. 2018 Oct 2;9:1293. doi: 10.3389/fphys.2018.01293

Table 2.

Baseline characteristics and physiologic findings in the dyspnea group (N = 215).

${\overset{°}{V}}_{O2}$ at peak exercise, mL · min⁻¹· kg⁻¹	A (n = 28)	B (n = 64)	C (n = 77)	D (n = 46)


	9.3 (1.4)	13.0 (1.1)	18.0 (1.8)	25.0 (2.9)
Age, years	71.6 (6.7) ^‡‡	71.4 (7.6) ^¶¶¶	70.7 (7.1) ^##	66.2 (6.1)
BMI, kg·m⁻²	19.6 (2.9)	20.6 (3.1)	20.6 (2.8)	20.8 (3.5)
PULMONARY FUNCTION TEST
FEV₁, L	0.69 (0.21) ^†††† ^‡‡‡‡	0.91 (0.34) ^§ ^¶¶¶¶	1.13 (0.40) ^####	1.57 (0.59)
% Predicted FEV₁, %	29.1 (9.3) ^†††† ^‡‡‡‡	36.1 (11.6) ^§ ^¶¶¶¶	43.6 (14.7) ^####	57.0 (18.3)
VC, L	2.43 (0.68) ^† ^‡‡‡‡	2.66 (0.68) ^¶¶¶¶	2.92 (0.68) ^##	3.36 (0.80)
CARDIOPULMONARY EXERCISE TESTING
At Rest
Plasma norepinephrine, ng·mL⁻¹	0.80 (0.43) ^‡‡‡	0.71 (0.31) ^¶	0.70 (0.32) ^#	0.52 (0.18)
At Peak Exercise
Dyspnea, Borg scale	7.7 (2.3)	6.8 (2.6)	7.5 (2.4)	8.0 (1.7)
Dyspnea index, %	100.4 (19.1)	102.9 (22.6)	108.3 (26.1)	107.8 (28.9)
Breathing reserve, L·min⁻¹	0.5 (5.2)	0.8 (7.8)	−0.6 (10.9)	−0.2 (13.8)
%HR reserve, %	77.1 (10.6) ^† ^‡‡	78.2 (15.5) ^§§ ^¶¶¶	85.7 (12.4)	88.7 (12.1)
${\overset{°}{V}}_{E}$ , L·min⁻¹	23.6 (6.4) ^**^†††† ^‡‡‡‡	31.2 (7.6) ^§§§§ ^¶¶¶¶	40.0 (8.7) ^####	55.1(14.7)
V_T, mL	780 (245) ^*^†††† ^‡‡‡‡	981 (253) ^§§§§ ^¶¶¶¶	1245 (295) ^####	1561 (372)
Breathing frequency, breaths·min⁻¹	32 (8)	33 (6)	34 (7)	36 (6)
${\overset{°}{V}}_{E}$ /VCO₂	54 (12) ^**^††††^‡‡‡‡	47 (9) ^§ ^¶¶¶¶	42 (9) ^#	37 (9)
V_D/V_T	0.39 (0.05) ^†††† ^‡‡‡‡	0.35 (0.06) ^§§§§ ^¶¶¶¶	0.30 (0.06) ^####	0.22 (0.07)
PaO₂, mmHg	53.5 (11.4) ^† ^‡‡	59.1 (10.6)	61.2 (12.2)	63.6 (11.2)
PaO₂-slope, mmHg/(mL·min⁻¹)⁻¹	−7.2 (3.6) ^****^†††† ^‡‡‡‡	−3.8 (2.5) ^¶¶	−3.2 (1.7)	−2.2 (1.9)
PaCO₂, mmHg	44.2 (7.9) ^‡	42.9 (6.9)	41.9 (6.7)	39.7 (5.6)
A-aDo₂, mmHg	41.0 (10.6)	37.0 (11.8)	36.7 (13.8)	36.5 (12.2)
Plasma lactate, mg·dL⁻¹	18.2 (4.9) ^†† ^‡‡‡‡	20.8 (7.4) ^§§ ^¶¶¶¶	27.6 (9.0) ^####	40.0 (17.4)
${HCO}_{3}^{-}$ , mEq·L⁻¹	25.2 (4.0) ^† ^‡‡‡‡	24.4 (2.7) ^¶¶¶¶	23.3 (2.6) ^#	21.7 (3.0)
Plasma norepinephrine, ng·mL⁻¹	2.35 (1.47)	2.03 (1.17) ^§	2.72 (1.51)	2.66 (1.38)
Increase in plasma norepinephrine/Δ $\overset{°}{V}$ O₂ ng·mL⁻² · min	7.0 (6.0) ^****^†††† ^‡‡‡‡	3.0 (2.3)	3.0 (2.1)	2.2 (2.2)
pH	7.370 (0.029)	7.371 (0.043)	7.359 (0.039)	7.355 (0.035)

Values are presented as mean (SD) and were analyzed using the Tukey–Kramer honestly significant difference test. A-aDo₂, alveolar-arterial oxygen difference; BMI, body mass index; FEV₁, forced expiratory volume in one second; ${HCO}_{3}^{-}$ , bicarbonate ion; HR, heart rate; PaO₂, arterial oxygen tension; PaCO₂, arterial carbon dioxide tension; VC, vital capacity; ${\overset{°}{V}}_{D}$ / ${\overset{°}{V}}_{T}$ , physiologic dead space/tidal volume ratio; ${\overset{°}{V}}_{E}$ , minute ventilation; ${\overset{°}{V}}_{T}$ , tidal volume; ${\overset{°}{V}}_{O 2}$ , oxygen uptake; ${\overset{°}{V}}_{E}$ / $\overset{°}{V}$ CO₂, ventilatory equivalent for carbon dioxide; PaO₂-slope, peak PaO₂ – resting PaO₂/Δ ${\overset{°}{V}}_{O 2}$ (peak ${\overset{°}{V}}_{O2}$ – resting ${\overset{°}{V}}_{O2}$ ).

A vs. B;

p < 0.05,

^**

p < 0.01,

^***

p < 0.001,

^****

p < 0.0001.

A vs. C:

^†

p < 0.05,

^††

p < 0.01,

^††††

p < 0.0001.

A vs. D:

^‡

p < 0.05,

^‡‡

p < 0.01,

^‡‡‡

p < 0.001,

^‡‡‡‡

p < 0.0001.

B vs. C:

^§

p < 0.05,

^§§

p < 0.01,

^§§§§

p < 0.0001.

B vs. D:

^¶

p < 0.05,

^¶¶

p < 0.01,

^¶¶¶

p < 0.001,

^¶¶¶¶

p < 0.0001.

C vs. D:

p < 0.05,

^##

p < 0.01,

^####

p < 0.0001.