The validation of heart rate variability in individuals with spinal cord injury

The current classification system for spinal cord injury (SCI) considers only somatic information and neglects autonomic damage after injiuy. Heart rate variability (HRV) has the potential to be a valuable measure of cardiac autonomic control after (SCI). Five individuals with tetraplegia and four able-bodied controls underwent 1 min continuous ECG recordings during rest, after Metoprolol administration (max dose=3x5mg) and after Atropine administration (0.02mg/kg) in both supine and 40° head-up tilt. After Metoprolol administration there was a 61.8% decrease in the LF:HF ratio in the SCI participants suggesting that the LF:HF ratio is a reflection of cardiac sympathetic outflow. After Atropine administration there was a 99.1% decrease in the HF power in the SCI participants suggesting that HF power is highly representative of cardiac parasympathetic outflow. There were no significant differences between the SCI and able-bodied participants. Thus, HRV measures are a valid index of cardiac autonomic control after SCI.

Reduced heart rate responding to trauma reliving in trauma survivors with PTSD: correlates and consequences

The authors investigated whether heart rate (HR) responses to voluntary recall of trauma memories (a) are related to posttraumatic stress disorder (PTSD), and (b) predict recovery 6 months later. Sixty-two assault survivors completed a recall task modeled on imaginal reliving in the initial weeks postassault. Possible cognitive modulators of HR responsivity were assessed; dissociation, rumination, trauma memory disorganization. Individuals with PTSD showed a reduced HR response to reliving compared to those without PTSD, but reported greater distress. Notably, higher HR response but not self-reported distress during reliving predicted greater symptom reduction at follow-up in participants with PTSD. Engagement in rumination was the only cognitive factor that predicted lower HR response. The data are in contrast to studies using trauma reminders to trigger memories, which have found greater physiological reactivity in PTSD. The authors' observations are consistent with models of PTSD that highlight differences between cued or stimulus-driven retrieval and intentional trauma recall, and with E B. Foa and M.J. Kozak (1986) hypothesis that full activation of trauma memories facilitates emotional processing.

Heart rate variability is associated with amygdala functional connectivity with MPFC across younger and older adults

The ability to regulate emotion is crucial to promote well-being. Evidence suggests that the medial prefrontal cortex (mPFC) and adjacent anterior cingulate (ACC) modulate amygdala activity during emotion regulation. Yet less is known about whether the amygdala-mPFC circuit is linked with regulation of the autonomic nervous system and whether the relationship differs across the adult lifespan. The current study tested the hypothesis that heart rate variability (HRV) reflects the strength of mPFC-amygdala interaction across younger and older adults. We recorded participants’ heart rates at baseline and examined whether baseline HRV was associated with amygdala-mPFC functional connectivity during rest. We found that higher HRV was associated with stronger functional connectivity between the amygdala and the mPFC during rest across younger and older adults. In addition to this age-invariant pattern, there was an age-related change, such that greater HRV was linked with stronger functional connectivity between amygdala and ventrolateral PFC (vlPFC) in younger than in older adults. These results are in line with past evidence that vlPFC is involved in emotion regulation especially in younger adults. Taken together, our results support the neurovisceral integration model and suggest that higher heart rate variability is associated with neural mechanisms that support successful emotional regulation across the adult lifespan.

Brainstem oxytocinergic modulation of heart rate control in rats: effects of hypertension and exercise training

Oxytocinergic brainstem projections participate in the autonomic control of the circulation. We investigated the effects of hypertension and training on cardiovascular parameters after oxytocin (OT) receptor blockade within the nucleus tractus solitarii (NTS) and NTS OT and OT receptor expression. Male spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were trained (55% of maximal exercise capacity) or kept sedentary for 3 months and chronically instrumented (NTS and arterial cannulae). Mean arterial blood pressure (MAP) and heart rate (HR) were measured at rest and during an acute bout of exercise after NTS pretreatment with vehicle or OT antagonist (20 pmol of OT antagonist (200 nl of vehicle)-1). Oxytocin and OT receptor were quantified (35S-oligonucleotide probes, in situ hybridization) in other groups of rats. The SHR exhibited high MAP and HR (P < 0.05). Exercise training improved treadmill performance and reduced basal HR (on average -11%) in both groups, but did not change basal MAP. Blockade of NTS OT receptor increased exercise tachycardia only in trained groups, with a larger effect on trained WKY rats (+31 +/- 9 versus +12 +/- 3 beats min-1 in the trained SHR). Hypertension specifically reduced NTS OT receptor mRNA density (-46% versus sedentary WKY rats, P < 0.05); training did not change OT receptor density, but significantly increased OT mRNA expression (+2.5-fold in trained WKY rats and +15% in trained SHR). Concurrent hypertension- and training-induced plastic (peptide/receptor changes) and functional adjustments (HR changes) of oxytocinergic control support both the elevated basal HR in the SHR group and the slowing of the heart rate (rest and exercise) observed in trained WKY rats and SHR.

Effect of dietary omega-3 fatty acid deficiency on heart rate variability in hooded rats

Introduction: Recent reports in adult humans suggest that heart rate variability is modulated by the concentration of omega-3 polyunsaturated fatty acids (PUFA) contained in blood cell membranes. Material and methods: Hurst analysis of ECG data was conducted on 12 male adult hooded (Long-Evans) rats, representing the 3rd generation to be fed diets that were either deficient in, or supplemented with, omega-3 PUFA. ECG data were obtained from surface electrodes and 4000 beats were analyzed for each animal. Results: Dietary manipulation, despite leading to large changes in tissue omega- 3 PUFA levels, did not significantly affect the complexity of heart rate dynamics, with Hurst exponent (H) values of 0.15±0.02 and 0.12±0.03, for animals fed omega- 3 fatty acid-adequate and -deficient diets, respectively. Mean heart rate was also unaffected by the diets. A power calculation revealed that about one hundred animals per group would have been required to avoid a type II error. Conclusions: According to this model of dietary PUFA manipulation, omega-3 fatty acids are unlikely to exert a large effect on the autonomic functions that control heart rate variability. Prospective studies into the effect of omega-3 fatty acids on HRV should consider the need for large sample size as estimated by the results contained in this report.

Moderate-intensity resistance exercise training in patients with chronic heart failure improves strength, endurance, heart rate variability, and forearm blood flow

Thirty-nine CHF patients (New York Heart Association Functional Class = 2.3±0.5; left ventricular ejection fraction 28%±7%; age 65±11 years; 33:6 male:female) underwent 2 identical series of tests, 1 week apart, for strength and endurance of the knee and elbow extensors and flexors, VO_2peak, HRV, FBF at rest, and FBF activated by forearm exercise or limb ischemia. Patients were then randomized to 3 months of resistance training (EX, n = 19), consisting of mainly isokinetic (hydraulic) ergometry, interspersed with rest intervals, or continuance with usual care (CON, n = 20), after which they underwent repeat endpoint testing. Combining all 4 movement patterns, strength increased for EX by 21±30% (mean±SD, P<.01) after training, whereas endurance improved 21±21% (P<.01). Corresponding data for CON remained almost unchanged (strength P<.005, endurance P<.003 EX versus CON). VO_2peak improved in EX by 11±15% (P<.01), whereas it decreased by 10±18% (P<.05) in CON (P<.001 EX versus CON). The ratio of low-frequency to high-frequency spectral power fell after resistance training in EX by 44±53% (P<.01), but was unchanged in CON (P<.05 EX versus CON). FBF increased at rest by 20±32% (P<.01), and when stimulated by submaximal exercise (24±32%, P<.01) or limb ischemia (26±45%, P<.01) in EX, but not in CON (P<.01 EX versus CON).

Dose-dependent increases in heart rate variability and arterial compliance in overweight and obese adults with DHA-rich fish oil supplementation

Heart rate (HR) variability and large arterial compliance can be improved using fish oils. DHA, a component of fish oil, has cardiovascular health benefits, but its effect on HR variability (HRV) and arterial compliance is yet to be quantified. Sixty-seven overweight or obese adults (thirty-six males and thirty-one females; 53 (sem 2) year; BMI 31·7 (sem 1·1) kg/m²) were randomly allocated to consume either 6 g/d sunola oil (control; n 17), fish oil (260 mg DHA+60 mg EPA per g) at doses of 2 g/d (n 16), 4 g/d (n 17) or 6 g/d (n 17). Blood pressure, HR and compliance of large and small arteries were measured while supine at baseline and after 12 weeks in all participants, and HRV was assessed in a subgroup of forty-six participants. There was no effect of fish oil on blood pressure, small artery compliance or HR. However, the low frequency:high frequency ratio of HRV decreased with increasing doses of fish oil (r − 0·34, P = 0·02), while large artery compliance increased (r 0·34, P = 0·006). Moreover, the changes in these biomarkers were significantly correlated (r − 0·31, P = 0·04) and may reflect fish oil-induced improvements in arterial function and cardiac autonomic regulation.

The impact of sleep restriction while performing simulated physical firefighting work on cortisol and heart rate responses

PURPOSE: Physical work and sleep restriction are two stressors faced by firefighters, yet the combined impact these demands have on firefighters' acute stress responses is poorly understood. The purpose of the present study was to assess the effect firefighting work and sleep restriction have on firefighters' acute cortisol and heart rate (HR) responses during a simulated 3-day and 2-night fire-ground deployment. METHODS: Firefighters completed multiple days of simulated physical work separated by either an 8-h (control condition; n = 18) or 4-h sleep opportunity (sleep restriction condition; n = 17). Salivary cortisol was sampled every 2 h, and HR was measured continuously each day. RESULTS: On day 2 and day 3 of the deployment, the sleep restriction condition exhibited a significantly higher daily area under the curve cortisol level and an elevated cortisol profile in the afternoon and evening when compared with the control condition. Firefighters' HR decreased across the simulation, but there were no significant differences found between conditions. CONCLUSION: Findings highlight the protective role an 8-h sleep opportunity between shifts of firefighting work has on preserving normal cortisol levels when compared to a 4-h sleep opportunity which resulted in elevated afternoon and evening cortisol. Given the adverse health outcomes associated with chronically high cortisol, especially later in the day, future research should examine how prolonged exposure to firefighting work (including restricted sleep) affects firefighters' cortisol levels long term. Furthermore, monitoring cortisol levels post-deployment will determine the minimum recovery time firefighters need to safely return to the fire-ground.

Cortisol, blood pressure, and heart rate responses to food intake were independent of physical fitness levels in women

This research tested the hypothesis that women who had higher levels of physical fitness will have lower hypothalamo-pituitary-adrenal axis (cortisol) and sympatho-adrenal medullary system (blood pressure and heart rate) responses to food intake compared with women who had low levels of physical fitness. Lower fitness (n = 22; maximal oxygen consumption = 27.4 ± 1.0 mL∙kg(-1)·min(-1)) and higher fitness (n = 22; maximal oxygen consumption = 41.9 ± 1.6 mL∙kg(-1)·min(-1)) women (aged 30-50 years; in the follicular phase of the menstrual cycle) who participated in levels of physical activity that met (lower fitness = 2.7 ± 0.5 h/week) or considerably exceeded (higher fitness = 7.1 ± 1.4 h/week) physical activity guidelines made their own lunch using standardised ingredients at 1200 h. Concentrations of cortisol were measured in blood samples collected every 15 min from 1145-1400 h. Blood pressures and heart rate were also measured every 15 min between 1145 h and 1400 h. The meal consumed by the participants consisted of 20% protein, 61% carbohydrates, and 19% fat. There was a significant overall response to lunch in all of the parameters measured (time effect for all, p < 0.01). The cortisol response to lunch was not significantly different between the groups (time × treatment, p = 0.882). Overall, both groups showed the same pattern of cortisol secretion (treatment p = 0.839). Systolic blood pressure, diastolic blood pressure, mean arterial pressure, or heart rate responses (time × treatment, p = 0.726, 0.898, 0.713, and 0.620, respectively) were also similar between higher and lower fitness women. Results suggest that the physiological response to food intake in women is quite resistant to modification by elevated physical fitness levels.

Analysis of fetal heart rate asymmetry before and after 35 weeks of gestation

In this study, we have investigated the evidence of fetal heart rate asymmetry and how the fetal heart rate asymmetry changes before and after 35 weeks of gestation. Noninvasive fetal electrocardiogram (fECG) signals from 45 pregnant women at the gestational age from16 to 41 weeks with normal single pregnancies were analysed. A nonlinear parameter called heart rate asymmetry (HRA) index that measures time asymmetry of RR interval time-series signal was used to understand the changes of HRA in early and late fetus groups. Results indicate that fetal HRA measured by Porta's Index (PI) consistently increases after 35 weeks gestation compared to foetus before 32 weeks of gestation. It might be due to significant changes of sympatho-vagal balance towards delivery with more sympathetic surge. On the other hand, Guzik's Index (GI) showed a mixed effect i.e., increases at lower lags and decreases at higher lags. Finally, fHRA could potentially help identify normal and the pathological autonomic nervous system development.

Oxygen uptake and heart rate during simulated wildfire suppression tasks performed by Australian rural firefighters

Objective: Australian rural fire crews safeguard the nation against the annual devastation of wildfire. We have previously reported that experienced firefighters identified seven physically demanding tasks for Australian rural fire crews suppressing wildfires. These firefighters rated the operational importance, typical duration, core fitness components, and likely frequency of the seven tasks. The intensity of these duties remains unknown. The aim of this study was to quantify the oxygen uptake (VO2), heart rate (HR) and movement speed responses during simulations of these physically demanding wildfire suppression tasks. Method: Twenty six rural firefighters (20 men, six women) performed up to seven tasks, during which time their HR and movement speed were recorded. The VO2 for each task was also calculated from the analysis of expired air collected in Douglas bags. Firefighters’ HR and movement speed were measured using HR monitors and portable global positioning system units, respectively. Results: The hose work tasks elicited a VO2 of 21-27 mL·kg-1·min-1 and peak HR of 77-87% age-predicted maximal HR (HRmax). Hand tool tasks were accompanied by VO2 of 28-34 mL·kg-1·min-1 and peak HR of 85-95%HRmax. Firefighters’ movement speed spanned 0.2 ± 0.1 to 1.8 ± 0.2 m·s-1 across the seven tasks. The cardiovascular responses in the hand tool tasks were, in most cases, higher (P<0.05) than during those elicited by the hose work tasks. Conclusions: The cardiovascular responses elicited during simulations of physically demanding wildfire suppression approximated those reported for similar tasks in urban and forestry fire fighting jurisdictions. The findings may prompt Australian rural fire agencies to consider cardiovascular disease risk screening and physical selection testing to ensure that healthy and fit firefighters are deployed to the fire ground.