# -*- coding: utf-8 -*-
from warnings import warn
import matplotlib.patches
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
from ..complexity import entropy_approximate, entropy_sample, fractal_dfa
from ..misc import NeuroKitWarning
from ..signal import signal_power, signal_rate
from ..signal.signal_formatpeaks import _signal_formatpeaks_sanitize
from ..stats import mad
[docs]
def rsp_rrv(rsp_rate, troughs=None, sampling_rate=1000, show=False, silent=True):
"""**Respiratory Rate Variability (RRV)**
Computes time domain and frequency domain features for Respiratory Rate Variability (RRV)
analysis.
Parameters
----------
rsp_rate : array
Array containing the respiratory rate, produced by :func:`.signal_rate`.
troughs : dict
The samples at which the inhalation onsets occur.
Dict returned by :func:`rsp_peaks` (Accessible with the key, ``"RSP_Troughs"``).
Defaults to ``None``.
sampling_rate : int
The sampling frequency of the signal (in Hz, i.e., samples/second).
show : bool
If ``True``, will return a Poincaré plot, a scattergram, which plots each breath-to-breath
interval against the next successive one. The ellipse centers around the average
breath-to-breath interval. Defaults to ``False``.
silent : bool
If ``False``, warnings will be printed. Default to ``True``.
Returns
-------
DataFrame
DataFrame consisting of the computed RRV metrics, which includes:
.. codebookadd::
RRV_SDBB|The standard deviation of the breath-to-breath intervals.
RRV_RMSSD|The root mean square of successive differences of the breath-to-breath intervals.
RRV_SDSD|The standard deviation of the successive differences between adjacent \
breath-to-breath intervals.
RRV_BBx|The number of successive interval differences that are greater than x seconds.
RRV_pBBx|the proportion of breath-to-breath intervals that are greater than x seconds, \
out of the total number of intervals.
RRV_VLF|Spectral power density pertaining to very low frequency band (i.e., 0 to\
.04 Hz) by default.
RRV_LF|Spectral power density pertaining to low frequency band (i.e., .04 to \
.15 Hz) by default.
RRV_HF|Spectral power density pertaining to high frequency band (i.e., .15 to \
.4 Hz) by default.
RRV_LFHF|The ratio of low frequency power to high frequency power.
RRV_LFn|The normalized low frequency, obtained by dividing the low frequency power by \
the total power.
RRV_HFn|The normalized high frequency, obtained by dividing the low frequency power by \
total power.
RRV_SD1|SD1 is a measure of the spread of breath-to-breath intervals on the Poincaré \
plot perpendicular to the line of identity. It is an index of short-term variability.
RRV_SD2|SD2 is a measure of the spread of breath-to-breath intervals on the Poincaré \
plot along the line of identity. It is an index of long-term variability.
RRV_SD2SD1|The ratio between short and long term fluctuations of the breath-to-breath \
intervals (SD2 divided by SD1).
RRV_DFA_alpha1|The "short-term" fluctuation value generated from Detrended Fluctuation \
Analysis i.e. the root mean square deviation from the fitted trend of the \
breath-to-breath intervals. Will only be computed if mora than 160 breath cycles \
in the signal.
RRV_DFA_alpha2|The long-term fluctuation value. Will only be computed if mora than \
640 breath cycles in the signal.
RRV_ApEn|The approximate entropy of RRV, calculated by :func:`.entropy_approximate`.
RRV_SampEn|The sample entropy of RRV, calculated by :func:`.entropy_sample`.
* **MFDFA indices**: Indices related to the :func:`multifractal spectrum <.fractal_dfa()>`.
See Also
--------
signal_rate, rsp_peaks, signal_power, entropy_sample, entropy_approximate
Examples
--------
.. ipython:: python
import neurokit2 as nk
rsp = nk.rsp_simulate(duration=90, respiratory_rate=15)
rsp, info = nk.rsp_process(rsp)
nk.rsp_rrv(rsp, show=True)
References
----------
* Soni, R., & Muniyandi, M. (2019). Breath rate variability: a novel measure to study the
meditation effects. International Journal of Yoga, 12(1), 45.
"""
# Sanitize input
rsp_rate, troughs = _rsp_rrv_formatinput(rsp_rate, troughs, sampling_rate)
# Get raw and interpolated R-R intervals
bbi = np.diff(troughs) / sampling_rate * 1000
rsp_period = 60 * sampling_rate / rsp_rate
# Get indices
rrv = {} # Initialize empty dict
rrv.update(_rsp_rrv_time(bbi))
rrv.update(
_rsp_rrv_frequency(rsp_period, sampling_rate=sampling_rate, show=show, silent=silent)
)
rrv.update(_rsp_rrv_nonlinear(bbi))
rrv = pd.DataFrame.from_dict(rrv, orient="index").T.add_prefix("RRV_")
if show:
_rsp_rrv_plot(bbi)
return rrv
# =============================================================================
# Methods (Domains)
# =============================================================================
def _rsp_rrv_time(bbi):
diff_bbi = np.diff(bbi)
out = {} # Initialize empty dict
# Mean based
out["RMSSD"] = np.sqrt(np.mean(diff_bbi**2))
out["MeanBB"] = np.nanmean(bbi)
out["SDBB"] = np.nanstd(bbi, ddof=1)
out["SDSD"] = np.nanstd(diff_bbi, ddof=1)
out["CVBB"] = out["SDBB"] / out["MeanBB"]
out["CVSD"] = out["RMSSD"] / out["MeanBB"]
# Robust
out["MedianBB"] = np.nanmedian(bbi)
out["MadBB"] = mad(bbi)
out["MCVBB"] = out["MadBB"] / out["MedianBB"]
# # Extreme-based
# nn50 = np.sum(np.abs(diff_rri) > 50)
# nn20 = np.sum(np.abs(diff_rri) > 20)
# out["pNN50"] = nn50 / len(rri) * 100
# out["pNN20"] = nn20 / len(rri) * 100
#
# # Geometrical domain
# bar_y, bar_x = np.histogram(rri, bins=range(300, 2000, 8))
# bar_y, bar_x = np.histogram(rri, bins="auto")
# out["TINN"] = np.max(bar_x) - np.min(bar_x) # Triangular Interpolation of the NN Interval Histogram
# out["HTI"] = len(rri) / np.max(bar_y) # HRV Triangular Index
return out
def _rsp_rrv_frequency(
rsp_period,
vlf=(0, 0.04),
lf=(0.04, 0.15),
hf=(0.15, 0.4),
sampling_rate=1000,
method="welch",
show=False,
silent=True,
):
power = signal_power(
rsp_period,
frequency_band=[vlf, lf, hf],
sampling_rate=sampling_rate,
method=method,
max_frequency=0.5,
show=show,
)
power.columns = ["VLF", "LF", "HF"]
out = power.to_dict(orient="index")[0]
if silent is False:
for frequency in out.keys():
if out[frequency] == 0.0:
warn(
"The duration of recording is too short to allow"
" reliable computation of signal power in frequency band " + frequency + "."
" Its power is returned as zero.",
category=NeuroKitWarning,
)
# Normalized
total_power = np.sum(power.values)
out["LFHF"] = out["LF"] / out["HF"]
out["LFn"] = out["LF"] / total_power
out["HFn"] = out["HF"] / total_power
return out
def _rsp_rrv_nonlinear(bbi):
diff_bbi = np.diff(bbi)
out = {}
# Poincaré plot
out["SD1"] = np.sqrt(np.std(diff_bbi, ddof=1) ** 2 * 0.5)
out["SD2"] = np.sqrt(2 * np.std(bbi, ddof=1) ** 2 - 0.5 * np.std(diff_bbi, ddof=1) ** 2)
out["SD2SD1"] = out["SD2"] / out["SD1"]
# CSI / CVI
# T = 4 * out["SD1"]
# L = 4 * out["SD2"]
# out["CSI"] = L / T
# out["CVI"] = np.log10(L * T)
# out["CSI_Modified"] = L ** 2 / T
# Entropy
out["ApEn"] = entropy_approximate(bbi, dimension=2)[0]
out["SampEn"] = entropy_sample(bbi, dimension=2, tolerance=0.2 * np.std(bbi, ddof=1))[0]
# DFA
if len(bbi) / 10 > 16:
out["DFA_alpha1"] = fractal_dfa(bbi, scale=np.arange(4, 17), multifractal=False)[0]
# For multifractal
mdfa_alpha1, _ = fractal_dfa(
bbi, multifractal=True, q=np.arange(-5, 6), scale=np.arange(4, 17)
)
for k in mdfa_alpha1.columns:
out["MFDFA_alpha1_" + k] = mdfa_alpha1[k].values[0]
if len(bbi) > 65:
out["DFA_alpha2"] = fractal_dfa(bbi, scale=np.arange(16, 65), multifractal=False)[0]
# For multifractal
mdfa_alpha2, _ = fractal_dfa(
bbi, multifractal=True, q=np.arange(-5, 6), scale=np.arange(16, 65)
)
for k in mdfa_alpha2.columns:
out["MFDFA_alpha2_" + k] = mdfa_alpha2[k].values[0]
return out
# =============================================================================
# Internals
# =============================================================================
def _rsp_rrv_formatinput(rsp_rate, troughs, sampling_rate=1000):
if isinstance(rsp_rate, tuple):
rsp_rate = rsp_rate[0]
troughs = None
if isinstance(rsp_rate, pd.DataFrame):
df = rsp_rate.copy()
cols = [col for col in df.columns if "RSP_Rate" in col]
if len(cols) == 0:
cols = [col for col in df.columns if "RSP_Troughs" in col]
if len(cols) == 0:
raise ValueError(
"NeuroKit error: _rsp_rrv_formatinput(): Wrong input, "
"we couldn't extract rsp_rate and respiratory troughs indices."
)
else:
rsp_rate = signal_rate(
df[cols], sampling_rate=sampling_rate, desired_length=len(df)
)
else:
rsp_rate = df[cols[0]].values
if troughs is None:
try:
troughs = _signal_formatpeaks_sanitize(df, key="RSP_Troughs")
except NameError as e:
raise ValueError(
"NeuroKit error: _rsp_rrv_formatinput(): "
"Wrong input, we couldn't extract "
"respiratory troughs indices."
) from e
else:
troughs = _signal_formatpeaks_sanitize(troughs, key="RSP_Troughs")
return rsp_rate, troughs
def _rsp_rrv_plot(bbi):
# Axes
ax1 = bbi[:-1]
ax2 = bbi[1:]
# Compute features
poincare_features = _rsp_rrv_nonlinear(bbi)
sd1 = poincare_features["SD1"]
sd2 = poincare_features["SD2"]
mean_bbi = np.mean(bbi)
# Plot
fig = plt.figure(figsize=(12, 12))
ax = fig.add_subplot(111)
plt.title("Poincaré Plot", fontsize=20)
plt.xlabel("BB_n (s)", fontsize=15)
plt.ylabel("BB_n+1 (s)", fontsize=15)
plt.xlim(min(bbi) - 10, max(bbi) + 10)
plt.ylim(min(bbi) - 10, max(bbi) + 10)
ax.scatter(ax1, ax2, c="b", s=4)
# Ellipse plot feature
ellipse = matplotlib.patches.Ellipse(
xy=(mean_bbi, mean_bbi),
width=2 * sd2 + 1,
height=2 * sd1 + 1,
angle=45,
linewidth=2,
fill=False,
)
ax.add_patch(ellipse)
ellipse = matplotlib.patches.Ellipse(
xy=(mean_bbi, mean_bbi), width=2 * sd2, height=2 * sd1, angle=45
)
ellipse.set_alpha(0.02)
ellipse.set_facecolor("blue")
ax.add_patch(ellipse)
# Arrow plot feature
sd1_arrow = ax.arrow(
mean_bbi,
mean_bbi,
-sd1 * np.sqrt(2) / 2,
sd1 * np.sqrt(2) / 2,
linewidth=3,
ec="r",
fc="r",
label="SD1",
)
sd2_arrow = ax.arrow(
mean_bbi,
mean_bbi,
sd2 * np.sqrt(2) / 2,
sd2 * np.sqrt(2) / 2,
linewidth=3,
ec="y",
fc="y",
label="SD2",
)
plt.legend(handles=[sd1_arrow, sd2_arrow], fontsize=12, loc="best")
return fig
