Tristan Dorey: APNM Undergraduate Research Excellence Award Winner
November 30, 2017
Canadian Science Publishing sponsors the Applied Physiology, Nutrition, and Metabolism Undergraduate Research Excellence Awards, which are awarded in partnership with the Canadian Society for Exercise Physiology and the Canadian Nutrition Society. Award winner Tristan Dorey shares his research on compression socks.
By Tristan Dorey
A year before starting my honours thesis I approached Dr. Derek Kimmerly, an Assistant Professor in the School of Health and Human Performance at Dalhousie University, to discuss a project I had in mind. I had always seen athletes, especially runners, wear knee-high compression socks during races but never understood their purpose. I did some research as to why these garments had become such a phenomenon among athletes but found little to no evidence to suggest they improve exercise performance. However, what I did notice was their potential clinical utility for preventing blood pooling and fainting in certain populations. Dr. Kimmerly and I questioned if compression socks may be of use following long endurance exercise where fainting can be quite common.
Why are athletes pulling up their socks?A common symptom that individuals experience when they suddenly stand up from a supine or sitting position is the feeling of light-headedness. This phenomenon, termed postural or orthostatic hypotension, is a result of decreased oxygen delivery to the brain due to a sudden drop in blood pressure. When standing up suddenly, blood has a tendency to pool in the veins in our lower limbs due to gravity (i.e., venous pooling). Despite one-way valves located within these veins to counteract the pooling of blood away from the heart, blood volumes of about 500–600 mL move into the legs during standing causing reduced blood flow to the heart. This in turn reduces the amount of blood, and therefore oxygen, supplied to the brain. While this is a relatively benign condition, in some cases individuals may faint and suffer the consequences of accidental falls.
Compression garments, including socks, are clinically used to prevent venous pooling and increase blood flow back to the heart. However, previous studies have generally found limited evidence to suggest they are effective at reducing the symptoms and physiological responses to orthostatic stress in a non-exercised state. But do compression garments mitigate these symptoms and responses immediately following exercise?
The occurrence of orthostatic hypotension can be exaggerated following aerobic exercise and is commonly reported after endurance exercise (e.g., 60 minutes at moderate–vigorous intensity). Persistent vasodilation (or widening) of blood vessels after aerobic exercise provides conditions for exacerbated venous pooling beyond levels observed from standing. Orthostatic stress following exercise elicits larger reductions in stroke volume (i.e., amount of blood pumped by the left ventricle per heart beat) and middle cerebral artery velocity (MCAv; a marker of brain blood flow) as well as an increased prevalence of fainting compared with a non-exercised state.
Until now, no studies had examined the effects of compression socks on physiological responses to orthostatic stress immediately following exercise. We expected that knee-high compression socks would minimize the post-exercise reductions in stroke volume (SV) and brain blood flow (i.e., MCAv) during head-up tilt (HUT; a test to induce orthostatic stress) after a bout of continuous aerobic exercise.
Do compression socks ease post-exercise orthostatic stress?Ten young, healthy participants (six males and four females) volunteered to participate in this study. No participants reported a history of cardiovascular, metabolic, pulmonary, or neurological disorders. Participants underwent a randomly assigned crossover of the compression (CS) or no-compression socks conditions, that is, participants either wore compression socks on the first day of the study and "regular" ankle socks on the second day, or vice versa.
For each day of the study, participants were placed in a quiet, temperature-controlled room while lying on their left side on a tilt table before being instrumented for measurements of heart rate, SV, blood pressure (finger and upper arm), and MCAv. Participants were secured by wide velcro straps around their mid-chest and hips to help support them during the tilt test in case of syncope (i.e., temporary loss of consciousness). A 10-minute rest period started once stable physiological recordings were attained while the participant was in a supine, rest position. After the 10-minute rest period, the motorized tilt table was raised to 60° above horizontal for 15 minutes (i.e., HUT). Participants then cycled for 60 minutes at 60% of maximum workload before repeating the HUT procedure.
Pre-exercise, compression socks did not affect HUT-mediated reductions in SV and MCAv. As predicted, compression socks attenuated HUT-mediated reductions in SV and MCAv following exercise (Fig. 1). These findings are most likely the result of the mechanical compression by the socks of lower limb venous vascular beds. This compression in turn reduces lower leg venous cross-sectional area and counteracts venous pooling by increasing central venous pressure and cardiac filling. In other words, compression socks may be squeezing veins in our legs causing more blood to be pushed back up to the heart and in turn the amount pumped out.
|Fig. 1: Percent change in stroke volume (SV) and brain blood flow (MCAv) from supine rest to head-up tilt when wearing compression socks (CS) relative to control (CTL; no compression socks), pre-exercise (PRE-EX) and post-exercise (POST-EX). *, p < 0.05 POST-EX CTL vs. PRE-EX CTL and PRE-EX CS;
†, p < 0.05 POST-EX CS vs. POST-EX CTL
Compression therapy has become a growing fad used by athletes and exercise enthusiasts. Additionally, healthcare providers commonly prescribe compression socks for individuals who suffer from orthostatic syncope. Our results suggest that individuals should be wary when adopting the use of knee-high compression socks as a method to prevent the physiological responses to orthostatic stress during the non-exercised state in healthy individuals. However, compression socks could be recommended as a countermeasure to reduce the risk of post-exercise syncope, especially for populations at higher risk for syncopal events after exercise such as endurance athletes or those with autonomic dysfunction.
Tristan Dorey holds a Bachelor of Science Degree in Kinesiology with Honours from Dalhousie University. Tristan is currently pursuing his Master’s degree in Cardiovascular and Respiratory Science at the University of Calgary. While Tristan is still extensively involved in research surrounding exercise and the cardiovascular system, his current research focuses on the effects signalling peptides on cardiac autonomic function in hypertensive heart disease.
Filed Under: Applied Physiology Nutrition and Metabolism