Significant Reduction In Heart Rate Variability Research Articles

Physiological responses and cognitive behaviours: Measures of heart rate variability index language knowledge

Over the past decades, focus has been on developing methods that allow tapping into aspects of cognition that are not directly observable. This includes linguistic knowledge and skills which develop largely without awareness and may therefore be difficult or impossible to articulate. Building on the relation between language cognition and the nervous system, we examine whether Heart Rate Variability (HRV), a cardiovascular measure that indexes Autonomic Nervous System activity, can be used to assess implicit language knowledge. We test the potential of HRV to detect whether individuals possess grammatical knowledge and explore how sensitive the cardiovascular response is.41 healthy, British English-speaking adults listened to 40 English speech samples, half of which contained grammatical errors. Thought Technology's 5-channel ProComp 5 encoder tracked heart rate via a BVP-Flex/Pro sensor attached to the middle finger of the non-dominant hand, at a rate of 2048 samples per second. A Generalised Additive Mixed Effects Model confirmed a cardiovascular response to grammatical violations: there is a statistically significant reduction in HRV as indexed by NN50 in response to stimuli that contain errors. The cardiovascular response reflects the extent of the linguistic violations, and NN50 decreases linearly with an increase in the number of errors, up to a certain level, after which HRV remains constant.This observation brings into focus a new dimension of the intricate relationship between physiology and cognition. Being able to use a highly portable and non-intrusive technique with language stimuli also creates exciting possibilities for assessing the language knowledge of individuals from a range of populations in their natural environment and in authentic communicative situations.

Acute Severe Heart Failure Reduces Heart Rate Variability: An Experimental Study in a Porcine Model.

There are substantial differences in autonomic nervous system activation among heart (cardiac) failure (CF) patients. The effect of acute CF on autonomic function has not been well explored. The aim of our study was to assess the effect of experimental acute CF on heart rate variability (HRV). Twenty-four female pigs with a mean body weight of 45 kg were used. Acute severe CF was induced by global myocardial hypoxia. In each subject, two 5-min electrocardiogram segments were analyzed and compared: before the induction of myocardial hypoxia and >60 min after the development of severe CF. HRV was assessed by time-domain, frequency-domain and nonlinear analytic methods. The induction of acute CF led to a significant decrease in cardiac output, left ventricular ejection fraction and an increase in heart rate. The development of acute CF was associated with a significant reduction in the standard deviation of intervals between normal beats (50.8 [20.5−88.1] ms versus 5.9 [2.4−11.7] ms, p < 0.001). Uniform HRV reduction was also observed in other time-domain and major nonlinear analytic methods. Similarly, frequency-domain HRV parameters were significantly changed. Acute severe CF induced by global myocardial hypoxia is associated with a significant reduction in HRV.

Heart rate variability and blood pressure during and after three CrossFit® sessions

CrossFit® is a training program characterized by high intensity stimulus with constantly varied and multifunctional movements that induces a significant range of physiological, hemodynamic and biochemical responses. Heart rate variability (HRV) can be used to measure how individuals react to physiological stress and fatigue. Thus, the aim of this study was to verify HRV and blood pressure acute responses during and after three sessions of Crossfit®. Nine subjects with more than one year of experience performed three different sessions of CrossFit® to verify the response of systolic blood pressure (SBP), diastolic blood pressure (DBP) and HRV. Significant reductions in HRV were observed through parasympathetic indexes (High Frequency(HF), p&lt;0.001) and an increase in the activity of sympathetic indexes (Low Frequency (LF), p &lt; 0.01; LF/HF, p&lt;0.001) after all Crossfit® workouts. SBP decreased ​​(p&lt;0.05) and there were no significant differences between workouts of the day in both HRV and SBP. Different CrossFit® sessions induced similar activity of the autonomic nervous system with reduced HRV and post-exercise hypotension. Keywords. high intensity interval training; Fran; Megan; Diane; autonomic response; post-exercise hypotensive effect.

Decreased sympathetic cardiovascular influences and hormone-physiological changes in response to Covid-19-related adaptations under different learning environments.

To examine the implications of the transition from face-to-face to online learning from a psychobiological perspective, this study investigated potential differences in physiological stress parameters of students engaged in online or face-to-face learning and determined whether these can be identified as possible mediators between learning experience and achievement emotions. In a randomized experimental field study, medical students (n=82) attended either regular face-to-face classes of the microscopic anatomy course or the same practical course online using Zoom videoconferencing platform. The present study investigated Heart Rate Variability (HRV) and salivary cortisol concentration as stress correlates, within the contexts of online and face-to-face learning and compared these parameters with a control group that was measured at rest. Additionally, participants completed a standardized questionnaire about their experienced emotions in relation to task achievement and subjective stress levels. A significant reduction in HRV was found in face-to-face learning, suggesting stronger stress responses in the face-to-face learning environment (η2 =0.421, P < 0.001). Furthermore, participants engaged in face-to-face learning showed significantly higher cortisol concentrations (η2 =0.115, P=0.032). Additionally, increased sympathetic activation correlated with the discrete positive emotion of enjoyment exclusively within the face-to-face condition (r=0.365, P=0.043). These results indicate that the transfer of a face-to-face practical course in microscopic anatomy to an online learning environment is associated with decreased sympathetic and enhanced vagal cardiovascular influences, together with lower cortisol concentrations in healthy medical students.

Changes in heart rate variability pre and postoperative coronary artery bypass grafting

Introduction and objectives: Previous studies have shown that after coronary artery bypass grafting (CABG), heart rate variability (HRV) becomes decreased. The loss of the peripheral autonomic sympathetic and parasympathetic control in Sinoatrial Node in the form of an autonomic cardioneuropathy syndrome is the predictor of the pre and postoperative complications after CABG. The aim of this study was to establish the temporal pattern of change in the decrease of HRV observed after CABG. Methods: The study involved 119 consecutive patients who underwent the first CABG operation with sinus rhythm. All subjects underwent assessed with 24-hour Holter recordings 2 days preoperative and 7 days, 3 months, 6 months postoperative at Hanoi Heart Hospital from 6/2016 to 8/2018. Main results: All indicators of heart rate variability decreased to the lowest level after surgery 7 days, recovers to the preoperative values within three to six months of the procedure. The incidence of pre and postoperative low HRV varies from 28.6% (preop) to 51.8% (postop 7 days), 19.6% (postop 3 months) and 12.7% (postop 6 months). Conclusions: This study have showed that CABG surgery generally leads to significant reduction in HRV. HRV gradually recovers to the preoperative values within three to six months of the procedure.

Longitudinal relationships between polycyclic aromatic hydrocarbons exposure and heart rate variability: Exploring the role of transforming growth factor-β in a general Chinese population

We aim to investigate the long-term adverse effects of polycyclic aromatic hydrocarbons (PAHs) exposure on heart rate variability (HRV) reduction, and to assess the potential role of transforming growth factor-β1 (TGF-β1) in such relationship. We enrolled 2985 adult residents with 4100 observations who participated at baseline and 6-years follow-up from Wuhan-Zhuhai cohort. Ten detectable urinary PAHs metabolites and two HRV indices were repeatedly measured at baseline and follow-up; and plasma TGF-β1 levels were also determined for all subjects. We observed that both total urinary low molecular weight PAHs (ΣLWM OH-PAH) and total urinary high molecular weight PAHs (ΣHWM OH-PAH) were negatively associated with HRV reductions (P < 0.05). Subjects with persistent high levels of ΣHWM OH-PAH had a significant reduction in HRV over 6 years, and the incensement of TGF-β1 could aggravate above adverse effects in a dose-response manner. All kinds of PAHs were positively associated with plasma TGF-β1 elevation, which in turn, were negatively related to HRV indices. Increased TGF-β1 significant mediated 1.34–3.62% of PAHs-associated HRV reduction. Our findings demonstrated that long-term high levels of PAHs exposure could cause HRV reductions, and TGF-β1 may play an essential role in such association.

REGRESSION TO THE MEAN: METHODOLOGICAL ISSUES FOR EVALUATION OF HEART RATE VARIABILITY VARIABLES FOR STRESS ASSESSMENT

There is now a substantial body of evidence linking the baseline level of heart rate variability (HRV) with the magnitude of stress-induced reduction in respiratory sinus arrhythmia. However, it remains to be proved to what extent these interindividual differences in stress responses may be attributed to the statistical phenomenon of regression to the mean (RTM). We sought to test the hypothesis that the statistical artifact RTM explains pan of the baseline effect. Heart rate recording was carried out in 1156 volunteers. To obtain an estimate of the stress response. 148 persons were randomly selected. Participants were monitored on a rest day and just before an academic examination for state anxiety and HRV. Participants were divided into quartiles according to baseline HRV levels and were compared for response to academic stress. We observed a significant reduction in HRV in subjects with a high baseline HRV (&gt; 75th percentile), while a significant increase was found in the group with low baseline HRV. Regression analysis demonstrated that the value of baseline HRV correlated with the magnitude of stress reaction consistent with the RTM model. Baseline-adjusted ANCOVA does not reveal significant intergroup differences in the changes hi heart rate (HR) and HRV from rest to exam. RTM-adjusted estimates confirmed an exam effect for HR and HRV. The results of our study strongly support RTM as the source of variability of stress-related changes in HRV.

Continuous cardiac autonomic and haemodynamic responses to isometric exercise in females.

Hypertension is associated with impaired haemodynamic control mechanisms and autonomic dysfunction. Isometric exercise (IE) interventions have been shown to improve autonomic modulation and reduce blood pressure (BP) predominantly in male participants. The physiological responses to IE are unexplored in female populations; therefore, this study investigated the continous cardiac autonomic and haemodynamic response to a single bout of IE in a large female population. Forty physically inactive females performed a single, individually prescribed isometric wall squat training session. Total power spectral density of heart rate variability (HRV) and associated low-frequency (LF) and high-frequency (HF) power spectral components were recorded in absolute (ms2) and normalised units (nu) pre, during and post an IE session. Heart rate (HR) was recorded via electrocardiography and baroreceptor reflex sensitivity (BRS) via the sequence method. Continuous blood pressure was recorded via the vascular unloading technique and stroke volume via impedance cardiography. Total peripheral resistance (TPR) was calculated according to Ohm's law. During IE, there were significant reductions in HRV (p < 0.001) and BRS (p < 0.001), and significant increases in heart rate (p < 0.001), systolic, mean and diastolic BP (p < 0.001 for all). In recovery following the IE session, cardiac autonomic parameters returned to baseline (p = 0.974); however, total peripheral vascular resistance significantly reduced below baseline (p < 0.001). This peripheral vascular response was associated with significant reductions in systolic (-17.3 ± 16.5mmHg, p < 0.001), mean (-18.8 ± 17.4mmHg, p < 0.001) and diastolic BP (-17.3 ± 16.2mmHg, p < 0.001), below baseline. A single IE session is associated with improved haemodynamic cardiovascular responses in females. Cardiac autonomic responses return to baseline values, which suggests that alternative mechanisms are responsible for the post-exercise haemodynamic improvements in females. Future mechanistic research is required to investigate the acute and chronic effects of IE in female populations with different resting BP profiles.

Novel heart rate variability index for wrist-worn wearable devices subject to motion artifacts that complicate measurement of the continuous pulse interval

Objective: Wearable health monitoring devices have recently become popular, but they can still only measure the average heart rate. Heart rate variability (HRV) is known to represent changes in the autonomic nervous system and analysis of HRV has the potential to be used for monitoring various wellness-related parameters such as sleep or stress. HRV analysis requires accurate measurement of the heartbeat interval. In wearable devices, it is difficult to accurately measure the heartbeat interval due to motion noise. In this paper we propose a new method for performing HRV analysis on photoplethysmographic (PPG) signals corrupted by motion artifacts measured at the wrist. Approach: A frequency-tracking algorithm based on the oscillator-based adaptive notch filter was used to measure instantaneous heart rate. The algorithm consists of a time-varying bandpass filter for enhancing the heartbeat signal and an adaptive mechanism for tracking heart rate frequency. By optimizing the filter bandwidth and forgetting factor of the adaptive mechanism, the frequency-tracking algorithm better reflects the variability of instantaneous heart rate. The new HRV index was calculated as the standard deviation of the heartbeat interval data converted using the heart rate estimated by the frequency-tracking algorithm. In order to verify the effectiveness of the proposed index, the new HRV index calculated for each sleep stage was compared with SDNN, the standard deviation of the heartbeat interval, which was calculated using simultaneous electrocardiogram measurements. In addition, changes in SDNN and the new index were compared during a socially evaluated speech task. Finally, the relationship between the new index and SDNN was compared with the data collected during daily activities over a 24 h period. Main results: Experimental results showed that statistically significant changes in HRV could be monitored in different sleep stages using the proposed method. In addition, when subjects were stressed by a socially evaluated speech task, significant reduction in HRV was observed using the proposed method. Finally, HRV values measured during daily activities over a 24 h period showed a high correlation coefficient of 0.812 with reference HRVs. Significance: The new HRV index calculated by the proposed method is expected to be an effective new solution for noisy PPG signals.

Neonatal Skin-to-Skin Contact: Implications for Learning and Autonomic Nervous System Function in Infants With Congenital Heart Disease.

Infants with complex congenital heart disease (CCHD) often develop neurodevelopmental disabilities. Cognitive abilities are associated with vagally mediated autonomic function. Skin-to-skin contact (SSC) interventions enhance infant neurodevelopment and autonomic function in other high-risk populations. To examine the effects of a neonatal SSC intervention on learning and autonomic function in 3-month-old infants: infants with CCHD who received neonatal SSC ( n = 10), typically developing (TD) infants ( n = 16), and infants with CCHD without SSC ( n = 10). This secondary data analysis measured cognitive function using the mobile paradigm (MP), a classic measure of learning based on operant conditioning. Autonomic function was assessed with heart rate (HR) and HR variability (HRV). Data were analyzed with repeated-measures general linear mixed modeling with α = .10 for this exploratory study. Learning rates were TD = 75%, cardiac-SSC = 70%, and cardiac-control = 40%. Learners demonstrated significant reductions in HRV during the MP; nonlearners exhibited no change. TD and cardiac-SSC groups exhibited increases in HR and reductions in HRV during the MP. No significant changes occurred in the cardiac-control group. Nonlinear HRV during the MP differed only in the TD group. Findings suggest improvements in cognitive and autonomic development in 3-month-old infants with CCHD who received neonatal SSC. Learning and autonomic function results in infants with CCHD who had not received SSC suggest reduced capacity to muster the physiologic resources to carry out this cognitive task. Findings provide preliminary evidence in support of implementation of SSC with infants with CCHD and support additional research.

EFFECT OF THE QUALITY OF LABORATORY RATS ON THE DYNAMICS OF PARAMETERS IN THE DEVELOPMENT OF VASORENAL HYPERTENSION IN THE “2 KIDNEYS, 1 CLAMP” MODEL

The aim of this study was to investigate the effects of the quality of laboratory rats on the dynamics of vasorenal hypertension in model “2 kidneys, 1 clamp”. Experiments were conducted on rats strain Wistar - conventional and SPF status. The dynamics of systolic blood pressure (SBP), beat-to-beat interval (RR) and components of the spectrum of heart rate variability (HRV) were explored via 1, 2 and 8 weeks after renal artery clipping. It was found, that conventional and SPF animals differ in basic parameters. SPF rats have a SBP below, RR and HRV more, compared to conventional animals. Through 8 weeks after renal artery clipping in rats with SPF status rise SBP was lower, compared to conventional animals. Marked similarities in the dynamics of vasorenal hypertension for both groups of animals: increase sympathetic nervous system activity markers of spectrum HRV in the initial weeks after renal artery clipping, stable vasorenal hypertension did not develop in all clipped rats, and the tendency to decrease the length of RR in the development of stable vasorenal hypertension. In addition, there was a significant reduction in HRV through 8 weeks following renal artery clipping in SPF rats. As a result, although vasorenal hypertension developed better in the group of conventional rats, the dynamics of variability of RR was more pronounced in animals with SPF status, besides, fewer animals with SPF status were required to detect changes in the components of the HRV spectrum than conventional animals.

Reduced heart rate variability in a treatment-seeking early psychosis sample

Reduced cardiac autonomic function is associated with increased risk of cardiovascular disease (CVD), with heart rate variability (HRV) providing an accessible index of cardiac autonomic function. HRV may provide a candidate physiological mechanism linking reduced cardiac autonomic function to increased risk for CVD in schizophrenia illness. This study examines whether HRV is also reduced in a community sample of treatment-seeking participants experiencing early psychosis (n = 48) compared to healthy volunteers (n = 48) and social anxiety control groups (n = 48) matched by gender and age. HRV was assessed during a five-minute interbeat interval recording at rest. Participants also completed self-report psychiatric symptom measures. Early psychosis participants showed significant reductions in HRV compared to social anxiety and healthy control groups. Reductions in HRV were also observed in early psychosis participants taking anticholinergic medications compared to both control groups taking cardio-benign medications or who were non-medicated. Lastly, whether or not early psychosis participants were taking anticholinergic medications was not associated with reductions in HRV. Findings provide preliminary evidence that early psychosis is associated with reduced HRV. This study supports further research with larger sample sizes to precisely determine the influence of anticholinergic drugs on HRV in early psychosis populations.

Poincaré plot indices as measures of sympathetic cardiac regulation: Responses to psychological stress and associations with pre-ejection period

The Poincaré plot is a visual representation of the R-R time series within a Cartesian plane constructed by plotting each R-R interval as a function of the previous one. The plot can be characterized by parameters that quantify the standard deviation (SD) of short- and long-term R-R interval variability (SD1 and SD2, respectively). Claims regarding the use of Poincaré plot analysis as an alternative to conventional time-domain and spectral analytic measures of parasympathetic contributions to heart rate variability (HRV) have been evaluated somewhat extensively. However, its proposed utility for characterizing sympathetic influences on HRV during periods of acute mental stress, using SD2 and the SD1/SD2 ratio, has received minimal attention. In the present study, the electrocardiogram was used to record R-R interval variability in healthy participants during a resting baseline period, while they performed a challenging reaction time task, and then during a recovery period. Simultaneously, the thoracic impedance cardiogram was used to derive the pre-ejection period (PEP), which reflects sympathetic cardiac control. HRV was quantified using time-domain, spectral analytic, and Poincaré plot indices. Task performance elicited significant reductions in HRV and PEP parameters, indicating withdrawal of parasympathetic tone with concomitant sympathetic activation. Following cessation of task performance, all HRV and impedance measures returned to baseline levels, signaling resumption of parasympathetic dominance. Bivariate associations linking SD2 and the SD1/SD2 ratio to PEP were observed; however, these were not large in magnitude, were exceeded in size by associations between the Poincaré metrics and conventional HRV markers of parasympathetic cardiac influences, and were eliminated when the latter were controlled statistically. These observations challenge the proposal that the Poincaré SD2 and SD1/SD2 metrics are suitable markers of sympathetic cardiac regulation in research concerned with mental and physical health.

Autonomic Cardiac Response to Static and Dynamic Muscle Contractions in Post-Stroke and Healthy Subjects

Aim: To describe the response of the cardiac autonomic nervous system to static and dynamic muscle contractions in post ischemic stroke patients 2 and 7 weeks post event, compared with the response of age- and gender-matched healthy controls. Methods: Participants: 12 patients post first stroke at the subacute phase and 12 healthy age-matched controls. Tools: the Polar Advanced Heart Rate Monitor (RS800CX) was used to record inter bit intervals at rest and during grip and cycling. Results: Patients post stroke, both at 2 and 7 weeks post onset time, had higher heart rate and lower heart rate variability (HRV) values at rest compared to controls. A significant reduction in HRV values was noted among healthy controls during static and dynamic muscle contractions compared to baseline. In contrast, stroke patients 2 weeks after onset did not show a cardiac reaction to static contractions. At 7 weeks post onset examination, the stroke patients showed a significant reduction in HRV both during static and dynamic contractions compared to the rest state. Conclusion: Patients post stroke in the subacute phase have alterations in cardiac rhythm regulation both at rest and during muscle effort. The extent of the cardiac autonomic response to muscle contraction is associated with contraction type and time post event. Simple measurement of HRV in different conditions enables monitoring of recovery of autonomic nervous system cardiac control.

Autonomic nervous system dysfunction in psychiatric disorders and the impact of psychotropic medications: a systematic review and meta-analysis.

Autonomic nervous system (ANS) dysfunction is a putative underlying mechanism for increased cardiovascular disease risk in individuals with psychiatric disorders. Previous studies suggest that this risk may be related to psychotropic medication use. In the present study we systematically reviewed and analyzed published studies of heart rate variability (HRV), measuring ANS output, to determine the effect of psychiatric illness and medication use. We searched for studies comparing HRV in physically healthy adults with a diagnosed psychiatric disorder to controls and comparing HRV pre- and post-treatment with a psychotropic medication. In total, 140 case-control (mood, anxiety, psychosis, dependent disorders, k = 151) and 30 treatment (antidepressants, antipsychotics; k = 43) studies were included. We found that HRV was reduced in all patient groups compared to controls (Hedges g = -0.583) with a large effect for psychotic disorders (Hedges g = -0.948). Effect sizes remained highly significant for medication-free patients compared to controls across all disorders. Smaller and significant reductions in HRV were observed for specific antidepressants and antipsychotics. Study quality significantly moderated effect sizes in case-control analyses, underscoring the importance of assessing methodological quality when interpreting HRV findings. Combined findings confirm substantial reductions in HRV across psychiatric disorders, and these effects remained significant even in medication-free individuals. Reductions in HRV may therefore represent a significant mechanism contributing to elevated cardiovascular risk in individuals with psychiatric disorders. The negative impact of specific medications on HRV suggest increased risk for cardiovascular disease in these groups, highlighting a need for treatment providers to consider modifiable cardiovascular risk factors to attenuate this risk.

Anxiety as a Risk Factor for Cardiovascular Diseases.

Anxiety as a Risk Factor for Cardiovascular Diseases.

Short-term Recovery Following Resistance Exercise Leading or not to Failure.

This study analyzed the time course of recovery following 2 resistance exercise protocols differing in level of effort: maximum (to failure) vs. half-maximum number of repetitions per set. 9 males performed 3 sets of 4 vs. 8 repetitions with their 80% 1RM load, 3×4(8) vs. 3×8(8), in the bench press and squat. Several time-points from 24 h pre- to 48 h post-exercise were established to assess the mechanical (countermovement jump height, CMJ; velocity against the 1 m·s(-1) load, V1-load), biochemical (testosterone, cortisol, GH, prolactin, IGF-1, CK) and heart rate variability (HRV) and complexity (HRC) response to exercise. 3×8(8) resulted in greater neuromuscular fatigue (higher reductions in repetition velocity and velocity against V1-load) than 3×4(8). CMJ remained reduced up to 48 h post-exercise following 3×8(8), whereas it was recovered after 6 h for 3×4(8). Significantly greater prolactin and IGF-1 levels were found for 3×8(8) vs. 3×4(8). Significant reductions in HRV and HRC were observed for 3×8(8) vs. 3×4(8) in the immediate recovery. Performing a half-maximum number of repetitions per set resulted in: 1) a stimulus of faster mean repetition velocities; 2) lower impairment of neuromuscular performance and faster recovery; 3) reduced hormonal response and muscle damage; and 4) lower reduction in HRV and HRC following exercise.

Effect of hypoxia on heart rate variability and baroreflex sensitivity during hypoglycemia in type 1 diabetes mellitus.

Patients with type 1 diabetes mellitus exhibit impairments in autonomic and cardiovascular control which are worsened with acute hypoglycemia--thus increasing the risk of adverse cardiovascular events. Hypoxia, as seen with the common comorbidity of sleep apnea, may lead to further autonomic dysfunction and an increased risk of ventricular arrhythmias. Therefore, we hypothesized that heart rate variability (HRV) and baroreflex sensitivity (BRS) would be reduced during hypoglycemia in adults with type 1 diabetes, with a further decline when combined with hypoxia. Subjects with type 1 diabetes (n=13; HbA1c=7.5±0.3%, duration of diabetes=17±5 yrs) completed two 180min hyperinsulinemic (2mU/kg TBW/min), hypoglycemic (~3.3µmol/mL) clamps separated by a minimum of 1week and randomized to normoxia (SpO2~98%) or hypoxia (SpO2~85%). Heart rate (electrocardiogram) and blood pressure (finger photoplethysmography) were analyzed at baseline and during the hypoglycemic clamp for measures of HRV and spontaneous cardiac BRS (sCBRS). Hypoglycemia resulted in significant reductions in HRV and sCBRS when compared with baseline levels (main effect of hypoglycemia: p<0.05). HRV and sCBRS were further impaired during hypoxia (main effect of hypoxia: p<0.05). Acute hypoxia worsens hypoglycemia-mediated impairments in autonomic and cardiovascular control in patients with type 1 diabetes and may increase the risk of cardiovascular mortality. These results highlight the potential cumulative dangers of hypoglycemia and hypoxia in this vulnerable population.

Cardiac autonomic modulation in healthy elderly after different intensities of dynamic exercise.

PurposeTo investigate the heart rate (HR) and its autonomic modulation at baseline and during dynamic postexercise (PEX) with intensities of 40% and 60% of the maximum HR in healthy elderly.MethodsThis cross-sectional study included ten apparently healthy people who had been submitted to a protocol on a cycle ergometer for 35 minutes. Autonomic modulation was evaluated by spectral analysis of HR variability (HRV).ResultsA relevant increase in HR response was observed at 15 minutes postexercise with intensities of 60% and 40% of the maximum HR (10±2 bpm versus 5±1 bpm, respectively; P=0.005), and a significant reduction in HRV was also noted with 40% and 60% intensities during the rest period, and significant reduction in HRV (RR variance) was also observed in 40% and 60% intensities when compared to the baseline, as well as between the post-exercise intensities (1032±32 ms versus 905±5 ms) (P<0.001). In the HRV spectral analysis, a significant increase in the low frequency component HRV and autonomic balance at 40% of the maximum HR (68±2 normalized units [nu] versus 55±1 nu and 2.0±0.1 versus 1.2±0.1; P<0.001) and at 60% of the maximum HR (77±1 nu versus 55±1 nu and 3.2±0.1 versus 1.2±0.1 [P<0.001]) in relation to baseline was observed. A significant reduction of high frequency component at 40% and 60% intensities, however, was observed when compared to baseline (31±2 nu and 23±1 nu versus 45±1 nu, respectively; P<0.001). Moreover, significant differences were observed for the low frequency and high frequency components, as well as for the sympathovagal balance between participants who reached 40% and 60% of the maximum HR.ConclusionThere was an increase in the HR, sympathetic modulation, and sympathovagal balance, as well as a reduction in vagal modulation in the elderly at both intensities of the PEX.

Autonomic control during acute hypoglycemia in type 1 diabetes mellitus.

We hypothesized that adults with type 1 diabetes mellitus (T1DM) would exhibit impaired heart rate variability (HRV), QT interval, T-wave amplitude, and baroreflex sensitivity (BRS) when compared with healthy controls. In addition, we hypothesized that acute hypoglycemia would result in further adverse changes in measures of autonomic and cardiovascular function. A single 180-min hyperinsulinemic (2mU/kg TBW/min), hypoglycemic (~3.3 umol/mL) clamp was completed in 10 healthy adults and 13 adults with T1DM. Counterregulatory hormones were assessed and measures of heart rate (electrocardiogram) and blood pressure (intra-arterial catheter or finger photoplethysmography) were analyzed at baseline and during the hypoglycemic clamp for measures of HRV, QT interval, T-wave amplitude, and spontaneous cardiac BRS (sCBRS). Baseline measures of HRV, sCBRS, and T-wave amplitude were blunted in adults with T1DM when compared with healthy controls. Hypoglycemia resulted in significant reductions in HRV, sCBRS, and T-wave amplitude and prolonged QT intervals; these changes were not different between adults with T1DM and healthy controls. Results from the current study show that adults with T1DM exhibit impaired autonomic and cardiovascular function. Additionally, novel findings highlight an effect of acute hypoglycemia to further reduce measures of autonomic and cardiovascular function similarly between adults with T1DM and healthy controls. These results suggest that acute hypoglycemia may worsen impairments in autonomic and cardiovascular control in patients with T1DM, thus increasing the risk of ventricular arrhythmias and cardiovascular mortality.