START CARE: a protocol for a randomised controlled trial of step-wise budesonide-formoterol reliever-based treatment in children.

Background: Asthma is the most common chronic childhood respiratory condition globally. Inhaled corticosteroid (ICS)-formoterol reliever-based regimens reduce the risk of asthma exacerbations compared with conventional short-acting ß2-agonist (SABA) reliever-based regimens in adults and adolescents. The current limited evidence for anti-inflammatory reliever therapy in children means it is unknown whether these findings are also applicable to children. High-quality randomised controlled trials (RCTs) are needed. Objective: The study aim is to determine the efficacy and safety of budesonide-formoterol reliever alone or maintenance and reliever therapy (MART) compared with standard therapy: budesonide or budesonide-formoterol maintenance, both with terbutaline reliever, in children aged 5 to 11 years with mild, moderate and severe asthma. Methods: A 52-week, multicentre, open-label, parallel group, phase III, two-sided superiority RCT will recruit 400 children aged 5 to 11 years with asthma. Participants will be randomised 1:1 to either budesonide-formoterol 100/6 µg Turbuhaler reliever alone or MART; or budesonide or budesonide-formoterol Turbuhaler maintenance, with terbutaline Turbuhaler reliever. The primary outcome is moderate and severe asthma exacerbations as rate per participant per year. Secondary outcomes are asthma control, lung function, exhaled nitric oxide and treatment step change. Assessment of Turbuhaler technique and cost-effectiveness analysis are also planned. Conclusion: This will be the first RCT to compare the efficacy and safety of a step-wise budesonide-formoterol reliever alone or MART regimen with conventional inhaled ICS or ICS-long-acting ß-agonist maintenance plus SABA reliever in children. The results will provide a much-needed evidence base for the treatment of asthma in children.

Emotion constructs and outcome measures following false positive breast screening test results: A systematic review of reporting clarity and selection rationale.

OBJECTIVE: (i) To systematically identify constructs and outcome measures used to assess the emotional and mood impact of false positive breast screening test results; (ii) to appraise the reporting clarity and rationale for selecting constructs and outcome measures. METHODS: Databases (MEDLINE, CINAHL, PsycINFO) were systematically searched from 1970. Studies using standardised and non-standardised outcome measures to evaluate the emotion or mood impact of false positive breast screening test results were eligible. A 15-item coding scheme was devised to appraise articles on clarity and rationale for selected constructs and measures. RESULTS: Forty-seven articles were identified. The most investigated constructs were general anxiety and depression and disease-specific anxiety and worry. Twenty-two standardised general outcome questionnaire measures and three standardised disease-specific outcome questionnaire measures were identified. Twenty articles used non-standardised scales/items. Reporting of constructs and outcome measures was generally clear, but rationales for their selection were lacking. Anxiety was typically justified, but justification for depression was almost always absent. Practical and psychometric justification for selecting outcome measures was lacking, and theoretical rationale was absent. CONCLUSIONS: Heterogeneity in constructs and measures, coupled with unclear rationale for these, impedes a thorough understanding of why there are emotional effects of false positive screening test results. This may explain the repeated practice of investigating less relevant outcomes such as depression. There is need to develop a consensual conceptual model of and standardised approach to measuring emotional impact from cancer screening test results, to address heterogeneity and other known issues of interpreting an inconsistent evidence base.

The Anti-Inflammatory Reliever (AIR) Algorithm Study: a protocol for a single-group study of an AIR stepwise approach to the treatment of adult asthma.

Background: The stepwise approach to long-term asthma management, which traditionally incorporates short-acting ß2-agonist reliever therapy, has been a core feature of asthma guidelines for over 30 years. There have been no studies, however, directly investigating the use of an entire guideline-recommended track. Recently, inhaled corticosteroid-formoterol has been recommended as the preferred reliever therapy in adult asthma, in accordance with a stepwise "Anti-Inflammatory Reliever" (AIR) treatment track. Objective: The aim of this study was to evaluate the AIR stepwise approach recommended by the New Zealand adolescent and adult asthma guidelines, in combination with a novel algorithm for transitioning between treatment steps. Methods: This 52-week, open-label, single-group study will recruit 100 adults aged 18 to 75 years with mild, moderate and moderate-severe asthma (ACTRN12620001010987). Participants will be allocated to budesonide-formoterol 200/6 µg, one actuation as needed (Step 1), one actuation twice daily and as needed (Step 2), or two actuations twice daily and one as needed (Step 3). Treatment steps will be adjusted throughout the study, in response to reliever use and asthma attacks, according to a stepwise AIR algorithm. Following a 26-week period of investigator-led transitions, participants will adjust their own treatment step. The primary outcome is participant satisfaction as measured by the Global Satisfaction score of the Treatment Satisfaction Questionnaire for Medication. Secondary outcomes will assess efficacy and safety, and describe patterns of medication use and participant flow through the treatment steps. Conclusion: This is the first trial to assess the AIR treatment track and algorithm. The results will provide knowledge to guide the clinical use of this approach.

The Children's Anti-inflammatory Reliever (CARE) study: a protocol for a randomised controlled trial of budesonide-formoterol as sole reliever therapy in children with mild asthma.

BACKGROUND: Asthma is the most common chronic disease in children, many of whom are managed solely with a short-acting ß2-agonist (SABA). In adults, the evidence that budesonide-formoterol as sole reliever therapy markedly reduces the risk of severe exacerbations compared with SABA alone has contributed to the Global Initiative for Asthma recommending against SABA monotherapy in this population. The current lack of evidence in children means it is unknown whether these findings are also relevant to this demographic. High-quality randomised controlled trials (RCTs) are needed. OBJECTIVE: The aim of this study is to determine the efficacy and safety of as-needed budesonide-formoterol therapy compared with as-needed salbutamol in children aged 5 to 15 years with mild asthma, who only use a SABA. METHODS: A 52-week, open-label, parallel group, phase III RCT will recruit 380 children aged 5 to 15 years with mild asthma. Participants will be randomised 1:1 to either budesonide-formoterol (Symbicort Rapihaler®) 50/3 µg, two actuations as needed, or salbutamol (Ventolin®) 100  µg, two actuations as needed. The primary outcome is asthma attacks as rate per participant per year. Secondary outcomes assess asthma control, lung function, exhaled nitric oxide and treatment step change. A cost-effectiveness analysis is also planned. CONCLUSION: This is the first RCT to assess the safety and efficacy of as-needed budesonide-formoterol in children with mild asthma. The results will provide a much-needed evidence base for the treatment of mild asthma in children.

How big is your bubble? Characteristics of self-isolating household units ('bubbles') during the COVID-19 Alert Level 4 period in New Zealand: a cross-sectional survey.

OBJECTIVE: To characterise the self-isolating household units (bubbles) during the COVID-19 Alert Level 4 lockdown in New Zealand. DESIGN, SETTING AND PARTICIPANTS: In this cross-sectional study, an online survey was distributed to a convenience sample via Facebook advertising and the Medical Research Institute of New Zealand's social media platforms and mailing list. Respondents were able to share a link to the survey via their own social media platforms and by email. Results were collected over 6 days during Alert Level 4 from respondents living in New Zealand, aged 16 years and over. MAIN OUTCOMES MEASURES: The primary outcome was the mean size of a self-isolating household unit or bubble. Secondary outcomes included the mean number of households in each bubble, the proportion of bubbles containing essential workers and/or vulnerable people, and the mean number of times the home was left each week. RESULTS: 14 876 surveys were included in the analysis. The mean (SD) bubble size was 3.58 (4.63) people, with mean (SD) number of households 1.26 (0.77). The proportion of bubbles containing one or more essential workers, or one or more vulnerable persons was 45.3% and 42.1%, respectively. The mean number of times individual bubble members left their home in the previous week was 12.9 (12.4). Bubbles that contained at least one vulnerable individual had fewer outings over the previous week compared with bubbles that did not contain a vulnerable person. The bubble sizes were similar by respondent ethnicity. CONCLUSION: In this New Zealand convenience sample, bubble sizes were small, mostly limited to one household, and a high proportion contained essential workers and/or vulnerable people. Understanding these characteristics from a country which achieved a low COVID-19 infection rate may help inform public health interventions during this and future pandemics.

Budesonide-formoterol reliever therapy versus maintenance budesonide plus terbutaline reliever therapy in adults with mild to moderate asthma (PRACTICAL): a 52-week, open-label, multicentre, superiority, randomised controlled trial.

BACKGROUND: In adults with mild asthma, a combination of an inhaled corticosteroid with a fast-onset long-acting ß-agonist (LABA) used as reliever monotherapy reduces severe exacerbations compared with short-acting ß-agonist (SABA) reliever therapy. We investigated the efficacy of combination budesonide-formoterol reliever therapy compared with maintenance budesonide plus as-needed terbutaline. METHODS: We did a 52-week, open-label, parallel-group, multicentre, superiority, randomised controlled trial at 15 primary care or hospital-based clinical trials units and primary care practices in New Zealand. Participants were adults aged 18-75 years with a self-reported doctor's diagnosis of asthma who were using SABA for symptom relief with or without maintenance low to moderate doses of inhaled corticosteroids in the previous 12 weeks. We randomly assigned participants (1:1) to either reliever therapy with budesonide 200 µg-formoterol 6 µg Turbuhaler (one inhalation as needed for relief of symptoms) or maintenance budesonide 200 µg Turbuhaler (one inhalation twice daily) plus terbutaline 250 µg Turbuhaler (two inhalations as needed). Participants and investigators were not masked to group assignment; the statistician was masked for analysis of the primary outcome. Six study visits were scheduled: randomisation, and weeks 4, 16, 28, 40, and 52. The primary outcome was the number of severe exacerbations per patient per year analysed by intention to treat (severe exacerbations defined as use of systemic corticosteroids for at least 3 days because of asthma, or admission to hospital or an emergency department visit because of asthma requiring systemic corticosteroids). Safety analyses included all participants who had received at least one dose of study treatment. This trial is registered with the Australian New Zealand Clinical Trials Registry, number ACTRN12616000377437. FINDINGS: Between May 4, 2016, and Dec 22, 2017, we assigned 890 participants to treatment and included 885 eligible participants in the analysis: 437 assigned to budesonide-formoterol as needed and 448 to budesonide maintenance plus terbutaline as needed. Severe exacerbations per patient per year were lower with as-needed budesonide-formoterol than with maintenance budesonide plus terbutaline as needed (absolute rate per patient per year 0·119 vs 0·172; relative rate 0·69, 95% CI 0·48-1·00; p=0·049). Nasopharyngitis was the most common adverse event in both groups, occurring in 154 (35%) of 440 patients receiving as-needed budesonide-formoterol and 144 (32%) of 448 receiving maintenance budesonide plus terbutaline as needed. INTERPRETATION: In adults with mild to moderate asthma, budesonide-formoterol used as needed for symptom relief was more effective at preventing severe exacerbations than maintenance low-dose budesonide plus as-needed terbutaline. The findings support the 2019 Global Initiative for Asthma recommendation that inhaled corticosteroid-formoterol reliever therapy is an alternative regimen to daily low-dose inhaled corticosteroid for patients with mild asthma. FUNDING: Health Research Council of New Zealand.

Refinement of optical imaging spectroscopy algorithms using concurrent BOLD and CBV fMRI.

We describe the use of the three dimensional characteristics of the functional magnetic resonance imaging (fMRI) blood oxygenation level dependent (BOLD) and cerebral blood volume (CBV) MRI signal changes to refine a two dimensional optical imaging spectroscopy (OIS) algorithm. The cortical depth profiles of the BOLD and CBV changes following neural activation were used to parameterise a 5-layer heterogeneous tissue model used in the Monte Carlo simulations (MCS) of light transport through tissue in the OIS analysis algorithm. To transform the fMRI BOLD and CBV measurements into deoxy-haemoglobin (Hbr) profiles we inverted an MCS of extra-vascular MR signal attenuation under the assumption that the extra-/intravascular ratio is 2:1 at a magnetic field strength of 3 T. The significant improvement in the quantitative accuracy of haemodynamic measurements using the new heterogeneous tissue model over the original homogeneous tissue model OIS algorithm was demonstrated on new concurrent OIS and fMRI data covering a range of stimulus durations.

Theory and generalization of Monte Carlo models of the BOLD signal source.

The dependency of the blood oxygenation level dependent (BOLD) signal on underlying hemodynamics is not well understood. Building a forward biophysical model of this relationship is important for the quantitative estimation of the hemodynamic changes and neural activity underlying functional magnetic resonance imaging (fMRI) signals. We have developed a general model of the BOLD signal which can model both intra- and extravascular signals for an arbitrary tissue model across a wide range of imaging parameters. The model of the BOLD signal was instantiated as a look-up-table (LuT), and was verified against concurrent fMRI and optical imaging measurements of activation induced hemodynamics.

Preservation of visual cortical function following retinal pigment epithelium transplantation in the RCS rat using optical imaging techniques.

The aim of this study was to determine the extent of cortical functional preservation following retinal pigment epithelium (RPE) transplantation in the Royal College of Surgeons (RCS) rat using single-wavelength optical imaging and spectroscopy. The cortical responses to visual stimulation in transplanted rats at 6 months post-transplantation were compared with those from age-matched untreated dystrophic and non-dystrophic rats. Our results show that cortical responses were evoked in non-dystrophic rats to both luminance changes and pattern stimulation, whereas no response was found in untreated dystrophic animals to any of the visual stimuli tested. In contrast, a cortical response was elicited in most of the transplanted rats to luminance changes and in many of those a response was also evoked to pattern stimulation. Although the transplanted rats did not respond to high spatial frequency information we found evidence of preservation in the cortical processing of luminance changes and low spatial frequency stimulation. Anatomical sections of transplanted rat retinas confirmed the capacity of RPE transplantation to rescue photoreceptors. Good correlation was found between photoreceptor survival and the extent of cortical function preservation determined with optical imaging techniques. This study determined the efficacy of RPE transplantation to preserve visual cortical processing and established optical imaging as a powerful technique for its assessment.

Haemodynamic and neural responses to hypercapnia in the awake rat.

The relationship between localized changes in brain activity and metabolism, and the blood oxygenation level-dependent (BOLD) signal used in functional magnetic resonance imaging studies is not fully understood. One source of complexity is that stimulus-elicited changes in the BOLD signal arise both from changes in oxygen consumption due to increases in activity and purely 'haemodynamic' changes such as increases in cerebral blood flow. It is well established that robust cortical haemodynamic changes can be elicited by increasing the concentration of inspired CO(2) (inducing hypercapnia) and it is widely believed that these haemodynamic changes occur without significant effects upon neural activity or cortical metabolism. Hypercapnia is therefore commonly used as a calibration condition in functional magnetic resonance imaging studies to enable estimation of oxidative metabolism from subsequent stimulus-evoked functional magnetic resonance imaging BOLD signal changes. However, there is little research that has investigated in detail the effects of hypercapnia upon all components of the haemodynamic response (changes in cerebral blood flow, volume and oxygenation) in addition to recording neural activity. In awake animals, we used optical and electrophysiological techniques to measure cortical haemodynamic and field potential responses to hypercapnia (60 s, 5% CO(2)). The main findings are that firstly, in the awake rat, the temporal structure of the haemodynamic response to hypercapnia differs from that reported previously in anaesthetized preparations in that the response is more rapid. Secondly, there is evidence that hypercapnia alters ongoing neural activity in awake rats by inducing periods of cortical desynchronization and this may be associated with changes in oxidative metabolism.

Investigating neural-hemodynamic coupling and the hemodynamic response function in the awake rat.

An understanding of the relationship between changes in neural activity and the accompanying hemodynamic response is crucial for accurate interpretation of functional brain imaging data and in particular the blood oxygen level-dependent (BOLD) fMRI signal. Much physiological research investigating this topic uses anesthetized animal preparations, and yet, the effects of anesthesia upon the neural and hemodynamic responses measured in such studies are not well understood. In this study, we electrically stimulated the whisker pad of both awake and urethane anesthetized rats at frequencies of 1-40 Hz. Evoked field potential responses were recorded using electrodes implanted into the contralateral barrel cortex. Changes in hemoglobin oxygenation and concentration were measured using optical imaging spectroscopy, and cerebral blood flow changes were measured using laser Doppler flowmetry. A linear neural-hemodynamic coupling relationship was found in the awake but not the anesthetized animal preparation. Over the range of stimulation conditions studied, hemodynamic response magnitude increased monotonically with summed neural activity in awake, but not in anesthetized, animals. Additionally, the temporal structure of the hemodynamic response function was different in awake compared to anesthetized animals. The responses in each case were well approximated by gamma variates, but these were different in terms of mean latency (approximately 2 s awake; 4 s anesthetized) and width (approximately 0.6 s awake; 2.5 s anesthetized). These findings have important implications for research into the intrinsic signals that underpin BOLD fMRI and for biophysical models of cortical hemodynamics and neural-hemodynamic coupling.

Concurrent fMRI and optical measures for the investigation of the hemodynamic response function.

Functional magnetic resonance imaging (fMRI) signal variations are based on a combination of changes in cerebral blood flow (CBF) and volume (CBV), and blood oxygenation. We investigated the relationship between these hemodynamic parameters in the rodent barrel cortex by performing fMRI concurrently with laser Doppler flowmetry (LDF) or optical imaging spectroscopy (OIS), following whisker stimulation and hypercapnic challenge. A difference between the positions of the maximum blood oxygenation level-dependent (BOLD) and CBV changes was observed in coronal fMRI maps, with the BOLD region being more superficial. A 6.5% baseline blood volume fraction in this superficial region dropped to 4% in deeper cortical layers (corresponding to total hemoglobin baseline volumes Hbt0 = 110 microM and 67 microM, respectively), as inferred from maps of deltaR2*. Baseline volume profiles were used to parameterize the Monte Carlo simulations (MCS) to interpret the 2D OIS. From this it was found that the optical blood volume measurements (i.e., changes in total hemoglobin) equated with CBV-MRI measurements when the MRI data were taken from superficial cortical layers. Optical measures of activation showed a good spatial overlap with fMRI measurements taken in the same plane (covering the right hemisphere surface). Changes in CBV and CBF followed the scaling relationship CBV = CBF(alpha), with mean alpha = 0.38 +/- 0.06.

How visual stimuli activate dopaminergic neurons at short latency.

Unexpected, biologically salient stimuli elicit a short-latency, phasic response in midbrain dopaminergic (DA) neurons. Although this signal is important for reinforcement learning, the information it conveys to forebrain target structures remains uncertain. One way to decode the phasic DA signal would be to determine the perceptual properties of sensory inputs to DA neurons. After local disinhibition of the superior colliculus in anesthetized rats, DA neurons became visually responsive, whereas disinhibition of the visual cortex was ineffective. As the primary source of visual afferents, the limited processing capacities of the colliculus may constrain the visual information content of phasic DA responses.

Long duration stimuli and nonlinearities in the neural-haemodynamic coupling.

Recent studies have shown that the haemodynamic responses to brief (<2 secs) stimuli can be well characterised as a linear convolution of neural activity with a suitable haemodynamic impulse response. In this paper, we show that the linear convolution model cannot predict measurements of blood flow responses to stimuli of longer duration (>2 secs), regardless of the impulse response function chosen. Modifying the linear convolution scheme to a nonlinear convolution scheme was found to provide a good prediction of the observed data. Whereas several studies have found a nonlinear coupling between stimulus input and blood flow responses, the current modelling scheme uses neural activity as an input, and thus implies nonlinearity in the coupling between neural activity and blood flow responses. Neural activity was assessed by current source density analysis of depth-resolved evoked field potentials, while blood flow responses were measured using laser Doppler flowmetry. All measurements were made in rat whisker barrel cortex after electrical stimulation of the whisker pad for 1 to 16 secs at 5 Hz and 1.2 mA (individual pulse width 0.3 ms).

Further nonlinearities in neurovascular coupling in rodent barrel cortex.

An essential prerequisite for the accurate interpretation of noninvasive functional brain imaging techniques, such as blood oxygen level dependent (BOLD) fMRI, is a thorough understanding of the coupling relationship between neural activity and the haemodynamic response. The current study investigates this relationship using rat barrel cortex as a model. Neural input was measured by applying current source density (CSD) analysis to multi-laminar field potentials to remove ambiguities regarding the origin of the signal inherent in single electrode recordings. Changes in cerebral blood flow (CBF) were recorded with a laser Doppler flowmetry probe. The magnitude of neural and CBF responses were modulated over a large range by altering both the intensity and frequency of electrical whisker pad stimulation. Consistent with previous findings [Devor, A., et al., 2003. Neuron 39, 353-359; Sheth, S.A., et al., 2004. Neuron 42, 347-355] a power law function well described the relationship between neural activity and haemodynamics. Despite the nonlinearity of the coupling over the whole data set, the relationship was very well approximated by a linear function over mid-range stimuli. Altering the frequency of stimulation at 1.2 mA shifted the neural activity and corresponding haemodynamic response along this linear region, reconciling recent reports of a nonlinear relationship [Devor, A., et al., 2003. Neuron 39, 353-359; Jones, M., et al., 2004. NeuroImage 22, 956-965; Sheth, S.A., et al., 2004. Neuron 42, 347-355] with previous work that found a linear coupling relationship when altering stimulation frequency [Martindale, J., et al., 2003. J. Cereb. Blood Flow Metab. 23, 546-555; Ngai, A.C., et al., 1999. Brain Res. 837, 221-228; Sheth, S., et al., 2003. NeuroImage 19, 884-894]. Using stimuli within this linear range in imaging studies would simplify the interpretation of findings.

A model of the dynamic relationship between blood flow and volume changes during brain activation.

The temporal relationship between changes in cerebral blood flow (CBF) and cerebral blood volume (CBV) is important in the biophysical modeling and interpretation of the hemodynamic response to activation, particularly in the context of magnetic resonance imaging and the blood oxygen level-dependent signal. measured the steady state relationship between changes in CBV and CBF after hypercapnic challenge. The relationship CBV is proportional to CBFphi has been used extensively in the literature. Two similar models, the Balloon and the Windkessel , have been proposed to describe the temporal dynamics of changes in CBV with respect to changes in CBF. In this study, a dynamic model extending the Windkessel model by incorporating delayed compliance is presented. The extended model is better able to capture the dynamics of CBV changes after changes in CBF, particularly in the return-to-baseline stages of the response.

Nonlinear coupling of neural activity and CBF in rodent barrel cortex.

The relationship between neural activity and accompanying changes in cerebral blood flow (CBF) and oxygenation must be fully understood before data from brain imaging techniques can be correctly interpreted. Whether signals in fMRI reflect the neural input or output of an activated region is still unclear. Similarly, quantitative relationships between neural activity and changes in CBF are not well understood. The present study addresses these issues by using simultaneous laser Doppler flowmetry (LDF) to measure CBF and multichannel electrophysiology to record neural activity in the form of field potentials and multiunit spiking. We demonstrate that CBF-activation coupling is a nonlinear inverse sigmoid function. Comparing the data with previous work suggests that within a cortical model, CBF shows greatest spatial correlation with a current sink 500 microm below the surface corresponding to sensory input. These results show that care must be exercised when interpreting imaging data elicited by particularly strong or weak stimuli and that hemodynamic changes may better reflect the input to a region rather than its spiking output.

The hemodynamic impulse response to a single neural event.

This article investigates the relation between stimulus-evoked neural activity and cerebral hemodynamics. Specifically, the hypothesis is tested that hemodynamic responses can be modeled as a linear convolution of experimentally obtained measures of neural activity with a suitable hemodynamic impulse response function. To obtain a range of neural and hemodynamic responses, rat whisker pad was stimulated using brief (

Optical imaging spectroscopy in the unanaesthetised rat.

We describe a method for imaging the local cortical haemodynamic response to whisker stimulation in the rat without use of anaesthetic or paralytic agents. Female Hooded Lister rats were anaesthetised and a section of skull overlying somatosensory cortex thinned to translucency. A stainless steel chamber was then secured over the thin cranial window. Following recovery, animals were supported in a harness whilst the head was held by the implanted chamber using a pneumatically driven clamp. Optical imaging and optical imaging spectroscopy (OIS) of somatosensory cortex were performed whilst the contralateral whiskers were stimulated using a computer controlled air-puffer. Imaging sessions lasted approximately 15 min and data were collected for at least three consecutive days. Experiments were then repeated with the animals under urethane anaesthesia. Spectral analysis revealed qualitatively similar haemodynamic response functions across both anaesthetic states. However, our results indicate that the cortical haemodynamic response to somatosensory stimulation is larger by a factor of approximately 5 in the unanaesthetised rat compared with the anaesthetised rat. This preparation may make possible the investigation of the haemodynamic correlates of a broad range of neurological processes in the awake, behaving rodent.

A model of the hemodynamic response and oxygen delivery to brain.

A recent nonlinear system by Friston et al. (2000. NeuroImage 12: 466-477) links the changes in BOLD response to changes in neural activity. The system consists of five subsystems, linking: (1) neural activity to flow changes; (2) flow changes to oxygen delivery to tissue; (3) flow changes to changes in blood volume and venous outflow; (4) changes in flow, volume, and oxygen extraction fraction to deoxyhemoglobin changes; and finally (5) volume and deoxyhemoglobin changes to the BOLD response. Friston et al. exploit, in subsystem 2, a model by Buxton and Frank coupling flow changes to changes in oxygen metabolism which assumes tissue oxygen concentration to be close to zero. We describe below a model of the coupling between flow and oxygen delivery which takes into account the modulatory effect of changes in tissue oxygen concentration. The major development has been to extend the original Buxton and Frank model for oxygen transport to a full dynamic capillary model making the model applicable to both transient and steady state conditions. Furthermore our modification enables us to determine the time series of CMRO(2) changes under different conditions, including CO(2) challenges. We compare the differences in the performance of the "Friston system" using the original model of Buxton and Frank and that of our model. We also compare the data predicted by our model (with appropriate parameters) to data from a series of OIS studies. The qualitative differences in the behaviour of the models are exposed by different experimental simulations and by comparison with the results of OIS data from brief and extended stimulation protocols and from experiments using hypercapnia.