scholarly journals Ectothermy and cardiac shunts profoundly slow the equilibration of inhaled anaesthetics in a multi-compartment model

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Catherine J. A. Williams ◽  
Christian Lind Malte ◽  
Hans Malte ◽  
Mads F. Bertelsen ◽  
Tobias Wang
Keyword(s):  
Minute Ventilation ◽  
Compartment Model ◽  
Cardiorespiratory System ◽  
Solubility Coefficient ◽  
Terrestrial Vertebrates ◽  
Arterial Blood ◽  
Inhalational Anaesthesia ◽  
The Right ◽  
The Impact ◽  
Lower Cardiac Output

Abstract The use of inhalational anaesthesia is ubiquitous in terrestrial vertebrates. Given the dependence of these agents on delivery by the cardiorespiratory system, we developed a new computational model predicting equilibration of inhaled anaesthetics in mammalian and ectotherm conditions including the ability of reptiles to maintain vascular shunts. A multi-compartment model was constructed from simultaneously-solved equations, verified by comparison to the literature for endo and ectotherm physiology. The time to 90% equilibration of anaesthetic in arterial blood (t90) is predicted and used to compare anaesthetics and physiologies. The five to tenfold lower cardiac output and minute ventilation of ectothermic vertebrates is predicted to slow equilibration times by five to ten times leading to 90% equilibration in ectotherm arterial blood of over 200 min, compounded by reduction in body temperature, and the extent of right-to-left vascular shunts. The impact of these findings is also influenced by the solubility coefficient of the anaesthetic, such that at net right-to-left shunt fractions of over 0.8, sevoflurane loses the advantage of faster equilibration, in comparison with isoflurane. We explore clinical strategies to regulate anaesthetic uptake in ectotherms by managing convectional flow especially by supportive ventilation and reduction of the right-to-left shunt.

Response of newborn lambs to CO-induced hypoxia

1988 ◽  
Vol 64 (5) ◽  
pp. 1870-1877 ◽  
Author(s):  
M. A. Bureau ◽  
J. L. Carroll ◽  
E. Canet
Keyword(s):  
Minute Ventilation ◽  
Blood Gases ◽  
Periodic Breathing ◽  
Respiratory Frequency ◽  
Gas Mixture ◽  
Arterial Blood Gases ◽  
Small Shift ◽  
Arterial Blood ◽  
The Right ◽  
Very High

This study was undertaken to measure the neonate's response to CO-induced hypoxia in the first 10 days of life. CO breathing was used to induce hypoxia because CO causes tissue hypoxia with no or minimal chemoreceptor stimulation. An inspired gas mixture of 0.25 to 0.5% CO in air was used to raise the blood carboxyhemoglobin (HbCO) progressively from 0 to 60% over approximately 20 min. The study, conducted in awake conscious lambs aged 2 and 10 days, consisted in measuring the response of ventilation and the change in arterial blood gases during the rise of HbCO. The results showed that the 2- and 10-day-old lambs tolerated very high HbCO levels without an increase in minute ventilation (VE) and without metabolic acidosis. At both ages, HbCO caused no VE change until HbCO levels rose to between 45 and 50% after which the VE change was exponential in some animals but minimal in others. The VE change was brought about by a rise in tidal volume and respiratory frequency. During the period of maturation from 2 to 10 days, there was a small shift to the right in the VE-HbCO response. In the 10-day-old lambs the VE response to high HbCO was greater than that of the 2-day-olds because of the lambs' higher respiratory frequency response. Six of the 10-day-old lambs but only two of the 2-day-old lambs showed a hypoxic tachypnea to HbCO of 55–65%. None of the lambs developed periodic breathing, dysrhythmic breathing, or recurrent apneas with an HbCO level as high as 60%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of O2 affinity on arterial PO2 in animals with central vascular shunts

1982 ◽  
Vol 53 (6) ◽  
pp. 1360-1364 ◽  
Author(s):  
S. C. Wood
Keyword(s):  
Body Temperature ◽  
Compartment Model ◽  
Congenital Defects ◽  
Arterial Blood ◽  
Venous Shunt ◽  
Two Compartment Model ◽  
Ectothermic Vertebrate ◽  
The Right ◽  
Dissociation Curves

Central vascular or intracardiac shunts result in venous admixture and reduced saturation of systemic arterial blood. This is pronounced in most species of amphibians and reptiles and may occur as congenital defects in homeotherms. A two-compartment model is useful to analyze the effects of shunt on O2 transport. The PO2 of a mixture of pulmonary (ideal) and mixed venous (shunt) blood will be a function of the resulting O2 saturation, analogous to the principle of the “mixing method” in vitro. Furthermore, for a given saturation, the PO2 of systemic arterial blood (PaO2) should be inversely related to the O2 affinity of the mixed blood. The present study tested this two-compartment model of shunt in animals with normally occurring right-to-left shunts (amphibians and reptiles) and with dogs having artificial shunts. The O2 dissociation curves (ODC) of the blood were manipulated by varying body temperature and blood pH. For any level of saturation of systemic arterial blood, the PaO2 was found to increase with factors that shifted the ODC to the right. This experimental support of mathematical models of shunting and PaO2 suggests that animals with intracardiac or central vascular shunts are benefited by low-O2-affinity blood, a condition that is common in amphibians and reptiles. For an individual ectothermic vertebrate, an increase in O2 demand due to increased body temperature would, because of decreased O2 affinity, be accompanied and perhaps facilitated by an increase in PaO2 if saturation remained constant.

External thoracic restriction, respiratory sensation, and ventilation during exercise in men

1999 ◽  
Vol 86 (4) ◽  
pp. 1142-1150 ◽  
Author(s):  
Helen R. Harty ◽  
Douglas R. Corfield ◽  
Richard M. Schwartzstein ◽  
Lewis Adams
Keyword(s):  
Chest Wall ◽  
Minute Ventilation ◽  
Residual Volume ◽  
Exercise Tests ◽  
Arterial Blood ◽  
Residual Capacity ◽  
Respiratory Discomfort ◽  
End Tidal ◽  
The Impact ◽  
Insight Into

Multiple factors may contribute to the dyspnea associated with restrictive ventilatory disease (RVD). Simple models that examine specific features of this problem are likely to provide insight into the mechanisms. Previous models of RVD utilizing elastic loads may not represent completely the impact on pulmonary and chest wall receptors derived from breathing at low thoracic volumes. The purpose of this study was to investigate the sensory consequences of breathing at low lung volumes induced by external thoracic restriction in an attempt to further elucidate the etiology of dyspnea in this setting. Ten men were studied, with and without an inelastic corset applied at residual volume (restriction resulted in mean reductions in vital capacity, functional residual capacity, residual volume, and forced expired volume in 1 s of 44, 31, 12.5, and 42%, respectively). During 10-min steady-state exercise tests (at a workload set to achieve ∼65% maximum heart rate), restriction resulted in significant increases, compared with control, in minute ventilation (61 vs. 49 l/min), respiratory frequency (43 vs. 23 breaths/min), and visual analog scale measurements of respiratory discomfort (65 vs. 20 mm). Alveolar hyperventilation (end-tidal [Formula: see text] = 39 vs. 44 Torr for control) and mild O2 desaturation (arterial blood O2 saturation = 93 vs. 95% for control) occurred. Hypoxemia, atelectasis, increased work and effort of breathing, or a decrease in the volume-related feedback from chest wall and/or lungs could be responsible for the increased dyspnea reported. External thoracic restriction provides a useful model to study mechanisms of dyspnea in RVD.

scholarly journals Krogh’s capillary recruitment hypothesis, 100 years on: Is the opening of previously closed capillaries necessary to ensure muscle oxygenation during exercise?

2020 ◽  
Vol 318 (2) ◽  
pp. H425-H447 ◽  
Author(s):  
Hugo Angleys ◽  
Leif Østergaard
Keyword(s):  
Blood Flow ◽  
Capillary Flow ◽  
Compartment Model ◽  
Muscle Oxygenation ◽  
Arterial Blood Flow ◽  
Oxygen Extraction ◽  
Model Calculations ◽  
Capillary Recruitment ◽  
Arterial Blood ◽  
The Impact

In 1919, August Krogh published his seminal work on skeletal muscle oxygenation. Krogh’s observations indicated that muscle capillary diameter is actively regulated, rather than a passive result of arterial blood flow regulation. Indeed, combining a mathematical model with the number of ink-filled capillaries he observed in muscle cross sections taken at different workloads, Krogh was able to account for muscle tissue’s remarkably efficient oxygen extraction during exercise in terms of passive diffusion from nearby capillaries. Krogh was awarded the 1920 Nobel Prize for his account of muscle oxygenation. Today, his observations are engrained in the notion of capillary recruitment: the opening of previously closed capillaries. While the binary distinction between “closed” and “open” was key to Krogh’s model argument, he did in fact report a continuum of capillary diameters, degrees of erythrocyte deformation, and perfusion states. Indeed, modern observations question the presence of closed muscle capillaries. We therefore examined whether changes in capillary flow patterns and hematocrit among open capillaries can account for oxygen extraction in muscle across orders-of-magnitude changes in blood flow. Our four-compartment model of oxygen extraction in muscle confirms this notion and provides a framework for quantifying the impact of changes in microvascular function on muscle oxygenation in health and disease. Our results underscore the importance of capillary function for oxygen extraction in muscle tissue as first proposed by Krogh. While Krogh’s model calculations still hold, our model predictions support that capillary recruitment can be viewed in the context of continuous, rather than binary, erythrocyte distributions among capillaries. NEW & NOTEWORTHY Oxygen extraction in working muscle is extremely efficient in view of single capillaries properties. The underlying mechanisms have been widely debated. Here, we develop a four-compartment model to quantify the influence of each of the hypothesized mechanisms on muscle oxygenation. Our results show that changes in capillary flow pattern and hematocrit can account for the high oxygen extraction observed in working muscle, while capillary recruitment is not required to account for these extraction properties.

An analog computer analysis of Cheyne-Stokes breathing

1965 ◽  
Vol 20 (2) ◽  
pp. 328-333 ◽  
Author(s):  
Howard T. Milhorn ◽  
A. C. Guyton
Keyword(s):  
Mathematical Model ◽  
Minute Ventilation ◽  
Respiratory Control ◽  
Periodic Breathing ◽  
Compartment Model ◽  
Analog Computer ◽  
Respiratory Center ◽  
Sustained Oscillation ◽  
Cheyne Stokes Breathing ◽  
The Right

A mathematical model of the human respiratory control system has been developed and utilized, with the aid of an analog computer, to study the influence of the various factors of the system in producing or enhancing Cheyne-Stokes breathing. The model is an extension of Grodins' (1954) two-compartment model (lung and tissue compartments) to which circulation times and ventilatory dead space have been added. The study has shown that only two factors, increased arterial circulation time and increased controller gain (Δ minute ventilation/Δ in respiratory center CO2 concentration), can alone produce sustained oscillation. However, several other factors, such as decreased CO2 production rate and a shift of the controller equation [minute ventilation = a function of respiratory center CO2 concentration] to the right so that more CO2 is exchanged per amount of alveolar ventilation, can enhance the oscillation. periodic breathing; mathematical model Submitted on May 7, 1964

Remifentanil Pharmacokinetics in Obese versus Lean Patients

1998 ◽  
Vol 89 (3) ◽  
pp. 562-573. ◽  
Author(s):  
Talmage D. Egan ◽  
Bernou Huizinga ◽  
Samir K. Gupta ◽  
Rudy L. Jaarsma ◽  
Richard J. Sperry ◽  
...  
Keyword(s):  
Body Weight ◽  
Population Model ◽  
Elective Surgery ◽  
Compartment Model ◽  
Pharmacokinetic Parameters ◽  
Blood Concentrations ◽  
Arterial Blood ◽  
Final Population ◽  
Two Compartment Model ◽  
The Impact

Background Remifentanil is a short-acting opioid whose pharmacokinetics have been characterized in detail. However, the impact of obesity on remifentanil pharmacokinetics has not been specifically examined. The goal of this study was to investigate the influence of body weight on remifentanil pharmacokinetics. Methods Twelve obese and 12 matched lean subjects undergoing elective surgery received a 1-min remifentanil infusion after induction of anesthesia. Arterial blood samples were collected for determination of remifentanil blood concentrations. Each subject's pharmacokinetic parameters were estimated by fitting a two-compartment model to the concentration versus time curves. Nonlinear mixed-effects population models examining the influence of lean body mass (LBM) and total body weight (TBW) were also constructed. Clinical simulations using the final population model were performed. Results The obese patient cohort reached substantially higher remifentanil concentrations. The individual pharmacokinetic parameters of a two-compartment model were not significantly different between the obese versus lean cohorts (unless normalized to TBW). The final population model scaled central clearance and the central and peripheral distribution volumes to LBM. The simulations illustrated that remifentanil pharmacokinetics are not grossly different in obese versus lean subjects and that TBW based dosing in obese patients can result in excessively high remifentanil concentrations. Conclusions The essential findings of the study are that remifentanil's pharmacokinetics are not appreciably different in obese versus lean subjects and that remifentanil pharmacokinetic parameters are therefore more closely related to LBM than to TBW. Clinically this means that remifentanil dosing regimens should be based on ideal body weight (or LBM) and not TBW.

Emotional Reactivity to Visual Content as Revealed by ERP Component Clustering

2015 ◽  
Vol 29 (4) ◽  
pp. 135-146 ◽  
Author(s):  
Miroslaw Wyczesany ◽  
Szczepan J. Grzybowski ◽  
Jan Kaiser
Keyword(s):  
Emotional Reactivity ◽  
Brain Activity ◽  
Affective State ◽  
Occipital Lobe ◽  
Stimulus Onset ◽  
Emotional States ◽  
Neural Basis ◽  
Temporoparietal Junction ◽  
The Right ◽  
The Impact

Abstract. In the study, the neural basis of emotional reactivity was investigated. Reactivity was operationalized as the impact of emotional pictures on the self-reported ongoing affective state. It was used to divide the subjects into high- and low-responders groups. Independent sources of brain activity were identified, localized with the DIPFIT method, and clustered across subjects to analyse the visual evoked potentials to affective pictures. Four of the identified clusters revealed effects of reactivity. The earliest two started about 120 ms from the stimulus onset and were located in the occipital lobe and the right temporoparietal junction. Another two with a latency of 200 ms were found in the orbitofrontal and the right dorsolateral cortices. Additionally, differences in pre-stimulus alpha level over the visual cortex were observed between the groups. The attentional modulation of perceptual processes is proposed as an early source of emotional reactivity, which forms an automatic mechanism of affective control. The role of top-down processes in affective appraisal and, finally, the experience of ongoing emotional states is also discussed.

The Impact of Internal Work Environment on the Retention of Healthcare Providers at Turaif General Hospital

2019 ◽  
Vol 10 (12) ◽  
pp. 1183-1199
Author(s):  
Mohammed Alrouili ◽  
Keyword(s):  
Work Environment ◽  
General Hospital ◽  
Professional Growth ◽  
Healthcare Providers ◽  
Entire Study ◽  
Internal Work ◽  
Research Findings ◽  
Study Population ◽  
The Right ◽  
The Impact

This study attempted to identify the impact of internal work environment on the retention of healthcare providers at Turaif General Hospital in the Kingdom of Saudi Arabia. In particular, the study aimed to identify the dimensions of work circumstances, compensation, and relationship with colleagues, professional growth, and the level of healthcare providers’ retention. In order to achieve the study goals, the researcher used the descriptive analytical approach. The researcher used the questionnaire as the study tool. The study population comprised all the healthcare providers at Turaif General Hospital. Questionnaires were distributed to the entire study sample that consisted of 220 individuals. The number of questionnaires valid for study was 183 questionnaires. The research findings were as follows: the participants’ estimate of the work circumstances dimension was high (3.64), the participants’ estimate of the compensation dimension was moderate (3.32), the participants’ estimate of the relationship with colleagues dimension was high (3.62), the participants’ estimate of the professional growth dimension was weak (2.39), and the participants’ estimate of healthcare providers’ retention level was intermediate (2.75). Accordingly, the researcher’s major recommendations are: the need to create the right atmosphere for personnel in hospitals, the interest of the hospital to provide the appropriate conditions for the staff in terms of the physical and moral aspects for building the work adjustment in the staff, and conducting training courses and educational lectures for personnel in hospitals on how to cope with the work pressures.

The Right to Housing: Challenges Associated with the ‘Waiting List System’ Ekurhuleni Metropolitan Municipality V Various Occupiers, Eden Park Extension 5 2014 3 SA 23 (SCA)

2017 ◽  
Vol 30 (1) ◽  
pp. 112-121
Author(s):  
Shamier Ebrahim
Keyword(s):  
Supreme Court ◽  
Waiting Lists ◽  
The State ◽  
Waiting List ◽  
Allocation Process ◽  
The Supreme Court ◽  
The Right ◽  
The Impact ◽  
Court Of Appeal

The right to adequate housing is a constitutional imperative which is contained in section 26 of the Constitution. The state is tasked with the progressive realisation of this right. The allocation of housing has been plagued with challenges which impact negatively on the allocation process. This note analyses Ekurhuleni Metropolitan Municipality v Various Occupiers, Eden Park Extension 51 which dealt with a situation where one of the main reasons provided by the Supreme Court of Appeal for refusing the eviction order was because the appellants subjected the unlawful occupiers to defective waiting lists and failed to engage with the community regarding the compilation of the lists and the criteria used to identify beneficiaries. This case brings to the fore the importance of a coherent (reasonable) waiting list in eviction proceedings. This note further analyses the impact of the waiting list system in eviction proceedings and makes recommendations regarding what would constitute a coherent (reasonable) waiting list for the purpose of section 26(2) of the Constitution.

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