Local heating decreases muscle sympathetic nerve activity in normal subjects

 

Noriyo Takahashi

Division of Comprehensive Medicine Department of Rehabilitation Medicine Osaka Medical College

 

Objective: To assess the effects of local heating (LH) on post-ganglionic muscle sympathetic nerve activity (MSNA) in 9 healthy subjects.

Methods: In the first protocol, MSNA of the left peroneal nerve, blood pressure (BP), heart rate (HR), and skin temperature of the calf (Tsk) were recorded. Leg blood flow (LBF) was measured by plethysmography in the second protocol. In both tests, after 10 min of rest, a hot pack was applied to the anterior tibial portion and foot for 15 min and recovery was observed for 20 min.

Results: Tsk increased from 31.7±0.1 to 41.9±0.5°C during LH. No subject complained of pain, and BP and HR remained relatively constant. The burst rate of MSNA (16.1±2.1 beats/min) during control significantly decreased by 72.0±2.3% during LH. Total MSNA also decreased by 59.2±2.6% during LH, but both returned to baseline at recovery. LBF significantly increased 8min after commencement of LH and remained significantly elevated throughout recovery.

Conclusion: LH significantly attenuates MSNA without any change in HR and BP. MSNA might modulate LBF, but not totally control LBF in the lower extremity during LH.

 

Key word: thermal stress, muscle blood flow, microneurogram