Bronchiectasis destroys the lung structure and shows rapid progression, increasing patients’ risk of cardiovascular complications. PH is a common severe complication of bronchiectasis. It can be diagnosed using RHC, which is invasive and unacceptable to some patients. Therefore, determining a noninvasive and accurate test to identify PH in patients with bronchiectasis is vital for early diagnosis and intervention.
A previous study showed that 32.9% of patients with bronchiectasis had PH, diagnosed based on an SPAP of ≥ 40 mmHg on echocardiography [14]. However, it empirically and arbitrarily diagnosed PH based on an SPAP of ≥ 40 mmHg, a criterion established by the World Health Organization Symposium on Primary PH. Another study evaluated the prognostic value of computed tomography (CT) signs of PH in determining mortality in patients with bronchiectasis, showing that average right and left MPA diameter was the best predictor [15]. However, there was no RHC data to confirm the CT signs of PH.
RHC is the gold standard for diagnosing PH. PH was previously diagnosed based on an mPAP of ≥ 25 mmHg measured by RHC at rest. However, this standard was somewhat empirically and arbitrarily defined [5]. Kovacs et al. [16] identified an mPAP of > 20 mmHg as the upper limit of normal and proposed it as the new definition at the Sixth World Symposium on PH [5]. Our study used an mPAP of > 20 mmHg to diagnose PH in patients with idiopathic bronchiectasis.
In our study, PASP had the best correlation and consistency with the mPAP or sPAP and a higher AUC with mPAP than the MPA diameter and MPA/AA ratio. These results were consistent regardless of whether PH was diagnosed based on an mPAP of > 20 mmHg or ≥ 25 mmHg. The echocardiographically estimated PASP is an ideal noninvasive indicator. Echocardiography is the most widely used noninvasive diagnostic method for assessing PH in previous guidelines [7]. Based on an mPAP of > 20 mmHg, the optimal threshold for PASP for preliminary PH screening was > 44 mmHg. The American Society of Echocardiography indicated that PH might exist if the estimated PASP was > 35–40 mmHg [17]. In a meta-analysis examining echocardiography’s diagnostic accuracy for PH, the thresholds used in nearly 60% of studies were ≥ 40 mmHg [18].
Based on the optimal PASP threshold of > 44 mmHg, 11.3% of patients with idiopathic bronchiectasis had PH. A previous study found that up to 48.4% of patients with bronchiectasis had PH, likely reflecting their use of a PASP threshold of ≥ 36 mmHg and that their patients with bronchiectasis had multiple etiologies or comorbidities [19]. PH morbidity among patients with bronchiectasis differed slightly between those with COPD and ILD [20, 21], which may be ascribed to the different etiologies. Regardless, these studies showed that PH was more likely secondary to more serious primary pulmonary disease.
The Bronchiectasis Severity Index is a disease-specific severity index that predicts future risk of exacerbations and mortality from bronchiectasis. It includes age, BMI, % predicted FEV1, the number of hospitalizations in the last two years, the number of acute exacerbations in the last year, the modified Medical Research Council dyspnea score, colonization status and bacteriology, and radiological severity [22]. In our study, age was an independent risk factor for PH in patients with idiopathic bronchiectasis. Another study associated age with moderate-to-severe chronic respiratory disease-associated PH [23]. Moreover, emaciation was an independent risk factor for severe PH in patients with COPD [24]. Our results showed that patients with idiopathic bronchiectasis and PH had lower BMI, which may be related to increased consumption due to repeated infection and aggravation.
Chronic lung disease was found to be the second leading cause of PH, and these patients often showed impairment of lung function [25]. In our study, patients with idiopathic bronchiectasis with PH had lower FVC, FEV1, and PaO2 than those without PH. A small study indicated that hypoxemia was more likely to occur in patients with bronchiectasis and PH [10], consistent with our study. Another previous study found that oxygen therapy had potential therapeutic benefits for all patients with PH [26].
In our study, more involved lobes and segments and cystic or mixed bronchiectasis were independent risk factors for PH in patients with idiopathic bronchiectasis. These results suggest that PH is more likely to occur in patients with severe structural lung damage, consistent with a previous study [9]. In addition, patients with idiopathic bronchiectasis and PH had significantly more hospitalizations and emergency visits in the past 12 months. These results suggest that more attention should be paid to patients with bronchiectasis with frequent exacerbations, and the possibility of PH should be considered.
The N-proBNP is released from cardiac myocytes in response to mechanical load and wall stress, and its elevation is incorporated into several PH risk stratification tools [27]. A previous study indicated that N-proBNP was related to right ventricular function and elevated in patients with severe COPD or ILD-associated PH [28]. Elevated N-proBNP might be an early-warning index for recognizing PH in patients with idiopathic bronchiectasis without cardiovascular diseases.
P. aeruginosa is one of the most common pathogens isolated from respiratory tract specimens in patients with bronchiectasis. Some studies have reported that P. aeruginosa increased mortality and decreased quality of life in patients with bronchiectasis [29, 30]. In our study, patients with idiopathic bronchiectasis and PH had higher proportions of P. aeruginosa in their respiratory tract specimens.
In our study, the mortality risk was significantly higher for patients with idiopathic bronchiectasis with than without PH, consistent with two small studies [9, 10]. A previous study has associated PH with reduced survival in patients with COPD, ILD, and sleep-disordered breathing [31]. In addition, echocardiographic evidence of PH was associated with increased one-year mortality in patients admitted with COPD exacerbation [32]. These results suggest that secondary PH could increase the mortality risk of patients with chronic lung disease.
The main limitation of our study was that relatively few patients without PH were evaluated by RHC. Because of its invasiveness and required tolerance, RHC is only recommended if its results are expected to aid management decisions [7]. In our study, we demonstrated the convenience and accuracy of echocardiography, which showed the best consistency with RHC. We defined a more rigorous, evidence-based critical point to identify PH in patients with idiopathic bronchiectasis. Our results have considerable clinical value in the early identification of and clinical decision-making for PH in patients with idiopathic bronchiectasis. Future larger-scale prospective studies examining patients with bronchiectasis using RHC are needed.