Functional and structural impairments of the pulmonary system in middle-aged people with cervical and upper thoracic spinal cord injuries

Figures & data

Table 1 Functional and structural assessments of the pulmonary system.

Assessment	Definition of parameter
Functional assessments
Spirometry
Vital capacity (VC)	The volume change between full inspiration and complete expiration (L)
Slow vital capacity (SVC)	Vital capacity performed with an unforced and complete expiration (L)
Forced vital capacity (FVC)	Vital capacity performed with a maximally forced and complete inspiration/expiration (L)
Forced expiratory volume in 1 s (FEV1)	The volume of air exhaled during the first second of the FVC (L)
FEV1/FVC	FEV1 to FVC ratio
MEF50	Maximal forced expiratory flow after 50% of the FVC has been exhaled (L/s)
Diffusing capacity
Diffusing capacity of the lungs for carbon monoxide (DLCO)	Total CO uptake by the lung per unit of time per unit CO driving pressure (mmol/(min kPa))
Alveolar volume (VA)	Alveolar volume measured by gas dilution (L)
Carbon monoxide transfer coefficient (kCO)	The concentration fall in alveolar CO per unit CO driving pressure (ml/(min kPa L))
Impulse oscillometry
Resistance at 5 Hz (R5)	The resistive component of the respiratory impedance including central and peripheral airways, lung tissue and chest wall resistance measured at 5 Hz (kPa/(L/s))
Resistance at 20 Hz (R20)	The resistive component of the respiratory impedance measured at 20 Hz, including mainly central airway resistance and to a lesser extent peripheral airways, lung tissue and chest wall resistance (kPa/(L/s))
Resistance at 5 Hz minus 20 Hz (R5-R20)	The resistive component of the respiratory impedance measured at 5 Hz minus the component measured at 20 Hz, indicating the resistive component of the small airways (kPa/(L/s))
Reactance at 5 Hz (X5)	The reactive component of the respiratory impedance incorporating the mass-inertive forces of the moving air column (inertance) and the elastic properties of lung periphery (elastance) at 5 Hz (kPa/(L/s))
Resonant frequency (Fres)	The point at which elastance and inertance are equal (Hz)
Reactance curve area below zero (AX)	The quantitative index of the total respiratory reactance between 5 Hz and the resonant frequency (kPa/L)
Structural assessments
Computed tomography
Emphysema	Focal/regional areas with low attenuation (Yes/No)
Bronchial wall thickening	Abnormal thickening of bronchial walls (Yes/No)
Bronchiectasis	Dilatation of bronchi with respect to the pulmonary artery, no tapering of bronchi and bronchi should be identified within 1 cm of the pleural surface (Yes/No)
Consolidation	Homogenous increase in the pulmonary parenchyma obscuring the margins of airway walls and vessels (Yes/No)
Cysts	A round area with well-defined interface with normal lung appearing lucent or low-attenuated (Yes/No)
Ground glass	An area of hazy increased opacity of lung. Bronchial and vascular margins are preserved (Yes/No)
Honeycombing	Cystic air spaces appearing in clusters with well-defined walls (Yes/No)
Linear scars of atelectasis	Reduced volume and increased attenuation with a subsegmental distribution and a linear configuration (Yes/No)
Mosaic attenuation	Regions appearing with a patchwork of differing attenuation (Yes/No)
Reticular abnormality	A collection of small linear opacities resembling a net constituted by interlobular septal thickening, intralobular lines or cyst walls of honeycombing (Yes/No)
Solid nodules	A rounded or irregular opacity with homogenous attenuation measuring up to 3 cm in diameter (Yes/No)
Lymphadenopathy	Enlarged mediastinal or hilar lymph node (Yes/No)
Any structural impairment	The presence of any of the abovementioned structural impairments (Yes/No)

CO, carbon monoxide; kPa, kilopascal.

Table 2 Socio-demographics, injury characteristics, pulmonary history, and anthropometry of the participants with spinal cord injury and the matched controls from the general population.^a

	Participants with SCI	Matched controls	P value
Sex (n (%))
Women	5 (20)	20 (20)
Men	20 (80)	80 (80)
Age (years) (mean ± SD; median, min-max)	58 ± 5; 58, 50–65	58 ± 4; 58, 50–64	0.74
Age at injury (years) (mean ± SD; median, min-max)	30 ± 12; 28, 7–56
Time since injury (years) (mean ± SD; median, min-max)	28 ± 13; 31, 6–53
Injury level (n (%))
C1-C4	10 (40)
C5-C8	6 (24)
T1-T6	9 (36)
Severity of injury (n (%))
AIS A	15 (60)
AIS B	8 (32)
AIS C	2 (8)
Socio-demographics (n %)
Marital status^b	18 (72)	77 (77)	0.77
Vocational situation			<0.001
Working full-time or part-time	10 (40)	79 (79)
Disability pension, old age pension or paid sick leave	15 (60)	21 (21)
Educational level			0.83
Low (Elementary school)	1 (4)	10 (10)
Medium (Upper secondary school, vocational training)	14 (56)	47 (47)
High (University or college degree)	10 (40)	43 (43)
Smoking history
Non-smoker (n (%))	11 (44)	44 (44)
Ex-smoker (n (%))	12 (48)	48 (48)
Current smoker (n (%))	2 (8)	8 (8)
Pack years^c,d (mean ± SD; median, min-max)	8 ± 11; 4, 0–46	12 ± 20; 5, 0–140	0.18
Asthma (n (%))	2 (8)	4 (4)
Chronic obstructive pulmonary disease (n (%))	0 (0)	0 (0)
Anthropometrics (mean ± SD; median, min-max)
Height^e; cm	175 ± 8; 175, 160–190	175 ± 8; 175, 149–191	0.93
BMI; kg/m^Citation2	25.1 ± 5.3; 25.4, 14.1–34.4	27.4 ± 3.9; 26.9, 19.2–39.6	0.015
Waist circumference; cm	101 ± 14; 103, 70–127	97 ± 12; 96, 72–129	0.081

^a Comparison using conditional logistic regression analyses.

^b Living in a relationship (married/cohabiting/partner).

^c One pack years is defined as smoking 20 cigarettes (or equivalent consumption of cigar, pipe) each day for a whole year.

^d Conditional logistic regression computed on transformed data because of highly skewed data.

^eThe matching criteria for height had to be extended due to lack of controls in a few cases.

AIS, American Spinal Injury Association (ASIA) Impairment Scale¹¹; BMI, body mass index; SCI, spinal cord injury.

Table 3 Descriptive findings and conditional logistic regression analyses of functional and structural impairments of the participants with SCI and matched controls from the general population.

	Participants with SCI (n = 25)	Matched controls (n = 100)	P value
Functional impairments^a (mean ± SD; median, min-max)
Spirometry
VC (% predicted)	69 ± 21; 70, 30–106	107 ± 14; 108, 63–150	<0.001
FEV1 (% predicted)	70 ± 24; 71, 33–111	109 ± 15; 108, 69–148	<0.001
FEV1/FVC	0.78 ± 0.10; 0.80, 0.48–0.93	0.80 ± 0.05; 0.80, 0.61-0.90	0.26
MEF50 (% predicted)	65 ± 30; 66, 17–115	100 ± 30; 97, 27–164	<0.001
Diffusing capacity
DLCO (% predicted)	64 ± 20; 65, 26–115	93 ± 12; 93, 63–117	<0.001
kCO (% predicted)	90 ± 22; 84, 38–130	100 ± 14; 100, 71–129	0.011
Impulse oscillometry
R5 (kPa/(L/s))	0.36 ± 0.11; 0.34, 0.19–0.66	0.30 ± 0.08; 0.29, 0.17–0.53	0.018
R20 (kPa/(L/s))	0.29 ± 0.08; 0.29, 0.16-0.54	0.26 ± 0.06; 0.25, 0.14–0.42	0.038
R5-R20 (kPa/(L/s))	0.062 ± 0.055; 0.050, −0.01–0.21	0.041 ± 0.043; 0.030, −0.03–0.26	0.087
X5 (kPa/(L/s))	−0.12 ± 0.07; −0.11, −0.32, −0.03	−0.08 ± 0.04; −0.07, −0.24, −0.03	0.003
Fres (Hz)	13.69 ± 4.99; 13.39, 7.42–24.65	10.60 ± 3.16; 9.85, 6.40–24.37	0.002
AX^b (kPa/(L)	0.55 ± 0.60; 0.39, 0.04–2.60	0.23 ± 0.28; 0.14, 0.02–2.05	0.001
Structural impairments^c (n (%))
Emphysema	3 (13)	4 (4)
Bronchial wall thickening	1 (4)	14 (15)
Bronchiectasis	0 (0)	1 (1)
Consolidation	1 (4)	1 (1)
Cysts	1 (4)	2 (2)
Ground glass	2 (8)	10 (10)
Honeycombing	0 (0)	1 (1)
Linear scars of atelectasis	13 (54)	35 (37)
Mosaic attenuation	0 (0)	0 (0)
Reticular abnormality	0 (0)	1 (1)
Solid nodules	12 (50)	34 (35)
Lymphadenopathy	1 (4)	1 (1)
Any structural impairment	18 (75)	62 (65)	0.36

^aIn four participants, diffusing capacity could not be measured due to VC <1.5 L (n = 2) and logistical reasons (n = 2). IOS data were missing from two participants for logistical reasons.

^bConditional logistic regression computed on transformed data because of highly skewed data.

^cComputed tomography assessments could not be performed in one participant for logistical reasons.

AX, Reactance curve area below zero; D_LCO, diffusing capacity of lung for carbon monoxide; FEV₁, forced expiratory volume in 1 s; Fres, resonant frequency; FVC, forced vital capacity; k_CO, carbon monoxide transfer coefficient; MEF₅₀, maximal expiratory flow at 50%; R5, Resistance at 5 Hz; R5-R20, Resistance at 5 Hz minus 20 Hz; R20, Resistance at 20 Hz; SCI, spinal cord injury; VC, vital capacity; X5, Reactance at 5 Hz;

Table 4 Spearman rank correlation between injury level and functional and structural impairments.

	Variable	Correlation coefficient (r)	P value
Injury level^a	Functional impairments
	VC (% predicted)	−0.58	0.002
	FEV1 (% predicted)	−0.57	0.003
	FEV1/FVC	−0.53	0.007
	MEF50 (% predicted)	−0.64	0.001
	DLCO (% predicted)	−0.30	0.19
	kCO (% predicted)	−0.02	0.94
	R5 (kPa/(L/s))	0.42	0.046
	R20 (kPa/(L/s))	0.36	0.090
	R5-R20 (kPa/(L/s))	0.26	0.24
	X5 (kPa/(L/s))	−0.40	0.058
	Fres (Hz)	0.34	0.12
	AX (kPa/(L)	0.33	0.12
	Structural impairments
	Any structural impairment	0.51	0.012
	Linear scars of atelectasis	0.31	0.14

^a Defined as each higher Injury level C1-T6.

AX, Reactance curve area below zero; D_LCO, diffusing capacity of lung for carbon monoxide; FEV₁, forced expiratory volume in 1 s; Fres, resonant frequency; FVC, forced vital capacity; k_CO, carbon monoxide transfer coefficient; MEF₅₀, maximal expiratory flow at 50%; R5, Resistance at 5 Hz; R5-R20, Resistance at 5 Hz minus 20 Hz; R20, Resistance at 20 Hz; VC, vital capacity; X5, Reactance at 5 Hz.

Table 5 Associations between chronological age and structural impairments of the participants with SCI and matched controls, respectively, and comparison of ORs using conditional logistic regression analyses.^a

	Participants with SCI (n = 24)	Matched controls (n = 96)	P value
Structural impairments (OR; 95% CI)
Any structural impairment	1.04 (0.84–1.29)	1.03 (0.93–1.14)	0.88
Linear scars of atelectasis	1.3 (1.04–1.74)	0.9 (0.88–1.07)	0.025

^a Investigated using age as an interaction variable.

OR, odds ratio; SCI, spinal cord injury.

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