Is cardiac autonomic modulation during upper limb isometric contraction and Valsalva maneuver impaired in COPD patients?

Figures & data

Figure 1 Flowchart – sampling and study phases.

Notes: 5′: 5 minutes; 2′: 2 minutes; 15″: 15 seconds.
Abbreviations: n, number of patients; IC, isometric contraction; VM, Valsalva maneuver.

Table 1 COPD patients’ clinical characteristics

Variables	COPD (n=22)
Age (years)	63.5±7.3
Sex, male, n (%)	15 (68.2)
BMI (kg/m^2)	26.0±5.2
BMI classification
Underweight, n (%)	5 (22.7)
Eutrophic, n (%)	7 (31.8)
Obese, n (%)	10 (45.5)
Pulmonary volumes
FEV1 (L/s)	1.0±0.6
FEV1 (% predicted)	38.0±19.5
FVC (L/s)	1.9±0.5
FVC (% predicted)	56.2±16.5
FEV1/FVC	0.5±0.1
FEV1/FVC (% predicted)	65.3±21.3
Staging (GOLD)
Stage II, n (%)	5 (22.7)
Stage III, n (%)	10 (45.5)
Stage IV, n (%)	7 (31.8)
Respiratory muscle strength
MIP (cmH2O)	−68.0±29.9
MIP (% predicted)	72.9±33.9
MEP (cmH2O)	99.2±38.3
MEP (% predicted)	98.6±33.3
Hand-grip strength
Dominant (kgf)	30.3±11.1
30% (sustained)	9.0±3.4
MIP <60 cmH2O, n (%)
Yes	11 (50.0)
No	11 (50.0)

Note: Data presented as mean ± standard deviation unless stated otherwise.

Abbreviations: n (%), number of patients (% of sample size); BMI, body mass index; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; GOLD, Global Initiative for Chronic Obstructive Lung Disease; MIP, maximum inspiratory pressure; MEP, maximum expiratory pressure.

Table 2 Clinical and HRV parameters at rest, during IC and during recovery

Variables	COPD n=22
	Rest	IC	Recovery
SBP (mmHg)	109.5±11.8	124.0±15.8*	117.6±10.4
DBP (mmHg)	70.2±7.7	73.9±7.1*	67.8±6.7α
RF (rpm)	18.6±2.9	21.6±2.9*	19.8±3.0
BORG – upper	6.0 (6.0–6.0)	13.0 (9.2–14.0)*	8.0 (6.2–9.0)α,#
limb
SpO2 (%)	93.1±2.2	93.4±1.7	94.0±1.9
Mean RR (ms)	720.9±120.5	717.5±87.2	715.4±86.7
STD RR (ms)	17.6±9.0	12.8±7.4	18.4±7.3
Mean HR (1/min)	79.4±13.4	86.9±12.0*	80.1±13.9
STD HR (1/min)	2.0 (1.7–2.3)	1.5 (1.0–1.9)*	2.2 (1.5–2.9)
RMSSD (ms)	17.0 (10.0–29.9)	12.4 (9.2–15.7)*	17.6 (11.3–22.0)α
RR tri index	4.4 (2.8–6.2)	3.7 (2.2–4.5)*	4.8 (3.3–6.5)α
HF (nu)	41.7±20.5	35.5±14.8*	45.3±23.3α
LF (nu)	53.3±21.8	61.0±19.6*	48.3±23.2α
LF/HF	1.3 (0.6–4.2)	1.4 (1.1–2.7)*	0.9 (0.2–1.4)α

Notes: Data are presented as mean ± standard deviation or as median and interquartile range. ANOVA with Tukey’s post hoc analysis was performed:

* (P<0.05) for IC vs rest;

α (P<0.05) for recovery vs IC;

# (P<0.05) for recovery vs rest.

Abbreviations: HRV, heart rate variability; IC, isometric contraction; SBP, systolic blood pressure; DBP, diastolic blood pressure; RF, respiratory frequency; SpO₂, peripheral oxygen saturation; mean RR, mean RR interval; STD RR, RR interval standard deviation; mean HR, mean heart rate; STD HR, heart rate standard deviation; RMSSD, square root of the mean squared differences of successive RR intervals; RR tri index, HRV triangular index; LF, low frequency; HF, high frequency; nu, normalized units; LF/HF, ratio between LF power and HF power; ANOVA, analysis of variance.

Figure 2 Relationship between respiratory muscle strength and lung function, and heart rate variability index during upper limb isometric contraction.

Notes: (A) Negative correlation between RMSSD (ms) and FEV₁ (L/s); (B) negative correlation between mean HR (1/min) and FEV₁ (L/s); (C) negative correlation between RMSSD (ms) and FVC (L/s); (D) positive correlation between HF (nu) and MIP (cmH₂O). The Pearson correlation analysis was performed. Significance level: P≤0.05.
Abbreviations: RMSSD, square root of the mean squared differences of successive RR intervals; FEV₁, forced expiratory volume in 1 second; mean HR, mean heart rate; FVC, forced vital capacity; HF, high frequency; nu, normalized units; MIP, maximum inspiratory pressure; cmH₂O, centimeters of water.

Table 3 Results of multiple linear regression to determine the influence of FEV₁ and FVC on mean HR during upper limb isometric contraction

Variables	β coefficient	P-value
Constant	64.58	<0.001
FEV1	−18.92	0.018
FVC	21.64	0.014

Notes: Adjusted R²=0.298; F=3.67 (P=0.045). Equation to predict mean HR during isometric contraction: 64.58 + (21.64× FVC) – (18.92× FEV₁).

Abbreviations: FEV₁, forced expiratory volume in 1 second; mean HR, mean heart rate; FVC, forced vital capacity.

Figure 3 Response of HR during the VM in COPD patients.

Notes: (A) Beat-to-beat HR response during the VM of one patient. a, rest; b, peak of the VM; c, Nadir value and d, recovery. COPD patients presented an expected HR response pattern, with an increase during the VM, followed by bradycardia after cessation of the VM, and with a final increase during recovery. (B) VI of the COPD patients. The mean VI value (=0.75±0.0) indicates an ANS integrity loss in these patients.
Abbreviations: ANS, autonomic nervous system; HR, heart rate; VM, Valsalva maneuver; VI, Valsalva index.

Figure 4 HR values during the VM.

Notes: ANOVA with Tukey’s post hoc analysis was performed. Significance level: P<0.05.
Abbreviations: HR, heart rate; VM, Valsalva maneuver; ANOVA, analysis of variance.

Figure 5 Relationship between lung function and HR values during the VM in COPD patients.

Notes: (A) Negative correlation between FEV₁/FVC (% predicted) and HR; (B) negative correlation between FEV₁/FVC (% predicted) and HR during the VM. Significance level: P<0.05. The Pearson correlation analysis was performed.
Abbreviations: HR, heart rate; VM, Valsalva maneuver; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity.