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Oximetry (SpO2) metrics

Source: R/spo2.R
spo2Metrics.Rd

Computes the standard blood-oxygen summary indices from an SpO2 series. Accepts SpO2 as a percentage (90) or a fraction (0.90; auto-detected and scaled). When time is supplied the time-below-threshold and desaturation index are duration-weighted; otherwise they are sample proportions/counts.

Usage

spo2Metrics(spo2, time = NULL, threshold = 90, desat = 3, window = 12)

Arguments

spo2

Numeric SpO2 series (percent or 0-1 fraction).

time

Optional sample times as POSIXct or numeric seconds (same length and order as spo2). Enables t90_min and per-hour odi.

threshold

Desaturation threshold percent for T90/CT90 (default 90).

desat

Drop (percentage points) below the rolling baseline that defines a desaturation event (default 3; 4 is also common).

window

Rolling-baseline length in samples for event detection (default 12).

Value

An spo2_metrics object: mean, nadir, pct_below, ct90, t90_min, n_desat, odi (events/hour), plus the settings.

References

Chung F et al. (2012) oximetry desaturation indices; standard ODI/CT90 definitions used in sleep-disordered-breathing screening.

See also

summarizeAppleSleep()

Examples

set.seed(1)
spo2 <- pmin(100, pmax(80, 97 + round(rnorm(200))))
spo2[50:55] <- 88   # a desaturation
spo2Metrics(spo2)
#> <spo2_metrics> n=200  mean=96.8%  nadir=88.0%
#>   <90%: 3.0% of samples
#>   desaturations (>=3 pt): 31
#>   note: no timing supplied (or Apple Watch spot checks) -> ODI/T90 unavailable or approximate