Respiratory muscle strength effect on linear and nonlinear heart rate variability parameters in COPD patients

Figures & data

Table 1 COPD patients’ clinical characteristics

Variables	COPD (n=10)
Age (years)	61.2±6.7
Males, n (%)	8 (80)
Caucasian, n (%)	10 (100)
BMI (kg/m^2)	25.6±4.8
BMI classification
Underweight, n (%)	4 (40)
Eutrophic, n (%)	2 (20)
Obese, n (%)	4 (40)
Smoking status
Ex-smoker, n (%)	9 (90)
Current smoker, n (%)	1 (10)
Cigarettes/year	7,665.0±3,101.9
PImax (cm H2O)	−72.1±30.8
PImax (% predicted)a	63.3±27.5
PEmax (cm H2O)	110.4±33.9
PEmax (% predicted)a	91.1±26.6
SVC (L/s)	0.9±0.4
FEV1 (L/s)	0.9±0.4
FEV1 (% predicted)b	31.9±13.6
FEV1/FVC (L/s)	46.5±11.6
FEV1/FVC (% predicted)b	58.7±15.4
Staging (GOLD)
Stage II, n (%)	2 (20)
Stage III, n (%)	3 (30)
Stage IV, n (%)	5 (50)

Notes: Data are presented as mean ± standard deviation and n (%).

a % of values predicted by Neder et al.¹⁶

b % of values predicted by Pereira et al.¹⁵

Abbreviations: COPD, chronic obstructive pulmonary disease; BMI, body mass index; PImax, maximum inspiratory pressure; PEmax, maximum expiratory pressure; SVC, slow vital capacity; FEV₁, forced expiratory volume in 1 second; FEV₁/FVC, ratio between FEV₁ and forced vital capacity; GOLD, Global Initiative for Chronic Obstructive Lung Disease.

Table 2 HRV indices at rest and during the RSA maneuver

Variables	COPD, n=10
	Rest	Respiratory sinus arrhythmia maneuver	P-value
RF (rpm)	19.4±2.3	–	–
I/E	–	1.1±0.1	–
ΔI/E	–	12.9±6.8	–
Mean RR (ms)*	714.4 (609.0–1,073.0)	699.1 (553.0–808.0)	0.57
SD RR (ms)*	16.0 (7.4–38.2)	30.3 (11.6–89.3)	0.08
Mean HR (1/min)	82.4±14.5	87.7±12.0	0.38
SD HR (1/min)*	2.5 (0.9–4.8)	4.8 (1.0–9.0)	0.06
RMSSD (ms)*	20.8 (5.5–43.7)	19.5 (9.8–70.2)	0.42
RR tri-index	5.0±2.9	8.6±5.4	0.07
LF (nu)*	46.2 (12.9–72.8)	88.7 (27.4–97.6)	0.01
HF (nu)*	53.5 (26.8–86.2)	11.2 (2.3–72.0)	0.01
LF/HF*	0.9 (0.1–2.7)	9.0 (0.3–42.2)	0.01
ApEn*	1.0 (0.8–1.1)	0.8 (0.6–1.1)	0.03
SampEn	1.6±0.3	1.0±0.2	,0.01

Notes: Data are presented as mean ± standard deviation or as median and (interquartile range). Student’s t-test was used for parametric data and the *Mann–Whitney test was used for nonparametric data. Significance level: P≤0.05.

Abbreviations: HRV, heart rate variability; RF, respiratory frequency; I/E, ratio between the average of the highest R–R interval values during expiration and the average of the lowest R–R interval values during inspiration, during the RSA-M; ∆I/E, difference between the average of the highest R–R interval values during expiration and the average of the lowest R–R interval values during inspiration, during the RSA-M; Mean RR, mean R–R interval; SD RR, R–R interval standard deviation; Mean HR, mean heart rate; SD HR, heart rate standard deviation; RMSSD, square root of the mean-squared differences of successive iR–R; RR tri-index, HRV triangular index; LF, power in the low-frequency band; HF, power in the high-frequency band; nu, normalized units; LF/HF, ratio between LF power and HF power; ApEn, approximate entropy; SampEn, sample entropy; RSA-M, respiratory sinus arrhythmia maneuver.

Figure 1 Moderate-to-strong correlations were found between PImax and PEmax, and spectral HRV indices during the RSA-M.

Notes: (A) Negative correlation between LF (nu) and PImax (cm H₂O); (B) negative correlation between LF (nu) and PEmax (cm H₂O); (C) positive correlation between HF (nu) and PImax (cm H₂O); (D) Positive correlation between HF (nu) and PEmax (cm H₂O). The Spearman’s correlation analysis was performed. Significance level: P≤0.05.
Abbreviations: HRV, heart rate variability; RSA-M, respiratory sinus arrhythmia maneuver; HF, power in the high-frequency band; LF, power in the low-frequency band; PImax, maximum inspiratory pressure; PEmax, maximum expiratory pressure; nu, normalized units; cm H₂O, centimeters of water.

Table 3 Linear regression analysis to predict LF from PImax, during the RSA-M

Variables	B coefficient	P-value
Constant	120.71	<0.001
PImax	−0.623	0.022

Notes: R²_adjusted =0.437; F=7.99 (P=0.022). LF prediction equation during the RSA-M: LF =120.71–(0.623× PImax).

Abbreviations: PImax, maximum inspiratory pressure; LF, power in the low-frequency band; RSA-M, respiratory sinus arrhythmia maneuver.

Figure 2 Strong correlations were also observed between HRV complexity indices (ApEn and SampEn) and PEmax during the RSA-M.

Notes: (A) Positive correlation between SampEn and PEmax (cm H₂O); (B) Positive correlation between ApEn and PEmax (cm H₂O). The Spearman’s correlation analysis was performed. Significance level: P≤0.05.
Abbreviations: HRV, heart rate variability; RSA-M, respiratory sinus arrhythmia maneuver; PEmax, maximum expiratory pressure; SampEn, sample entropy; ApEn, approximate entropy; cm H₂O, centimeters of water.

NederJAAndreoniSCastelo-FilhoANeryLEReference values for lung function tests. I. Static volumesBraz J Med Biol Res19993270371710412549

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PereiraCACSatoTRodriguesSCNew reference values for forced spirometry in white adults in BrazilJ Bras Pneumol200733439740617982531

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