Private Function FindFirstNumber(ByVal text As String, _
                    Optional ByVal startindex As Integer = 0, _
                    Optional ByVal length As Integer = -1, _
                    Optional ByRef positionbehind As Integer = -1) As String
 
        positionbehind = -1
 
        If String.IsNullOrEmpty(text) Then Return ""
        If startindex < 0 Or startindex >= text.Length Then Return ""
 
        Dim lastindex As Integer
        If length < 0 Then
            lastindex = text.Length - 1
        Else
            lastindex = Math.Min(text.Length - 1, startindex + length - 1)
        End If
 
        Dim num As New System.Text.StringBuilder
 
        For i As Integer = startindex To lastindex
 
            If Char.IsDigit(text(i)) Then
                num.Append(text(i))
            ElseIf num.Length > 0 Then
                If i < text.Length - 1 Then positionbehind = i
                Exit For
            End If
        Next i
 
        Return num.ToString
    End Function

   Dim field As String = "asasdasd H0 weqwewqe  345 asdsd"
 
   Dim startindex As Integer = 0, positionbehind As Integer = -1
   Dim numberpart As String
 
   Do
       numberpart = FindFirstNumber(field, startindex, , positionbehind)
       startindex = positionbehind
   Loop While startindex > 0 And numberpart = "0"