Zabbix API Unixtime from/till

[imjules]

I'm getting the trends via PhpZabbixApi on my PHP Website. But now I want to have only the avg_value from now. So if I refresh the page, it should get the actual avg_value from API.

 $params = array(       
                           'groupids'         => '2',
                           'search' => array('item' => 'Disk root used p'),
                           'search' => array('value' => 'value_avg'),
                           'output'           => 'extend' ); 

What do I have to add to get only the actual avg_value from trends?