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Anesthesiology:
doi: 10.1097/ALN.0b013e31816c89e1
Review Article

Utility of the Photoplethysmogram in Circulatory Monitoring

Reisner, Andrew M.D.*; Shaltis, Phillip A. Ph.D.†; McCombie, Devin‡; Asada, H Harry Ph.D.§
Section Editor(s): Warner, David S. M.D.; Warner, Mark A. M.D., Editors

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Abstract

The photoplethysmogram is a noninvasive circulatory signal related to the pulsatile volume of blood in tissue and is displayed by many pulse oximeters and bedside monitors, along with the computed arterial oxygen saturation. The photoplethysmogram is similar in appearance to an arterial blood pressure waveform. Because the former is noninvasive and nearly ubiquitous in hospitals whereas the latter requires invasive measurement, the extraction of circulatory information from the photoplethysmogram has been a popular subject of contemporary research. The photoplethysmogram is a function of the underlying circulation, but the relation is complicated by optical, biomechanical, and physiologic covariates that affect the appearance of the photoplethysmogram. Overall, the photoplethysmogram provides a wealth of circulatory information, but its complex etiology may be a limitation in some novel applications.
THE photoplethysmogram is a noninvasive circulatory signal related to the pulsatile volume of blood in tissue. Pulse oximeters, which compute fractional arterial oxygen saturation (Sao2) using photoplethysmography with at least two different light wavelengths, often display a photoplethysmogram to help clinicians distinguish between reliable Sao2 measurements (associated with clean, physiologic waveforms) and unreliable measurements (associated with noisy waveforms). The photoplethysmogram is cosmetically similar to an arterial blood pressure waveform (ABP). Because the former is noninvasive and nearly ubiquitous in hospitals, it is intuitive to seek circulatory information from the photoplethysmogram, and the extraction of circulatory information from the photoplethysmogram has been a popular subject of contemporary research.
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Origins of the Photoplethysmogram

Many decades before the advent of pulse oximetry, the simple photoplethysmogram was used as a measure of tissue blood volume.1 It is related to, but not equivalent to, the measurement of pulsatile tissue volume, plethysmography. Pulsatile tissue volume can be directly measured, e.g., placing a strain gauge that measures changes in the circumference of an extremity.2 Plethysmography measures the sum total of volume changes in any and all blood vessels (e.g., large and small arteries, arterioles, venules, and veins). Arterial pulsations are the most significant.3 Capillaries and terminal arterioles are noncompliant,4,5 with minor beat-to-beat pulsations. Venous oscillations due to respiration and the beating of the right heart may be evident, but many measurement techniques apply enough external pressure to partially or fully collapse veins.
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Optical Factors

Fig. 1
Fig. 1
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Complicated optic phenomena distinguish photoplethysmography from plethysmography. In the most common photoplethysmography modality (transmission mode), tissue is irradiated by a light-emitting diode, and light intensity is measured by a photodetector on the other side of the tissue, e.g., across a fingertip or an earlobe. A pulse of blood increases both the optical density and path length through the illuminated tissue (due to intravascular increases of erythrocytes and the light-absorbing hemoglobin they carry), which decreases the light intensity at the photodetector. By convention, the photoplethysmogram is inverted so that it correlates positively with blood volume. Figure 1 is an abstraction of the processes that underlie a photoplethysmogram. Intravascular volume changes comprise the middle row (across the pyramid), whereas the top contains additional optic phenomena that are wavelength dependent. Light intensity is attenuated by oxygenated and deoxygenated hemoglobin (in blood cells), myoglobin (in muscle), and cytochromes, as well as melatonin (in skin) and other optically significant compounds in bone and connective tissue.1
The photoplethysmogram is usually a qualitative measurement, where reductions in light intensity indicate relative increases in blood volume and vice versa. The quantitative relation between blood volume, which is distributed throughout an irregular network of vessels, and the fraction of emitted photons that successfully pass through the tissue is complicated. The Beer-Lambert law offers some insight: If a homogenous layer of blood lies perpendicular to a beam of light, light intensity decays exponentially as a function of distance (i.e., % transmission = 100 * e−αlc, where α is the absorption coefficient of the material, l is the length of the layer, and c is the concentration of the absorbing material). The Beer-Lambert law only considers light absorption, the major cause of light attenuation, but not other causes of attenuation (scatter, refraction, and reflection). Also, the Beer-Lambert law assumes a simple, homogenous tissue geometry. This approximation may be more reasonable given a relatively uniform, diffuse vascular bed, as in an instrumented earlobe or fingertip. In such common measurement locations, the photoplethysmogram is primarily cutaneous,6 perhaps arising largely from volume changes in venules that are fed by arteriovenous fistulas.7,8 However, when the irradiated tissue includes larger, distinct blood vessels, as are found in the forehead, neck, or inguinal canal, the optics are more complex; distinct vessels can alter the photoplethysmogram (as well as the accuracy of pulse oximeters).9–11 Light propagation through a heterogeneous medium has been subjected to substantial theoretical consideration (e.g., references 12–16). The tissue volume assayed by photoplethysmography does not have precise boundaries: Components along the primary optical path contribute more to the photoplethysmogram, whereas tissue components on the periphery are gradually less significant. The properties of the light-emitting diode (location, size, light intensity, light wavelength) and the photodetector (location, size, photovoltaic properties) further complicate the relation between blood volume and the photoplethysmogram.
It should also be noted that the velocity of blood flow affects the photoplethysmogram, probably because of reorientation and/or packing of erythrocytes that is flow dependent.17,18 Even in a rigid (i.e., constant volume) glass pipe, oscillating blood flow gives rise to an oscillating photoplethysmogram.1 There are classic references to photoplethysmography as a flow (rather than volume) measurement (e.g., references 1 and 19), although flow effects may be minor in vivo.1,20–23 It is difficult to sort out the effects of blood flow versus volume pulsations in vivo.24
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Reflectance-mode Photoplethysmography

A photodetector can be placed on a tissue's surface alongside the light-emitting diode and record the light that returns back, known as reflectance-mode photoplethysmography. Theoretical analysis suggests that, for typical wavelengths, the emitted photons that arrive at the photodetector follow a banana-shaped primary light path through the tissue, barely penetrating deeper than the skin.22,25,26 In vitro, reflectance photoplethysmography can demonstrate a notably different relation with blood volume: The more blood in the vessel, the brighter the photodetector intensity will be. This is because nonhemolyzed erythrocytes are reflective and can act as little mirrors.20 When a reflectance sensor is placed directly over a large superficial artery, the photodetector light intensity demonstrates a strong positive correlation with ultrasonic diameter measurements.11 Yet in the majority of in vivo reflectance-mode applications, the relation between blood volume and the photoplethysmogram is similar to transmission modes1: Light from the diode enters the tissue, is reflected by deeper structures, and “backlights” superficial blood vessels. Then, as superficial blood vessels fill with more blood, they absorb more light returning from the deeper tissues, and photodetector light intensity diminishes. Any increase in directly reflected light is negligible compared with the absorption of light returning from the deeper tissues.
Note that reflectance-mode probes are often adhered to the patient and may not apply enough pressure to collapse the low-pressure venous system, so venous oscillations can be more significant than in transmission-mode photoplethysmography.27,28 Oscillations in low-pressure vasculature are, in part, due to respiratory effort, so reflectance mode has been used to extract respiratory rate and volume data from the photoplethysmogram.29,30 A finger probe, i.e., transmission-mode photoplethysmography, can compress the tissue with a variable range of pressures, whereas a reflectance sensor that is adhered to the skin can avoid the major confounding effects of probe pressure on the photoplethysmogram (discussed in the next section). On the other hand, minimal skin pressure applied by the probe often means a worse signal-to-noise ratio. Overall, there is insufficient experience to judge when reflectance or transmission-mode photoplethysmography is preferable for the hemodynamic applications that are reviewed in the next section.
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Hemodynamic Monitoring Applications of Photoplethysmography

Fig. 2
Fig. 2
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Since the 1930s, decades of physiology research have been conducted using the baseline level of the photoplethysmogram (often referred to as the direct current [DC] component) as a relative, nonquantitative index of skin vascularity (e.g., local hyperemia or hypoemia) caused by perturbations in temperature, metabolic state, drug effects, and central or local regulatory mechanisms; this extensive body of literature has been previously reviewed.1,6 In practice, the photoplethysmogram baseline is dictated by the interplay of physiologic mechanisms. Figure 2 demonstrates a step increase in arterial pressure, which engorges a finger with blood (the baseline of the photoplethysmogram rises). Note that there is a subsequent downward drift in the baseline, or DC level, reflecting the tissue's autoregulatory compensation to the rapid increase in volume.
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Oscillations in the Baseline of the Photoplethysmogram

It is a misnomer to use the term DC in reference to the baseline of the photoplethysmogram; the baseline is not steady, but displays low-frequency oscillations due to changes in capillary density (e.g., due to episodic sympathetic outflow23,31–34 and local autoregulation) and venous volume fluctuations (e.g., due to respiration-induced fluctuations in central venous pressure). Baseline oscillations in a fingertip photoplethysmogram have been reported distal to an arterial tourniquet; the authors suggest this may represent sympathetically mediated shifting of blood between different compartments of the peripheral microcirculation.35 While oscillations in the baseline of the photoplethysmogram are technically part of the alternating current (AC) component, most medical literature uses the AC specifically in reference to pulsations in the photoplethysmogram generated by individual heart beats, not oscillations in the baseline.
The baseline level of the photoplethysmogram is not displayed by most commercial pulse oximeters. In fact, the photoplethysmogram is highly electronically processed by most nonresearch pulse oximeters to remove these baseline vacillations and, in general, to reduce signal distortions due to patient motion and yield a photoplethysmogram that appears “cleaner.” There is no singular method for removing oscillations in the DC baseline of the photoplethysmogram, and the specific algorithm used by a device can dramatically alter the waveform morphology.36 The processing algorithms vary between manufacturers, and their precise methods are often proprietary. Most commercial monitors also “autoscale” the photoplethysmogram so that the amplitude of the signal is adjusted (increased or decreased) to fit neatly in the display window. When not properly accounted for by the instrumentation, changes in ambient light can also be a source of error in analysis of the DC-level baseline (e.g., if an instrumented hand moves away from an overhead light, less light reaches the photodetector so it may appear as if the digit had become hyperemic). In a cautionary example of how postprocessing must be borne in mind when examining a monitor's photoplethysmogram, there is a case report of a patient who experienced cardiac arrest while an undisrupted photoplethysmogram was displayed by the bedside monitor. The user manual for the Masimo SatShare tool (Masimo Corporation, Irvine, CA) expressly warns that the photoplethysmogram exported to the bedside monitor is simulated and not physiologic, but in this reported case, the clinicians were unaware of that proviso.37
Note that changes in the DC baseline impact the amplitude of the AC pulsatile waveform. Each AC pulse of blood causes a fractional loss of light (in accordance with the Beer-Lambert law), at most a few percent of the total intensity. When there is less baseline light, the fractional loss yields a low-amplitude AC signal. When there is more baseline light, the same fractional loss produces a higher-amplitude AC signal. Hence, an AC amplitude can increase when a tissue's baseline optic density is reduced, e.g., hypoemia, or if the incident light is increased, e.g., turning on an overhead light.
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The Photoplethysmogram versus Arterial Blood Pressure

The pulsatile AC signal of the photoplethysmogram is similar in morphology to an ABP waveform, so it is intuitive that they are related and to seek information about ABP from a readily available photoplethysmogram. First, we consider the relation between the ABP and basic (i.e., not photo-) plethysmography (fig. 1). Time plots of arterial diameter share a similar shape with ABP plots, although the typical diameter change is only 1–5% whereas the pressure change is on the order of 50%.38 Recall that volume will be proportional to the square of a vessel's radius.
Fig. 3
Fig. 3
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There are two major complications to the arterial pressure–volume relation. First, arterial volume is determined by the balance of internal blood pressure and external pressure, not by blood pressure alone. Blood vessels grow ever less compliant at extremes of pressure (e.g., nonlinear compliance), so plotting vascular transmural pressure versus volume yields a sigmoid-shaped curve.39,40 Although the photoplethysmogram is not a true plethysmogram, Ando et al.41 reported that the AC signal of the photoplethysmogram versus arterial transmural pressure yields a similar sigmoid-shaped curve. Our group has been able to replicate similar curves using a plethysmogram measured over the digital artery, after signal processing to remove fluctuations in the DC baseline in a photoplethysmogram (fig. 3).42 In more distal measurement locations, the pressure–volume relation of smaller vessels dictates this relation. Note that a photoplethysmogram will be altered dramatically (both in amplitude and shape) when the pressure applied by a probe is altered.43 This is intuitive when one considers the sigmoid curve, and appreciates that it is the transmural pressure (blood pressure minus external pressure) that determines vessels’ volumes (fig. 3).
Fig. 4
Fig. 4
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Second, as shown in figure 4, on a beat-to-beat basis, it is more accurate to think of pressure–volume loops rather than static curves, because of hysteresis.27 The loops occur because of dynamic compliance and stress–relaxation, which are intrinsic properties of arteries and veins. Dynamic compliance means that vessels are stiffer when their pressure changes quickly (e.g., intrabeat) and more compliant when their pressure changes slowly (e.g., interbeat), as illustrated in figure 4. Therefore, a photoplethysmogram can appear dampened relative to the ABP, lacking in higher-frequency waveform features.44 Electronic processing of the photoplethysmogram also can create an artifactual appearance of hysteresis. The specific slope of a photoplethysmogram–versus–transmural pressure curve is a function of the mechanical properties of the pulsating vessels and is sensitive to the subject's physiologic state.27 It can take a blood vessel minutes to alter its mechanical properties in response to physiologic stimuli.45
Computational devices to estimate ABP from the photoplethysmogram have included linear transfer functions and neural networks. Millasseau et al. 46 showed that the shape (but not absolute value) of ABP can be estimated from the photoplethysmogram using a population-averaged transfer function. Allen and Murray47 showed that, using a neural network that was first individually calibrated to each subject, the ABP could be subsequently estimated from the photoplethysmogram during controlled laboratory conditions. In the 1980s, Yamakoshi et al.48 used photoplethysmography in a variation of conventional oscillometry that attached to the finger base.
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The Volume Clamp Method

The Finapres/Portapres/Finometer family of devices (Finapres Medical Systems, Amsterdam, The Netherlands) enables noninvasive measurement of the ABP waveform from a finger using an inflatable cuff in conjunction with photoplethysmography. In numerous instances, published works may refer to this measurement modality as “photoplethysmography” (e.g., references 49–51) although such usage is imprecise, and it can leave the incorrect impression that the photoplethysmogram and the ABP signal are interchangeable. The Finapres uses the volume clamp method of Penaz, which is based on the following insight: If a photoplethysmogram is not changing, neither is the arterial transmural pressure, and vice versa. Using an extremely rapid servo system with a finger cuff actuator, the Finapres adjusts the pressure in a finger cuff to keep a reference photoplethysmogram flat throughout systole and diastole; the method is thus known as the volume clamp because the finger's blood volume in held constant. The waveform of whatever cuff pressure is necessary to keep the photoplethysmogram flat must be equal to and opposite the digital arterial ABP. The method is attractive in that it offers a noninvasive, continuous ABP digital artery measurement, although historically it tends to underestimate blood pressures.52 Moreover, differences in systolic blood pressure (SBP) measured in the finger versus brachial SBP are a function of arterial compliance, changing with age.53 A newer model seems to have improved accuracy that is comparable to other noninvasive blood pressure devices,54 although there remain questions about its performance in subpopulations (e.g., pregnant patients55) and the validity of its reliance on a generalized transfer function for all patients and physiologic states (e.g., references 56 and 57).
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The Perfusion Index and Other Correlates of Hemodynamic State

The new Masimo SET pulse oximeter (Masimo Corporation, Irvine, CA) reports a perfusion index, the ratio of the pulsatile amplitude of a photoplethysmogram to its DC component. Early reports suggest that the perfusion index is sensitive to proximal sympathectomy,58 proximal arterial clamping,59 and neonatal left heart obstruction.60 Other metrics from a photoplethysmogram that have been recently investigated are related to beat-to-beat waveform variability of either peak levels or amplitude, which are nonspecific metrics analogous to ABP pulsus paradoxus. Changes in waveform variability metrics have been significantly associated with hypotension (for systolic variation and δ-down: r = 0.6 correlation with ΔSBP61), respiratory volume (for a novel oscillation metric: r = 0.89 correlation with breath volume30), wedge pressure (for δ-down: r = −0.6 correlation with wedge pressure62), and hypovolemia (systolic variation of 17 ± 12SD% at baseline vs. systolic variation of 32 ± 12SD% after loss of 10% blood volume63). The Masimo SET pulse oximeter reports perfusion index variability, which will presumably show similar correlations.
There are a number of other waveform features that correlate with central hemodynamic parameters. In the operating room, a measure of the photoplethysmogram's systolic width correlated with mean arterial pressure (r = 0.80).64 In a cardiac catheterization suite, the “maximum decreasing systolic slope” correlated with changes in peripheral vascular resistance (r = 0.66).65 Features from the second derivative of the photoplethysmogram have been correlated with vascular compliance.66–68
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Correlations and Covariates

Table 1
Table 1
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That features of a photoplethysmogram are correlates of important hemodynamic parameters is not surprising. What is crucial to appreciate is how a multitude of effects can confound any of the preceding correlations when not carefully controlled. We note that the majority of photoplethysmography investigations to date report significant correlation statistics but do not report test characteristics (e.g., sensitivity and specificity). Novel photoplethysmography applications may be most useful when one clear-cut factor is changing at a time, e.g., ventilation or circulatory state or anesthetic state. For example, it has been observed that the pulsatile amplitude of a photoplethysmogram, which is a major determinant of the perfusion index, may serve as a measure of depth of anesthesia, with higher amplitude indicating deeper anesthesia.69 But in practice, an increase in amplitude could be caused by other physiologic or external phenomena (table 1). To apply photoplethysmogram waveform analysis in a reliable and reproducible manner (i.e., without dangerous false positives and false negatives), it is important to consider all potential confounding effects. Was the probe's skin pressure kept constant? Exactly how were baseline oscillations mathematically removed (as noted above, the photoplethysmogram displayed is a function of the manufacturer's postprocessing algorithms)? Was the height of the sensor (relative to the subject's heart) held constant? Did medication or temperature effects alter the local tissue vascularity? Pending further contributions to the literature, notable changes in the photoplethysmogram should make a prudent clinician reassess the patient's condition to seek an explanation. However, photoplethysmogram changes will likely be nonspecific, and they are not necessarily sensitive enough to substitute for standard diagnostic practices.
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Indication of Pulsatile Perfusion

The simplest photoplethysmography application is to test for the presence or absence of measurable perfusion (e.g., a measurable pulsatile photoplethysmogram). One case series explored photoplethysmography as an indicator of efficacious chest compressions during cardiac arrest, with mixed success.70 Chest compressions can lead to a deceptively pulsatile photoplethysmogram (i.e., related to jolting movements, not vascular pulsation). It has been suggested that with placement of the photoplethysmography probe in an isolated location, i.e., a finger, and with careful inspection of the waveform, i.e., visualization of a dicrotic notch, the photoplethysmogram can be helpful during cardiopulmonary resuscitation.71 In a related application, photoplethysmography was used in a small case series as a continuous indicator of graft viability after revascularization.72 Note that a pulsatile photoplethysmogram can be misleading in the setting of venous obstruction73: The upstream arteries may still pulsate (hence the photoplethysmogram appears pulsatile) without any net flow through the tissues.
Loss of a pulsatile photoplethysmogram distal to a cuff being inflated indicates when the cuff pressure is close to a subject's SBP. The use of photoplethysmography to determine when distal flow is cut off by the cuff is comparable to other indicators that pulsatile flow has ceased, including direct arterial cannulation (r = 0.99),74 Doppler ultrasound (r = 0.99),75 and manual palpation (r = 0.97).76 In some studies, actual SBP was slightly higher than what was estimated,74,75 although one investigation found that photoplethysmography-based SBP measurement was superior to standard cuff oscillometry for small pediatric patients.77 Note that hypotension (e.g., SBP <60 mmHg78), peripheral vasoconstriction (e.g., pressor therapy78 or cold79), or vascular lesions may reduce or eliminate any measurable pulsatile photoplethysmogram in distal and/or cutaneous beds and confound this method of measuring SBP.
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Measuring Pulse Transit Time

As an indicator of pulsatile flow, photoplethysmography can also be used to measure the pulse transit time (PTT) between an upstream arterial pressure pulse and a distal peripheral pulse. PTT is a function of pulse wave velocity, which is a function of blood pressure. In some conditions, pulse wave velocity and blood pressure are highly correlated (e.g., r = 0.97).80 However, pulse wave velocity is more accurately a function of arterial compliance, which is certainly a function of blood pressure but also of the subject's arterial properties and physiologic state. Also, to compute PTT, a proximal and a distal measurement are necessary. Options for the proximal signal include the sound of the mitral valve, a proximal photoplethysmogram or ABP signal, or an electrocardiogram, although the electrocardiogram is not a reliable indicator of mechanical systole.81 Such issues have been reviewed, with recommendations available for PTT/pulse wave velocity applications.82,83 In general, PTT is not an acceptable alternative to standard noninvasive blood pressure measurements, although the capability to continuously monitor trends in arterial compliance is valuable for physiologic research.
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Measuring Heart Rate

A pulsatile photoplethysmogram of course reveals the heart rate (HR) and could be used to monitor HR variability. General Electric's new IntelliRate algorithm (GE Healthcare, Little Chalfont, United Kingdom) uses the photoplethysmogram as an ancillary to electrocardiography, to reduce false electrocardiographic alarms related to nonperfusing arrhythmias. But as an HR-monitoring modality, photoplethysmography is unable to distinguish between electrically narrow-complex and wide-complex beats, and electrical–mechanical disassociation will cause a discrepancy between a photoplethysmographic HR and electrocardiographic HR. There is insufficient evidence to warrant the use of photoplethysmography for primary HR monitoring, because the shape of a normal pulse may be less morphologically distinct than the QRS complex of an electrocardiogram, particularly in the setting of motion artifact.84
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Conclusion

Recent evidence suggests that photoplethysmography offers a fruitful avenue for new technologic developments in noninvasive circulatory monitoring. The challenge is the many covariates that affect the appearance of the photoplethysmogram. In the future, novel bedside devices and alarm algorithms might exploit the richness of the photoplethysmogram, although these may demand some compensation for ambiguities in the signal.
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References

1. Challoner AVJ: Photoelectric plethysmograph, Non-Invasive Physiological Measurements. Edited by Rolfe P. London, Academic Press, 1979, pp 125–51

2. Whitney RJ: The measurement of volume changes in human limbs. J Physiol 1953; 121:1–27

3. Fitchett DH: Forearm arterial compliance: A new measure of arterial compliance? Cardiovasc Res 1984; 18:651–6

4. Fung YC, Zweifach BW, Intaglietta M: Elastic environment of the capillary bed. Circ Res 1966; 19:441–61

5. Meyer JU, Borgstrom P, Lindbom L, Intaglietta M: Vasomotion patterns in skeletal muscle arterioles during changes in arterial pressure. Microvasc Res 1988; 35:193–203

6. Sara CA, Shanks CA: The peripheral pulse monitor: A review of electrical plethysmography. Anaesth Intensive Care 1978; 6:226–33

7. Secker C, Spiers P: Accuracy of pulse oximetry in patients with low systemic vascular resistance. Anaesthesia 1997; 52:127–30

8. Kim JM, Arakawa K, Benson KT, Fox DK: Pulse oximetry and circulatory kinetics associated with pulse volume amplitude measured by photoelectric plethysmography. Anesth Analg 1986; 65:1333–9

9. Nijland R, Jongsma HW, van den Berg PP, Nijhuis JG, Oeseburg B: The effect of pulsating arteries on reflectance pulse oximetry: Measurements in adults and neonates. J Clin Monit 1995; 11:118–22

10. Nijland R, Jongsma HW, Verbruggen IM, Nijhuis JG: Reflectance pulse oximetry in fetal lambs: Subcutaneous vessels and vasoconstriction affect its reliability. J Clin Monit 1996; 12:225–30

11. Weinman J, Hayat A, Raviv G: Reflection photoplethysmography of arterial-blood volume pulses. Med Biol Eng Comput 1977; 15:22–31

12. Keijzer M, Star WM, Storchi PRM: Optical diffusion in layered media. Appl Optics 1988; 27:1820–4

13. Wilson BC, Adam G: A Monte Carlo model for the absorption and flux distributions of light in tissue. Med Phys 1983; 10:824–30

14. Reuss JL, Siker D: The pulse in reflectance pulse oximetry: Modeling and experimental studies. J Clin Monit Comput 2004; 18:289–99

15. Schmitt JM: Simple photon diffusion analysis of the effects of multiple scattering on pulse oximetry. IEEE Trans Biomed Eng 1991; 38:1194–203

16. Takatani S, Graham MD: Theoretical analysis of diffuse reflectance from a two-layer tissue model. IEEE Trans Biomed Eng 1979; 26:656–64

17. Visser KR, Lamberts R, Korsten HH, Zijlstra WG: Observations on blood flow related electrical impedance changes in rigid tubes. Pflugers Arch 1976; 366:289–91

18. D'Agrosa LS, Hertzman AB: Opacity pulse of individual minute arteries. J Appl Physiol 1967; 23:613–20

19. Almond NE, Jones DP, Cooke ED: Noninvasive measurement of the human peripheral circulation: Relationship between laser Doppler flowmeter and photoplethysmograph signals from the finger. Angiology 1988; 39:819–29

20. Nijboer JA, Dorlas JC, Mahieu HF: Photoelectric plethysmography: Some fundamental aspects of the reflection and transmission method. Clin Phys Physiol Meas 1981; 2:205–15

21. Loukogeorgakis S, Dawson R, Phillips N, Martyn CN, Greenwald SE: Validation of a device to measure arterial pulse wave velocity by a photoplethysmographic method. Physiol Meas 2002; 23:581–96

22. Ugnell H, Oberg PA: The time-variable photoplethysmographic signal: Dependence of the heart synchronous signal on wavelength and sample volume. Med Eng Phys 1995; 17:571–8

23. Kamal AA, Harness JB, Irving G, Mearns AJ: Skin photoplethysmography: A review. Comput Methods Programs Biomed 1989; 28:257–69

24. Zweifler AJ, Cushing G, Conway J: The relationship between pulse volume and blood flow in the finger. Angiology 1967; 18:591–8

25. Kumar G, Schmitt JM: Optimal probe geometry for near-infrared spectroscopy of biological tissue. Appl Opt 1997; 36:2286–93

26. Feng W, Haishu D, Fenghua T, Jun Z, Qing X, Xianwu T: Influence of overlying tissue and probe geometry on the sensitivity of a near-infrared tissue oximeter. Physiol Meas 2001; 22:201–8

27. Shelley KH, Murray WB, Chang D: Arterial-pulse oximetry loops: A new method of monitoring vascular tone. J Clin Monit 1997; 13:223–8

28. Shelley KH, Tamai D, Jablonka D, Gesquiere M, Stout RG, Silverman DG: The effect of venous pulsation on the forehead pulse oximeter wave form as a possible source of error in Spo2 calculation. Anesth Analg 2005; 100:743–7

29. Nilsson L, Johansson A, Kalman S: Macrocirculation is not the sole determinant of respiratory induced variations in the reflection mode photoplethysmographic signal. Physiol Meas 2003; 24:925–37

30. Johansson A, Oberg PA: Estimation of respiratory volumes from the photoplethysmographic signal: I. Experimental results. Med Biol Eng Comput 1999; 37:42–7

31. Nitzan M, Babchenko A, Khanokh B, Landau D: The variability of the photoplethysmographic signal: A potential method for the evaluation of the autonomic nervous system. Physiol Meas 1998; 19:93–102

32. Khanokh B, Slovik Y, Landau D, Nitzan M: Sympathetically induced spontaneous fluctuations of the photoplethysmographic signal. Med Biol Eng Comput 2004; 42:80–5

33. Babchenko A, Davidson E, Ginosar Y, Kurz V, Faib I, Adler D, Nitzan M: Photoplethysmographic measurement of changes in total and pulsatile tissue blood volume, following sympathetic blockade. Physiol Meas 2001; 22:389–96

34. Nitzan M, Babchenko A, Khanokh B: Very low frequency variability in arterial blood pressure and blood volume pulse. Med Biol Eng Comput 1999; 37:54–8

35. Nitzan M, Faib I, Friedman H: Respiration-induced changes in tissue blood volume distal to occluded artery, measured by photoplethysmography. J Biomed Opt 2006; 11:040506

36. Allen J, Murray A: Effects of filtering on multi-site photoplethysmography pulse waveform characteristics. Comput Cardiol 2004; 31:485–8

37. Kuroda M, Kawamoto M, Yuge O: Undisrupted pulse wave on pulse oximeter display monitor at cardiac arrest in a surgical patient. J Anesth 2005; 19:164–6

38. Nichols WW, O'Rourke MF: The nature of flow in a liquid, McDonald's Blood Flow in Arteries, 4th edition. New York, Oxford University Press, 1998, pp 11–53

39. Langewouters GJ, Wesseling KH, Goedhard WJ: The static elastic properties of 45 human thoracic and 20 abdominal aortas in vitro and the parameters of a new model. J Biomech 1984; 17:425–35

40. Langewouters GJ, Zwart A, Busse R, Wesseling KH: Pressure-diameter relationships of segments of human finger arteries. Clin Phys Physiol Meas 1986; 7:43–56

41. Ando J, Kawarada A, Shibata M, Yamakoshi K, Kamiya A: Pressure-volume relationships of finger arteries in healthy subjects and patients with coronary atherosclerosis measured non-invasively by photoelectric plethysmography. Jpn Circ J 1991; 55:567–75

42. Shaltis P, Reisner A, Asada H: Consistency of calibrated peripheral PPG signals: Capabilities and limitations for continuous blood pressure monitoring, Proceedings of the 27th Annual EMBS Conference. Shanghai, China, IEEE Engineering in Medicine and Biology Society and Biomedical Engineering Society, 2005

43. Teng XF, Zhang YT: The effect of contacting force on photoplethysmographic signals. Physiol Meas 2004; 25:1323–35

44. Avolio A: The finger volume pulse and assessment of arterial properties. J Hypertens 2002; 20:2341–3

45. Guyton AC, Hall JE: Vascular distensibility, and functions of the arterial and venous systems, Textbook of Medical Physiology, 10th edition. Philadelphia, WB Saunders, 2000, pp 152–61

46. Millasseau SC, Guigui FG, Kelly RP, Prasad K, Cockcroft JR, Ritter JM, Chowienczyk PJ: Noninvasive assessment of the digital volume pulse: Comparison with the peripheral pressure pulse. Hypertension 2000; 36:952–6

47. Allen J, Murray A: Modelling the relationship between peripheral blood pressure and blood volume pulses using linear and neural network system identification techniques. Physiol Meas 1999; 20:287–301

48. Yamakoshi K, Rolfe P, Murphy C: Current developments in non-invasive measurement of arterial blood pressure. J Biomed Eng 1988; 10:130–7

49. Buclin T, Buchwalder-Csajka C, Brunner HR, Biollaz J: Evaluation of noninvasive blood pressure recording by photoplethysmography in clinical studies using angiotensin challenges. Br J Clin Pharmacol 1999; 48:586–93

50. Tardy Y, Meister JJ, Perret F, Brunner HR, Arditi M: Non-invasive estimate of the mechanical properties of peripheral arteries from ultrasonic and photoplethysmographic measurements. Clin Phys Physiol Meas 1991; 12:39–54

51. Zion AS, Bartels MN, Wecht JM, Sloan RP, Downey JA, De Meersman RE: Evaluation of blood pressure and baroreflex sensitivity by radial artery tonometry versus finger arteriolar photoplethysmography. Am J Hypertens 2003; 16:371–4

52. Staessen JA, Fagard R, Thijs L, Amery A: A consensus view on the technique of ambulatory blood pressure monitoring: The Fourth International Consensus Conference on 24-Hour Ambulatory Blood Pressure Monitoring. Hypertension 1995; 26:912–8

53. O'Rourke M: Arterial haemodynamics and ventricular-vascular interaction in hypertension. Blood Press 1994; 3:33–7

54. Guelen I, Westerhof BE, Van Der Sar GL, Van Montfrans GA, Kiemeneij F, Wesseling KH, Bos WJ: Finometer, finger pressure measurements with the possibility to reconstruct brachial pressure. Blood Press Monit 2003; 8:27–30

55. Elvan-Taspinar A, Uiterkamp LA, Sikkema JM, Bots ML, Koomans HA, Bruinse HW, Franx A: Validation and use of the Finometer for blood pressure measurement in normal, hypertensive and pre-eclamptic pregnancy. J Hypertens 2003; 21:2053–60

56. Maestri R, Pinna GD, Robbi E, Capomolla S, La Rovere MT: Noninvasive measurement of blood pressure variability: Accuracy of the Finometer monitor and comparison with the Finapres device. Physiol Meas 2005; 26:1125–36

57. Stok WJ, Westerhof BE, Karemaker JM: Changes in finger-aorta pressure transfer function during and after exercise. J Appl Physiol 2006; 101:1207–14

58. Klodell CT, Lobato EB, Willert JL, Gravenstein N: Oximetry-derived perfusion index for intraoperative identification of successful thoracic sympathectomy. Ann Thorac Surg 2005; 80:467–70

59. Moxey P, Sieunarine K, Cox J, Lawson AD, Ungar L, Smith JR: Pulse oximetry and perfusion index measurement to assess uterine perfusion and viability. Int Surg 2006; 91:223–7

60. Granelli AD, Ostman-Smith I: Noninvasive peripheral perfusion index as a possible tool for screening for critical left heart obstruction. Acta Paediatr 2007; 96:1455–9

61. Golparvar M, Naddafnia H, Saghaei M: Evaluating the relationship between arterial blood pressure changes and indices of pulse oximetric plethysmography. Anesth Analg 2002; 95:1686–90

62. Xu H, Zhou S, Ma W, Yu B: Prediction of pulmonary arterial wedge pressure from arterial pressure or pulse oximetry plethysmographic waveform. Chin Med J (Engl) 2002; 115:1372–5

63. Shamir M, Eidelman LA, Floman Y, Kaplan L, Pizov R: Pulse oximetry plethysmographic waveform during changes in blood volume. Br J Anaesth 1999; 82:178–81

64. Awad AA, Ghobashy MA, Stout RG, Silverman DG, Shelley KH: How does the plethysmogram derived from the pulse oximeter relate to arterial blood pressure in coronary artery bypass graft patients? Anesth Analg 2001; 93:1466–71

65. Haffty BG, O'Hare NE, Singh JB, Spodick DH: Noninvasive tracking of peripheral resistance by ear densitography. Chest 1983; 83:771–5

66. Hashimoto J, Chonan K, Aoki Y, Nishimura T, Ohkubo T, Hozawa A, Suzuki M, Matsubara M, Michimata M, Araki T, Imai Y: Pulse wave velocity and the second derivative of the finger photoplethysmogram in treated hypertensive patients: Their relationship and associating factors. J Hypertens 2002; 20:2415–22

67. Miyai N, Miyashita K, Arita M, Morioka I, Kamiya K, Takeda S: Noninvasive assessment of arterial distensibility in adolescents using the second derivative of photoplethysmogram waveform. Eur J Appl Physiol 2001; 86:119–24

68. Millasseau SC, Kelly RP, Ritter JM, Chowienczyk PJ: The vascular impact of aging and vasoactive drugs: Comparison of two digital volume pulse measurements. Am J Hypertens 2003; 16:467–72

69. Ezri T, Steinmetz A, Geva D, Szmuk P: Skin vasomotor reflex as a measure of depth of anesthesia. Anesthesiology 1998; 89:1281–2

70. Spittal MJ: Evaluation of pulse oximetry during cardiopulmonary resuscitation. Anaesthesia 1993; 48:701–3

71. Griffin M, Cooney C: Pulse oximetry during cardiopulmonary resuscitation. Anaesthesia 1995; 50:1008

72. Eldrup-Jorgensen SV, Schwartz SI, Wallace JD: A method for clinical evaluation of peripheral circulation: Photoelectric hemodensitometry. Surgery 1966; 59:505–13

73. Galla TJ, Hellekes D, Feller AM: Differentiation between arterial and venous vessel occlusion by simultaneous measurement with laser Doppler flowmetry and photoplethysmography. J Reconstr Microsurg 1999; 15:67–72

74. Talke PO: Measurement of systolic blood pressure using pulse oximetry during helicopter flight. Crit Care Med 1991; 19:934–7

75. Talke P, Nichols RJ Jr, Traber DL: Does measurement of systolic blood pressure with a pulse oximeter correlate with conventional methods? J Clin Monit 1990; 6:5–9

76. McCluskey B, Addis M, Tortella BJ, Lavery RF: Out-of-hospital use of a pulse oximeter to determine systolic blood pressures. Prehospital Disaster Med 1996; 11:105–7

77. Movius AJ, Bratton SL, Sorensen GK: Use of pulse oximetry for blood pressure measurement after cardiac surgery. Arch Dis Child 1998; 78:457–60

78. Severinghaus JW, Spellman MJ Jr: Pulse oximeter failure thresholds in hypotension and vasoconstriction. Anesthesiology 1990; 73:532–7

79. Kober A, Scheck T, Lieba F, Barker R, Vlach W, Schramm W, Hoerauf K: The influence of active warming on signal quality of pulse oximetry in prehospital trauma care. Anesth Analg 2002; 95:961–6

80. Lu W, Li H, Tao S, Zhang D, Jiang Z, Cui L, Tu J, Gou D: Research on the main elements influencing blood pressure measurement by pulse wave velocity. Front Med Biol Eng 1992; 4:189–99

81. Payne RA, Symeonides CN, Webb DJ, Maxwell SR: Pulse transit time measured from the ECG: An unreliable marker of beat-to-beat blood pressure. J Appl Physiol 2006; 100:136–41

82. Davies JI, Struthers AD: Pulse wave analysis and pulse wave velocity: A critical review of their strengths and weaknesses. J Hypertens 2003; 21:463–72

83. Van Bortel LM, Duprez D, Starmans-Kool MJ, Safar ME, Giannattasio C, Cockcroft J, Kaiser DR, Thuillez C: Clinical applications of arterial stiffness, Task Force III: Recommendations for user procedures. Am J Hypertens 2002; 15:445–52

84. Yu C, Liu Z, McKenna T, Reisner A, Reifman J: A method for automatic identification of reliable heart rates calculated from ECG and PPG waveforms. JAMA 2006; 13:309–20

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