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Results for “Surrogate variables analysis”

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PubMed2001

Clinical deterioration following improvement in the NINDS rt-PA Stroke Trial.

BACKGROUND AND PURPOSE: Little is known in regard to cerebral arterial reocclusion after successful thrombolysis. In the absence of arteriographic information, the National Institute of Neurological Disorders and Stroke (NINDS) rt-PA Stroke Trial investigators prospectively identified clinical deterioration following improvement (DFI) as a possible surrogate marker of cerebral arterial reocclusion after rt-PA-induced recanalization. Also, we identified any significant clinical deterioration (CD) even if not preceded by improvement. This observational analysis was designed to determine the incidence of DFI and CD in each treatment group, to identify baseline or posttreatment variables predictive of DFI or CD, and to determine any relationship between DFI, CD, and clinical outcome. METHODS: DFI was defined as any 2-point deterioration on the NIH Stroke Scale after an initial 2-point improvement after treatment. CD was defined as any 4-point worsening after treatment compared with baseline. All data were collected prospectively by investigators blinded to treatment allocation. A noncontrast brain CT was mandated when a 2-point deterioration occurred. All cases were validated by a central review committee. RESULTS: DFI was identified in 81 of the 624 patients (13%); 44 were treated with rt-PA and 37 were treated with placebo (P:=0.48). DFI occurred more often in patients with a higher baseline NIH Stroke Scale score. CD within the first 24 hours occurred in 98 patients (16% of all patients); 43 were given rt-PA and 55 were given placebo (P:=0.19). Baseline variables associated with CD included a less frequent use of prestroke aspirin and a higher incidence of early CT changes of edema or mass effect or dense middle cerebral artery sign. Patients with CD had higher rates of increased serum glucose and fibrin degradation products, and they also had higher rates of symptomatic intracranial hemorrhage and death. Patients who experienced either DFI or CD were less likely to have a 3-month favorable outcome. CONCLUSIONS: We found no association between DFI, CD, and rt-PA treatment, and no clinical evidence to suggest reocclusion. Deterioration was strongly associated with stroke severity and poor outcome and was less frequent in patients whose stroke occurred while they were on aspirin.

Disease Progression↗

PubMed2006

Patterns of C-reactive protein release following allogeneic stem cell transplantation are correlated with leukemic relapse.

The C-reactive protein (CRP) is an acute-phase protein produced by hepatocytes, and is a reliable marker of systemic inflammation, which is relevant to the release of the proinflammatory cytokines. The value of monitoring the CRP levels after stem cell transplantation (SCT) can identify patients at risk of treatment-related complications and mortality. Inflammatory cytokines facilitate donor T-cell activation via antigen presenting cells immediately after SCT. This study examined the relationship between the post-SCT CRP levels and a leukemic relapse. Fifty-four consecutively transplanted patients who relapsed after the allogeneic SCT were compared with nonrelapsing patients. The serum CRP levels were measured on day 0 and every 7 days thereafter until 4 weeks after the SCT. The mean CRP levels throughout the early post-SCT episode were significantly lower in the relapsing patients than in those who did not experience relapse (mean+/-s.e.: 26.8 +/- 6.3 vs 65.3 +/- 9.4 for first week, P = 0.001; 23.9 +/- 3.8 vs 44.6 +/- 6.6 for second week, P = 0.008). Univariate analysis showed that the CRP level on the first and second week, and graft-versus-host disease were significantly associated with a relapse. Multivariate analysis showed that the CRP level on the first week was the strongest independent variable predicting the risk of a relapse after SCT (P = 0.04). These results indicate that the serum CRP levels early after allogeneic SCT might display the graft-versus-leukemia (GvL) effect. CRP is a surrogate of the proinflammatory cytokine release that was not measured in this study. The GvL effect appears to be efficiently strengthened by the high CRP levels that may be reflecting T-cell activation.

Adolescent↗

PubMed1995

Nonlinear time series analysis of electrocardiograms.

In recent years there has been an increasing number of papers in the literature, applying the methods and techniques of Nonlinear Dynamics to the time series of electrical activity in normal electrocardiograms (ECGs) of various human subjects. Most of these studies are based primarily on correlation dimension estimates, and conclude that the dynamics of the ECG signal is deterministic and occurs on a chaotic attractor, whose dimension can distinguish between healthy and severely malfunctioning cases. In this paper, we first demonstrate that correlation dimension calculations must be used with care, as they do not always yield reliable estimates of the attractor's "dimension." We then carry out a number of additional tests (time differencing, smoothing, principal component analysis, surrogate data analysis, etc.) on the ECGs of three "normal" subjects and three "heavy smokers" at rest and after mild exercising, whose cardiac rhythms look very similar. Our main conclusion is that no major dynamical differences are evident in these signals. A preliminary estimate of three to four basic variables governing the dynamics (based on correlation dimension calculations) is updated to five to six, when temporal correlations between points are removed. Finally, in almost all cases, the transition between resting and mild exercising seems to imply a small increase in the complexity of cardiac dynamics. (c) 1995 American Institute of Physics.

Journal Article↗

PubMed2000

Stress test and gastric-arterial PCO2 measurement improve prediction of successful extubation.

OBJECTIVE: Correct early prediction of successful extubation decreases morbidity and mortality. The use of single time point measurements and surrogate markers of true extubation success limits weaning studies. Our aim was to determine whether a "stress test" improves prediction of extubation outcome and to determine the most predictive variables. DESIGN: Observational study. SETTING: Intensive care unit of a teaching hospital. PATIENTS: A convenience sample of 68 patients judged to be ready for extubation. INTERVENTIONS: We decreased pressure support from 5 to 0 cm H2O for 1 hr before extubation (stress test) while patients were on 5 cm H2O continuous positive airway pressure. MEASUREMENTS AND MAIN RESULTS: We measured respiratory frequency, tidal volume, ratio of respiratory frequency to tidal volume (f/VT), airway occlusion pressure after onset of inspiration (P0.1), and gastric-arterial PCO2 (deltaPg-aCO2 both on 5 cm H2O and 0 cm H2O pressure support. Then all patients were extubated. Failure of extubation was defined as reintubation within 24 hrs. Seventeen patients (25%) failed extubation. With pressure support of 5 cm H2O and continuous positive airway pressure of 5 cm H2O, most predictors were not different between patients who failed and patients who were successfully extubated. After the stress test, deltaPg-aCO2 was 2 (-5; 15) mm Hg (median; quartiles) in successfully extubated patients vs. 28 (-9; 48) in failures (p = .0003), tidal volume was 473 (387; 558) vs. 400 (323; 435) mL (p = .02), and P0.1 was 2.8 (2; 4.1) vs. 4.1 (2.7; 5.3) mm Hg (p = .03), respectively. The stress test increased specificity of deltaPg-aCO2 from 0.45 to 0.94 and positive predictive value from 0.85 to 0.97. The specificity and positive predictive values for f/VT after the stress test were 0.23 and 0.78. CONCLUSIONS: A simple stress test improves prediction of extubation outcome. deltaPg-aCO2 has superior specificity and positive predictive value compared with other variables. The use of true clinical outcome (i.e., extubation) instead of the use of surrogate markers (e.g., tachypnea) distinguishes these results from previous studies.

Blood Gas Analysis↗

PubMed1987

Hypertension and the genetics of red cell membrane abnormalities.

Hypertension represents the upper 15-25% of the blood pressure distribution in industrialized countries. The trait is practically absent in primitive societies and is made manifest by diet and lifestyles in industrialized countries. High blood pressure is an important risk factor for strokes, heart disease and renal disease. The frequency of hypertension is higher among blacks than among whites in the USA. Various twin, family and adoption studies indicate a strong genetic effect on blood pressure. The genetic mechanisms are unknown. Membrane transport variability has been studied in red cells as a surrogate for analogous alterations in smooth muscle or renal cells. Among the various transport systems, erythrocyte sodium-lithium countertransport (CT) has been consistently elevated in variable proportions of Caucasian hypertensives. Genetic studies of countertransport levels have shown familial aggregation and higher concordance for monozygotic than dizygotic twins. Complex segregation analysis suggests the action of a major gene superimposed on a polygenic background. The postulated gene (B) raises CT activity and has a population frequency of 0.25. CT levels of the common AA homozygotes and AB heterozygotes cannot be distinguished from each other, whereas CT activity of BB homozygotes (6% of the population) is significantly elevated. Although the CT gene contributes only 2.7% to 3.5% of the variability of blood pressure over its entire range, 14% to 20% of persons with systolic hypertension (greater than 140 mmHg) are BB homozygotes rather than the expected 6% to 7%. A much lower frequency of elevated countertransport activity among black hypertensives suggests genetic heterogeneity in the pathogenesis of high blood pressure. Further investigations on the mechanism and genetic linkage relationships of the putative CT gene may aid in elucidating an important mechanism of blood pressure elevation and will allow molecular approaches in the future.

Antiporters↗

PubMed1999

Race is not an independent predictor of positive surgical margins after radical prostatectomy.

OBJECTIVES: To determine whether race is an independent predictor of positive surgical margins in patients who undergo radical prostatectomy. METHODS: Radical prostatectomies were performed on 750 patients at five Veterans Affairs hospitals: Shreveport, Louisiana (n = 451), Houston, Texas (n = 92), Jackson, Mississippi (n = 83), New Orleans, Louisiana (n = 69), and Little Rock, Arkansas (n = 55). All men who did not receive neoadjuvant hormonal therapy and for whom complete follow-up data were available were included in the analysis (of 607, 260 were African-American and 347 were white). Multiple logistic regression analysis was used to determine the significance of race as an independent predictor of surgical margin status after radical prostatectomy for clinically localized prostate cancer. RESULTS: After controlling for clinical stage, Gleason grade, and preoperative prostate-specific antigen (PSA), multivariable logistic regression analysis revealed that race was not an independent predictor of positive surgical margins (P = 0.9). Of the variables evaluated, both preoperative PSA (P = 0.0005) and biopsy Gleason grade (P = 0.047) were significant predictors of an increased risk of a positive surgical margin. CONCLUSIONS: Positive surgical margins are a widely accepted surrogate marker of increased biologic potential in patients with prostate cancer. In our study population, race was not an independent predictor of surgical margin status. Coupled with observations that survival is not related to race, this finding suggests that the biology of prostate cancer in African-American and white men is similar and that observed racial differences more likely are due to ethnic factors that influence tumorigenicity.

Aged↗

PubMed1998

Topics in dose-response modeling.

Great uncertainty exists in conducting dose-response assessment for microbial pathogens. The data to support quantitative modeling of dose-response relationships are meager. Our philosophy in developing methodology to conduct microbial risk assessments has been to rely on data analysis and formal inferencing from the available data in constructing dose-response and exposure models. The probability of illness is a complex function of factors associated with the disease triangle: the host, the pathogen, and the environment including the food vehicle and indigenous microbial competitors. The epidemiological triangle and interactions between the components of the triangle are used to illustrate key issues in dose-response modeling that impact the estimation of risk and attendant uncertainty. Distinguishing between uncertainty (what is unknown) and variability (heterogeneity) is crucial in risk assessment. Uncertainty includes components that are associated with (i) parameter estimation for a given assumed model, and (ii) the unknown "true" model form among many plausible alternatives such as the exponential, Beta-Poisson, probit, logistic, and Gompertz. Uncertainty may be grossly understated if plausible alternative models are not tested in the analysis. Examples are presented of the impact of variability and uncertainty on species, strain, or serotype of microbial pathogens; variability in human response to administered doses of pathogens; and effects of threshold and nonthreshold models. Some discussion of the usefulness and limitations of epidemiological data is presented. Criteria for development of surrogate dose-response models are proposed for pathogens for which human data are lacking. Alternative dose-response models which consider biological plausibility are presented for predicting the probability of illness.

Adult↗

PubMed2004

Evolutive algorithms for beat-by-beat estimation of left ventricular mechanics.

Traditional methods to evaluate the ventricular mechanics need intraventricular pressure and volume recordings for multiple variably loaded beats. To do this, a complex and invasive procedure must be applied, that may decrease the clinical use. To overcome this limitation, a method to estimate the ventricular mechanics beat-by-beat is presented, modeling the ventricular pressure-volume relationship with a time-varying elastance function. The ability of the genetic algorithms (GAs) as identification technique is exploited. Applying GAs on surrogated data simulating variably loading conditions, the parameters of the time-varying elastance function, considered a measure of the contractility of the myocardial fibers are identified. These single-beat estimates are highly correlated with the end systolic pressure-volume relationship slope obtained by conventional multiple-beat analysis. The main advantage in using GAs for single beat analysis may lie, in the perspective of an use for in vivo investigations, both in their stochastic nature, and in the guaranteed better performance with respect to other search techniques on problems involving noisy signals. Future studies will approach the reduction in GAs computational costs, for a real time in vivo application.

Algorithms↗

PubMed1997

Outcome variables for the study of periodontal regeneration.

The most reliable outcome variable for assessing periodontal regeneration is human histology; however, the morbidity associated with this technique makes it feasible only in isolated case studies designed to prove that a drug, device, or technique is capable of regenerating the lost periodontium including bone, cementum, and functionally oriented periodontal ligament. In the absence of this genuine variable, other "surrogate" variables must be used. Of these, measurement of new bone is the primary alternative. Direct bone measurements, including linear and volumetric assessment, are by far the best tools; however, the need for a second surgical procedure is a definite drawback of this technique. To overcome this problem, other outcomes have been employed: sounding bone measurements is a less invasive method, albeit it is also less accurate. Another tool that has been tested extensively is radiographic analysis. Conventional radiography is not useful in most regenerative trails where minimal or no crestal changes occur. The use of standardized radiographs and image processing techniques to measure alveolar bone changes has not significantly enhanced the applicability of this method. Digital subtraction radiography (DSR) offers some improvement over previous techniques; however, the correlation between the magnitude of clinical bone changes and changes in the digital image is yet to be substantiated. Other variables have been successfully used in regenerative studies. These include clinical attachment level changes, change in probing depth, and gingival recession. The information derived from these variables, especially attachment level changes, supplement and substantiate the direct bone measurements. Other variables that may be monitored are those associated with plaque formation, periodontal pathogens and gingival inflammation; while not direct measures of regeneration, these variables are likely to affect future prognosis and treatment stability. In summary, direct bone measurements are the most ideal surrogate outcome variable, although clinical attachment level measurements are commonly used in large-scale regenerative clinical trials. Clinical response may be assessed at different time intervals; however, the endpoint measurements for regenerative studies should be taken at least 12-months postoperatively.

Alveolar Bone Loss↗

PubMed2005

Weight loss reduces knee-joint loads in overweight and obese older adults with knee osteoarthritis.

OBJECTIVE: To determine the relationship between change in body mass and knee-joint moments and forces during walking in overweight and obese older adults with knee osteoarthritis (OA) following an 18-month clinical trial of diet and exercise. METHODS: Data were obtained from 142 sedentary, overweight, and obese older adults with self-reported disability and radiographic evidence of knee OA who underwent 3-dimensional gait analysis. Gait kinetic outcome variables included peak knee-joint forces and peak internal knee-joint moments. Mixed regression models were created to predict followup kinetic values, using followup body mass as the primary explanatory variable. Baseline body mass was used as a covariate, and thus followup body mass was a surrogate measure for change in body mass (i.e., weight loss). RESULTS: There was a significant direct association between followup body mass and peak followup values of compressive force (P = 0.001), resultant force (P = 0.002), abduction moment (P = 0.03), and medial rotation moment (P = 0.02). A weight reduction of 9.8 N (1 kg) was associated with reductions of 40.6 N and 38.7 N in compressive and resultant forces, respectively. Thus, each weight-loss unit was associated with an approximately 4-unit reduction in knee-joint forces. In addition, a reduction in body weight of 9.8 N (1 kg) was associated with a 1.4% reduction (0.496 Nm) in knee abduction moment. CONCLUSION: Our results indicate that each pound of weight lost will result in a 4-fold reduction in the load exerted on the knee per step during daily activities. Accumulated over thousands of steps per day, a reduction of this magnitude would appear to be clinically meaningful.

Aged↗

PubMedDate not supplied

Ambulatory blood pressure monitoring.

This paper will briefly summarize the available evidence on the diagnostic and prognostic relevance of a number of parameters derived from the analysis of 24 hour ambulatory blood pressure recordings. These parameters include the 24 h average blood pressure values, the difference between daytime and nighttime blood pressure, the difference between clinic blood pressure and daytime average blood pressure as a surrogate measure of the "white coat effect", and 24 hour blood pressure variability as quantified by the standard deviation of the 24 hour average value.

Blood Pressure↗

PubMed2005

Long-term health-related quality of life outcomes following Jefferson-type burst fractures of the atlas.

OBJECT: The primary goal of this study was to describe the long-term health-related quality of life (HRQOL) outcomes in patients who have suffered Jefferson-type fractures. These outcomes were compared with matched normative HRQOL data and with the patient's perceptions of their HRQOL prior to the injury. Variables that potentially influence these HRQOL outcomes were analyzed. No standardized outcome assessments have been published for patients who suffer these fractures; their outcomes have long thought to be excellent following treatment. Determining the optimal surrogate measure to represent preinjury HRQOL in trauma patients is difficult. METHODS: A retrospective review, radiographic analysis, and cross-sectional outcome assessment were performed. The Short Form (SF)-36 and the American Academy of Orthopaedic Surgeons/North American Spine Society (AAOS/NASS) outcome instruments were filled out by patients at final follow-up examination (follow-up period 75 months, range 19-198 months) to represent their current status as well as their perceptions of preinjury status. In 34 patients, the SF-36 physical component score and the AAOS/NASS pain values were significantly lower than normative values. There was no significant difference between normative and preinjury values. Spence criteria greater than 7 mm and the presence of associated injuries predicted poorer outcome scores during the follow-up period. CONCLUSIONS: Long-term follow-up examination of patients with Jefferson fractures indicated that patients' status does not return to the level of their perceived preinjury health status or that of normative population controls. Those with other injuries and significant osseous displacement (> or = 7 mm total) may experience poorer long-term outcomes. Limitations of the study included a relatively low (60%) response rate and the difficulties of identifying an appropriate baseline outcome in a trauma population with which the follow-up outcomes can be compared.

Adolescent↗

PubMed2002

Investigating the criterion validity of psychiatric symptom scales using surrogate marker validation methodology.

This work investigates whether techniques that are generally used for the validation of surrogate markers in clinical trials can be applied in the validation of psychiatric health measurements (often scales) and more generally to investigate relationships between treatment effects on different measurements. However, the categorical nature of some scales makes these techniques inapplicable in the way they were originally defined. In this work, we show a possible extension of this methodology to the setting in which one of the scales is an ordinal categorical variable. When psychiatric health measurements are either developed or used in a new population, reliability and validity must be investigated. Reliability, more specifically internal consistency, test-retest reliability, and inter-rater reliability, is focused on the reproducibility of the measurement. Validity is defined as the degree to which the scale measures what it purports to measure. This can be performed through the analysis of content, construct, and criterion validity. We argue that recent methodology, in particular developed to study surrogate endpoints, can be used to examine criterion validity, concurrent validity, and predictive validity. In concurrent validity, we correlate the measurement with a criterion measure, both of which are given at the same time. In predictive validity, the criterion will not be available to some point in time in the future. The surrogate methods were applied on pooled data from five trials in schizophrenia.

Clinical Trials as Topic↗

PubMed2004

Fractal characteristics of breath to breath timing in sleeping infants.

We examined interbreath interval (IBI) time series of 19 term infants during active and quiet sleep for fractal properties using Fano factor analysis. For each time series we calculated the fractal exponent (alpha), comparing alpha for the original time series with two forms of surrogate data, a temporally independent surrogate set and an autoregressive surrogate set. alpha values were normally distributed between 0.79 and -0.22, and did not differ with sleep state. The fractal characteristics of the original time series were not retained in the temporally independent surrogate time series indicating that the distribution of intervals alone was not fractal, but were retained using autoregressive surrogates with an order of 10, suggesting that the fractal properties of the IBI time series were related to correlations between successive breaths. These observations suggest that some of the respiratory variability that occurs during sleep in infants, which in the past has been regarded as stochastic noise, may be the product of deterministic processes.

Factor Analysis, Statistical↗

PubMed1995

Why do women report 'sick building symptoms' more often than men?

The prevalence of general, mucosal and skin symptoms compatible with the 'Sick Building Syndrome' (SBS) was studied in Swedish office workers. The marked excess in symptom prevalence among females, 12% SBS cases as compared to 4% among males, was analysed with respect to differences in biological or acquired risks and different illness and reporting (interview) behaviour among males and females. The distribution of risk indicators for symptoms was recorded in a questionnaire to 4943 employees. The skin symptom questions were validated in a clinical examination. Most risk indicators, such as paper work and psychosocial work load, had an unfavourable distribution for females. In the multivariate analysis however, female sex remained the most prominent risk indicator almost unaffected by the addition of other factors. Neither did effect modification contribute to the excess prevalence among females. The results from the clinical examination indicate that the excess symptom prevalence among females is real and not a reporting artefact. As the factors studied did not explain the excess symptom prevalence among females, the sex differential observed can be a reflection of a general excess of psychosomatic symptoms among women. Although inequalities in social conditions did not substantially explain the sex differential in symptom reporting, the importance of life situation and social roles should be further explored. As the studied variables are surrogates for actual measurements, another important issue is whether sex differences in working conditions, entailing different hierarchical positions in the office, have consequences for indoor air quality factors that are important for the symptoms. The study strongly underlines the importance of taking the sex distribution into account when surveying risk indicators for SBS symptoms.

Adult↗

PubMed2004

Biochemical markers of liver fibrosis and lymphocytic piecemeal necrosis in UDCA-treated patients with primary biliary cirrhosis.

BACKGROUND/AIM: We have previously shown that the histological stage and severity of lymphocytic piecemeal necrosis (LPN) are independent predictive factors of cirrhosis development in ursodeoxycholic acid (UDCA)-treated patients with primary biliary cirrhosis (PBC). Our aim during this study was to determine whether biochemical parameters classically used in PBC management and measured under UDCA could be considered as reliable surrogate markers for these histological prognostic indices in clinical practice. METHOD: The study included 153 patients with PBC who had undergone a control liver biopsy after 2 years of UDCA therapy. The relationships between histological and biological features were assessed by variance analysis and logistic regression. The diagnostic value of independent markers was assessed in terms of their sensitivity, specificity, positive predictive value (PPV) and negative value (NPV) and receiver-operating characteristic curves. RESULTS: Two variables were independently associated with extensive fibrosis (i.e. advanced histological stages): serum levels of bilirubin and hyaluronic acid (HA). A fibrosis index ([bilirubin (micromol/l)/14]+[HA (microg/l)/143]) higher than 1.5 exhibited good PPV and specificity (>74%) but rather poor NPV and sensitivity (<64%) regarding a diagnosis of extensive fibrosis. The only independent marker of LPN was aspartate aminotransferase (AST) activity. AST activity of more than twice the upper limit of normal showed acceptable PPV (>70%) but very low sensitivity (<25%) for a diagnosis of LPN. CONCLUSIONS: Serum bilirubin and HA levels measured under UDCA therapy are of acceptable diagnostic value for extensive fibrosis, but none of the biochemical tests commonly employed in the management of PBC can be considered as surrogate markers of LPN. Taken together with our previous results, these findings suggest that liver biopsy may be necessary to screen UDCA-treated patients who might require additional therapies.

Aspartate Aminotransferases↗

PubMed2006

Heart rate variability and 24-hour minimum heart rate.

Heart rate variability (HRV) indices based on 24-hr electrocardiograph recordings have been used in clinical research studies to assess the aggregate activity of the autonomic nervous system. Although 24-hr HRV is generally considered noninvasive, use in research protocols typically involves considerable data collection and processing expenses and substantial participant burden. The purposes of this research methods evaluation were to describe the relationships between 24-hr minimum heart rate (HR) and several 24-hr time domain HRV indices (Ln SDNN, Ln SDANN, Ln SDNNIDX, Ln RMSSD, and Logit50) across several research data sets (normal women, normal men, children enrolled in a study of recurrent abdominal pain, women with irritable bowel syndrome, sudden cardiac arrest survivors, and heart failure patients) and to explore the possibility that 24-hr minimum HR might serve as a simpler alternative or adjunct to HRV measures in some situations. The correlations of global HRV measures (e.g., Ln SDNN, Ln SDANN) with 24-hr minimum HR were consistently larger (typical r approximately -.80) than with average HR (typical r approximately -.50). In repeated measurements, change in minimum HR was also correlated with change in general HRV (typical r approximately -.60). However, modest differentiation of minimum HR and HRV measures was noted in patients taking certain classes of cardiac medications (e.g., anti-arrhythmics, beta blockers). Twenty-four-hour minimum HR is correlated with general time domain HRV measures and might be useful as a simpler proxy, surrogate, or auxiliary variable in some clinical research applications, especially those in which participants are not receiving cardiac medications.

Abdominal Pain↗

PubMed1994

Heart rate variability: a measure of cardiac autonomic tone.

Analysis of HRV based on routine 24-hour Holter recordings provides a sensitive, noninvasive measurement of autonomic input to the heart. HRV can be measured in the time or frequency domain. Each frequency domain variable correlates at least r = 0.85 with a time domain variable. Thus time domain measures can be used as surrogates for frequency domain measures which may simplify future studies. Abnormalities of autonomic input to the heart, which are indicated by decreased indices of HRV, are associated with increased susceptibility to ventricular arrhythmias. Decreased indices of HRV are also associated with CHF, diabetes, and alcoholic cardiomyopathy. Decreased indices of HRV are an independent risk factor for mortality post MI and in patients with advanced CHF. Medications can also affect HRV, and that effect may become an important clinical consideration, especially in high-risk patients.

Autonomic Nervous System↗