Relationship between exercise transcutaneous oxygen pressure measurements with constant and graded treadmill tests

Introduction: Exercise transcutaneous oxygen pressure measurement (Exercise-TcPO 2 ) that has been validated with a constant-load treadmill protocol, is useful to assess patients with suspected lower-extremity peripheral artery disease (PAD). To date, nothing is known about its use with a graded protocol. The aim of this study is to compare the Exercise-TcPO 2 results obtained in patients with suspected PAD using a graded Gardner–Skinner (3.2 km/h, 2% grade increase every 2 min) versus a constant modified Strandness (3.2 km/h, 10% grade) treadmill test. Methods: Patients with suspected PAD were assessed twice on the same day on a treadmill using the modified Strandness (Strand) followed by the Gardner–Skinner (Gard) tests. In both tests, the decrease from resting oxygen pressure (DROP) indexes were measured at the buttock and calf levels as previously validated. A DROP Strand index ⩽ −15 mmHg was considered positive for the diagnosis of PAD. The relationship between DROP Gard and DROP Strand as well as DROP value differences between the two tests and concordances were studied. Results: This prospective study included 40 patients. Using a linear mixed model, the relationship between DROP Gard and DROP Strand was defined as DROP Gard = 0.647 × DROP Strand – 1.858. The mean difference between DROP Gard and DROP Strand was −4.3 ± 7.3 mmHg. Positive and negative agreements were 78.0% and 86.3%, respectively. The kappa coefficient between DROP Gard and DROP Strand was 0.65 [0.54; 0.77]. Conclusion: Exercise-TcPO 2 results using the Gardner–Skinner and modified Strandness treadmill tests were highly correlated. This study suggests the use of a DROP Gard value ⩽ −12 mmHg to diagnose PAD when performing Exercise-TcPO 2 with a Gardner–Skinner test. However, this cut-off value should be confirmed against an imaging gold standard. ClinicalTrials.gov identifier: NCT03186391 .