Heart rate variability and autonomic nervous system changes in children with vasovagal syncope

The aim of this study was to evaluate the HRV at rest and during tilt test (HUTT) in children with a history of vasovagal syncope and to link the HRV indices with the clinical results of the test. HRV indices were assessed in the supine position and during the initial 5 minutes of the 60-degree HUTT in 49 patients (33 females, 16 males, mean age of 13 +/- 2.8 years) who were evaluated for recurrent syncope. The positive to negative results of the test were 21 to 28. The normalized power of high frequency component (npHF) decreased, normalized power of low frequency component (npLF) and the LF:HF ratio increased during HUTT of tilt-positive patients (P < 0.05 for each parameter). Parallel changes, but to a lesser degree, were observed for similar HRV parameters of tilt-negative patients. In addition, the HF and all the time-domain indices decreased significantly (P < or = 0.05) during HUTT in the latter group. When the tilt-positive and -negative patients were compared, the npHF was lower (P = 0.002), npLF and LF:HF ratio were higher (P = 0.01 and P = 0.001, respectively) during the test in tilt-positive patients, reflecting increased sympathetic tone in this group. A cut-off point for LF:HF was assigned as 2.7 for differentiating tilt-negative and tilt-positive results. The specificity, sensitivity, and positive and negative predictive values of this cut-off point were calculated as 93%, 52%, 85%, and 41%, respectively. Patients with vasovagal syncope show variations in vagal autonomic tone and appear to be more prone to syncope when their sympathetic tone is elevated at the beginning of the test. LF:HF > 2.7 is a specific marker (specificity 93%) and can correctly predict a positive tilt test in 85% of patients.     

Cardiovascular autonomic response during preoperative stress and postoperative pain

Heart rate response to physiologic maneuvers was used to evaluate autonomic nervous system (ANS) function in normal control subjects and during the stress and pain experienced by patients before and after surgery. In preoperative patients (stressed without pain) and postoperative patients (stressed with pain), maneuvers which routinely increase activity in the parasympathetic or sympathetic divisions of the ANS produced only 50% of the response seen in control subjects. The heart rate response was not further reduced in patients with pain compared to patients with stress alone. The difference in heart rate response between surgical patients and control subjects was not accompanied by a difference in baseline heart rate. The data suggest that tonic stress impairs the ability of the ANS to respond fully to perturbing influences.     

Heart rate variability analysis in the assessment of autonomic function in heart failure

Heart rate is not static, but rather changes continuously in response to physical and mental demands. In fact, an invariant heart rate is associated with disease processes such as heart failure. Heart rate variability analysis is a noninvasive technique used to quantify fluctuations in heart rate. In this article, the authors review neural control of heart rate, briefly describe heart rate variability, and summarize research data demonstrating that heart failure is associated with altered heart rate variability. In addition, the authors present evidence that heart failure patients with decreased heart rate variability are at risk for future cardiac events, heart transplantations, and death.     

Heart rate response to two lifting techniques

OBJECTIVE: To determine the heart rate response to repetitive lifting of light weights employing two techniques, stoop and squat. DESIGN: Randomized cross-over trial. PARTICIPANTS: Twenty healthy volunteers (11 women, 9 men), mean age of 25 years, recruited from the staff of a physical medicine and rehabilitation department. METHODS: Subjects lifted and lowered a box weighing 0, 1, or 3 kg, using the stoop (bent at waist with knees straight) and squat (knees bent) techniques, 20 times in 1 minute. MAIN OUTCOME MEASURES: The heart rate was recorded every 5 seconds during the effort aid 30 seconds and 1 minute after the test. RESULTS: Significantly higher heart rates were found during both the test and recuperation phases of the squat technique with each of the three loads (p < .05). The heart rate increase was also higher with the 3 kg load than with the 1 kg or 0 kg load (p = .0001). CONCLUSION: The heart rate is lower using the stoop technique for lifting. This may explain why individuals choose the more ergonomically risky stoop technique in everyday lifting tasks.     

Heart rate variability analysis: a tool to assess cardiac autonomic function

Heart rate monitoring is commonly used to provide an acute indicator of an individual's cardiovascular status and responsiveness. An increasingly popular technique involves quantifying the very small amounts by which the heart rate changes from one cardiac cycle to the next. This "heart rate variability (HRV) analysis" provides a substantial amount of additional information about the cardiovascular system and enables quantification of cardiac regulatory influences on the autonomic nervous system. The autonomic nervous system consists of two main components: the sympathetic system and the parasympathetic system. The relative influence of these two components on the sino-atrial node of the heart determines the heart rate. A number of physiological factors, including blood pressure and respiratory rate, can have a profound effect on this autonomic "balance." HRV analysis therefore provides a noninvasive method for investigating the dynamic influence of changing physiological parameters on cardiac regulation.     

Heart rate recovery: a practical clinical indicator of abnormal cardiac autonomic function

The autonomic nervous system (ANS) and cardiovascular function are intricately and closely related. One of the most frequently used diagnostic and prognostic tools for evaluating cardiovascular function is the exercise stress test. Exercise is associated with increased sympathetic and decreased parasympathetic activity and the period of recovery after maximum exercise is characterized by a combination of sympathetic withdrawal and parasympathetic reactivation, which are the two main arms of the ANS. Heart rate recovery after graded exercise is one of the commonly used techniques that reflects autonomic activity and predicts cardiovascular events and mortality, not only in cardiovascular system disorders, but also in various systemic disorders. In this article, the definition, applications and protocols of heart rate recovery and its value in various diseases, in addition to exercise physiology, the ANS and their relationship, will be discussed.     

Heart rate recovery: a practical clinical indicator of abnormal cardiac autonomic function

The autonomic nervous system (ANS) and cardiovascular function are intricately and closely related. One of the most frequently used diagnostic and prognostic tools for evaluating cardiovascular function is the exercise stress test. Exercise is associated with increased sympathetic and decreased parasympathetic activity and the period of recovery after maximum exercise is characterized by a combination of sympathetic withdrawal and parasympathetic reactivation, which are the two main arms of the ANS. Heart rate recovery after graded exercise is one of the commonly used techniques that reflects autonomic activity and predicts cardiovascular events and mortality, not only in cardiovascular system disorders, but also in various systemic disorders. In this article, the definition, applications and protocols of heart rate recovery and its value in various diseases, in addition to exercise physiology, the ANS and their relationship, will be discussed.     

Heart rate mediation of sex differences in pain tolerance in children

Despite evidence supporting the existence of important sex-related differences in pain, the mechanisms underpinning such differences are not well understood. The aim of this study is to examine the relationship between sex and pubertal differences in autonomic arousal and pain tolerance to laboratory pain stimuli in healthy children. We tested the following specific hypotheses: (1) females would have greater autonomic arousal and less pain tolerance than males, and (2) this sex difference in pain tolerance would be mediated by autonomic arousal. Participants were 244 healthy children (50.8% female, mean age 12.73+/-2.98 years, range 8-18 years). Separate 4-trial blocks of cutaneous pressure and thermal pain stimuli were presented in counterbalanced order. Heart rate (HR) was recorded during 2-3 min periods preceding each block and a 1-min period between trials. Results indicated lower tolerance in females for cutaneous pressure, but not thermal pain, compared to males. In addition, pre-trial HR was greater for females than males. Mediation analyses suggested that sex differences in pressure pain tolerance were accounted for by sex differences in pre-trial HR. There were also significant effects for puberty, but these did not vary by sex. Overall, early pubertal children had greater pre-trial HR and less pain tolerance than those in late puberty for both cutaneous pressure and thermal pain across sex. These results suggest that autonomic arousal may be a mediator of sex-related differences in pain responses in children.