Spread risk versus interest rate risk

How, if at all, does spread duration relate to the more familiar effective duration
value that describes a bond’s or portfolio’s sensitivity to changes in interest rates?
In this section, we attempt to provide some intuition for how spread risk compares
to interest rate risk for different types of securities. In attempting to understand
spread duration, it is necessary to think about how a change in spreads affects both
the present value of a security’s future cash flows and the amount and timing of the
cash flows themselves. In this respect, an interesting contrast between corporate
bonds and mortgage-backed securities may be observed when analyzing spread
duration.