Microvascular Perfusion and Intramuscular Temperature of the Calf During Cooling
Selkow NM, Day C, Liu Z, Hart JM, Hertel J, Saliba SA. Med Sci Sports Exerc. 2011 Oct 7. [Epub ahead of print].
Cryotherapy has been proposed to decrease local blood flow through vasoconstriction, decrease metabolic activity, reduce cellular oxygen requirements, and decrease local tissue temperature; however, the optimal physiological responses (e.g. how much should blood flow, cellular metabolism, and tissue temperature be decreased, if at all) are still unknown. The purpose of this single-blind crossover study was to examine microvascular perfusion changes in the gastrocnemius after a cryotherapy intervention. Nineteen healthy subjects (age = 18 to 30 years) completed 2 sessions (crushed ice bag and sham) in a random order. The treatment time of cryotherapy or sham was tailored to each patient based on the thickness of adipose tissue overlying the gastrocnemius (treatment time: 10 to 60 minutes). Outcome variables of microvascular perfusion (blood flow and blood volume) and intramuscular temperature were measured at baseline (pre-treatment) and immediately following crushed ice bag or sham. All measurements were performed 1 cm in to the muscle. Contrast enhanced ultrasound, which was used to measure microvascular perfusion, is also used in cardiac patients to determine blood flow to the heart. The results of this study show that compared to baseline measurements, microvascular blood flow and blood volume were not different immediately after ice bag treatment, but were increased after sham treatment. Intramuscular temperature decreased significantly during ice bag treatment, but did not change during sham treatment. Additionally, subcutaneous adipose tissue thickness at the treatment site was significantly correlated with change in intramuscular temperature immediately after cryotherapy treatment.
This is the first study in humans to suggest that microvascular blood flow and blood volume may not decrease during cryotherapy treatment, even though muscle temperature decreased significantly. It is commonly thought that lower tissue temperature will result in decreases in blood flow, but this study questions that theory. The sham group had an increase in microvascular perfusion immediately after treatment that may have been due to micro-trauma from insertion of the small temperature probe into the muscle. This suggests that ice bag application controlled the microvascular perfusion associated with the micro-trauma of probe insertion, indicating that cryotherapy treatment may have a protective function. This provides further support for the use of cryotherapy as quickly as possible after injury to control perfusion and potentially limit further injury, though more research needs to be completed to confirm this theory. This study also confirms a relationship between subcutaneous adipose tissue thickness and amount of time required for cooling, but this relationship implies that the currently recommended treatment times to achieve a meaningful change in tissue temperature based on adipose tissue thickness may not be correct. Clinicians and researchers should think critically about the timeframe after injury, patient’s body composition, and treatment goals before prescribing a cryotherapy treatment. We should also begin to consider different mechanisms in which cryotherapy may be acting to create a successful treatment, such as changes in cutaneous sensation, counter-irritation, or noxious inhibition. Do the results of this study change the way you view cryotherapy treatments after acute injury? Do you believe that cryotherapy treatments should be tailored to individuals based on their body composition or injury?
Written by: Kimberly Rupp
Reviewed by: Jeffrey Driban
Selkow NM, Day C, Liu Z, Hart JM, Hertel J, & Saliba SA (2011). Microvascular Perfusion and Intramuscular Temperature of the Calf During Cooling. Medicine and Science in Sports and Exercise PMID: 21988932