Light-absorption Variation Research Articles

Pulse Oximetry in Pediatric Practice

The introduction of pulse oximetry in clinical practice has allowed for simple, noninvasive, and reasonably accurate estimation of arterial oxygen saturation. Pulse oximetry is routinely used in the emergency department, the pediatric ward, and in pediatric intensive and perioperative care. However, clinically relevant principles and inherent limitations of the method are not always well understood by health care professionals caring for children. The calculation of the percentage of arterial oxyhemoglobin is based on the distinct characteristics of light absorption in the red and infrared spectra by oxygenated versus deoxygenated hemoglobin and takes advantage of the variation in light absorption caused by the pulsatility of arterial blood. Computation of oxygen saturation is achieved with the use of calibration algorithms. Safe use of pulse oximetry requires knowledge of its limitations, which include motion artifacts, poor perfusion at the site of measurement, irregular rhythms, ambient light or electromagnetic interference, skin pigmentation, nail polish, calibration assumptions, probe positioning, time lag in detecting hypoxic events, venous pulsation, intravenous dyes, and presence of abnormal hemoglobin molecules. In this review we describe the physiologic principles and limitations of pulse oximetry, discuss normal values, and highlight its importance in common pediatric diseases, in which the principle mechanism of hypoxemia is ventilation/perfusion mismatch (eg, asthma exacerbation, acute bronchiolitis, pneumonia) versus hypoventilation (eg, laryngotracheitis, vocal cord dysfunction, foreign-body aspiration in the larynx or trachea). Additional technologic advancements in pulse oximetry and its incorporation into evidence-based clinical algorithms will improve the efficiency of the method in daily pediatric practice.

Modeling ocean primary production: Sensitivity to spectral resolution of attenuation and absorption of light

Modeling the vertical penetration of photosynthetically active radiation (PAR) through the ocean, and its utilization by phytoplankton, is fundamental to simulating marine primary production. The variation of attenuation and absorption of light with wavelength suggests that photosynthesis should be modeled at high spectral resolution, but this is computationally expensive. To model primary production in global 3d models, a balance between computer time and accuracy is necessary. We investigate the effects of varying the spectral resolution of the underwater light field and the photosynthetic efficiency of phytoplankton ( α ∗), on primary production using a 1d coupled ecosystem ocean turbulence model. The model is applied at three sites in the Atlantic Ocean (CIS (∼60°N), PAP (∼50°N) and ESTOC (∼30°N)) to include the effect of different meteorological forcing and parameter sets. We also investigate three different methods for modeling α ∗ – as a fixed constant, varying with both wavelength and chlorophyll concentration [Bricaud, A., Morel, A., Babin, M., Allali, K., Claustre, H., 1998. Variations of light absorption by suspended particles with chlorophyll a concentration in oceanic (case 1) waters. Analysis and implications for bio-optical models. J. Geophys. Res. 103, 31033–31044], and using a non-spectral parameterization [Anderson, T.R., 1993. A spectrally averaged model of light penetration and photosynthesis. Limnol. Oceanogr. 38, 1403–1419]. After selecting the appropriate ecosystem parameters for each of the three sites we vary the spectral resolution of light and α ∗ from 1 to 61 wavebands and study the results in conjunction with the three different α ∗ estimation methods. The results show modeled estimates of ocean primary productivity are highly sensitive to the degree of spectral resolution and α ∗. For accurate simulations of primary production and chlorophyll distribution we recommend a spectral resolution of at least six wavebands if α ∗ is a function of wavelength and chlorophyll, and three wavebands if α ∗ is a fixed value.

The role of photochemistry in Titan’s atmospheric chemistry

Experimental studies were performed to simulate the action of long wavelength solar UV light on Titans atmosphere. The experiments were carried out in a photochemical flow reactor using a mixture of gases representative of Titans atmosphere at 70� north latitude (Titans north pole) in the winter. The solid analog of Titans haze formed has optical properties comparable to that determined for Titans haze from modeling Voyager 1 data. Since the optical properties of the haze analogs formed by discharge reactions also have optical properties similar to Titans haze. It was concluded that the variation in light absorption with wavelength of the haze in the UV–vis spectral region does not vary sufficiently to discriminate between different haze analogs. The C/N ratio of the haze analog prepared by UV radiation is in the 15–20 range while that formed by the action of magnetospheric electrons is in the 2–5 range. The infrared spectrum of the haze analog has absorption bands attributed to CH3 ,C H 2 ,C @CC„N, C@C and possibly N–H groups. The UV spectrum is consistent with the presence of double bonds and conjugated double bonds. No polycyclic aromatic compounds were detected. The volatile photoproducts mainly consist of saturated, olefinic and acetylenic hydrocarbons along with much smaller amounts of benzene and substituted benzenes. Among these volatiles hydrogen cyanide is probably the most abundant nitrogen containing with much less acetonitrile, and trace amounts of acrylonitrile. Some of these volatiles will condense on haze particles at the temperatures and pressures on Titan. The comparison of the volatiles formed by UV radiations are compared with those formed by three different discharges. � 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

Correction to “Variations of light absorption by suspended particles with chlorophyll a concentration in oceanic (case 1) waters: Analysis and implications for bio‐optical models” by A. Bricaud et al.

Correction to “Variations of light absorption by suspended particles with chlorophyll <i>a</i> concentration in oceanic (case 1) waters: Analysis and implications for bio‐optical models” by A. Bricaud et al.

Divinyl chlorophyll a-specific absorption coefficients and absorption efficiency factors for Prochlorococcus marinus:kinetics of photoacclimation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 188:21-32 (1999) - doi:10.3354/meps188021 Divinyl chlorophyll a-specific absorption coefficients and absorption efficiency factors for Prochlorococcus marinus: kinetics of photoacclimation Annick Bricaud1,*, Karima Allali1, André Morel1, Dominique Marie2, Marcel J. W. Veldhuis3, Frédéric Partensky2, Daniel Vaulot2 1Laboratoire de Physique et Chimie Marines, Université Pierre et Marie Curie and CNRS, BP 8, 06238 Villefranche-sur-Mer Cedex, France 2Station Biologique, Université Pierre et Marie Curie and CNRS, BP 74, 29680 Roscoff, France 3Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands *E-mail: bricaud@obs-vlfr.fr ABSTRACT: The photosynthetic prokaryote Prochlorococcus appears to have a high capacity to modify its physiological and optical properties in response to changes in available irradiance. In order to study the time scale of variations in light absorption induced by photoacclimation, 2 strains (MED, clone CCMP 1378, and SARG, unialgal strain) were grown in batch cultures at high (56.7 µmol quanta m-2 s-1) or low (8.4 µmol quanta m-2 s-1) irradiance. Then the temporal changes over 3 to 4 d in spectral absorption coefficients, pigment composition, cell number density and size distribution were followed for cultures transferred from high to low irradiance, and vice versa. Both strains experienced significant changes in their divinyl-chlorophyll a-specific absorption coefficients (a*) in response to the transfers. For the MED strain, photoacclimation appeared to be achieved within about 40 h (covering 2 cell generations) for the low to high irradiance transfer, while 3 to 4 d (corresponding to 1 doubling of the population) were necessary for the high to low irradiance transfer. For the SARG strain transferred from high to low irradiance, in spite of a rapid change in absorption during the first 25 h (i.e. within the same cell generation), full photoacclimation was not achieved after 3 d. The efficiency factors for absorption, <\2>Qa--(λ), and the a*( λ) coefficients, were reconstructed from theory at the different photoacclimation stages from the cell characteristics, i.e. intracellular concentrations of the various pigments and cell size distribution. This permitted the determination of the parameters which are mainly responsible for the observed changes. The <\2>Qa--(λ) values (and therefore the package effect) are enhanced at low irradiance by 2 effects resulting from photoacclimation: the increase of the intracellular concentration of divinyl-chlorophyll a, and (for the SARG strain only) the increase of the intracellular concentration of chlorophyll b. In addition, the presence of zeaxanthin, in stable amounts within the cells whatever the irradiance, enhances the Qa--(λ) values for all light conditions, and thus 'moderates' its variations with irradiance. Contrary to what is commonly admitted because of its tiny size, the absorption efficiency of Prochlorococcus (per pigment unit) is not always maximal, but can be reduced by 20 to 25% at low irradiances, such as those prevailing in the lower part of the euphotic zone. This reduction directly affects the amount of absorbed energy usable for photosynthesis. KEY WORDS: Prochlorococcus · Prochlorophyta · Optical properties · Absorption · Photoacclimation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 188. Publication date: November 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Variations of light absorption by suspended particles with chlorophyll a concentration in oceanic (case 1) waters: Analysis and implications for bio‐optical models

Spectral absorption coefficients of total particulate matter ap(λ) were determined using the in vitro filter technique. The present analysis deals with a set of 1166 spectra, determined in various oceanic (case 1) waters, with field chl a concentrations (〈chl〉) spanning 3 orders of magnitude (0.02–25 mg m−3). As previously shown [Bricaud et al., 1995] for the absorption coefficients of living phytoplankton aø(λ), the ap(λ) coefficients also increase nonlinearly with 〈chl〉. The relationships (power laws) that link ap(λ) and aø(λ) to 〈chl〉 show striking similarities. Despite large fluctuations, the relative contribution of nonalgal particles to total absorption oscillates around an average value of 25–30% throughout the 〈chl〉 range. The spectral dependence of absorption by these nonalgal particles follows an exponential increase toward short wavelengths, with a weakly variable slope (0.011±0.0025 nm−1). The empirical relationships linking ap(λ) to (〈chl〉) can be used in bio‐optical models. This parameterization based on in vitro measurements leads to a good agreement with a former modeling of the diffuse attenuation coefficient based on in situ measurements. This agreement is worth noting as independent methods and data sets are compared. It is stressed that for a given (〈chl〉), the ap(λ) coefficients show large residual variability around the regression lines (for instance, by a factor of 3 at 440 nm). The consequences of such a variability, when predicting or interpreting the diffuse reflectance of the ocean, are examined, according to whether or not these variations in ap are associated with concomitant variations in particle scattering. In most situations the deviations in ap actually are not compensated by those in particle scattering, so that the amplitude of reflectance is affected by these variations.