Pulmonary hypertension (PH) is recognized as a severe complication of ILD. The development of PH during the course of the disease has a negative impact on the functional status and quality of life of ILD patients and is associated with poor survival [1].

Patients with pulmonary hypertension (PH) in association with underlying interstitial lung disease (ILD) have worse survival rates than those with ILD alone [2].

PFTs and arterial blood gases are necessary to identify the contribution of parenchymal lung disease. Assessment of exercise capacity is a key part of the evaluation of PH. The most commonly used exercise tests are the 6-min walk test (6MWT) and cardiopulmonary exercise testing. Impaired gas exchange which worsens with exercise is a common feature in the pathophysiology of ILD and appears to have prognostic value as well [3-6].

There is paucity of studies on the Pulmonary artery hypertension (PAH) and it’s association with pulmonary function indices and arterial blood gas status among patients diagnosed with interstitial lung diseases (ILD), in this hilly area of northern India. The present study was done to evaluate the association of pulmonary function indices and arterial blood gas status with Pulmonary artery hypertension (PAH) among Interstitial Lung Diseases (ILDs) patients.

Aims and Objectives

To study the association of pulmonary function indices and arterial blood gas status with Pulmonary artery hypertension (PAH) among Interstitial Lung Diseases (ILDs) patients.

The present study was conducted at Indira Gandhi Medical College, Shimla which is a tertiary care center of Himachal Pradesh, located in North India in Asian Continent and covers the majority of the population of this state. All consecutive patients of Interstitial Lung Diseases (ILDs), attending the outpatient services of the Department of Pulmonary Medicine, IGMC Shimla from July 2018 to June 2019 were screened for enrolment in the study. All types of ILDs were enrolled in the study. 

Inclusion Criteria

• Stable ILD patients: diagnosis of ILD according to ATS/ERS guidelines based on an overall assessment of high-resolution computed tomography (HRCT) scan, lung function tests, (bronchoscopy and biopsy, if available.)

• Age >18 years, written consent

Exclusion Criteria

• Subjects with evidence of left heart disease, Chronic kidney disease, Liver disease

• Chronic lung diseases other than ILDs

• Patients with HIV.

• Pregnant

Patients presenting with respiratory symptoms such as cough, shortness of breath and diagnosed cases of ILD were evaluated.

All consecutive ILD patients were subjected to focused history and physical examination as structured questionnaire record information related to; Demographics, Duration of ILD, Pulmonary artery hypertension (PAH) and its Association with pulmonary function indices and arterial blood gas status etc.

The data was collected, entered in the MS Excel sheet and analyzed using Epi info V7 software. Continuous variables were reported as mean ± SD or median and interquartile range depending on the distribution of the variables. Categorical variables were recorded as counts and percentages. Differences between means of continuous variables were compared using the unpaired student’s’ test. A p-value of <0.05 was considered as statistically significant. 

Among the study population, 50 patients 27 54% were female and 23 46% were male. The mean age of the study population was 57.821+5.03years. The mean age of males and females was 62.561+3.84 years and 53.771+5.07 years respectively. The mean duration of symptoms of ILD was 3.034+2.62 years. There was no significant difference between males and females regarding the duration of illness (2.76+2.46 years versus 3.39+2.77 years, p = 0.40). Table 1

Table 1: Age and Gender Distribution of the Study Population (N = 50)

Pulmonary artery hypertension (PAH) was by derived Pulmonary flow acceleration time formula (PFAT) .Those who had Mean pulmonary artery pressure (MPAP) >25 mmHG was diagnosed as PAH case. Out of 50 patients, 44 88% had PAH. 

Out of 50 patients, the mean hemoglobin concentration was 15.24+2.19 g%. Among patients with PH group the mean HB was15.61+1.52 g/dl vs. 12.5±4.0 gm/dl) with p value of 0.0006 Table 2.

Table 2: Association of, Arterial Blood Gas Status, Pulmomary Function Indices and Exercise Capacity with PAH

Out of 50 patients, the mean sO₂ and paO_{2 were} 82.50+10.79 mmHg and 55.77+10.30mm Hg respectively. Among patients who had PH the mean value of sO₂ and paO₂ were 82.09+11.11 mmHg and 55.54+10.54 mmHg respectively, with a p value of 0.47 and 0.31.Out of 50 patients 32 64% patients had sO_{2 <} 88mmHg and 2254% patients had paO₂ <55mmHg. Among those patients who had PH sO₂ < 88mmHg and paO₂ < 55mmHg were 30(68.18% and 25(46.82%)) respectively, with a p value of 0.11 and 0.25.

Among 50 patients the mean value of six-minute walk distance was 311.42+122.55meter, the mean value was 307.52+117.54(m) among the PH group, with a p value of 0.54. Out of 50 patients, 30 60% patients were walked less than 350meters, among these 26 59.09% patients had PH, with a p -value of 0.54.

Among patients with PH group, 6 13.64% had not performed PFT, 4 9.09% had an obstruction, 26 59.09% had restriction, 3 6.82% had mixed and 5 11.36% had normal PFT, with a p- value of 0.83

The association of ILD with Radiological and Electrocardiogram (ECG) findings was analyzed to determine the risk determinants of PAH.

The mean age of the study population was 57.821+5.03 with male and female mean age 62.561+3.84 and 53.77+15.07 respectively. Females were more than male and younger with a mean duration of ILD of 3.034±2.62 years. A similar finding was also reported in the study conducted by Agarwal et al. [7]. In the ILD registry of Indian data, it was reported that ILDs occur at a younger age compared to the western countries, and females are affected more [8].

In our study arterial blood gas (ABG) was done in all patients, we observed sO2, the mean value was 82.09+11.11 among the PH group (p = 0.47). The majority of patients had sO2 <88% i.e. 68.18% among patients with PH group. The mean value of paO2 was 55.54mmHg +10.54mmHg among patients with PH group. The majority of patients had paO2 <55mmHg among the PH group. Agarwal et al. [7] in their study reported the mean value of paO2 54.7+3.5mmHg which is comparable to our study. Hypoxemia is an important factor in developing PH in ILD patients.

In our study, the mean value of the six-minute walk distance was 307.52+117.54 meters among the PH group statistically significant of p-value 0.034. The majority of the patients in the study population walk less than 350 meters among the PH group. Baughman et al. [9] in their study reported the mean value of a six-minute walk distance 305 meters, the result is comparable with our study. From our observation reduced functional capacity is a clinical predictor of PH among ILD patients.

In our study, the majority of the patients had a restrictive pattern in pulmonary function test (PFT) among patients with a PH group of 59.09%. Agarwal et al.

[7] in their study found the majority had a restriction in PFT. Our sample in the study was large as compared to their sample size and in our study different type of ILD was included.

There was very high prevalence of PAH among ILD Patients. There was very high prevalence of PAH among ILD Patients. Among patients who had PAH, mean value of sO₂ and paO₂ and the mean value of six-minute walk distance was lower than those who didn’t had PAH. Also, the patients of PAH mostly had restriction pattern in PFT.

Limitations of the Study

The small number of the population were included in this study represents a methodological limitation and study over a larger population is recommended. 

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