dip_calc {bp}

Nocturnal Blood Pressure Dipping Calculation

Description

Calculate the percent and average decline (or potentially reverse) in nocturnal blood pressure. This function is typically used with ABPM data, or at minimum, data with a corresponding a WAKE column available to indicate awake vs asleep.

Nocturnal blood pressure decline is an indicator of an individual's natural circadian rhythm. Studies have shown that individuals with diminished circadian rhythms are more likely to exhibit target organ damage. There is a "U-shaped" relationship that exists among the magnitude of nocturnal blood pressure decline; the extreme dippers and the non-dippers (including reverse dippers) are both more prone to mortality risk than normal dippers.

NOTE: Any reference to "sleep" in the bp package refers to an individual's nocturnal period; "sleep" is used in an informal sense for intuitive purposes. Technically, from a clinical perspective, indication of sleep is currently obtained through means of EEG or other highly specialized equipment. For all intents and purposes, sleep in the context of this package refers to actigraphy-inferred nocturnal periods of rest.

Usage

dip_calc(
  data,
  sleep_start_end = NULL,
  dip_thresh = 0.1,
  extreme_thresh = 0.2,
  inc_date = FALSE,
  subj = NULL
)

Arguments

data

User-supplied data set that must contain SBP, DBP, and either DATE_TIME or WAKE columns in order to distinguish between sleep and awake

In the event of non-ABPM data (i.e. a data set without a corresponding WAKE column), then a DATE_TIME column must be present in order to denote which times correspond to sleep and which times correspond to awake.

sleep_start_end

(optional) User-supplied manual override to adjust sleep interval indicating indicate start and end time corresponding to the sleep interval of interest. Must only contain 2 values and must be 24-hour denoted integers

Example: sleep_start_end = c(22,5) indicates a sleep period from 10pm - 5am.

NOTE: If the sleep_start_end function argument is specified, and no WAKE column exists, then awake/asleep indicators will be assigned according the the DATE_TIME column (which must exist). Otherwise, if sleep_int is not supplied, then the WAKE column will default to a sleep period between 11PM - 6AM as specified in the literature (see reference).

Furthermore, the sleep_int argument will override the WAKE column, which may cause unintended consequences in the event that the data set already contains a WAKE column.

dip_thresh

Default threshold for normal "Dipping" set to 0.10 (i.e. 10%). This value represents the maximum percentage that BP can fall during sleep and be characterized as "Normal" nocturnal decline (dipping). Specifically, this category includes all dips between 0% and this value.

extreme_thresh

Default threshold for "Extreme Dipping" set to 0.20 (i.e. 20%). This value represents the maximum percentage that BP can fall during sleep and be characterized as "Extreme" nocturnal decline (dipping). Specifically, this category includes all dips between the Normal dipping threshold and this value. NOTE: dip_thresh cannot exceed extreme_thresh.

inc_date

Default to FALSE. Indicates whether or not to include the date in the grouping of the final output

subj

Optional argument. Allows the user to specify and subset specific subjects from the ID column of the supplied data set. The subj argument can be a single value or a vector of elements. The input type should be character, but the function will comply with integers so long as they are all present in the ID column of the data.

Value

A list containing 2 tibble objects. The first tibble object lists grouped average values for SBP and DBP for awake and asleep periods. The second dip_pct tibble object lists the dipping percentage and classification according to the results from the first dip tibble. If inc_date = TRUE these two tibbles will be broken down further by date. There are 4 classifications a subject can have (assuming a default dipping threshold of 10% and extreme dipping threshold of 20% according to the original source):

• Reverse Dipper - no nocturnal decline (greater or equal to 0%)

• Non-Dipper - a nocturnal decline between 0 - 10%

• Dipper - a nocturnal decline between 10% and the extreme dipping % (20%)

• Extreme Dipper - a nocturnal decline exceeding 20%

References

Okhubo, T., Imai, Y., Tsuji, K., Nagai, K., Watanabe, N., Minami, J., Kato, J., Kikuchi, N., Nishiyama, A., Aihara, A., Sekino, M., Satoh, H., and Hisamichi, S. (1997). Relation Between Nocturnal Decline in Blood Pressure and Mortality: The Ohasama Study, American Journal of Hypertension 10(11), 1201–1207, doi: 10.1016/S0895-7061(97)00274-4.

Examples

## Load bp_hypnos
data(bp_hypnos)

## Process bp_hypnos
hypnos_proc <- process_data(bp_hypnos,
                     sbp = 'syst',
                     dbp = 'diast',
                     date_time = 'date.time',
                     hr = 'hr',
                     pp = 'PP',
                     map = 'MaP',
                     rpp = 'Rpp',
                     id = 'id',
                     visit = 'Visit',
                     wake = 'wake')

dip_calc(hypnos_proc)