I think the relevant term is “Equity Duration,” which is the sensitivity of your fund’s equity value (i.e. Total Assets minus Debt ) to interest rate changes. That gets magnified by leverage so that the sensitivity of your fund’s “equity” is much higher.
The two relevant parts of the equation are the proportion of equity to debt (which is a magnification factor) and the spread between the bond’s return and the return on bonds you are buying (which is a correction for the fact that you pay interest to get leverage). They teach the formula at L3 but I’ve forgotten it and I’m too lazy/unmotivated to derive it here. It’s not that hard to derive, though.
There is a totally different meaning of “Equity Duration” which is the sensitivity of stock prices to interest rates. For a dividend paying stock in a mature company, this should be 1/(dividend yield). Interestingly, equities often have a very long duration, which probably has to do with the fact that stocks - like many people on AF - never mature.