Pulmonary arterial hypertension (PAH) is a progressive condition requiring precise measurement of pulmonary artery pressure (PAP), cardiac output (CO), and exercise capacity for diagnosis and therapeutic evaluation. Terminal digit preference, a form of observer bias favouring values ending in 0 and 5, has been reported in PAH clinical trials, potentially introducing significant measurement error. In the FIT-PH study (NCT04078243), we evaluated whether terminal digit preference occurs in remotely collected cardiopulmonary data from implanted monitors in 35 patients with PAH. Over 18,000 haemodynamic and 34,000 heart rate and activity measurements were analysed. No evidence of terminal digit preference was found in systolic or mean PAP, CO, heart rate, or physical activity. A non-uniform terminal digit distribution in diastolic PAP was observed but attributed to physiological constraints rather than rounding bias. These findings demonstrate that digital remote monitoring minimises observer-related bias, enhancing accuracy in PAH research and clinical care

The authors have declared no competing interest.

NCT04078243

MRC Exp Med MR/W026279/1 EPSRC EP/Z531297/1

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Feasibility of Novel Clinical Trial Infrastructure, Design and Technology for Early Phase Studies in Patients with Pulmonary Hypertension (FIT- PH, NCT04078243, REC 19/YH/0354). The Yorkshire & The Humber - Sheffield Research Ethics Committee approved the study.

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All data produced in the present study are available upon reasonable request to the author