Biomedical subjects

J J Sollers

Publications and source records attributed to J J Sollers.

11 recordsLinked to original sources

PubMed2001

Exogenous cortisol exerts effects on the startle reflex independent of emotional modulation.

Exogenous cortisol's modulation of the acoustic startle reflex (ASR) was tested alone and during exposure to affectively valenced photographs in healthy men and women. During nonmodulated startle, oral hydrocortisone had a biphasic dose effect, with 5 mg increasing and 20 mg decreasing, eyeblink reflex magnitude compared to placebo. During emotion modulation, 20 mg of hydrocortisone reduced reflex magnitude without affecting the usual pattern of modulation across positive, neutral, and negatively affective slides. Gender differences were not found in either relationship. These findings illustrate dose-dependent effects of cortisol on the startle pathway independent of emotional state and consistent across genders.

Adult↗

PubMed2001

Heart rate and heart rate variability changes in the intracarotid sodium amobarbital test.

PURPOSE: Changes in heart rate and heart rate variability have been found in prior studies performed during the intracarotid sodium amobarbital (ISA) test. However, these results are not entirely consistent with current models of differential cerebral involvement in the modulation of the heart. This study was designed to re-investigate this topic with a larger N than has heretofore been used. METHODS: The electrocardiogram was recorded during left and right ISAs in 73 subjects. Raw heart rate and heart rate variability were calculated. RESULTS: Raw heart rate increased during inactivation of either hemisphere, but more so for the right hemisphere. Heart rate variability changes consistent with decreasing parasympathetic tone also were found to occur during either ISA, but to a significant degree, only during right ISA. CONCLUSIONS: The right hemisphere appears to have a greater role in cerebral regulation of cardiac function, perhaps by virtue of the modification of parasympathetic effects.

Adolescent↗

PubMed2001

New ambulatory impedance cardiograph validated against the Minnesota Impedance Cardiograph.

The validity and reliability of a new ambulatory impedance cardiograph (AZCG) was tested against the Minnesota Impedance Cardiograph (ZCG) during rest, orthostasis, and mental stress. Impedance cardiography allows noninvasive assessment of stroke volume, cardiac output, and systolic time intervals. A reliable ambulatory device would allow studies outside the lab. The devices were compared at two sites in healthy subjects. In both studies, the AZCG tracked changes across conditions closely with the ZCG (all Period x Device interactions were nonsignificant). Pearson rs, were .65 to .93, random intraclass correlation coefficients ranged from .80 to .98, indicating high degrees of shared measurement variance, and Cronbach's alpha indicated very good internal reliabilities (.91 to .99). Relative to the ZCG, the new AZCG appears to provide valid and reliable estimates of cardiac function at rest and during behavioral challenges in the lab.

Adult↗

PubMed2000

Autonomic changes during orthostasis: a time-frequency analysis.

The transition between sitting and standing represents a period of dynamic changes in cardiac autonomic control. Previous research using heart rate (HR) has suggested a biphasic HR response from sitting to standing with an initial increase in HR followed by an HR decrease before stabilizing at a level above the sitting level. These HR changes have been interpreted as mediated by sympathetic nervous system (SNS) activity. However, more direct measures of cardiac autonomic control have not been investigated in an active orthostasis paradigm. This is due in part to the requirement of stationarity for traditional spectral analytic techniques. In the present study, time-frequency analysis was used to assess the relative contributions of sympathetic and parasympathetic nervous system activity to the cardiac autonomic control during the transition of orthostasis. We examined the heart rate time series during the transition between sitting and standing, and the 60 s prior and the 60 s following the transition. The high frequency component of the HR spectra (an index of parasympathetic activity) decreased sharply at the point of transition and remained depressed relative to the low frequency component (an index of sympathetic activity). These results suggest that time-frequency analysis may be a useful technique to examine non-stationary time series. Furthermore, the transition of orthostasis may be mediated more via parasympathetic activity than by sympathetic activity.

Adult↗

PubMed2000

A system for the ambulatory recording and analysis of nonlinear heart rate dynamics.

The study of cardiac dynamics is a topic of great clinic and experimental concern. However, the ability to apply methods from the emerging field of nonlinear dynamics to cardiac time series has been limited by the demand for large amounts of relatively artifact-free data. Both the ability to collect such data and the capacity to analysis such large data sets represents limits. In the present paper we describe a system that allows for the collection of large amounts of high quality data and the analysis of large data sets. The recording system consists of a miniature, single-module electrocardiogram-recording device. This module consists of an integrated three-electrode device that is attached to the chest of the subject. A low power 8-bit micro-controller detects the R-spike and stores the time between R-spikes in milliseconds on a 512 KB EEPROM. This system can record continuously for over four days. The output of this system is down-loaded to a PC and the RR intervals fed to a suite of digital signal processing programs. Among other things, estimates of Approximate Entropy and Poincaire plots are generated. This system will expand the capability of researchers and clinicians to investigate nonlinear cardiac dynamics in ambulatory subjects.

Heart Rate↗

PubMed2000

Autonomic control of the heart during circular breathing.

The analysis of heart rate variability (HRV) has become an increasingly popular method for probing the autonomic nervous system (ANS). A number of specific periodicities have been identified in the spectra of cardiac time series. One major mechanism involved in a number of these periodicities is respiratory modulation of neural traffic to the heart. One respiratory maneuver that has never been investigated is circular breathing. This technique is employed by wind musicians to produce an uninterrupted stream of sound without pauses for breathing. The current study examined the effects of circular breathing on ANS control of the heart in a highly proficient professional musician. Results indicated that circular breathing both with and without producing a sound was associated with altered autonomic control of the heart. Specifically, circular breathing was associated with increases in heart rate and decreases in high frequency HRV. This high frequency HRV has been most closely linked with respiratory sinus arrhythmia and respiratory modulation of vagal neural traffic. We conclude that the examination of novel breathing maneuvers may help to illuminate the role of respiratory modulation of HRV.

Autonomic Nervous System↗

PubMed1998

Heart period variability and depressive symptoms: gender differences.

BACKGROUND: Deceased heart period variability has been associated with cardiac events and depressive symptoms; however, the results of studies are not unequivocal. We hypothesize that gender differences in the various study samples may have contributed to the lack of uniformity of findings. METHODS: Time and frequency domain measures of heart period variability during a 5-min resting baseline were examined in 15 depressed (8 female) and 11 nondepressed (6 female) college students. RESULTS: Both time and frequency domain measures indicated an interaction between gender and depressive symptoms, such that depressed male subjects showed less heart period variability, whereas depressed female subjects showed more heart period variability compared to their nondepressed counterparts. CONCLUSIONS: These results suggest that future studies investigating the relationship between heart period variability and depressive symptoms examine gender differences.

Adult↗

PubMed1997

Effects of foreperiod duration on reflexive and voluntary responses to intense noise bursts.

The question of whether a common mechanism underlies the facilitation of voluntary and reflexive reactions by a warning stimulus was investigated in two experiments. In both studies, the foreperiod preceding an intense noise burst was manipulated within and between blocks of trials. Previous reaction time experiments have shown that individuals respond fastest at the shortest foreperiod for between-block manipulations and fastest at the longest foreperiod when foreperiod duration is varied unpredictably from trial to trial. In the present research, this pattern was found for voluntary hand-grip responses, but acoustic startle blinks were facilitated at long foreperiods for both within- and between-block manipulations. Invariance of the trisynaptic postauricular reflex across foreperiod conditions was evidence against any general activation of low-level motor pathways by warning stimuli. Analyses of nonreflexive lid movements subsequent to startle blink suggested that inhibition of spontaneous blinking during the foreperiod may have contributed to the unexpected divergence between voluntary reactions and eyeblink reflexes.

Adolescent↗

PubMed1997

Heart rate variability during exercise in the horse.

High heart rate variability (HRV) has been associated with more efficient autonomic control, allowing more responsivity and sensitivity to changing environmental demands. Previous results from spectral analysis of interbeat intervals of equine heart rate (HR) indicated increased HRV, reflecting more effective vagal control of the heart. This study focuses on characterizing equine HR and HRV during increasing then decreasing physical demand. A non-invasive ambulatory monitoring system continuously records HR and HRV as horses exercise on a high speed equine treadmill at increasing then decreasing workloads. After a 5 minute baseline, the horses walk, then trot, then canter or trot fast, return to the slower trot, then walk, and then remain quiet for a 5 minute recovery period. Results indicate a decrease of HRV and large individual differences in parasympathetic activity during exercise. Resulting patterns of HR fluctuation indicate a nonlinear dynamical approach may describe the task responses more completely than the more traditional models.

Animals↗

PubMed1997

Thermoregulation and cardiac variability: a time-frequency analysis.

High heart rate variability (HRV) has been associated with more efficient autonomic control, allowing more responsivity and sensitivity to changing environmental demands. A number of specific periodicities have been identified in the spectra of cardiac time series. A high frequency component related to respiratory sinus arrhythmia, a low frequency component related to blood pressure variability, and a very low frequency component thought to reflect thermoregulation have been reported in the literature. However, the source of the very low frequency component has not been extensively investigated in humans using non-invasive methods and analytic techniques that do not rely upon stationarity. We investigated HRV in response to both hot and cold thermal challenge in healthy adults using time-frequency analysis. This analytic technique does not rely upon signal stationarity. The results suggest that very low frequency power may reflect thermoregulation to ambient temperature changes. Implications for prediction of cardiac events are discussed.

Adult↗

PubMed1997

Heart rate variability in the horse by ambulatory monitoring.

Using a microprocessor controlled Ambulatory Monitoring System (AMS) developed by one of us (LvD), we have been studying the changes in and control of heart rate in the resting horse. The system provides us with InterBeat Intervals (IBI in milliseconds), motion sensing, and a time domain measure (mean successive differences: MSD) of heart rate variability for periods up to 72 hours. Thoracic impedance is also available but parameters for the equine chest are not currently available. The system is completely noninvasive, small, and carried on a surcingle worn by the subject. The equine subject is confined to a stall in our teaching hospital but not otherwise restrained. Recording is virtually unobtrusive. Ten horses (judged to be clinically normal) were used in this preliminary study. After collection, the data were "offloaded" to a laptop computer for additional analysis. The electrocardiogram could be recorded on each of the ten animals. Complete data, suitable for spectral analysis, were obtained from four of the animals. Spectral estimates were calculated on periods of varying lengths (3-5 minutes) with more stable spectral estimates associated with longer recording periods. Results indicated the preponderance of parasympathetic control in equid heart rate. These results provide support for the utility of this method for the study of heart rate variability in the freely behaving horse.

Animals↗