PHP ストアド プロシージャから出力パラメータ値を取得するにはどうすればよいですか?

<code class="php">// Establish a connection to the database
$mysqli = new mysqli("HOST", "USR", "PWD", "DBNAME");

// Input parameter value
$ivalue = 1;

// Execute the stored procedure and capture the result
$res = $mysqli->multi_query("CALL myproc($ivalue, @x);SELECT @x");

// Check if the execution was successful
if ($res) {
    $results = 0;

    // Iterate through the results
    do {
        // Store the result
        if ($result = $mysqli->store_result()) {
            printf("<b>Result #%u</b>:<br/>", ++$results);

            // Fetch and display the rows
            while ($row = $result->fetch_row()) {
                foreach ($row as $cell) echo $cell, " ";
            }
            $result->close();
        }
    } while ($mysqli->next_result());
}

// Close the connection
$mysqli->close();</code>