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Repeated moderate heat exposure decreases resting sympathetic activity in humans
Author(s) -
Cui Jian,
Blaha Cheryl,
Sinoway Lawrence I.
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.997.1
Subject(s) - heart rate , medicine , blood pressure , sphygmomanometer , baroreflex , hemodynamics , repeated measures design , sympathetic nervous system , cardiorespiratory fitness , thermoregulation , anesthesia , cardiology , statistics , mathematics
Acute whole‐body heat stress evokes sympathetic activation. However, the chronic effects of repeated moderate heat exposure (RMHE) on muscle sympathetic nerve activity (MSNA) remains unclear. We performed the RMHE with 4 weeks (5 days/week) of warm baths (39–42 °C for 30 min) in 6 elder volunteers (5 M and 1 F, 59 ± 3 yrs, 177 ± 4 cm, 88 ± 10 kg, BMI 27.6 ± 2.3). Subjects were in the recumbent position in the bathtub with water up to their mid chest. Blood pressure (BP) and heart rate (HR) were monitored with an automated sphygmomanometer throughout each bath. The internal temperature (Tcore) was measured via an ingestible pill telemetry system during the 1st, 11th (i.e. day 15th), and last bath in each subject. Hemodynamic variables and MSNA were examined prior, 1 day post 4 weeks of RMHE and 1 week after end of RMHE in a laboratory at ~23 °C. During the baths, the maximal increase in Tcore was Δ0.9 ± 0.1 °C, the maximal increase in HR was Δ12 ± 2 beats/min, and the maximal drop in mean BP was Δ15 ± 2 mmHg. Under normothermic condition, the resting MSNA significantly decreased after RMHE (prior, post, post 1‐wk: 32.6 ± 2.5, 27.4 ± 2.4, 27.6 ± 2.2 bursts/min; P <0.001; one‐way repeated measures ANOVA). The MSNA burst incidence (i.e. bursts/100 heart beats) also decreased significantly ( P =0.002). The resting HR decreased in all subjects after RMHE (60.2 ± 1.6, 56.5 ± 2.1, 56.8 ± 1.8 beats/min, P <0.05), while supine BP was not significantly altered ( P >0.05). These data suggest that the RMHE evoked by warm bath is a simple and safe approach to decrease baseline sympathetic activity and HR. The mechanism(s) should be examined in future studies. Support or Funding Information AHA 15GRNT24480051 (JC) and P01 HL096570‐05 (LIS)