Heart Rate Changes In Response Research Articles

Dissociating the physiological components of unconscious emotional responses.

Conscious emotional processing is characterized by a coordinated set of responses across multiple physiological systems. Although emotional stimuli can evoke certain physiological responses even when they are suppressed from awareness, it is not known whether unconscious emotional responses comprise a similar constellation or are confined to specific systems. To compare physiological responses to emotional stimuli with and without awareness, we measured a range of responses while participants viewed positive, negative and neutral images that were accompanied by noise bursts to elicit startle reflexes. We measured four responses simultaneously – skin conductance and heart rate changes in response to the images themselves; and startle eye-blink and post-auricular reflexes in response to the noise bursts that occurred during image presentation. For half of the participants, the images were masked from awareness using continuous flash suppression. The aware group showed the expected pattern of response across physiological systems: emotional images (regardless of valence) evoked larger skin conductance responses (SCRs) and greater heart rate deceleration than neutral images, negative images enhanced eye-blink reflexes and positive images enhanced post-auricular reflexes. In contrast, we found a striking dissociation between measures for the unaware group: typical modulation of SCRs and post-auricular reflexes, but no modulation of heart rate deceleration or eye-blink reflexes. Our findings suggest that although some physiological systems respond to emotional stimuli presented outside of awareness, conscious emotional processing may be characterized by a broad and coordinated set of responses across systems.

Abstract P154: Hypertension in Obese African American Women is Not Caused by Increased Sympathetic Activity

African American (AA) women have the highest prevalence of hypertension and obesity in the United States. We tested the hypothesis that sympathetic activity contributes to hypertension in obese AA women, as we previously shown to be the case in Caucasians. We studied 42 obese women (16 whites, body mass index (BMI) 36± 4 kg/m 2 , 44% with diagnosis of hypertension (HTN) and 26 AA, BMI 35± 4 kg/m 2 , 46% HTN). Anti-HTN medications were discontinued for 2 weeks prior to the study day. All subjects underwent complete autonomic blockade with the ganglionic blockade trimethaphan at doses of 4 mg/min. Autonomic blockade was evaluated by the lack of heart rate changes in response to ~25 mm Hg increase in blood pressure produced by a bolus infusion of the alpha 1 adrenergic agonist, phenylephrine and the decrease in norepinephrine levels. Results: Plasma norepinephrine significantly decreased during trimethaphan infusion (from baseline 253±1107 to 61±29 pg/ml, trimethaphan). The decrease in mean arterial blood pressure (MAP) produced by trimethaphan was greater in obese HTN compared with normotensive (NTN) Caucasians (-27±10 vs. -15±8 mm Hg, P=0.016). In contrast, no difference in the decrease in MAP induced by trimethaphan was found between HTN and NTN obese AA women (-16±11 vs. -12±10, P=0.451, figure ). Heart rate increased similarly with trimethaphan between HTN and NTN caucasians (+9.1± 6 vs. 16± 9, P=0.109) and AA women (+22± 7 vs. 21±12 bpm, P=0.760). MAP remained elevated in HTN obese AA women during trimethaphan infusion (84±15 vs. 72±9.8 mm Hg in NTN AA, P=0.021). Conclusion: Sympathetic activity does not contribute to hypertension in AA women

ARMAX‐based Method Extends Knowledge of the Baroreflex

IntroductionThe arterial baroreceptor‐heart rate reflex (baroreflex) is a key mechanism in regulating the cardiovascular system, and alterations in baroreceptor function are seen in many disease states, including heart failure, obesity and hypertension. Recent studies have identified impairment of the baroreflex early in the clinical course of hypertension. We propose a new and simple method for analyzing these alterations in baroreceptor function. The method is validated to describe dynamic relationships in causal systems with feedback, and in addition to the traditional estimate of baroreflex sensitivity (BRS) it adds information on two new valuable components of the reflex. Firstly, the average time for the baroreflex to reach its maximal effect on heart rate (HR) following a change in blood pressure (BP), and secondly, the average maximal change in HR produced by the baroreflex. This study aims to validate the method against a traditional method of estimating BRS in both healthy animals and in a verified model of diet‐induced obesity and hypertension.Methods48‐hour data series of continuous BP and HR recordings were collected with telemetry and used for analysis. 16‐weeks‐old SD rats on standard chow (n=11) served as healthy controls, while a similar group of rats on a high‐fat, high‐fructose (HFHC) diet from 4 weeks of age (n=6) constituted the obese hypertension model. An Autoregressive–moving‐average model with exogenous inputs (ARMAX)‐based algorithm was applied to the data series and compared with the α‐coefficient.ResultsThe ARMAX‐based method matched the traditional method, and interestingly when comparing the obese hypertension group with controls (body weight 531±27 vs. 458±19 g, p<0.05; mean arterial pressure 119±3 vs. 102±1 mmHg, p<0.05) the same degree of attenuation in BRS of ~50 % could be observed in the obese hypertensive group compared with controls with both methods (ARMAX: −0.08±0.01 vs. −0.15±0.01 Δbpm/heartbeat, p<0.05; α‐coefficient: 0.51±0.07 vs. 0.89±0.07 ms/mmHg, p<0.05). The ARMAX‐based method additionally demonstrated the maximal change in HR following a BP change to be reduced by ~50 % in the obese hypertensive group compared with controls (1.3±0.2 vs. −2.6±0.2 Δbpm, p<0.05), while the time until the maximal change in HR was reached was similar between groups.ConclusionThe ARMAX‐based method confirms traditional methods and presents an unbiased method of characterizing HR changes in response to changes in BP. The method further contributes to our understanding of the reflex by providing information on time to maximal change in HR as well as the degree of maximal change in HR. The presented algorithm can potentially be applied to other species including humans.Support or Funding InformationPregraduate Research Scholarship from The Danish Council for Independent Research, Grant from Fru Ruth König Petersens Foundation, Helge Peetz and Verner Peetz and Hustrus Scholarship.

Cerebral Hemispheric Lateralization Associated with Hippocampal Sclerosis May Affect Interictal Cardiovascular Autonomic Functions in Temporal Lobe Epilepsy.

It is well established that the temporal lobe epilepsy (TLE) is linked to the autonomic nervous system dysfunctions. Seizures alter the function of different systems such as the respiratory, cardiovascular, gastrointestinal, and urogenital systems. The aim of this work was to evaluate the possible factors which may be involved in interictal cardiovascular autonomic function in temporal lobe epilepsy with complex partial seizures, and with particular attention to hippocampal sclerosis. The study was conducted in 30 patients with intractable temporal lobe epilepsy (19 with left hippocampal sclerosis, 11 with right hippocampal sclerosis). All subjects underwent four tests of cardiac autonomic function: heart rate changes in response to deep breathing, heart rate, and blood pressure variations throughout resting activity and during hand grip, mental stress, and orthostatic tests. Our results show that the right cerebral hemisphere predominantly modulates sympathetic activity, while the left cerebral hemisphere mainly modulates parasympathetic activity, which mediated tachycardia and excessive bradycardia counterregulation, both of which might be involved as a mechanism of sudden unexpected death in epilepsy patients (SUDEP).

The cognitive, affective and physiological impact of infant crying: a comparison of two laboratory methodologies

Objective: The present study investigated two experimental paradigms to explore whether individual differences in adult responses to crying were related to the method of presentation of the crying infant – namely, a video simulation or a life-like programmable doll. Background: The importance of understanding individual differences in caregiver responses to infant crying is well recognised, but assessment of caregiver responses presents considerable methodological challenges. Method: Participants were 106 female childless undergraduate students. Responses assessed included self-report measures of self-efficacy beliefs, feelings of empathy toward the crying infant, caregiver concern and irritation, and heart-rate reactivity. Participants were randomly allocated to exposure to either a life-like crying doll or to a video of a crying infant. Results: Compared to those in the video condition, participants exposed to the crying doll showed lower self-efficacy beliefs, experienced greater feelings of irritation and a greater change in heart-rate responses, p < .05, but no differences in feelings of concern or empathy towards the infant. Conclusion: Findings provide preliminary evidence that the crying doll paradigm may be a more ecologically valid approach to exploring the impact of crying on adults; however, methodological considerations related to individual differences in physiological responses need further clarification in future research.

Alterations in Heart Rate Responses and the Effect of Supine and Sitting Recovery Positions on Heart Rate Recovery and Rate Pressure Product Following Submaximal Exercise Test in Patients Undergoing Coronary Artery Bypass Graft Surgery

Objectives: The aim of the study was to determine a) Whether there is any change in heart rate responses following submaximal exercise test in patients undergoing CABG b) Is there any effect of recovery position on heart rate recovery and myocardial oxygen consumption following submaximal exercise test in patients undergoing CABG surgery??? Background: The imbalance in the autonomic cardiovascular control has been shown to increase the risk for adverse cardiac events and sudden cardiac death, which has been observed following CABG. Thus, it is important to clinically assess the status of the autonomic nervous system which is a major determinant of cardiovascular health and prognosis. Interventions: The patients were randomly assigned to the two groups: group A and group B. Two six minute walk tests were performed each on the day at 9 a.m. and 1 p.m.; before surgery and following CABG on fourth and seventh postoperative day and the dependent variables were measured. Results: The Peak Heart Rate improved highly significantly from 93.65 + 8.78 per minute on day 0 to 128.24 + 11.94 per minute on day 7 (p<0.0001). The Chronotropic Response Index improved significantly (p<0.0001) from 0.24 + 0.07 to 0.53 + 0.15 from day 0 to day 7. The Six Minute Walk Distance also improved significantly from day 0 to day 7 (p=0.000) from 299.93 + 66.63 m to 380.65 + 109.68 m. The results showed that the HRR increased from 23.06 + 10.43 per minute at first minute to 29.00 + 12.19 per minute at fifth minute, while RPP reduced significantly (p=0.000) from 12005.31 + 2681.83 mmHg/min at first minute to 10232.19 + 1783.22 mmHg/min at fifth minute of recovery. The results show the moderately significant (p=0.00) correlation between the HRR and the peak heart rate, and the HRR, chronotropic response index. Conclusion: The study concluded that there is improvement in the heart rate measures and functional capacity following CABG. The heart rate recovery was also found to vary with different recovery positions and was better in the supine lying position, when compared to sitting position.

Listen to your heart: the cultural shaping of interoceptive awareness and accuracy.

West African cultural contexts foster higher levels of attention to the bodily signals compared with the European American contexts. Interoception, or the processing of signals from the body, is a key component of emotional reactivity. Interoceptive awareness (i.e., the self-reported tendency to attend to physiological changes) and accuracy (i.e., the ability to accurately detect physiological changes) are distinct aspects of interoception. Does the West African cultural emphasis on interoceptive awareness affect individuals' abilities to accurately perceive physiological changes in response to emotional stimuli? West African and European American young adults watched a fear-inducing film clip and continuously rated their perception of heart rate changes in response to the clip. Actual heart rates were also recorded continuously. Cross-correlations were calculated between measures of perceived and actual heart rate. Although average levels of coherence between these measures were low across groups, West Africans showed higher levels of interoceptive awareness, but lower levels of interoceptive accuracy than European Americans. These results suggest that cultural scripts of attending to the body may affect coupling between actual and perceived physiological reactivity in the context of emotions. These results have implications for studying cultural shaping of somatic presentation of mood and anxiety disorders.

The effect of talking about psychological trauma with a significant other on heart rate reactivity in individuals with posttraumatic stress disorder

Individuals with posttraumatic stress disorder (PTSD) commonly make efforts to avoid trauma-oriented conversations with their significant others, which may interfere with the natural recovery process. Trauma-oriented conversations can be experienced as physiologically arousing, depending on the intensity of PTSD symptoms and perceptions of social support. In the current investigation, changes in heart rate responses to a trauma-oriented social interaction with a significant other were assessed. Perceived supportive and unsupportive or negative social interactions were examined as moderators of the association between heart rate changes to this context and intensity of PTSD symptoms. A total of 46 individuals with PTSD completed diagnostic interviews and self-report measures of symptoms and perceived supportive and negative social interactions during a trauma-oriented social interaction with a significant other. Heart rate was continuously measured during this interaction. Results showed that engagement in a trauma-oriented social interaction was predictive of elevations in heart rate that positively correlated with intensity of PTSD symptoms. The moderation hypothesis was partially supported. In addition, perceived negative social interactions positively correlated with elevations in heart rate. These findings can inform social intervention efforts for individuals with PTSD.

Ketanserin improves cardiac performance after myocardial infarction in spontaneously hypertensive rats partially through restoration of baroreflex function

Baroreflex dysfunction is associated with a higher rate of sudden death after myocardial infarction (MI). Ketanserin enhances baroreflex function in rats. The present work was designed to examine whether ketanserin improves the post-MI cardiac function and to explore the possible mechanism involved. Spontaneously hypertensive rats (SHR) were treated with ketanserin (0.3 mg·kg(-1)·d(-1)). Two weeks later, blood pressure and baroreflex function were measured, followed by a ligation of the left coronary artery. The expressions of vesicular acetylcholine transporter (VAChT) and α7 nicotinic acetylcholine receptor (α7-nAChR) in ischemic myocardium, angiogenesis, cardiac function, and left ventricular (LV) remodeling were evaluated subsequently. Ketanserin significantly improved baroreflex sensitivity (0.62±0.21 vs 0.34±0.12 ms/mmHg, P<0.01) and vagal tonic activity (heart rate changes in response to atropine, 54.8±16.2 vs 37.6±13.4 bpm, P<0.01) without affecting the blood pressure or basic heart rate in SHR. Treatment of SHR with ketanserin prominently improved cardiac function and alleviated LV remodeling, as reflected by increases in the ejection fraction, fractional shortening, and LV systolic pressure as well as decreases in LV internal diameter and LV relative weight. The capillary density, vascular endothelial growth factor expression, and blood flow in the ischemic myocardium were significantly higher in the ketanserin-treated group. In addition, ketanserin markedly increased the expression of VAChT and α7-nAChR in ischemic myocardium. Ketanserin improved post-MI cardiac function and angiogenesis in ischemic myocardium. The findings provide a mechanistic basis for restoring baroreflex function using ketanserin in the treatment of MI.

The effect of heart rate on the heart rate variability response to autonomic interventions

Heart rate variability (HRV), the beat-to-beat variation in either heart rate (HR) or heart period (R-R interval), has become a popular clinical and investigational tool to quantify cardiac autonomic regulation. However, it is not widely appreciated that, due to the inverse curvilinear relationship between HR and R-R interval, HR per se can profoundly influence HRV. It is, therefore, critical to correct HRV for the prevailing HR particularly, as HR changes in response to autonomic neural activation or inhibition. The present study evaluated the effects of HR on the HRV response to autonomic interventions that either increased (submaximal exercise, n = 25 or baroreceptor reflex activation, n = 20) or reduced (pharmacological blockade: β-adrenergic receptor, muscarinic receptor antagonists alone and in combination, n = 25, or bilateral cervical vagotomy, n = 9) autonomic neural activity in a canine model. Both total (RR interval standard deviation, RRSD) and the high frequency (HF) variability (HF, 0.24–1.04 Hz) were determined before and in response to an autonomic intervention. All interventions that reduced or abolished cardiac parasympathetic regulation provoked large reductions in HRV even after HR correction [division by mean RRsec or (mean RRsec)2 for RRSD and HF, respectively] while interventions that reduced HR yielded mixed results. β-adrenergic receptor blockade reduced HRV (RRSD but not HF) while both RRSD and HF increased in response to increases in arterial blood (baroreceptor reflex activation) even after HR correction. These data suggest that the physiological basis for HRV is revealed after correction for prevailing HR and, further, that cardiac parasympathetic activity is responsible for a major portion of the HRV in the dog.

Baroreflex Sensitivity in Relation to Clinical Characteristics in Subject Aged 40 to 80 Years

Baroreflex function measured as baroreflex sensitivity (BRS) mirrors an integrated capacity of the autonomic nervous system. We aimed to assess the relationship between measures of BRS and age and relevant clinical characteristics. 80 subjects participating in the Copenhagen City Heart study (43 women) with a mean age of 59 ± 11 years (range 41-79 years) were included. Baroreceptor activity was quantified through the Valsalva manoeuvre (VM) and as a spontaneous function. BRS was tested against age, gender, smoking status, body size and predicted risk of coronary heart disease based on the Framingham score. BRS was found to decline with age, but this change disappeared when correcting for the age related increase in systolic blood pressure. We found that the VM-derived indices of sympathetic vascular control declined with age as did the vagally controlled heart rate changes in response to deep breathing and VM. We could not demonstrate any correlation between BRS, smoking status, and body size when adjusting for age and gender, whereas spontaneous BRS was reduced with increasing Framingham risk score. Principal component analysis revealed three component explaining 69% of the total variance in our population comprising one component reflecting the sympathetic activity, the parasympathetic system, and the integrated spontaneous BRS, respectively. The parasympathetic component was the only one correlating with clinical characteristics of declining age, smoking habits, systolic blood pressure and Framingham score. It is concluded that the parasympathetic and sympathetic parts of the baroreflex arch behave differently with respect to aging and cardiovascular risk factors. The most prominent changes are seen in cardiovagal control whereas the effects of age related changes in sympathetic vascular control are less noticeable. Our study supports the use of the cardiovagal part of the baroreflex arch as an indicator of cardiovascular risk.

Restrained rats and the observer effect in physiology

Restrained rats and the observer effect in physiology

Heart rate and hemocyte number as stress indicators in disturbed hibernating vineyard snails, Helix pomatia

In humans and other vertebrates, mental or physical stressors may trigger a variety of symptoms generally referred to as the fight/flight response (Cannon 1929). The processes also include variability of the heart frequency as well as leukocytosis. We monitored both body responses in disturbed hibernating vineyard snails, H. pomatia, to obtain information on the stress sensitivity of these “sleeping” invertebrates. The first mild stressor, a 100meter transport of hibernating snails from the cold room to the laboratory, caused cardiac arrhythmia in the animals. This reaction could have been provoked by mechanical disturbances and/or by raising the body temperature to room temperature. But a change in the ambient temperature did not trigger an abnormal heart rhythm. Different from this observation, we recorded instant heart rate changes in response to knocking on the shell and a very irregular heartbeat occurred when a hole was punched in the shell. With a short time delay upon damaging the shell, a large increase in the number of circulating cells also occurred. This was not observed after knocking on the shell or when snails were adapted to different temperatures for each 48h. Thus, hibernating snails sense environmental variations which cause an immediate change of the heart frequency and an elevated stimulus level initiates in addition leukocytosis which occurs at a post-stimulus latency. This disparity could indicate the activity of two different stress regulation pathways.Furthermore, the assays demonstrate an increasing linear relation between rising temperature and frequency of heart pulsations (y=1.01x−2.1); but the results do not indicate a correlation between heartbeat frequency and the number of cells in circulation. Consequently, neither temperature nor heart frequency seems to influence the number of circulating cells in hibernating H. pomatia.

A Physiological Model for Autonomic Heart Rate Regulation in Human Endotoxemia

The systemic inflammatory response syndrome often accompanies critical illnesses and can be an important cause of morbidity and mortality. Marked abnormalities in cardiovascular function accompany acute illnesses manifested as sustained tachyarrhythmias, which are but one component of systemic dysregulation. The realization that cardiac pacemaker activity is under control of the autonomic nervous system has promoted the analysis of heart rate (HR) variation for assessing autonomic activities. In acute illnesses, autonomic imbalance manifesting in part as parasympathetic attenuation is associated with increased morbidity in patients who manifest systemic inflammatory response syndrome phenotype. Driven by the premise that biological phenotypes emerge as the outcome of the coordinated action of network elements across the host, a multiscale model of human endotoxemia, as a prototype model of systemic inflammation in humans, is developed that quantifies critical aspects of the complex relationship between inflammation and autonomic HR regulation. In the present study, changes in HR response to acute injury, phenotypically expressed as tachycardia, are simulated as a result of autonomic imbalance that reflects sympathetic activity excess and parasympathetic attenuation. The proposed model assesses both the anti-inflammatory and cardiovascular effects of antecedent stresses upon the systemic inflammatory manifestations of human endotoxemia as well as a series of nonlinear inflammatory relevant scenarios. Such a modeling approach provides a comprehensive conceptual framework linking inflammation and physiological complexity via a multiscale model that may advance the translational potential of systems modeling in clinical research.

Maturation of the Cardiac Response to Sound in High-Risk Preterm Infants

Noise is considered a potential source of stress in the neonatal intensive care unit (NICU); yet, it is unknown how preterm infants habituate to sound in the NICU. Heart rate responses to sound were evaluated in 12 preterm infants from 32 weeks' gestational age through hospital discharge. Heart rate response changes to auditory stimuli were recorded for 10 habituation and 10 dishabituation trials. Significant heart rate deceleration began to appear by 34 weeks postconceptional age. With weeks 32 to 38 combined, a significant response was noted for the novel response. Responses differed significantly for weeks 34, 35, and 36. Infants at 36 weeks had a significant heart rate response at T17 to T20, suggesting anticipation of a third stimulus. Infants with higher Apgar 5 scores had smaller heart rate responses. Findings suggest that preterm infants, especially those with lower Apgar scores, may be vulnerable to larger heart rate changes in response to sound and may require additional consideration.

Cardiac sympatho-excitatory action of PVN-spinal oxytocin neurones

A significant proportion of the spinally projecting neurones in the paraventricular nucleus are immunoreactive for oxytocin. Some of these oxytocin neurones terminate on sympathetic preganglionic neurones in the upper thoracic spinal cord, a region from which cardiac sympathetic neurones originate. No studies have so far identified a cardiac action of the supraspinal oxytocin neurones. The present study was designed to test the hypothesis that these oxytocin neurones excite spinal cardiac sympathetic neurones. This was done by measuring heart rate changes in response to intrathecal oxytocin and a selective agonist, and to stimulation of paraventricular neurones before and during blockade of spinal sites with selective antagonists. Rats were anaesthetised with chloralose and urethane (50 mg and 650 mg/kg) and recordings were made of heart rate and blood pressure. Drugs in a volume of 10 µl were applied to the upper thoracic spinal cord via a catheter placed intrathecally with its tip at T2. The paraventricular nucleus was explored with a glass micropipette, placed stereotaxically, and filled with d, l-homocysteic acid (DLH, 200 mM) for exciting neurones and pontamine sky blue for marking the position. Oxytocin (0.002 mM) applied to the spinal cord elicited increases in heart rate (26 ± 5 beats per minute). This was mimicked by a highly selective oxytocin agonist. These heart rate increases were blocked selectively by two different oxytocin antagonists but unaffected by a V 1a vasopressin antagonist. Excitation of sites in dorsal and medial parvocellular sub-nuclei of the paraventricular nucleus elicited increases in heart rate (36 ± 3 bpm) which were significantly reduced by oxytocin antagonists but not affected by V 1a antagonist. Also these induced increases in heart rate were unaffected by vagotomy or i.v. atropine but were abolished by i.v. esmolol. It is concluded that there is a population of paraventricular-spinal oxytocin neurones that excite cardiac sympathetic preganglionic neurones controlling heart rate.

Developmental change in fetal response to repeated low‐intensity sound

The aim of this study was to investigate developmental changes in heart rate response to repeated low-intensity (85 dB) sound stimulation in fetuses between 32 and 37 weeks of gestation. We measured amplitude changes in heart rate as our index of fetal response. At 35 to 37 weeks of gestation, the majority of fetuses showed a deceleratory response at the first trial. Amplitude decreased with further trials using the same stimulus before recovering when exposed to another type of stimulation. In contrast, responses in fetuses at 32 to 34 weeks of gestation were variable across trials and there was no recovery with exposure to another type of stimulation. Our results suggest that fetal habituation of cardiac response changes with developmental age.

Novel technology for the provision of power to implantable physiological devices

We report the development of a novel technology that enables the wireless transmission of sufficient amounts of power to implantable physiological devices. The system involves a primary unit generating the magnetic field and a secondary pickup unit deriving power from the magnetic field and a power conditioner. The inductively coupled system was able to supply a minimum of 20 mW at all locations and pickup orientations across a rat cage, although much higher power of up to 10 W could be achieved. We hypothesized that it would be possible to use this technology to record a high-fidelity ECG signal in a conscious rat. A device was constructed in which power was utilized to recharge a battery contained within a telemetry device recording ECG signal sampled at 2,000 Hz in conscious rats (200-350 g) living in their home cage. Attributes of the ECG signal (QT, QRS, and PR interval) could be obtained with a high degree of accuracy (<1 ms). ECG and heart rate changes in response to treatment with the beta blocker propranolol and the proarrhythmic alkaloid aconitine were measured. Transmitters were implanted for up to 4 mo, and the characteristic circadian variation in heart rate was recorded. Such technology allows potentially lifetime monitoring without the need for implant refurbishment. The ability to provide suitable power levels to implanted devices without concern to the orientation of the device and without causing heating provides the basis for the development of new devices to record or influence physiological signals in animals or humans over significantly longer time periods than can currently be accommodated.

Do former preterm infants remember and respond to neonatal intensive care unit noise?

Background Previous studies have shown that 4-month-old infants have a decrease in heart rate, a component of the orienting reflex, in response to interesting auditory stimuli and an increase in heart rate to aversive auditory stimuli. Objective To compare the heart rate responses of former preterm and term infants at 4–5 months corrected age to a recording of NICU noises. Methods 13 former preterm infants and 17 full-term infants were presented NICU noise and another noise of similar level and frequency content in random order. Heart rate 10 s prior to the stimulus and for 20 s during the stimulus was analyzed. Group differences in second by second heart rate changes in response to the two noise stimuli were compared by analysis of covariance. Results Both the preterm and term newborns responded similarly to the NICU noise and the control noise. The preterm infants did not alter their heart rate in response to either stimulus. In contrast, the term infants displayed an orienting response to the second stimulus presented regardless of whether it was the NICU or control noise. Conclusions Former preterm infants at 4–5 months corrected age have reduced responsiveness to auditory stimulation in comparison to 4- to 5-month-old term infants. Furthermore, they did not respond to the NICU noise as an aversive stimulus.

Identification of anaerobic threshold using heart rate response during dynamic exercise

The objective of the present study was to characterize the heart rate (HR) patterns of healthy males using the autoregressive integrated moving average (ARIMA) model over a power range assumed to correspond to the anaerobic threshold (AT) during discontinuous dynamic exercise tests (DDET). Nine young (22.3 +/- 1.57 years) and 9 middle-aged (MA) volunteers (43.2 +/- 3.53 years) performed three DDET on a cycle ergometer. Protocol I: DDET in steps with progressive power increases of 10 W; protocol II: DDET using the same power values as protocol 1, but applied randomly; protocol III: continuous dynamic exercise protocol with ventilatory and metabolic measurements (10 W/min ramp power), for the measurement of ventilatory AT. HR was recorded and stored beat-to-beat during DDET, and analyzed using the ARIMA (protocols I and II). The DDET experiments showed that the median physical exercise workloads at which AT occurred were similar for protocols I and II, i.e., AT occurred between 75 W (116 bpm) and 85 W (116 bpm) for the young group and between 60 W (96 bpm) and 75 W (107 bpm) for group MA in protocols I and II, respectively; in two MA volunteers the ventilatory AT occurred at 90 W (108 bpm) and 95 W (111 bpm). This corresponded to the same power values of the positive trend in HR responses. The change in HR response using ARIMA models at submaximal dynamic exercise powers proved to be a promising approach for detecting AT in normal volunteers.