Heart rate control during treadmill exercise using input-sensitivity shaping for disturbance rejection of very-low-frequency heart rate variability

AbstractBackgroundAutomatic and accurate control of heart rate (HR) during treadmill exercise is important for prescription and implementation of training protocols. The principal design issue for feedback control of HR is to achieve disturbance rejection of very-low-frequency heart rate variability (VLF-HRV) with a level of control signal activity (treadmill speed) which is sufficiently smooth and acceptable to the runner. This work aimed to develop a new method for feedback control of heart rate during treadmill exercise based on shaping of the input sensitivity function, and to empirically evaluate quantitative performance outcomes in an experimental study.MethodsThirty healthy male subjects participated. 20 subjects were included in a preceding study to determine an approximate, average nominal model of heart rate dynamics, and 10 were not. The design method guarantees that the input sensitivity function gain monotonically decreases with frequency, is therefore devoid of peaking, and has a pre-specified value at a chosen critical frequency, thus avoiding unwanted amplification of HRV disturbances in the very-low-frequency band. Controllers were designed using the existing approximate nominal plant model which was not specific to any of the subjects tested.ResultsAccurate, stable and robust overall performance was observed for all 30 subjects, with a mean RMS tracking error of 2.96beats/min and a smooth, low-power control signal. There were no significant differences in tracking accuracy or control signal power between the 10 subjects who were not in the preceding identification study and a matched subgroup of subjects who were (respectively: mean RMSE 2.69 vs. 3.28beats/min, p=0.24; mean control signal power 15.62 vs. 16.31×10−4m2/s2, p=0.37). Substantial and significant reductions over time in RMS tracking error and average control signal power were observed.ConclusionsThe input-sensitivity-shaping method provides a direct way to address the principal design challenge for HR control, namely disturbance rejection in relation to VLF-HRV, and delivered robust and accurate tracking with a smooth, low-power control signal. Issues of parametric and structural plant uncertainty are secondary because a simple approximate plant model, not specific to any of the subjects tested, was sufficient to achieve accurate, stable and robust heart rate control performance

Identification of heart rate dynamics during moderade-to-vigorous treadmill exercise

BACKGROUND: Heart rate can be used to prescribe exercise intensity for development and maintenance of cardiorespiratory fitness. The aim of this study was to identify the dynamics of heart rate response during moderate-to-vigorous treadmill exercise and to explore parameter dependencies with respect to time, intensity level and step-change direction. The focus was on simple approximate models for subsequent design of heart rate control systems. METHODS: 24 healthy, able-bodied male subjects each did two separate, 35-min tests on a treadmill, one at moderate and one at vigorous intensity. Each test had four individual upward and downward steps (1–4). Heart rate responses were modelled as first-order transfer functions with steady-state gain k and time constant [Formula: see text] . Models were estimated both for the overall testing periods and for individual step responses within each test. RESULTS: There were no significant differences in the overall mean values of k [24.3 vs. 24.1 bpm/(m/s), [Formula: see text] ] and [Formula: see text] (55.7 vs. 59.5 s, [Formula: see text] ) between the two intensity levels. The overall nominal gain for both conditions was [Formula: see text] , 21.9–26.6 bpm/(m/s) (mean [Formula: see text] standard deviation, 95 % confidence interval), and the overall nominal time constant was [Formula: see text] , 50.9–64.3 s. Analysis of models estimated from the individual steps revealed a significant difference in steady-state gain k for upward and downward steps [30.2 vs. 23.6 bpm/(m/s), [Formula: see text] ], but no difference in time constant [Formula: see text] between these two directions (57.5 vs. 54.4 s, [Formula: see text] ). For gain k, there was no significant main effect of intensity ([Formula: see text] ) or intensity–time ([Formula: see text] ) interactions, but there was a significant main effect of time ([Formula: see text] ). Pairwise comparison with respect to time showed a significant difference between the upward steps at times 1 and 3 [33.0 vs. 27.3 bpm/(m/s), [Formula: see text] ], but no significant difference between the downward steps at times 2 and 4 [24.4 vs. 22.8 bpm/(m/s), [Formula: see text] ]. For time constant [Formula: see text] , there were no significant main effects of intensity ([Formula: see text] ) or time ([Formula: see text] ), or intensity–time interactions ([Formula: see text] ). CONCLUSIONS: The tight CI-bounds obtained, and the observed parameter dependencies, suggest that the overall nominal model with [Formula: see text] and [Formula: see text] might serve as the basis for design of a linear time-invariant (LTI) feedback system for real-time control of heart rate. Future work should focus on this hypothesis and on direct comparison of LTI and nonlinear/time-varying control approaches

Using Light to Improve Commercial Value

The plasticity of plant morphology has evolved to maximize reproductive fitness in response to prevailing environmental conditions. Leaf architecture elaborates to maximize light harvesting, while the transition to flowering can either be accelerated or delayed to improve an individual's fitness. One of the most important environmental signals is light, with plants using light for both photosynthesis and as an environmental signal. Plants perceive different wavelengths of light using distinct photoreceptors. Recent advances in LED technology now enable light quality to be manipulated at a commercial scale, and as such opportunities now exist to take advantage of plants' developmental plasticity to enhance crop yield and quality through precise manipulation of a crops' lighting regime. This review will discuss how plants perceive and respond to light, and consider how these specific signaling pathways can be manipulated to improve crop yield and quality

Caregiver rating bias in mild cognitive impairment and mild Alzheimer's disease: impact of caregiver burden and depression on dyadic rating discrepancy across domains

ABSTRACT Background: Caregivers of individuals with dementia are biased in their rating of mental health measures of the care receiver. This study examines caregiver burden and depression as predictors of this bias for mild cognitive impairment and mild Alzheimer's disease in different domains. Methods: The sample consisted of 202 persons: 60 with mild cognitive impairment, 41 with mild Alzheimer's disease, and 101 caregivers. Discrepancy scores were calculated by subtracting the mean caregiver score from the respective mean patient score on the following assessment instruments: the Geriatric Depression Scale, Apathy Evaluation Scale, Bayer-Activities of Daily Living Scale, and Quality of Life-AD scale. Caregiver burden and depression were assessed by the Zarit Burden Interview and the Center for Epidemiologic Studies Depression Scale. Results: Intraclass correlation coefficients were low for apathy (0.38), daily functioning (0.38), and quality of life (0.30) and moderate for depression (0.49). These domains showed negative rating discrepancies, which indicates caregiver rating bias for all four domains. Regression analyses revealed that caregiver burden significantly contributed to explaining these discrepancies in the domains apathy, daily functioning, and quality of life. Conclusion: Caregiver rating bias can be attributed to caregiver burden. When caregiver burden is present, data based on caregiver ratings should therefore be interpreted with caution

Climate policy under sustainable discounted utilitarianism

Empirical evaluation of policies to mitigate climate change has been largely confined to the application of discounted utilitarianism (DU). DU is contro-versial, both due to the conditions through which it is justifed and due to its consequences for climate policies, where the discounting of future utility gains from present abatement efforts makes it harder for such measures to justify their present costs. In this paper, we propose sustainable discounted utilitari- anism (SDU) as an alternative principle for evaluation of climate policy. Unlike undiscounted utilitarianism, which always assigns zero relative weight to present utility, SDU is an axiomatically based criterion, which departs from DU by assigning zero weight to present utility if and only if it exceeds future welfare. Using the DICE integrated assessment model to run risk analysis, we show that it is possible for future welfare to be below present utility along a `business as usual' development path. Consequently SDU and DU differ, and willingness to pay for emissions reductions is (sometimes signifcantly) higher under SDU than under DU. Under SDU, stringent schedules of emissions reductions increase social welfare, even if the discount rate is relatively high

The genome of the obligate intracellular parasite Trachipleistophora hominis : new insights into microsporidian genome dynamics and reductive evolution

The dynamics of reductive genome evolution for eukaryotes living inside other eukaryotic cells are poorly understood compared to well-studied model systems involving obligate intracellular bacteria. Here we present 8.5 Mb of sequence from the genome of the microsporidian Trachipleistophora hominis, isolated from an HIV/AIDS patient, which is an outgroup to the smaller compacted-genome species that primarily inform ideas of evolutionary mode for these enormously successful obligate intracellular parasites. Our data provide detailed information on the gene content, genome architecture and intergenic regions of a larger microsporidian genome, while comparative analyses allowed us to infer genomic features and metabolism of the common ancestor of the species investigated. Gene length reduction and massive loss of metabolic capacity in the common ancestor was accompanied by the evolution of novel microsporidian-specific protein families, whose conservation among microsporidians, against a background of reductive evolution, suggests they may have important functions in their parasitic lifestyle. The ancestor had already lost many metabolic pathways but retained glycolysis and the pentose phosphate pathway to provide cytosolic ATP and reduced coenzymes, and it had a minimal mitochondrion (mitosome) making Fe-S clusters but not ATP. It possessed bacterial-like nucleotide transport proteins as a key innovation for stealing host-generated ATP, the machinery for RNAi, key elements of the early secretory pathway, canonical eukaryotic as well as microsporidian-specific regulatory elements, a diversity of repetitive and transposable elements, and relatively low average gene density. Microsporidian genome evolution thus appears to have proceeded in at least two major steps: an ancestral remodelling of the proteome upon transition to intracellular parasitism that involved reduction but also selective expansion, followed by a secondary compaction of genome architecture in some, but not all, lineages.Publisher PDFPeer reviewe