Great — let’s unpack this step by step so you can confidently convert frequency domain measures of heart rate variability (HRV) from units of ms²/Hz (power spectral density) to total ms² (absolute power).

✅ The key concept:

Frequency-domain HRV measures (e.g., LF, HF) are derived from the power spectral density (PSD), which shows power per unit frequency — hence the unit ms²/Hz. To get the total power in ms² over a specific frequency band, you need to integrate the PSD over that frequency band, which in discrete data means you multiply the average PSD by the bandwidth:

\text{Power in ms}^2 = \text{PSD (ms}^2/\text{Hz)} \times \text{Bandwidth (Hz)}

🔎 Example

Let’s say:

• The average power spectral density (PSD) in the LF band (0.04–0.15 Hz) is 50 ms²/Hz.
• The LF bandwidth is Hz.

Then,

\text{LF Power (ms}^2) = 50 \, \text{ms}^2/\text{Hz} \times 0.11 \, \text{Hz} = 5.5 \, \text{ms}^2

⚠️ Important notes:

• Band definition matters: LF is typically 0.04–0.15 Hz; HF is 0.15–0.4 Hz.
• This assumes your PSD value is already averaged over the band; if you have the full PSD curve, you would numerically integrate over your frequency range.
• Many HRV software packages already report total power in ms² for each band, but if you see ms²/Hz, you’ll need to convert as above.

🔹 In summary: To convert ms²/Hz → ms² for an HRV frequency band:

\boxed{\text{Power (ms}^2) = \text{Average PSD (ms}^2/\text{Hz)} \times \text{Frequency Bandwidth (Hz)}}