Paul N. Kizakevich

New ambulatory impedance cardiograph validated against the Minnesota Impedance Cardiograph

The validity and reliability of a new ambulatory impedance cardiograph (AZCG) was tested against the Minnesota Impedance Cardiograph (ZCG) during rest, orthostasis, and mental stress. Impedance cardiography allows noninvasive assessment of stroke volume, cardiac output, and systolic time intervals. A reliable ambulatory device would allow studies outside the lab. The devices were compared at two sites in healthy subjects. In both studies, the AZCG tracked changes across conditions closely with the ZCG (all Period x Device interactions were nonsignificant). Pearson rs, were .65 to .93, random intraclass correlation coefficients ranged from .80 to .98, indicating high degrees of shared measurement variance, and Cronbachs alpha indicated very good internal reliabilities (.91 to .99). Relative to the ZCG, the new AZCG appears to provide valid and reliable estimates of cardiac function at rest and during behavioral challenges in the lab.

Noninvasive ambulatory assessment of cardiac function in healthy men exposed to carbon monoxide during upper and lower body exercise

Abstract Very little is known about the cardiovascular responses of exercising individuals when exposed to carbon monoxide (CO). Sixteen healthy nonsmoking men aged 18–29u2009years participated in the study. Using a combination of exposures to CO by breathing from a bag or in an environmental chamber, subjects performed a randomized sequence of brief (5u2009min) multi-level treadmill and hand-crank exercises on different days at less than 2% carboxyhemoglobin (COHb) and after attaining target levels of 5%, 10%, 15%, and 20% COHb. To assess cardiac function changes we employed noninvasive impedance cardiography (ICG) and three-lead electrocardiograms (ECG). The ICG was used to estimate cardiac output, stroke volume, heart rate, cardiac contractility, and time-to-peak ejection time. The ECG was used to assess myocardial irritability and ischemia, and changes in cardiac rhythm. The results showed that the cardiovascular system compensated for the reduced O2-carrying capacity of the blood by augmenting heart rate, cardiac contractility, and cardiac output for both upper-body and lower-body exercise. While this mechanism served well in submaximal exercise, the enhanced cardiovascular response to exercise was not without physiological costs because it began to fail at moderate levels of CO exposure and exercise. We concluded that young, apparently healthy men can perform submaximal upper and lower-body exercise without overt impairment of cardiovascular function after CO exposures attaining 20% COHb.

Comparative measures of systolic ejection during treadmill exercise by impedance cardiography and Doppler echocardiography

Measurements of systolic ejection dynamics by impedance cardiography were compared with simultaneous Doppler echocardiography in normal subjects and coronary artery disease patients. Patients with chest pain admitted for elective coronary angiography were monitored by simultaneous impedance cardiography and Doppler echocardiography before, during, and after treadmill exercise. Ensemble-averaged ECG, impedance cardiogram (ICG), the first derivative of ICG (dZ/dt), and Doppler waveforms were analyzed to identify systolic ejection variables. The timing of aortic valve opening was well correlated (r = 0.78) the timing of peak ejection velocity was very well correlated (r = 0.86), and the timing of aortic valve closure was moderately correlated (r = 0.69 and r = 0.73) in these subjects. The thoracic electrical impedance acceleration and normalized impedance acceleration indices were moderately correlated with Doppler model acceleration (r = 0.74, r = 0.79). The impedance cardiogram waveforms are of complex origin and are related to both aortic blood velocity and aortic blood acceleration. Users of dZ/dt timing features for determining aortic valvular events might consider alternative impedance features to improve ejection time accuracy.

Relaxation training assisted by heart rate variability biofeedback: Implication for a military predeployment stress inoculation protocol

Decreased heart rate variability (HRV) is associated with posttraumatic stress disorder (PTSD) and depression symptoms, but PTSDs effects on the autonomic stress response and the potential influence of HRV biofeedback in stress relaxation training on improving PTSD symptoms are not well understood. The objective of this study was to examine the impact of a predeployment stress inoculation training (PRESTINT) protocol on physiologic measures of HRV in a large sample of the military population randomly assigned to experimental HRV biofeedback-assisted relaxation training versus a control condition. PRESTINT altered the parasympathetic regulation of cardiac activity, with experimental subjects exhibiting greater HRV, that is, less arousal, during a posttraining combat simulation designed to heighten arousal. Autonomic reactivity was also found to be related to PTSD and self-reported use of mental health services. Future PRESTINT training could be appropriate for efficiently teaching self-help skills to reduce the psychological harm following trauma exposure by increasing the capacity for parasympathetically modulated reactions to stress and providing a coping tool (i.e., relaxation method) for use following a stressful situation.

A personal health information toolkit for health intervention research.

With the emergence of mobile health (mHealth) apps, there is a growing demand for better tools for developing and evaluating mobile health interventions. Recently we developed the Personal Health Intervention Toolkit (PHIT), a software framework which eases app implementation and facilitates scientific evaluation. PHIT integrates self-report and physiological sensor instruments, evidence-based advisor logic, and self-help interventions such as meditation, health education, and cognitive behavior change. PHIT can be used to facilitate research, interventions for chronic diseases, risky behaviors, sleep, medication adherence, environmental monitoring, momentary data collection health screening, and clinical decision support. In a series of usability evaluations, participants reported an overall usability score of 4.5 on a 1-5 Likert scale and an 85 score on the System Usability Scale, indicating a high percentile rank of 95%.

A comprehensive cardiac exercise stress processor for environmental health effects studies

We have shown that an interactive microcomputer system using noninvasive cardiovascular measurements during exercise is both possible and practical. Experimental use of the system has verified our choice of variables as appropriate for automatic generation of a cardiovascular data base, but additional studies are required to determine the systems sensitivity for assessing health-effect decrements.

A Platform to Build Mobile Health Apps: The Personal Health Intervention Toolkit (PHIT).

Personal Health Intervention Toolkit (PHIT) is an advanced cross-platform software framework targeted at personal self-help research on mobile devices. Following the subjective and objective measurement, assessment, and plan methodology for health assessment and intervention recommendations, the PHIT platform lets researchers quickly build mobile health research Android and iOS apps. They can (1) create complex data-collection instruments using a simple extensible markup language (XML) schema; (2) use Bluetooth wireless sensors; (3) create targeted self-help interventions based on collected data via XML-coded logic; (4) facilitate cross-study reuse from the library of existing instruments and interventions such as stress, anxiety, sleep quality, and substance abuse; and (5) monitor longitudinal intervention studies via daily upload to a Web-based dashboard portal. For physiological data, Bluetooth sensors collect real-time data with on-device processing. For example, using the BinarHeartSensor, the PHIT platform processes the heart rate data into heart rate variability measures, and plots these data as time-series waveforms. Subjective data instruments are user data-entry screens, comprising a series of forms with validation and processing logic. The PHIT instrument library consists of over 70 reusable instruments for various domains including cognitive, environmental, psychiatric, psychosocial, and substance abuse. Many are standardized instruments, such as the Alcohol Use Disorder Identification Test, Patient Health Questionnaire-8, and Post-Traumatic Stress Disorder Checklist. Autonomous instruments such as battery and global positioning system location support continuous background data collection. All data are acquired using a schedule appropriate to the app’s deployment. The PHIT intelligent virtual advisor (iVA) is an expert system logic layer, which analyzes the data in real time on the device. This data analysis results in a tailored app of interventions and other data-collection instruments. For example, if a user anxiety score exceeds a threshold, the iVA might add a meditation intervention to the task list in order to teach the user how to relax, and schedule a reassessment using the anxiety instrument 2 weeks later to re-evaluate. If the anxiety score exceeds a higher threshold, then an advisory to seek professional help would be displayed. Using the easy-to-use PHIT scripting language, the researcher can program new instruments, the iVA, and interventions to their domain-specific needs. The iVA, instruments, and interventions are defined via XML files, which facilities rapid app development and deployment. The PHIT Web-based dashboard portal provides the researcher access to all the uploaded data. After a secure login, the data can be filtered by criteria such as study, protocol, domain, and user. Data can also be exported into a comma-delimited file for further processing. The PHIT framework has proven to be an extensible, reconfigurable technology that facilitates mobile data collection and health intervention research. Additional plans include instrument development in other domains, additional health sensors, and a text messaging notification system.

PHIT for duty, a mobile approach for psychological health intervention.

The goal of this effort is to support prevention of psychological health problems through innovation in mobile personal health assessment and self-help intervention (SHI). For the U.S. military, we are developing and evaluating a field-deployable personalized application, PHIT for DutyTM, to help build resilience in healthy troops and support prevention in high-risk personnel. PHIT for Duty is delivered using any smartphone or tablet with optional nonintrusive physiological and behavioral sensors for health status monitoring. The application integrates a suite of health assessments with an intelligent advisor that recommends, tailors, and presents self-help advisories. PHIT for Duty is intended for secondary prevention of psychological health problems in persons who have been exposed to psychological trauma and may be showing some symptoms of distress, but have not been diagnosed with any psychological disease or disorder.

Detection of ischemic responses during treadmill exercise by computer-aided impedance cardiography

The hemodynamic response to treadmill exercise by electrocardiography, impedance cardiography, and Doppler echocardiography is measured to compare the ability of these methods to detect coronary artery disease (CAD). Thirty-one hospitalized male patients with chest pain syndromes admitted for elective coronary angiography are monitored before, during, and after performing a Bruce or modified Bruce treadmill protocol. A personal computer system is used for acquisition, processing, and graphic analysis of the cardiac signals. By coronary angiography, patients were classified as having zero, one, two, three, or left-main CAD. By analysis of maximal exercise response (X/sub max/-X/sub rest/), aortic acceleration indices by both Doppler and impedance methods are shown to be the most sensitive indicators of CAD (P<0.05).<<ETX>>

Reproducibility of impedance cardiogram waveform analysis in lower-body and upper-body exercise

Measurements of nine impedance cardiograph variables made on 17 young (21-29 yr, mean 24.6 yr), healthy males during rest and three levels of treadmill and hand-crank exercise showed no significant difference (ANOVA, p>0.05) among the three days, except for heart rate (p<0.01, treadmill; p<0.02, hand crank), time-to-aortic closing (p<0.01, treadmill), and mean thoracic impedance (p<0.01, hand crank). Stroke volume, cardiac output, time-to-peak ejection, time-to-aortic opening, (dZ/dt)/sub peak/, and d/sup 2/Z/dt/sup 2/ were invariant with day of exercise.<<ETX>>