You’re not imagining it — and neither is the research.

Perigee is a wellness companion, not a medical device. The studies below describe findings across groups of people; they are not claims about your body, and nothing here diagnoses or treats anything. One night cannot give an answer on its own; your doctor interprets it in the context of your health.

What group-level HRV research reports

HRV is the tiny beat-to-beat variation in heart rhythm. It is influenced by autonomic activity, breathing, sleep, alcohol, illness, measurement timing and other factors, so it is not a direct readout of one system or cause. In one study of midlife women, ECG-derived cardiac vagal control changed during physiologically measured vasomotor events, including during sleep³.

Other studies report group-level HRV differences across menopause status and associations with symptom intensity⁴⁵. These findings do not predict how one person’s intermittent Apple Watch HRV samples should move, and a lower sample cannot identify hormones, stress or a hot flash as the cause.

Periodic heart-rate samples, read as a trend

A wearable study reported group-level differences in sleeping pulse across menstrual-cycle phases⁷, while other research describes autonomic differences across menopause status⁴. Neither finding means that a daily resting-heart-rate estimate can identify a hormonal phase or explain an individual episode of palpitations.

The American Heart Association describes the menopause transition as a window of cardiovascular change and an opportunity for prevention⁶. A watch trend can support a clinical conversation, but it cannot assess whether palpitations are safe. Palpitations with chest pain, shortness of breath, fainting or near-fainting, or an episode that will not settle require prompt medical attention rather than interpretation in an app¹⁷.

A baseline-relative temperature trend

A wearable study using an Oura ring, not Apple Watch, reported nocturnal finger skin temperature about 0.30 °C higher in the luteal phase than the follicular phase at the group level⁸. Other wrist-temperature research has examined cycle-related trends⁹. These device-specific findings do not validate Apple Watch for identifying cycle phase, perimenopause or a night sweat.

Laboratory and review research describes thermoregulatory differences associated with hot flashes. In a small 1999 study, the measured thermoneutral zone was narrower in participants with hot flashes than in those without them¹⁰; later work discusses possible mechanisms¹¹¹⁴. These group findings are specific to their methods and participants. They do not show why one person had a symptom, and they do not validate Apple Watch wrist temperature as a hot-flash detector.

The 3 a.m. wake-up isn’t in your head

Across large cohorts, the share of women reporting disturbed sleep ranges from roughly 16–42% before the transition to 39–47% during it, and higher still afterward¹². Studies using polysomnography and actigraphy also report associations between nighttime vasomotor symptoms and objectively measured sleep fragmentation¹². These group findings do not explain one person’s wake-up.

Perigee reads your night against your own recent baseline — never a population average — so a broken night shows up as what it is: a data point in your pattern, not a verdict.

Breathing adds context, not a diagnosis

Apple Watch can record respiratory rate during sleep and show it beside other overnight metrics in Health and Vitals¹⁵¹⁶. It is a non-specific measurement: a change does not determine a menopause stage, label a hot flash, or establish any other cause. Apple also states that respiratory-rate measurements are not intended for medical use¹⁵.

Perigee therefore treats respiratory rate as supporting context only. When a sample is available, it can be compared with your own recent nights and considered alongside the rest of the night. When it is missing, the other available signals still stand; Perigee does not fill the gap or turn one breathing-rate value into a conclusion.