Exercise Performance of Lowlanders with Chronic Obstructive Pulmonary Disease Acutely Exposed to 2048 m: A Randomized Cross-Over Trial

Figures & data

Table 1 Patients’ Characteristics (per-Protocol-Analysis)

Demographics
n, (Men/Women)	29 (14/15)
Age, y	65 (62; 69)
Height, m	1.68 (1.65; 1.73)
Weight, kg	70 (62; 83)
Body mass index, kg/m^2	26.2 (22.5; 28.7)
Current smokers, n (%)	7 (24)
Current smoking, pack-years	23 (3; 25)
Smoking, pack-years	40 (30; 53)
GOLD grade 2, n (%)	19 (66)
GOLD grade 3, n (%)	10 (34)
Medication
Inhaled β-adrenergics, n (%)	24 (83)
Inhaled anticholinergics, n (%)	22 (76)
Inhaled glucocorticosteroids, n (%)	14 (48)
Lung function
FVC, Liters	2.93 (2.54; 3.78)
FVC, % predicted	87 (79; 95)
FEV1, Liters	1.57 (1.22; 2.05)
FEV1, % predicted	60 (46; 69)
FEV1 / FVC	0.52 (0.43; 0.60)
Arterial blood gases
pH	7.44 (7.43; 7.46)
PaO2, kPa	8.7 (8.3; 9.6)
PaCO2, kPa	5.0 (4.6; 5.2)
SaO2, %	94.4 (92.4; 95.3)
Hemoglobin concentration, g/dL	14.2 (13.8; 15.2)
Comorbidities
Coronary artery disease, n (%)	1 (3)
Peripheral artery disease, n (%)	4 (14)
Diabetes mellitus, n (%)	4 (14)

Note: Values presented in median (interquartile range) or numbers and proportions.

Abbreviations: FVC, forced vital capacity; FEV₁, forced expiratory volume in the first second of expiration; PaO₂, partial pressure of arterial oxygen; PaCO₂, partial pressure of arterial carbon dioxide; SaO2, oxygen saturation by arterial blood gas analysis.

Figure 1 Study flow chart. Cardiopulmonary exercise tests were performed at 490 m and within 2–6 hours after arriving at 2048 m. *Cardiopulmonary exercise test from 1st sojourn included in the per-protocol analysis.

Abbreviations: CVD, cardiovascular disease; COPD, chronic obstructive pulmonary disease.

Table 2 Results at Peak Exercise

	490 m	2048 m	Median Difference (95% CI)^a
Time, min:sec	10:22 (9:37; 10:45)	9:40 (8:27; 10:05)	−0:36 (−1:05 to −0:14)*
Work rate, Watt	88 (75; 112)	77 (62; 104)	−5 (−8 to −2)*
% predicted	70 (60; 78)	68 (49; 75)	−4 (−7 to −1)*
% 490 m	100	94 (88; 100)	−6 (−11 to −2)*
SpO2, %	93 (90; 98)	86 (83; 90)	−8 (−9 to −4)*
V’O2, L/min	1.18 (1.04;1.61)	1.09 (0.89; 1.32)	−0.07 (−0.16 to −0.05)*
% predicted	79 (63; 90)	70 (56; 86)	−6 (−9 to −3)*
V’O2, mL/min/kg	17.85 (13.39; 19.98)	15.79 (12.02; 18.61)	−1.30 (−1.98 to −0.63)*
V’CO2, L/min	1.18 (1.04; 1.61)	1.09 (0.89; 1.32)	−0.07 (−0.10 to −0.05)*
% predicted	53 (41; 61)	48 (37; 55)	−3 (−6 to −2)*
VE/V’O2	37.6 (34.7; 41.5)	44.6 (36.2; 48.3)	4.8 (4.2 to 6.1)*
VE/V’CO2	37.8 (33.5; 41.3)	41.9 (36.9; 44.5)	4.4 (3.9 to 5.4)*
RER	1.00 (0.93; 1.04)	0.99 (0.97; 1.07)	0.02 (0.01 to 0.05)*
Tidal volumes, L	1.55 (1.18; 1.77)	1.54 (1.27; 1.82)	0.03 (−0.06 to 0.07)
Breathing frequency, 1/min	33 (28; 37)	32 (29; 38)	1 (−1 to 2)
VE, L/min	48.4 (34.7; 60.9)	48.6 (39.4; 61.8)	2.8 (0.9 to 4.2)*
MVV, L/min	62 (41; 82)	65 (45; 78)	2 (0 to 5)
Breathing reserve, L/min	11 (5; 16)	12 (7; 18)	1 (−2 to 3)
Breathing reserve, %MVV	15 (8; 30)	21 (11; 25)	−1 (−3 to 3)
Heart rate, 1/min	127 (119; 136)	127 (118; 140)	3 (−3 to 6)
HRR, 1/min	29 (19; 39)	25 (17; 36)	−3 (−6 to 3)
Borg CR10 Dyspnea	5 (4; 6)	5 (4; 5)	0 (0 to 1)
Borg CR10 Leg fatigue	3 (3; 5)	3 (3; 5)	0 (0 to 0)

Notes: Median (interquartile range) and median difference (95% confidence interval). ^aMedian differences were calculated by the approach from Hodges–Lehman median difference in the individuals, and does not represent the difference in medians between both altitudes. SpO₂, oxygen saturation by pulse oximetry; V’O₂, oxygen uptake; V’CO₂, output of carbon dioxide; V’_E, minute ventilation; RER, respiratory exchange ratio (V’CO₂/V’O₂); MVV, maximal voluntary ventilation; Breathing reserve, MVV – V’_E; HRR, heart rate reserve (220-age-heart rate). *P <0.05 vs 490 m.

Figure 2 Relative change of maximum power output in Watts from 490 to 2048 m. Lines represent individual patients.

Figure 3 Relative changes of physiological variables at peak exercise at 2048 m compared to 490 m. The bars represent the differences of the median values and the whiskers the 95% confidence interval.

Abbreviations: Wmax, maximal Watt; SpO₂, oxygen saturation by pulse oximetry; V’O₂, oxygen uptake; V’_E, minute ventilation.

Table 3 Mixed Linear Regression Analysis for the Work Rate Reduction, % Predicted

	Coef ± SE	95% CI	p-value
Wmax in COPD GOLD grade 2 at 490 m, % predicted	80 ± 4	72 to 88	<0.001
Difference in Wmax between GOLD 3 vs GOLD 2 at 490 m, % predicted	−28 ± 7	−41 to −14	<0.001
Altitude-induced change in Wmax in GOLD 2, % predicted	−4 ± 1	−7 to −2	0.002
Difference in altitude-induced change in Wmax between GOLD 3 vs GOLD 2	−3 ± 2	−8 to 1	0.128

Notes: N = 58 assessments. Wmax, maximal work capacity in percent predicted. Mixed linear regression analysis with work rate % predicted as dependent variable. COPD GOLD grade 2 represent patients with a forced expiratory volume in the first second of expiration (FEV₁) between ≥50 to <80% predicted; GOLD grade 2 represent patients with a FEV₁ between ≥30 to <50% predicted. Based on the regression model, the equation to calculate the Wmax can be outlined as follows: Wmax[%predicted]=80-28 x GOLD[0=GOLD 2;1=GOLD 3]-4 x Altitude[0=490 m; 1=2048 m]-3 x Altitude x GOLD. As an example, Wmax in % predicted in a COPD GOLD 3 patient at 2048 m would be: Wmax[% predicted]=80-28-4-3=45% predicted.