Non-arterial line cardiac output calculation misclassifies exercise pulmonary hypertension and increases risk of data loss particularly in black, scleroderma and Raynaud's patients during invasive exercise testing

Background The direct Fick principle is the standard for calculating cardiac output (CO) to detect CO-dependent conditions like exercise pulmonary hypertension (ePH). Fick CO arterial incorporates arterial haemoglobin (Hb a ) and oxygen saturation ( S aO 2 ) with oxygen consumption from exercise testing, while Fick CO non-arterial substitutes mixed venous haemoglobin (Hb mv ) and peripheral oxygen saturation ( S pO 2 ) in the absence of an arterial line. The decision to employ an arterial catheter for exercise testing varies, and discrepancies in oxygen saturation and haemoglobin between arterial and non-arterial methods may lead to differences in Fick CO, potentially affecting ePH classification. Methods We performed a retrospective analysis of 296 consecutive invasive cardiopulmonary exercise testing (iCPET) studies comparing oxygen saturation from pulse oximetry ( S pO 2 ) and radial arterial ( S aO 2 ), Hb a and Hb mv , and CO calculated with arterial (CO arterial ) and non-arterial (CO non-arterial ) values. We assessed the risk of misclassification of pre- and post-capillary ePH and data loss due to inaccurate S pO 2 . Results When considering all stages from rest to peak exercise, Hb a and Hb mv demonstrated high correlation, while S pO 2 and S aO 2 as well as CO arterial and CO non-arterial demonstrated low correlation. Data loss was significantly higher across all stages of exercise for S pO 2 (n=346/1926 (18%)) compared to S aO 2 (n=17/1923 (0.88%)). We found that pre- and post-capillary ePH were misclassified as CO non-arterial data (n=7/41 (17.1%) and n=2/23 (8.7%), respectively). Patients with scleroderma and/or Raynaud's (n=11/33 (33.3%)) and black patients (n=6/19 (31.6%)) had more S pO 2 data loss. Conclusion Reliance upon S pO 2 during invasive exercise testing results in the misclassification of pre- and post-capillary ePH, and unmeasurable S pO 2 for black, scleroderma and Raynaud's patients can preclude accurate exercise calculations, thus limiting the diagnostic and prognostic value of invasive exercise testing without an arterial line.