Observations on the response of human spermatozoa to gravity, boundaries and fluid shear

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Abstract
Human sperm motility response to 3 mechanical stimuli, gravity, fluid flow shear and rigid boundaries, was measured in a tube of 310 .times. 400 .mu.m caliber. Data were gathered by cine recordings at various focussing levels, d, across the tube and analyzed with a computerized image analysis system. The most influential stimulus was the tube wall near (more than at) which the swimmers tended to accumulate, leaving the fluid beyond 100 .mu.m from the wall (d = 100) vacant of motile spermatozoa. The boundary effect was evident as soon as the spermatozoa could be viewed after loading, and accumulation, measured as frequency, as a function of d did not change with time t. This response was not significantly altered by the addition of laminar flow with a center line velocity of .apprx. 400 .mu.m/s. In flow shear, spermatozoa aligned positively (in the flow direction) at the wall but negatively by about 30 .mu.m from the wall where the velocity gradient (= shear rate) was .apprx. 3.5 s-1. The response to gravity was relatively weak with 11 spermatozoa positive (swimming downwards) for each 9 negative. Neither the boundary effect nor the ''rheotaxic'' effect were influenced by gravity as there was no statistical difference in orientation or distribution patterns between vertically and horizontally flowing suspensions. The boundary effect apparently cannot be ignored in in vitro manipulations, particularly when spermatozoa are observed or extracted. Its importance in vivo lies in the degree to which the tubes transporting motile spermatozoa seem to have mechanisms for reversing the wall accumulation tendency.

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