Cerebrovascular responses to submaximal exercise in women with COPD
BMC Pulmonary Medicine
Cerebrovascular responses to submaximal exercise in women with COPD
Sara E Hartmann 0 1
Richard Leigh 1 2 6
Marc J Poulin 0 1 3 4 5
0 Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary , Calgary, AB , Canada
1 Department of Physiology and Pharmacology, Faculty of Medicine, University of Calgary , Calgary, AB , Canada
2 Department of Medicine, University of Calgary , Calgary, AB , Canada
3 Libin Cardiovascular Institute of Alberta, Faculty of Medicine, University of Calgary , Calgary, AB , Canada
4 Department of Clinical Neurosciences, Faculty of Medicine, University of Calgary , Calgary, AB , Canada
5 Faculty of Kinesiology, University of Calgary , Calgary, AB , Canada
6 Snyder Institute of Infection , Immunity, and Inflammation , University of Calgary , Calgary, AB , Canada
Background: COPD patients have decreased physical fitness, and have an increased risk of vascular disease. In the general population, fitness is positively associated with resting cerebral blood flow velocity, however, little is known about the cerebrovascular response during exercise particularly in COPD patients. We hypothesized that COPD patients would have lower cerebral blood flow during exercise secondary to decreased physical fitness and underlying vascular disease. Methods: Cardiopulmonary exercise testing was conducted in 11 women with GOLD stage I-II COPD, and 11 healthy controls to assess fitness. Cerebro- and cardio-vascular responses were compared between groups during two steady-state exercise tests (50% peak O2 consumption and 30 W). The main outcome variable was peak middle cerebral artery blood flow velocity (VP) during exercise using transcranial Doppler ultrasonography. Results: Physical fitness was decreased in COPD patients. VP was comparable between COPD and controls (25 22% versus 15 13%, respectively; P > 0.05) when exercising at the same relative intensity, despite patients having higher blood pressure and greater arterial desaturation. However, VP was elevated in COPD (31 26% versus 13 10%; P 0.05) when exercising at the same workload as controls. Conclusions: Our results are contradictory to our a-priori hypothesis, suggesting that during matched intensity exercise, cerebral blood flow velocity is similar between COPD and controls. However, exercise at a modestly greater workload imposes a large physical demand to COPD patients, resulting in increased CBF compared to controls. Normal activities of daily living may therefore impose a large cerebrovascular demand in COPD patients, consequently reducing their cerebrovascular reserve capacity.
COPD; Exercise; Transcranial Doppler ultrasound; Cerebral blood flow; Women
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Background
The regulation of cerebral blood flow (CBF) is
imperative for adequate delivery of O2 and energy supply to the
brain. During cerebral activation and increased
metabolism, cerebral arterioles dilate, thereby increasing CBF,
and ultimately O2 delivery. This process of neurovascular
coupling (i.e., neural activation coupled with an adequate
increase in blood flow) is challenged during dynamic
exercise. Factors such as age and physical fitness have been
suggested to play an important role in this regulatory
process both at rest [1], and during exercise [2].
The reduction of physical activity levels and exercise
capacity in COPD patients [3-5] may pose a risk to
patients cerebrovascular health. Even in the early stages of
COPD, patients with mild and moderate obstruction are
reported to have reduced exercise capacity [6]. Evidence
suggests that patients with moderate COPD are already
at an increased risk of cardiovascular disease and stroke,
thereby suggesting an underlying vascular pathology. We
have previously reported decreased CBF responsiveness
to CO2 in women with COPD, suggesting reduced
cerebral dilatory function [7].
Cycle ergometry testing offers a functional and
translational tool to test integrated responses during exercise.
COPD patients may exhibit arterial hypercapnia [8] and
hypoxemia, exaggerated vasopressor response [9], and
ventilatory limitations [10] during exercise which all
have implications on the regulation of CBF.
Furthermore, greater distribution of cardiac output to
respiratory or peripheral muscles could impact the blood flow
delivery to the brain. Presently, few studies have focused
on the cerebrovascular response of COPD patients
during exercise [11,12], and of these studies, focus has been
on exercise limitations. It is currently unknown if the
cerebrovascular response to exercise in COPD patients
differs from that of a healthy control group.
We therefore tested the hypothesis that women with
mild-moderate COPD would have reduced cerebral
blood flow during exercise, secondary to reduced
physical fitness. Women were of particular interest in this
study due to a shift in the disease burden from men to
women [13], and comparatively, women report worse
symptoms for a similar severity of disease to men, and
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