Output Filter for Meta Description - How can I display only paragraphs?

Hi all,

first of all – MODX IS GREAT!!! The flexibility is amazing!

But now, I have this littel problem ;-) ...

I want to fill out the content of the meta description tag automatically with the first 160 characters from the first paragraph of a resource.
I want to use an output filter for this ... that’s what I have:
It wors perfect, but the problem is, that the <h1> tag before the <p> is included in the content, but I want to grab the text only from the first <p> of every resource.

How can I do that?

Greetings

Micha