Utility of ultrasound assessment of diaphragmatic function before and after pulmonary rehabilitation in COPD patients

Figures & data

Table 1 Baseline characteristics of the population

Characteristics	N=25
Age (years)	70.6±6.5
BMI (kg/m^2)	25.04±4.88
Gender n (%)
Female	2 (8.0%)
Male	23 (92.0%)
Smoking history
No smoker	1 (4%)
Current smoker	7 (28%)
Ex-smoker	17 (68%)
GOLD stages
1	0 (0%)
2	5 (20%)
3	14 (56%)
4	6 (24%)
Charlson index
3	5 (20%)
4	8 (32%)
5	12 (48%)

Note: Data are presented as mean ± SD or n (%).

Abbreviations: BMI, body mass index; GOLD, Global Initiative for Chronic Obstructive Lung Disease; Charlson index, Charlson comorbidity index.

Table 2 Patients’ characteristics before and after pulmonary rehabilitation

N=25	Pre-PR	Post-PR	P-value
Spirometry
FVC%	83 (73–101)	89 (76–102)	0.020
FEV1%	43 (34–50)	48 (39–55)	0.001
PEF%	41 (40–50)	45 (40–51)	0.024
FEV1/FVC%	41 (34–46)	53 (47–63)	<0.001
VR%	132 (103–155)	129 (100–144)	0.002
TLC%	105 (97–115)	102 (97–112)	0.040
RV/TLC%	48 (38–52)	45 (36–50)	<0.01
Arterial blood gas
pH	7.41 (7.40–7.42)	7.41 (7.40–7.42)	1
SaO2%	94 (91–95)	93 (92–95)	0.008
PaO2, mmHg	65 (59–70)	67 (60–71)	0.016
PaCO2, mmHg	45 (41–49)	43 (40–45)	0.041
6MWD (m)	250 (150–350)	300 (210–400)	<0.001
CAT	26 (21–34)	24 (20–30)	<0.001
MRC	4 (3–4)	3 (2–3)	<0.001
BODE	6 (4–7)	4 (3–6)	0.001

Note: Data are presented as median (25th–75th percentiles).

Abbreviations: PFTs, pulmonary function tests; PR, pulmonary rehabilitation; FVC, forced vital capacity; FEV₁, forced expiratory volume in 1 second; PEF, peak forced expiratory flow; FEV₁/FVC, Tiffeneau index; RV, residual volume; TLC, total lung capacity; RV/TLC, Motley index; ABG, arterial blood gas; 6MWD, 6-minute walking distance; CAT, COPD Assessment Test; MRC, Medical Research Council dyspnea score; BODE, BODE index (Body mass index, airflow Obstruction, Dyspnea, and Exercise).

Table 3 Patients’ ultrasonographic characteristics before and after pulmonary rehabilitation

N=25	Pre-PR	Post-PR	P-value
Diaphragm zapp (mm)
Lzapp TLC	26 (18–31)	23 (19–26)	0.002
Lzapp FRC	38 (32–41)	41 (35–44)	<0.001
Szapp TLC	5 (3–6)	4 (3–5)	0.001
Szapp FRC	4 (3–4)	3 (3–4)	0.027
Diaphragmatic excursion (mm)
Quiet breathing	23 (16–27)	27 (22–31)	<0.001
Deep breathing	36 (25–53)	50 (35–58)	<0.001
Rectus femoris area (m^2)	4 (3–4)	4 (3–5)	<0.001

Note: Data are presented as median (25th–75th percentiles).

Abbreviations: PR, pulmonary rehabilitation; zapp, diaphragm zone of apposition; Lzapp, length of diaphragm zone of apposition; Szapp, thickness of diaphragm zone of apposition; TLC, total lung capacity; FRC, functional residual capacity.

Table 4 Patients’ percentage of change of ultrasonographic measurements after pulmonary rehabilitation between “markedly improved” and “slightly improved” patients based on MCID at 6MWT

Ultrasonographic measurements	6MWD >54 m N=8	6MWD <54 m N=17	P-value
Diaphragm zapp
ΔLzapp TLC%	−15 (−26 to −12)	−18 (−23 to −9)	0.791
ΔLzapp FRC%	12 (10–15)	8 (3–11)	0.023
ΔSzapp TLC%	−5 (−8 to −2)	−5 (−10 to −3)	0.733
ΔSzapp FRC%	−6 (−9 to 0)	−7 (−11 to 0)	0.850
Diaphragmatic excursion
ΔQuiet breathing, %	5 (2–10)	15 (3–44)	0.112
ΔDeep breathing, %	6 (1–12)	17 (5–47)	0.132
ΔRectus femoris area, %	10 (6–15)	8 (4–12)	0.850

Note: Data are presented as median (25th–75th percentiles).

Abbreviations: MCID, minimally clinical important difference; PR, pulmonary rehabilitation; zapp, diaphragm zone of apposition; Lzapp, length of diaphragm zone of apposition; Szapp, thickness of diaphragm zone of apposition; TLC, total lung capacity; FRC, functional residual capacity; 6MWD, 6-minute walking distance; 6MWT, 6-minute walking test.

Figure 1 Correlation between Lzapp and 6MWT.

Note: Spearman rank order correlation between the change (%) of Lzapp at FRC and the change (delta meters) in 6MWD before and after PR (rho=0.49, P=0.02).

Abbreviations: Lzapp, diaphragm zone of apposition length; FRC, functional residual capacity; 6MWD, 6-minute walking distance; 6MWT, 6-minute walking test.

Figure 2 Difference in ΔLzapp% between patients with a minimal clinically significant difference for 6MWD after PR.

Notes: Box plots illustrating the change (%) of Lzapp at FRC between patients who “slightly improved” (who performed a 6MWD of <54 m) or “markedly improved” (who performed a 6MWD of >54 m) at the 6MWT after PR, *P<0.05 (Mann–Whitney U-test). The red line represents the ΔLzapp% cutoff value determined by the receiver operating characteristic (ROC) curve analysis showed in Figure 4.
Abbreviations: Lzapp, length of diaphragm zone of apposition; FRC, functional residual capacity; 6MWD, 6-minute walking distance; 6MWT, 6-minute walking test; PR, pulmonary rehabilitation.

Table 5 Patients’ percentage of change of ultrasonographic measurements after pulmonary rehabilitation between “markedly improved” and “slightly improved” patients based on MCID at CAT

Ultrasonographic measurements	CAT ≥2 N=14	CAT <2 N=11	P-value
Diaphragm Zapp
ΔLzapp TLC%	−18 (−26 to −15)	−13 (−23 to −2)	0.197
ΔLzapp FRC%	11 (10–12)	4 (2–11)	0.043
ΔSzapp TLC%	−4 (−8 to −3)	−6 (−10 to −2)	0.863
ΔSzapp FRC%	−5 (−10 to 0)	−8 (−12 to 0)	0.756
Diaphragmatic excursion
ΔQuiet breathing, %	10 (1–15)	38 (3–60)	0.180
ΔDeep breathing, %	14 (6–31)	17 (3–47)	0.913
ΔRectus femoris area, %	8 (3–17)	8 (4–12)	1

Note: Data are presented as median (25th–75th percentiles).

Abbreviations: MCID, minimally clinical important difference; PR, pulmonary rehabilitation; Zapp, diaphragm zone of apposition; Lzapp, length of diaphragm zone of apposition; Szapp, thickness of diaphragm zone of apposition; TLC, total lung capacity; FRC, functional residual capacity; CAT, COPD Assessment Test.

Figure 3 Difference in ΔLzapp% between patients with a minimal clinically significant difference for CAT after PR.

Notes: Box plots illustrating the change (%) of Lzapp at FRC between patients “slightly improved” (who achieved a <2 points reduction of CAT score) or “markedly improved” (who achieved ≥2 points reduction in CAT score), *P<0.05 (Mann–Whitney U-test). The red line represents the ΔLzapp% cutoff value determined by the receiver operating characteristic (ROC) curve analysis showed in Figure 5.
Abbreviations: Lzapp, length of diaphragm zone of apposition; FRC, functional residual capacity; CAT, COPD Assessment Test; PR, pulmonary rehabilitation.

Figure 4 Receiver operating characteristic (ROC) curve for ΔLzapp% in relation to 6MWD.

Note: ROC curves estimate the ability of Lzapp change (as percentage of baseline) to predict a significant improvement in 6MWD after PR (AUC=0.83, cutoff ≥10%, sensitivity=83%, specificity=74%).

Abbreviations: AUC, area under the curve; Lzapp, length of diaphragm zone of apposition; FRC, functional residual capacity; 6MWD, 6-minute walking distance; 6MWT, 6-minute walking test; PR, pulmonary rehabilitation.

Figure 5 Receiver operating characteristic (ROC) curve for ΔLzapp% in relation to CAT.

Note: ROC curves estimate the ability of Lzapp change (as percentage of baseline) to predict a significant improvement in CAT after PR (AUC=0.76, cutoff >9%, sensitivity=80%, specificity=62%).
Abbreviations: AUC, area under the curve; Lzapp, length of diaphragm zone of apposition; FRC, functional residual capacity; CAT, COPD Assessment Test; PR, pulmonary rehabilitation.