Cerebrovascular responses to submaximal exercise in women with COPD

The Exercising Brain: An Overlooked Factor Limiting the Tolerance to Physical Exertion in Major Cardiorespiratory Diseases?

“Exercise starts and ends in the brain”: this was the title of a review article authored by Dr. Bengt Kayser back in 2003. In this piece of work, the author highlights that pioneer studies have primarily focused on the cardiorespiratory-muscle axis to set the human limits to whole-body exercise tolerance. In some circumstances, however, exercise cessation may not be solely attributable to these players: the central nervous system is thought to hold a relevant role as the ultimate site of exercise termination. In fact, there has been a growing interest relative to the “brain” response to exercise in chronic cardiorespiratory diseases, and its potential implication in limiting the tolerance to physical exertion in patients. To reach these overarching goals, non-invasive techniques, such as near-infrared spectroscopy and transcranial magnetic stimulation, have been successfully applied to get insights into the underlying mechanisms of exercise limitation in clinical populations. This review provides an up-to-date outline of the rationale for the “brain” as the organ limiting the tolerance to physical exertion in patients with cardiorespiratory diseases. We first outline some key methodological aspects of neuromuscular function and cerebral hemodynamics assessment in response to different exercise paradigms. We then review the most prominent studies, which explored the influence of major cardiorespiratory diseases on these outcomes. After a balanced summary of existing evidence, we finalize by detailing the rationale for investigating the “brain” contribution to exercise limitation in hitherto unexplored cardiorespiratory diseases, an endeavor that might lead to innovative lines of applied physiological research.

Cerebrovascular function in patients with chronic obstructive pulmonary disease: the impact of exercise training

This study examined cerebral blood flow (CBF) and its regulation before and after a short-term periodized aerobic exercise training intervention in patients with chronic obstructive pulmonary disease (COPD). Twenty-eight patients with COPD (forced expiratory volume in 1 s/forced vital capacity < 0.7 and <lower limit of normal) and 24 healthy control subjects participated in the study. Extracranial CBF (duplex ultrasound), middle cerebral artery velocity (MCAv; transcranial Doppler), cerebrovascular reactivity to hypocapnia and hypercapnia, and dynamic cerebral autoregulation (transfer function analysis) were quantified. These tests were repeated in both patients with COPD ( n = 23) and control subjects ( n = 20) after 8 wk of periodized upper and lower body aerobic exercise training (3 sessions/wk). At baseline, global extracranial CBF was comparable between the COPD and control groups (791 ± 290 vs. 658 ± 143 ml/min, P = 0.25); however, MCAv was lower in patients with COPD compared with control subjects (46 ± 9 vs. 53 ± 10 cm/s, P = 0.05). Although there were no group differences in dynamic cerebral autoregulation or the MCAv response to hypercapnia, patients with COPD had a lower MCAv response to hypocapnia compared with control subjects (−1.1 ± 1.5 vs. −1.6 ± 1.3 cm·s−1·mmHg−1, P = 0.02). After aerobic training, absolute peak O2 consumption increased in both groups, with a greater improvement in control subjects (1.7 ± 0.4 vs. 4.1 ± 0.2 ml·kg−1·min−1, respectively, P = 0.001). Despite these improvements in peak O2 consumption, there were no significant alterations in CBF or any measures of cerebrovascular function after exercise training in either group. In conclusion, patients with COPD have a blunted cerebrovascular response to hypocapnia, and 8 wk of aerobic exercise training did not alter cerebrovascular function despite significant improvements in cardiorespiratory fitness.

NEW & NOTEWORTHY No study to date has investigated whether exercise training can alter resting cerebral blood flow (CBF) regulation in patients with chronic obstructive pulmonary disease (COPD). This study is the first to assess CBF regulation at rest, before, and after aerobic exercise training in patients with COPD and healthy control subjects. This study demonstrated that while exercise training improved aerobic fitness, it had little effect on CBF regulation in patients with COPD or control subjects.

Cerebral oxygen availability during exercise in COPD patients with cognitive impairment

Insufficient cerebral blood flow regulation to meet increasing metabolic demand during physical exertion could be associated with cognitive impairment. We compared cerebral oxygen availability during exercise in cognitively impaired (CI) to cognitively normal (CN) COPD patients. Fifty-two patients (FEV₁: 51 ± 16%) were classified as CN or CI according to the Montreal Cognitive Assessment. Patients performed cycle-ergometry at 75% peak capacity with continuous measurement of Near-Infrared Spectroscopy frontal-cortex Tissue oxygen Saturation Index (TSI), cerebral haemoglobin indices (oxy/deoxy/total- Hb), transcutaneous carbon-dioxide partial pressure (TcPCO₂), and arterial oxygen saturation (SpO₂). Twenty-one patients (40%) presented evidences of CI. During exercise, CN and CI patients exhibited mild to moderate SpO₂decline (nadir[Δ]≥ -3 ± 2% and -5 ± 3%, respectively) but preserved baseline frontal-cortex TSI levels, whilst presenting small TcPCO₂ perturbations and increased cerebral total-Hb (post [Δ]≥ 2.0 ± 3 μM sec^-1). CI patients preserve the capacity to adequately maintain cerebral oxygen availability during submaximal exercise. Therefore, rehabilitative exercise training in CI patients with COPD exhibiting mild to moderate exercise-induced SpO₂ decline does not appear to lead to reduced cerebral oxygen availability.

Human cerebral blood flow control during hypoxia: focus on chronic pulmonary obstructive disease and obstructive sleep apnea

The brain is a vital organ that relies on a constant and adequate blood flow to match oxygen and glucose delivery with the local metabolic demands of active neurons. Thus exquisite regulation of cerebral blood flow (CBF) is particularly important under hypoxic conditions to prevent a detrimental decrease in the partial pressure of oxygen within the brain tissues. Cerebrovascular sensitivity to hypoxia, assessed as the change in CBF during a hypoxic challenge, represents the capacity of cerebral vessels to respond to, and compensate for, a reduced oxygen supply, and has been shown to be impaired or blunted in a number of conditions. For instance, this is observed with aging, and in clinical conditions such as untreated obstructive sleep apnea (OSA) and in healthy humans exposed to intermittent hypoxia. This review will 1) provide a brief overview of cerebral blood flow regulation and results of pharmacological intervention studies which we have performed to better elucidate the basic mechanisms of cerebrovascular regulation in humans; and 2) present data from studies in clinical and healthy populations, using a translational physiology approach, to investigate human CBF control during hypoxia. Results from studies in patients with chronic obstructive pulmonary disease and OSA will be presented to identify the effects of the disease processes on cerebrovascular sensitivity to hypoxia. Data emerging from experimental human models of intermittent hypoxia during wakefulness will also be reviewed to highlight the effects of intermittent hypoxia on the brain.

Heliox-Driven Nebulization Has a Positive Effect on the Lung Function in Lipopolysaccharide-Induced Chronic Obstructive Pulmonary Disease Rat Model

Background

Chronic obstructive pulmonary disease (COPD) is a serious lung disease that severely threatens people’s health. This study aimed to investigate the effects of heliox-driven nebulization (HDN) on lung function and arterial blood gases in a COPD rat model.

Material/Methods

Twelve healthy male Wistar rats were selected as controls and 34 rats were used to establish a COPD model induced by lipopolysaccharide. Then 6 rats each from the control and model groups were selected for their symptoms to be observed. The remaining 6 normal rats were used as control group (group A) and the remaining 28 experimental COPD rats were randomly assigned to 4 groups: experimental COPD group (group B), medical oxygen group (group C), and heliox groups (group D, He/O₂=63%/37%; group E, He/O₂=71%/29%). The lung function indicators and arterial blood gases were analyzed to evaluate the effects of different driving gases on COPD rats.

Results

The COPD model was successfully established with slow growth and severe lung dysfunction. Inspiratory resistance, expiratory resistance, and forced expiratory volume at 0.10 s (FEV0.10)/FVC were significantly decreased, whereas dynamic lung compliance was significantly increased in groups D and E, compared with the experimental COPD group (group B; P<0.05). Meanwhile, compared with the model group, the values of partial pressure of carbon dioxide in arterial blood were significantly higher, whereas the potential of hydrogen values were significantly lower after atomization in groups C and D but not in group E (P<0.05). The obvious increase in arterial oxygen saturation was found only in group E (P<0.05).

Conclusions

HDN improved the lung function and arterial blood gas analysis results in experimental COPD rats, with an optimal percentage of He/O₂=71%/29%.