Abstract
The photoplethysmographic waveform sits at the core of the most used, and arguably the most important, clinical monitor, the pulse oximeter. Interestingly, the pulse oximeter was discovered while examining an artifact during the development of a noninvasive cardiac output monitor. This article will explore the response of the pulse oximeter waveform to various modes of ventilation. Modern digital signal processing is allowing for a re-examination of this ubiquitous signal. The effect of ventilation on the photoplethysmographic waveform has long been thought of as a source of artifact. The primary goal of this article is to improve the understanding of the underlying physiology responsible for the observed phenomena, thereby encouraging the utilization of this understanding to develop new methods of patient monitoring. The reader will be presented with a review of respiratory physiology followed by numerous examples of the impact of ventilation on the photoplethysmographic waveform.
Highlights
Assessment of fluid responsiveness is an important issue in the fluid management of critically ill patients
The impact of breathing through incentive spirometry is considered an exaggerated response of normal spontaneous breathing (Figure 2), as pleural pressure (Ppl) fell more than did chamber pressures, transmural left atrial pressure (LAP), pulmonary artery pressure (PAP) and aortic transmural pressure increased and that was associated with increased Left Ventricle (LV) preload and afterload of both
The use of the photoplethysmographic (PPG) waveform for patient monitoring offers a number of significant advantages
Summary
Assessment of fluid responsiveness is an important issue in the fluid management of critically ill patients. A fluid challenge in patients with borderline cardiac reserve may result in an overt pulmonary edema, necessitating ventilatory support [1,2] Static measures such as central venous pressure or the Sensors 2012, 12 pulmonary artery wedge pressure, if not extremely low, are not useful for assessment of fluid responsiveness [3,4,5], while dynamic measures such as pulse pressure variation (PPV), systolic pressure variation (SPV) and stroke volume variation (SVV) predict fluid responsiveness well during mechanical ventilation. This is accomplished by an increase in alveolar pressure during positive pressure inspiration or by a decrease in Ppl during spontaneous inspiration Because of their anatomic position in the closed thoracic cavity, the heart and lungs interact during each ventilation cycle
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