The IRS-cl and SF-36 questionnaires were administered to 268 patients, all with CGRF in stable phase. Twenty patients were excluded for not completing the IRS-cl, 19 for not answering item #31, " My marriage/relationship is suffering because of my illness", corresponding to patients without a partner. Finally, the valid sample with 100% of the items answered comprised 248 patients, of whom 132 were women (53.2%), with median age of 62 ± 17.5 years, age range of 20 and 88 years, thus predominantly older adults. A total of 40% of the sample had a low educational level (incomplete primary education, 36%; no schooling, 4.0%), most of whom were women.
A total of 51% of the sample was in a relationship (48% married, 3% cohabitating). Regarding occupation, 22.2% were retired due to old age and 24.2% due to disability, followed by 30.6% who were homemakers.
The sample was grouped into eight diagnostic groups found in the MINSAL databases: 1) COPD 2) COPD and obstructive sleep apnea-hypopnea syndrome (COPD-OSA); 3) Tuberculosis (TB) sequelae; 4) Non-cystic fibrosis bronchiectasis (non-CF BE); 5) Neuromuscular diseases; 6) Kyphoscoliosis (KYPH); 7) Obesity hypoventilation syndrome (OHS) and 8) Miscellaneous disorders (Table 2).
A total of 68.5% (n = 170) of the patients used continuous oxygen therapy, 34.7% of them 24 hours a day. Regarding smoking, 61.3% reported stopping smoking (for at least 6 months), and 2.4% reported active smoking.
Table 1
Distribution by diagnosis, age, sex and times on home ventilation
Diagnostic groups
|
Age in years
(median ± SD)
|
Sex
male/female
|
Months on NIHMV
(mean ± SD)
|
Use of NIHMV (hr/day)
|
COPD
|
71 ± 8.2
|
33/33
|
29.7 ± 25.6
|
7.4 ± 2.3
|
COPD-OSA
|
67 ± 10.7
|
18/16
|
41.4 ± 25.0
|
7.5 ± 1.7
|
TB sequelae
|
67 ± 8.7
|
3/5
|
44.5 ± 27.1
|
8.3 ± 1.4
|
Non-CF bronchiectasis
|
46 ± 15.1
|
11/7
|
31.0 ± 22.1
|
8.4 ± 2.0
|
Neuromuscular
|
24 ± 15.2
|
17/11
|
55.1 ± 42.6
|
8.1 ± 3.2
|
Kyphoscoliosis
|
54 ± 20.8
|
15/12
|
39.0 ± 27.1
|
8.4 ± 3.9
|
OHS
|
61 ± 11.6
|
18/42
|
37.2 ± 25.9
|
7.0 ± 1.4
|
Miscellaneous
|
59 ± 21.6
|
1/6
|
30.0 ± 16.1
|
7.8 ± 1.1
|
The completion time of the IRS-cl was 18.8 ± 9.1 minutes, which was considered viable. It was self-administered in 46.8% (n = 116) of the patients, and 53.2% required interviewer assistance, reporting difficulty in reading and writing due to low educational level, severe dyspnea, essential hand tremor and visual difficulty. In these cases, the interviewer used an enlarged printed Likert scale as an aid for the patients to indicate their response.
Analysis of the instrument items
The distribution of the raw responses showed that the IRS-cl items were heterogeneous and had discriminatory capacity (34). The item-scale correlations between the 49 items and their theoretical dimensions were significant and direct (positive), with rho values > 0.40, being higher than the correlations with other scales (Table 2).
Table 2
Summary of item-scale correlations of the Chilean SRI using Spearman´s correlation coefficient
Chilean SRI Dimensions
|
Number of items
|
Correlation range of the items with their theoretical scale
|
Correlation range of the items with other scales
|
Respiratory Complaints (RC)
|
8
|
0.59–0.84*
|
0.20–0.57
|
Physical Functioning (PF)
|
6
|
0.50–0.79*
|
0.02–0.68
|
Attendant Symptoms and Sleep (AS)
|
7
|
0.45–0.69*
|
0.04–0.58
|
Social Relationships (SR)
|
6
|
0.52–0.74*
|
0.09–0.63
|
Anxiety (Ax)
|
5
|
0.61–0.75*
|
0.11–0.55
|
Psychosocial Well-Being (WB)
|
9
|
0.49–0.74*
|
0.16–0.56
|
Social Functioning (SF)
|
8
|
0.46–0.74*
|
0.19–0.64
|
*p-value < 0.01. Range expressed as minimum - maximum |
Reliability
The IRS-cl presented very good overall reliability (0.95), higher than the original SRI (0.89). Its seven theoretical dimensions showed good internal consistency of between 0.71 and 0.84. The lowest alpha was obtained for Attendant Symptoms and Sleep, and the highest for Respiratory Complaints. The alphas by dimension were similar between the IRS-cl and the original SRI, indicating that both measure their constructs in a similar way. The ICC was very good (> 0.8) in the seven dimensions, indicating excellent agreement and temporal stability of the instrument at both times (Table 3). At this stage, it was not indicated to change or exclude any item from the theoretical dimensions.
Table 3
Analysis of internal consistency according to subscale by the intraclass correlation coefficient (ICC) and Cronbach's alpha.
SRI Dimensions
|
Number of items
|
ICC (95% CI)
SRI Chile
|
Cronbach's α
SRI Chile
|
Cronbach's α
SRI Germany
|
Cronbach's α
SRI Spain
|
Respiratory Complaints (RC)
|
8
|
0.84 (0.63–0.94)
|
0.84
|
0.83
|
0.81
|
Physical Functioning (PF)
|
6
|
0.94 (0.85–0.98)
|
0.73
|
0.80
|
0.82
|
Attendant Symptoms and Sleep (AS)
|
7
|
0.91 (0.78–0.96)
|
0.71
|
0.76
|
0.73
|
Social Relationships (SR)
|
6
|
0.92 (0.80–0.97)
|
0.72
|
0.73
|
0.63
|
Anxiety (AX)
|
5
|
0.95 (0.87–0.98)
|
0.78
|
0.79
|
0.73
|
Psychosocial Well-Being (WB)
|
9
|
0.93 (0.83–0.97)
|
0.82
|
0.89
|
0.85
|
Social Functioning (SF)
|
8
|
0.91 (0.77–0.96)
|
0.80
|
0.84
|
0.82
|
SRI Global (Summary Scale)
|
49
|
0.97 (0.92–0.99)
|
0.95
|
0.89
|
0.93
|
Construct validity assessment by exploratory factor analysis
The table of extracted commonalities (common variance) according to the Kaiser criterion favored a solution of 12 factors explaining 64.5% of the variance. However, this analysis suggested, according to the percentage of variance criterion, a model with only 2 factors but this is not convenient because of their low significance in the weightings (36.31%), and so the use of the eigenvalue > 1.0 criterion was prioritized.
To clarify the structure of the factors in the matrix and optimize the differentiation of the items, orthogonal rotations were applied. First, varimax was used, but it did not achieve a completely satisfactory model when extracting 6 to 10 factors. It then decided to use equimax to simplify the factors, finding a solution of 8 factors explaining 55.58% of the total variance, which satisfactorily simplified the model. The factors showed good correlation and number of items; conceptually, they demonstrated that all the constructs of the original instrument are present and that they are relevant for patients with CGRF (Fig. 2). Although the factors found do not conform identically to the dimensions of the theoretical instrument, their organization in the Chilean sample is consistent.
Modifying the structure of the Chilean SRI subscales based on the EFA was rejected, since when performing the reliability analysis of the new factors, the Cronbach's alpha values decreased with respect to the original 7-scale structure.
Construct validity assessment by hypothesis testing
Four out of the five hypotheses were consistent with the results. The worst scores (expressed as medians) on the RC dimension were observed for COPD = 53 vs. Neuromuscular disease = 75 (p < 0.001), vs. Kyphoscoliosis = 69 (p < 0.003) and vs. OHS = 69 (p < 0.002). In addition, on the RC dimension, the group of patients with obstructive disease (n = 129) scored worse than the group with restrictive disease, 53 vs. 69 (p < 0.001). Additionally, in the group of patients with obstructive disease, there was not significant difference in scores on the RC among the diagnostic subgroups, as expected: COPD = 53 vs. TB = 44 (p = 0.65) and vs. BE = 58 (p = 0.50).
On the AX dimension, COPD = 40 was more affected than Neuromuscular disease = 68 (p < 0.001) and Kyphoscoliosis = 55 (p < 0.03). Conversely, there was no difference in the AX subscale score in the group of patients with obstructive disease: COPD = 40 vs TB = 35 (p = 0.99) vs BE = 45 (p = 0.80).
Regarding the PF dimension, the score of patients with Neuromuscular vs. Non neuromuscular disease showed no significant difference (p = 0.60), contrary to expectations. This may be explained by the severe deterioration in lung function of the sample (higher of PaCO2 levels) at the time of start of NIHMV compared to European patients.
The correlation between hours of ventilation/day and quality of life was negative and significant only for the PF dimension (rho = -152 and p = 0.05), and according to diagnostic group, it was only significant for COPD (rho = -0.198 p = 0.024).
Criterion or convergent validity
According to Table 4, the IRS-cl showed positive and significant (p < 0.01) correlations with the SF-36 v2 in its related dimensions, which were considered good. The strongest correlations were observed for PF, WB and SF.
Table 4
Convergent validity between the dimensions of the Chilean SRI questionnaire and general quality of life measured by the SF-36 v2 (n = 248).
Chilean SRI Questionnaire
|
SF-36 v2 Questionnaire
|
Physical Functioning
|
Physical Role Functioning
|
Bodily Pain
|
General Health Perception
|
Vitality
|
Social Role Functioning
|
Emotional Role Functioning
|
Mental Health
|
Respiratory Complaints
|
0.39
|
0.50
|
0.29
|
0.57
|
0.44
|
0.46
|
0.44
|
0.42
|
Physical Functioning
|
0.77
|
0.67
|
0.30
|
0.55
|
0.56
|
0.55
|
0.57
|
0.53
|
Attendant Symptoms and Sleep
|
0.35
|
0.44
|
0.35
|
0.46
|
0.44
|
0.38
|
0.43
|
0.49
|
Social Relationships
|
0.40
|
0.47
|
0.22
|
0.40
|
0.55
|
0.48
|
0.49
|
0.57
|
Anxiety
|
0.33
|
0.50
|
0.27
|
0.56
|
0.45
|
0.42
|
0.43
|
0.43
|
Psychosocial Well-Being
|
0.45
|
0.55
|
0.31
|
0.64
|
0.70
|
0.57
|
0.59
|
0.77
|
Social Functioning
|
0.53
|
0.61
|
0.33
|
0.61
|
0.62
|
0.59
|
0.59
|
0.58
|
Total SRI Summary Scale
|
0.57
|
0.67
|
0.37
|
0.69
|
0.68
|
0.62
|
0.64
|
0.67
|
Spearman’s rho correlation coefficient. |
The correlation is significant at the 0.01 level (one-tailed) for all dimensions.
Correlations > 0.50 are bolded, and the highest correlations (> 0.60) are bolded and underlined.
General results of the Chilean version of the SRI
The studied sample showed that patients with CGRF on NIHMV perceived their HRQL as fair, with a summary scale score of 57%, with greater deterioration in HRQL observed in women (51%).
The IRS-cl dimensions with the worst score were Anxiety with 45% and Physical Functioning with 50% and those with the best score were Social Relationships with 65% and Respiratory Complaints with 63%. In the seven dimensions, women presented a worse perception of HRQL than men (Fig. 3).
Table 5. Results of the Chilean SRI according to diagnostic group and instrument dimension

Results expressed as the median. Legend: COPD: chronic obstructive pulmonary disease; OSA: obstructive sleep apnea; TB: pulmonary tuberculosis; Non-CF BE: Non-Cystic Fibrosis Bronchiectasis; Neuromusc.: neuromuscular disease; OHS: hypoventilation obesity syndrome. DG: diagnostic groups.