J. Patrick Neary

Cerebrovascular Reactivity Impairment after Sport-Induced Concussion

PURPOSE This study evaluated cerebrovascular reactivity (CVR) after a sport-induced concussion, also called mild traumatic brain injury (mTBI), by monitoring middle cerebral artery blood velocity (vMCA) with transcranial Doppler ultrasonography and simultaneous end-tidal carbon dioxide (PETCO(2)) measurements. METHODS Thirty-one athletes (16-25 yr old) participated in this study. The participants were divided into two groups-healthy (n = 21) and mTBI (n = 10). Participants in the mTBI group suffered an mTBI within the last 7 d (x- = 4.5 ± 1.1 d). Outcome measures included vMCA and PETCO(2) in response to breath holding (5 × 20 s, 40-s rest) and hyperventilation (5 × 20 s, 40-s rest). RESULTS Resting vMCA values between groups were not significantly different. Percentage change of vMCA was significantly different after the recovery period of the second hyperventilation (P = 0.034). mTBI subjects failed to return to resting levels after each breath hold. PETCO(2) changes mirrored the vMCA changes. CONCLUSIONS These data suggest that normal CVR responses may be disrupted in the days immediately after occurrence of mTBI. Transcranial Doppler ultrasonography combined with expired gas measurements provides a useful method for assessing CVR impairment after mTBI. Further research, including serial monitoring after mTBI and analysis of CVR response to exercise, is warranted before any firm conclusions can be drawn.

Prefrontal cortex oxygenation during incremental exercise in chronic fatigue syndrome

This study examined the effects of maximal incremental exercise on cerebral oxygenation in chronic fatigue syndrome (CFS) subjects. Furthermore, we tested the hypothesis that CFS subjects have a reduced oxygen delivery to the brain during exercise. Six female CFS and eight control (CON) subjects (similar in height, weight, body mass index and physical activity level) performed an incremental cycle ergometer test to exhaustion, while changes in cerebral oxy‐haemoglobin (HbO2), deoxy‐haemoglobin (HHb), total blood volume (tHb = HbO2 + HHb) and O2 saturation [tissue oxygenation index (TOI), %)] was monitored in the left prefrontal lobe using a near‐infrared spectrophotometer. Heart rate (HR) and rating of perceived exertion (RPE) were recorded at each workload throughout the test. Predicted VO2peak in CFS (1331 ± 377 ml) subjects was significantly (P ≤ 0·05) lower than the CON group (1990 ± 332 ml), and CFS subjects achieved volitional exhaustion significantly faster (CFS: 351 ± 224 s; CON: 715 ± 176 s) at a lower power output (CFS: 100 ± 39 W; CON: 163 ± 34 W). CFS subjects also exhibited a significantly lower maximum HR (CFS: 154 ± 13 bpm; CON: 186 ± 11 bpm) and consistently reported a higher RPE at the same absolute workload when compared with CON subjects. Prefrontal cortex HbO2, HHb and tHb were significantly lower at maximal exercise in CFS versus CON, as was TOI during exercise and recovery. The CFS subjects exhibited significant exercise intolerance and reduced prefrontal oxygenation and tHb response when compared with CON subjects. These data suggest that the altered cerebral oxygenation and blood volume may contribute to the reduced exercise load in CFS, and supports the contention that CFS, in part, is mediated centrally.

Effects of taper on endurance cycling capacity and single muscle fiber properties

PURPOSE It was hypothesized that metabolic adaptations in single muscle cells after a taper period are fiber type (I and II) specific and protocol regimen dependent. METHODS After 7-wk intensive endurance training, 22 male cyclists (VO2max=4.42 +/- 0.40 L.min(-1)) were randomly assigned to one of three 7-d taper groups: the control group (CON, N=7) continued weekly training, the first experimental group (INT) maintained training intensity but reduced duration (N=7), and the second experimental group (DUR) maintained training duration but reduced exercise intensity (N=8). Each cyclist completed a simulated 40-km time trial (40TT) before and after tapering on a set of wind-loaded rollers using their own bicycle. Muscle biopsies were taken immediately before the 40TT both before and after tapering, and analyzed for mATPase, succinate dehydrogenase (SDH), cyctochrome oxidase (CYTOX), alpha-glycerolphosphate dehydrogenase (alpha-GPD), and beta-hydroxyacyl CoA dehydrogenase (beta-HOAD) in Type I and II fibers, separately, using quantitative histochemistry. RESULTS The results showed significant (P< or =0.05) increases in SDH (Type I) and mATPase, CYTOX, beta-HOAD, and SDH (Type II fibers) in the INT group, and significant increases in CYTOX (Type I) and beta-HOAD (Type I and II fibers) in the DUR group. Regression analysis showed that the change (posttaper minus pretaper) in simulated 40-km endurance time was correlated with the change in CYTOX and SDH activity for all groups combined (r2=0.62-0.72). CONCLUSION These results demonstrated that the metabolic properties of different fiber types are altered with tapering, that the type of taper protocol used influences their physiological adaptation, and that improvements in simulated 40-km endurance time were related to changes in metabolic properties of the muscle at the single fiber level.

Assessment of neuromuscular and haemodynamic activity in individuals with and without chronic low back pain

BackgroundBiering-Sørenson (1984) found that individuals with less lumbar extensor muscle endurance had an increased occurrence of first episode low back pain. As a result, back endurance tests have been recommended for inclusion in health assessment protocols. However, different studies have reported markedly different values for endurance times, leading some researchers to believe that the back is receiving support from the biceps femoris and gluteus maximus. Therefore, this study was designed to examine the haemodynamic and neuromuscular activity of the erector spinae, biceps femoris, and gluteus maximus musculature during the Biering-Sørenson Muscular Endurance Test (BSME).MethodsSeventeen healthy individuals and 46 individuals with chronic low back pain performed the Biering-Sørenson Muscular Endurance Test while surface electromyography was used to quantify neuromuscular activity. Disposable silver-silver-chloride electrodes were placed in a bipolar arrangement over the right or left biceps femoris, gluteus maximus, and the lumbosacral paraspinal muscles at the level of L3. Near Infrared Spectroscopy was used simultaneously to measure tissue oxygenation and blood volume changes of the erector spinae and biceps femoris.ResultsThe healthy group displayed a significantly longer time to fatigue (Healthy: 168.5s, LBP: 111.1s; p ≤ 0.05). Significant differences were shown in the median frequency slope of the erector spinae between the two groups at 90–100% of the time to fatigue while no significant differences were noted in the haemodynamic data for the two groups.ConclusionAlthough the BSME has been recognized as a test for back endurance, individuals with chronic LBP appear to incorporate a strategy that may help support the back musculature by utilizing the biceps femoris and gluteus maximus to a greater degree than their healthy counterparts.

Serial monitoring of CO2 reactivity following sport concussion using hypocapnia and hypercapnia

Primary objective: This study examined the effects of mild traumatic brain injury (mTBI) on cerebrovascular reactivity (CVR). Research design: A repeated measures design was used to examine serial changes in CVR. Methods and procedures: Twenty subjects who recently suffered a mTBI were subjected to a respiratory challenge consisting of repeated 20 s breath-holds (BH) and hyperventilations (HV). Testing occurred on days 2 (D2), 4 (D4) and 8 (D8) post-injury as well as a baseline (BASE) assessment (after return-to-play). Transcranial Doppler was used to assess mean cerebral blood velocity (vMCA) and expired gas analysis provided end-tidal carbon dioxide (PETCO2) levels. Results: There was no significant difference in resting vMCA across all testing days for mTBI. No significant differences in PETCO2 were found throughout the testing protocol. A significant effect (p < 0.001) of testing day on vMCA was found during BH and HV challenges for mTBI. Post-hoc analysis revealed significant differences (p < 0.05) in vMCA between D2 and the other testing days. Conclusions: These data suggest that, following mTBI: (1) CVR is not impaired at rest; (2) CVR is impaired in response to respiratory stress; and (3) the impairment may be resolved as early as 4 days post-injury.

Measuring Neuromuscular Fatigue in Cervical Spinal Musculature of Military Helicopter Aircrew

UNLABELLED Neck pain and muscle function in aircrew have received considerable attention. We hypothesized normalized electromyography (EMG) frequency would provide insight into appropriate methods to assess muscle fatigue in helicopter aircrew. METHODS 40 helicopter aircrew performed isometric testing that included maximal voluntary contractions (MVC) and 70% MVC endurance protocols of extension, flexion, and left and right lateral flexion for cervical muscles. Bilateral muscle activity in the splenius capitis, sternocleidomastoid, and upper trapezius was monitored with EMG. Normalized mean EMG frequency was calculated for each muscle at the start and end of the 70% MVC trials to determine which muscles fatigued and limited force maintenance during each isometric movement. RESULTS For extension, the left and right splenius capitis fatigued by approximately 21-22% (p < 0.01); for flexion, the left and right sternocleidomastoid fatigued by approximately 11-14% (p < 0.01); for right flexion, the right sternocleidomastoid fatigued by approximately 15% (p < 0.01); for left flexion, the left spenus capitis and left sternocleidomastoid fatigued by approximately 7.2% (p = 0.02) and approximately 11.2% (p = 0.03), respectively; in no trials did the trapezius muscles display fatigue as measured by EMG. CONCLUSION The smaller agonist muscles were the most susceptible to fatigue during submaximal isometric endurance movements in the cervical muscles of helicopter aircrew.

Physiological Effects of Night Vision Goggle Counterweights on Neck Musculature of Military Helicopter Pilots

UNLABELLED Increased helmet-mounted mass and specific neck postures have been found to be a cause of increased muscular activity and stress. However, pilots who use night vision goggles (NVG) frequently use counterweight (CW) equipment such as a lead mass that is attached to the back of the flight helmet to provide balance to counter the weight of the NVG equipment mounted to the front of the flight helmet. It is proposed that this alleviates this stress. However, no study has yet investigated the physiological effects of CW during an extended period of time during which the pilots performed normal operational tasks. METHODS Thirty-one Canadian Forces pilots were monitored on consecutive days during a day and a NVG mission in a CH-146 flight simulator. Near infrared spectroscopy probes were attached bilaterally to the trapezius muscles and hemodynamics, i.e., total oxygenation index, total hemoglobin, oxyhemoglobin, and deoxyhemoglobin, were monitored for the duration of the mission. Pilots either wore CW (n = 25) or did not wear counterweights (nCW, n = 6) as per their usual operational practice. RESULTS Levenes statistical tests were conducted to test for homogeneity and only total oxygenation index returned a significant result (p < or = 0.05). For the near infrared spectroscopy variables, significant differences were found to exist between CW and nCW pilots for total hemoglobin, deoxyhemoglobin, and oxyhemoglobin during NVG flights. The CW pilots displayed less metabolic and hemodynamic stress during simulated missions as compared to the nCW pilots. CONCLUSION The results of this study would suggest that the use of CW equipment during NVG missions in military helicopter pilots does minimize the metabolic and hemodynamic responses of the trapezius muscles.

Helicopter cockpit seat side and trapezius muscle metabolism with night vision goggles.

INTRODUCTION Documented neck strain among military helicopter aircrew is becoming more frequent and many militaries use helicopters that provide pilots with the option of sitting in the left or right cockpit seat during missions. PURPOSE The purpose of this study was to use near infrared spectroscopy (NIRS) to investigate the physiological changes in trapezius muscle oxygenation and blood volume during night vision goggle (NVG) flights as a function of left and right cockpit seating. METHODS There were 25 pilots who were monitored during NVG flight simulator missions (97.7 +/- 16.1 min). Bilateral NIRS probes attached to the trapezius muscles at C7 level recorded total oxygenation index (TOI, %), total hemoglobin (tHb), oxyhemoglobin (Hbo2), and deoxyhemo-globin (HHb). RESULTS No significant differences existed between variables for pilots seated in the right cockpit seat as compared with the pilots seated in the left cockpit seat in either trapezius muscle (pTOI = 0.72; ptHb = 0.72; pHbo2 = 0.57; pHHb = 0.21). CONCLUSION Alternating cockpit seats on successive missions is not a means to decrease metabolic stress for helicopter pilots using NVG. This suggests that cockpit layout and location of essential instruments with respect to the horizontal and the increased head supported mass of the NVG may be important factors influencing metabolic stress of the trapezius muscle.

Assessment of Mechanical Cardiac Function in Elite Athletes

Hypertrophic cardiomyopathy (HCM) is the number one cause of sudden cardiac death in elite athletes. This project used resting 12-lead electrocardiography (ECG) and ballistocardiography (BCG) to assess cardiac cycle timing events as simple screening techniques to rule out cardiac abnormalities for the safety of a group of elite ice hockey players. Clinical cardiac (ECG) and physiological (maximal aerobic power [VO2max], anaerobic [Wingate peak power, Watts] and musculoskeletal strength) data is presented here on an elite group of ice hockey players (n=34; age=17-18 yrs) that participated in a professional medical and fitness evaluation. Subsequently one subject was diagnosed with #1 Apical HCM and his cardiac data is compared with the group. The HCM subject performed all fitness testing and was determined to be physically fit (%BF=7.2%; VO2max=59.4 mL•kg -1 •min -1 ; Wingate peak power output=15.1 Watt•kg -1 ; Heart Rate max=200 beats•min -1 ). However, the ECG showed extreme voltage and deeply inverted T-waves, and the BCG showed abnormal waveform complexes and cardiac timing events in comparison to the group means. Mean BCG systolic timing events for isovolumic contraction time (54.7±7.1 vs 49.5±12.4 msec), acceleration time (49.1±1.8 vs 56.3±9.1 msec), diastole (470.8±25.3 vs 531.4±166.7 msec), and isovolumic relaxation time (88.5±7.4 vs 100.8± 16 msec) were significantly different (p<0.05). Atrial systole amplitude was statistically higher for this subject (9.2±3.7 vs 5.3±3 mG). Subsequent follow-up assessment showed abnormal echocardiogram (Echo) dimensions (ventricular septum [12mm]; posterior wall [16 mm]), velocities (mitral valve deceleration [233 msec], LV systolic strain [14%]), and volumes (LV stroke volume [38 mL•metre -1 body surface area]), with normal E:A ratio (1.75) and LV ejection fraction (62%). Cardiac magnetic resonance imaging (MRI) showed apical septal wall thickness (24-25 mm) in the HCM player. In conclusion, BCG was able to corroborate a cardiac abnormality that was later confirmed with echocardiography and MRI, suggesting that BCG is a potential technology to detect anomalies that alter cardiac timing and amplitude.

Parasympathetic baroreflexes and heart rate variability during acute stage of sport concussion recovery

Abstract Primary objective: To assess and compare the parasympathetic state of individuals in healthy vs concussion groups, by measuring cardiovascular metrics under resting and baroreflex conditions using a squat-stand manoeuvre. Research design: This was a retrospective mixed-method study, with participants who sustained a medically diagnosed sport concussion (n = 12), being tested within 72-hours post-injury. Methods and procedures: Participant’s heart rate (Electrocardiogram, ECG) and blood pressure (finger plethysmography) data was collected during rest and during 10-second squat-stands (10SS, 0.05 Hz). Blood pressure and heart rate standard deviation data was analysed in the 0–5 seconds and 6–10 seconds periods of squatting and standing. Resting and baroreflex ECG data were analysed via Fourier Transformations for %Low Frequency and %High Frequency (%LF and %HF). Results: The control group alleviated more pressure and had a significantly higher standard deviation of heart rate during the 6–10 seconds of squatting (p < 0.05). Overall heart rate standard deviation in the concussion group was significantly lower than healthy controls when standing (p < 0.05). There were no differences in %LF and % HF between groups or between rest and 10SS. Conclusion: This study provides preliminary evidence that autonomic function is dysregulated following mTBI within the initial 72 hours of injury.