Add additional request headers in nusoap PHP

I want to add request headers to send request soap with nusoap library.

How to add another request headers.. I want to add for example lie this :

"Connection : Keep-Alive", "Except:", etc.

I have code to call soap like this

$client->call($param['wsdl_function'], $requestParams, $param['wsdl_namespace'], $param['wsdl_action'],$headers);

where I must to put the request headers and how?

thanks