How to increase stream rate in pixhawk on output telemetry

I want to get telemetry RAW_IMU and ATTITUDE from pixhawk (telem1) by arduino. In mission planner or QGC, I can put stream rate in intervals from 0 to 10 Hz. In actual I can get 5-8 Hz from telem1. I wish to increase the stream rate. I try to increase data rate by arduino function mavlink_msg_request_data_stream_pack(… , uint16_t req_message_rate, …). The function changes rate value in a list from mission planner, but the real value is not changed.

#include <mavlink.h>
#include <SoftwareSerial.h>
SoftwareSerial _MavLinkSerial(10, 11); 

  // Mavlink variables
  unsigned long previousMillisMAVLink = 0;     // will store last time MAVLink was transmitted and listened
  unsigned long next_interval_MAVLink = 1000;  // next interval to count
  const int num_hbs = 60;                      // # of heartbeats to wait before activating STREAMS from Pixhawk. 60 = one minute.
  int num_hbs_pasados = num_hbs;

  

void Mav_Request_Data()
{
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];


  // To be setup according to the needed information to be requested from the Pixhawk
  const int  maxStreams = 1;
  const uint8_t MAVStreams[maxStreams] = {MAV_DATA_STREAM_ALL};
  const uint16_t MAVRates[maxStreams] = {0x0F};

  for (int i = 0; i < maxStreams; i++) {
      mavlink_msg_request_data_stream_pack(6, 200, &msg, 1, 0, MAVStreams[i], MAVRates[i], 1);
    uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
    _MavLinkSerial.write(buf, len);
  }
}



receive_imu() 
{
   
  mavlink_message_t msg;
  mavlink_status_t status;

  while (_MavLinkSerial.available() > 0) 
  {
    Serial.println(msg.msgid);

    float c = _MavLinkSerial.read();

    if (mavlink_parse_char(MAVLINK_COMM_0, c, &msg, &status))
    {     
     /* if(msg.msgid==30) // #30: ATTITUDE
          {
            mavlink_attitude_t attitude;
            mavlink_msg_attitude_decode(&msg, &attitude);

           }
*/
      if(msg.msgid==27) // #27: MAVLINK_MSG_ID_RAW_IMU 
          {            
            mavlink_raw_imu_t raw_imu;
            mavlink_msg_raw_imu_decode(&msg, &raw_imu);
           Serial.println(raw_imu.zacc);                
          } 
      }
   }
}

void setup() {
  
  _MavLinkSerial.begin(57600);
  Serial.begin(57600);
  Mav_Request_Data();

}

void loop() {

  receive_imu();
 
}