Response of breasts to different stimulation patterns of an electric breast pump.

To test the effect on milk ejection, an electric breast pump was programmed to provide pumping patterns with frequencies of 45 to 125 cycles/min and vacuums of 45 to -273 mm Hg. The time taken for milk ejection to occur (measured using ultrasound to detect a dilation of a lactiferous duct in the opposite breast) in response to the current Medela electric breast pump pattern (45 cycles/min) was 147 +/- 13 s. For patterns that more closely resemble the sucking frequency of an infant when it first attaches to the breast, milk ejection occurred between 136 +/- 12 and 104 +/- 10 s, although this difference was not statistically significant. Milk ejection in response to breastfeeding occurred after 56 +/- 4 s. The applied vacuum affected the amount of milk that was removed up to 50 to 70 s after milk ejection but not the time for milk ejection.