Read data from multiple serial port

Hi guys, i want to ask about read data from serial port using background worker. Is it possible to retrieve data from one serial port or more using one worker? I can retrieve data when only use one serial port in worker. When i use two or more ports, i can't retrieve data anymore (without error message). Here is my code :

private void worker_DoWork(object sender, DoWorkEventArgs e)
        {
            String p = "";
            String s = "";
            Int32 b = 0;
            MethodInvoker get_selectedPort = new MethodInvoker(() =>
                {
                    p = comboBoxPressure.SelectedItem.ToString();
                    s = comboBoxStrain.SelectedItem.ToString();
                    b = Convert.ToInt32(comboBoxBaudrate.SelectedItem.ToString());
                });
            this.Invoke(get_selectedPort);

            SerialPort portPressure = new SerialPort();  // serial port 1
            portPressure.PortName = p;
            portPressure.BaudRate = b;
            portPressure.Parity = Parity.None;
            portPressure.StopBits = StopBits.One;
            portPressure.DataBits = 8;
            portPressure.Handshake = Handshake.None;

            SerialPort portStrain = new SerialPort(); // serial port 2
            portStrain.PortName = s;
            portStrain.BaudRate = b;
            portStrain.Parity = Parity.None;
            portStrain.StopBits = StopBits.One;
            portStrain.DataBits = 8;
            portStrain.Handshake = Handshake.None;
           
            try
            {
                portPressure.Open();
                portStrain.Open();
            }
            catch (Exception error)
            {
                MessageBox.Show("Error while trying open serial port!\r\n" + error.Message, "COM Port Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                worker.CancelAsync();
                return;
            }

            while (!worker.CancellationPending)
            {               
                System.Threading.Thread.Sleep(100);
                this.dataPressure = portPressure.ReadExisting();
                this.dataStrain = portStrain.ReadExisting();
                BeginInvoke((Action)(() => updateData()));
            }

            portPressure.Close();
            portStrain.Close();
        }