Passive muscle heating attenuates the decline in vascular function caused by limb disuse

Area of Science:

• Physiology
• Vascular Biology
• Muscle Physiology

Background:

• Limb disuse, common after injury or during bed rest, negatively impacts vascular and skeletal muscle health.
• Immobilization leads to reduced blood vessel function and potential muscle atrophy.
• Understanding interventions to counteract disuse effects is crucial for patient recovery.

Purpose of the Study:

• To investigate if repeated passive heat application to knee extensor muscles can prevent vascular dysfunction during limb immobilization.
• To assess the efficacy of pulsed shortwave diathermy in mitigating immobilization-induced vascular impairments.
• To explore the molecular mechanisms underlying heat therapy's effects on vascular health during disuse.

Main Methods:

• A randomized, single-blinded, placebo-controlled trial involving 21 healthy volunteers undergoing 10 days of unilateral lower limb immobilization.
• Participants received either sham (Imm) or heat treatment (Imm+H) daily for 2 hours using pulsed shortwave diathermy.
• Vascular function was measured using Doppler ultrasound and passive leg movement technique; muscle biopsies analyzed capillary density and molecular markers.

Main Results:

• Immobilization reduced femoral artery diameter (FAD) by 7.3% and passive leg movement-induced hyperaemia (HYP) by 34.3%.
• Heat treatment (Imm+H) significantly attenuated these declines, with only a 4% decrease in FAD and a 7.8% increase in HYP.
• While immobilization altered vascular endothelial growth factor and angiopoietin 2 expression, heat therapy did not change capillary density but induced vascular remodeling markers.

Conclusions:

• Limb immobilization significantly impairs vascular endothelial function.
• Daily passive muscle heating using diathermy effectively counteracts the adverse vascular effects of limb disuse.
• Passive muscle heating represents a promising therapeutic strategy to preserve vascular function during periods of immobilization.