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Results for “physiologic variables”

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At least 343 records · Page 19Linked to original sources

PubMed1989

The propagation of uncertainty in human mortality processes operating in stochastic environments.

This paper presents a model describing how the uncertainty due to influential exogenous processes combines with stochasticity intrinsic to physiological aging processes and propagates through time to generate uncertainty about the future physiological state of the population. Variance expressions are derived for (a) the future values of the physiological variables under the assumption that external factors evolve under a linear stochastic diffusion process, and (b) the cohort survival functions and cohort life expectancies which reflect the uncertainty in the future values of the physiological variables. The model implies that a major component of uncertainty in forecasts of the physiological characteristics of a closed cohort is due to differential rates of survival associated with different realizations of the external process. This suggests that the limits to forecasting may be different in physiological systems subject to systematic mortality than in physical systems such as weather where the concepts of closed cohorts and of mortality selection have no simple analog.

Aging↗

PubMed1980

A computer simulation of physiological factors contributing to hyperventilation and breathlessness in cardiac patients.

A computer model of human respiration is of value for teaching the basic principles of respiratory physiology to students. An extension of this educational use is in the theoretical exploration of the relative importance of individual factors which may be contributing to disordered function in common clinical problems. For example, when a cardiac patient becomes breathless with increase in ventilation during exercise there are alterations in many physiological variables. The influence of their individual contributions on the total ventilation and thence possibly on breathlessness is often difficult to estimate. We present a theoretical analysis using MACPUF, a digital computer simulation of circulation and gas exchange which can be used to extimate the quantitative contribution of relevant physiological variables by altering them singly and in combination. Alterations in dead space, physiological shunt and pulmonary compliance individually produce only small increases in ventilation. Increased neurogenic drive (e.g. from lung reflexes triggered by pulmonary congestion) is a potentially important but very variable factor. A more important influence on ventilation appears when cardiac output is reduced and anaerobic metabolism simulated, causing changes in blood gas tensions and acidaemia which then change ventilation. Any increase in ventilation becomes more significant as a cause of breathlessness when ventilatory capacity is reduced, which in cardiac patients it not infrequently is.

Cardiac Output↗

PubMed2005

Correlations between granule cell physiology and bioenergetics in human temporal lobe epilepsy.

Human temporal lobe epilepsy (TLE) is associated with bioenergetic abnormalities including decreased phosphocreatine (PCr) normalized to ATP. The physiological consequences of these metabolic alterations have not been established. We hypothesized that impaired bioenergetics would correlate with alterations in physiological functions under conditions that strongly activate neural metabolism. We correlated several physiological variables obtained from epileptic human dentate granule cells studied in slices with hippocampal PCr/ATP measured using in vivo magnetic resonance spectroscopy. The physiological variables included: the ability to fire multiple action potentials in response to single stimuli, the inhibitory postsynaptic potential (IPSP) conductance and the responses to a 10 Hz, 10 s stimulus train. We noted a significant negative correlation between the ability to fire multiple spikes in response to single synaptic stimulation and PCr/ATP (P < 0.03) and a positive correlation between the IPSP conductance and PCr/ATP (P < 0.05). Finally, there was a strong correlation between PCr/ATP and the recovery of the membrane potential following a stimulus train (P < 0.01), with low PCr/ATP being associated with prolonged recovery times. These data suggest that the bioenergetic impairment seen in this tissue is associated with specific changes in excitatory and inhibitory neuronal responses to synchronized synaptic inputs.

Adenosine Triphosphate↗

PubMedDate not supplied

The relationship of depression to survival in chronic renal failure.

The authors examine the relationship between psychosocial factors and factors and survival of patients with chronic renal failure, while considering simultaneously the influence of parameters of physiologic functioning. Psychosocial and physiologic variables selected for discriminant analysis were extracted from data on 285 home-dialysis patients in Ontario, Canada. This analytical procedure defined which variables best discriminated between the survivor and nonsurvivor groups. The findings suggest that demographic and psychosocial factors may be more important than physiologic variables in determination of survival on home dialysis. The severity and type of depression is of particular importance to outcome.

Adjustment Disorders↗

PubMed1990

Plasma concentrations of salbutamol in acute severe asthmatics.

We studied prospectively 11 asthmatic patients presenting to the Accident and Emergency department with acute asthma. (Four patients reported historically that they were taking some form of oral salbutamol as part of their maintenance therapy.) Standard cardiovascular and respiratory parameters and plasma salbutamol concentrations were measured before and one hour after treatment with five milligrams of nebulised salbutamol. The median plasma salbutamol concentration before treatment was below the level of detection of the assay (less than 3 micrograms.l-1) with a range from less than 3 micrograms.l-1 to 34.6 micrograms.l-1. One hour post treatment the median plasma salbutamol concentration was 7.4 micrograms.l-1 (range less than 3.0 micrograms.l-1 to 56.0 micrograms.l-1) p less than 0.05. (Wilcoxons test). Correlations were investigated between the measured pretreatment physiological variables and pre-treatment plasma salbutamol concentrations. None were found to be significant. Similar analysis of the measured post-treatment physiological variables and post-treatment plasma salbutamol concentrations again revealed no significant correlations. However, a significant negative correlation was noted between the change in plasma salbutamol concentration with treatment and the change in respiratory rate (Rs = -0.56, p = 0.04). If asthmatics do indeed use high doses of inhaled beta-2-agonists (salbutamol) in an attempt to abort an acute attack (as many clinicians suspect), little, if any, of the drug appears to reach the systemic circulation. In this study the administration of five milligrams of nebulised salbutamol to acute asthmatics did not produce excessive increases in plasma salbutamol concentration, even in those patients taking oral salbutamol as part of their maintenance therapy.

Acute Disease↗

PubMed2000

Heart rate variability and physiological arousal in men exposed to 60 Hz magnetic fields.

In previous research, intermittent exposure to sinusoidal 60 Hz magnetic fields at a resultant flux density of 28.3 microT was found to alter heart rate variability (HRV) in men during night sleep. When the 24 men in the present study were exposed under similar conditions, HRV was not altered. The previous studies included the hourly collection of blood samples via an indwelling venous catheter, while the present study did not. This may account for the observed differences in results. Further research is needed to determine if field exposure interacts with physiological arousal mechanisms to alter autonomic nervous system control over cardiac rhythms.

Adolescent↗

PubMed1998

Chronobiological effects on exercise performance and selected physiological responses.

Previous studies investigating the impact of circadian rhythms on physiological variables during exercise have yielded conflicting results. The purpose of the present investigation was to examine maximal aerobic exercise performance, as well as the physiological and psychophysiological responses to exercise, at four different intervals (0800 hours, 1200 hours, 1600 hours, and 2000 hours) within the segment of the 24-h day in which strenuous physical activity is typically performed. Ten physically fit, but untrained, male university students served as subjects. The results revealed that exercise performance was unaffected by chronobiological effects. Similarly, oxygen uptake, minute ventilation and heart rate showed no time of day influences under pre-, submaximal, and maximal exercise conditions. Ratings of perceived exertion were unaffected by time of day effects during submaximal and maximal exercise. In contrast, rectal temperature exhibited a significant chronobiological rhythm under all three conditions. Under pre- and submaximal exercise conditions, significant time of day effects were noted for respiratory exchange ratio, while a significant rhythmicity of blood pressure was evident during maximal exercise. However, none of these physiological variables exhibited significant differential responses (percent change from pre-exercise values) to the exercise stimulus at any of the four time points selected for study. Conversely, resting plasma lactate levels and lactate responses to maximal exercise were found to be significantly sensitive to chronobiological influences. Absolute post-exercise plasma norepinephrine values, and norepinephrine responses to exercise (percent change from pre-exercise values), also fluctuated significantly among the time points studied. In summary, these data suggest that aerobic exercise performance does not vary during the time frame within which exercise is normally conducted, despite the fact that some important physiological responses to exercise do fluctuate within that time period.

Adult↗

PubMed2005

Assessment of sedation levels in pediatric intensive care patients can be improved by using the COMFORT "behavior" scale.

OBJECTIVES: The original COMFORT scale, including both observational and physiologic items, has been validated for measuring distress in children admitted to a pediatric intensive care unit. However, physiologic variables are influenced by drugs given in the pediatric intensive care unit setting. The objectives of this study were to assess the usefulness of physiologic variables in judgment of sedation and to determine new cutoff points for the COMFORT "behavioral" scale (COMFORT-B), using only observational items. DESIGN: Prospective observational study. SETTING: Pediatric intensive care unit in a university hospital. PATIENTS: Seventy-eight patients admitted to the pediatric intensive care unit. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: COMFORT scores were obtained in this patient group. Similar to the original COMFORT scale validation, the expert opinion of nurses (Nurse Interpretation Score of Sedation) served to determine optimal cutoff scores for the COMFORT-B scale. A total of 843 combined COMFORT and Nurse Interpretation Score of Sedation scores were obtained in 78 patients. Cronbach's alpha for the COMFORT scale was .78, increasing to .84 when the physiologic items, blood pressure and heart rate, were excluded. COMFORT scores were significantly different for the three Nurse Interpretation Score of Sedation categories (Kruskal-Wallis, p < .001). According to the pediatric intensive care unit nurses, undersedation was present in 11% and oversedation in 3% of all observations. Cutoff points for the COMFORT-B scale were </=10 for oversedation and >/=23 for undersedation. The area in the COMFORT-B score between 11 and 22 does not adequately predict under- or oversedation, pointing to a need for supplemental observation. CONCLUSIONS: The COMFORT-B scale is a reliable alternative to the original COMFORT scale. The cutoff points of the COMFORT-B scale in conjunction with the Nurse Interpretation Score of Sedation facilitate the use of sedation algorithms on the pediatric intensive care unit.

Adolescent↗

PubMedDate not supplied

Relationships among physiological and self-report responses produced by cocaine-related cues.

In response to cocaine cues, 150 subjects with a history of cocaine abuse showed decreases in skin temperature and skin resistance and increases in heart rate and reported craving, high, and withdrawal responses. These responses were consistent across four years of data collection. Craving reports were not consistently associated with either high or withdrawal responses, and many subjects endorsed increases in both high and withdrawal states. Correlations revealed no pattern of association among physiological variables and responding did not differ between subjects who did and those who did not report increases in each of the drug states. Finally, physiological variables did not predict reported drug states in discriminant analyses. Cocaine cue reactivity cannot be easily related to a unitary state of high, withdrawal, or craving. It is suggested that future studies focus more on the prediction and measurement of treatment outcome than on the form of cue responses.

Adult↗

PubMed1998

Fundamentals of tracer kinetics for radiologists.

With the increasing application of dynamic and functional techniques to radiological imaging modalities other than nuclear medicine, it is becoming increasingly important for radiologists to understand the principles of tracer kinetics and for functional and physiological aspects of imaging to be expanded in radiological training. Tracer, or indicator, kinetics can be broken down in six fundamental physiological variables (transit time, distribution volume, clearance, extraction fraction, blood flow and permeability-surface area product), three fundamental physical variables (time, mass and volume) and three fundamental equations (transit time equation, dilution equation and Fick equation). This teaching review defines the six fundamental physiological variables, discusses their relevance to functional imaging and describes how they may be measured using radiological techniques. It also illustrates how most of their tracer kinetics are based on one or other of the three fundamental equations.

Contrast Media↗

PubMed1985

Safe use of PEEP in patients with severe head injury.

Thirty-three patients with severe head trauma were studied to determine whether the use of positive end-expiratory pressure (PEEP) would cause an increase in intracranial pressure (ICP). Changes in ICP induced by PEEP were then correlated with a panel of physiological variables to try to explain these changes. Mean ICP increased from 13.2 +/- 7.7 mm Hg (+/- standard deviation) to 14.5 +/- 7.5 mm Hg (p less than 0.005) due to 10 cm H2O PEEP, but the eight patients with elevated baseline ICP experienced no significant increase. Cardiac output and venous admixture (Qs/Qt) declined significantly, while central venous pressure, peak inspiratory pressure, functional residual capacity, and arterial pCO2 increased significantly due to PEEP. Blood pressure and cerebral perfusion pressure were unchanged. The change in ICP due to PEEP correlated significantly with a combination of cardiac output, peak inspiratory pressure, Qs/Qt, and changes in blood pressure and arterial pCO2 due to PEEP, indicating that the effect of PEEP on ICP could be largely explained by its effect on hemodynamic and respiratory variables. No patient deteriorated clinically due to PEEP. It is concluded that 10 cm H2O PEEP increases ICP slightly via its effect on other physiological variables, but that this small increase in ICP is clinically inconsequential.

Brain Injuries↗

PubMed1998

The use of intensive care information systems alters outcome prediction.

OBJECTIVE: To study the effect of using an Intensive Care Information System (ICIS) on severity scores and prognostic indices: Acute Physiology and Chronic Health Evaluation II (APACHE II), Simplified Acute Physiology Score II (SAPS II), and Mortality Probability Models II (MPM II). DESIGN: Prospective pilot study. SETTING: A 20-bed medical-surgical intensive care unit (ICU) in a teaching hospital. PATIENTS: 50 consecutive adult patients admitted to the ICU on a bed equipped with an ICIS. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: In each patient all the physiologic variables, as required by the severity scores, were both manually charted and recorded by ICIS. ICIS registration resulted in the extraction of more abnormal values for all physiologic variables (except temperature): p < 0.05. Higher severity scores and mortality prediction were achieved by using ICIS charting: predicted mortality increased by 15% for APACHE II compared to manual charting, 25% for SAPS II, and 24% for MPM0. ICIS charting resulted in higher severity scores and mortality prediction for 29 of the 50 patients using APACHE II with a mean increase in mortality prediction in this subgroup of 27%. In the case of SAPS II, ICIS charting resulted in higher scores in 23 of the 50 patients and in the case of MPM0 in 13 patients, the mean increase in mortality in these subgroups being 64 and 148%, respectively. CONCLUSIONS: The use of ICIS charting to acquire the most abnormal physiologic values for severity scores and the derived prognostic indices results in a higher mortality prediction. Comparison of groups of patients and/or ICUs based on severity scores is impossible without standardization of data collection. The mortality prediction models have to be revalidated for the use of ICIS charting. While awaiting this, we suggest that every patient record in local regional, national, or international ICU databases should be marked as being recorded by manual or by ICIS charting.

Humans↗

PubMed1995

Intrahospital transport of critically ill pediatric patients.

OBJECTIVES: To determine the frequency of adverse events during intrahospital transport; to determine the requirement of therapeutic interventions during transport; to test the hypothesis that adverse events that occur during intrahospital transport are due to the transport process itself; and to determine the factors that predict the occurrence of adverse events and the requirement of major therapeutic interventions during transport. DESIGN: A two-phase study in which data were prospectively collected. In phase I, we examined the occurrence rate of adverse events, the requirement for therapeutic interventions, and the factors that predicted adverse events and the requirement of therapeutic interventions. In phase II, we tested the hypothesis that adverse events during transport were due to the transport process itself. SETTING: A 250-bed university children's hospital with a 50-bed intensive care unit (ICU). PATIENTS: Phase I of the study consisted of one hundred and eighty intrahospital transports in 139 patients. These transports included patients who were transferred: a) to the ICU from the operating room, emergency department, or the general ward; b) from the ICU to the operating room; and c) from the ICU for diagnostic or therapeutic procedures. Phase II of the study consisted of 89 transports in 85 patients. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Vital signs and oxygen saturation were measured before and during transport. In phase I, there were no adverse events in 23.9% of transports. There was a significant change in at least one physiologic variable in 71.7% of transports, and at least one equipment-related mishap in 10% of transports. At least one major intervention was performed in 13.9% of transports in response to physiologic deterioration or an equipment-related mishap. There were no arrests or deaths during transport. The requirement for a major procedure was 34.4% in mechanically ventilated patients vs. 9.5% in nonventilated patients. Logistic regression analysis showed that both pretransport Therapeutic Intervention Scoring System and the duration of transport were significantly associated with the requirement of a major intervention and physiologic deterioration, while only the duration of transport was associated with an equipment-related event. The age of the patient and the number of escorts accompanying the transport did not affect the frequency of adverse events. Before transport in phase II study patients, no patient became hypothermic, the changes in physiologic variables were always < 20%, and there was no change > or = 5% in oxygen saturation. Hypothermia occurred in 11.2% of transports. A > or = 20% change in heart rate (15.7%), blood pressure (21.3%), and respiratory rate (23.6%) was seen only during transport. A > 5% change in oxygen saturation (5.6%) was seen only during transport. CONCLUSIONS: Serious physiologic deterioration occurs during intrahospital transport of critically ill children. Severity of illness and the duration of transport are associated with the occurrence of adverse events during transport. The team composition and equipment required on transport must be commensurate with the pretransport severity of illness and the anticipated duration of transport.

Adolescent↗

PubMed1984

Biological 'markers' for endogenous depression. Effect of age, severity of illness, weight loss, and polarity.

The dexamethasone suppression test (DST) can differentiate between endogenous and nonendogenous depression. Similarly, EEG sleep patterns can differentiate primary from secondary depression, and this technique has also been used to make the endogenous-nonendogenous discrimination. However, a number of physiological variables associated with this diagnostic distinction may also affect the DST results and sleep architecture. With the use of multivariate statistical procedures, we found that although age and weight loss affect the results of both tests, both the DST and sleep EEG differentiate endogenous from nonendogenous depression when these variables are taken into account. Severity of illness affected both proposed diagnostic markers, but did not account for the differences between diagnostic groups, alone or when added to the physiological variables. The DST was more sensitive in unipolar than in bipolar endogenous depression, but there were no significant differences in the sleep of unipolar and bipolar patients.

Adult↗

PubMed1989

Physiologic testing of the ultraendurance triathlete.

With the ever growing popularity of the sport of triathlon, numerous studies have been done in an attempt to characterize the triathlete and to identify physiologic variables important to success in triathlon racing. Studies of the ultraendurance triathlete fall into the following categories: 1) general physical and physiologic characterizations, 2) metabolic responses to prolonged exercise, and 3) the relationship of physiologic test variables to actual competitive performance. Physically and physiologically, triathletes tend to resemble other endurance athletes, with many characteristics similar to elite endurance cyclists. VO2max is widely variable in triathletes and has been reported to range from 40 to 85 ml.kg-1.min-1. The physiologic bases for success in ultraendurance triathlons are not clearly understood at this time. Physiologic variables that have been investigated include VO2max, cycling economy, %VO2max, and %HRmax at lactate and ventilatory thresholds and sustained %HRmax under actual race conditions. Although all of these factors appear to interrelate to influence actual triathlon race performance, the exact interrelationship is unclear at this time.

Adult↗

PubMed1996

The influence of genotype and environment on the physiological and metabolic diversity of Fusarium compactum.

Fungal species produce a large variety of secondary metabolites which are of considerable interest to the pharmaceutical industry. It is clear that the secondary metabolite production of a species varies significantly in strains from different geographic locations and from different habitats. The influence of genotype and environment on metabolite production is, however, poorly understood. In this study we examined the influence of genotypic variability, physiological variability, environmental location, and habitat on metabolite production by Fusarium compactum. Isolates of the fungus from two geographic locations and two distinct habitat types were examined for growth on 95 different carbon sources, and genotypic variability was determined using RAPDs and rDNA-RFLP analysis. In a blind test secondary metabolite production was assessed using HPLC profiles of methanolic cell extracts. A number of correlations were observed between genotypic groupings, as determined using parsimony, and specific metabolic production. Similar correlations were also observed with physiological groups although genotypic analysis proved to be a more sensitive predictor of metabolite variability. The data suggest a complex relationship between environment, genotype, and metabolite production but highlight the use of genetic screening as a means of optimizing the changes of identifying a wide range of metabolites from a given species.

Base Sequence↗

PubMed2005

Homeostasis as basis of acute stroke treatment: stroke units are the key.

INTRODUCTION: Several studies suggest that the control of blood pressure (BP), blood glucose level, body temperature, and oxygen saturation, when analyzed separately, is related with successful acute stroke outcome. However, in a biological system these parameters are interrelated and could influence the process. Recent studies highlight the importance of the appropriate maintenance of these variables that are involved in homeostasis in patients with stroke and the influence they have on outcome. METHODS: A review was conducted of published studies which analyzed the influence of control of these physiological variables in acute stroke, whether in isolation or combinations, and we have contributed our own data derived from observational studies. RESULTS: The maintenance of homeostasis forms the basis of acute stroke treatment, in what is termed nonpharmacological neuroprotection. Stroke units (SU) are the ideal environment for this therapeutic approach since their favorable influence on the correct management of BP, body temperature, oxygen saturation, and blood glucose in the progress of stroke patients have been proved. CONCLUSIONS: The proper management of physiological variables (homeostasis) such as BP, body temperature, blood glucose, and oxygen saturation is the basis of acute stroke treatment, and SU are the key to this approach.

Blood Glucose↗

PubMed1988

Pediatric risk of mortality (PRISM) score.

The Pediatric Risk of Mortality (PRISM) score was developed from the Physiologic Stability Index (PSI) to reduce the number of physiologic variables required for pediatric ICU (PICU) mortality risk assessment and to obtain an objective weighting of the remaining variables. Univariate and multivariate statistical techniques were applied to admission day PSI data (1,415 patients, 116 deaths) from four PICUs. The resulting PRISM score consists of 14 routinely measured, physiologic variables, and 23 variable ranges. The performance of a logistic function estimating PICU mortality risk from the PRISM score, age, and operative status was tested in a different sample from six PICUs (1,227 patients, 105 deaths), each PICU separately, and in diagnostic groups using chi-square goodness-of-fit tests and receiver operating characteristic (ROC) analysis. In all groups, the number and distribution of survivors and nonsurvivors in adjacent mortality risk intervals were accurately predicted: total validation group (chi 2(5) = 0.80; p greater than .95), each PICU separately (chi 2(5) range 0.83 to 7.38; all p greater than .10), operative patients (chi 2(5) = 2.03; p greater than .75), nonoperative patients (chi 2(5) = 2.80, p greater than .50), cardiovascular disease patients (chi 2(5) = 4.72; p greater than .25), respiratory disease patients (chi 2(5) = 5.82; p greater than .25), and neurologic disease patients (chi 2(5) = 7.15; p greater than .10). ROC analysis also demonstrated excellent predictor performance (area index = 0.92 +/- 0.02).

Child, Preschool↗