Arterial vascular compliance response to vasodilators by Fourier and pulse contour analysis.

Vasodilator drugs are widely used in the management of cardiovascular disease. They decrease systemic vascular resistance, but they also may influence vascular arterial compliance. This study evaluated the effects of three vasodilators--nitroprusside, nitroglycerin, and hydralazine--on vascular compliance using impedance parameters determined by pulse contour and Fourier analyses. The open chest study was performed on anesthetized dogs. Mean arterial pressure decreased by a minimum of 20% after vasodilator intervention. The decrease in systemic vascular resistance was significant (p less than 0.01) only after hydralazine treatment. Proximal compliance increased after administration of all drugs, but the increase was not statistically significant. Distal compliance determined by pulse contour analysis increased by 60 to 120% after all three drug treatments (p less than 0.05 for nitroprusside, p less than 0.02 for nitroglycerin and hydralazine). Characteristic impedance from Fourier analysis responded variably, and changes were not statistically significant. The sensitivity of changes in distal compliance as a marker for the vascular effect of these drugs suggests that it might be used as a more reliable guide than blood pressure or vascular resistance in monitoring clinical response to such intervention. The more traditional measure of characteristic impedance provides a vascular measurement that is less sensitive than distal compliance to the effects of these vasodilator drugs.

Age-related abnormalities in arterial compliance identified by pressure pulse contour analysis: aging and arterial compliance.

The objective of this study was to evaluate age-related changes in pulsatile arterial function. Aging alters arterial pulsatile function and produces consistent changes in the pressure pulse contour. A reduced systemic arterial compliance that can be derived from analysis of the pulse contour is regarded as the best clinical index of impaired pulsatile arterial function and may mark the presence of early vascular damage. We analyzed intra-arterial brachial artery waveforms in 115 healthy normotensive volunteers (83 men, 32 women) and radial artery waveforms obtained with the use of a calibrated tonometer device in 212 healthy volunteers (147 women, 65 men). A computer-based assessment of the diastolic pressure decay and a modified Windkessel model of the circulation were used to quantify changes in arterial waveform morphology in terms of large artery or capacitive compliance, oscillatory or reflective compliance in the small arteries, inertance, and systemic vascular resistance. Large artery compliance and oscillatory compliance correlated negatively with age for both invasive and noninvasive groups (r=-0.50 and r=-0.55; r=-0.37 and r=-0.66; P<0.001 for all). The slopes of the regression lines for the decline in oscillatory compliance with age were significantly steeper than those recorded for large artery compliance estimates. The change in blood pressure with age independently contributed to the decrease in large artery compliance but not oscillatory compliance in both groups. Consistent age-related changes were found in the pressure pulse contour by analysis of waveforms obtained invasively or noninvasively from the upper limb. The change in the oscillatory or reflective compliance estimate was independent of blood pressure change and may represent a better marker than large artery or capacitive compliance of the degenerative aging process in altering pulsatile arterial function.

Vascular abnormalities associated with long-term cigarette smoking identified by arterial waveform analysis.

PURPOSE: Consistent changes in the arterial pulse contour are found with aging and disease states that impair the compliance characteristics of blood vessels that buffer pulsatile phenomena in the arterial tree. We assessed whether vascular adaptation in structure or tone of blood vessels associated with long-term cigarette smoking would influence steady state or pulsatile hemodynamics at a preclinical stage. PATIENTS AND METHODS: We analyzed intraarterial brachial artery waveforms in 35 healthy long-term cigarette smokers and 32 nonsmoking control subjects matched for age and gender. The diastolic pressure decay was segmented into two components: an exponential decay that reflects the compliance characteristics of the large arteries and an oscillatory diastolic waveform generated principally by pulse-wave reflections from small arteries and arterioles. RESULTS: Resting heart rate was higher in smokers than nonsmokers, mean +/- SD (66 +/- 9 versus 60 +/- 10; P < 0.05). Systolic, diastolic, and mean arterial pressures were lower in smokers compared with nonsmokers (P < 0.01 for all). No differences in cardiac output, large artery compliance, or systemic vascular resistance estimates where apparent between groups. A decrease in the amplitude and duration of the diastolic wave, produced by peripheral pulse-wave reflections in the arterial system, was found in smokers compared with nonsmokers (0.04 +/- 0.02 versus 0.7 +/- 0.03; P < 0.001). CONCLUSIONS: Quantitative changes in the arterial waveform were found in long-term smokers compared with nonsmoking control subjects. The altered arterial wave shape marks the presence of abnormal structure or tone in the peripheral vasculature that affects pulsatile arterial function. This measure of vascular injury is detectable at a preclinical stage and may relate to the subsequent risk of morbid events in chronic smokers and aid in clinical risk stratification.

Vascular hemodynamic impedance in congestive heart failure.

The objective of this study was to determine whether pulse-contour analysis could provide a measure of the differences in peripheral vascular state between patients with congestive heart failure (CHF) and healthy persons. Vascular hemodynamic impedance parameters were determined from brachial artery pressure waveforms recorded in 14 patients with CHF, aged 20 to 55 years (mean 36 +/- 12) and in 7 healthy control subjects, aged 22 to 55 years (mean 33 +/- 12). Cardiac output, heart sounds and electrocardiogram were also monitored. Cardiac output was 32% lower (p less than 0.01) and heart rate was 43% higher (p less than 0.001) in the CHF group than in the control group. The mean arterial pressure did not differ between groups. Systemic vascular resistance was 47% higher (p less than 0.05) and distal vascular compliance 73% lower (p less than 0.001) in the CHF group than in control group. Proximal vascular compliance was unchanged. These studies suggest that distal compliance assessed from pulse-contour analysis is a more sensitive and specific index than systemic vascular resistance to the vascular changes in CHF.

A rule for the early detection of chronic changes in cystic fibrosis patient status.

A statistical decision-making system has been developed which will predict the clinical status of a patient with cystic fibrosis based on daily self measurements obtained at home. The data for the study were collected from CF patients within 7-12 years of age. Thirty-two participants recorded four daily measurements (weight, vital capacity, breathing rate, and resting pulse) and one weekly measurement (height). In addition to the 4 daily measured values, the clinical status of each patient at his/her most recent previous clinic visit was used as a predictor variable. The measured values were used as the basis for the development of a discriminant rule. The goal of the rule was to determine whether each patient's clinical status was deteriorating, stable, or improving at the time of the most recent set of weekly measurements. Three types of analysis were performed: linear discriminant analysis, quadratic discriminant analysis, and nearest neighbor. Quadratic discriminant analysis provided the best discrimination due to the differences in the covariance matrices among the populations. The rule was able to correctly classify 77% of the 103 cases in the learning set. To further evaluate the rule, both a weighted classification percentage and weighted kappa statistic were calculated for the rule. Bootstrapping was used to predict the performance of the rule on the population with results of 77% correctly classified overall.

Staging of bronchiolitis obliterans syndrome using home spirometry.

OBJECTIVES: To compare the detection of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients by clinic pulmonary function laboratory measurement and home spirometry. DESIGN: The subjects served as their own control group. SETTING: A university-based thoracic transplant center. SUBJECTS: Forty-five lung transplant recipients (26 women and 19 men; average +/- SD age, 47.7+/-11.4 years old at the time of transplantation). Lung function declined to at least BOS stage 1 in 17 of the 45 subjects. MEASUREMENTS: All subjects were participants in a home monitoring program utilizing home spirometry measurements. Clinic spirometry and home spirometry measurements were collected concurrently. The determinations of BOS staging were based on home and clinic FEV1 values using retrospective analysis and development of the home-based BOS staging algorithm. RESULTS: BOS stage 1 was detected an average of 341 to 276 days earlier with home spirometry than with clinic pulmonary function testing in the 17 subjects who had a pulmonary decline to BOS stage 1, depending on the persistence of the decline (1 day or 3 days, respectively). The difference in BOS detection time was statistically significant for both persistence requirements (p < 0.001). CONCLUSIONS: Home spirometry detects pulmonary decline earlier than clinic spirometry; home spirometry can be a reliable and safe alternative to frequent pulmonary function testing in lung recipients.

Arterial compliance abnormalities in isolated systolic hypertension.

Arterial compliance measurements using intraarterial pulse contour analysis and a modified Windkessel model were carried out in 19 patients with isolated systolic hypertension (> or = 160/< or = 90 mm Hg) and compared to measurements in 29 patients with essential hypertension (diastolic blood pressure [BP] > or = 95 mm Hg) and 47 normotensive control subjects. Arterial capacitive compliance was significantly lower in isolated systolic hypertension than in essential hypertension (P < .0002) and significantly lower in essential hypertension than in normotensive control subjects (P < .0001). Although the isolated systolic hypertension group was older than the essential hypertension group, the reduction of capacitive compliance in isolated systolic hypertension persisted even when comparison was made with a more nearly age-matched group of essential hypertension. In contrast, oscillatory compliance was reduced similarly in isolated systolic hypertension and essential hypertension compared to normotensive control subjects (P < .0001). Although pulse pressure was greater in isolated systolic hypertension than in essential hypertension, only a weak correlation (r = -0.34) existed between pulse pressure and capacitive compliance. These data indicate that both essential hypertension and isolated systolic hypertension patients exhibit comparably abnormal structure or tone of the small vessels that are the site of oscillations or reflections in the arterial vasculature. In isolated systolic hypertension there is a profound reduction in large artery or capacitive compliance that accounts for the increase in systolic BP and decrease in diastolic BP. This abnormality cannot be accurately assessed by pulse pressure alone.

Reduced vascular compliance as a marker for essential hypertension.

In 38 patients with established essential hypertension and 32 age-matched normotensive control subjects proximal and distal arterial compliance were determined by computer-based assessment of the diastolic decay of a brachial arterial tracing and a modified Windkessel model of the circulation. In the hypertensive subjects compared to the normotensive subjects mean arterial pressure was 25% higher (P less than .001), systemic vascular resistance 23% higher (P less than .01), proximal compliance 19% lower (P less than .01), and distal compliance 72% lower (P less than .001). The reduction in distal compliance was highly age-dependent. In the youngest age range (45 to 54 years) little overlap appeared between hypertensive and normotensive groups, whereas in the oldest subjects studied (65 to 75 years) distal compliance was comparably low in the two groups. Thus, distal vascular compliance provides a sensitive and specific marker for the abnormal vasculature associated with hypertension and may be particularly useful in identifying the disease in young individuals with borderline blood pressure.

Considerations for the design of a Web-based clinical monitoring and educational system for elderly patients.

Designing a Web system for elderly patients requires attention to the users' functional impairments and inexperience with computers. The authors reviewed published guides for the design of Web-based clinical systems for elderly patients and identified additional design considerations that have not been reported in the literature. The resulting recommendations are related to the system interface, the training and support of users, and the content of Web pages. The recommendations can be used as design objectives for Web-based systems for elderly patients, which emphasize system usability and aim to optimize patients' error-free use of these systems.

The importance of arterial compliance in cardiovascular drug therapy.

Arterial compliance, defined as a change in dimension in response to a given change in stress, is becoming an increasingly important clinical parameter. Related concepts, such as distensibility, elasticity, and stiffness, and more traditional concepts such as resistance, afterload, and impedance need to be differentiated from compliance, although they are frequently (inappropriately) used interchangably. Many studies cannot differentiate between compliance changes due to a drug's effect on blood pressure and those due to a drug's effect on vessel wall integrity. This differentiation is important because a more physiologic therapy, one that benefits pulsatile and nonpulsatile flow, should be of greater clinical benefit than a therapy that only lowers blood pressure. A number of methods have been used to estimate compliance, but to date there is no generally agreed-on best method. There also are no longitudinal studies that relate abnormal compliance and drug effects to outcome. Nonetheless, patients at risk from a variety of disease states, such as hypertension, diabetes mellitus, and hypercholesterolemia, may benefit from earlier recognition of abnormal compliance. Earlier recognition may lead to interventions that would reduce their risk. This review includes a discussion of compliance and related estimates of blood vessel function and attempts to summarize the data currently available regarding the effects of cardioactive drugs on arterial compliance.

Contrasting clinical and statistical significance within the research setting.

When designing a clinical trial or study, the value of the following interrelated parameters should be determined prior to collecting data: clinical significance, statistical significance, power, and sample size. Too often, clinical importance and the other design issues are ignored and only statistical significance dictates the conclusions of the study. In order to evaluate the frequency that each of these design parameters is addressed in the published literature, the topic of pulmonary function tests (specifically forced vital capacity) was chosen, and all relevant articles for one year (1990) were identified using Minnesota MEDLINE. A total of 121 articles met the selection criteria and were reviewed. Of all the articles, 13.2% discussed clinical significance, 21.5% discussed sample size, and only 5.0% addressed statistical power. As expected, the majority of the articles (92.6%) discussed statistical significance (P values). None of the articles mentioned all four factors. When choosing the level of clinical significance several methods may be used. Such might be well established in certain clinical areas or available from previous publications and references or they may be attainable from pilot study data and, in the absence of any prior information, a clinician may use personal experience. To minimize subjectivity, the clinical effect-size can be based on the population distribution of the measurement of interest.

The impact of home monitoring and daily diary recording on patient status in cystic fibrosis.

An experimental home monitoring system for assessing the progress and planning changes in the care of patients with cystic fibrosis (CF) has been implemented at the University of Minnesota Cystic Fibrosis Center. One group of patients and families did daily recording of physical measurements and symptoms, and sent the diary to the data coordinating center weekly for analysis. The remaining patients were not part of the home monitoring program. Twenty-five patients were randomly selected from the home monitoring group. They were compared to an age- and sex-matched control group not doing home monitoring to ascertain if home self-measurement and daily diary recording, in the absence of any therapeutic intervention, produced any change in physical or psychological status, pulmonary function, or growth over a 4-year study period. Subjects ranged in age from 6 to 43 years. Clinical status was measured by the National Institutes of Health cystic fibrosis scoring system. Pulmonary function was assessed as percent of predicted forced vital capacity and percent of predicted forced expiratory volume in 1 sec (FEV1). Growth was analyzed as percent of predicted weight based on age-, sex-, and height-dependent equations. Psychological status was determined by self-assessment and referral for conseling. Only percent predicted FEV1 in the control group declined significantly. There were no statistically significant changes in any other measures either within or between diary and nondiary groups over the 4-year period.(ABSTRACT TRUNCATED AT 250 WORDS)

Monitor: an expert system that validates and interprets time-dependent partial data based on a cystic fibrosis home monitoring program.

The use of health diaries to monitor patients with chronic diseases has often been complicated by difficulties encountered in data quality assurance and interpretation. An expert system, Monitor, has been developed to predict the health status of cystic fibrosis patients based on daily home measurements of pulse, respiratory rate, weight, inspired vital capacity, and a check list of symptoms of acute illness. This system ensures data reliability beyond what can be achieved in most current automatic error detection procedures by validating inputs against patient-specific expectations. Its explicit representation of the time dimension and the hierarchical structure of its knowledge base facilitate the abstraction of trends and relationships among the time-dependent data. Dynamically imposed expectations also lend flexibility to the interpretation process by allowing the processing of partial (incomplete) data. Monitor correctly classified 86 percent (three-category classification) and 94 percent (two-category classification) of 111 cases. This demonstrates that expert systems can be a feasible approach in building more robust diary monitoring systems.

Reliability and validity of spirometry measurements in a paperless home monitoring diary program for lung transplantation.

OBJECTIVE: To demonstrate that home spirometry measurements are reliable and valid and can be used as part of a home measurement monitoring system by lung transplant recipients. DESIGN: Longitudinal, observational. SETTING: University medical center. SUBJECTS: Eighteen patients who have undergone lung transplantation; age range was 24 to 63 years (mean of 49.5 years). OUTCOME MEASURES: Reliability and validity of forced expiratory volume at 1 second (FEV1) and forced vital capacity (FVC). INTERVENTION: Recording of spirometry, vital signs, and symptom measures at home each day by use of a paperless electronic diary/spirometer instrument. RESULTS: Day-to-day variability as measured by the standard deviation ranged from 0.013 L to 0.202 L for FVC and 0.015 L to 0.117 L for FEV1. The correlation between the two best forced expiratory maneuvers on any given day was 0.98 for both FVC and FEV1, with percent differences between the measurements of 2% for FVC and 3% for FEV1. The correlation between measurements performed in the pulmonary function laboratory and measurements done by the patient at home on the same day was 0.94 for FVC and 0.99 for FEV1. CONCLUSIONS: This evaluation demonstrated that home measurements are both reliable (i.e., repeatable) and valid when compared with the "gold standard" of the pulmonary function laboratory. The home monitoring program has been well accepted by patients, is easy to use, and provides data comparable to that collected during clinic visits.

Non-invasive studies of peripheral vascular compliance using a non-occluding photoplethysmographic method.

A non-invasive technique is implemented to measure a peripheral vascular compliance index Cindex, using an infrared photoplethysmographic waveform as an indicator of intravascular volume change and a continuous blood pressure monitor to measure the blood pressure during each heart-beat. The non-linear behaviour of Cindex with pressure and the effect of age on Cindex are studied in 62 males (15-73 years). Repeatability tests and the effect of ice-water exposure of a portion of a limb are studied in 10 and 14 subjects, respectively. For each individual, Cindex measurements are taken at discrete values of local mean arterial pressure (Pmean), and a Cindex against Pmean plot is obtained. There is a statistically significant difference (p < 0.05) in Cindex for the lower values of Pmean (60-100 mmHg) between two age groups formed (15-52 and 58-73 years). The cold-pressor test (CPT) shows a 68% median decrease in Cindex, with an inter-quartile range of 60-77%, in a matter of seconds. The results suggest that Cindex may be a useful noninvasive indicator of peripheral vascular compliance in humans.

Biomedical information technology: medicine and health care in the digital future.

Advancements in medicine and health care are being significantly influenced by the exploding information technology developments. The IEEE Transactions on Information Technology in Biomedicine will address the applications and the infrastructure innovations that would harness biomedical and health care programs in the 21st century.

Comparison of two teaching strategies: adherence to a home monitoring program.

Two strategies for teaching lung and heart-lung transplant subjects to use an electronic spirometer/diary instrument at home to input and transmit daily respiratory, vital sign, and symptom measurements were compared. The first strategy integrated teaching into subjects' postoperative clinic visits, whereas the second strategy involved referral to a Patient Learning Center (PLC) for instruction. Adherence was increased by 30% when the teaching was transferred from the clinic setting to the PLC. These findings suggest that the PLC is an effective resource for preparing patients to manage their care after discharge from a hospital or clinic.

An expert system for diagnosis and therapy in lung transplantation.

An expert system for diagnosis and therapy after lung transplantation has been developed and evaluated by domain experts. The system captures a total of 21 diagnoses encompassing rejection, pulmonary infection, and some diseases of gastrointestinal origin. The disease hypotheses are scored and ranked by their ability to explain the patient findings. A hypothesis is accepted as a candidate disease if it is ranked high on the list and is able to account for the cardinal findings of the disease. The therapy knowledge is captured in the form of rules. The results demonstrate the feasibility of an expert system for diagnosis and therapy after lung transplantation.

Monitoring progress after lung transplantation from home-patient adherence.

A paperless electronic spirometer/diary instrument has been employed in a home monitoring programme for lung and heart-lung transplant patients at the University of Minnesota. The monitoring programme is part of a long term study to develop a system which will detect the earliest signs of developing rejection or infection in the transplanted organs. It is based on patient daily self-measurements of standard spirometry, vital signs, and symptoms recorded at home and transmitted weekly to the study data center over the telephone using a modern built into the instrument. This report summarizes adherence behaviour for 41 subjects enrolled in the study over a 12 month period. The number of subjects from whom home data has been received each week was used to measure adherence at the subject level. The number of records received each week measured adherence at the daily recording level. A data record consists of a daily set of spirometry, vital signs, and symptom values from a given subject. Approximately 82% of subjects transmitted records each week, over the 52 week review period. There was an average of 4.5 records received each week from each subject. Transmitted records had missing vital sign or symptom items in less than 2% of cases, spirometry data was always present. This evaluation showed than lung transplant recipients are willing and able to use a home-monitoring instrument, and that basic spirometry, data entry, and data transmission can be performed satisfactorily.

First- and third-order models for determining arterial compliance.

BACKGROUND: Engineering models of the arterial vasculature have been used to describe vascular properties of resistance and compliance. These approaches have used either Fourier frequency analysis, based on transmission line equations, or time domain analysis of the circuit equations describing modified Windkessel models of the vasculature. DESIGN: A third-order, four-element modified Windkessel model can reproduce arterial pressure waveforms, including both exponential and oscillatory pressure decays observed during the diastolic portion of the cardiac cycle. METHOD: A method to determine both capacitive and oscillatory compliance of the arterial vasculature was developed, and the effect of these compliance properties on the blood pressure waveform was examined.