Decremental Changes Research Articles

The Effects of Milk Yield and Stage of Lactation on the Partitioning of Nutrients in Lactating Dairy Cows

The objective of the experiment was to examine, using indirect calorimetry, the effects of milk yield and stage of lactation on the response in milk and body tissue energy, and heat production, to a reduction (decrement) in nutrient intake (assessed as metabolizable energy intake). Eight lactating dairy cows, four representing each of two stages of lactation [either mean initial days in milk (DIM) 158 (SD 6.1) or 414 (SD 51.1)] were used. Each cow underwent four 17-d periods incorporating two physiological states [number of mammary glands milked: either four (periods 1 and 2), or two (periods 3 and 4)], and two levels of metabolizable energy intake within each physiological state [either sufficient to meet requirements for zero tissue balance plus 10 MJ/d (periods 1 and 3)] or these allowances reduced by 20 MJ/d in the subsequent period (periods 2 and 4, respectively). Partitioning was calculated from the changes in metabolizable energy intake, milk energy, tissue energy, and heat production between DIM groups and between four and two gland milking (milk yield) components of the study. Partitioning of the changes in metabolizable energy intake was not influenced by DIM, but milk yield response was greater in the early lactation cows compared with the late group. Cows milked in four glands (higher milk yield) partitioned a significantly greater proportion of decremental changes in metabolizable energy intake to milk energy and less to tissue energy, than when milked in only two glands (lower milk yield).

Correlation of electric field and critical design parameters for ferroelectric tunable microwave filters

The correlation of electric field and critical design parameters such as the insertion loss, frequency tunability, return loss, and bandwidth of conductor/ferroelectric/dielectric microstrip tunable K-band microwave filters is discussed in this work. This work is based primarily on barium strontium titanate (BSTO) ferroelectric thin film based tunable microstrip filters for room temperature applications. Two new parameters which we believe will simplify the evaluation of ferroelectric thin films for tunable microwave filters, are defined. The first of these, called the sensitivity parameter, is defined as the incremental change in center frequency with incremental change in maximum applied electric field (EPEAK) in the filter. The other, the loss parameter, is defined as the incremental or decremental change in insertion loss of the filter with incremental change in maximum applied electric field. At room temperature, the Au/BSTO/LAO microstrip filters exhibited a sensitivity parameter value between 15 and 5 MHz/cm/kV. The loss parameter varied for different bias configurations used for electrically tuning the filter. The loss parameter varied from 0.05 to 0.01 dB/cm/kV at room temperature.

Paget’s disease of bone: benefits of neridronate as a first treatment and in cases of relapse after clodronate

This study assessed the efficacy of 200 mg of aminohexane bisphosphonate (neridronate) administered by intravenous infusion in a single dose or in two separate doses on consecutive days in 32 patients (16 males and 16 females, average age 66 years) affected by active Paget’s disease of bone. Fifteen patients had never been treated with any antiresorptive agent and 17 had had unsatisfactory results from a prior clodronate treatment. All of the latter patients had failed to enter a remission stage (i.e., normalization of bone turnover was not reported at any time during treatment) and had had a full relapse within 6 months after clodronate infusion. In the present study bone-specific alkaline phosphatase (bAp), deoxypyridinoline (dPyr), and N- and C-terminal polypeptide of collagen type 1 (Ntx, Ctx) were determined before neridronate administration and at 1, 3, 6, and 12 months thereafter. Basal values of bAp were 51.7 ± 2.3 μg/L, range 31.7–92.5 (normal range 6.2–23.6). No statistical differences in markers of bone turnover were evident in the basal state between new pagetic patients (bAp = 55.1 ± 4.1) and those suffering a relapse after clodronate (bAp = 48.8 ± 2.6). Neridronate induced an average percent change from baseline in excess bAp of 68.0 ± 4.3 and in excess dPyr, Ntx, and Ctx of 68.1 ± 11, 60.6 ± 8.5, and 86.7 ± 7.8, respectively. Markers of bone resorption declined more slowly in patients treated previously with clodronate, although the average change in percent decrement from baseline in excess bAp as well as in excess of bone resorption markers was not different from that registered in untreated pagetic patients. Response to treatment, defined as a percent decrement from baseline in excess bAp of 50% or more at any time during the 12-month follow-up, was observed in 27 patients (84.4%). Remission (a drop in bAp to within normal range) was achieved in 21 patients (65.6%) and was maintained in 12 at 12-month follow-up, with no significant differences between either 1- or 2-day infusions, or between new pagetic patients and those relapsing after clodronate. In 15 of 21 patients requiring analgesics to alleviate bone pain, pain was reduced or completely alleviated in 8. A slight, short-lived acute phase reaction (fever and/or arthromyalgia) occurred in 6 patients. To summarize, 200 mg of intravenous neridronate, in one or two doses, significantly reduced the biochemical indices of disease activity in the majority of patients, showing a normalization of bAp in more than 60%. We conclude that neridronate can be used safely in the treatment of patients with Paget’s disease of bone either as a first bisphosphonate treatment or as retreatment for patients relapsing after clodronate.

Shared attention to simultaneous stimulation

Shared attention is studied using a dual task, where observers respond independently to two simultaneously presented signals. Cost is defined by a loss in performance relative to one signal tested alone. Standard stimuli are followed by signals that can be either incremental or decremental changes in level, frequency, or spatial location, relative to the standard. In a ‘‘detection’’ paradigm, the subject says ‘‘change’’ for signals of either polarity, but in an ‘‘identification’’ paradigm where all trials present signals, the subject responds with the polarities. Comparing results with fixed standards to those with a standard that roves from trial to trial shows that a major determinant of the cost of shared attention is the type of memory used in the task. Fixed standards, which show reliance on absolute memory, yield relatively high performance, but there is a cost of shared attention. Conversely, with roved standards, where absolute memory cannot be used, performance is relatively low and there is no cost. Thus a dissociation is found in which the additional process used in the context-coding mode is costly for attention but not performance. [Research supported by the Natl. Inst. of Health (NIDCD 07787), USA, Univ. of California, USA, and CNRS, France.]

Change in internal friction in coated specimens during wear

The present paper is devoted to the laws of change in the vibration decrement in the process of wear of high-strength coatings and the effect of its restoration in heating of coated specimens damaged to various degrees under friction.

A Light Microscopic Radioautographic Study on Protein Synthesis in Pulmonary Cells of Aging Mice.

In the present study we first investigated the changes in protein synthesis of respective cell types of mouse pulmonary alveoli from 16 days of fetal life to senility (postnatal 22 months) by using 3H-leucine light microscopic radioautography. The results revealed that the protein syntheses in type I epithelial cells, type II epithelial cells, interstitial cells and endothelial cells in the mouse lung changed due to aging. The protein synthesis of type I epithelial cells was the highest on postnatal day 1, increased again at 1 week after birth, and then decreased gradually to 22 months after birth with aging. The protein syntheses of type II epithelial cells, interstitial cells and endothelial cells reached the highest level on fetal day 16, declined progressively with age, and increased again at postnatal 1 week, and then decreased gradually from 2 weeks to senility. Our results suggest that the decreases in protein synthesis are correlated with the decremental changes in DNA and RNA synthesis in the lung with aging.

Systematic evaluation of the damage to a material during plastic deformation

Aluminum alloy D16 is used as an example to systematically evaluate the damage to metal on the basis of characteristics of its damping capacity (logarithmic vibration decrement), acoustic emission, and weight as determined by a new method developed by the authors. It is shown that the damage sustained by metallic materials during static loading can be estimated from the change in the vibration decrement and certain acoustic-emission parameters. These conclusions are substantiated by similar relations expressing the dependence of these parameters on the dilatation of the material in an evaluation of its volume change.

Relationship Between Volume Fraction of Strain-Induced Martensite Under Tension and Electrical Resistivity in a Ti-Ni SMA Wire

Relationships among plastic strain, volume fraction of SIM, stress-strain curve, electrical resistivity of a Ti.50.5 at.% Ni wire are investigated under tension at temperature from 30 °C to -20 °C and also under repeated tensile cycles up to N=200 at 20°C. The relative electrical resistivity Δρ/ρ 0 decreases as the volume fraction of SIM increases to nearly 90%, resulting in the more decrement in Δρ/ρ 0 the lower the temperature and after that Δρ/ρ 0 increases with a steep gradient. The decrement stage is supposedly due to the formation and deformation of SIM by twinning and the succeeding increment stage is due to the deformation by dislocation. The decremental change is nicely fitted by an equation of a logarithmic mixture-rule (LMR) for electrical resistivity [1]. The relation between Δρ/ρ 0 and plastic strain at various temperatures also shows the decremental curve within the thermo-elastic strain range, after that it increases as the plastic strain increases. Effects of repeated cycles to those relations give the similar experimental results as the above where the major test variable is repeated cycles instead of test temperature in this case.

Distribution of Discretionary Time by Retired People

This study is a survey of the activities of retirees of a Fortune 500 manufacturing company. The objective was to provide a baseline description of activities as people adjust to changes associated with retirement and decremental changes of aging. A sample of 40 retirees was interviewed to obtain information on 1) demographics, living conditions, and health; 2) distribution of time over activities of work, recreation, family, and volunteering; 3) changes associated with aging and socio-economic factors. It is intended to provide an activity picture that will be a context for identifying behavioral problems and devices, organizations, and supporting aids to enhance quality of life. Respondents represent the gamut of occupations and skill levels, socio-economic conditions, and ethnic diversity characteristics of a large, midwestern manufacturing corporation. The distribution of ages in the retiree population and sample were equivalent The activities surveyed include reading, watching television, household chores and maintenance, skill or craft hobbies, intentional exercise, care-giving, volunteer work, and work for pay. Analyses include differences and changes in activities as a function of gender, age, length of retirement, health, and living situation. Volunteer work is analyzed in detail concerning type, location of the work, and time spent on it.

Social support. Among elderly in two community programs.

Elderly individuals lacking adequate social support have shown greater deficits and difficulties in illness recovery, length of hospitalization, and development of cognitive and emotional changes than those who do receive adequate social support. This study evidenced a very meaningful finding for nurses--older adults who are often dependent upon others for support in some or most facets of daily living specified love and respect as the type of support most needed, rather than tangible aid. In most communities, a wide array of educational and support group programs are offered to older adults. Social networking and the enhancement of social support among participants should be primary goals of such programs.

Adult life span changes in immediate visual memory and verbal intelligence.

A sample of 558 women and 1,163 men 17 to 102 years old, screened for neurodegenerative and neuropsychiatric disease, was administered tests of immediate visual memory (Benton Visual Retention Test) and crystallized intelligence (Wechsler Adult Intelligence Scale Vocabulary subtest) from 1 to 5 times over 27.7 years. Cross-sectional and longitudinal evidence led to the conclusion that the 65-74-year decade was a watershed for decremental changes in immediate visual memory and verbal intelligence. Age accounted for considerably less variance in vocabulary than in immediate memory. The proportion of individuals whose longitudinal trajectories were contrary to group trends decreased substantially with increased age; observed age changes remained when analyses were restricted to individuals who had perfect or near-perfect mental status scores. Selected neuronal loss and slower reproduction times were considered as possible causes.

Adult life span changes in immediate visual memory and verbal intelligence.

A sample of 558 women and 1,163 men 17 to 102 years old, screened for neurodegenerative and neuropsychiatric disease, was administered tests of immediate visual memory (Benton Visual Retention Test) and crystallized intelligence (Wechsler Adult Intelligence Scale Vocabulary subtest) from 1 to 5 times over 27.7 years. Cross-sectional and longitudinal evidence led to the conclusion that the 65-74-year decade was a watershed for decremental changes in immediate visual memory and verbal intelligence. Age accounted for considerably less variance in vocabulary than in immediate memory. The proportion of individuals whose longitudinal trajectories were contrary to group trends decreased substantially with increased age; observed age changes remained when analyses were restricted to individuals who had perfect or near-perfect mental status scores. Selected neuronal loss and slower reproduction times were considered as possible causes.

Optimizing the visibility of displays for older observers.

Aging is associated with a variety of decremental visual changes, including reductions in retinal illuminance, color discrimination, static and dynamic acuity, near focus, contrast sensitivity, smooth and saccadic eye movements, visual field, visual search, and the ability to see in and recover from glare. Laboratory research, field studies, and self-report data all indicate that many older persons experience significant difficulty in carrying out tasks that depend on these visual functions. It is also increasingly clear that older observer's performance in finding, extracting, and using visual information can be enhanced significantly by designing task environments to minimize the effects of visual deficits. Recent research indicates that optical simulation of visual loss and contrast sensitivity testing, used in conjunction with image processing, may be very powerful tools for designing displays for the elderly and others with diminished spatial vision. These developments are reviewed, and general guidelines for creating ergonomically correct visual task environments for older observers are offered.

Endogenous adenosine, A1 adenosine receptor, and pertussis toxin sensitive guanine nucleotide binding protein mediate hypoxia induced AV nodal conduction block in guinea pig heart in vivo

The aim was to study the mechanism of global hypoxia induced atrioventricular (AV) nodal conduction block in vivo using a guinea pig model. Animals subjected to 10 min periods of global hypoxia, induced by decremental changes in O2 content in the inhaled gas mixture, were randomly divided into three groups: group I = control; group II = animals treated with a new selective A1 adenosine receptor antagonist, N0861 (N6-endo-norbornan-2-yl-9-methyladenine); and group III-animals treated with pertussis toxin, an irreversible inhibitor of specific guanine nucleotide binding proteins (G protein). Progressive incremental hypoxia was associated with progressive AV nodal conduction delay culminating in a complete block. In addition, there was an inverse relationship between the severity of hypoxia and time to AV nodal block. Both N0861 and pertussis toxin treatment significantly reduced the degree of hypoxia induced AV nodal conduction block and delayed its appearance. (1) Endogenous adenosine released during acute global hypoxia causes AV nodal conduction block observed under these conditions in the guinea pig heart in vivo; and (2) this action of adenosine in the AV node is mediated by an A1 adenosine receptor and a pertussis toxin sensitive G protein.

Glyburide and tolbutamide induce desensitization of insulin release in rat pancreatic islets by different mechanisms

Insulin secretion was studied in rat pancreatic islets after 24-h exposure to various glyburide or tolbutamide concentrations. Glucose-induced insulin release was significantly (P < 0.05) reduced in islets cultured with 0.1 microM glyburide or 100 microM tolbutamide (2098 +/- 187, 832 +/- 93, and 989 +/- 88 pg/islet.h in control, glyburide-exposed, and tolbutamide-exposed islets, respectively). When glyburide-treated islets were stimulated with glyburide or tolbutamide, insulin release was also impaired compared to that in control islets (P < 0.05). In contrast, tolbutamide-exposed islets showed an impaired response to tolbutamide, but a normal response to glyburide. To investigate the mechanism of the sulfonylurea-induced impairment of insulin secretion, we measured insulin release and Rb+ efflux (a marker of the K+ channel activity) in a perifusion system and islet Ca2+ uptake under static conditions. Insulin release in response to 16.7 mM glucose increased in control islets from 9.4 +/- 1.1 to 131 +/- 19 pg/islet.min (first phase secretion peak). Simultaneously, the fractional 86Rb+ efflux declined from 0.015 +/- 0.002% to 0.006 +/- 0.001% (change in decrement, -63.5%). Glucose-induced insulin release in glyburide- and tolbutamide-treated islets was significantly reduced (first phase peak, 22.1 +/- 5 and 39.7 +/- 8 pg/islet.min, respectively; P < 0.05), and the fractional 86Rb+ efflux decrement was -21 +/- 6% for glyburide (P < 0.005 vs. control islets) and -65 +/- 4% (not different from control) for tolbutamide. When glyburide- or tolbutamide-exposed islets were stimulated with the corresponding sulfonylurea, insulin release was impaired compared to that in control islets (P < 0.05), but, again, 86Rb+ efflux was impaired (P < 0.05) only in glyburide-exposed islets. When 45Ca2+ uptake was studied, the increase in glucose concentration from 2.8 to 16.7 mM increased calcium uptake in control islets from 1.76 +/- 0.58 to 7.27 +/- 1.36 pmol/islet.2 min (n = 4). Preexposure to 0.1 microM glyburide did not change calcium uptake at a glucose concentration of 2.8 mM (1.44 +/- 0.45 pmol/islet.2 min) but significantly reduced calcium uptake stimulated by 16.7 mM glucose (3.21 +/- 0.35 pmol/islet.2 min; n = 4; P < 0.005 compared to control islets). In contrast, preexposure to 100 microM tolbutamide did not change either basal or glucose-stimulated calcium uptake (1.44 +/- 0.45 and 6.90 +/- 0.81 pmol/islet.2 min, respectively; n = 4). These data show that in vitro chronic exposure of pancreatic islets to the sulfonylureas glyburide and tolbutamide impairs their ability to respond to a subsequent glucose or sulfonylurea stimulation.

Glyburide and tolbutamide induce desensitization of insulin release in rat pancreatic islets by different mechanisms.

Insulin secretion was studied in rat pancreatic islets after 24-h exposure to various glyburide or tolbutamide concentrations. Glucose-induced insulin release was significantly (P < 0.05) reduced in islets cultured with 0.1 microM glyburide or 100 microM tolbutamide (2098 +/- 187, 832 +/- 93, and 989 +/- 88 pg/islet.h in control, glyburide-exposed, and tolbutamide-exposed islets, respectively). When glyburide-treated islets were stimulated with glyburide or tolbutamide, insulin release was also impaired compared to that in control islets (P < 0.05). In contrast, tolbutamide-exposed islets showed an impaired response to tolbutamide, but a normal response to glyburide. To investigate the mechanism of the sulfonylurea-induced impairment of insulin secretion, we measured insulin release and Rb+ efflux (a marker of the K+ channel activity) in a perifusion system and islet Ca2+ uptake under static conditions. Insulin release in response to 16.7 mM glucose increased in control islets from 9.4 +/- 1.1 to 131 +/- 19 pg/islet.min (first phase secretion peak). Simultaneously, the fractional 86Rb+ efflux declined from 0.015 +/- 0.002% to 0.006 +/- 0.001% (change in decrement, -63.5%). Glucose-induced insulin release in glyburide- and tolbutamide-treated islets was significantly reduced (first phase peak, 22.1 +/- 5 and 39.7 +/- 8 pg/islet.min, respectively; P < 0.05), and the fractional 86Rb+ efflux decrement was -21 +/- 6% for glyburide (P < 0.005 vs. control islets) and -65 +/- 4% (not different from control) for tolbutamide. When glyburide- or tolbutamide-exposed islets were stimulated with the corresponding sulfonylurea, insulin release was impaired compared to that in control islets (P < 0.05), but, again, 86Rb+ efflux was impaired (P < 0.05) only in glyburide-exposed islets. When 45Ca2+ uptake was studied, the increase in glucose concentration from 2.8 to 16.7 mM increased calcium uptake in control islets from 1.76 +/- 0.58 to 7.27 +/- 1.36 pmol/islet.2 min (n = 4). Preexposure to 0.1 microM glyburide did not change calcium uptake at a glucose concentration of 2.8 mM (1.44 +/- 0.45 pmol/islet.2 min) but significantly reduced calcium uptake stimulated by 16.7 mM glucose (3.21 +/- 0.35 pmol/islet.2 min; n = 4; P < 0.005 compared to control islets). In contrast, preexposure to 100 microM tolbutamide did not change either basal or glucose-stimulated calcium uptake (1.44 +/- 0.45 and 6.90 +/- 0.81 pmol/islet.2 min, respectively; n = 4). These data show that in vitro chronic exposure of pancreatic islets to the sulfonylureas glyburide and tolbutamide impairs their ability to respond to a subsequent glucose or sulfonylurea stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Age-correlated changes and juvenile hormone III regulation of the syllable period specific responses of the L3 auditory interneurons in the cricket, Acheta domesticus

1. L3 is an auditory interneuron in the prothoracic ganglion of the cricket, Acheta domesticus. The degree of syllable period (SP) specific decrement to model calling songs is age-specific in L3. In response to calling songs having 50 ms SPs, L3s in old females (23–28 days) exhibit less response decrement than those in young (4 days) females (Figs. 1, 2). 2. Two to 4 days after juvenile hormone III (JHIII) application to old females, L3s respond in a decrementing manner similar to those of young females. The changes in the SP selectivity of L3 by age and JHIII application, correlate well with changes that have been demonstrated to occur in the selectivity of phonotaxis under similar conditions (Fig. 3). 3. The threshold of L3 does not change with age, while changes in L3's decrement result from decreased excitation in old females in response to the first syllable of a chirp (Figs. 4, 5). 4. Injection of patterned current pulses (which reproduce the temporal pattern of the calling song) do not elicit decrement (Fig. 6). 5. Age-related changes in selectivity to SP of the calling song occurs above and below L3s threshold (Fig. 7).

Parathyroid Hormone-(1-34) [PTH-(l-34)]: Demonstration of Suppression of Endogenous Secretion Using Immunoradiometric Intact PTH-(l-84) Assay*

Alterations in the sensitivity of the parathyroid gland to both stimulative and suppressive stimuli may be partially responsible for skeletal changes that occur with age, estrogen deficiency, osteoporosis, and estrogen treatment of osteoporosis. We sought to define the changes in intact PTH-(1-84) secretion in normal premenopausal and postmenopausal, osteoporotic and estrogen-treated osteoporotic women during the infusion of human (h) PTH-(1-34). hPTH-(1-34) was infused at 0.55 U/kg.h for 24 h, with serum sampling every 4 h. Serum was analyzed for calcium (ionized and total), hPTH-(1-34), and PTH-(1-84). Basal chemistries were no different among groups, except for serum phosphorus, which was highest in osteoporotic women (1.31 vs. 1.07 mmol/L in premenopausal; P less than 0.02), and hPTH-(1-34), which was slightly higher in normal postmenopausal women (19.31 vs. 13.24 ng/L in estrogen treated; P less than 0.02). No differences in PTH-(1-84) were found among groups. hPTH-(1-34) rose similarly in all patient groups, while the calcemic response was somewhat more sluggish in estrogen-treated women, although statistically significant differences were not found. PTH-(1-84) declined rapidly in all patient groups, although estrogen-treated women had a smaller maximal decrease in PTH-(1-84), and the slope of the decremental change in PTH-(1-84) was lower in estrogen-treated women than in osteoporotic or normal postmenopausal women. Untreated osteoporotic women had less suppression of PTH-(1-84) than normal postmenopausal women at every calcium level. Estrogen treatment decreases the calcemic effects of infused hPTH-(1-34) and at the same time reduces calcium-induced suppression of parathyroid secretion. It is possible that such changes in the set-point of the gland contribute to the alterations in bone turnover that result in osteoporosis and the mechanisms by which estrogen prevents bone loss.

Effects of age on diabetes- and insulin-induced changes in pancreatic levels of α-amylase and its mRNA

During aging, protein synthesis undergoes decremental changes in many organs and tissues. In the pancreas, as well as in other exocrine glands, the rate of protein synthesis declines with age. However, it is unknown whether this decline is related to intrinsic aging changes which affect the secretory cell function. In this study, we compared the ability of pancreatic acinar cells to synthesize amylase and its messenger RNA (mRNA) in response to insulin treatment of young and old rats rendered diabetic with streptozotocin (STZ). In STZ-induced diabetic rats, amylase protein and its mRNA levels were reduced drastically in the pancreas of young and old groups. Injections of these diabetic rats with insulin increased pancreatic amylase mRNA contents significantly in both young and old rats. Insulin also increased proportions of amylase protein synthesis in the pancreas of both age groups. These results indicate that the pancreatic cells remain effective during aging in their transcriptional activity for functional amylase mRNA in response to an exogenous stimulus of insulin.

Non-invasive monitoring of brain oxygen metabolism during cardiopulmonary bypass by near-infrared spectrophotometry.

A new portable high performance apparatus for near-infrared (NIR) laser spectrophotometry was developed to monitor the oxygenation state of the human brain. Three different wavelengths of the NIR laser beam were used, 780, 805 and 830 nm, to illuminate the head through a fiber optic bundle. The amount of light reflected by or transmitted from the tissue was detected by a photomultiplier or photodiode. Equations as explained here, were used to calculate the oxy and deoxy Hb content and blood volume changes non-invasively. The equations were verified in vivo with the rat head in order to confirm the reliability and acceptability of our methodology. NIR monitoring was applied to 15 cases of cardiopulmonary bypass (CPB) in reflectance mode. The results demonstrated that using current CPB technique, cerebral oxygenation levels during bypass were maintained within the physiological range and changes in brain blood volume corresponded well to the pump flow balance. That is, the brain oxygenation level was maintained roughly constant at a mean perfusion pressure of over 60 mmHg during CPB, whereas below 50 mmHg, apparent decremental changes in oxy Hb content were observed. These findings led us to conclude that non-invasive monitoring of cerebral oxygenation using NIR light can provide valuable bedside data about tissue metabolism and allow for the proper management of critical patients.