Effect of the knee-chest position on cerebral blood flow in patients undergoing lumbar spinal surgery

Body Position-Dependent Shift in Odor Percept Present Only for Perithreshold Odors

We recently demonstrated that a supine position causes a decrease in olfactory sensitivity compared with an upright position. We pursued that initial finding in 3 separate experiments in which we explored the extent of, and mechanism underlying, this phenomenon. In Experiment 1, we replicated the decrease in olfactory sensitivity when in a supine compared with an upright position. In Experiment 2, we measured body position-dependent shifts in physiological variables and sniff measures while smelling suprathreshold odorants and performing a perithreshold odor intensity discrimination task. Olfactory performances were reduced while supine. However, no relationships between the shift in olfactory performances and either the physiological variables or sniff measures were found. In Experiment 3, we determined that there were no position-dependent shifts in ability to discriminate or identify suprathreshold odors or rate them for pleasantness, intensity, or familiarity. However, a drop in scores was observed, and performance was slowed, on a cognitive skill while supine. These results demonstrate a body position-dependent shift in olfactory sensitivity only for perithreshold odors that appears to be mediated by cognitive rather than physiological factors. Implications for olfactory imaging studies are discussed.

Sit Up and Smell the Roses Better: Olfactory Sensitivity to Phenyl Ethyl Alcohol Is Dependent on Body Position

Previous studies have demonstrated that body position can alter auditory sensitivity. Here we demonstrate for the first time that olfactory sensitivity for the commonly used odor phenyl ethyl alcohol (PEA) (rose odor) is also dependent on body position. By using successive dilutions presented in a staircase protocol, we determined olfactory thresholds for PEA in 36 healthy participants (18 women) in both an upright and a supine position. Participants had a significantly greater olfactory sensitivity when tested in an upright than a supine position, with no significant differences between the sexes. This preliminary study sets the stage for further work on the interaction between olfactory functions and our biology. The implications for olfactory neuroimaging studies are discussed.