This article is worth a read in how it relates to our pranayama practice:

 

https://www.psychologytoday.com/us/blog/the-athletes-way/201905/longer-exhalations-are-easy-way-hack-your-vagus-nerve?fbclid=IwAR2x2G2Yzyos_E2Y1pzmpqs6Xc8NZfrPEOWiR7zQGbCIRUidP7StmjpIQOY