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.

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 nature of communication in virtual home care visits.

The study's objective was to analyze "virtual" home care visits that utilize telemedicine technology and to investigate the type and quality of interaction between provider and patient. The setting was the TeleHomeCare Project which provides TV-based videoconferencing. Patients are receiving standard home care services with an addition of virtual visits. 122 virtual visits were reviewed and a content analysis was performed for 30 of these. Time was apportioned among the following categories of communication: assessing the patient's clinical status, promoting compliance, addressing psychosocial issues, general informal talk, education, administrative issues, technical issues, assessing patient satisfaction and ensuring accessibility. The findings indicate that technology does not interfere with but rather enriches the care process. Although there are activities that cannot be conducted in virtual visits, they can address most of the important aspects of care delivery giving strength to the argument that they could in some cases substitute traditional visits.

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.

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.

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.

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.

Determination of reliability and validity in home monitoring data of pulmonary function tests following lung transplantation.

Electronic spirometry units were used to monitor lung transplantation recipients upon their return home. The data from 77 participants were used to develop methods to verify that the pulmonary function measurements, forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1), were reliable and valid. The standard deviation was calculated for the best daily effort on consecutive days of home spirometry. An acceptable upper limit for the standard deviation, as the measure of day-to-day reliability, was 0.20 for FVC and 0.15 for FEV1. Validity was determined by examining the mean difference (bias) between the spirometry done in the pulmonary function laboratory and the home monitoring results. The clinic values were slightly higher, with an average difference of 0.15 for FVC and 0.12 for FEV1. Therefore, the home spirometry measurements have a high degree of reliability and validity and can now be used for early detection of serious complications.

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.

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.

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.

Effects of aging per se on arterial stiffness: systemic and regional compliance in beagles.

Although previous studies have suggested that aging results in an increase in vascular stiffness, diseases that increase in prevalence with advanced age may have confounded the results of some of this past research. The purpose of this investigation was to determine whether aging per se results in reduced arterial compliance by using animals that are resistant to atherosclerosis and do not develop hypertension or hyperlipidemias with advanced age. We evaluated systemic and regional (femoral) arterial compliance in older (110 +/- 8 months old) and in younger (27 +/- 2 months old) female beagle dogs by using a computer-based assessment of the diastolic decay of arterial pressure waveforms and a modified Windkessel model of the circulation. Although systemic arterial pressure was very similar in both age groups, cardiac output was 29% lower (p = 0.03) and systemic vascular resistance was 24% higher (p = 0.02) in the older dogs. Moreover, there was an age-related reduction in systemic arterial compliance, derived both from the exponential decay in the arterial pulse (C1) (p = 0.05) and that derived from the oscillatory component of the diastolic pulse wave (C2) (p = 0.04). By contrast, although femoral vascular resistance was 25% higher in the older dogs (p = 0.04), regional (femoral) vascular compliance measured after femoral arterial occlusion was also 25% reduced but was not significantly changed with age (p = 0.14). These results demonstrate that systemic arterial compliance is reduced with age in dogs, extending this finding to animals without age-related diseases that frequently occur in older human beings. Regional compliance, evaluated in the isolated femoral vascular bed, also tends to be reduced with age, but variability in this parameter in dogs reduces the significance of this finding.

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.

Fish oil improves arterial compliance in non-insulin-dependent diabetes mellitus.

In a double-blind, placebo-controlled study we investigated the effects of dietary fish oil supplementation on arterial wall characteristics in 20 patients with non-insulin-dependent diabetes mellitus. Estimates reflecting compliance values in the large arteries and more peripheral vasculature, as measured by pulse-contour analysis, improved significantly after 6 weeks of fish oil therapy compared with values recorded at baseline and after 6 weeks' administration of olive oil. The large-artery compliance estimate increased from 1.50 (confidence interval [CI], 1.31 to 1.69) mL/mm Hg at baseline to 1.68 (CI, 1.52 to 1.84) mL/mm Hg after fish oil administration (P < .01). The oscillatory compliance value increased from 0.015 (CI, 0.011 to 0.019) mL/mm Hg at baseline to 0.022 (CI, 0.016 to 0.028) mL/mm Hg after fish oil ingestion (P < .05). No changes occurred in arterial blood pressure, cardiac output, stroke volume, or systemic vascular resistance with either intervention. The improved compliance estimates with fish oil ingestion occurred without altering fasting blood glucose and cholesterol concentrations. These results support the hypothesis that fish oils alter vascular reactivity and favorably influence arterial wall characteristics in patients with non-insulin-dependent diabetes mellitus. These direct vascular effects, expressed at the level of the vessel wall, may contribute to the cardioprotective actions of fish oil in humans.

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.

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.

Assessment of arterial compliance in hypertension.

Traditionally, hypertension has been defined in terms of an elevated resistance to flow confined predominantly to the precapillary vasculature. More recently, changes in arterial compliance have been used to estimate vascular adaptations in the larger conduit arteries. This review outlines and updates the many varied techniques employed to estimate arterial compliance changes during hypertension. Most measures of compliance assess changes in small segments of the arterial vasculature. Because hypertension is a disease that influences structure and reactivity in all parts of the systemic circulation, it is desirable that clinical techniques for monitoring vascular adaptations with disease should address the generalized changes in the systemic vasculature.