Low-frequency Power Of Heart Rate Variability Research Articles

Differences in heart rate responses to upright posture are associated with variations in the high-frequency power of heart rate variability.

High resting heart rate is a cardiovascular risk factor, but limited data exist on the underlying hemodynamics and reproducibility of supine-to-upright increase in heart rate. We recorded noninvasive hemodynamics in 574 volunteers [age, 44.9 yr; body mass index (BMI), 26.4 kg/m2; 49% male] during passive head-up tilt (HUT) using whole body impedance cardiography and radial artery tonometry. Heart rate regulation was evaluated using heart rate variability (HRV) analyses. Comparisons were made between quartiles of supine-to-upright heart rate changes, in which heart rate at rest ranged 62.6-64.8 beats/min (P = 0.285). The average upright increases in heart rate in the quartiles 1-4 were 4.7, 9.9, 13.5, and 21.0 beats/min, respectively (P < 0.0001). No differences were observed in the low-frequency power of HRV, whether in the supine or upright position, or in the high-frequency power of HRV in the supine position. Upright high-frequency power of HRV was highest in quartile 1 with lowest upright heart rate and lowest in quartile 4 with highest upright heart rate. Mean systolic blood pressure before and during HUT (126 vs. 108 mmHg) and the increase in systemic vascular resistance during HUT (650 vs. 173 dyn·s/cm5/m2) were highest in quartile 1 and lowest in quartile 4. The increases in heart rate during HUT on three separate occasions several weeks apart were highly reproducible (r = 0.682) among 215 participants. To conclude, supine-to-upright increase in heart rate is a reproducible phenotype with underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. As heart rate at rest influences prognosis, future research should elucidate the prognostic significance of these phenotypic differences.NEW & NOTEWORTHY Subjects with similar supine heart rates are characterized by variable increases in heart rate during upright posture. Individual heart rate increases in response to upright posture are highly reproducible as hemodynamic phenotypes and present underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. These results indicate that resting heart rate obtained in the supine position alone is not an optimal means of classifying people into groups with differences in cardiovascular function.

Autonomic modulation by low-intensity focused ultrasound stimulation of the vagus nerve

Objective. Our previous study has shown that low-intensity focused ultrasound stimulation (FUS) of the vagus nerve could modulate blood pressure (BP), but its underlying mechanisms remain unclear. We hypothesized that low-intensity FUS of the vagus nerve would regulate autonomic function and thus BP. Approach. 17 anesthetized spontaneously hypertensive rats were treated with low-intensity FUS of the left vagus nerve for 15 min each trial. Continuous BP, heart rate, respiration rate (RR), and core body temperature were simultaneously recorded to evaluate the effects on BP and other physiological parameters. Heart rate variability (HRV), systolic BP variability, and baroreflex sensitivity were computed to evaluate the autonomic modulation function. A Control-sham group without stimulation and another Control-FUS group with non-target stimulation were also examined to exclude the influence of potential confounding factors on autonomic modulation. Main results. A prolonged significant decrease in BP, pulse pressure, RR, the normalized low-frequency power of HRV, and the low-to-high frequency power ratio of HRV were found after the low-intensity FUS of the left vagus nerve in comparison with the baseline and those of the control groups, demonstrating that activities of the sympathetic nervous system were inhibited. The prolonged significant increase of the normalized high-frequency power of HRV suggested the activation of parasympathetic activity. Significance. Low-intensity FUS of the left vagus nerve effectively improved the autonomic function by activating parasympathetic efferent and inhibiting sympathetic efferent, which contributes to BP reduction. The findings shed light on the hypotensive mechanism underlying FUS.

TWO-YEAR RESPONSES OF HEART RATE AND HEART RATE VARIABILITY TO FIRST OCCUPATIONAL LEAD EXPOSURE

Objective: Because of the falling lead exposure, the literature relating autonomous nervous function to blood lead has limited relevance. Design and method: In the longitudinal Study for Promotion of Health in Recycling Lead (URL: https://www.clinicaltrials.gov; Unique identifier: NCT02243904), we recorded the 2-year responses of heart rate, heart rate variability (Cardiax, International Medical Equipment Developing, Budapest, Hungary), and median nerve conduction velocity (Brevio, NeuMed, West Trenton, NJ), a routine test in occupational medicine, to first lead exposure in 195 newly hired workers (91.3% men; mean age, 27.8 years). High- and low-frequency heart rate variability power and orthostatic heart rate variability responses were derived from 5-minute eletrocardiograms in the supine and standing positions by Fourier transform and autoregression. Blood lead was determined by inductively coupled plasma mass spectrometry. Results: From baseline to follow-up, blood lead increased from 4.22 to 14.1 ug/dL and supine/standing HR from 63.6/75.5 to 67.1/78.8 beats per minute. In analyses stratified by fourths of blood lead changes, trends in heart rate and Fourier/autoregressive heart rate variability did not reveal a dose-response curve (0.074&lt; = P&lt; = 0.98). In multivariable-adjusted mixed models, heart rate, Fourier/autoregressive heart rate variability, and nerve conduction velocity changes were unrelated to blood lead except for a weak inverse association between supine heart rate and blood lead changes (-0.55%; P = 0.029). The expected associations between heart rate variability and heart rate changes were preserved with no differences at baseline/follow-up. Analyses ichotomised by baseline median blood lead or cumulative blood lead index (4.30 ug/dL or 32.1 ug/dL × year) suggested an heart rate variability increase versus decrease in the low versus high baseline exposure group. Conclusions: Thus, a &gt; 3-fold blood lead increment did not affect autonomous neural function as captured by heart rate variability.

Effect of various exercise training interventions on cardiac autonomic function in obese individuals: A systematic review and meta-analysis

The aim of the systematic review and meta-analysis was to investigate the effect of various exercise training interventions on cardiac autonomic function (CAF) in obese. We conducted electronic database search from SCOPUS, PubMed, Web of science and cochrane library from inception till August 2021. Among 3234 articles retrieved, 9 were found to be eligible for the present review. Studies investigating the effect of exercise interventions on CAF assessed either by linear or non-linear measures of heart rate variability (HRV), baroreflex sensitivity, or heart rate recovery were included. Of the studies retrieved, 9 were included in the systematic review. Meta-analysis was conducted on 5 studies. The findings of the qualitative analysis revealed low to moderate certainty of evidence for aerobic exercise (AE) while low to very low was documented for combined training (CT). Standardized mean differences (SMD) showed a large effect of AE on SD of normal to normal (N–N) intervals (SDNN) [SMD 1.35, 95% confidence interval (CI) −0.11, 2.81; p = 0.07] and root mean square of successive differences between adjacent inter-beat (R-R) intervals (RMSSD) [SMD 1.50, 95% confidence interval (CI) 0.12, 2.88; p = 0.03]. CT depicted moderate insignificant change in low-frequency power of HRV (LF; SMD −0.55, 95% CI −1.52, −0.42; p = 0.27). This systematic analysis revealed positive effect of exercise training on CAF in obese individuals. AE and CT have large and moderate impact on CAF respectively though the pooled result was insignificant for majority of the variables, while effect of HIIT and RT yet remains to be fully elucidated. • Obesity is strongly linked with the development of cardiac autonomic dysfunction. • Exercise training improves markers of cardiac autonomic function in obese. • Aerobic exercise has large impact on linear and non linear indices of heart rate variability. • In future, trials focusing on high intensity interval training and resistance training must be conducted.

Early sinusoidal heart rate patterns and heart rate variability to assess hypoxia-ischaemia in near-term fetal sheep.

•Therapeutic hypothermia needs to be started as early as possible in the first 6h after acute injury caused by hypoxia-ischaemia (HI), but the severity and timing of HI are often unclear. In this study we evaluated whether measures of heart rate variability (HRV) might provide early biomarkers of HI. •The duration but not magnitude of suppression of HRV power and conversely increased sample entropy of the heart rate were associated with severity of HI, such that changes in the first 3h did not discriminate between groups. •Relative changes in HRV power bands showed different patterns between groups and therefore may have the potential to evaluate the severity of HI. •Aberrant fetal heart rate patterns and increased arginine vasopressin levels in the first hour after moderate and severe HI were correlated with loss of EEG power after 3days' recovery, suggesting potential utility as early biomarkers of outcome. Therapeutic hypothermia is partially neuroprotective after acute injury caused by hypoxia-ischaemia (HI), likely because the timing and severity of HI are often unclear, making timely recruitment for treatment challenging. We evaluated the utility of changes in heart rate variability (HRV) after HI as biomarkers of the timing and severity of acute HI. Chronically instrumented fetal sheep at 0.85 gestational age were exposed to different durations of umbilical cord occlusion to produce mild (n=6), moderate (n=8) or severe HI (n=8) or to sham occlusion (n=5). Heart rate (HR) and HRV indices were assessed until 72h after HI. All HI groups showed suppressed very low frequency HRV power and elevated sample entropy for the first 3h; more prolonged changes were associated with greater severity of HI. Analysis of relative changes in spectral power showed that the moderate and severe groups showed a shift towards higher HRV frequencies, which was most marked after severe HI. This shift was associated with abnormal rhythmic HR patterns including sinusoidal patterns in the first hour after HI, and with elevated plasma levels of arginine vasopressin, which were correlated with subsequent loss of EEG power by day3. In conclusion, absolute changes in HRV power in the first 3h after acute HI were not significantly related to the severity of HI. The intriguing relative shift in spectral power towards higher frequencies likely reflects greater autonomic dysfunction after severe HI. However, sinusoidal HR patterns and elevated vasopressin levels may have utility as biomarkers of severe HI.

Age and autonomic control, but not cerebral oxygenation, are significant determinants of EEG spectral power in children.

Sleep disordered breathing (SDB) in children has significant effects on daytime functioning and cardiovascular control; attributed to sleep fragmentation and repetitive hypoxia. Associations between electroencephalograph (EEG) spectral power, autonomic cardiovascular control and cerebral oxygenation have been identified in adults with SDB. To date, there have been no studies in children. We aimed to assess associations between EEG spectral power and heart rate variability as a measure of autonomic control, with cerebral oxygenation in children with SDB. One hundred sixteen children (3-12 years) with SDB and 42 controls underwent overnight polysomnography including measurement of cerebral oxygenation. Power spectral analysis of the EEG derived from C4-M1 and F4-M1, quantified delta, theta, alpha, and beta waveforms during sleep. Multiple regression tested whether age, SDB severity, heart rate (HR), HR variability (HRV), and cerebral oxygenation were determinants of EEG spectral power. There were no differences in EEG spectral power derived from either central or frontal regions for any frequency between children with different severities of SDB so these were combined. Age, HR, and HRV low frequency power were significant determinants of EEG spectral power depending on brain region and sleep stage. The significant findings of this study were that age and autonomic control, rather than cerebral oxygenation and SDB severity, were predictive of EEG spectral power in children. Further research is needed to elucidate how the physiology that underlies the relationship between autonomic control and EEG impacts on the cardiovascular sequelae in children with SDB.

Vagal Mediation of Low-Frequency Heart Rate Variability During Slow Yogic Breathing.

Changes in heart rate variability (HRV) associated with breathing (respiratory sinus arrhythmia) are known to be parasympathetically (vagally) mediated when the breathing rate is within the typical frequency range (9-24 breaths per minute [bpm]; high-frequency HRV). Slow yogic breathing occurs at rates below this range and increases low-frequency HRV power, which may additionally reflect a significant sympathetic component. Yogic breathing techniques are hypothesized to confer health benefits by increasing cardiac vagal control, but increases in low-frequency HRV power cannot unambiguously distinguish sympathetic from parasympathetic contributions. The aim of this study was to investigate the autonomic origins of changes in low-frequency HRV power due to slow-paced breathing. Six healthy young adults completed slow-paced breathing with a cadence derived from yogic breathing patterns. The paced breathing took place under conditions of sympathetic blockade, parasympathetic (vagal) blockade, and placebo. HRV spectral power was compared under 11 breathing rates during each session, in counterbalanced order with frequencies spanning the low-frequency range (4-9 bpm). HRV power across the low-frequency range (4-9 bpm) was nearly eliminated (p = .016) by parasympathetic blockade (mean (SD) spectral power at breathing frequency = 4.1 (2.1)) compared with placebo (69.5 (8.1)). In contrast, spectral power during sympathetic blockade 70.2 (9.1) and placebo (69.5 (8.1)) was statistically indistinguishable (p = .671). These findings clarify the interpretation of changes in HRV that occur during slow-paced breathing by showing that changes in low-frequency power under these conditions are almost entirely vagally mediated. Slow-paced breathing is an effective tool for cardiac vagal activation.

Increasing Performance of Professional Soccer Players and Elite Track and Field Athletes with Peak Performance Training and Biofeedback: A Pilot Study.

The aim of this pilot study was to investigate the effects of an intervention consisting of mental coaching combined with either electro encephalogram (EEG) alpha power feedback or heart rate variability (HRV) feedback on HRV, EEG outcomes and self-reported factors related to stress, performance, recovery and sleep quality in elite athletes. A prospective pilot study was performed with two distinct cohorts. Soccer players were provided with four sessions of mental coaching combined with daily HRV biofeedback (Group A); track and field athletes were provided with four sessions of mental coaching in combination with daily neurofeedback (Group B). Measurements were performed at baseline, post intervention and at 5 weeks follow-up. Objective measures: EEG and ECG. Subjective measures: Numeric Rating Scale for performance, Pittsburgh Sleep Quality Index, Rest and Stress Questionnaire and Sports Improvement-60. Group characteristics were too distinct to compare the interventions. Linear mixed models were used to analyze differences within groups over time. In Group A, significant changes over time were present in alpha power at 5 of 7 EEG locations (p < 0.01–0.03). LF/HF ratio significantly increased (p = 0.02) and the concentration (p = 0.02) and emotional scale (p = 0.03) of the SIM-60 increased significantly (p = 0.04). In Group B, the HRV low frequency power and recovery scale of the REST-Q significantly increased (p = 0.02 and <0.01 resp.). Other measures remained stable or improved non-significantly. A mental coaching program combined with either HRV or EEG alpha power feedback may increase HRV and alpha power and may lead to better performance-related outcomes and stress reduction. Further research is needed to elucidate the effects of either type of feedback and to compare effects with a control group.

Subclinical Vitamin B12 Deficiency and Heart Rate Variability Across Life Cycle.

The present study aimed to evaluate association between plasma vitamin B12 and heart rate variability in clusters of population of various ages across life cycle. 47 healthy children from an ongoing pregnancy and birth cohort, 32 young adults and 47 healthy elderly subjects were recruited following inclusion and exclusion criteria. All subjects underwent plasma vitamin B12, anthropometry and heart rate variability (HRV). The prevalence of vitamin B12 deficiency (&lt;148 pmol/l) across age groups were 51.1 % for children, 56.2 % for young adults and 61.7 % for the elderly group respectively. There was large variability in vitamin B12 status across the age groups. Frequency distribution of low frequency (LF) absolute units HRV in the elderly was skewed, whereas in children and young adult group there was wide distribution of LF HRV. Association between Log LF absolute units HRV and plasma vitamin B12 across groups were tested using curve fit models. In children a linear curve estimation best fitted and explained 9.3 % of the association (n=47, .=0.003, P=0.03, R2=0.09). There was no association between log LF absolute units HRV and plasma vitamin B12 in the young adult group. In the elderly group a power curve fit model best fitted and explained 8.9 % of the association. Inspection of the power curve fit model demonstrated a curvilinear pattern; there was a linear association in the elderly with vitamin B12 levels less than 200 pmol/l. However, elderly with vitamin B12 values &gt;200 pmol/l demonstrated saturation (plateauing) of log LF HRV. The study demonstrated varied pattern of responses between vitamin B12 status and LF power of HRV across age groups. Thus, it is important to consider these associations before planning supplementation of vitamin B12.

Baroreflex mechanisms in Irritable Bowel Syndrome: Part I. Traditional indices

ObjectiveThis study was conducted to present evidence of differences in autonomic regulation of cardiovascular activity and its role in the severity of specific (disease-related) and non-specific (negative affect and chronic pain-related) symptoms in individuals with Irritable Bowel Syndrome (IBS). MethodsSeventy-eight female patients with IBS and 27 healthy women age 18–62years were assessed for IBS symptoms, negative affect, and baroreceptor sensitivity (BRS), blood pressure (BP), heart rate, and heart rate variability (HRV) at rest. Direct and indirect regression effects were examined with application of the bootstrap procedure to validate findings. ResultsIBS was reliably related to lower resting BRS, higher BP, and higher negative affect compared to healthy controls. Longer disease duration (chronicity) was related to BRS decrease coupled with systolic BP increase (95% CIs=−0.14 to −0.01). Three autonomic mechanisms associated with BRS decrease were found to further regulate severity of IBS symptoms. Lower BRS was related to higher IBS severity in general if the effect was transferred through the decrease of low frequency power of HRV (e.g., 95% CIs=−0.039 to −0.001 for abdominal pain severity). However, lower BRS was related to lower IBS severity in general if the effect was transferred through diastolic BP increase (95% CIs=0.01–0.11 for abdominal pain severity). Lower BRS was related to higher abdominal pain severity coupled with high negative affect if the effect was transferred through the decrease of higher frequency power of HRV (95% CIs=−0.026 to −0.003). ConclusionsThese findings indicate that different cardiovascular mechanisms are associated with IBS development and the increase and decrease of severity of IBS symptoms. Their assessment suggests ways to personalize treatment of IBS.

Association between impaired cardiovascular autonomic function and hypoglycemia in patients with type 1 diabetes.

OBJECTIVEWe studied the association between glycemic variability (GV) reflecting hypoglycemic stress and cardiovascular autonomic function in subjects with type 1 diabetes.RESEARCH DESIGN AND METHODSForty-four type 1 diabetic patients (mean age 34 ± 13 years, 40% male, 86% Caucasian, mean diabetes duration 13 ± 6 years, mean hemoglobin A1c [HbA1c] 8.0 ± 1.2% [64 ± 5 mmol/mol]) without cardiovascular disease, dyslipidemia, or hypertension participated in this pilot study. Indices of GV reflective of hypoglycemic stress (low blood glucose index [LBGI] and area under the curve [AUC] for hypoglycemia) were computed using data obtained during 5-day continuous glucose monitoring. Cardiovascular autonomic neuropathy (CAN) was assessed using standardized cardiovascular reflex testing and measures of heart rate variability (HRV), which were analyzed as time and frequency domain measures.RESULTSBoth LBGI and AUC hypoglycemia had a significant negative association with the low-frequency power of HRV (r = −0.47, P = 0.002; r = −0.43, P = 0.005, respectively) and with the high-frequency power of HRV (r = −0.37, P = 0.018; r = −0.38, P = 0.015, respectively). These inverse associations persisted after adjusting for HbA1c, although they were attenuated in multivariable analysis after adjustment for age, diabetes duration, and several other covariates.CONCLUSIONSIncreased GV promoting hypoglycemic stress was associated with reduced HRV independent of glycemic control as assessed by HbA1c. These pilot data suggest that glucose variability may contribute to cardiovascular autonomic dysfunction among adults with type 1 diabetes.

Heart rate variablity indices are poor predictors of exercise capacity in healthy type 1 diabetics (LB664)

People with diabetes often have chronotropic incompetence and reduced exercise tolerance. Chronotropic incompetence has been associated with autonomic dysfunction, thus we determined the ability of resting heart rate variability (HRV) to predict an altered exercise response in healthy individuals with type 1 diabetes (T1D). Baseline measures were taken followed by quantification of HRV with power spectral analysis during controlled breathing (15 breaths·min‐1) in 20 T1D (10 male &amp; 10 female) screened for ischaemic cardiac disease and 12 age‐, weight‐, and training‐matched non‐diabetics (CON: 7 male &amp; 5 female). These measurements were followed by a VO2max test (with ECG). Resting HR (73 ± 10 vs. 64 ± 10 beats·min‐1; P = 0.01) was higher and mean arterial blood pressure (92 ± 12 vs. 90 ± 11 mm Hg; P = 0.68) was not different between T1D and CON respectively. HR reserve (104 ± 17 vs. 121 ± 11 beats·min‐1; P &lt; 0.001), VO2max (31 ± 9 vs. 41 ± 9 mL·min‐1·Kg‐1; P =0.005), HRV total power (1317 ± 1146 vs. 7493 ± 15080 ms2; P = 0.024), and HRV high frequency power (441 ± 491 vs. 3840 ± 9883 ms2; P = 0.029) were lower in T1D vs. CON respectively. Absolute max HR (177 ± 15 vs. 185 ± 10 beats·min‐1; P = 0.09), % of age predicted max HR (95 ± 6 vs. 97 ± 2 %; P = 0.07), and HRV low frequency power (328 ± 279 vs. 1672 ± 3433 ms2; P = 0.09) were not different in T1D vs. CON respectively. Despite group differences in HRV, linear correlations showed that resting HRV total, high frequency, and low frequency power accounted for &lt; 20% of the variability in resting HR, HR reserve, max HR, and VO2max in T1D. Resting HRV indices are poor predictors of cardiovascular exercise response in healthy T1D.Grant Funding Source: Supported by Anderson's trust

Openness to experience and aesthetic chills: Links to heart rate sympathetic activity

Openness to experience has important links to cognitive processes such as creativity, and to values, such as political attitudes. The biological origins of variation in openness to experience are, however, obscure. The centrality of “aesthetic chills” to high openness suggests that sympathetic nervous system activation may play a role. Here, we tested this using the low-frequency heart rate variability power measure (LF) as biomarker of sympathetic activation, tested under baseline and stress conditions in a sample of 952 subjects, and controlling for measured confounders of age, sex, height, weight and BMI. A significant association was found between LF and openness to experience (β=0.10, 95% CI [0.02, 0.17], p<.01). These results suggest links between openness to experience and sympathetic nervous system activity explaining, at least in part, relationships of openness to such traits as aesthetic chills.

GW24-e3615 The effects of slow breathing rate on heart rate variability and blood pressure variability

ObjectivesThe objective of this study was to investigate the effects of slow breathing rate on heart rate variability (HRV) and blood pressure variability (BPV) in healthy subjects.Methods53 healthy volunteers underwent...

Temporal development of baroreceptor dysfunction in a rodent model of chronic kidney disease

Altered autonomic control of the cardiovascular system in chronic kidney disease (CKD) contributes to an increased risk of cardiovascular events. The aim of the present study was to determine whether and when autonomic dysfunction occurs in a conscious, telemetered, rodent model of CKD. In Lewis polycystic kidney (LPK; n=8) and Lewis (n=8) rats, blood pressure (BP), heart rate (HR), HR variability (HRV), systolic BP variability (SBPV) and baroreflex sensitivity (BRS) were determined from 10 to 16weeks of age. The LPK rats had higher systolic BP (average across all ages: 230±10 vs 122.6±0.3mmHg; P<0.001), increased SBPV (average across all ages: 13.9±1.9 vs 5.2± 0.2mmHg(2) ; P<0.01) and reduced low-frequency HRV power (average across all ages: 1.5±0.3 vs 2.6±0.2msec(2) ; P<0.05). Between 10 and 12weeks of age, SBPV increased twofold in the LPK rat (8.13±1.05 vs 16.10±1.31mmHg(2) for 10 vs 12weeks of age, respectively; P<0.001), coinciding with an approximate 40% reduction in BRS (1.32±0.14 vs 0.79±0.11ms/mmHg for 10 vs 12weeks of age, respectively; P<0.05). There was no difference in BRS between LPK and Lewis rats at 10weeks of age; however, from 12weeks onwards, BRS was reduced in LPK rats (0.75± 0.01 vs 1.17±0.04ms/mmHg; P<0.01). Baroreceptor regulation of HR becomes impaired between 10 and 12weeks of age in the LPK rat, coinciding with an increase in SBPV. Preventing baroreflex dysfunction in CKD may reduce SBPV and the associated mortality risks.

Autonomic impairment after myocardial infarction: Role in cardiac remodelling and mortality

1. Impairmant of baroreflex sensitivity (BRS) has been implicated in the reduction of heart rate variability (HRV) and in the increased risk of death after myocardial infarction (MI). In the present study, we investigated whether the additional impairment in BRS induced by sinoaortic baroreceptor denervation (SAD) in MI rats is associated with changes in the low-frequency (LF) component of HRV and increased mortality rate. 2. Rats were randomly divided into four groups: control, MI, denervated (SAD) and SAD + MI rats. Left ventricular (LV) function was evaluated by echocardiography. Autonomic components were assessed by power spectral analysis and BRS. 3. Myocardial infarction (90 days) reduced ejection fraction (by approximately 42%) in both the MI and SAD + MI groups; however, an increase in LV mass and diastolic dysfunction were observed only in the SAD + MI group. Furthermore, BRS, HRV and the LF power of HRV were reduced after MI, with an exacerbated reduction seen in SAD + MI rats. The LF component of blood pressure variability (BPV) was increased in the MI, SAD and SAD + MI groups compared with the control group. Mortality was higher in the MI groups compared with the non-infarcted groups, with an additional increase in mortality in the SAD + MI group compared with the MI group. Correlations were obtained between BRS and the LF component of HRV and between LV mass and the LF component of BPV. 4. Together, the results indicate that the abolishment of BRS induced by SAD in MI rats further reduces the LF band of HRV, resulting in a worse cardiac remodelling and increased mortality in these rats. These data highlight the importance of this mechanism in the prognosis of patients after an ischaemic event.

Heart rate variability is related to impaired haemorheology in older women with type 2 diabetes

Impaired heart rate variability (HRV)and haemorheology are independently associated with cardiovascular disease and diabetic complications. The aim of the present study was to investigate the relationships between parameters of HRV,and red blood cell (RBC) aggregation and deformability, in older women with type 2 diabetes. Twenty women (age 69 ± 2 yr) with uncomplicated type 2 diabetes and twenty controls (age 69 ± 3 yr) participated in the study. Beat-to-beat cardiac (RR) intervals over 5 min were analysed for HRV parameters in the time and frequency domains. Blood was sampled for RBC deformability, as well as RBC aggregation in two suspending mediums: haematocrit adjusted plasma and 3% dextran 70. RBC aggregation was increased and HRV was impaired for those with type 2 diabetes when compared with control. RBC aggregation was negatively related to low frequency power of HRV, and was positively related to high frequency power of HRV, for subjects with type 2 diabetes. RBC deformability was positively related to HRV only for those with type 2 diabetes. Impaired haemorheology is associated with reduced HRV in older women with type 2 diabetes, suggesting changes in the microcirculation may result in impaired modulation of cardiac cycles.

Supine low-frequency power of heart rate variability reflects baroreflex function, not cardiac sympathetic innervation

Power spectral analysis of heart rate variability (HRV) has been used to indicate cardiac autonomic function. High-frequency power relates to respiratory sinus arrhythmia and therefore to parasympathetic cardiovagal tone; however, the relationship of low-frequency (LF) power to cardiac sympathetic innervation and function has been controversial. Alternatively, LF power might reflect baro reflexive modulation of autonomic outflows. We studied normal volunteers and chronic autonomic failure syndrome patients with and without loss of cardiac noradrenergic nerves to examine the relationships of LF power with cardiac sympathetic innervation and baroreflex function. We compared LF power of HRV in patients with cardiac sympathetic denervation, as indicated by low myocardial concentrations of 6-[(18)F]fluorodopamine-derived radioactivity or low rates of norepinephrine entry into coronary sinus plasma (cardiac norepinephrine spillover) to values in patients with intact innervation, at baseline, during infusion of yohimbine, which increases exocytotic norepinephrine release from sympathetic nerves, or during infusion of tyramine, which increases non-exocytotic release. Baroreflex-cardiovagal slope (BRS) was calculated from the cardiac interbeat interval and systolic pressure during the Valsalva maneuver. Results. LF power was unrelated to myocardial 6-[(18)F]fluorodopamine-derived radioactivity or cardiac norepinephrine spillover. In contrast, the log of LF power correlated positively with the log of BRS (r = 0.72, P < 0.0001). Patients with a low BRS (</=3 msec/mm Hg) had low LF power, regardless of cardiac innervation. Tyramine and yohimbine increased LF power in subjects with normal BRS but not in those with low BRS. BRS at baseline predicted LF responses to tyramine and yohimbine. LF power reflects baroreflex function, not cardiac sympathetic innervation.

Spectral Analysis of Finger Photoplethysmographic Waveform Variability in a Model of Mild to Moderate Haemorrhage

Slow fluctuations in cardiovascular signals such as heart rate variability (HRV) are believed to carry important clinical information. This study investigated whether frequency spectrum analysis of the finger photoplethysmographic waveform variability (PPGV) could characterize a hypovolaemic response by using a blood donation as a model of controlled mild to moderate haemorrhage. This was a prospective, observational study carried out in a convenience sample of blood donors. Spectral analysis was performed on the finger infrared photoplethysmographic waveform and on the electrocardiogram- derived R-R intervals obtained from 43 healthy volunteers during blood donation. Spectral powers were calculated from low frequency (LF), mid frequency (MF) and high frequency (HF) bands of the spectrum of HRV and the coherence-weighted cross-spectrum of PPGV. Comparison was made between the four stages of blood donation: pre-donation (PRE), first half of donation (FIRST), second half of donation (SECOND) and post-donation (POST). A significant increase in the sum of the sympathetic-related MF and respiratory HF powers of finger PPGV (in mean-scaled units) was observed in SECOND and POST (P < 0.01). The post-donation increase in this PPGV spectral measure occurred in 77% of the subjects, which was higher than the percentage of subjects experiencing a blood pressure drop (71% or below). Normalized LF power of HRV showed a significant rise in SECOND (P < 0.01) but not in POST. Spectral analysis of finger PPGV may provide valuable information in addition to vital sign measurements in characterizing a hypovolaemic response. Given the limitations of the current blood loss model, further studies are required to assess the usefulness of finger PPGV for early haemorrhage detection in the clinical setting.

Variability of QT Interval Duration in Obstructive Sleep Apnea: An Indicator of Disease Severity

To determine OSA-related changes in variability of QT interval duration and in heart rate variability (HRV), and to evaluate the relationship of these parameters to disease severity. Retrospective analysis of diagnostic sleep records. Clinical sleep laboratory in a hospital setting. Twenty patients (12 males and 8 females) without significant comorbidities who were undergoing polysomnography were studied. Standard heart rate variability measures and QT variability (Berger algorithm) were computed over consecutive 5-minute ECG epochs throughout the night. The effect of sleep stage and the relationship between these parameters and the severity of OSA as determined by the respiratory disturbance index (RDI) were explored. Further, a linear regression model of QT variability was developed. Severity of OSA (RDI) was 49 +/- 28 (range from 17-107) events/ hr. QT variability was the only ECG measure significantly correlated with RDI (both log-transformed; r = 0.6, P = 0.006). Further, QT variability was correlated with the minimum oxygen saturation (r = -0.55, P = 0.01). Sleep stage showed a significant effect on HRV, but not on QT variability. In the regression model, RDI was the strongest predictor of QT variability (R2 increase 38%), followed by high and low frequency power of HRV (R2 increase 10% each). Obstructive sleep apnea is associated with changes in QT interval variability during sleep. The variance of beat-to-beat QT intervals correlates more strongly with the severity of OSA (as determined by RDI) than standard measures of heart rate variability, and is correlated with blood oxygenation, but not sleep stage.