Respiratory modulations in the photoplethysmogram (DPOP) as a measure of respiratory effort

Abstract

DPOP is a measure of the strength of respiratory modulations present in the pulse oximetry photoplethysmogram (pleth) waveform. It has been proposed as a non-invasive parameter for the prediction of the response to volume expansion in hypovolemic patients. The effect of resistive breathing on the DPOP parameter was studied to determine whether it may have an adjunct use as a measure of respiratory effort. Healthy volunteers were tasked to breathe at fixed respiratory rates over a range of airway resistances generated by a flow resistor inserted within a mouthpiece. Changes in respiratory efforts, effected by the subjects and measured as airway pressures at the mouth, were compared to DPOP values derived from a finger pulse oximeter probe. It was found that the increased effort to breathe manifests itself as an associated increase in DPOP. Further, a relationship between DPOP and percent modulation of the pleth waveform was observed. A version of the DPOP algorithm that corrects for low perfusion was implemented which resulted in an improved relationship between DPOP and PPV. Although a limited cohort of seven volunteers was used, the results suggest that DPOP may be useful as a respiratory effort parameter, given that the fluid level of the patient is maintained at a constant level over the period of analysis.

Keywords: DPOP; Fluid responsiveness; Hemodynamic monitoring; PPV; Pulse oximetry.

Fig. 1

Deriving DPOP from the pleth

Fig. 2

Airflow (top), Arterial blood pressure (middle) and pleth (bottom). a Signals for the whole four tasks. b Zoom into the signal segments denoted by the arrow in (a)

Fig. 3

Relationships between airway pressure, DPOP and PPV. a Relationship between DPOP and PPV. b Relationship between PPV and APM. c Relationship between DPOP and APM. Subjects are differentiated by color. Linear resistors of 5/20/50 cmH₂O/l are indicated by solid/dashed/dotted lines with circles/triangles/squares respectively. High/low breathing efforts are indicated by large/small symbols at the end of each line. All data were collected with a coached breathing at a respiration rate of 8 brpm

Fig. 4

Difference plots of respiratory effort induced parameter changes. a DPOP change versus PPV change; b PPV change versus mean absolute airway pressure change; c DPOP change versus mean absolute airway pressure change

Fig. 5

Relationship between DPOP and PMod. Linear resistors of 5/20/50 cmH₂O/l are indicated by solid/dashed/dotted lines with circles/triangles/squares respectively. High/low breathing efforts are indicated by large/small symbols at the end of each line. All data were collected with a coached breathing at a respiration rate of 8 brpm

Fig. 6

Respiration effort induced change in DPOP and PPV using the modified DPOP algorithm. a Relationship between DPOP and PPV, b DPOP change versus PPV change