"A normal heart has lots of spare capacity. In patients with heart failure it is working flat out just to sit down [and] it's like running a marathon," he said.
"It ACTS as a kind of subliminal zone, an exclusive forum where the normal social rules are suspended," said Kate Fox, director of the social Issues Research Centre.
Volunteers were told to think about yawning, while they breathed either normal air, pure oxygen, or an air mixture with an above-normal level of carbon dioxide.
Volunteers were told to think about yawning while they breathed either normal air, pure oxygen, or an air mixture with an above-normal level of carbon dioxide.