Cardiac Autonomic Function and Reactivity Tests in Physically Active Subjects with Moderately Severe COPD

Figures & data

Table 1. Baseline characteristics.

Variables	COPD (n, 26) M ± SD	Controls (n, 22) M ± SD	p-Value
Age (years)	65.8 ± 8.99	64.2 ± 8.5	0.538^t
Sex, male (%)	23 (88.5%)	19 (86.4%)	0.582^X
Height (m)	1.70 ± 0.06	1.76 ± 0.08	0.008^*^t
Weight (kg)	75.3 ± 10.22	76.0 ± 10.57	0.807^t
BMI (Kg/m^2)	26.2 ± 3.47	24.6 ± 2.82	0.102^t
HR (bpm)	72.9 ± 11.48	61.3 ± 7.82	0.001^*^t
Systolic blood pressure	139.7 ± 23.48	136.8 ± 17.67	0.642^t
Diastolic blood pressure	75.5 ± 11.7	71.7 ± 7.50	0.191^t
MAP	99.1 ± 15.69	95.2 ± 9.64	0.313^t
Lung function
FEV1 (% FEV1 predicted)	1.17 ± 0.53 (39.5%)	—
FVC (% FVC predicted)	2.97 ± 0.79 (79.6%)	—
FEV1/ FVC	36.4 ± 14.83%	—
PEF(% PEF predicted)	6.0 ± 9.65 (52.9%)	—
Medication (vasoactive) use
Opiates	1(3.8%)	0(0%)	0.364^X
Antidepressants (tricyclic)	2(11.5%)	0(0%)	0.194^X
Diuretics	2(7.7%)	0(0%)	0.194^X
Beta-blockers	7(26.9%)	0(0%)	0.010^*^X
Calcium channel blockers	2(7.7%)	0(0%)	0.194^X
ACE inhibitors	8(30.8%)	1(4.5%)	0.044^*^X
Sedatives	1(3.8%)	0(0%)	0.364^X
Anticonvulsants	1(3.8%)	0(0%)	0.364 ^X

Notes: bpm, beats per minute; M ± SD, mean and standard deviation; m, meters; kg, kilogram; ms, milliseconds; %, percentage; mmHg, millimeter of mercury; MAP, mean arterial pressure; BP, blood pressure; FEV₁, forced expiratory volume in first second; FVC, forced vital capacity; PEF, peak expiratory flowrate; ACE, angiotensin converting enzyme; HR, heart rate; BMI, body mass index; MAP, mean arterial pressure.

^* significant difference at p < 0.05 alpha probability level;

^t results based upon independent samples T-test statistics;

^X results based on Chi² tests.

Table 2. Comparison of resting autonomic function parameters between COPD and controls.

Variables	COPD (n,26) M ± SD	Controls (n,22) M ± SD	p-Value
Time domain HRV analyses
SDNN (ms)	31.0 ± 13.18	40.38 ± 17.64	0.067^m
RMSSD(ms)	18.5 ± 5.78	22.9 ± 10.13	0.065^t
NN50(count)	6.9 ± 8.89	7.5 ± 7.18	0.359^m
pNN50(%)	2.3 ± 3.09	2.6 ± 2.34	0.263^m
RR tri	6.8 ± 2.13	8.4 ± 3.46	0.055^t
TINN	113.5 ± 58.43	116.1 ± 88.03	0.917^m
Mean RR (ms)	865.6 ± 185.75	991.8 ± 133.43	0.011^*^t
Frequency domain HRV analyses
LF (ms^2)	219.9 ± 158.56	351.9 ± 256.66	0.035^*^t
HF (ms^2)	144.9 ± 93.62	189..8 ± 277.65	0.442^t
LF (n.u.)	56.8 ± 18.96	65.5 ± 17.96	0.113^t
HF (n.u.)	43.1 ± 18.95	34.4 ± 17.92	0.113^t
LF/HF ratio	2.2 ± 2.29	2.9 ± 2.37	0.104^m
Nonlinear HRV analyses
SD1(ms)	13.1 ± 4.09	19.4 ± 14.63	0.041^*^t
SD2(ms)	41.7 ± 18.53	54.2 ± 25.15	0.056^m
Lmean (beats)	12.3 ± 5.30	14.8 ± 6.25	0.104^m
Lmax (beats)	241.6 ± 112.92	227.3 ± 97.11	0.645^t
Detrended fluctuations (DFA): α1	1.1 ± 0.21	1.2 ± 0.28	0.437^t
Detrended fluctuations (DFA): α2	1.0 ± 0.18	1.0 ± 0.29	0.646^m
Shannon entropy (ShannEn)	3.2 ± 0.36	3.4 ± 0.38	0.158^t
Approximate entropy (ApEn)	1.1 ± 0.12	0.98 ± 0.14	0.02^*^t
Sample entropy (SampEn)	1.6 ± 0.38	1.4 ± 0.51	0.170^t
Correlation dimension (D2)	0.9 ± 0.84	1.3 ± 1.13	0.242^m
BRS
xBRS (ms.mmHg)	5.4 ± 3.18	8.0 ± 5.99	0.138^m
Mean tau (s)	1.7 ± 0.94	2.2 ± 0.68	0.051^m
R^2	0.70 ± 0.04	0.70 ± 0.03	0.918^t
Interval (ms)	120.2 ± 97.99	122.3 ± 80.97	0.650^m

Notes: M ± SD, mean and standard deviation; SDNN, standard deviation of all normal R-R intervals; RMSSD, the root mean square of differences of successive RR intervals; NN50, number of consecutive RR intervals that differ more than 50 ms; pNN50, the percentage of NN50, SD₁, the standard deviation of the Poincaré plot perpendicular to the line-of-identity; SD₂, the standard deviation of the Poincaré plot along the line-of-identity; RR tri, the integral of the RR interval histogram divided by the maximum of the histogram; LF, low frequency; HF, high frequency; LF/HF, ratio of LF and HF frequency band powers; ms = milliseconds, nu = normalized units; xBRS, cross-correlational baroreceptor sensitivity; %, percentage;

^* significant difference at p < 0.05 alpha probability level;

^t results based upon independent samples T-test;

^m results based on Mann–Whitney U-test.

Table 3. Results of cardio-vagal indices for COPD and control subjects following autonomic reactivity tests.

	COPD (n, 26) M ± SD	Controls (n, 22) M ± SD	p-Value
Deep breathing
HRDB (bpm)	12.1 ± 6.87	12.3 ± 7.09	0.869^m
Valsalva maneuver
VR	1.66 ± 0.44	1.41 ± 0.25	0.076^m
VI	1.55 ± 0.44	1.44 ± 0.3	0.488^m
BRS_a (mmHg/sec)	5.4 ± 2.55	5.4 ± 3.84	0.972^t
BRS_v (sec/mmHg)	2.8 ± 2.34	2.2 ± 1.6	0.547^m
BRS_g	12.4 ± 7.68	15.6 ± 20.42	0.399^m
PRT (sec)	5.5 ± 3.78	4.6 ± 2.58	0.374^t
PP drop	6.1 ± 4.74	7.9 ± 7.81	0.419^t
Inadequate VM (loss of any phase)	11(42%)	4(18%)	0.121^X
Head up tilt
Initial OH	5(19.2%)	1(4.5%)	0.139^X
OH	7(26.9%)	2(9%)	0.132^X
Delayed OH	7(26.9%)	3(13%)	0.293^X
POTS	1(3.8%)	0(0%)	0.364^X
Early stop due to other reasons	1(3.8%)	0(0%)	0.364^X

Notes: data expressed as mean ± standard deviation for continuous variables and as absolute frequency and percentages for categorical variables. Bpm, beats per minute; mmHg, millimeter of mercury; OH, orthostatic intolerance; POTS, postural orthostatic tachycardia syndrome; HR_DB, heart rate response to deep breathing; BRS_a, adrenergic baroreceptor sensitivity; BRS_v, vagal baroreceptor sensitivity; BRS_g, global baroreceptor sensitivity; PP drop, pulse pressure drop; PRT, Pressure recovery time; VI, valsalva index, VR, valsalva ratio; VM, Valsalva maneuver.

^* = significant difference at p < 0.05 alpha probability level,

^X = results based upon Chi² tests,

^m = results based on Mann–Whitney U-test.

Figure 1. Cardiovascular responses to head up tilt (HUT). Graphs are plotted as a function the relevant time (categorical) intervals of HUT parameter. The standard deviation (SD) of each time point is represented by the error bars.