A Realistic and Inexpensive Ultrasound Phantom for Teaching M-Mode Measurement of Fetal Heart Rate.

BACKGROUND: M-mode ultrasound is frequently used to measure a fetal heart rate. Phantoms are used to simulate clinical conditions for teaching ultrasound-related skills. This is particularly important in the case of early pregnancy, when it is not ethical to use a live fetus in utero for teaching purposes. OBJECTIVES: To date, no phantom has been created to model the beating heart of an intrauterine pregnancy. Our goal was to create such a model for use in teaching M-mode ultrasound. MATERIALS AND METHODS: The phantom is constructed using a toy fish, several balloons, and water-absorbing gel crystals. RESULTS: We have created a novel phantom for use in teaching M-mode measurements. The cost per phantom is around $20 and the phantom can be constructed in about 20 min. CONCLUSION: This phantom is easily constructed and cost-effective. It gives learners the opportunity to practice measuring an intrauterine fetal heart rate in a learning environment without exposing a live fetus to unnecessary ultrasound.

Larger sperm size may contribute to reproductive isolation between Etheostoma species.

Etheostoma is a genus of North American darter fish whose species have similar habitats and breeding seasons, yet hybridization is rare. Behavioral barriers have been demonstrated to play a key role in maintaining species boundaries. Further, conspecific (same species) sperm precedence has also been observed when the gametes of two different species come into contact. In this study, we investigated if physical characteristics of sperm could be a mechanism for the lower fertilization success of heterospecific (different species) males when eggs are simultaneously exposed to conspecific and heterospecific sperm. We chose to examine the sperm of two closely related species, E. zonale and E. barrenense. Using toluidine blue and immunofluorescent labeling methods, we compared head diameter and tail length of sperm cells between the two species. We found that head diameter was significantly larger for E. barrenense sperm compared to E. zonale. This difference in cell morphology may point to a physical mechanism underlying conspecific sperm precedence in Etheostoma. Our results are the first to describe a morphological difference in sperm between species in this genus and provide initial evidence for the role of sperm morphology in prezygotic reproductive isolation.