Andrology: Kinematics of capacitating human spermatozoa analysed at 60 Hz

Hyperactivation is a concomitant of eutherian sperm capacitation, characterized by the development of high amplitude flagellar waves with a corresponding increase in velocity. In humans, kinematic values have been derived which describe the movement characteristics of spermatozoa analysed at 30 images/s. However, these values are frame rate-dependent, and modern computer-aided sperm analysis (CASA) instruments used for studying sperm movement now use 60 images/s. This study used first-principles manual track analysis to derive the range of movement characteristics which describe hyperactivated motility of human spermatozoa at 60 images/s. Standard terminology for centroid-derived movement characteristics, as recommended by the World Health Organization, was used. US-standard (NTSC) video recordings of capacitating human sperm populations were replayed using a noninterlaced freeze-frame video cassette recorder, and individual tracks reconstructed on acetate overlays. Tracks were classified as either forward progressive or hyperactivated based upon flagellar beating patterns, then reconstructed manually at ×3540 and analysed using both manual methods and basic geometric calculations from (x, y) coordinates (Cartesian methods) similar to those used by CASA instruments. In all, 40 hyperactivated and 40 forward progressive tracks were studied. A set of Boolean arguments defining hyperactivated motility was derived, and there was generally good agreement between the limits derived by manual and Cartesian methods. The limits for the definition of hyperactivated motility of human spermatozoa at 60 Hz derived by Cartesian methods were: curvilinear velocity ≥180 μm/s AND linearity ≤45% AND wobble 6.0 μm OR ALHmax >10.0 μm. The same limits were derived by manual methods, except for ALHmax >7.0 μm. It is suggested that the manually derived limits be applied in CASA instruments which use adaptive smoothing programs to derive the average path.