Michaël Sage

Impact of a Single Bout of Aerobic Exercise on Regional Brain Perfusion and Activation Responses in Healthy Young Adults

Purpose Despite the generally accepted view that aerobic exercise can have positive effects on brain health, few studies have measured brain responses to exercise over a short time span. The purpose of this study was to examine the impact within one hour of a single bout of exercise on brain perfusion and neuronal activation. Methods Healthy adults (n = 16; age range: 20–35 yrs) were scanned using Magnetic Resonance Imaging (MRI) before and after 20 minutes of exercise at 70% of their age-predicted maximal heart rate. Pseudo-continuous arterial spin labeling (pcASL) was used to measure absolute cerebral blood flow (CBF) prior to exercise (pre) and at 10 min (post-10) and 40 min (post-40) post-exercise. Blood oxygenation level dependent (BOLD) functional MRI (fMRI) was performed pre and post-exercise to characterize activation differences related to a go/no-go reaction time task. Results Compared to pre-exercise levels, grey matter CBF was 11% (±9%) lower at post-10 (P<0.0004) and not different at post-40 (P = 0.12), while global WM CBF was increased at both time points post-exercise (P<0.0006). Regionally, the hippocampus and insula showed a decrease in perfusion in ROI-analysis at post-10 (P<0.005, FDR corrected), whereas voxel-wise analysis identified elevated perfusion in the left medial postcentral gyrus at post-40 compared to pre (pcorrected = 0.05). BOLD activations were consistent between sessions, however, the left parietal operculum showed reduced BOLD activation after exercise. Conclusion This study provides preliminary evidence of regionalized brain effects associated with a single bout of aerobic exercise. The observed acute cerebrovascular responses may provide some insight into the brain’s ability to change in relation to chronic interventions.

Physical activity in the prevention of ischemic stroke and improvement of outcomes: A narrative review

Physical activity is an integral component of stroke prevention. Although approximately 80% of strokes are due to cerebral ischemia, the mechanisms linking physical activity to the incidence of and recovery from ischemic stroke are not completely understood. This review summarizes evidence from human and animal studies regarding physical activity in the prevention of overt and covert ischemic stroke and associated injury. In cohort studies, people who are physically active have reduced rates of overt ischemic stroke and ischemic stroke mortality. However, few human studies have examined physical activity and the incidence of covert stroke. Evidence from animal models of ischemic stroke indicates that physical activity reduces injury after ischemic stroke by reducing infarct size and apoptotic cell death. Accordingly, physical activity may reduce the magnitude of injury from ischemic stroke so that there are fewer or less severe symptoms. Future research should investigate physical activity and incidence of covert stroke prospectively, ascertain the optimal dose and type of exercise to prevent ischemic injury, and identify the underlying neuroprotective mechanisms.

Thermal Dynamics in Newborn and Juvenile Models Cooled by Total Liquid Ventilation

Background: Total liquid ventilation (TLV) consists in filling the lungs with a perfluorocarbon (PFC) and using a liquid ventilator to ensure a tidal volume of oxygenated, CO2-free and temperature-controlled PFC. Having a much higher thermal capacity than air, liquid PFCs assume that the filled lungs become an efficient heat exchanger with pulmonary circulation. Objective: The objective of the present study was the development and validation of a parametric lumped thermal model of a subject in TLV. Methods: The lungs were modeled as one compartment in which the control volume varied as a function of the tidal volume. The heat transfer in the body was modeled as seven parallel compartments representing organs and tissues. The thermal model of the lungs and body was validated with two groups of lambs of different ages and weights (newborn and juvenile) undergoing an ultrafast mild therapeutic hypothermia induction by TLV. Results: The model error on all animals yielded a small mean error of -0.1 ± 0.4 °C for the femoral artery and 0.0 ± 0.1 °C for the pulmonary artery. Conclusion: The resulting experimental validation attests that the model provided an accurate estimation of the systemic arterial temperature and the venous return temperature. Significance: This comprehensive thermal model of the lungs and body has the advantage of closely modeling the rapid thermal dynamics in TLV. The model can explain how the time to achieve mild hypothermia between newborn and juvenile lambs remained similar despite of highly different physiological and ventilatory parameters. The strength of the model is its strong relationship with the physiological parameters of the subjects, which suggests its suitability for projection to humans.

Nasal continuous positive airway pressure influences bottle-feeding in preterm lambs

BackgroundIn preterm infants, the time from initiation to full oral feeding can take weeks, which represents a very worrisome problem in neonatal medicine. Although current knowledge suggests that oral feeding should be introduced early, this is often delayed due to the need for prolonged nasal continuous positive airway pressure (nCPAP). Indeed, most caregivers fear that nCPAP could disrupt sucking–swallowing–breathing coordination and induce tracheal aspiration. The goal of the present study was to assess the impact of nCPAP delivered by the Infant Flow System on the physiology of sucking–swallowing–breathing coordination during bottle-feeding in preterm lambs over 24 h.MethodsSeventeen lambs (8 control, 9 nCPAP of 6 cmH2O) born 14 days prematurely were instrumented to record sucking, swallowing, respiration, ECG, and oxygenation. They were fed via a nasogastric tube for the first 5 days of life until introduction of bottle-feeding every 4 h for 24 h.ResultsnCPAP increased the feeding efficiency while maintaining higher oxygenation without any deleterious cardiorespiratory events. However, coughs were observed in lambs under nCPAP immediately following bottle-feeding and may be related to the high milk flow in preterm lambs.ConclusionFurther studies documenting tracheal aspirations are needed, especially in preterm lambs under nCPAP for moderate respiratory difficulties, to further inform future clinical studies.

Assessing the impacts of total liquid ventilation on left ventricular diastolic function in a model of neonatal respiratory distress syndrome

Background Filling the lung with dense liquid perfluorocarbons during total liquid ventilation (TLV) might compress the myocardium, a plausible explanation for the instability occasionally reported with this technique. Our objective is to assess the impacts of TLV on the cardiovascular system, particularly left ventricular diastolic function, in an ovine model of neonatal respiratory distress syndrome. Method Eight newborns lambs, 3.0 ± 0.4 days (3.2 ± 0.3kg) were used in this crossover experimental study. Animals were intubated, anesthetized and paralyzed. Catheters were inserted in the femoral and pulmonary arteries. A high-fidelity pressure catheter was inserted into the left ventricle. Surfactant deficiency was induced by repeated lung lavages with normal saline. TLV was then conducted for 2 hours using a liquid ventilator prototype. Thoracic echocardiography and cardiac output assessment by thermodilution were performed before and during TLV. Results Left ventricular end diastolic pressure (LVEDP) (9.3 ± 2.1 vs. 9.2 ± 2.4mmHg, p = 0.89) and dimension (1.90 ± 0.09 vs. 1.86 ± 0.12cm, p = 0.72), negative dP/dt (-2589 ± 691 vs. -3115 ± 866mmHg/s, p = 0.50) and cardiac output (436 ± 28 vs. 481 ± 59ml/kg/min, p = 0.26) were not affected by TLV initiation. Left ventricular relaxation time constant (tau) slightly increased from 21.5 ± 3.3 to 24.9 ± 3.7ms (p = 0.03). Mean arterial systemic (48 ± 6 vs. 53 ± 7mmHg, p = 0.38) and pulmonary pressures (31.3 ± 2.5 vs. 30.4 ± 2.3mmHg, p = 0.61) were stable. As expected, the inspiratory phase of liquid cycling exhibited a small but significant effect on most variables (i.e. central venous pressure +2.6 ± 0.5mmHg, p = 0.001; LVEDP +1.18 ± 0.12mmHg, p<0.001). Conclusions TLV was well tolerated in our neonatal lamb model of severe respiratory distress syndrome and had limited impact on left ventricle diastolic function when compared to conventional mechanical ventilation.

A single session of exercise as a modulator of short-term learning in healthy individuals.

BACKGROUND A single session of aerobic exercise is linked to faster motor responses; however, the effect on rate of short-term learning is less clear. The objective was to evaluate the influence of a single bout of aerobic exercise on the rate of short-term acquisition of a shape-letter association task requiring a motor response. METHODS 23 [11 females, age 20.8±2.7years] healthy young adults were evaluated using a randomly assigned crossover design which was counterbalanced for order before and after moderate (exercise) and light (control) intensity cycle ergometry. Participants performed 3 blocks, with each block consisting of one round of training and testing. During training, participants were tasked with learning 6 unique shape-letter associations. Subsequent testing required a key press response to a visually presented shape pattern. Response time and error rates were used to assess acquisition over the 3 blocks of testing. RESULTS Mean response time was faster post-exercise relative to the other testing periods, and approached statistical significance compared to post-control (p<0.07). However, no significant difference in response time reduction (difference between test block 1 and test block 3) was identified between the four evaluations (pre and post the exercise and control conditions). Error rate reduction (test block 1 minus test block 3) revealed that individuals had the smallest change in error rate post-exercise (p<0.05). Follow-up analyses revealed fewer errors in test block 1 and test block 2 post-exercise which approached statistical significance (p=0.06) suggesting near-perfect error rates were obtained after only 2 testing blocks post-exercise compared to 3 blocks in the other testing periods. CONCLUSIONS Support for augmentation of short-term learning was mixed as errors were reduced post-exercise while response time was not different between evaluations. Future work should include neurophysiological evaluation and a retention test to better elucidate the influence of aerobic exercise on rate of short-term learning.

A single aerobic exercise session accelerates movement execution but not central processing

Previous research has demonstrated that aerobic exercise has disparate effects on speed of processing and movement execution. In simple and choice reaction tasks, aerobic exercise appears to increase speed of movement execution while speed of processing is unaffected. In the flanker task, aerobic exercise has been shown to reduce response time on incongruent trials more than congruent trials, purportedly reflecting a selective influence on speed of processing related to cognitive control. However, it is unclear how changes in speed of processing and movement execution contribute to these exercise-induced changes in response time during the flanker task. This study examined how a single session of aerobic exercise influences speed of processing and movement execution during a flanker task using electromyography to partition response time into reaction time and movement time, respectively. Movement time decreased during aerobic exercise regardless of flanker congruence but returned to pre-exercise levels immediately after exercise. Reaction time during incongruent flanker trials decreased over time in both an aerobic exercise and non-exercise control condition indicating it was not specifically influenced by exercise. This disparate influence of aerobic exercise on movement time and reaction time indicates the importance of partitioning response time when examining the influence of aerobic exercise on speed of processing. The decrease in reaction time over time independent of aerobic exercise indicates that interpreting pre-to-post exercise changes in behavior requires caution.

Lumped Thermal Model of a Newborn Lamb and a Liquid Ventilator in Total Liquid Ventilation

Total liquid ventilation (TLV) is an emerging and promising mechanical ventilation method in which the lungs are filled with a breathable liquid. Perfluorocarbon (PFC) is the predominant liquid of choice due to its high O2 and CO2 solubility. In TLV, a dedicated liquid ventilator ensures gas exchange by renewing a tidal volume of PFC, which is temperature-controlled, oxygenated and free of CO2. A fundamental difference between TLV and conventional mechanical ventilation relates to the fact that PFCs are approximately 1500 times denser than air. This high density provides PFCs with a large heat capacity, turning the lungs into an efficient heat exchanger with circulating blood. The originality of this study is the development of a lumped thermal model of the body as a heat exchanger coupled to a liquid ventilator. The model was validated with an animal experimentation on a newborn lamb with the Inolivent-5.0 liquid ventilator prototype. TLV was initiated with a fast hypothermia induction, followed successively by a slow posthypothermic rewarming, a fast rewarming and finally a second fast hypothermia induction. Results demonstrate that the model was able to aptly predict, in every phase, the temperature of the lungs, the eardrum, the rectum as well as the various compartments of the liquid ventilator.Copyright

Optimal control of inspired perfluorocarbon temperature for induction of hypothermia by total liquid ventilation in juvenile lamb model

Mild hypothermia is well known for its therapeutic value in cardio- and neuroprotection. Many recent experimental studies have shown that the swiftness of the cooling offered by total liquid ventilation (TLV) holds great promise in achieving maximal therapeutic effect. TLV is an emerging ventilation technique in which the lungs are filled with breathable liquids, namely perfluorocarbons (PFCs). A liquid ventilator ensures subject ventilation by periodically renewing a volume of oxygenated, CO2-free and temperature-controlled breathable PFC. The substantial difference between breathing air and liquid is related to the fact that PFCs have over 500 times the volumetric thermal capacity of air 100% relative humidity. The PFC-filled lungs thus turn into an efficient heat exchanger with pulmonary circulation. The objective of the present study was to compute a posteriori the optimal inspired PFC temperature for ultrafast induction of mild hypothermia by TLV in a juvenile lamb experimentation using direct optimal control. The continuous time model and the discretized cycle-by-cycle model are presented. The control objectives of the direct optimal control are also presented and the results are compared with experimental data in order to validate the improved control performances. The computed direct optimal control showed that the inspired PFC temperature command can be improved to avoid temperature undershoots without altering the cooling performances.

Liquid ventilator for ultrafast hypothermia induction in juvenile lambs: Preliminary results.

Total liquid ventilation (TLV) is an emerging mechanical ventilation technique. In this technique, the lungs are filled with liquid perfluorocarbons (PFC) and a liquid ventilator assures ventilation by periodically renewing a volume of oxygenated, CO2 freed and temperature controlled PFC. A huge difference between conventional mechanical ventilation and TLV relates to the fact that PFCs are about 1500 times denser than air. Thus, the PFCs filled lungs turn into an efficient heat exchanger with the circulating blood. One of the most appealing utilization of the lungs as a heat exchanger in TLV is for ultrafast induction of mild therapeutic hypothermia (MTH) for neuroprotection and cardioprotection after ischemia-reperfusion injuries. This study aimed to perform ultrafast MTH induction by TLV in animals up to 25 kg, then perform a fast post-hypothermic rewarming while maintaining proper ventilation. A thermal model of the lamb and liquid ventilator was developed to predict the dynamic and the control strategy to adopt for MTH induction. Two juvenile lambs were instrumented with temperature sensors in the femoral artery, pulmonary artery, oesophagus, right eardrum and rectum. After stabilization in conventional mechanical ventilation, TLV was initiated with ultrafast MTH induction, followed by posthypothermic rewarming. Preliminary results in the two juvenile lambs reveal that the liquid ventilator Inolivent-6.0 can induce MTH by TLV in less than 2.5 min for systemic arterial blood and in less than 10 min for venous return, esophagus and eardrum. Rectal temperature reached MTH in respectively 19.4 and 17.0 min for both lambs. Experimental results were consistent with the model predictions. Moreover, blood gas analysis exhibited that the gas exchange in the lungs was maintained adequately for the entire experiments.