STRUCTURAL AND FUNCTIONAL CORRELATES OF EXERCISE VENTILATORY INEFFICIENCY IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE PATIENTS WITH MILD-TO-MODERATE SPIROMETRIC ABNORMALITIES

Background: Individuals with chronic obstructive pulmonary disease (COPD) have higher than normal ventilatory equivalents for carbon dioxide (VE/VCO2) during exercise. There is growing evidence that emphysema on thoracic computed tomography (CT) scans is associated with poor exercise capacity in COPD patients with only mild-to-moderate airflow obstruction. We hypothesized that emphysema is an underlying cause of microvascular dysfunction and ventilatory inefficiency, which in turn contributes to reduced exercise capacity. We expected ventilatory inefficiency to be associated with a) the extent of emphysema; b) lower diffusing capacity for carbon monoxide; c) a reduced pulmonary blood flow response to exercise; and d) reduced exercise capacity. Methods: In a cross-sectional study, 19 subjects with mild-to-moderate COPD (mean ± SD FEV1= 82 ± 13% predicted, 12 GOLD grade 1) and 26 age-, sex-, and activity-matched controls underwent a ramp-incremental symptom-limited exercise test on a cycle ergometer. Ventilatory inefficiency was assessed by the minimum VE/VCO2 value (nadir). A subset of subjects also completed repeated constant work rate exercise bouts with non-invasive measurements of pulmonary blood flow. Emphysema was quantified as the percentage of attenuation areas below -950 Housefield Units on CT scans. An electronic scoresheet was used to keep track of emphysema sub-types. Results: COPD subjects typically had centrilobular emphysema (76.8 ± 10.1% of total emphysema) in the upper lobes (upper/lower lobe ratio= 0.82 ± 0.04). They had lower peak oxygen uptake (VO2), higher VE/VCO2 nadir and greater dyspnea scores than controls (p<0.05). Lower peak O2 and worse dyspnea were found in COPD subjects with VE/VCO2 nadirs ≥ 30. COPD subjects had blunted increases in pulmonary blood flow from rest to iso-VO2 exercise (p<0.05). Higher VE/VCO2 nadir in COPD subjects correlated with emphysema severity (r= 0.63), which in turn correlated with reduced lung diffusing capacity (r= -0.72) and blunted changes in pulmonary blood flow from rest to exercise (r= -0.69) (p<0.01). Conclusions: Ventilation “wasted” in emphysematous areas is associated with reduced exercise ventilatory efficiency in mild-to-moderate COPD. Exercise ventilatory inefficiency links structure (emphysema) and function (gas transfer) to a key clinical outcome (reduced exercise capacity) in COPD patients with modest spirometric abnormalities.

The Use of Nudges in Exergames to Moderate Player Exertion

Exergames are digital games with a physical exertion component. Exergames can help motivate fitness in people not inclined toward exercise. However, players of exergames sometimes over-exert, risking adverse health effects. These players must be told to slow down, but doing so may distract them from gameplay and diminish their desire to keep exercising. In this thesis we apply the concept of nudges—indirect suggestions that gently push people toward a desired behaviour—to keeping exergame players from over-exerting. We describe the effective use of nudges through a set of four design principles: natural integration, comprehension, progression, and multiple channels. We describe two exergames modified to use nudges to persuade players to slow down, and describe the studies evaluating the use of nudges in these games. PlaneGame shows that nudges can be as effective as an explicit textual display to control player over-exertion. Gekku Race demonstrates that nudges are not necessarily effective when players have a strong incentive to over-exert. However, Gekku Race also shows that, even in high-energy games, the power of nudges can be maintained by adding negative consequences to the nudges. We use the term "shove" to describe a nudge using negative consequences to increase its pressure. We were concerned that making players slow down would damage their immersion—the feeling of being engaged with a game. However, testing showed no loss of immersion through the use of nudges to reduce exertion. Players reported that the nudges and shoves motivated them to slow down when they were over-exerting, and fit naturally into the games.