SEARCH · PubMed Health

Results for “physiologic variables”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources

PubMed2001

Thermoregulation through skin under variable atmospheric and physiological conditions.

Considering three layers of the skin and subcutaneous region, an attempt has been made to obtain the analytical and numerical solutions for temperature distribution of the bioheat equation. The problem is studied under variable physiological parameters and atmospheric conditions. The role of metabolic heat generation, blood mass flow and perspiration in different thicknesses have been noted. The numerical solutions for different parametric values are shown graphically.

Body Temperature Regulation↗

PubMed1989

Blood doping--a literature review.

There is increasing evidence that the technique of reinfusing an athlete's stored blood prior to competition to improve performance has been used on many occasions. Although early experimental results were controversial and the precise mechanism by which the technique improves performance is still debated, there is now strong evidence that if the blood doping produces a sufficient rise in total red cell mass there are significant improvements in physiological variables such as maximum oxygen uptake, lactate buffering and thermoregulation. These physiological changes are matched by improvements in endurance performance. These may persist in diminishing degree for several weeks, but have to be weighed against the detraining effect produced by the repeated venesection required to obtain an adequate amount of stored blood for autologous reinfusion. Experimental evidence suggests that the transient increase in blood volume and cardiac output following reinfusion is too short lived to be of any real importance and the major effect is related to the increase in total red blood cell mass and haemoglobin enabling an increased transport of oxygen and therefore a potentially greater reserve of blood which can be diverted to non-exercising tissues to improve thermoregulation. The increased red cell mass also improves lactate buffering. Although these benefits have been shown in several studies the increases in performance and measured physiological parameters do not bear a direct relationship to the changes in haematological variables. Blood doping is of considerable importance, not only as an abuse of fair competition, but also because of the light it throws on the physiological limits to endurance performance. It has reawakened controversy as to whether oxygen transport is the limiting factor in endurance.

Blood↗

PubMed2003

Precision of the CASL-perfusion MRI technique for the measurement of cerebral blood flow in whole brain and vascular territories.

PURPOSE: To analyze the precision of cerebral blood flow (CBF) measurements made with continuous arterial spin labeling(CASL) perfusion magnetic resonance imaging (MRI) over experimentally relevant intervals. MATERIALS AND METHODS: CASL perfusion MRI measurements of CBF on a 1.5-T GE Signa magnet were repeated in young healthy male and female subjects at one hour and one week. Precision of the measurement was evaluated at both time intervals. RESULTS: CASL perfusion MRI measurements of CBF yielded within-subject coefficients of variation (wsCV) of 5.8% for global and 13% for individual vascular regions when measurements were repeated within one hour. Differences in these values represent the error in post-processing. Global and regional CBF measurements over one week yielded wsCVs of 13% and 14%, respectively. At one week, error secondary to physiologic variability affected global and regional measurements to the same degree and masked the software post-processing error seen at one hour. The magnitude of the difference in repeated measures correlated with the magnitude of the measurement. CONCLUSION: CASL perfusion MRI CBF measurements are accurate and precise. Variability over longer periods of time appears attributable to physiologic factors. Repeatability of the CASL measurement is sensitive to the magnitude of the measurement. This should be taken into account when studies requiring repeated measures involve subjects with significant variability in CBF.

Adult↗

PubMed2000

Negative fluid balance predicts survival in patients with septic shock: a retrospective pilot study.

OBJECTIVE: We hypothesized that patients with septic shock who achieve negative fluid balance (< or =-500 mL) on any day in the first 3 days of management are more likely to survive than those who do not. DESIGN: Retrospective chart review. PATIENTS: Thirty-six patients admitted with the diagnosis of septic shock. SETTING: Twelve-bed medical ICU of a 300-bed community teaching hospital. METHODS: Medical records of 36 patients admitted to our medical ICU over a 21-month period were examined. Patients with septic shock who required dialysis prior to hospitalization were not included. A number of demographic and physiologic variables were extracted from the medical records. Admission APACHE (acute physiology and chronic health evaluation) II and daily sequential organ failure assessment (SOFA) scores were computed from the extracted data. Variables were compared between survivors and nonsurvivors and in patients who did vs those who did not achieve negative (< or = 500 mL) fluid balance in > or = 1 day of the first 3 days of management. Survival risk ratios (RRs) were used as the measure of association between negative fluid balance and survival. RRs were adjusted for age, APACHE II scores, SOFA scores on the first and third days, and the need for mechanical ventilation, by stratified analyses. RESULTS: Patients ranged in age from 16 to 85 years with a mean (+/- SE) age of 67.4 +/- 3.3 years. The mean admission APACHE II score was 25.4 +/- 1.4, and the day 1 SOFA score was 9.0 +/- 0.8. Twenty patients did not survive; nonsurvivors had higher mean APACHE II scores than survivors (29.8 vs 20.4, respectively) and higher first day SOFA scores than survivors (10.8 vs 6.9, respectively), and they were more likely to require vasopressors and mechanical ventilation compared to patients who survived. Whereas all 11 patients who achieved a negative balance of > 500 mL on > or = 1 of the first 3 days of treatment survived, only 5 of 25 patient who failed to achieve a negative fluid balance of > 500 mL by the third day of treatment survived (RR, 5.0; 95% CI, 2.3 to 10.9; p = 0.00001). At least 1 day of net negative fluid balance in the first 3 days of treatment strongly predicted survival across the strata of age, APACHE II scores, first- and third-day SOFA scores, the need for mechanical ventilation, and creatinine levels measured at admission. CONCLUSION: These results suggest that at least 1 day of negative fluid balance (< or = -500 mL) achieved by the third day of treatment may be a good independent predictor of survival in patients with septic shock. These findings suggest the hypothesis "that negative fluid balance achieved in any of the first 3 days of septic shock portends a good prognosis," for a larger prospective cohort study.

APACHE↗

PubMed1993

Outcome of intra-abdominal infection in pigs depends more on host responses than on microbiology.

OBJECTIVE: To assess the effects of mortality of the presence and proliferation of bacteria, and the host's response to infection, in pigs with peritonitis. DESIGN: Laboratory study. SETTING: University hospital. MATERIAL: 71 Swedish Landrace pigs, 63 with peritonitis and 8 without (controls). INTERVENTIONS: Induction of peritonitis by intraperitoneal infusion of equal amounts of Escherichia coli and Bacteroides fragilis (10(9) to 10(11) bacteria/animal); sterile faeces were added in half the experiments. MAIN OUTCOME MEASURES: Microbiological events were quantified as the area under the bacterial concentration curve from 0-6 hours. Host responses were quantified with a score of 8 physiological variables measured between 4-6 hours after the induction of peritonitis. RESULTS: Of the 63 infected animals, 37 (59%) died within 6-24 hours and both the physiological response and the bacterial load were significantly higher in those that died. Logistic regression analysis with death as the dependent variable showed that the physiology score carried more predictive information than the quantification of bacterial load. CONCLUSION: The quantification of local events within the abdomen is of only limited predictive value compared with the extent of the physiological alterations.

Animals↗

PubMed2000

Head injury as a predictor of psychological outcome in combat veterans.

Although it is recognized that psychosocial variables influence the expression of psychopathology following trauma exposure, physiological variables have received less attention as potential mediators of psychological outcome in trauma victims. The purpose of this study was to examine the relationship of head injury to psychological outcome in 171 combat veterans seeking compensation for service-connected disabilities for mental disorders attributed to etiologies other than head injury. Veterans underwent structured psychiatric diagnostic interview and completed self-report measures of combat exposure, posttraumatic stress disorder (PTSD), depression, and occurrence of head injury. Comparisons between veterans with and without history of head injury indicated that head injury was associated with more severe depression. Regression analysis suggested that head injury predicted depression, but not PTSD, severity.

Adult↗

PubMed1997

Relationship of body mass index to subsequent mortality among seriously ill hospitalized patients. SUPPORT Investigators. The Study to Understand Prognoses and Preferences for Outcome and Risks of Treatments.

OBJECTIVE: To determine if body mass Index (BMI = weight [kg]/height [m]2), predictive of mortality in longitudinal epidemiologic studies, was also predictive of mortality in a sample of seriously ill hospitalized subjects. DESIGN: Prospective, multicenter study. SETTING: Five tertiary care medical centers in the United States. PATIENTS: Patients > or = 18 yrs of age who had one of nine illnesses of sufficient severity to anticipate a 6-month mortality rate of 50% were enrolled at five participating sites in the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Patients were asked their current height and weight as part of the demographic data. Stratifying body mass index by percentile rank (< or = 15, 15 to 85, and > or = 85th percentiles), risk ratios for mortality were calculated by Cox Proportional Hazards using the 15th to 85th percentile of body mass index as the reference group while controlling for multiple variables such as prior weight loss, albumin, and Acute Physiology Score. A body mass index in the < or = 15th percentile was associated with an excess risk of mortality (risk ratio = 1.23; p < .001) within 6 months. High body mass index (> or = 85th percentile) was not significantly related to risk of mortality. CONCLUSIONS: Body mass index, a simple anthropometric measure of nutrition employed in community epidemiologic studies, has now been demonstrated to be a predictor of mortality in an acutely ill population of adults at five different tertiary centers. Even when controlling for multiple disease states and physiologic variables and removing from the analysis all patients with significant prior weight loss, a body mass index below the 15th percentile remained a significant and independent predictor of mortality. Examination of patient vs. proxy data did not change the results. Future studies examining variables predictive of mortality should include body mass index, even in acutely ill populations with a poor probability of survival.

APACHE↗

PubMed1990

Computer-assisted long-term measurements of urinary output and other biological data.

A computerized system is described, combining automatic collection of urine in short intervals (minutes) over long periods (days) and recordings of body temperature, MABP, and heart rate in chronically instrumented conscious dogs. During the studies the dogs are housed in metabolic cages. Indwelling catheters and electrical wires are connected to a specially designed swivel and directed out of the cage to the next room. Infusions, blood sampling, and monitoring can be performed from this room without disturbance to the dogs. Three examples of recordings are given. In one of these examples the sodium excretion patterns on 5 consecutive days under continuous saline infusion in one dog is evaluated. Urine was collected every 20 min. Sodium excretion showed cyclic variations. Fourier analysis exhibited 18-h periods and 4- to 8-h periods. The described system renders, e.g., coherent time series analysis possible for a variety of simultaneously recorded physiological variables and may thus acquire considerable importance for integrative physiology.

Animals↗

PubMed1984

Cardiovascular risk factors and life changes.

Many variables are considered risk factors for cardiovascular disease. This study examines the associations among a psychological variable (type A personality measurement), a social variable (Holmes and Rahe Schedule of Recent Events), and physiologic variables (age, blood pressure, smoking, and cholesterol), as measured to fill out a health hazard appraisal. These tests and questionnaires were administered to 572 persons from the San Francisco Bay area when they enrolled in a health promotion program (Common Health Care). Recent life changes and a self-measurement of coronary prone behavior showed no significant correlations to major heart disease risk factors.

Adult↗

PubMedDate not supplied

Fatigue in early pregnancy. An exploratory study.

The experience of fatigue in early pregnancy was studied, using a general model of fatigue as the conceptual framework. A convenience sample of 30 women, age 20-35 years, who were at less than 20 weeks' gestation and without health problems were included in the study. Physiologic, psychological, and environmental factors were measured and related to the occurrence and intensity of fatigue. Pearson correlations and content analysis were used to analyze the data. Results showed that a large portion of the sample (90%) experienced fatigue and that this fatigue had a significant impact on their ability to maintain personal and social activities. Significant correlations were observed between fatigue and the physiologic variables of nausea and feeling tired upon awakening from sleep. There was no significant relationship between fatigue and environmental variables such as number of hours worked or the number of children living in the home. In addition, significant correlations were observed between fatigue and psychological variables that included depression, anger, anxiety, and confusion. These data suggest that fatigue is a significant problem for pregnant women and is not relieved by rest. These data further suggest that the fatigue may be related to other physiologic changes, perhaps hormonal, that mediate physiologic and psychological variables, including fatigue.

Adaptation, Psychological↗

PubMed1983

Expectancy and heart rate as predictors of the speech performance of stutterers.

Three adult stutterers who displayed a preexperimental pattern of consistent expectation and occurrence of stuttering were studied in a single-subject design. Multiple linear regression analyses led to the conclusion that cognitive (signalled) expectancy was predictive of stuttering for two of the subjects. The third subject evidenced essentially no relationship between signalled expectancy and disfluent performance. For two subjects, neither mean heart rate nor heart rate variability was predictive of speech performance. For the third subject, mean heart rate was predictive but heart rate variability was not. For two subjects, there was essentially no relationship between the measured physiologic variables and cognitive expectancy. However, for the third subject both mean heart rate and heart rate variability were significantly predictive of cognitive expectancy. These results suggest that adult stutterers should not be viewed as a homogeneous group with respect to preutterance activity that is either cognitive or physiologic. The relationship between preutterance heart rate, heart rate variability, and expectancy responses and between these preutterance variables and subsequent stuttering appears to be individualistic.

Adolescent↗

PubMed2005

Control of end-tidal PCO2 reduces middle cerebral artery blood velocity variability: implications for physiological neuroimaging.

Breath-by-breath variability of the end-tidal partial pressure of CO2 (Pet(CO2)) has been shown to be associated with cerebral blood flow (CBF) fluctuations. These fluctuations can impact neuroimaging techniques that depend on cerebrovascular blood flow. We hypothesized that controlling Pet(CO2) would reduce CBF variability. Dynamic end-tidal forcing was used to control Pet(CO2) at 1.5 mm Hg above the resting level and to hold the end-tidal partial pressure of oxygen (Pet(O2)) at the resting level. Peak blood velocity in the middle cerebral artery (MCA) was measured by transcranial Doppler ultrasound (TCD) as an index of CBF. Blood velocity parameters and timing features were determined on each waveform and the variance of these parameters was compared between Normal (air breathing) and Forcing (end-tidal gas control) sessions. The variability of all velocity parameters was significantly reduced in the Forcing session. In particular, the variability of the average velocity over the cardiac cycle was decreased by 18.2% (P < 0.001). For the most part, the variability of the timing parameters was unchanged. Thus, we conclude that controlling Pet(CO2) is effective in reducing CBF variability, which would have important implications for physiologic neuroimaging.

Adult↗

PubMed2001

Can nutrition influence circadian rhythm and heart rate variability?

Recent studies indicate that there is an interaction between biorhythms, the biological clock and triggers, which may be important in the pathogenesis of altered heart rate variability (HRV) and blood pressure variability (BPV). Circadian rhythms are under the influence of, and physiological variables are mediated by the activation of the adrenals, sympathetic/parasympathetic, hypothalamic and pituitary activity. Emotional stress, physical exertion, sleep deprivation and large fatty meals are major triggers of myocardial ischemia, angina, infarction, sudden cardiac death (SCD) and stroke. These events have been reported to exhibit a circadian variation with increased frequency in the second quarter of the day, which has also been observed in our studies on Indians. Recent studies indicate that altered HRV and BPV are also important in the pathogenesis and progression of heart failure, atheroma and thrombosis. Mediation via beta-blockers, oestrogens, n-3 fatty acids, vitamin E and coenzyme Q10 and fasting appears to have a beneficial influence whereas progestins, nifedipine, stress and exercise may have an adverse effect on HRV and BPV. We have reported that plasma levels of vitamin E and C are lower in the second quarter of the day than at other times, indicating their role in the pathogenesis of variability and cardiac events. Prospective studies also indicate that HRV and BPV are important and independent risk factors for cardiovascular events. However, no study has yet been conducted in patients with abnormal HRV and BPV in a randomized, placebo-controlled intervention trial to find out whether improvement in variability can cause a significant reduction in cardiovascular events. There is a need to study the role of n-3 fatty acids, coenzyme Q10, the effect of regular physical training, medication and ACE inhibitors in patients with abnormal HRV and BPV to demonstrate that improving variability can modulate cardiovascular events.

Animals↗

PubMed2004

Effectiveness of multidisciplinary patient counselling in reducing cardiovascular disease risk factors through nonpharmacological intervention: results from the Healthy Heart Program.

BACKGROUND: The value of lifestyle modification in reducing physiological cardiovascular disease (CVD) risk factors remains controversial because changes in patient behaviour following CVD prevention counseling have failed to correlate with or impact reductions in physiological variables. OBJECTIVES: To determine whether nonpharmacological CVD prevention counselling significantly reduces behavioural and physiological risk factors, and to examine correlations between changes in these variables. METHODS: At baseline, dyslipidemic individuals with or at risk of developing CVD completed CVD risk factor questionnaires. At baseline and three months, participants submitted dietary logs, self-classified their readiness for behaviour change for eight lifestyles, and had their blood lipid profiles, weight and height assessed. Following CVD risk factor screening, lower and higher risk participants were recommended for multidisciplinary group counselling (GC) or group plus individual counselling (GIC), respectively. A prospective time series design assessed behavioural and physiological risk factor changes. RESULTS: Participants progressed forward (P<0.01) through the stage of change continuum for all behaviours. GIC participants progressed to a higher average stage of behaviour change for achieving optimal body weight (P<0.01), drinking less alcohol (P<0.05) and controlling blood pressure (P<0.05). Significant reductions in body mass index (2.1% and 1.9%), total cholesterol (7.0% and 5.5%), low density lipoprotein cholesterol (6.2% and 5.4%), total cholesterol to high density lipoprotein cholesterol ratio (5.1% and 3.8%) and triglyceride levels (10.8% and 8.5%) were observed in GC and GIC participants, respectively. Furthermore, significant correlations were observed between concurrent changes in lifestyle behaviour and physiological risk factors. CONCLUSIONS: Multidisciplinary CVD prevention counseling positively influenced participant readiness for lifestyle behaviour change which translated into significant reductions in several physiological risk factors.

Adult↗

PubMed1989

Sleep-related bruxism and sleep variables: a critical review.

Relationships between sleep-related bruxing, electroencephalographic phenomena, and other physiologic variables are reviewed. Bruxing occurs during all sleep stages but occurs disproportionately during stage 2 and REM. Bruxing during deeper sleep stages frequently is followed by a transition to lighter sleep. Bruxing occurs in conjunction with K-complexes in the EEG, tachycardia and peripheral blood volume changes, and gross body movements; however, the exact nature of the relationship between bruxing and "arousal" is unknown. Methodological problems are pervasive. On-line computer-based event recording is called for along with time series analyses of moment-to-moment psychophysiologic data.

Bruxism↗

PubMed2002

Comparison of five bilevel pressure ventilators in patients with chronic ventilatory failure: a physiologic study.

OBJECTIVE: To compare patient-ventilator interaction and comfort in patients with chronic ventilatory failure (CVF) who are undergoing noninvasive positive-pressure ventilation with five different commercial bilevel pressure home ventilators. Also, we wanted to evaluate the short-term effects of the five ventilators on physiologic variables, namely, breathing patterns and inspiratory muscles. DESIGN: Randomized, controlled physiologic study. SETTING: Pulmonary division of a rehabilitation institution. PATIENTS: Twenty-eight patients with CVF due to COPD (17 patients) and restrictive chest wall diseases (11 patients). MEASUREMENTS: Sensation of comfort, breathing patterns and minute ventilation (E), respiratory muscles and mechanics, and patient-ventilator interaction during both unassisted and assisted ventilation with the five ventilators applied randomly. RESULTS: The five ventilators showed different flow and pressure waveforms. The level of comfort was somehow different among the studied ventilators. When compared to unassisted ventilation, all ventilators induced a significant increase in E (p < 0.01) without any significant difference among ventilators. Use of the five ventilators resulted in significant differences in peak airway opening pressure (Pao,peak) but not in mean airway opening pressure computed over a period of 1 min (PTPao,min), and in a duty cycle. Ineffective efforts (IEs) were similar among the studied ventilators. In comparison with unassisted ventilation, all ventilators induced significant reductions in inspiratory muscle effort (p < 0.001). No significant relationship was found between level of comfort and PTPao,min, Pao,peak, or the number of IEs. CONCLUSIONS: In stable, awake patients with CVF, all of the studied ventilators were well-tolerated, although with a great intersubject variability in comfort, and performed well in terms of improvement in E and inspiratory muscle unloading, thus fulfilling the aims of mechanical ventilation. This effect was obtained with similar levels of PTPao,min, despite the fact that Pao,peak was different among some ventilators. The number of IEs was similar among the studied ventilators.

Aged↗

PubMed1990

Mild hypoglycemia associated with deterioration of mental efficiency in children with insulin-dependent diabetes mellitus.

To assess the effects of mild hypoglycemia on cognitive functioning in diabetic children, we used an insulin glucose clamp technique to induce and maintain a hypoglycemic state. Eleven patients, 11 to 18 years of age, completed a series of cognitive tests during a baseline euglycemic state (100 mg/dl (5.5 mmol/L] and repeated those measures at the beginning and end of a hypoglycemic plateau (55 to 65 mg/dl (3.1 to 3.6 mmol/L], and again at restoration of euglycemia. At plasma glucose levels of 60 to 65 mg/dl (3.3 to 3.6 mmol/L), a significant decline in mental efficiency was found. This was most apparent on measures of mental "flexibility" (Trial Making Test) and on measures that required planning and decision making, attention to detail, and rapid responding. Moreover, complete recovery of cognitive function was not contemporaneous with restoration of euglycemia, particularly on those tests requiring rapid responding and decision making (choice reaction time). Not all subjects showed evidence of cognitive impairment during hypoglycemia. The very high degree of intersubject variability suggests that, in addition to plasma glucose values, unknown physiologic variables are responsible for triggering cognitive impairments in school-aged youngsters with diabetes during an episode of mild hypoglycemia.

Adolescent↗

PubMedDate not supplied

Construction of age-related reference limits for 24-h blood pressure pattern.

Blood pressure (BP) is recursively variable during the day-night cycle because of a physiological circadian rhythm. The aim of this study is, therefore, to show how to construct the population reference limits (desms) for BP in its time varying 24-h pattern, starting from a small sample, in order to facilitate their use in a local context. The sample for standardization comprised 427 clinically healthy subjects (211 males and 216 females), ranging in age from 16 to 100 years, attending their routine activities. The procedure begins with the statistical biometry related to the sample, and proceeds with the computation of the BP desms related to (1) the time-qualified discrete values; (2) the parameters of circadian rhythm; (3) the daily pressure load. The pertaining rules are explained step by stop, allowing each one to prepare the proper local desms for BP 24-h pattern. These standards may be useful for validating the individual BP monitoring according to the upper limits of the circadian physiological variability in the diagnostic procedure for identifying hypertensive subjects.

Adolescent↗