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

Exercise transcutaneous oxygen pressure measurement (Exercise-TcPO₂) 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-TcPO₂ 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.

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.

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].

Exercise-TcPO₂ 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-TcPO₂ with a Gardner-Skinner test. However, this cut-off value should be confirmed against an imaging gold standard. ClinicalTrials.gov identifier: NCT03186391.