Autonomic regulation and blood pressure in children

Vagal baroreflex sensitivity (BRS) is a measure of short term blood pressure (BP) regulation through alterations in heart rate. Low BRS reflects impaired autonomic system regulation and has been found to be a surrogate marker for cardiovascular health. In particular, it has found to be associated with the pathogenesis of adult hypertension. However, only limited information exists as to the negative consequences of childhood BP on baroreflex function. The objective of this study was to investigate BRS in children with 2 different BP profiles while controlling for the effects of age, maturation, sex, and body composition. A preliminary subsample of 11-14 year-old children from the HBEAT (Heart Behavioural Environmental Assessment Team) Study was selected. The children were divided into 2 BP groups; high BP (HBP; 2:95tl1 percentile, n=21) and normal BP (NBP; <90th percentile, n=85). Following an initial 15 minutes of supine rest, 5 minutes of continuous beat-to-beat BP (Finapres) and RR interval (RRI) were recorded (standard ECG). Spectral indices were computed using Fast Fourier Transform and transfer function analysis was used to compute BRS. High frequency (HF) and low frequency (LF) power spectral areas were set to 0.15-0.4 Hz and 0.04-0.15 Hz, respectively. Body composition was measured using body mass index. After adjusting for body composition, maturation, age and sex ANCOV A results were as follows; LF and HF BRS, LF and HF RRI, and RRI total power were lower in the HBP versus NBP participants (p<0.05). As well, LF IHF SBP ratio was significantly higher in the HBP compared to the NBP group (p<0.05). The regression coefficients (unstandardized B) indicated that in changing groups (NBP to HBP) LF and HF BRS decreases by 4.04 and 6.18 ms/mmHg, respectively. Thus, as BP increases, BRS decreases. These data suggest that changes in autonomic activity occur in children who have HBP, regardless of age, sex, maturation, and body composition. Thus, despite their young age and relatively short amount of time having high BP compared with adults, these children are already demonstrating poor BP regulation and reduced cardiovagal activity. Given that childhood BP is associated with hypertension in adulthood, there is a growing concern in regards to the current cardiovascular health of our children and future adults.

The association between blood pressure and vascular characteristics in children

Hypertension is thought to exist in up to five percent of children. A select number of studies have investigated the role elevated blood pressure plays in pediatric atherosclerotic progression. However these studies contain significant methodological flaws and fail to recognize important confounding factors. Therefore, the influence of elevated blood pressure on arterial health in children remains to be clearly understood. The purpose of this study was to investigate the association between blood pressure (BP) and arterial thickness and stiffuess in children. Common carotid artery (CCA) intima-media thickness (IMT) and distensibility (Dist), as well as systemic pulse wave velocity (PWV) were measured in 21 elevated blood pressure (EBP; BP ~ 95th percentile) and 83 normal blood pressure (NBP; BP < 90th percentile) children 11-14 years of age. Both EBP and NBP groups demonstrated BP within the normal clinical range, but EBP showed significantly elevated BP as compared to the NBP group. Independent t-tests failed to show significant differences between the EBP and NBP groups for CCA IMT (0.43 ± 0.05 mm and 0.42 ± 0.06 mm, respectively) and Dist (0.0058 ± 0.0024 mmHg-1 and 0.0064 ± 0.0019 mmHil respectively). In contrast, a significantly elevated PWV (p

The cardiovascular hemodynamic responses to various levels of orthostatic stress in children

The ability of the cardiovascular system to quickly and efficiently adapt to an orthostatic stress is vital for the human body to function on earth. The way in which the various aspects of the cardiovascular system work together to counteract an orthostatic stress has been previously quantified in the adult population. However, there are still many unknowns surrounding the topic of how the cardiovascular system functions to cope with this same stress in children. The purpose of this study was to describe the cardiovascular hemodynamic adaptations to various levels of orthostatic stress induced using a lower body negative pressure (LBNP) chamber in pre-pubertal boys. A secondary purpose was to determine indices of baroreceptor sensitivity (BRS) at both rest and during low levels of LBNP in this same pediatric sample. Finally, this study aimed to compare the relative responses to LBNP between the children and adults. To complete the study 20 healthy pre-pubertal boys and adult males (9.3 ± 1.1 and 23 ± 1.8 years of age respectively) were recruited and randomly exposed to three levels of LBNP (15, 20 and 25 mmHg). At rest and during the application of the LBNP heart rate (HR), manual and bcat-by-beat systolic (SBP), diastolic (DBP) and mean arterial blood pressure (MAP) were monitored continuously. Aortic diameter was measured at rest and peak aortic blood velocity (PV) was recorded continuously for at least I minute during each baseline and LBNP condition. From the raw data HR, stroke volume (SV), cardiac output (Q), total peripheral resistance (TPR), low frequency baroreceptor sensitivity (LF BRS), high frequency baroreceptor sensitivity (HF BRS) and LFIIIF ratio were calculated. At rest, llR wa'i higher and SBP, SV, Q and LF/HF ratio were lower in the children compared to the adult males (pgJ.05). In response to the increasing LEN!> IIR and TPR increased, and LF BRS. SV and Q decreased in the adult group (pSf).05). while the same levels of LBNP caused an increase in TPR and a decrease in SBP, SV and Q in the children (pSf).05). Although not significant, the LF/HF ratio in the adult group showed an increasing trend in response to increased negative pressure (p=O.088). As for resting BRS, there were no significant differences in LF or HF BRS between the children and the adults despite a tendency for both measures to be 18% lower in the children. Also the LF/HF ratio was almost significantly greater in the adults compared to the children (p=O.057). In addition, a comparison between the relative adult and child responses to LBNP yielded no significant group by level interactions. This result should be taken with caution though, as the low sample size and high measurement variability generated very low statistical power for this analysis. In conclusion, the results of this study suggest that the hemodynamic adaptations to an orthostatic stress were less pronounced in the prepubertal males, most likely due to an underdeveloped autonomic system. These results need to be strengthened by further research before any implications can be derived for health care purposes.

Cardiovascular health risk profiling of Niagara Region grade 9 students : implications for elementary curriculum /

The purpose of this study was to determine if Ontario's health and physical education curriculum contributes sufficiently to ensure the health of our children and young adults. To determine the curriculum effect, the health risk profile of Niagara Region's grade 9 students was compared to Canada's adolescent population. All subjects completed a "Heart Health Lifestyle" survey and were measured for height, weight, percent body fat, blood pressure, and total cholesterol and performed the 20-metre shuttle run test as part of their physical and health education classes. The Niagara Region grade 9 population had a healthy risk profile. Aerobic power was inversely related, and cholesterol levels were positively associated to body mass index and percent body fat in the whole group analysis. These results indicate that physical education can offer unique and essential aspects allowing individuals a means to learn and control body movements and keep physically fit while providing protection against modern disease. Ontario's health and physical education curriculum does contribute to the health of our children and adolescents; however, there is a need to implement a stronger mandate for daily vigorous physical activity.

Does altering brachial artery tone with lower-body negative pressure and flow-mediated dilation affect arterial stiffness?

Although medium sized, muscular vessels normally respond to sympathetic stimulation by reducing compliance, it is unclear whether the large brachial artery is similarly affected by sympathetic stimulation induced via lower-body negative pressure (LBNP). Similarly, the impact of flow-mediated dilation (FMD) on brachial artery compliance and distensibility remains unresolved, hi addition, before such measures can be used as prognostic tools, it is important to investigate the reliability and repeatability of both techniques. Using a randomized order design, the effects of LBNP and FMD on the mechanical properties of the brachial artery were examined in nine healthy male subjects (mean age 24y). Non-invasive Doppler ultrasound and a Finometer were used to measure simultaneously the variation in systolic and diastolic diameter, and brachial blood pressure, respectively. These values were used to calculate compliance and distensibility values at baseline, and during both LBNP and FMD. The within-day and between-day repeatability of arterial diameter, compliance, distensibility, and FMD measures were assessed using the error coefficient and intra-class correlation coefficient (ICC). While heart rate (P<0.01) and peripheral resistance increased during LBNP (P<0.05), forearm blood flow and pulse pressure decreased (P<0.01). hi terms of mechanical properties, vessel diameters decreased (P<0.05), but both compliance and distensibility were not changed. On the other hand, FMD resulted in a significant increase in diameter (P<0.001), with no change in compliance or distensibility. hi summary, LBNP and FMD do not appear to alter brachial artery compliance or distensibility in young, healthy males. Whereas measures ofFMD were not found to be repeatable between days, the ICC indicated that compliance and distensibility were repeatable only within-day.

Preadjunct questions as a learning strategy for older adults

This study investigated the effectiveness of comprehension level preadjunct questions as a learning strategy for older adults in a classroom setting. Fifty-five adults from 55 to 70 years of age were randomly assigned to two groups, the preadjunct question group and a no-question control group. They viewed a video on high blood pressure and completed a recall posttest immediately after viewing the video and again seven days tater. Results demonstrated that there was no significant difference between groups. However, the no-question control group obtained a higher mean score on both the immediate and delayed recall tests than did the preadjunct question group. Nevertheless, significant differences in posttest scores were found related to educational levels and prior knowledge about high blood pressure. Results obtained were explained in terms of resource theory of cognitive aging.

The influence of recreational ball hockey play on cardiovascular risk factors in sedentary males

Introduction: The prevalence of coronary artery disease (CAD) is ever increasing in western industrialized societies. An individuals overall risk for CAD may be quantified by integrating a number of factors including, but not limited to, cardiorespiratory fitness, body composition, blood lipid profile and blood pressure. It might be expected that interventions aimed at improving any or all of these independent factors might improve an individual 's overall risk. To this end, the influence of standard endurance type exercise on cardiorespiratory fitness, body composition, blood lipids and blood pressure, and by extension the reduction of coronary risk factors, is well documented. On the other hand, interval training (IT) has been shown to provide an extremely powerful stimulus for improving indices of cardiorespiratory function but the influence of this training type on coronary risk factors is unknown. Moreover, the vast majority of studies investigating the effects of IT on fitness have used laboratory type training protocols. As a result of this, the influence of participation in interval-type recreational sports on cardiorespiratory fitness and coronary risk factors is unknown. Aims: The aim of the present study was to evaluate the effectiveness of recreational ball hockey, a sport associated with interval-type activity patterns, on indices of aerobic function and coronary risk factors in sedentary men in the approximate age range of 30 - 60 years. Individual risk factors were compiled into an overall coronary risk factor score using the Framingham Point Scale (FPS). Methods: Twenty-four sedentary males (age range 30 - 60) participated in the study. Subject activity level was assessed apriori using questionnaire responses. All subjects (experimental and control) were assessed to have been inactive and sedentary prior to participation in the study. The experimental group (43 ± 3 years; 90 ± 3 kg) (n = 11) participated in one season of recreational ball hockey (our surrogate for IT). Member of this group played a total of 16 games during an 11 week span. During this time, the control group (43 ± 2 years; 89 ± 2 kg) (n = 11) performed no training and continued with their sedentary lifestyle. Prior to and following the ball hockey season, experimental and control subjects were tested for the following variables: 1) cardiorespiratory fitness (as V02 Max) 2) blood lipid profile 3) body composition 5) waist to hip ratio 6) blood glucose levels and 7) blood pressure. Subject V02 Max was assessed using the Rockport submaximal walking test on an indoor track. To assess body composition we determined body mass ratio (BMI), % body fat, % lean body mass and waist to hip ratio. The blood lipid profile included high density lipoprotein, low density lipoprotein and total cholesterol levels; in addition, the ratio of total cholesterol to high density was calculated. Blood triglycerides were also assessed. All data were analyzed using independent t - tests and all data are expressed as mean ± standard error. Statistical significance was accepted at p :S 0.05. Results: Pre-test values for all variables were similar between the experimental and control group. Moreover, although the intervention used in this study was associated with changes in some variables for subjects in the experimental group, subjects in the control group did not exhibit any changes over the same time period. BODY COMPOSITION: The % body fat of experimental subjects decreased by 4.6 ± 0.5%, from 28.1 ± 2.6 to 26.9 ± 2.5 % while that of the control group was unchanged at 22.7 ± 1.4 and 22.2 ± 1.3 %. However, lean body mass of experimental and control subjects did not change at 64.3 ± 1.3 versus 66.1 ± 1.3 kg and 65.5 ± 0.8 versus 64.7 ± 0.8 kg, respectively. In terms of body mass index and waist to hip ratio, neither the experimental nor the control group showed any significant change. Respective values for the waist to hip ratio and body mass index (pre and post) were as follows: 1 ± 0.1 vs 0.9 ± 0.1 (experimental) and 0.9 ± 0.1 versus 0.9 ± 0.1 (controls) while for BMI they were 29 ± 1.4 versus 29 ± 1.2 (experimental) and 26 ± 0.7 vs. 26 ± 0.7 (controls). CARDIORESPIRATORY FITNESS: In the experimental group, predicted values for absolute V02 Max increased by 10 ± 3% (i.e. 3.3 ± 0.1 to 3.6 ± 0.1 liters min -1 while that of control subjects did not change (3.4 ± 0.2 and 3.4 ± 0.2 liters min-I). In terms of relative values for V02 Max, the experimental group increased by 11 ± 2% (37 ± 1.4 to 41 ± 1.4 ml kg-l min-I) while that of control subjects did not change (41 ± 1.4 and 40 ± 1.4 ml kg-l min-I). BLOOD LIPIDS: Compared to pre-test values, post-test values for HDL were decreased by 14 ± 5 % in the experiment group (from 52.4 ± 4.4 to 45.2 ± 4.3 mg dl-l) while HDL data for the control group was unchanged (49.7 ± 3.6 and 48.3 ± 4.1 mg dl-l, respectively. On the other hand, LDL levels did not change for either the experimental or control group (110.2 ± 10.4 versus 112.3 ± 7.1 mg dl-1 and 106.1 ± 11.3 versus 127 ± 15.1 mg dl-1, respectively). Further, total cholesterol did not change in either the experimental or control group (181.3 ± 8.7 mg dl-1 versus 178.7± 4.9 mg dl-l) and 190.7 ± 12.2 versus 197.1 ± 16.1 mg dl-1, respectively). Similarly, the ratio of TC/HDL did not change for either the experimental or control group (3.8 ± 0.4 versus 4.5 ± 0.5 and 4 ± 0.4 versus 4.2 ± 0.4, respectively). Blood triglyceride levels were also not altered in either the experimental or control group (100.3 ± 19.6 versus 114.8 ± 15.3 mg dl-1 and 140 ± 23.5 versus 137.3 ± 17.9 mg dl-l, respectively). BLOOD GLUCOSE: Fasted blood glucose levels did not change in either the experimental or control group. Pre- and post-values for experimental and control groups were 92.5 ± 4.8 versus 93.3 ± 4.3 mg dl-l and 92.3 ± 11.3 versus 93.2 ± 2.6 mg dl-1 , respectively. BLOOD PRESSURE: No aspect of blood pressure was altered in either the experimental or control group. For example, pre- and post-test systolic blood pressures were 131 ± 2 versus 129 ± 2 mmHg (experimental) and 123 ± 2 and 125 ± 2 mmHg (controls), respectively. Pre- and post-test diastolic blood pressures were 84 ± 2 and 83 ± 2 mmHg (experimental) and 81 ± 1 versus 82 ± 1 mmHg, respectively. Similarly, calculated pulse pressure was not altered in the experimental or control as pre- and post-test values were 47 ± 1 versus 47 ± 2 mmlHg and 42 ± 2 versus 43 ± 2 mmHg, respectively. FRAMINGHAM POINT SCORE: The concerted changes reported above produced an increased risk in the Framingham Point Score for the subjects in the experimental group. For example, the pre- and post-test FPS increased from 1.4 ± 0.9 to 2.7 ± 0.7. On the other hand, pre- and post-test scores for the control group were 1.8 ± 1 versus 1.8 ± 0.9. Conclusions: Our data confirms previous studies showing that interval-type exercise is a useful intervention for increasing aerobic fitness. Moreover, the increase in V02 Max we found in response to limited participation in ball hockey (i.e. 16 games) suggests that recreational sport may help reduce this aspect of coronary risk in previously sedentary individual. On the other hand, our results showing little or no positive change in body composition, blood lipids or blood pressures suggest that one season of recreational sport in not in of itself a powerful enough stimulus to reduce the overall risk of coronary artery disease. In light of this, it is recommended that, in addition to participation in recreational sport, the performance of regular physical activity is used as an adjunct to provide a more powerful overall stimulus for decreasing coronary risk factors. LIMITATIONS: The increase in the FPS we found for the experimental group, indicative of an increased risk for coronary disease, was largely due to the large decrease in HDL we observed after compared to above one season of ball hockey. In light of the fact that cardiorespiratory fitness was increased and % body fat was decreased, as well as the fact that other parameters such as blood pressure showed positive (but non statistically significant) trends, the possibility that the decrease in HDL showed by our data was anomalous should be considered. FUTURE DIRECTIONS: The results of this study suggesting that recreational sport may be a potentially useful intervention in the reduction of CAD require to be corroborated by future studies specifically employing 1) more rigorous assessment of fitness and fitness change and 2) more prolonged or frequent participants.