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Mild Whole Body Heating Decreases Muscle Sympathetic Nerve Activity in Middle Aged and Older Individuals
Author(s) -
Cui Jian,
Gao Zhaohui,
Blaha Cheryl,
Sinoway Lawrence I.
Publication year - 2017
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.31.1_supplement.1040.1
Subject(s) - medicine , sweat , heart rate , thermoregulation , blood pressure , heat stress , hyperthermia , microneurography , skin temperature , forearm , endocrinology , cardiology , anesthesia , baroreflex , zoology , anatomy , biology , biomedical engineering
A number of reports suggest that whole body heat stress (i.e. increase in core temperature (Tcore) > 0.5 °C) induces a significant increase in muscle sympathetic nerve activity (MSNA) in young and older individuals. However, the effects of mild whole body heating (MWBH) on MSNA have not been specifically examined. A prior report from this laboratory suggests that MSNA is lower in the summer than it is in the winter. In this study, we hypothesized that MWBH would decrease the resting MSNA in middle aged and older individuals. MSNA from a peroneal nerve, ECG and heart rate (HR), blood pressure (BP), Tcore with telemetry temperature pill, mean skin temperature (Tsk), forearm skin blood flow (SkBF) and sweat rate (SR) were measured throughout the study in 8 male healthy subjects (59.6 ± 2.4 years, 177 ± 3 cm, 88 ± 6 kg). After the normothermic (Tsk at ~34 °C) data collection, passive whole body heating was applied via water‐perfused suits with ~46 °C water. After Tsk reached ~36 °C, the water temperature was slightly decreased. The MWBH data were collected during a period (1522 ± 61 sec) with Tsk > 36 °C and the peak increase in Tcore < 0.35 °C. Cardiac output was measured with echocardiography during baseline and MWBH. During a separate visit, a time control trial (non‐heating trial) was performed when the Tsk was controlled at ~34 °C throughout the study. The data were collected during the same time windows as those in the heating trial. Over the MWBH period, the averaged Tsk was 36.8 ± 0.3 °C, and the averaged increase in Tcore was 0.09 ± 0.05 °C. From normothermic baseline, SkBF (100 to 174 ± 31%) and cutaneous vascular conductance (CVC, 100 to 190 ± 43%) increased. Systolic BP (117.5 ± 1.3 to 113.5 ± 2.2 mmHg) did not significantly change, while diastolic BP (75.3 ± 1.9 to 70.7 ± 2.5 mmHg) and mean BP (89.4 ± 1.3 to 85.0 ± 2.3 mmHg, both P < 0.05) fell. MSNA burst rate (38.9 ± 3.0 to 28.9 ± 3.4 bursts/min), burst incidence (60.4 ± 4.5 to 42.4 ± 5.2 bursts/100 beats) and total activity (847 ± 47 to 583 ± 66 units/min, all P < 0.05) decreased, while HR (64.7 ± 2.9 to 69.1 ± 3.0 beats/min) increased. Cardiac output increased ( P < 0.05). In the non‐heating time control trial, none of these variables changed. These data suggest that the MWBH may decrease resting MSNA and BP in middle aged and older individuals. Further studies are necessary to examine the mechanisms. Support or Funding Information Supported by American Heart Association Grant 15GRNT24480051 (Cui), National Institutes of Health Grants P01 HL096570 (Sinoway) and UL1 TR000127 (Sinoway).