Prenatal exposure to maternal cigarette smoking and structural properties of the human corpus callosum.

Alterations induced by prenatal exposure to nicotine have been observed in experimental (rodent) studies. While numerous developmental outcomes have been associated with prenatal exposure to maternal cigarette smoking (PEMCS) in humans, the possible relation with brain structure is less clear. Here we sought to elucidate the relation between PEMCS and structural properties of human corpus callosum in adolescence and early adulthood in a total of 1,747 youth. We deployed three community-based cohorts of 446 (age 25-27 years, 46% exposed), 934 (age 12-18 years, 47% exposed) and 367 individuals (age 18-21 years, 9% exposed). A mega-analysis revealed lower mean diffusivity in the callosal segments of exposed males. We speculate that prenatal exposure to maternal cigarette smoking disrupts the early programming of callosal structure and increases the relative portion of small-diameter fibres.

Structural properties of the human corpus callosum: Multimodal assessment and sex differences.

A number of structural properties of white matter can be assessed in vivo using multimodal magnetic resonance imaging (MRI). We measured profiles of R1 and R2 relaxation rates, myelin water fraction (MWF) and diffusion tensor measures (fractional anisotropy [FA], mean diffusivity [MD]) across the mid-sagittal section of the corpus callosum in two samples of young individuals. In Part 1, we compared histology-derived axon diameter (Aboitiz et al., 1992) to MRI measures obtained in 402 young men (19.55 ± 0.84 years) recruited from the Avon Longitudinal Study on Parents and Children. In Part 2, we examined sex differences in FA, MD and magnetization transfer ratio (MTR) across the corpus callosum in 433 young (26.50 ± 0.51 years) men and women recruited from the Northern Finland Birth Cohort 1986. We found that R1, R2, and MWF follow the anterior-to-posterior profile of small-axon density. Sex differences in mean MTR were similar across the corpus callosum (males > females) while these in FA differed by the callosal segment (Body: M>F; Splenium: F>M). We suggest that the values of R1, R2 and MWF are driven by high surface area of myelin in regions with high density of "small axons".

Cyclodextrin mediated delivery of NF-κB and SRF siRNA reduces the invasion potential of prostate cancer cells in vitro.

Prostate cancer is the most common cancer in men of the western world. To date, no effective treatment exists for metastatic prostate cancer and consequently, there is an urgent need to develop new and improved therapeutics. In recent years, the therapeutic potential of RNA interference (RNAi) has been extensively explored in a wide range of diseases including prostate cancer using numerous gene delivery vectors. The aims of this study were to investigate the ability of a non-viral modified cyclodextrin (CD) vector to deliver siRNA to the highly metastatic PC-3 prostate cancer cell line, to quantify the resulting knockdown of the two target genes (RelA and SRF) and to study the effects of the silencing on metastasis. Data from a Matrigel in vitro invasion assay indicated that the silencing of the target genes achieved by the CD vector resulted in significant reductions (P=0.0001) in the metastatic potential of these cells. As the silencing of these target genes was shown not to have a negative impact on cell viability, we hypothesise that the mechanism of invasion inhibition is due, in part, to the significant reduction observed (P⩽0.0001) in the level of pro-inflammatory cytokine, MMP9, which is known to be implicated in the metastasis of prostate cancer.

Off label use of devices and drugs in interventional radiology.

AIM: To establish how often off-label device and drug use occurs in interventional radiology (IR) in a UK tertiary referral hospital and consider the wider implications for the interventional radiologist. MATERIALS AND METHODS: Prospective data were collected during interventional procedures for 1 working week in a university hospital. Out-of-hours procedures and procedures outside the department were excluded. Operators were asked to record the drugs and devices used, the indication, and method of use. The instructions for use/summary of product characteristics were then studied for each device/drug used to assess if the use was on or off-label. RESULTS: During the study period 52 cases were performed and data were available on 26 cases (50%). In 22 of the 26 cases (84%) there was evidence of off-label use of devices or drugs. Off-label use of drugs included treatment of venous malformations with Fibrovein(©) (sodium tetradecyl sulphate), which is licensed for the treatment of varicose veins in the leg, and intra-arterial injection of heparin, which is licensed for intravenous and subcutaneous use. Off-label device use included placing vascular sheaths in the urinary tract, using angiographic catheters to guide wires in the urinary tract, using sheaths for thrombosuction, reshaping of the tip of most guidewires, and using angioplasty balloons to dislodge the arterial plug at fistula thrombectomy. CONCLUSION: Off-label device and drugs use is common in a UK tertiary hospital IR department and literature suggests this is common in the wider IR community. There are important clinical and legal implications for off-label use for patients and physicians.

Nucleon stability: a geochemical test independent of decay mode.

By analyzing published geochemical data on xenon isotopes measured in a 2.46 x 10(9)-year-old telluride ore, a lower limit of 1.6 x 10(25) years has been obtained for the mean lifetime of the nucleons in the tellurium-130 nucleus. This result is insensitive to the particular mode by which the nucleons decay and therefore provides a rigorous limit on possible baryon number nonconservation. The new limit is about two orders of magnitude better than the previous rigorous limit on nucleon stability.

Pattern of bombardment-produced radionuclides in rock 10017 and in lunar soil.

A large number of radionuclides have been measured as a function of depth in lunar rock 10017 and in bulk fines. Data are reported on (10)Be, (22)Na, (26)Al, (36)Cl, (49)V, (53)mn, (54)Mn (55)Fe, (56)Co, (57)Co, and (59)Ni and on upper limits for (46)Sc, (48)V, (51)Cr, and (60)Co. The results for several nuclides show striking evidence of excess surface production attributable to solar flare particles. Data for short-lived species, (56)Co, (57)CO, (54)Mn, (55)Fe, and (22)Na, appear consistent with fluxes from known recent events. Long-lived species demonstrate the existence of solar flare protons and alphas at least for the last 10(5) to 10(6) years, at fluxes comparable to those now observerved.

Mount st. Helens ash from the 18 may 1980 eruption: chemical, physical, mineralogical, and biological properties.

Samples of ash from the 18 May 1980 eruption of Mount St. Helens were collected from several locations in eastern Washington and Montana. The ash was subjected to a variety of analyses to determine its chemical, physical, mineralogical, and biological characteristics. Chemically, the ash samples were of dacitic composition. Particle size data showed bimodal distributions and differed considerably with location. However, all samples contained comparable amounts of particles less than 3.5 micrometers in diameter (respirable fraction). Mineralogically, the samples ranged from almost totally glassy to almost totally crystalline. Crystalline samples were dominated by plagioclase feldspar (andesine) and orthopyroxene (hypersthene), with smaller amounts of titanomagnetite and hornblende. All but one of the samples contained from less than 1 percent to 3 percent free crystalline silica (quartz, trydimite, or cristobalite) in both the bulk samples and 1 to 2 percent in the fractions smaller than 3.5 micrometers. The long-lived natural radionuclide content of the ash was comparable to that of crustal material; however, relatively large concentrations of short-lived radon daughters were present and polonium-210 content was inversely correlated with particle size. In vitro biological tests showed the ash to be nontoxic to alveolar macrophages, which are an important part of the lungs' natural clearance mechanism. On the basis of a substantial body of data that has shown a correlation between macrophage cytotoxicity and fibrogenicity of minerals, the ash is not predicted to be highly fibrogenic.

The ethics of fish welfare.

The topic of fish welfare in the context of commercial fisheries is a difficult one. From traditionally anthropocentric or human-centred perspectives, fishes are simply objects for humans to use as they see fit. When it is argued that anthropocentrism is arbitrary, it may appear that a strong animal rights position is the only recourse, with the result that humans ought not to use animals in the first place, if it is at all possible. It can be argued that both positions fail to view human beings as part of the natural world. If human beings are viewed as part of the world from which they live, then it has to be asked what it means to be respectful of the animals which humans use and from which they live. From this perspective, concern for the welfare of the fishes humans eat is simply what should be expected from humans as good citizens in the community of living creatures.

Angina pectoris is a stronger indicator of diffuse vascular atherosclerosis than intermittent claudication: Framingham study.

OBJECTIVE: To compare implications of Angina Pectoris (AP) and Intermittent Claudication (IC) as indicators of clinical atherosclerosis in other vascular territories. STUDY DESIGN AND SETTING: Prospective cohort study of cardiovascular disease (CVD) in 5,209 men and women of Framingham, MA, aged 28-62 years at enrollment in 1948-1951, who received biennial examinations during the first 36 years of follow-up. Comparative 10-year incidence of subsequent atherosclerotic CVD in participants with IC and AP relative to a reference sample free of CVD was determined. RESULTS: On follow-up, 95 CVD events occurred in 186 participants with IC and 206 of 413 with AP. After age, sex, and risk-factor adjustment, the proportion acquiring other CVD was 34.0% for IC and 43.4% for AP. Relative to the reference sample, those with IC had a 2.73-fold higher age and sex-adjusted 10-year hazard of CVD (95% CI 2.21, 3.38) and for AP was 3.17 (95% CI 2.73, 3.69). CVD hazard ratios remained more elevated for AP and statistically significant after standard risk factor adjustment. Risk factors accounted for more of the excess CVD risk associated with IC (34.8%) than AP (9.5%). CONCLUSION: AP is as useful as IC as a hallmark of diffuse atherosclerotic CVD and an indication for comprehensive preventive measures.

Missense mutations in the insulin promoter factor-1 gene predispose to type 2 diabetes.

The transcription factor insulin promoter factor-1 (IPF-1) plays a central role in both the development of the pancreas and the regulation of insulin gene expression in the mature pancreatic beta cell. A dominant-negative frameshift mutation in the IPF-l gene was identified in a single family and shown to cause pancreatic agenesis when homozygous and maturity-onset diabetes of the young (MODY) when heterozygous. We studied the role of IPF-1 in Caucasian diabetic and nondiabetic subjects from the United Kingdom. Three novel IPF-1 missense mutations (C18R, D76N, and R197H) were identified in patients with type 2 diabetes. Functional analyses of these mutations demonstrated decreased binding activity to the human insulin gene promoter and reduced activation of the insulin gene in response to hyperglycemia in the human beta-cell line Nes2y. These mutations are present in 1% of the population and predisposed the subject to type 2 diabetes with a relative risk of 3.0. They were not highly penetrant MODY mutations, as there were nondiabetic mutation carriers 25-53 years of age. We conclude that mutations in the IPF-1 gene may predispose to type 2 diabetes and are a rare cause of MODY and pancreatic agenesis, with the phenotype depending upon the severity of the mutation.

Gross rearrangements of the MECP2 gene are found in both classical and atypical Rett syndrome patients.

MECP2 mutations are identifiable in approximately 80% of classic Rett syndrome (RTT), but less frequently in atypical RTT. We recruited 110 patients who fulfilled the diagnostic criteria for Rett syndrome and were referred to Cardiff for molecular analysis, but in whom an MECP2 mutation was not identifiable. Dosage analysis of MECP2 was carried out using multiplex ligation dependent probe amplification or quantitative fluorescent PCR. Large deletions were identified in 37.8% (14/37) of classic and 7.5% (4/53) of atypical RTT patients. Most large deletions contained a breakpoint in the deletion prone region of exon 4. The clinical phenotype was ascertained in all 18 of the deleted cases and in four further cases with large deletions identified in Goettingen. Five patients with large deletions had additional congenital anomalies, which was significantly more than in RTT patients with other MECP2 mutations (2/193; p<0.0001). Quantitative analysis should be included in molecular diagnostic strategies in both classic and atypical RTT.

Temporal trends in event rates after Q-wave myocardial infarction: the Framingham Heart Study.

BACKGROUND: Short-term (<30 day) mortality after Q-wave myocardial infarction (MI) has declined over the decades, but it is unclear if rates of long-term sequelae after Q-wave MI have improved. METHODS AND RESULTS: In 546 Framingham Heart Study subjects (388 men with a mean age of 60 years; 158 women with a mean age of 69 years) with an initial recognized Q-wave MI from 1950 through 1989, we investigated time trends in risk for coronary heart disease (CHD) death (n=199), all-cause mortality (n=287), reinfarction (n=108), and congestive heart failure (CHF; n=121). With 1950 through 1969 as the reference period, hazards ratios (HRs) for these outcomes were determined for the 1970s and 1980s. Trend analyses across the 3 time periods were performed for each outcome. Compared with the 1950 through 1969 reference period, the HRs for CHD death were lower in subsequent decades (1970 through 1979: HR, 0.69; 95% CI, 0.49 to 0.98; 1980 through 1989: HR, 0.48; 95% CI, 0.33 to 0.72). All-cause mortality also declined (1970 through 1979: HR, 0.70; 95% CI, 0.0.52 to 0.94; 1980 through 1989: HR, 0.59; 95% CI, 0.43 to 0.81). There were no significant temporal changes in the risks for recurrent MI or CHF. CONCLUSIONS: Substantial reductions in risk of CHD death and all-cause mortality occurred over these 4 decades, coincident with improvements in post-MI therapies. The absence of a decline in CHF incidence may be due to improved post-MI survival of individuals with depressed left ventricular systolic function who are at high risk for CHF.

Heritability of heart rate variability: the Framingham Heart Study.

BACKGROUND: There is evolving evidence that heart rate (HR) is genetically determined. Heart rate variability (HRV) measured by power spectral analysis provides quantitative phenotypic markers of autonomic nervous system activity. Reported determinants of HR and HRV only partially explain their variability in the population. The purpose of this study was to assess the heritability of HR and HRV and estimate the contribution of genetic factors to their variance. METHODS AND RESULTS: Subjects who underwent ambulatory recordings at a routine examination were eligible; subjects with congestive heart failure, coronary artery disease, diabetes mellitus, and those taking cardioactive medications were excluded. We analyzed high-frequency power, low-frequency power, very low-frequency power, total power, low-frequency/high-frequency ratio, and the standard deviation of normal R-R intervals from 2-hour continuous ECG recordings. Heritability analysis was done by studying correlations between siblings (n=682, in 291 sibships, 517 pairs) and between spouse pairs (n=206 pairs) after adjusting for important covariates. Results from separate models were combined to estimate the components of variance attributable to measured covariates, additive genetic effects (heritability), and household effects. After adjusting for covariates, the correlations were consistently higher among siblings (0.21 to 0.26) compared with spouses (0.01 to 0.19). The measured covariates in general accounted for 13% to 40% of the total phenotypic variance, whereas genetic factors accounted for 13% to 23% of the variation among HR and HRV measures. CONCLUSIONS: Heritable factors may explain a substantial proportion of the variance in HR and HRV. These results highlight the contribution of genetic versus environmental factors to autonomic nervous system activity.

Blood pressure response during treadmill testing as a risk factor for new-onset hypertension. The Framingham heart study.

BACKGROUND: Although systolic blood pressure (SBP) response to exercise has been shown to predict subsequent hypertension in small samples of men, this association has not been studied in a large population-based sample of middle-aged men and women. The purpose of this study was to examine, in normotensive subjects, the relations of SBP and diastolic blood pressure (DBP) during the exercise and recovery periods of a graded treadmill test to the risk of developing new-onset hypertension. METHODS AND RESULTS: BP data from exercise testing in 1026 men and 1284 women (mean age, 42+/-10 years; range, 20 to 69 years) from the Framingham Offspring Study who were normotensive at baseline were related to the incidence of hypertension 8 years later. New-onset hypertension, defined as an SBP >/=140 mm Hg or DBP >/=90 mm Hg or the initiation of antihypertensive drug treatment, occurred in 228 men (22%) and 207 women (16%). Exaggerated SBP (Ex-SBP 2) and DBP (Ex-DBP 2) response and delayed recovery of SBP (R-SBP 3) and DBP (R-DBP 3) were defined as an age-adjusted BP greater than the 95th percentile during the second stage of exercise and third minute of recovery, respectively. After multivariable adjustment, Ex-DBP 2 was highly predictive of incident hypertension in both men (OR, 4.16; 95% CI, 2.15, 8.05) and women (OR, 2.17; CI, 1.19, 3.96). R-SBP 3 was predictive of hypertension in men in a multivariable model that included exercise duration and peak exercise BP (OR, 1.92; CI, 1.00, 3.69). Baseline resting SBP (chi2, 23.4 in men and 34.7 in women) and DBP (chi2, 11.3 in men and 13.1 in women) had stronger associations with new-onset hypertension than exercise DBP (chi2, 16.4 in men and 6.1 in women) and recovery SBP (chi2, 6.5 in men and 2.1 in women) responses. CONCLUSIONS: An exaggerated DBP response to exercise was predictive of risk for new-onset hypertension in normotensive men and women. An elevated recovery SBP was predictive of hypertension in men. These findings may reflect subtle pathophysiological features in the preclinical stage of hypertension.

Association of blood pressure with fibrinolytic potential in the Framingham offspring population.

BACKGROUND: Hypertension is an established risk factor for acute coronary events. Because fibrinolytic and hemostatic factors are also associated with cardiovascular disease, we examined the relations of systolic and diastolic blood pressures (SBP and DBP) to levels of plasminogen activator inhibitor antigen, tissue plasminogen activator antigen, fibrinogen, factor VII, von Willebrand factor, fibrinogen, and plasma viscosity in subjects of the Framingham Offspring Study. METHODS AND RESULTS: We studied 1193 men and 1459 women after the exclusion of subjects with known cardiovascular disease and those receiving anticoagulant or antihypertensive therapy. Linear regression models were used to evaluate SBP and DBP as predictors of fibrinolytic and hemostatic factor levels in separate sex models, with adjustment for age, body mass index, smoking, diabetes, total cholesterol, HDL, triglycerides, alcohol intake, and estrogen use (in women). In both sexes, levels of plasminogen activator inhibitor and tissue plasminogen activator antigen were positively related to SBP and DBP (P<0.001). Plasma viscosity was positively related to SBP (P=0.008) and DBP (P=0.001) in women only. There was no association between SBP or DBP and fibrinogen, factor VII, or von Willebrand factor in either sex. CONCLUSIONS: These data suggest that impaired fibrinolysis may play an important role in the pathogenesis of cardiovascular disease in hypertensive patients.

Association of HbA1c with prevalent cardiovascular disease in the original cohort of the Framingham Heart Study.

We studied the cross-sectional relationship between HbA1c and cardiovascular disease (CVD) in the survivors of the original cohort of the Framingham Heart Study (n = 1045). HbA1c was significantly related to prevalent CVD among women but not men. HbA1c was also related to hypertension and to the ratio of total to high-density lipoprotein cholesterol levels. In regression analyses that controlled for these and other potential risk factors, HbA1c remained significantly related to CVD among women. The relative odds of CVD increased 1.39-fold (95% confidence interval 1.06-1.83) for increases in HbA1c of 1% (e.g., for HbA1c from 5 to 6%). The relationship was not weakened when known diabetic subjects or subjects taking beta-blocker or thiazide medications were excluded from analysis. In contrast, there was no significant relationship between "casual" blood glucose and prevalent CVD. Our results reveal a strong, significant, independent association between hyperglycemia, measured by HbA1c, and CVD among older women.

beta-cell genes and diabetes: molecular and clinical characterization of mutations in transcription factors.

beta-Cell transcription factor genes are important in the pathophysiology of the beta-cell, with mutations in hepatocyte nuclear factor (HNF)-1alpha, HNF-4alpha, insulin promoter factor (IPF)-1, HNF-1beta, and NeuroD1/BETA2, all resulting in early-onset type 2 diabetes. We assessed the relative contribution of these genes to early-onset type 2 diabetes using linkage and sequencing analysis in a cohort of 101 families (95% U.K. Caucasian). The relative distribution of the 90 families fitting maturity-onset diabetes of the young (MODY) criteria was 63% HNF-1alpha, 2% HNF-4alpha, 0% IPF-1, 1% HNF-1beta, 0% NeuroD1/ BETA2, and 20% glucokinase. We report the molecular genetic and clinical characteristics of these patients including 29 new families and 8 novel HNF-1alpha gene mutations. Mutations in the transactivation domain are more likely to be protein truncating rather than result in amino acid substitutions, suggesting that a relatively severe disruption of this domain is necessary to result in diabetes. Mutations in the different transcription factors result in clinical heterogeneity. IPF-1 mutations are associated with a higher age at diagnosis (42.7 years) than HNF-1alpha (20.4 years), HNF-1beta (24.2 years), or HNF-4alpha (26.3 years) gene mutations. Subjects with HNF-1beta mutations, in contrast to the other transcription factors, frequently present with renal disease. A comparison of age at diagnosis between subjects with different types and locations of HNF-1alpha mutations did not reveal genotype-phenotype correlations. In conclusion, mutations in transcription factors expressed in the beta-cell are the major cause of MODY, and the phenotype clearly varies with the gene that is mutated. There is little evidence to indicate that different mutations within the same gene have different phenotypes.

Parent-offspring trios: a resource to facilitate the identification of type 2 diabetes genes.

The transmission disequilibrium test with use of trios (an affected proband with both parents) is a robust method for assessing the role of gene variants in disease that avoids the problem of population stratification that may confound conventional case/control studies and allows the detection of parent-of-origin effects. Trios have played a major role in defining genes in a number of polygenic conditions, including type 1 diabetes. We assessed the prevalence, clinical characteristics, and suitability for defining type 2 susceptibility genes of European type 2 diabetes trios. In a Caucasian population in the U.K., only 2.5% of type 2 patients had both parents alive. Using a nationwide strategy, we collected 182 trios defined by strict clinical criteria. Immunological and genetic testing resulted in the exclusion of 25 trios as a result of latent autoimmune diabetes (n = 13), inconsistent family relationships (n = 7), and maternally inherited diabetes and deafness (n = 5). The 157 remaining probands had similar treatment requirements to familial type 2 diabetic subjects but presented at a younger age, were more obese, and more frequently had affected parents. Using this resource, we have not found any evidence for linkage disequilibrium between type 2 diabetes and the glucokinase gene markers GCK1 and GCK2 and the chromosome 20 marker D20S197. We conclude that European type 2 diabetes trios are difficult to collect but provide an important additional approach to dissecting the genetics of type 2 diabetes.

Congestive heart failure in subjects with normal versus reduced left ventricular ejection fraction: prevalence and mortality in a population-based cohort.

OBJECTIVES: The purpose of this study was to assess the relative proportions of normal versus impaired left ventricular (LV) systolic function among persons with congestive heart failure (CHF) in the community and to compare their long-term mortality during follow-up. BACKGROUND: Several hospital-based investigations have reported that a high proportion of subjects with CHF have normal LV systolic function. The prevalence and prognosis of CHF with normal LV systolic function in the community are not known. METHODS: We evaluated the echocardiograms of 73 Framingham Heart Study subjects with CHF (33 women, 40 men, mean age 73 years) and 146 age- and gender-matched control subjects (nested case-control study). Impaired LV systolic function was defined as an LV ejection fraction (LVEF) <0.50. RESULTS: Thirty-seven CHF cases (51%) had a normal LVEF; 36 (49%) had a reduced LVEF. Women predominated in the former group (65%), whereas men constituted 75% of the latter group. During a median follow-up of 6.2 years, CHF cases with normal LVEF experienced an annual mortality of 8.7% versus 3.0% for matched control subjects (adjusted hazards ratio = 4.06, 95% confidence interval 1.61 to 10.26). Congestive heart failure cases with reduced LVEF had an annual mortality of 18.9% versus 4.1% for matched control subjects (adjusted hazards ratio = 4.31, 95% confidence interval 1.98 to 9.36). CONCLUSIONS: Normal LV systolic function is often found in persons with CHF in the community and is more common in women than in men. Although CHF cases with normal LVEF have a lower mortality risk than cases with reduced LVEF, they have a fourfold mortality risk compared with control subjects who are free of CHF.

Determinants of heart rate variability.

OBJECTIVES: This study sought to examine clinical determinants of heart rate variability and to report normative reference values for eight heart rate variability measures. BACKGROUND: Although the clinical implications of heart rate variability have been described, clinical determinants and normative values of heart rate variability measures have not been studied systematically in a large community-based population. METHODS: The first 2 h of ambulatory electrocardiographic recordings obtained in Framingham Heart Study subjects attending a routine examination were reprocessed for heart rate variability. Recordings with transient or persistent nonsinus rhythm, premature beats > 10% of total beats, < 1-h recording time or processed time < 50% of recorded time were excluded; subjects receiving antiarrhythmic medications also were excluded. Among five frequency domain and three time domain measures that were obtained, low frequency power (0.04 to 0.15 Hz), high frequency power (0.15 to 0.40 Hz) and the standard deviation of total normal RR intervals based on 2-h recordings were selected for the principal analyses. Variables with potential physiologic effects or possible technical influences on heart rate variability measures were chosen for multiple linear regression analysis. Normative values, derived from a subset of healthy subjects, were adjusted for age and heart rate. RESULTS: There were 2,722 eligible subjects with a mean age (+/-SD) of 55 +/- 14 years. Three separate multiple linear regression analyses revealed that higher heart rate, older age, beta-adrenergic blocking agent use, history of myocardial infarction or congestive heart failure, diuretic use, diastolic blood pressure > or = 90 mm Hg, diabetes mellitus, consumption of three or more cups of coffee per day and smoking were associated with lower values of one or more heart rate variability measures, whereas longer processed time, start time in the morning, frequent supraventricular and ventricular premature beats, female gender and systolic blood pressure > or = 160 mm Hg were associated with higher values. Age and heart rate were the major determinants of all three selected heart rate variability measures (partial R2 values 0.125 to 0.389). Normative reference values for all eight heart rate variability measures are presented. CONCLUSIONS: Age and heart rate must be taken into account when assessing heart rate variability.