1. Department of Respiratory Medicine
Relationship between the incremental shuttle walk test (ISWT) and full cardiopulmonary exercise testing (CPET) in patients with Idiopathic Interstitial Pneumonia (IIP).
Shakespeare J, Archer L, Hastings R, Woodhead F, Helm E, Hughes R, Parr D.
Department of Respiratory Medicine
Introduction
Results
Lung function impairment was consistent with a diagnosis of IIP (Table 2). Median walking distance was 367m (IQR 180 – 370m). There was a significant relationship between walking distance on ISWT and Peak VO2 (Graph 1).
The Idiopathic Interstitial Pneumonias (IIP) are a complex group of diffuse parenchymal lung diseases that cause significant morbidity and mortality. The most common form of IIP is Idiopathic Pulmonary Fibrosis (IPF). Exercise tolerance in patients with IPF is limited by mechanics and gas exchange. FVC, TLCO and exercise desaturation are predictive of mortality(1).
CPET is considered the ‘gold standard’ exercise test but it is demanding of resources. ISWT has been validated as a reliable alternative to CPET in many disease states. ISWT can predict maximal oxygen uptake (VO2) in some disease groups, however data is limited in IPF. Small studies have suggested a relationship between walking distance on ISWT and peak VO2 (r=0.74 p<0.05)(2).
Aim:
To evaluate the relationship between ISWT and peak VO2 in a group of patients with IIP.
Secondary aim:
To evaluate the impact of exercise induced desaturation on indices of lung function and CPET.
Half of the study group demonstrated a significant fall in oxygen saturation whilst undertaking an ISWT (>4% and to <90%). Significant differences in some static lung function measures were identified between patients who desaturated and those that did not (Table 3). There was no significant difference between any of the commonly reported CPET parameters such as VO2, VE/VCO2, VE/VO2, AT, maximal load, VE max, O2/HR or heart rate reserve.
There was a significant correlation between walking distance and Peak VO2 in patients that did not desaturate (Graph 2)
Methods
43 patients were recruited from a specialist ILD clinic. 23 were classified as definite IPF through MDT outcome(1).
All patients performed full lung function testing (spirometry, lung volumes and gas transfer) and an incremental shuttle walk test(3). Patients returned within 1 week to perform a symptom-limited, maximal, incremental work rate exercise test using a cycle ergometer.
Comparison of the medians for the two groups was with Mann-Whitney, Wilcoxan ranked sum and Spearman correlation using the GraphPad Instat 3 programme. A p value of <0.05 was considered statistically significant.
Bibliography
Conclusions
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ISWT relates to Peak VO2 in IPF patients who do not have exercise-induced desaturation. In this patient group, resting lung function predicts exercise desaturation better than gas exchange measurements obtained during exercise. A TLCO <50% predicted(4-5) is predictive of exercise induced desaturation of >4% and to <90% and should therefore prompt assessment for ambulatory O2 therapy.