The purpose of the present study was to determine the cortical structures involved with integrated baroreceptor-mediated modulation of autonomic cardiovascular function in conscious humans independent of changes in arterial blood pressure. We assessed the brain regions associated with lower body negative pressure (LBNP)-induced baroreflex control using functional magnetic resonance imaging with blood oxygen level-dependent (BOLD) contrast in eight healthy male volunteer subjects. The levels of LBNP administered were 5, 15 and 35 mmHg. Heart rate (HR; representing the cardiovascular response) and LBNP (representing the baroreceptor activation level) were simultaneously monitored during the scanning period. In addition, estimated central venous pressure (CVP), arterial blood pressure (ABP) and muscle sympathetic nerve activity were recorded on a separate session. Random effects analyses (SPM2) were used to evaluate significant (P < 0.05) BOLD signal changes that correlated separately with both LBNP and HR (15-and 35-mmHg versus 5-mmHg LBNP). Compared to baseline, steady-state LBNP at 15 and 35 mmHg decreased CVP (from 7 ± 1 to 5 ± 1 and 4 ± 1 mmHg, respectively) and increased MSNA (from 12 ± 1 to 23 ± 3 and 36 ± 4 bursts min −1 , respectively, both P < 0.05 versus baseline). Furthermore, steady-state LBNP elevated HR from 54 ± 2 beats min −1 at baseline to 64 ± 2 beats min −1 at 35-mmHg suction. Both mean arterial and pulse pressure were not different between rest and any level of LBNP. Cortical regions demonstrating increased activity that correlated with higher HR and greater LBNP included the right superior posterior insula, frontoparietal cortex and the left cerebellum. Conversely, using the identical statistical paradigm, bilateral anterior insular cortices, the right anterior cingulate, orbitofrontal cortex, amygdala, midbrain and mediodorsal nucleus of the thalamus showed decreased neural activation. These data corroborate previous investigations highlighting the involved roles of the insula, anterior cingulate cortex and amygdala in central autonomic cardiovascular control. In addition, we have provided the first evidence for the identification of the cortical network involved specifically with baroreflex-mediated autonomic cardiovascular function in conscious humans.

We tested the hypothesis that kinetics of O(2) uptake (VO(2)) measured in the transition to exercise near or above peak VO(2) (VO(2 peak)) would be slower than those for subventilatory threshold exercise. Eight healthy young men exercised at approximately 57, approximately 96, and approximately 125% VO(2 peak). Data were fit by a two- or three-component exponential model and with a semilogarithmic transformation that tested the difference between required VO(2) and measured VO(2). With the exponential model, phase 2 kinetics appeared to be faster at 125% VO(2 peak) [time constant (tau(2)) = 16.3 +/- 8.8 (SE) s] than at 57% VO(2 peak) (tau(2) = 29. 4 +/- 4.0 s) but were not different from that at 96% VO(2 peak) exercise (tau(2) = 22.1 +/- 2.1 s). VO(2) at the completion of phase 2 was 77 and 80% VO(2 peak) in tests predicted to require 96 and 125% VO(2 peak). When VO(2) kinetics were calculated with the semilogarithmic model, the estimated tau(2) at 96% VO(2 peak) (49.7 +/- 5.1 s) and 125% VO(2 peak) (40.2 +/- 5.1 s) were slower than with the exponential model. These results are consistent with our hypothesis and with a model in which the cardiovascular system is compromised during very heavy exercise.

Twitch contractions of the ankle dorsiflexors were evoked before and after applied 7-s tetanic stimulation at 100 Hz in 20 young adults. Torque decreased 15% during the tetanus. At 5 s after tetanus, twitch peak torque had potentiated 45%. Potentiation declined to 28% after 1 min, rose slightly to 33% at 2 min, and declined slowly with potentiation still 25% after 5 min. There was large intersubject variation in the amount of potentiation (5-140%) and its persistence (5 to >/=20 min). The muscle compound action potential (M wave) did not change significantly (from pretetanic value) at 5 s after tetanus but increased sharply (26%) at 2 min and then subsided. Twitch half relaxation time (23%) decreased significantly more than twitch rise time (13%) 5 s after tetanus and recovered more slowly. Twitch rates of torque development (75%) and relaxation (71%) increased similarly 5 s after tetanus and were still elevated (approximately 25%) at 5 min. The extent of twitch torque potentiation was significantly inversely correlated with pretetanic twitch rise time (r = -0.69), half relaxation time (r = -0.61), and twitch-to-tetanus ratio (r = -0.66). The data indicate that posttetanic potentiation has a greater effect on twitch half relaxation time than on time to peak torque and is more prominent in muscles with a short twitch time course and small twitch-to-tetanus ratio.

Background and Purpose-Cerebrovascular autoregulation has been described with a phase lead of cerebral blood flow preceding changes in cerebral perfusion pressure (CPP), but there has been less focus on the effect of CPP on cerebral vascular resistance. We investigated these relations during spontaneous fluctuations (control) and repeated head-up tilt. Methods-Eight healthy adults were studied in supine rest and repeated tilt with 10-second supine, 10 seconds at 45°h ead-up tilt for a total of 12 cycles. Cerebral blood flow was estimated from mean flow velocity (MFV) by transcranial Doppler ultrasound, CPP was estimated from corrected finger pressure (CPP F ), and cerebrovascular resistance index (CVRi) was calculated in the supine position from CPP F /MFV. Gain and phase relations were assessed by cross-spectral analysis. Results-In the supine position, MFV preceded CPP F , but changes in CVRi followed CPP F . Gain and phase relations for CPP F as input and MFV as output were similar in supine and repeated tilt experiments. Thus, changes in cerebrovascular resistance must have had a similar pattern in the supine and tilt experiments. Conclusions-Cerebrovascular

BackgroundAdverse childhood experiences (ACEs), such as abuse, household dysfunction, and neglect, have been shown to increase adults’ risk of developing chronic conditions and risk factors for chronic conditions, including cardiovascular disease (CVD). Much less work has investigated the effect of ACEs on children’s physical health status that may lead to adult chronic health conditions. Therefore, the present study examined the relationship between ACEs and early childhood risk factors for adult cardiovascular disease.Methods1 234 grade six to eight students participated in school-based data collection, which included resting measures of blood pressure (BP), heart rate (HR), body mass index (BMI) and waist circumference (WC). Parents of these children completed an inventory of ACEs taken from the Childhood Trust Events Survey. Linear regression models were used to assess the relationship between experiencing more than 4 ACEs experienced, systolic BP, HR, BMI and WC. In additional analysis, ACEs were assessed ordinally in their relationship with systolic BP, HR, and BMI as well as clinical obesity and hypertension status.ResultsAfter adjustment for family education, income, age, sex, physical activity, and parental history of hypertension, and WC for HR models, four or more ACEs had a significant effect on HR (b = 1.8 bpm, 95% CI (0.1-3.6)) BMI (b =1.1 kg/m2, 95% CI (0.5-1.8)), and WC (b = 3.6 cm, 95% CI (1.8-5.3)). A dose–response relationship between ACE accumulation and both BMI and WC was also found to be significant. Furthermore, accumulation of 4 or more ACEs was significantly associated with clinical obesity (95th percentile), after controlling for the aforementioned covariates.ConclusionsIn a community sample of grade six to eight children, accumulation of 4 or more ACEs significantly increased BMI, WC and resting HR. Therefore, risk factors related to reported associations between ACEs and cardiovascular outcomes among adults are identifiable in childhood suggesting earlier interventions to reduce CVD risk are required.