Resting heart rate and HRV are less sensitive to short-term stress changes compared to respiratory rate.

“Respiratory Rate: Highly sensitive—a subtle 1 breath/min increase overnight predicts a 20–30% higher risk of moderate-to-high stress almost immediately”

“One study found that a 1 breath per minute increase in respiratory rate raised the risk of experiencing moderate-to-severe stress by 23%.”

“In contrast to respiratory rate, resting heart rate and HRV take longer to respond to stress (they aren't as sensitive), meaning it could take several days to weeks for stress to manifest in these metrics.”