Osmotic response during kidney perfusion with cryoprotectant in isotonic or hypotonic vehicle solution

Organ cryopreservation would revolutionize transplantation by overcoming the shelf-life limitations of conventional organ storage. To prepare an organ for cryopreservation, it is first perfused with cryoprotectants (CPAs). These chemicals can enable vitrification during cooling, preventing ice damage. However, CPAs can also cause toxicity and osmotic damage. It is a major challenge to find the optimal balance between protecting the cells from ice and avoiding CPA-induced damage. In this study, we examined the organ perfusion process to shed light on phenomena relevant to cryopreservation protocol design, including changes in organ size and vascular resistance. In particular, we compared perfusion of kidneys (porcine and human) with CPA in either hypotonic or isotonic vehicle solution. Our results demonstrate that CPA perfusion causes kidney mass changes consistent with the shrink-swell response observed in cells. This response was observed when the kidneys were relatively fresh, but disappeared after prolonged warm and/or cold ischemia. Perfusion with CPA in a hypotonic vehicle solution led to a significant increase in vascular resistance, suggesting reduced capillary diameter due to cell swelling. This could be reversed by switching to perfusion with CPA in isotonic vehicle solution. Hypotonic vehicle solution did not cause notable osmotic damage, as evidenced by low levels of lactate dehydrogenase (LDH) in the effluent, and it did not have a statistically significant effect on the delivery of CPA into the kidney, as assessed by computed tomography (CT). Overall, our results show that CPA vehicle solution tonicity affects organ size and vascular resistance, which may have important implications for cryopreservation protocol design.

Multiple cryoprotectant toxicity model for vitrification solution optimization

Vitrification is a promising cryopreservation technique for complex specimens such as tissues and organs. However, it is challenging to identify mixtures of cryoprotectants (CPAs) that prevent ice formation without exerting excessive toxicity. In this work, we developed a multi-CPA toxicity model that predicts the toxicity kinetics of mixtures containing five of the most common CPAs used in the field (glycerol, dimethyl sulfoxide (DMSO), propylene glycol, ethylene glycol, and formamide). The model accounts for specific toxicity, non-specific toxicity, and interactions between CPAs. The proposed model shows reasonable agreement with training data for single and binary CPA solutions, as well as ternary CPA solution validation data. Sloppy model analysis was used to examine the model parameters that were most important for predictions, providing clues about mechanisms of toxicity. This analysis revealed that the model terms for non-specific toxicity were particularly important, especially the non-specific toxicity of propylene glycol, as well as model terms for specific toxicity of formamide and interactions between formamide and glycerol. To demonstrate the potential for model-based design of vitrification methods, we paired the multi-CPA toxicity model with a published vitrification/devitrification model to identify vitrifiable CPA mixtures that are predicted to have minimal toxicity. The resulting optimized vitrification solution composition was a mixture of 7.4 molal glycerol, 1.4 molal DMSO, and 2.4 molal formamide. This demonstrates the potential for mathematical optimization of vitrification solution composition and sets the stage for future studies to optimize the complete vitrification process, including CPA mixture composition and CPA addition and removal methods.

Toxicokinetic Modeling of Per- and Polyfluoroalkyl Substance Concentrations within Developing Zebrafish (Danio rerio) Populations

Per- and polyfluoroalkyl substances (PFAS) are pervasive environmental contaminants, and their relative stability and high bioaccumulation potential create a challenging risk assessment problem. Zebrafish (Danio rerio) data, in principle, can be synthesized within a quantitative adverse outcome pathway (qAOP) framework to link molecular activity with individual or population level hazards. However, even as qAOP models are still in their infancy, there is a need to link internal dose and toxicity endpoints in a more rigorous way to further not only qAOP models but adverse outcome pathway frameworks in general. We address this problem by suggesting refinements to the current state of toxicokinetic modeling for the early development zebrafish exposed to PFAS up to 120 h post-fertilization. Our approach describes two key physiological transformation phenomena of the developing zebrafish: dynamic volume of an individual and dynamic hatching of a population. We then explore two different modeling strategies to describe the mass transfer, with one strategy relying on classical kinetic rates and the other incorporating mechanisms of membrane transport and adsorption/binding potential. Moving forward, we discuss the challenges of extending this model in both timeframe and chemical class, in conjunction with providing a conceptual framework for its integration with ongoing qAOP modeling efforts.

General tissue mass transfer model for cryopreservation applications

Successful cryopreservation of complex specimens, such as tissues and organs, would greatly benefit both the medical and scientific research fields. Vitrification is one of the most promising techniques for complex specimen cryopreservation, but toxicity remains a major challenge because of the high concentration of cryoprotectants (CPAs) needed to vitrify. Our group has approached this problem using mathematical optimization to design less toxic CPA equilibration methods for cells. To extend this approach to tissues, an appropriate mass transfer model is required. Fick's law is commonly used, but this simple modeling framework does not account for the complexity of mass transfer in tissues, such as the effects of fixed charges, tissue size changes, and the interplay between cell membrane transport and transport through the extracellular fluid. Here, we propose a general model for mass transfer in tissues that accounts for all of these phenomena. To create this model, we augmented a previously published acellular model of mass transfer in articular cartilage to account for the effects of cells. We show that the model can accurately predict changes in CPA concentration and tissue size for both articular cartilage and pancreatic islets, tissue types with vastly different properties.

Mathematical Modeling of Protectant Transport in Tissues

Mass transfer of protectant chemicals is a fundamental aspect of cryopreservation and freeze-drying protocols. As such, mass transfer modeling is useful for design of preservation methods. Cell membrane transport modeling has been successfully used to guide design of preservation methods for isolated cells. For tissues, though, there are several mass transfer modeling challenges that arise from phenomena associated with cells being embedded in a tissue matrix. Both cells and the tissue matrix form a barrier to the free diffusion of water and protective chemicals. Notably, the extracellular space becomes important to model. The response of cells embedded in the tissue is dependent on the state of the extracellular space which varies both spatially and temporally. Transport in the extracellular space can also lead to changes in tissue size. In this chapter, we describe various mass transfer models that can be used to describe transport phenomena occurring during loading of tissues with protective molecules for cryopreservation applications. Assumptions and simplifications that limit the applicability of each of these models are discussed.

Rapid quantification of multi-cryoprotectant toxicity using an automated liquid handling method

Cryopreservation in a vitrified state has vast potential for long-term storage of tissues and organs that may be damaged by ice formation. However, the toxicity imparted by the high concentration of cryoprotectants (CPAs) required to vitrify these specimens remains a hurdle. To address this challenge, we previously developed a mathematical approach to design less toxic CPA equilibration methods based on the minimization of a toxicity cost function. This approach was used to design improved methods for equilibration of bovine pulmonary artery endothelial cells (BPAEC) with glycerol. To fully capitalize on the toxicity cost function approach, it is critical to describe the toxicity kinetics of additional CPAs, including multi-CPA mixtures that are commonly used for vitrification. In this work, we used automated liquid handling to characterize the toxicity kinetics of five of the most common CPAs (glycerol, dimethyl sulfoxide (DMSO), propylene glycol, ethylene glycol, and formamide), along with their binary and ternary mixtures for BPAEC. In doing so, we developed experimental methods that can be used to determine toxicity kinetics more quickly and accurately. Our results highlight some common CPA toxicity trends, including the relatively low toxicity of ethylene glycol and a general increase in toxicity as the CPA concentration increases. Our results also suggest potential new approaches to reduce toxicity, including a surprising toxicity neutralization effect of glycerol on formamide. In the future, this dataset will serve as the basis to expand our CPA toxicity model, enabling application of the toxicity cost function approach to vitrification solutions containing multiple CPAs.

Health services research

Health services research (HSR) is the science of the evaluation and improvement of health care provision. HSR can be used by health care organisations to develop and understand administrative, financial and organisational processes in order to improve efficacy of clinical treatments, efficiency of their delivery, and ultimately patient outcomes. HSR applies both quantitative and qualitative methodology, utilising data collected from real-life clinical practice, rather than the confines of more controlled traditional efficacy trials. With new and developing therapies, HSR provides an opportunity to enhance the delivery of cost-effective and efficient health care.

Level of evidence: Not applicable (educational article).

A comparison of the National Institute for Health and Care Excellence (NICE) and European Association of Urology (EAU) guidelines for the assessment and management of urinary incontinence in women

Objective:

The objective of this paper is to identify the similarities and key differences between the National Institute for Health and Care Excellence (NICE) and European Association of Urology (EAU) guidelines on the management of urinary incontinence (UI) in women.

Methods:

We reviewed the most recent iterations of both full guidelines to identify all key recommendations and their associated level/grade of evidence. Guidance on the management of urinary incontinence in men and neuropathic patients was excluded.

Results:

There is a significant overlap in the recommendations of both guidelines. Key differences include the indications for performing urodynamics, pharmacological agents in stress UI, the dose of botulinum toxin A (200 units by NICE, 100 units by EAU), the hierarchy of surgical options for primary stress UI and the role of the multi-disciplinary team (MDT).

Conclusion:

This review provides the various stakeholders involved in the management of female UI with a summary of the strength of evidence supporting the recommendations by these two key guidelines. We have provided an evidence-based framework to support clinical experience from which to base management decisions.

Macrodactyly - options and outcomes

We report the outcomes of 32 patients diagnosed with macrodactyly. The average age at presentation was 46 months and there was an equal distribution across the sexes, although there was a male predominance in the upper limb and female predominance in the lower limb. There were 20 cases of upper limb macrodactyly and 13 cases affecting the lower limb. Multiple digits were more commonly affected than isolated digits, with an average of 2.5 digits affected. Static disease required significantly fewer operations than progressive disease. The need for repeated procedures must be highlighted in cases of progressive macrodactyly. In the vast majority of cases the functional and cosmetic outcome is good, with good patient acceptance.

Changing referral patterns to a designated craniofacial centre over a four-year period

Craniofacial conditions are mainly treated within England by four supra-regional centres. Due to a continuous increase in the number of cases referred to our service we audited the source and nature of these referrals. Data was prospectively collected over a four-year period from April 2004 to March 2008. The speciality of the referring clinicians was recorded, along with the diagnosis. A year-by-year increase in the number of referrals from 138 in 2004-2005 to 253 in 2007-2008 was seen. There was a 214% increase in the number of patients referred with single suture craniosynostosis, a 520% increase in patients with benign hyperplastic conditions such as fibrous dysplasia, neurofibromatosis and vascular anomalies and a 220% increase in patients treated elsewhere but now needing revision surgery. A 407% increase in referrals for positional plagiocephaly was recorded. Our referral pattern reflects the internationally accepted increase in the incidence of metopic synostosis and positional plagiocephaly. Due to the skill mix and experience present in a designated craniofacial service other benign hyperplastic and hypoplastic conditions are increasingly being referred. Additional referrals have come from a change in the referral pathway. To manage the increased workload we have established separate clinics to manage vascular anomalies and have adopted a policy of not reviewing patients with positional plagiocephaly.

Protean manifestations of intravenous drug use

Intravenous drug use is an increasing social problem. Repeated venepunctures, injection of insoluble substances and needle sharing habits in intravenous drug users result in complications leading to admissions under various medical specialities. Many of these patients, however, manifest soft tissue wounds requiring specialised care from plastic surgeons. Typical presentations include injection site related abscess, cellulitis, necrotising fasciitis and non-healing wounds. We present a series of 11 consecutive cases treated in our unit over a six-month period, to highlight the varied clinical presentations and potential difficulties in their management.

An easy and accurate preoperative method for determining tibial nail lengths

Estimating the correct nail length for solid tibial nails can be problematic. Most techniques reported in the literature for determining tibial nail length are not accurate. In a retrospective study of 16 patients in our unit, only three had ideal nail sizes. In these patients, as part of phase I of our study, we measured their normal leg's length from knee joint line to ankle joint line. An ideal nail length for each of these patients was estimated from a whole length radiograph of the nailed tibia. Comparing these two data, we found that deducting 20 mm from the leg measurement gave appropriate nail lengths. We also compared this with three other anthropometric measurements; tibial tuberosity to medial malleolus, joint line to medial malleolus and olecranon to head of V metacarpal head distance. The joint line to joint line measurement was the most reliable and showed the best correlation with ideal nail lengths (0.982). In phase II, a prospective study on 15 patients, we used the joint line to joint line measurement to determine nail sizes. A postoperative review of the radiographs showed all the nails to be of adequate length. This strengthened the fact that the joint line to joint line measurement is the most accurate and easy method to determine tibial nail lengths.

External aperture of the vestibular aqueduct in Meniere's disease

OBJECTIVE

To study the relationship of the length of the external aperture of the vestibular aqueduct and the ratio of the summating potential and action potential (SP:AP) in patients with Meniere's disease.

STUDY DESIGN

Retrospective case study.

SETTING

Neurotology referral center.

PATIENTS

Fifty-four patients with Meniere's disease and nine control subjects without Meniere's disease.

INTERVENTION

The external aperture of the vestibular aqueduct was measured from a three-dimensional surface reconstruction computed tomography scan. Transtympanic electrocochleography was performed on patients with Meniere's disease.

MAIN OUTCOME MEASURE

The length of the external aperture of the vestibular aqueduct in the Meniere's disease ears was related to the SP:AP ratio in the Meniere's disease ears and compared with controls.

RESULTS

The average length of the external aperture was 3.79 +/- 2.92 mm in Meniere's disease ears and 5.35 +/- 1.73 mm in the control ears (p < 0.05). An enlarged SP:AP ratio was found in 95% of ears in the group with nonvisible external apertures of the vestibular aqueduct, 91% of ears in the <5 mm group, 58% of ears in the 5-7 mm group, and 29% of ears in the >7 mm group (chi-square = 24.814; p = 0.000).

CONCLUSIONS

The length of the external aperture of the vestibular aqueduct in patients with Meniere's disease is significantly shorter than in those without Meniere's disease. Endolymphatic hydrops, evidenced by an enlarged SP:AP ratio, was related to the length of the external aperture of the vestibular aqueduct. The shorter the external aperture, the more often the SP:AP ratio was enlarged. A short or nonvisible external aperture of the vestibular aqueduct is a predisposing factor to the development of Meniere's disease.

Family stressors as predictors of codependency

Codependency has been defined as an extreme focus on relationships, caused by a stressful family background (J. L. Fischer, L. Spann, & D. W. Crawford, 1991). In this study the authors assessed the relationship of the Spann-Fischer Codependency Scale (J. L. Fischer et al., 1991) and the Potter-Efron Codependency Assessment (L. A. Potter-Efron & P. S. Potter-Efron, 1989) with self-reported chronic family stress and family background. Students (N = 257) completed 2 existing self-report codependency measures and provided family background information. Results indicated that women had higher codependency scores than men on the Spann-Fischer scale. Students with a history of chronic family stress (with an alcoholic, mentally ill, or physically ill parent) had significantly higher codependency scores on both scales. The findings suggest that other types of family stressors, not solely alcoholism, may be predictors of codependency.

Cardiovascular reactivity and positive/negative affect during conversations

Systolic and diastolic blood pressures (SBP, DBP) were measured for 70 college students before, during and after informal dyadic conversations. Participants rated the positive and negative affect they experienced during conversation. SBP and DBP increased significantly from baseline to conversation. Increases in SBP and DBP were associated with more positive affect and unrelated to negative affect. Blood pressure measures taken one week later provided a more useful assessment of resting levels than measures taken before the conversation. Relationships between BP reactivity and positive affect remained significant after controlling for resting levels of BP, amount of talk during conversation, and sex of speaker in hierarchical regression. Blood pressure elevation during social interaction may be associated with involvement or enthusiasm, rather than emotional distress; this association is not simply an artifact of talkativeness. We suggest that cardiovascular reactivity in healthy young adults engaged in nonthreatening conversations may be a widespread phenomenon and not necessarily pathological.

Graduate and post-graduate medical education with the synchronous systems model

Behavioral sciences have an important new role, particularly in medicine and prevention (Revans, 1990; Starr, 1982). A decade ago when the ideology of medical care shifted from a biomedical to a biopsychosocial model, behavioral and social factors ascended in importance in modern health concerns (see Engel, 1977). Now, a living systems model called Synchronous Systems (Jasnoski & Schwartz, 1985) incorporates environmental (including the social and physical) along with physiological and psychological factors into its structure. The environment has been gaining recognition as an important determinant in health, disease, and wellness (Daniel, 1990; Demick & Wapner, 1990; Lawton, 1990; Stokols, 1990). The phrase "Synchronous Systems" departs from the traditional linear thought patterns to depict contemporaneous occurrences. Synchrony refers to simultaneous experiences or events, with an emphasis on healthy, congruent process and function. Positive, beneficial process in human functioning emphasizes prevention as found in public health efforts but refers also to dysfunctional and recuperative foundation of medicine as a departure from the healthy norm. These process and functional dynamics in the Synchronous Systems Model derive conceptually from systems theory, specifically from control and cybernetic theories (Cannon, 1932; Weiner, 1948). The dynamic complexity of health in the whole human system, which also incorporates the environment, requires synthesis of knowledge from the biological, social, behavioral, and ecological sciences. This article provides the fundamentals of the structural and functional synthesis possible in the Synchronous Systems Model. Its direct application to multidisciplinary research is also presented along with its specific application to medical education, policy, research, and service delivery.

Sensitive analysis of the mycotoxin zearalenone and its metabolites in biological fluids by high-performance liquid chromatography alpha

A method is described for the analysis of zearalenone and its metabolites, alpha- and beta-zearalenol, in small volumes (0.5-2.0 ml) of biological fluids including milk, blood, plasma, urine and bile, using high-performance liquid chromatography with fluorescence detection. Isolation of the toxins from biological fluids was achieved using a series of pH-controlled solvent extractions. Detection limits for zearalenone and alpha-zearalenol were 1 ng/ml, and for beta-zearalenol ca. 5 ng/ml, both at a signal-to-noise ratio of 3. In bile, however, the detection was ca. five times less sensitive owing to interfering substances. Recoveries at low ng/ml concentrations were highest from urine (87-94%) and plasma (85-93%), slightly lower from whole blood (78-88%) and milk (75-84%), and lowest from bile (66-77%).

Assessment of extraction procedures in the analysis of naturally contaminated grain products for deoxynivalenol (vomitoxin)

A comparison of 2 extraction solvent systems (acetonitrile-water, 21 + 4 and methanol-water, 1 + 1) and 3 mixing apparatus (high-speed blender, wrist-action shaker, and mechanical stirrer) was carried out for different extraction time periods. Methods were evaluated using uncontaminated corn spiked with pure deoxynivalenol (DON), field-inoculated (Fusarium graminearum) corn, and uncontaminated and naturally infected wheat in swine diets. After sample extraction, aliquots were passed through alumina-charcoal cleanup columns, evaporated to dryness, dissolved in 8% aqueous methanol, and injected onto the liquid chromatograph. Results confirm published reports of recoveries from DON-spiked samples; however, longer extraction times (less than or equal to 120 min) were required for naturally contaminated samples. Use of the high-speed blender resulted in faster extractions, but in our laboratory more samples could be more conveniently extracted simultaneously with the wrist-action shaker or mechanical stirrer. Less carryover (co-extraction) of interfering contaminants was observed when acetonitrile-water was used vs methanol-water. Results emphasize the importance of careful evaluation of extraction procedures with not only spiked samples but also naturally contaminated samples to establish extraction times required for maximum deoxynivalenol recoveries.

Rapid, sensitive liquid chromatographic method for determination of zearalenone and alpha- and beta-zearalenol in wheat

A rapid, sensitive liquid chromatographic (LC) method is described for quantitative determination of zearalenone and alpha- and beta-zearalenol in wheat. The procedure incorporates an internal standard, zearalenone oxime, to facilitate quantitation and automated analysis. A sample, buffered with pH 7.8 phosphate, is extracted with water-ethanol-chloroform (2 + 50 + 75) and cleaned up. The final residue is dissolved in LC mobile phase and injected onto a reverse phase RP-18 column under the following conditions: water-methanol-acetonitrile (5 + 3 + 2) mobile phase; fluorescence (excitation wavelength 236 nm, 418 nm cut-off emission filter) and UV (254 nm, range 0.0025 AU) detectors. The limit of detectability (twice background) is 0.5 ng for zearalenone and alpha-zearalenol standards on the fluorescence detector and 4 ng for beta-zearalenol on the UV detector, which is equivalent to 20 micrograms zearalenone and 20 micrograms alpha-zearalenol/kg, and 160 micrograms beta-zearalenol/kg feed. Standard curves are linear over the range 0-35 ng zearalenone and alpha-zearalenol on the fluorescence detector and 0-50 ng beta-zearalenol on the UV detector. Recoveries of all compounds are 87.5-101% in the range 0.1-3.0 mg/kg (ppm).

Thermal balance and sleep state in the newborn

The thermal balance of 35 healthy newborn term infants was measured during active (AS) and quiet sleep (QS) in thermoneutral and cool environments. As conductive heat loss was found to be small, some 3% of the total, only the effective surface area involved in insensible heat loss was used in calculating insulation values. This area varied with posture, being 84% of the total when supine and 70% in the prone, crouched position. In thermoneutrality oxygen consumption rose significantly when the change was from QS to AS, but the associated fall in insulation did not reach significance. In a cool environment the differences were in the same direction but of greater magnitude, and the decrease in insulation of 17% found in AS was significant.

Synchronized cycles in ventilation and vocal activity during spontaneous conversational speech

Ventilation was monitored in 10 human subjects during spontaneous conversational speech to determine whether oscillatory patterns in vocal activity were correlated with oscillatory patterns in ventilation. The 10 subjects were studied as five pairs (or dyads), and spontaneous conversation occurred within each dyad. Patterns with cycle times ranging from 16 to 512 s were studied. Of the 10 subjects in this study, 1 subject showed a very striking pattern of mutual entrainment between low-frequency oscillations in ventilation and in vocal activity, 5 subjects showed somewhat weaker coordination between oscillations in ventilation and vocal activity, and the remaining 4 subjects showed little or no coupling between ventilation and vocal activity. Mutual entrainment between rhythms in ventilation and vocal activity can occur, but this study suggests that there may be great differences among individuals in the degree to which ventilation covaries with vocal activity in spontaneous conversational speech. We hypothesize that degree of entrainment is affected both by the strength of any spontaneous ventilatory patterns and by the extent to which any individual's spontaneous ventilatory pattern matches that of his conversational partner.

CT demonstration of fat tissue in malignant renal neoplasms: atypical Wilms' tumors

It has been implied that the recognition of fat in a renal tumor suggests that the lesion is benign. Several authors have suggested tht angiomyolipoma is the only common renal tumor containing mature adipose tissue. Other neoplasms may contain mature fat that can be identified with current diagnostic imaging techniques. Under discussion is our experience with Wilms' tumor containing a predominance of adipose tissue.

High performance liquid chromatographic method using fluorescence detention for quantitative analysis of zearalenone and alpha-zearalenol in blood plasma

A sensitive, high performance liquid chromatographic method is described for quantitative determination of zearalenone and alpha-zearalenol in blood plasma. Blood plasma is extracted with 2-propanol in ether, the extract is evaporated to dryness, and the residue is dissolved in 0.18N NaOH. The aqueous phase is washed with chloroform, dichloromethane, and benzene, neutralized with 0.10M H3PO4, and extracted with benzene. The extract is evaporated, dissolved in methanol, and injected onto a reverse phase column containing LiChrosorb RP-8 under the following conditions: methanol-acetonitrile-water mobile phase, fluorescence detector, excitation wavelength 236 nm, and 418 nm cut-off emission filter. The limit of detectability (twice background) is 0.5 ng standard which is equivalent to 0.6 ng standard/mL blood plasma. Linear standard curves are observed over the range of 0-35 ng of injected zearalenone and alpha-zearalenol. The recoveries from blood plasma are 76-101% in the range of 1.5-6.0 ng standard/mL blood.

Effect of feeding on neonatal oxygen consumption

Oxygen consumption was measured in 9 short-gestation infants before feeding and for an hour after, using a closed-circuit metabolism chamber. Using the same system, O2 consumption of 9 term infants was measured for varying periods, beginning one hour from the end of the last feed. In the short-gestation infants a rise was found in the 15--45 minutes after feeding; O2 consumption then fell, and after 60 minutes had reached prefeed levels. The term infants showed no decrease with time after the first hour, as would be expected if the effect of feeding on O2 consumption extended beyond this. It is concluded that increased O2 demand after appropriate feeding does not extend beyond one hour postprandially.

Oxygen consumption and neonatal sleep states

1. In thirty full-term infants in the first week of life, nursed in a constant volume, closed-circuit metabolism chamber in a neutral thermal environment (31.5-33.5 degrees C), measurements were made of oxygen consumption ( V(O2)) during periods of rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep.2. The mean V(O2) during REM sleep was 5.97 ml. kg(-1). min(-1). In NREM sleep the mean V(O2) was 5.72 ml. kg(-1). min(-1). This difference was significant (paired t test P < 0.05).3. When the direction of sleep state change was taken into account the difference in V(O2) between the two states was much less when REM sleep preceded NREM than when the change was in the opposite direction. In nineteen infants in whom the change was from REM to NREM the difference in V(O2) (6.18 and 6.03 ml. kg(-1). min(-1)) was not significant (P > 0.05). The mean difference when the sleep state change was from NREM to REM was significant (P < 0.01), the values being 5.54 and 5.81 ml. kg(-1). min(-1) respectively.4. In the NREM state, a gradual diminution of V(O2) with time was consistently found. This was not the case in REM sleep.5. In twelve infants studied in a cool environment (29 +/- 0.5 degrees C) V(O2) during REM sleep was 7.77, and during NREM sleep it was 6.58 ml. kg(-1). min(-1), (P < 0.001). Thus even the maximum difference found in a neutral thermal environment of 6.6% was significantly increased to 14.9% (P < 0.01) with mild thermal stress.6. No consistent changes in V(O2) with time were found in either REM or NREM sleep in twelve infants studied in a cool environment, in contrast to the findings in thermal neutrality