Thanks Ronald,
I have been practising the C#,D and C harmonic slurs and am sure that I am not using any abdominal kick to change notes but unsure if I am using the start of a valsalva to make the change.
You may be right in thinking that I am simply feeling that movement from my lip change causing a movement of the hyoid bone.
I have been holding my trumpet with one hand and placing the other gently on the Adams apple region and can feel a small movement when doing these slurs.
Thanks for the feed back.
cheers