Comparison of the finger plethysmography derived stroke volumes by Nexfin CO Trek and suprasternal aortic Doppler derived stroke volume measurements in adults with myalgic encephalomyelitis/chronic fatigue syndrome and in healthy controls

Abstract

BACKGROUND:

Finger plethysmography derived stroke volumes are frequently measured during tilt table testing. There are two algorithms to determine stroke volumes: Modelflow and Nexfin CO Trek. Most tilt studies used Modelflow, while there are differences between the two algorithms.

OBJECTIVE:

To compare stroke volume indices by Nexfin CO Trek (SVI ${}_{\text{NexfinCOTrek}}$ ) with suprasternal Doppler derived SVI (SVI ${}_{\text{Doppler}}$ ) in healthy controls (HC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) patients during tilt testing. These patients may have a large SVI decrease during the tilt enabling a large range of SVI to be studied.

METHODS:

One hundred and fifty-four patients and 39 HC with a normal tilt test were included. Supine and end-tilt SVI ${}_{\text{Doppler}}$ and SVI ${}_{\text{NexfinCOTrek}}$ were compared using the Bland-Altman analysis. Also, the effect of calibrating supine SVI ${}_{\text{NexfinCOTrek}}$ to SVI ${}_{\text{Doppler}}$ was studied.

RESULTS:

Supine and end-tilt SVI ${}_{\text{NexfinCOTrek}}$ were significantly higher than SVI ${}_{\text{Doppler}}$ : both $P<$ 0.005. Bias, limits of agreement, and percent error (PE) were high with PE’s between 37 and 43%. The calibration procedure resulted in an acceptable variance with a PE of 29%.

CONCLUSIONS:

SVI ${}_{\text{NexfinCOTrek}}$ overestimates stroke volumes compared to SVI ${}_{\text{Doppler}}$ , leading to high PE’s. Calibration reduced variance to an acceptable level, allowing SVI ${}_{\text{NexfinCOTrek}}$ to be used for assessment of SVI changes during tilt testing.