Sensitivity and a Preferable Alternative to Re-aligned Models for Prediction in MPC

Most papers on predictive control use either state space models with an observer or transfer function models with output realignment for prediction purposes. Here it is shown that this approach can have weaknesses, especially with regard to noise rejection and the independent model approach should soften be preferred

Input shaping for PFC: how and why?

Predictive functional control (PFC) is a highly successful strategy within industry, but for cases with challenging dynamics the most effective tuning approaches are still an active research area. This paper shows how one can deploy some insights from the more traditional model predictive control literature in order to enable systematic tuning and in particular, to ensure that the key PFC tuning parameter, that is the desired closed-loop time constant, is effective. In addition to enabling easier and more effective tuning, the proposed approach has the advantage of being simple to code and thus retaining the simplicity of implementation and tuning that is a key selling point of PFC. This paper focuses on design for open-loop unstable and also processes with significant under-damping in their open-loop behaviour

Predictive Functional Control of Unstable Processes

Application of predictive functional control (PFC) has been very successful on many processes, however, application to unstable open-loop processes has met more varied success rates. Certain processes in particular with factors of the type (s-a) (s-ra), r-1 have proved very difficult to stabilise. This paper illustrates how the pre-stabilisation approach to prediction can be used to overcome this bottleneck and with the added bonus of retaining the intuitive tuning parameters that make PFC popular

Handling Constraints with Predictive Functional Control of Unstable Processes

This paper tackles 2 major issues. The first is to develop a new means of including constraint handling for unstable processes into the industrial successful and computationally efficient algorithm, predictive functional control (PFC) ; the benefits are illustrated. The second is to show how the technique to be proposed has recursive feasibility in the nominal case, that is feasibility now implies feasibility at the next sampling instant. This is known to be essential for robust stabilisation of unstable processes

Low intense physical exercise in normobaric hypoxia leads to more weight loss in obese people than low intense physical exercise in normobaric sham hypoxia

Training in mild to moderate hypoxia (14–17% O2 in breathing air) and extended resting in moderate hypoxia (9–13% O2) have been shown to have effects in animals and humans on lipid and glucose metabolism, appetite loss, and, in part, on body weight. The causality for these effects is not yet known in detail, and the available data in humans from high-altitude and low-pressure chamber studies are scarce. New technical developments by German companies in the production of artificial climates with normobaric hypoxic conditions in larger rooms at reasonable energy costs allow now to perform hypoxia weight loss studies in obese humans with stable experimental conditions and protocols with a sham hypoxia control. Thirty-two obese people were recruited for a mild intense training study in normobaric hypoxia (15 vol.% O2) and normoxia/sham hypoxia (20.1 vol.% O2). Twenty of these [mean age 47.6 years, mean body mass index (BMI) 33.1, 16 m, 4 f) were willing to follow up on an 8-week, three times per week, 90-min low intense physical exercise in their individual fat burning mode, which has been determined by an exercise testing with spiro-ergometry upfront. The subjects were evenly randomized into a hypoxia and sham hypoxia group. The difference of the two groups in weight loss and changes in HBa1C values were analyzed before and after the training period. No nutritional diet was applied. Subjects in the hypoxia group in mean lost significantly more weight than in the sham hypoxia group (Δ1.14 kg vs Δ0.03 kg; p = 0.026). This resulted in a tendency to reduce the BMI more in the hypoxia group (p = 0.326). In the mean, there was no HbA1C exceeding normal values (mean 5.67 and 5.47%), and the HbA1C stayed basically unchanged after the 8-week training. Mild physical exercise three times per week for 90 min in normobaric hypoxia for 8 weeks led to significantly greater weight loss in obese persons than the exercise in sham hypoxia in this, to our knowledge, first sham hypoxia controlled study

Chemoreceptor responsiveness at sea level does not predict the pulmonary pressure response to high altitude

The hypoxic ventilatory response (HVR) at sea level (SL) is moderately predictive of the change in pulmonary artery systolic pressure (PASP) to acute normobaric hypoxia. However, because of progressive changes in the chemoreflex control of breathing and acid-base balance at high altitude (HA), HVR at SL may not predict PASP at HA. We hypothesized that resting peripheral oxyhemoglobin saturation (SpO2) at HA would correlate better than HVR at SL to PASP at HA. In 20 participants at SL, we measured normobaric, isocapnic HVR (L/min·-%SpO2 -1) and resting PASP using echocardiography. Both resting SpO2 and PASP measures were repeated on day 2 (n=10), days 4-8 (n=12), and 2-3 weeks (n=8) after arrival at 5050m. These data were also collected at 5050m on life-long HA residents (Sherpa; n=21). Compared to SL, SpO2 decreased from 98.6 to 80.5% (P<0.001), while PASP increased from 21.7 to 34.0mmHg (P<0.001) after 2-3 weeks at 5050m. Isocapnic HVR at SL was not related to SpO2 or PASP at any time point at 5050m (all P>0.05). Sherpa had lower PASP (P<0.01) than lowlanders on days 4-8 despite similar SpO2. Upon correction for hematocrit, Sherpa PASP was not different from lowlanders at SL, but lower than lowlanders at all HA time points. At 5050m, whilst SpO2 was not related to PASP in lowlanders at any point (all R2=0.50), there was a weak relationship in the Sherpa (R2=0.16; P=0.07). We conclude that neither HVR at SL nor resting SpO2 at HA correlates with elevations in PASP at HA

Alterations in cerebral blood flow and cerebrovascular reactivity during 14 days at 5050 m

Upon ascent to high altitude, cerebral blood flow (CBF) rises substantially before returning to sea-level values. The underlying mechanisms for these changes are unclear. We examined three hypotheses: (1) the balance of arterial blood gases upon arrival at and across 2 weeks of living at 5050 m will closely relate to changes in CBF; (2) CBF reactivity to steady-state changes in CO2 will be reduced following this 2 week acclimatisation period, and (3) reductions in CBF reactivity to CO2 will be reflected in an augmented ventilatory sensitivity to CO2. We measured arterial blood gases, middle cerebral artery blood flow velocity (MCAv, index of CBF) and ventilation () at rest and during steady-state hyperoxic hypercapnia (7% CO2) and voluntary hyperventilation (hypocapnia) at sea level and then again following 2–4, 7–9 and 12–15 days of living at 5050 m. Upon arrival at high altitude, resting MCAv was elevated (up 31 ± 31%; P < 0.01; vs. sea level), but returned to sea-level values within 7–9 days. Elevations in MCAv were strongly correlated (R2= 0.40) with the change in ratio (i.e. the collective tendency of arterial blood gases to cause CBF vasodilatation or constriction). Upon initial arrival and after 2 weeks at high altitude, cerebrovascular reactivity to hypercapnia was reduced (P < 0.05), whereas hypocapnic reactivity was enhanced (P < 0.05 vs. sea level). Ventilatory response to hypercapnia was elevated at days 2–4 (P < 0.05 vs. sea level, 4.01 ± 2.98 vs. 2.09 ± 1.32 l min−1 mmHg−1). These findings indicate that: (1) the balance of arterial blood gases accounts for a large part of the observed variability (∼40%) leading to changes in CBF at high altitude; (2) cerebrovascular reactivity to hypercapnia and hypocapnia is differentially affected by high-altitude exposure and remains distorted during partial acclimatisation, and (3) alterations in cerebrovascular reactivity to CO2 may also affect ventilatory sensitivity

Phosphodiesterase-5 Inhibition Mimics Intermittent Reoxygenation and Improves Cardioprotection in the Hypoxic Myocardium

Although chronic hypoxia is a claimed myocardial risk factor reducing tolerance to ischemia/reperfusion (I/R), intermittent reoxygenation has beneficial effects and enhances heart tolerance to I/R. Aim of the study: To test the hypothesis that, by mimicking intermittent reoxygenation, selective inhibition of phosphodiesterase-5 activity improves ischemia tolerance during hypoxia. Adult male Sprague-Dawley rats were exposed to hypoxia for 15 days (10% O2) and treated with placebo, sildenafil (1.4 mg/kg/day, i. p.), intermittent reoxygenation (1 h/day exposure to room air) or both. Controls were normoxic hearts. To assess tolerance to I/R all hearts were subjected to 30-min regional ischemia by left anterior descending coronary artery ligation followed by 3 h-reperfusion. Whereas hypoxia depressed tolerance to I/R, both sildenafil and intermittent reoxygenation reduced the infarct size without exhibiting cumulative effects. The changes in myocardial cGMP, apoptosis (DNA fragmentation), caspase-3 activity (alternative marker for cardiomyocyte apoptosis), eNOS phosphorylation and Akt activity paralleled the changes in cardioprotection. However, the level of plasma nitrates and nitrites was higher in the sildenafil+intermittent reoxygenation than sildenafil and intermittent reoxygenation groups, whereas total eNOS and Akt proteins were unchanged throughout. Conclusions: Sildenafil administration has the potential to mimic the cardioprotective effects led by intermittent reoxygenation, thereby opening the possibility to treat patients unable to be reoxygenated through a pharmacological modulation of NO-dependent mechanisms

Ventilatory and Autonomic Regulation in Sleep Apnea Syndrome: A Potential Protective Role for Erythropoietin?

Obstructive sleep apnea (OSA) is the most common form of sleep disordered breathing and is associated with wide array of cardiovascular morbidities. It has been proposed that during OSA, the respiratory control center (RCC) is affected by exaggerated afferent signals coming from peripheral/central chemoreceptors which leads to ventilatory instability and may perpetuate apnea generation. Treatments focused on decreasing hyperactivity of peripheral/central chemoreceptors may be useful to improving ventilatory instability in OSA patients. Previous studies indicate that oxidative stress and inflammation are key players in the increased peripheral/central chemoreflex drive associated with OSA. Recent data suggest that erythropoietin (Epo) could also be involved in modulating chemoreflex activity as functional Epo receptors are constitutively expressed in peripheral and central chemoreceptors cells. Additionally, there is some evidence that Epo has anti-oxidant/anti-inflammatory effects. Accordingly, we propose that Epo treatment during OSA may reduce enhanced peripheral/central chemoreflex drive and normalize the activity of the RCC which in turn may help to abrogate ventilatory instability. In this perspective article we discuss the potential beneficial effects of Epo administration on ventilatory regulation in the setting of OSA