If one hears Kadish or Nakdishach or Barechu while he recites the Beracha of Asher Yatzar (the blessing one recites after performing his bodily functions), may he interrupt his recitation to respond with "Amen," "Kadosh, Kadosh, Kadosh," and so on?
Halacha equates Asher Yatzar in this respect with the prayer of ‘Shema’, meaning one may interrupt Asher Yatzar in the same situations in which interruptions are permitted during Shema. Therefore, in the middle of Asher Yatzar one may interrupt for the first five responses of "Amen" in Kadish, as well as "Yihe Shemei Rabba" through "Da’amiran Be’alma." One may not however, interrupt Asher Yatzar for the other responses of "Amen," namely, after "Titkabal," after "Yehei Shelama" and after "Al Yisrael."
Furthermore, it is permissible to interrupt Asher Yatzar to respond to Barechu, and to join in the congregation’s responses of "Kadosh, Kadosh, Kadosh" and "Baruch Kevod Hashem" in Nakdishach.
One should be aware that the Chayei Adam (Rabbi Avraham Danzig, 19th century) writes that all this applies to a person who is already in the middle of Asher Yatzar. If one has recited only "Baruch Ata Hashem," and has not completed the phrase "Elokenu Melech Ha’olam," then it is forbidden for him to make any interruption. This entire discussion pertains only in situations where one hears Kadish, Nakdishach or Barchu after having recited the first line of Asher Yatzar, namely, "Baruch Ata Hashem Elokenu Melech Ha’olam Asher Yatzar."
In conclusion, once a person has recited "Baruch Ata Hashem Elokenu Melech Ha’olam," he may interrupt for the first five responses of "Amen" in Kadish, including "Yehei Shemei Rabba," for Barechu, and for the verses of "Kadosh" and "Baruch" in Nakdishach.
