Airflow impairment is common in patients with pulmonary TB. However, the extent of airflow obstruction in the elderly with pulmonary TB remains unclear. This study quantitatively evaluated the extent of PF impairment in elderly patients with TB before anti-TB therapy by measuring FEV1%. In addition, its corresponding risk factors, which may be helpful to improve the management of pulmonary TB among the elderly, were investigated. The aim of this study was to identify a more timely intervention during admission. The findings demonstrated that pulmonary TB causes significant airway obstruction and that albumin, BMI < 18.5 kg/m2, lesion number ≥ 3, cardiovascular disease, male, and respiratory disease were associated with airway obstruction.
Low albumin and BMI values were identified as risk factors for airway obstruction. This may be explained by the association between malnutrition and airway obstruction. Malnutrition is one of the most important risk factors associated with TB development. An estimated 2.3 million TB cases have been attributed to malnutrition, which is more common than other causes (such as Human immunodeficiency virus (HIV and diabetes mellitus) [9]. Malnutrition may result from insufficient energy intake [10], which presents with changes in the body composition, metabolism, and immune status. Furthermore, impairment of PF may then occur due to reduced physical activity (muscle atrophy) [11, 12]. The associations of albumin and BMI with PF have been addressed in several studies [13]. For example, BMI and albumin have been reported to be independently associated with the predicted FEV1% in children with cystic fibrosis [13]. In addition, a correlation between FEV1 and BMI has been found by Popova et al. in patients treated for pulmonary TB, with a level of 0.14 (P < 0.05) [14]. Moreover, Khatri et al. have shown that albumin levels are positively correlated with the predicted FEV1% among patients with asthma (R = 0.378; P = 0.010) [15].
A lesion number ≥ 3 was associated with a decreased FEV1. This finding suggests that impairment of PF is more likely to occur in the elderly TB patients with more lesions. Similarly, in a previous study, multilobar involvement has been associated with a marked lung function decline [16]. A report by Long et al. [17], who described that functional impairment is proportional to the number of diseased segments, is also consistent with our findings. This may be explained by three key factors: 1) immunosenescence, various anatomical and physiological changes linked to ageing, as well as malnutrition and comorbidities in the elderly can lead to the increased susceptibility of lung infection [2]; 2) the immunocompromised status resulting from underlying diseases (e.g., steroid use, immunosuppressant use, etc.) makes the situation more complex [18, 19]; and 3) pulmonary TB can lead to irreversible lung parenchymal destruction and lung remodeling [17, 20]. Therefore, in the elderly with pulmonary TB, chest computed tomography features include parenchymal density, cavitary lung lesions, ground glass opacities, and miliary nodules [21]. In addition, more segments distributed with lesions have been found in the elderly with pulmonary TB compared to those with community-acquired pneumonia [22].
Respiratory disease was also demonstrated to be a risk factor for impaired PF. The findings from several studies are consistent with our report. For example, Lee et al. have found that the FVC and postbronchodilator FEV1 of patients with chronic airflow obstruction were less than those of COPD patients (P < 0.05) [23]. Furthermore, Yang et al. have determined that severe obstructive ventilatory disorders are associated with more respiratory symptoms, and among subjects with prior TB, 29% developed obstructive ventilatory disorders [24]. Abnormal lung function associated with pulmonary TB was observed in 18–94% of patients. Additionally, Byrne et al. have stated that the presence of other respiratory comorbidities is one of the risk factors associated with the extent of the lung function abnormality [25]. In a previous study, 84% of patients with respiratory complaints had either obstructive or restrictive patterns on spirometry. However, all asymptomatic patients had normal spirometry readings [26]. Moreover, Poh et al. have reported that patients with respiratory symptoms have a higher risk of developing obstructive airway disease than asymptomatic patients [27].
Cardiovascular disease was another risk factor for impaired PF that was identified in this study. PF is known to be related to the incidence of cardiovascular disease [28]. Although the reasons for their association remain unclear, indirect evidence has been found in several studies. For example, COPD patients frequently have cardiac disease [29]. In addition, an elevated B-type natriuretic peptide level has been observed in COPD patients [30]. FEV1 and FVC also have been associated with cardiac parameters [31, 32]. Remarkably, FEV1 and FVC by spirometry are associated with smaller ventricular volumes and a reduced ventricular mass as determined by cardiovascular magnetic resonance imaging [33].
Finally, the male sex was found to be a risk factor for impaired PF among the elderly TB patients. This may be explained by the fact that men have longer airways than women, causing greater specific resistance in the respiratory tract [34]. Our findings are consistent with a previous report by Berglund et al. [35].
There are several limitations of this study that must be addressed. First, this study had a retrospective nature. Second, this study was conducted at a single center. Therefore, selection bias might have influenced the findings. Third, PF testing was performed at the time of admission. The anti-TB therapy could have partially improved the PF at the end of treatment. The comparison of PF between before and after treatment might be useful to understand its clinical significance among the elderly with pulmonary TB. Therefore, further evidence is required to validate our findings.