Many Berachot which we recite as part of the prayer service begin with the word “Baruch,” whereas others conclude with “Baruch” but do not begin with “Baruch.” For example, the Beracha of “Baruch She’amar” both begins and ends with “Baruch”; it begins with the phrase “Baruch She’amar,” and concludes with, “Baruch Ata Hashem…Ha’kel Ha’ab…” The Beracha of “Yishtabah,” by contrast, does not begin with “Baruch,” but concludes with “Baruch Ata Hashem Kel Melech…”
The fundamental rule that underlies this distinction is that a Beracha which is linked to a previous Beracha does not require an introduction of “Baruch.” If a Beracha is connected to a previous Beracha, then the previous Beracha’s introductory “Baruch” suffices for this Beracha, as well. This is why “Yishtabah” does not begin with “Baruch” – because it is connected to “Baruch She’amar.” The Pesukeh De’zimra section in between “Baruch She’amar” and “Yishtabah” does not interrupt between them, because this is all one continuous section of praises to Hashem. And therefore since “Yishtabah” is linked to “Baruch She’amar,” it does not require its own introductory “Baruch.”
The practical implication of this is that one may not engage in any sort of idle chatter in between “Baruch She’amar” and “Yishtabah,” because they are linked to one another. Speaking in between these two Berachot is tantamount to speaking in the middle of a Beracha. In fact, the Sefer Ha’manhig writes that one who speaks in between “Baruch She’amar” and “Yishtabah” is considered to be diminishing from the praises of God, and commits a sin. This issue is especially relevant on Shabbat morning, when many Hazanim chant the Pesukeh De’zimra such that there are those in the congregation who complete the recitation of Pesukeh De’zimra long before the Hazan. Unfortunately, this often results in idle chatter among the congregants. One who completes the recitation of Pesukeh De’zimra before the Hazan should open a Sefer and read, rather than speak to the person next to him, which is forbidden.
One may, however, respond to “Devarim She’bi’kdusha” during Pesukeh De’zimra. If someone hears Kaddish, for example, he may answer the first five “Amen” responses. According to the custom of the Arizal, he may answer “Yeheh Shemeh Rabba” and continue through “Da’amiran Be’alma,” even though he is in the middle of Pesukeh De’zimra. Similarly, if one hears Nakdishach during Pesukeh De’zimra, he may answer “Kadosh Kadosh Kadosh…” and “Baruch Shem…” One may also answer to Barechu during Pesukeh De’zimra, and recite the three words of “Modim Anahnu Lach” if the Hazan reaches Modim. But idle chatter, as mentioned, is strictly forbidden during Pesukeh De’zimra.
Summary: It is strictly forbidden to speak during Pesukeh De’zimra. One may, however, answer the first five “Amen” responses to Kaddish, respond “Kadosh Kadosh” and “Baruch Shem” in Nakdishach, answer to Barechu, and say the words “Modim Anahnu Lach” with the Hazan.