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Results for “physiologic variables”

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PubMed2006

Correlation between axonal morphologies and synaptic input kinetics of interneurons from mouse visual cortex.

Neocortical interneurons display great morphological and physiological variability and are ideally positioned to control circuit dynamics, although their exact role is still poorly understood. To better understand this diversity, we have performed a detailed anatomical and physiological characterization of 3 subtypes of visual cortex interneurons, isolated from transgenic mice which express green fluorescent protein in somatostatin, parvalbumin, and neuropeptide Y positive neurons. We find that these 3 groups of interneurons have systematic differences in dendritic and axonal morphologies and also characteristically differ in the frequencies, amplitude, and kinetics of the spontaneous excitatory and inhibitory synaptic currents they receive. Moreover, we detect a correlation between the kinetics of their synaptic inputs and quantitative aspects of their axonal arborizations. This suggests that different interneuron types could channel different temporal patterns of activity. Our results also confirm the importance of the axonal morphology to classify interneurons.

Animals↗

PubMed2000

The preanalytic phase. An important component of laboratory medicine.

The preanalytic phase is an important component of total laboratory quality. A wide range of variables that affect the result for a patient from whom a specimen of blood or body fluid has been collected, including the procedure for collection, handling, and processing before analysis, constitute the preanalytic phase. Physiologic variables, such as lifestyle, age, and sex, and conditions such as pregnancy and menstruation, are some of the preanalytic phase factors. Endogenous variables such as drugs or circulating antibodies might interact with a specific method to yield spurious analytic results. The preanalytic phase variables affect a wide range of laboratory disciplines.

Adolescent↗

PubMed1995

Estimates of myocardium at risk and collateral flow in acute myocardial infarction using electrocardiographic indexes with comparison to radionuclide and angiographic measures.

OBJECTIVES: This study sought to determine the accuracy of the initial 12-lead electrocardiogram (ECG) in predicting final infarct size after direct coronary angioplasty for myocardial infarction and to examine which physiologic variables known to be determinants of outcome the ST segment changes most closely reflect. BACKGROUND: Myocardium at risk, collateral flow and time to reperfusion have been shown to be independent physiologic predictors of infarct size in animal and clinical models. However, such measurements may be difficult to perform on a routine basis in patients with myocardial infarction. The standard 12-lead ECG is inexpensive and readily available. METHODS: Sixty-seven patients with acute myocardial infarction, ST segment elevation and duration of chest pain < 12 h had an initial injection of technetium-99m sestamibi. Tomographic imaging was performed 1 to 8 h later (after direct coronary angioplasty), and the images were quantified to measure perfusion defect size (myocardium at risk) and severity (a measure of collateral flow). Contrast agent injection and tomographic acquisition were repeated at hospital discharge to measure infarct size. The ST segment elevation score was calculated for each patient according to infarct location and using previously described formulas. RESULTS: ST segment elevation score correlated closest with the radionuclide measure of collateral flow (r = -0.44, p < or = 0.0001), as well as an angiographic measure of collateral flow (r = -0.38, p = 0.05). Although ST segment elevation score correlated weakly with the magnitude of myocardium at risk by technetium-99m sestamibi, it was not as strong as infarct location alone in predicting myocardium at risk ([mean +/- SD] anterior 51 +/- 13% left ventricle vs. inferior 17 +/- 10% left ventricle, p < 0.0001). ST segment elevation score was weakly associated with final infarct size (r = 0.34, p = 0.005). A multivariate ECG model was constructed with infarct location as a surrogate for myocardium at risk, ST segment elevation score as a surrogate for estimated collateral flow, and elapsed time to reperfusion from onset of chest pain. All three variables were independently associated with infarct size. CONCLUSIONS: The initial standard 12-lead ECG can provide insight into myocardium at risk and, to a greater extent, collateral flow and can consequently provide some estimate of subsequent infarct size. However, the confidence limits for such predictors are wide.

Adult↗

PubMed2006

A non-linear mixed effect dynamic model incorporating prior exposure and adherence to treatment to describe long-term therapy outcome in HIV-patients.

Long term therapy with antiretroviral agents in HIV-infected patients often result in failure to suppress the virus load. Imperfect adherence to prescribed antiviral drugs is an important factor explaining the resurgence of virus. A better understanding of the factors responsible for the virological failure is important for the development of new treatment strategies. Many complex non-linear models have been developed to describe and simulate the dynamics of HIV-1 virus. Those complicated viral dynamic models have not been used in clinical trials to estimate HIV dynamics parameters, due to their complexity, until the recent development of simplification and approximation techniques. The estimation of the parameters associated with the dynamics from real data has been mostly limited to linearized models that can only explain the decay (suppression) of the virus following antiviral treatment. Moreover, no complete characterization of typical clinical data in terms of inter-subject variability and identification of important covariates effecting HIV-1 dynamics has been attempted. The objective of our paper was to develop a hierarchical non-linear mixed effect model characterizing inter-subject variability in the long-term response to treatment of HIV-1 RNA, and show how the model can be used to quantify the effect of important covariates, such as physiological variables, adherence to treatment or previous exposure to treatment, on the dynamics of HIV-1 RNA. As an example we report the analysis of AIDS clinical trial data from AACTG 398, which shows that patients with previous exposure to treatment show faster death rates for HIV-1, and that higher adherence to treatment is associated with lower reproductive ratio.

Algorithms↗

PubMed1983

Instrumentation for the continuous measurement of gas exchange and ventilation of infants during assisted ventilation.

A system of instrumentation for continuous measurement of oxygen consumption (VO2), carbon dioxide production (VCO2) and minute ventilation (V1) in human newborns on assisted ventilation is described. VO2 and VCO2 are measured by open-circuit indirect calorimetry utilizing a Servomex OA 184 differential paramagnetic oxygen analyzer and a Beckman LB 2 infrared CO2 analyzer. Minute volume is measured with a body plethysmograph. Bench performance is described, limitations of the system are defined, and sample clinical data are presented. The instrumentation can measure safely, accurately, and continuously physiologic variables in sick infants on assisted ventilation.

Humans↗

PubMed1998

A computer model of intracranial dynamics integrated to a full-scale patient simulator.

The ability to visualize intracranial dynamics during simulated clinical scenarios is a valuable tool for teaching brain physiology and the consequences of different medical interventions on the brain. Studies have isolated physiologic variables and shown their effects on brain dynamics. However, no studies have shown the combined effects of these variables on intracranial dynamics. This brain model offers one approach that brings all these relationships together and shows how they affect the dynamics of the brain. The brain model obtains its physiologic inputs from a full-scale patient simulator which responds to clinical interventions. This integration allows individuals working on the patient simulator to see the effects of their actions on brain dynamics. The brain model gives a real-time display of intracranial events (cerebral metabolic rate, cerebral blood flow, cerebral blood volume, cerebral perfusion pressure, and intracranial pressure) and responds to changes in the pulmonary and cardiovascular condition of the patient simulator.

Blood Volume↗

PubMed1995

No influence of ACTH on maximal performance.

Although it is generally accepted in the sporting world that adrenocorticotropic hormones (ACTH) and corticosteroids enhance maximal performance, this claim has never been scientifically corroborated. In a counterbalanced, double-blind design, 1 mg ACTH or placebo was injected into 16 professional cyclists. They cycled for 1 h on a bicycle ergometer at a submaximal level, defined as 60% of maximal performance on a pretest with a load increase of 50 W per minute. After 1 h, load was increased by 10 W per minute until exhaustion. No increase of maximal performance was observed with ACTH, either on the day of drug intake, or on the following day, although substantial increases were measured in physiological variables such as cortisol, glucose, and white corpuscle concentrations. Feelings of fatigue, which were continuously self-rated, were diminished only during submaximal performance. The present technique of systematically distinguishing between physiological, psychological, and performance measurements could help in explaining the persistent belief in the performance enhancing properties of ACTH and other doping substances.

Adrenocorticotropic Hormone↗

PubMed1991

Classification of postoperative cardiac patients: comparative evaluation of four algorithms.

Four classification algorithms based on Bayes' rule for minimum error are compared by evaluating their ability to recognize high- and normal-risk cardio-surgical patients. These algorithms differ in the modelling of the probability density function (pdf) for each class and include: (a) two parametric algorithms based on the assumption of normal pdf; (b) two non-parametric algorithms using Parzen multidimensional approximation of pdf with normal kernels. In each case, classes with both equal and different covariance matrices were considered. A set of 200 patients in the 6 h immediately following cardiac surgery has been used to test the performance of the algorithms. For each patient the three measured variables most effective in representing the difference between the two classes were considered. We found that the two algorithms which explicitly incorporate the information on the different sample covariance between the physiological variables existing in the two classes generally provide better recognition of high- and normal-risk patients. Of these two algorithms the parametric one appears extremely attractive for practical applications, since it exhibits slightly better performance in spite of its great simplicity.

Algorithms↗

PubMed1997

Computer analysis of environmental temperature, light and noise in intensive care: chaos or chronome nurseries?

Lighting, noise and temperature were monitored in two perinatal nurseries. Rhythms of several frequencies were found, including prominent 24-hour rhythms with acrophases around 13:00 (light intensity) and 16:00 (noise). For light and noise, the ratio formed by dividing the amplitude of a 1-week (circaseptan) or half-week (circasemiseptan) fitted cosine curve by the amplitude of a 24-hour fitted cosine curve is smaller than unity, since 24-hour rhythms are prominent for these variables. The amplitude ratios are larger than unity for temperature in the newborns' unit but not in the infants' unit. Earlier, the origin of the about-7-day rhythms of neonatal physiologic variables was demonstrated to have, in addition to a major endogenous, also a minor exogenous component. Hence, the possibility of optimizing maturation by manipulating environmental changes can be considered, using, as gauges of development, previously mapped chronomes (time structures of biologic multifrequency rhythms, trends and noise).

Circadian Rhythm↗

PubMed2001

Blood pressure in the very low birth weight neonate.

Few aspects of management of very low birth weight (VLBW; <1500 g) neonates have generated as much controversy as the assessment of blood pressure (BP) and need for treatment of perceived abnormalities of this physiologic variable. The approach to this problem may differ greatly among various institutions and even among clinicians within a given center. The purpose of this manuscript is to review available information regarding physiologic determinants and measurement of BP in VLBW neonates, normative data for BP, clinical factors that may affect BP in these at-risk neonates and studies in which presumed abnormalities of BP resulted in adverse clinical outcomes. Options for treatment of low BP in VLBW neonates also will be discussed.

Animals↗

PubMed1990

[Effects of waiting times within simple problems: an analogy to waiting times in human-computer interaction].

The impact of forced intra-task waiting periods was evaluated in a laboratory study designed in analogy to forced waiting periods in human-computer interaction. Each task consisted of two lines of grouped capital letters (so-called Sterzinger lines) that had to be processed individually, separated by the experimental waiting period. The final response to both lines was taken after removal of the second line. The experiment was conducted according to a within-subjects design with the order of the two factors "duration" (2 s vs. 8 s) and "variability of the waiting periods" (constant vs. variable) controlled. The dependent variables were performance indices, heart rate, electrodermal activity, and subjective measures of mood and physical complaints. The results showed effects of the duration of waiting periods for the performance and the physiological variables, and effects of the variability factor for the subjective variables. Shorter waiting periods were associated with higher scores of heart rate and skin resistance responses, variable waiting periods seemed to confuse the subjects more than constant ones. The results are discussed with respect to the effects of the two experimental factors. With respect to dialog structures in human-computer interaction, the results lead to the conclusion that response interference could be avoided by giving the user the possibility to immediately input problem solutions. Partial and preliminary inputs should be permanently kept visible during the whole task cycle by the software.

Adult↗

PubMed1998

A three-dimensional virtual environment for modeling mechanical cardiopulmonary interactions.

We have developed a real-time computer system for modeling mechanical physiological behavior in an interactive, 3-D virtual environment. Such an environment can be used to facilitate exploration of cardiopulmonary physiology, particularly in situations that are difficult to reproduce clinically. We integrate 3-D deformable body dynamics with new, formal models of (scalar) cardiorespiratory physiology, associating the scalar physiological variables and parameters with the corresponding 3-D anatomy. Our framework enables us to drive a high-dimensional system (the 3-D anatomical models) from one with fewer parameters (the scalar physiological models) because of the nature of the domain and our intended application. Our approach is amenable to modeling patient-specific circumstances in two ways. First, using CT scan data, we apply semi-automatic methods for extracting and reconstructing the anatomy to use in our simulations. Second, our scalar physiological models are defined in terms of clinically measurable, patient-specific parameters. This paper describes our approach, problems we have encountered and a sample of results showing normal breathing and acute effects of pneumothoraces.

Computer Simulation↗

PubMed1979

Bedside determination of bicarbonate and base excess, blood oxygen saturation and content, VD/VT, and P50 using a programmable calculator.

Assessing and modifying oxygen transport are major parts of ICU patient management. Determination of base excess, blood oxygen saturation and content, dead space ventilation, and P50 helps in this management. A program is described for determining these variables using a T1 59 programmable calculator and PC 100A printer. Each variable can be independently calculated without running the whole program. The calculator-printer's small size, low cost, and hard copy printout make it a valuable and versatile tool for calculating physiological variables. The program is easily entered by an stored on magnetic card, and prompts the user to enter the appropriate variables, making is easy to run by untrained personnel.

Acid-Base Equilibrium↗

PubMed2005

Comparison of trend detection algorithms in the analysis of physiological time-series data.

This paper presents a comparative performance analysis of various trend detection methods developed using fuzzy logic, statistical, regression, and wavelet techniques. The main contribution of this paper is the introduction of a new method that uses noise rejection fuzzy clustering to enhance the performance of trend detection methodologies. Furthermore, another contribution of this work is a comparative investigation that produced systematic guidelines for the selection of a proper trend detection method for different application requirements. Examples of representative physiological variables considered in this paper to examine the trend detection algorithms are: 1) blood pressure signals (diastolic and systolic); and 2) heartbeat rate based on RR intervals of electrocardiography signal. Furthermore, synthetic physiological data intentionally contaminated with various types of real-life noise has been generated and used to test the performance of trend detection methods and develop noise-insensitive trend-detection algorithms.

Algorithms↗

PubMed2002

Further studies of shoulder and neck pain and exposures in customer service work with low biomechanical demands.

The aim of the study was to establish insight into work exposures that cause shoulder and neck pain among occupational groups that have low biomechanical exposure and experience work stress from client/customer contact, among other exposures. Four occupational groups were studied, in health care (n = 20), retail (n = 22), banking (n = 26), and university secretaries (n = 26), a total of 94 volunteers. Thirty-nine were classified as pain-afflicted in the shoulder and neck, while 55 were pain-free. The subjects' perceptions of biomechanical and psychosocial exposures were established by use of quantitative questionnaires and by explorative interviews with open-ended questions, covering the same themes. Heart rate and trapezius EMG were recorded over a full workday and the following leisure period. Trapezius median and static activity during work were 3.3% and 0.3% EMG(max), only marginally higher than trapezius activity in the leisure period (2.7% and 0.2% EMG(max)). The quantitative questionnaire did not identify any variable that correlated with shoulder and neck pain except perceived general tension. The interviews established that the interaction with clients or customers was an important source of work stress. Such stress appeared to be a complex entity not easily characterized by established psychosocial questionnaires. The physiological variables were at most weakly elevated in periods with high stress as compared to periods with low stress. The authors caution against relying on standardized quantitative questionnaires and/or physiological recordings to characterize work stress in occupations with emotional stress through client/customer service work.

Biomechanical Phenomena↗

PubMed1987

NMR spectroscopy as an investigative technique in physiology.

Relating physiological variables on an organ system level to metabolic function within the intracellular environment has been exceedingly difficult because of a paucity of techniques. Most of the tools at our command necessitate either the removal or destruction of tissues before measurements can be made. Recently, NMR spectroscopy has been applied to several important questions relating organ system and cellular physiology. NMR has the distinct advantage of being noninvasive and nondestructive, allowing the investigator to make repetitive measurements of intracellular variables while manipulating experimental variables that are important on the organ system level. In this review we shall present several examples of such NMR investigations so that the reader will gain some appreciation of the potential of this relatively new technique. Cellular acid-base homeostatic mechanisms, high-energy phosphate metabolism, and regulation of anaerobic glycolysis will be discussed for such diverse cellular populations as mammalian brain, mammalian heart muscle, salamander skeletal muscle, amphibian skin, and invertebrate muscle. In addition, the role of phosphomonoesters and phosphodiesters in lipid metabolism for several tissues in different species will be evaluated.

Animals↗

PubMed1991

Pathophysiology of the human brain after stroke, monitored by positron emission tomography.

Six stroke patients had positron tomograms both in the acute stage of the cerebrovascular accident (16 to 38 h after onset), and one week later. In and around the infarct, the studies revealed a wide range of metabolic states. In the healthy regions of the brain, all measured physiological variables, including the density of capillaries that transported glucose, blood flow, and oxygen and glucose metabolism, changed in parallel (recruitment). In the regions suffering the consequences of stroke, in the second study, the physiological couple between capillary density, metabolism, and flow was significantly impaired, and the impairment was proportional to the severity of ischemia in the first study. The research report of these findings appeared in the Journal of Cerebral Blood Flow and Metabolism (Gjedde et al. 1990).

Aged↗

PubMed2005

Progressive suppression of motor evoked potentials during general anesthesia: the phenomenon of "anesthetic fade".

Transcranial motor evoked potentials (MEPs) are useful for assessing the integrity of spinal cord motor tracts during major spine surgery. Anesthetic agents depress the amplitude of MEPs in a dose-dependent fashion. Anecdotal reports suggest that MEP responses degrade or "fade" over the duration of a surgery, despite unchanged anesthetic levels or other physiologic variables. This phenomenon has not been systematically analyzed. We performed a retrospective study of 418 patients who underwent spine surgery at UCSF using intraoperative MEP monitoring. We excluded patients who experienced variations in physiologic parameters that might affect MEP signals and those who developed new neurologic deficits. We identified 46 neurologically intact patients and 16 myelopathic patients who had surgery performed using a constant desflurane/N2O/narcotic or desflurane/propofol/narcotic anesthetic regimen. The minimum voltage threshold needed to produce an MEP response of at least 50 microV in amplitude was recorded at the beginning ("baseline") and end of surgery. The voltage threshold was higher at the end of the case than at baseline for each patient, regardless of anesthetic regimen. In normal patients, the rate of rise of the threshold was similar for those receiving propofol (11.4 +/- 6.9 V/hr) or N2O (9.7 +/- 5.9 V/hr) (P = not significant). Myelopathic patients demonstrated a larger rate of rise in voltage threshold, 23.4 +/- 12.2 V/hr, versus normal subjects (P < 0.01). The rate of rise of voltage threshold is inversely proportional to anesthetic duration. Prolonged exposure to anesthetic agents necessitates higher stimulating thresholds to elicit MEP responses, separate from the dose-dependent depressant effect. This retrospective study is limited and cannot explain the mechanism for this observed fade in signals. Recognition of anesthetic fade is essential when interpreting changes to the MEP response to avoid false-positive findings.

Adult↗