Autonomic cardiovascular response during and after a graded exercise test in concussed athletes and healthy controls

Objective Dysfunction of the autonomic cardiovascular system after a concussion is known to cause exercise intolerance due to symptoms exacerbation. The aim of this study was to compare athletes with symptoms of a sport-related concussion and healthy controls with regard to their heart rate during a graded exercise test and their heart rate recovery during the 5 min cool-down after the graded exercise test. Methods Sport-related concussion patients ( N = 61; 31% female) and controls ( N = 16; 50% female) participated in a graded exercise test on a cycle ergometer followed by 5 min active cool-down. Based on the results of graded exercise tests they were divided into four groups: (1) patients who reached the symptom threshold and had to stop the graded exercise test (symptom threshold; N = 39; 33.3% female), (2) patients with symptoms who finished the graded exercise test (S; N = 16; 25% female), (3) patients without symptoms (NS; N = 6; 33.3% female), (4) controls ( N = 16; 50% female). Main outcome measures Heart rate, severity of headache and dizziness during graded exercise test, heart rate recovery (median (heart rate recoveries/maximal heart rate) ± median absolute deviation (MAD)) 30, 60 and 300 s after the start of cool-down. Results Heart rate recovery at 30 s was significantly slower in symptom (0.95 ± 0.01) compared to all other groups ( p < 0.002; symptom threshold: 0.92 ± 0.02, NS: 0.91 ± 0.02, controls: 0.93 ± 0.02). Heart rate recovery at 60 s was significantly slower in symptom (0.90 ± 0.02) compared to the symptom threshold and controls ( p < 0.041; 0.86 ± 0.03, 0.85 ± 0.04). Heart rate recovery at 300 s was significantly slower in symptom threshold (0.72 ± 0.05) compared to controls ( p = 0.003; 0.66 ± 0.02). Conclusions Heart rate measurements in athletes with symptoms of sport-related concussion should be continued during cool-down after the graded exercise test, as dysfunction of the autonomic cardiovascular system might manifest also during cool-down.