Date of Award

January 2015

Document Type

Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

David G. Silverman

Subject Area(s)

Medicine

Abstract

Recent research in monitoring aims to the return to the roots of the

photoplethysmography (PPG) and extract volumetric information from its waveform.

Previous studies from our laboratory have shown that a voltage-to-volume conversion

based upon pulsatile volume at rest allows volume monitoring using the PPG. The current

study aims to further extract arterial and venous circulatory volume components from the

PPG via simulated volume loading of 0.75-2L upon release of lower body negative

pressure (LBNP).

Data were extracted retrospectively from LBNP studies on five healthy volunteers

with the Institutional Review Board approval. Stroke volumes (SV) were measured by

echocardiography, when available. All PPG waveforms were analyzed in ADInstruments

LabChart. AC and DC were found before LBNP (baseline) by averaging at least 75 beats,

and during LBNP by averaging 10 beats. The release segment (LBNP off) was roughly

divided into 4-8 successive phases. AC and DC of each phase were found by averaging

10-12 beats. ΔAC and ΔDC from baseline were calculated for each phase and converted

to a volume using AC at rest:

2

ΔAC = (AC recovery phase x - AC at rest) x (SV at rest /AC at rest)

ΔDC = (DC recovery phase x - DC at rest) x (SV at rest /AC at rest).

ΔAC and ΔDC during maximum LBNP and LBNP release were consistent with

literature values. Overshoot of volume return may be attributable to splanchnic

vasculature mobilization. ΔDC/ΔAC ratio tended to be smallest initially and greatest at

the end of volume resuscitation. Distortions in the relationship were accompanied by

abrupt hypotension and bradycardia.

PPG may be used as a non-invasive monitor of arterial and venous volume status,

which can be useful in assessing response to fluid resuscitation. Moreover, the evidence

of Frank-Starling relationship between AC (arterial) and DC (venous) may shed light on

physiologic processes and warrants further study.

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