Cardiorespiratory response to exercise testing in individuals with Alzheimer's disease

Abstract

Objective: To examine exercise testing response in Alzheimer's disease (AD) and possible disease-related change over time.

Design: Retrospective assessment of a 2-year observational study.

Setting: University medical center.

Participants: Individuals without dementia (n=50) and with AD (n=31).

Interventions: Not applicable.

Main outcome measures: Participants underwent a clinical dementia evaluation and performed an incremental exercise test using a treadmill and the modified Bruce protocol at baseline and at a 2-year follow-up. We examined oxygen consumption, minute ventilation, heart rate, and ventilatory equivalents for oxygen and carbon dioxide at submaximal and peak exercise intensities to determine whether the measures were different between groups or over time.

Results: Participants with AD and those without dementia performed similarly at submaximal effort, and both groups showed similar changes in exercise response over 2 years. However, nondemented individuals had consistently higher values of oxygen consumption (P≤.02) and minute ventilation at peak effort at baseline (P=.003).

Conclusions: Individuals with AD demonstrate physiologic responses to submaximal exercise effort that are not significantly different than individuals without dementia. However, differences are apparent at the extreme of effort.

Figure 1

Response to exercise in our 4 primary measures of interest are displayed for all participants for the initial six minutes of exercise and peak values for those who met 85% of age predicted maximal heart rate and RER > =1.0. Filled shapes represent the nondemented group and open shapes represent the group with AD. Row A) displays oxygen consumption, which rose significantly faster during the initial 6 minutes of the test during 2-year follow-up testing (right graph). VO₂ peak was greater in the nondemented group at both timepoints. Row B) At follow-up testing, the AD group began testing with a lower heart rate but increased over the initial 6 minutes of testing to match the nondemented group (right graph), resulting in an interaction of Test Minute and Group. Peak heart rates were different between groups at baseline testing but not at follow-up. Row C) In both groups, VE rose at faster rate during the initial 6 minutes of exercise testing at follow-up compared to baseline, resulting in a significant interaction between Study Visit and Test Minute. Peak VE was greater in the nondemented group at baseline. Row D) Ventilatory equivalent for O₂ (left Y axis) and CO₂ (right Y axis) are presented together for ease of comparison. Interaction of Test Minute and Study Visit were evident for both measures, with steeper decline in VE/VCO₂ and earlier rebound in VE/VO2 at follow-up testing. Peak values were not different between groups.