Corrected flow time: a noninvasive ultrasound measure to detect preload reduction by nitroglycerin

Monitoring of patient's intravascular volume status without invasive measures remains challenging and unreliable. Our objective was to determine if corrected flow time (FTc) measurement could detect preload reduction with administration of nitroglycerin (NTG) as a surrogate for volume loss.

Post hoc FTc analysis was performed for a prospective cohort study of pulsed wave spectral Doppler measurements before and after administration of NTG. Patients enrolled were eligible for inclusion if they were admitted to a chest pain center for cardiac evaluation. Descriptive statistics, t tests, bivariate regression, and intraclass correlation coefficient were performed as appropriate.

Fifty-four patients had Doppler measurements available for review. Mean FTc decreased from 339 milliseconds (95% confidence interval, 332-346) to 325 milliseconds (95% confidence interval, 318-331) with administration of 0.3 mg of sublingual NTG (P=.0001). Mean heart rate increased 5 beats/min with administration of NTG (P<.0001); however, there was no significant change in systolic or diastolic blood pressure.

Corrected flow time was able to detect a significant difference in preload reduction with 0.3 mg of NTG. The FTc may be an early reliable noninvasive measure to detect changes in intravascular volume status.