C, LDL-C and VLDL-C, respectively], and triglycerides [TG]), as well as aerobic power, activity level, anthropometric variables, and blood pressure. Multiple regression analyses assessed the most important determinants of the lipid and blood pressure profile.

RESULTS

None of the lipid variables were related to the lesion level. TC, HDL-C, and TC/HDL-C were not significantly different from the AB population. The most important determinants of TC, LDL-C, and the ratios TC/HDL and HDL-C/LDL-C were age, smoking behavior, and activity level. Aerobic power was not an important determinant of any lipid or (apo-)lipoprotein or blood pressure.

CONCLUSION

Men with long-standing SCI do not appear to have an essentially different coronary heart disease risk profile compared with AB persons. Modifiable risk factors such as activity level, smoking, alcohol consumption, body mass index, and adipose tissue were more important than lesion level and aerobic power in the determination of the lipid and lipoprotein profile, suggesting several potential interventions.

The Canadian consensus report on non-pharmacological approaches to the management of high blood pressure

The Canadian Consensus Conference on Non-Pharmacological Approaches to the Management of High Blood Pressure reviewed in March, 1989 on its meeting in Halifax, Nova Scotia, data concerning the efficacy of eight interventional strategies used for controlling hypertension. These strategies were as follows: alcohol restriction, weight reduction, physical exercise, reduction of salt intake, relaxation/stress management, increase of potassium and calcium intake and combination of pharmacological and non-pharmacological management. The Panel of the Consensus Conference recommended as efficacious the following interventions: alcohol restriction for less than two standard drinks per day, reduction of excessive body weight, and reduction of salt intake. There is sufficient scientific evidence for recommending potassium rich diet for normotensives and hypertensive persons. The Panel also concluded that a combination of pharmacological and non-pharmacological management is an efficacious measure. The Panel at this point of time could not issue recommendations as to the value of relaxation/stress management, physical exercise and calcium intake.