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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 9  |  Issue : 2  |  Page : 196-198

Desaturation on 6-min walk test: A test with high negative predictive value to rule out pulmonary hypertension in interstitial lung diseases


1 Department of Pulmonary Medicine, Gandhi Medical College and Hamidia Hospital, Bhopal, Madhya Pradesh, India
2 Department of Respiratory Medicine, Lokmanya Tilak Municipal Medical College, Mumbai, Maharashtra, India
3 Lilavati Hospital and Research Centre, Mumbai, Maharashtra, India

Date of Submission12-Dec-2019
Date of Decision22-Mar-2020
Date of Acceptance12-Apr-2020
Date of Web Publication07-Jul-2020

Correspondence Address:
Dr. Swapnil Manaji Thorve
Department of Respiratory Medicine, Lokmanya Tilak Municipal Medical College, Sion, Mumbai, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijrc.ijrc_63_19

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  Abstract 


Introduction: Pulmonary hypertension (PH) is one of the major complications of interstitial lung diseases (ILDs) that contributes to increased morbidity and mortality. Predicting and promptly diagnosing PH may improve the outcome in these patients. We evaluated the utility of 6-min walk test (6MWT) to predict PH earlier in the course of ILDs. Patients and Methods: A total of 113 patients diagnosed with ILD as per standard investigation protocols were included in this observational study. Patients were evaluated with 6MWT, pulmonary function tests, and two-dimensional echocardiogram. Patients having mean pulmonary arterial pressure >25 mmHg were labeled as PH, and 4% drop from pretest oxygen saturation was considered as significant desaturation. Results: It was observed that 40% of patients with desaturation on 6MWT had PH. None of the patients without significant desaturation had PH. Conclusion: Desaturation on 6MWT is not an early predictor of PH, which is one of the major complications of ILDs. However, it has a high negative predictive value in the prediction of PH in patients with ILD.

Keywords: 6-min walk test, desaturation, interstitial lung diseases, pulmonary hypertension


How to cite this article:
Gupta V, Thorve SM, Prabhudesai PP. Desaturation on 6-min walk test: A test with high negative predictive value to rule out pulmonary hypertension in interstitial lung diseases. Indian J Respir Care 2020;9:196-8

How to cite this URL:
Gupta V, Thorve SM, Prabhudesai PP. Desaturation on 6-min walk test: A test with high negative predictive value to rule out pulmonary hypertension in interstitial lung diseases. Indian J Respir Care [serial online] 2020 [cited 2020 Aug 11];9:196-8. Available from: http://www.ijrc.in/text.asp?2020/9/2/196/289095




  Introduction Top


Pulmonary hypertension (PH) is defined as mean pulmonary artery pressure (mPAP) >25 mmHg assessed by right heart catheterization. It is an important complication that occurs in various lung diseases secondary to long-standing hypoxia. As alveolar-to-arterial partial pressure gradient increases in interstitial lung diseases (ILDs), the hypoxia leads to the development of PH in ILDs. The gold standard for the diagnosis of PH is right heart catheterization. Echocardiography though not as accurate as right heart catheterization, remains the best noninvasive screening modality.[1],[2],[3] The severity of PH and the degree of lung fibrosis are not correlated directly.

The 6-min walk test (6MWT) is used to assess the exercise capacity in patients with chronic pulmonary diseases such as chronic obstructive pulmonary disease (COPD) and ILDs. Functional capacity is not assessed with 6MWT because most patients do not achieve maximal effort during this test.[4] The test is simple and requires walking with no equipment except a pulse oximeter and requires no training. It evaluates the combined response of the cardiovascular, pulmonary, and neuromuscular systems.[5]

The use of 6MWT has been studied in several lung diseases, especially COPD.[6] The 6MWT is used in various scoring systems for assessing outcome in patients with ILD, especially idiopathic pulmonary fibrosis (IPF). Its utility is less in other ILDs such as sarcoidosis and hypersensitivity pneumonitis (HP).

Decreased performance during 6MWT is a potential predictor for PH. Because it is a simple test with an ability to predict and compare outcome, we hypothesized that the 6MWT can be a tool to screen ILD-associated PH. To test this hypothesis, we evaluated 113 diagnosed ILD patients with 6MWT, PFT, and two-dimensional Doppler echocardiography (2D echo).

This study was aimed to study the incidence and association of significant desaturation and PH in various ILDs.


  Patients and Methods Top


The study was an observational study conducted in the Department of Pulmonary Medicine at a large hospital in Mumbai, India, after ethical committee approval. All patients diagnosed to have ILD from June 2014 to May 2016 were included in the study. After informed consent, patients were interviewed in detail for clinical history and investigations were noted. Patients underwent 6MWT and 2D echo, and findings were noted.

Patients with mPAP >25 mmHg calculated with tricuspid regurgitation jet values were labeled as PH. Desaturation was defined as fall in saturation on pulse oximetry/arterial blood gas analysis equal to or below 88% during the room air 6MWT. Drop in saturation by 4% or more was termed as significant desaturation.[7],[8]

Data were recorded in Microsoft Excel, and appropriate statistical methods were applied.


  Results Top


Our study included 113 ILD patients, of which 58 were male and 55 were female. Male preponderance was observed in IPF, while female preponderance was observed in all other ILDs. The mean age of the patients was 53.02 years, with mean age higher in IPF and less in other diseases. The distribution of various diagnoses of ILDs is given in [Table 1]. The association of PH with various diagnosis is given in [Table 2]. Significant desaturation was observed in 55 out of the 113 patients (48.7%). The details are given in [Table 2].
Table 1: Demographic profile and distribution of diagnosis among the cases of interstitial lung diseases

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Table 2: Patient profile of ILD - Type of ILD, those who developed significant desaturation on 6MWT and those who had pulmonary hypertension

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It was observed that all patients with ILD having PH had significant desaturation on 6MWT [Table 2]. None of the patients who did not desaturate on 6MWT had PH. It was observed that 54.5% of IPF, 33.3% of nonspecific interstitial pneumonia (NSIP), and 87.5% of connective tissue disease-interstitial lung disease (CTD-ILD) patients who had significant desaturation had PH. HP showed the highest incidence of desaturation on 6MWT among all ILDs, but none of the patients had PH.


  Discussion Top


The most common ILD in our study was IPF followed by sarcoidosis. This observation is in accordance with the study done in Mumbai by Udwadia et al. They conducted a retrospective study on 274 patients between 1994 and 2001. They found IPF in 43%, sarcoidosis in 22%, ILDs secondary to collagen vascular disease in 19%, and extrinsic allergic alveolitis/HP in 15% of cases.

The association between different types of ILDs and PH was found to be statistically significant. PASP was found to be elevated most commonly in CTD-ILD followed by IPF.

In this study, pulmonary arterial hypertension (PAH) was found in 12 (27.3%) patients in IPF. Kundu et al.[9] in their study also found that 23% of patients with IPF had PAH. Among Western literature, Lettieri et al. also found nearly similar results, and they found PAH in 31.6% of patients with IPF.

In NSIP, PAH was rare in this study; it was found only in three patients with NSIP. In this study, PAH was present in seven (63.6%) cases of CTD-ILD, while Kundu et al.[9] found it only in 33.3% of cases. The difference may be because of limited number of patients in CTD-ILD group in this study.

In this study, significant desaturation after 6MWT was found in 26 patients (59.1%) with IPF. This was similar to a study conducted by Lama et al.,[10] in which they found significant desaturation in 53% of patients with IPF. Among Indian literature, Kundu et al.[9] found significant desaturation in 43% of patients with IPF, while Kumar et al.[11] found significant desaturation only in 32.5% of IPF cases.

PAH is rare in sarcoidosis. In patients of sarcoidosis with significant parenchymal lung disease, the involvement of the pulmonary vasculature is seen in <5% of the cases. In this study, none of the patients of sarcoidosis showed significant desaturation in 6MWT, while the study done by Kumar et al.[11] found significant desaturation in 22.22% of sarcoidosis patients. The plausible explanation of this could be the advanced stage of the disease at presentation in their study. In sarcoidosis, the 6MWT can be affected by multiple factors, including respiratory status, cardiac function, PAP, muscle strength, and joint disease.[12]

In this study, 12 (75%) patients with HP showed significant desaturation in 6MWT. Kumar et al.[11] also found significant desaturation in >50% of patients (four out of seven patients). Lima et al.[13] found mean oxygen saturation (post 6-min walk) <88% in 46 patients with HP. Similarly, significant desaturation in 6MWT was observed in nine (64.3%) patients with NSIP. Lama et al.[10] found significant desaturation in 6MWT in 64% of patients, while Kumar et al.[11] found significant desaturation in 50% cases of NSIP.

6MWT showed significant desaturation in eight patients with CTD-ILD (72.7%). While Kundu et al.[9] found significant desaturation in 31.1% of patients. The difference in observation may be due to more cases of PAH in CTD-ILD group in this study.

In this study, all patients having PH had significant desaturation on 6MWT, whereas only 40% of all patients with ILDs who were desaturated on 6MWT had PH. None of the patients who did not have significant desaturation on 6MWT had PH.


  Conclusion Top


All patients with ILD with PH develop significant desaturation on 6MWT. However, only about half the patients who develop significant desaturation on 6MWT have PH. Thus, desaturation on 6MWT carries a high negative predictive value in ruling out PH in ILDs rather than being an early predictor of PH.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Goto K, Arai M, Watanabe A, Hasegawa A, Nakano A, Kurabayashi M. Utility of echocardiography versus BNP level for the prediction of pulmonary arterial pressure in patients with pulmonary arterial hypertension. Int Heart J 2010;51:343-7.  Back to cited text no. 1
    
2.
Arcasoy SM, Christie JD, Ferrari VA, Sutton MS, Zisman DA, Blumenthal NP, et al. Echocardiographic assessment of pulmonary hypertension in patients with advanced lung disease. Am J Respir Crit Care Med 2003;167:735-40.  Back to cited text no. 2
    
3.
Nathan SD, Shlobin OA, Barnett SD, Saggar R, Belperio JA, Ross DJ, et al. Right ventricular systolic pressure by echocardiography as a predictor of pulmonary hypertension in idiopathic pulmonary fibrosis. Respir Med 2008;102:1305-10.  Back to cited text no. 3
    
4.
ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories. ATS statement: Guidelines for the six-minute walk test. Am J Respir Crit Care Med 2002;166:111-7.  Back to cited text no. 4
    
5.
ERS Task Force, Palange P, Ward SA, Carlsen KH, Casaburi R, Gallagher CG, et al. Recommendations on the use of exercise testing in clinical practice. Eur Respir J 2007;29:185-209.  Back to cited text no. 5
    
6.
Celli BR, Cote CG, Marin JM, Casanova C, Montes de Oca M, Mendez RA, et al. The body-mass index, airflow obstruction, dyspnea, and exercise capacity index in chronic obstructive pulmonary disease. N Engl J Med 2004;350:1005-12.  Back to cited text no. 6
    
7.
AARC clinical practice guideline. Exercise testing for evaluation of hypoxemia and/or desaturation. American Association for Respiratory Care. Respir Care 1992;37:907-12.  Back to cited text no. 7
    
8.
Chang JA, Curtis JR, Patrick DL, Raghu G. Assessment of health-related quality of life in patients with interstitial lung disease. Chest 1999;116:1175-82.  Back to cited text no. 8
    
9.
Kundu S, Mitra S, Ganguly J, Mukherjee S, Ray S, Mitra R. Spectrum of diffuse parenchymal lung diseases with special reference to idiopathic pulmonary fibrosis and connective tissue disease: An eastern India experience. Lung India 2014;31:354-60.  Back to cited text no. 9
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10.
Lama VN, Flaherty KR, Toews GB, Colby TV, Travis WD, Long Q, et al. Prognostic value of desaturation during a 6-minute walk test in idiopathic interstitial pneumonia. Am J Respir Crit Care Med 2003;168:1084-90.  Back to cited text no. 10
    
11.
Kumar R, Gupta N, Goel N. Spectrum of interstitial lung disease at a tertiary care centre in India. Pneumonol Alergol Pol 2014;82:218-26.  Back to cited text no. 11
    
12.
Baughman RP, Sparkman BK, Lower EE. Six-minute walk test and health status assessment in sarcoidosis. Chest 2007;132:207-13.  Back to cited text no. 12
    
13.
Lima MS, Coletta EN, Ferreira RG, Jasinowodolinski D, Arakaki JS, Rodrigues SC, et al. Subacute and chronic hypersensitivity pneumonitis: Histopathological patterns and survival. Respir Med 2009;103:508-15.  Back to cited text no. 13
    



 
 
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