Diagnose sinus membrane perforation during implant surgery?

What is the most reliable way to determine if you perforate the sinus membrane? I was placing an implant in the maxillary first molar area using the Zimmer Sinus Crestal Approach Kit (Sinus Lift Kit). I used the S-reamer to get close to the membrane without perforating. It is designed to leave a thin layer of intact bone under the membrane. When I thought I had penetrated to the right depth, I held the patient’s nostrils and had her blow gently. No air bubbles appeared in the osteotomy but there was some turbulence in the blood pooling in the osteotomy. What diagnostic test could I have used to determine if I did perforate the membrane?