Do we have an option within Healthconnect to limit the number of messages sent at a time to downstream application from outbound

This seems like a perfect use case for InterSystems API Manager. Using this tool with Health Connect you can limit the number of messages per second to the downstream application. To learn more see: https://docs.intersystems.com/components/csp/docbook/Doc.View.cls?KEY=PA...

Your Business Operation has a setting called Throttle Delay. You could set this to the number of milliseconds you would like to delay before processing the next message.

https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls...