Changes in Short-Term and Ultra-Short Term Heart Rate, Respiratory Rate, and Time-Domain Heart Rate Variability Parameters during Sympathetic Nervous System Activity Stimulation in Elite Modern Pentathlonists—A Pilot Study

Monitoring of markers reflecting cardiac autonomic activity before and during stressful situations may be useful for identifying the physiological state of an athlete and may have medical or performance implications. The study aimed to determine group and individual changes in short-term (5 min) and ultra-short-term (1 min) heart rate (HR), respiratory rate (RespRate), and time-domain heart rate variability (HRV) parameters during sympathetic nervous system activity (SNSa) stimulation among professional endurance athletes. Electrocardiographic recordings were performed in stable measurement conditions (Baseline) and during SNSa stimulation via isometric handgrip in 12 elite modern pentathlonists. Significant increases in short-term HR and decreases in time-domain HRV parameters with no changes in RespRate were observed during SNSa stimulation. Significant differences were observed between Baseline (all minutes) and the last (i.e., 5th) minute of SNSa stimulation for ultra-short-term parameters. Analysis of intra-individual changes revealed some heterogeneity in responses. The study provides baseline responses of HR, RespRate, and time-domain HRV parameters to SNSa stimulation among elite pentathlonists, which may be useful for identifying abnormal responses among fatigued or injured (e.g., concussed) athletes. More attention to individual analysis seems to be necessary when assessing physiological responses to sympathetic stimuli in professional endurance athletes.

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Changes in the sympathetic nervous system induced by 42 days of head-down bed rest

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1998.274.6.h1875 ◽

1998 ◽

Vol 274 (6) ◽

pp. H1875-H1884 ◽

Cited By ~ 14

Author(s):

Dominique Sigaudo ◽

Jacques-Olivier Fortrat ◽

Anne-Marie Allevard ◽

Alain Maillet ◽

Jean-Marie Cottet-Emard ◽

...

Keyword(s):

Heart Rate ◽

Heart Rate Variability ◽

Nervous System ◽

Sympathetic Nervous System ◽

Baroreflex Sensitivity ◽

Bed Rest ◽

Urinary Catecholamines ◽

System Activity ◽

Nervous System Activity ◽

Sympathetic Nervous

Changes in autonomic nervous system activity could be linked to the orthostatic intolerance (OI) that individuals suffer after a spaceflight or head-down bed rest (HDBR). We examined this possibility by assessing the sympathetic nervous system activity during 42 days of HDBR in seven healthy men. Heart rate variability was studied with the use of power spectral analysis, which provided indicators of the sympathetic (SNSi) and parasympathetic (PNSi) nervous system influences on the heart. Urinary catecholamines and the spontaneous baroreflex sensitivity were measured. Urinary catecholamines decreased by 21.3%, showing a decrease in SNSi. Heart rate variability was greatly reduced during 42 days of HDBR with a drop in PNSi but with no significant changes in SNSi. The baroreflex sensitivity was greatly reduced (30.7%) on day 42 of HDBR. These results suggest a dissociation between the catecholamine response and the SNSi of the heart rate. This dissociation could be the consequence of an increase in β-adrenergic receptor density and/or activity induced by a decrease in catecholamines during HDBR. The subjects who suffered from OI also had a greater sympathetic response and much lower baroreflex sensitivity when supine than those who finished the stand test. However, the mean response of all subjects indicated that the sympathetic activity (catecholamine excretion) was probably slightly inhibited during HDBR and could contribute to OI.

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Short-term fluoxetine treatment enhances baroreflex control of sympathetic nervous system activity after hindlimb unloading

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00223.2002 ◽

2004 ◽

Vol 286 (3) ◽

pp. R584-R590 ◽

Cited By ~ 16

Author(s):

Julia A. Moffitt ◽

Alan Kim Johnson

Keyword(s):

Nervous System ◽

Sympathetic Nervous System ◽

Orthostatic Intolerance ◽

Hindlimb Unloading ◽

Sympathetic Nervous System Activity ◽

Short Term ◽

Baroreflex Control ◽

System Activity ◽

Nervous System Activity ◽

Sympathetic Nervous

Data in humans indicate that individuals with orthostatic hypotension that are refractory to other traditional forms of therapy are responsive to selective serotonin reuptake inhibitor (SSRI) treatment. We tested the hypothesis that SSRI administration would help correct the attenuated baroreflex control of sympathetic nervous system activity in the hindlimb-unloaded (HU) rat model of cardiovascular deconditioning. An initial study was conducted to determine the time course of effects of fluoxetine (Flu) administration on baroreflex control of lumbar sympathetic nerve activity (LSNA) in conscious, chronically instrumented rats. Animals received either vehicle (Veh, sterile water) or 10 mg/kg Flu for 1, 4, or 16 days of treatment. Data indicate that while 1-day and 16-day Flu administration did not affect baroreflex function, baroreflex control of LSNA was enhanced after 4-day (short term) Flu administration. HU rats were then treated with Flu for 4 days and compared with HU rats receiving Veh and to casted control rats maintained in the normal posture that received either Veh or short-term Flu treatment. Similar to pilot data, short-term Flu treatment enhanced baroreflex control of LSNA in both HU rats and control rats. These data taken together indicate that baroreflex control of sympathetic nervous system activity is a possible mechanism responsible for the successful treatment of orthostatic intolerance with Flu.

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