Lung function in relation to six-minute walk test in pulmonary hypertension

Figures & data

Table 1. Patient characteristics

Variables	All subjects (n = 50)
Female sex	26 (52%)
Age (years)	62.4 ± 11.8
BMI (kg/m^2)	25.5 ± 6.2
Smoking habit
Never smoker	20 (42%)
Ex-smoker	4 (8%)
Current smoker	24 (50%)
PH
Group 1	10 (20%)
Group 2	27 (54%)
Group 3	4 (8%)
Group 4	6 (12%)
Group 5	3 (6%)
LTOT	16 (32%)
OSAS	4 (8%)
COPD	10 (20%)
Pulmonary fibrosis	3 (6%)
Heart disease ^#	33 (66 %)
Diabetes	13 (26%)
History of cancer	16 (32%)

Values presented as means ± SD or N (%).

BMI = body mass index; PH = pulmonary hypertension; PH group 1 = pulmonary arterial hypertension; PH group 2 = PH due to left heart disease; PH group 3 = PH due to interstitial lung disease and/or hypoxia; PH group 4 = PH due to chronic thromboembolism; PH group 5 = PH with unclear and/or multifactorial mechanisms; LTOT = long-term oxygen therapy; OSAS = obstructive sleep apnoea syndrome; COPD = Chronic obstructive pulmonary disease.

^# Description of heart disease was following: 11 patients suffered from ischemic heart disease, 11 patients had valvular heart disease, 5 patients had dilated cardiomyopathy and 6 patients showed signs of left ventricular diastolic dysfunction, 3 patients had congenital heart disease.

Table 2. Indices of lung function, respiratory parameters and 6MWD

Variables	Absolute values	Percent predicted
FEV1 (L)	2.1 ± 0.7	76.4 ± 19.4
VC (L)	2.9 ± 1.0	81.7 ± 19.9
FEV1/VC (%)	70.0 ± 9.3	-
FEF25-75 (L/s)	1.6 ± 1.0	53.5 ± 29.4
PEF (L/s)	5.4 ± 2.2	78.6 ± 25.5
TLC (L)	5.1 ± 1.4	91.6 ± 17.8
RV (L)	2.1 ± 0.6	113.8 ± 40.0
RV/TLC (%)	42.4 ± 8.2	123.7 ± 26.9
DLCO (mmol/min/kPa)	4.1 ± 1.6	53.0 ± 17.4
DLCO/VA (mmol/min/kPa/L)	1.0 ± 0.3	70.3 ± 21.7
PaCO2 (kPa)	4.9 ± 0.6	-
PaO2 (kPa)	9.8 ± 1.9	-
SpO2 (%)	96 ± 3	-
6MWD (m)	343 ± 103	64.8 ± 18.8

Values presented as means ± SD. FEV₁ = forced expiratory volume during one second; VC = vital capacity; FEF_25–75 = forced expiratory flow between 25 % and 75 % of vital capacity; PEF = peak expiratory flow; TLC = total lung capacity; RV = residual volume; DLCO = diffusing capacity of the lung for carbon monoxide; PaCO₂ = arterial pressure of carbon dioxide; PaO₂ = arterial pressure of oxygen, SpO₂ = oxygen saturation; 6MWD: Six-minute walk distance.

Figure 1. Decreased lung function parameters in relation to 6MWD

6MWD (m) in relation to decreased FEV₁, PEF and VC (defined as <80% of predicted normal value) and FEV₁/VC (defined as <0.70).

Figure 2. Predictive value (expressed as r²) for 6MWD of single lung function measurements for all patients (a) and for PH due to left heart disease (b)

Correlations (expressed as Pearson’s r²-values from simple linear regression models) between a patient’s six-minute walk distance and different lung function parameters. (a) Only lung function parameters that were significantly correlated with 6MWD are shown. (b) * indicates significant relation, p < 0.05.

Table 3. Correlations between 6MWD and different lung function or physiological parameters

Lung function parameters	Pearson’s r^2 for correlation with 6MWT	p-Value	Adjusted^a p-value
PEF (L/s)	0.19	0.001	0.01
VC (L)	0.18	0.002	0.01
FEV1 (L)	0.18	0.002	0.02
RV/TLC (%)	0.14	0.01	0.07
FEF25-75 (L)	0.12	0.01	0.051
TLC (L)	0.11	0.02	0.08
FEV1/VC (%)	0.08	0.050	0.04
DLCO (mmol/min/kPa)	0.06	0.10	0.25
PaCO2 (kPa)	0.02	0.36	0.23
SpO2 (%)	0.01	0.51	0.67
PaO2 (kPa)	0.01	0.52	0.48
RV (L)	0.01	0.47	0.69
DLCO/VA (mmol/min/kPa/L)	< 0.01	0.86	0.89

* Adjusted for age, sex, BMI, and smoking habits.

Table 4. Lung function parameters in relation to desaturation during 6MWT

Variable	Non-desaturation (n = 28)	Desaturation (n = 22)	p-Value
DLCO/VA (mmol/min/kPa/L)	1.1 (1.0–1.2)	0.9 (0.7–1.0)	0.003
Baseline SpO2 (%)	97.1 (96.4–97.9)	94.9 (92.9–96.8)	0.02
(%)	72.4 (69.3–75.4)	67.1 (62.5–71.6)	0.04
PaO2 (kPa)	10.3 (9.6–10.9)	9.2 (8.2–10.1)	0.047
DLCO (mmol/min/kPa)	4.5 (3.8–5.1)	3.7 (3.0–0.9)	0.09
VC (L)	2.8 (2.5–3.1)	3.1 (2.6–3.6)	0.21
RV (L)	2.1 (1.8–2.3)	2.3 (2.0–2.6)	0.22
TLC (L)	4.9 (4.5–5.4)	5.4 (4.7–6.2)	0.22
PaCO2 (kPa)	5.0 (4.8–5.2)	4.8 (4.5–5.1)	0.29
FEF25-75 (L/s)	1.7 (1.4–2.0)	1.5 (1.0–1.9)	0.35
PEF (L/s)	5.2 (4.5–5.8)	5.7 (4.5–6.9)	0.39
FEV1 (L)	2.0 (1.8–2.2)	2.1 (1.8–2.5)	0.51
RV/TLC (%)	41.9 (38.7–45.2)	43.0 (39.2–46.7)	0.67

Values are presented as means (confidence interval) for patients who exhibited exertional desaturation and patients without exercise-induced desaturation. p-values pertain to the statistical outcomes of the t-tests between the groups.