Quantitative information of specific diagnostic tests.

The goal of diagnostic testing is to maximize information (I) of a specific disease of interest (D) resulting from the performance of a specific diagnostic test procedure (T). However, all tests suffer from errors which result in incomplete information and inaccurate diagnostic conclusions. The methods of Information Theory have successfully solved a range of signal transmission problems involving physical systems operating under conditions of noise. Medical testing procedures were found to be analogous to noisy systems; hence, Information Theory methods were applied to minimize errors in diagnostic testing. Prior to performing a diagnostic test, the quantity of information, Apriori Information (ID), regarding the presence or absence of the disease was only a function of the prevalence (P) of disease in the population. After performing a diagnostic test, the quantity of information, Aposteriori Information (IDIT) was a function of not only P but also the test sensitivity (A) and test specificity (B). The quantity of information gained by test performance was computed from the difference between aposteriori and apriori information. delta I = IDIT - ID To illustrate the relationship between pretest, apriori, and post-test, aposteriori, information the values of ID and IDIT were computed for five common cardiovascular tests applied to populations with different coronary artery disease prevalence. This cross-sectional analysis studied the quantitative information obtained from Electrocardiography (ECG), Bicycle Ergometer Stress Tests (BEST), Stress-Echo Ergometer Tests (SEET), Thallium 201 Stress Tests (ThST), and Coronary Arteriography (CorA). Apriori information ranged from a minimum of 0 (for prevalence = 0.5) to a maximum of 1.0 (for prevalence = 0 or 1.0) The aposteriori information was computed for all apriori information and occupied the range between that of a "perfect" test (A = 1.0 and B = 1.0) and that of a "worthless" test (A = 0.5 and B = 0.5). All tests demonstrated greater information gain when apriori information was minimal; Little additional information could be gained when the apriori information was close to certainty (i.e., for prevalence near 0 or 1.0). Electrocardiography demonstrated little significant IDIT at any value of ID. Thallium 201 stress tests provided similar aposteriori information values to those of Stress-Echo Ergometer Stress and either demonstrated greater information gain than Bicycle Ergometer Stress Tests. Coronary Arteriography provided the maximum values of aposteriori information. Information Theory methods provided an effective quantitative method to compare the effectiveness of diagnostic tests over a wide range of disease prevalence.

Heart rate response to exercise in normal women.

Heart rate is known to increase under the influence of increased sympathetic stimulation rates during exertion or stress. Few data are available regarding the rate response to exercise near the fatigue limit, for normal women. The effects on heart rate were studied of fatigue limiting exercise in 87 asymptomatic, normal female subjects employing a bicycle ergometer exercise protocol. The heart rate response to imposed exercise power closely followed a monotonic increasing, negative exponential function. Different age groups followed the same form of function but differed in parameter values. Group fitting was useful to develop parameters with which one group may be compared to another, establish referent ranges, and gain insight into cardiovascular models of exercise physiology.

Significant left ventricular hypertrophy in subjects with normal resting pressures but exaggerated pressure response during light exertion.

Concentric left ventricular hypertrophy (LVH) frequently occurs in subjects with normal resting systolic and diastolic pressures (SP and DP, respectively). LVH in this normotensive-hypertrophic group (NH) may be due to an abnormally exaggerated pressure response to exercise. The SP and DP responses to exercise were studied in 130 subjects free from coronary artery disease or cardiomyopathy. The NH subjects (n = 35) had normal resting pressure (SP < or = 140 and DP < or = 85 mmHg) and increased LV wall thickness (T) by echocardiography (T > 1.1 cm). A normal control group (NN) (n = 57) and a hypertensive control group (HH) (n = 23) were simultaneously evaluated. The original groups, subgroups censored for age and weight, and matched-pair subgroups demonstrated greater exercise SP for NH than for NN (p < 0.005). Moreover, the rate of SP increase with exercise was greater for NH than for NN or HH (p < 0.05). Hence, an exaggerated exercise SP response may have been the stimulus for LVH in these NH subjects.

Development of electrocardiographic teaching materials using an MC68000-based, interactive graphics microcomputer.

Interactive computer-graphics methods of computer-aided design (CAD) have been applied to problems in physical science and industry for several years; however, at the present time CAD methods have not been widely used to solve similar problems in medical education. Electrocardiogram waveform fabrication for the production of teaching materials seemed to be a well-defined area for CAD application. The availability of inexpensive, 16/32 bit word, MC68000-based microcomputers (e.g. Apple, Macintosh) and interactive graphics software (e.g. MacPaint and MacDraw) seemed to provide the necessary tools to make this application. This paper describes the authors' initial experience (from June 1984 to March 1985) in developing and employing an interactive computer graphics routine to produce ECG teaching materials.

Description of a novel microcomputer program to analyze left ventricular segmental wall motion during normal sinus rhythm and sinus tachycardia.

The authors have written a program to describe left ventricular (LV) regional wall motion (RWM) for a Tektronix 4051 graphic system and an MC68000, 32-bit word based microcomputer utilizing interactive graphics methods. Proper wall motion of 16 defined regions of the LV endocardial perimeter (RAO angiographic views) were computed from the magnitudes of fixed vectors fixed to analogous positions along the LV perimeter from end-diastole to end-systole (Figure 1). It was assumed that (1) LV contraction, tangential to the perimeter, produced RWM at large angles to the direction of contraction, and (2) LV contraction occurred uniformly along the anterolateral and posteromedial perimeters. All motion vectors were computed following digitization of the LV perimeters from projected images of 35-mm cineangiographic frames corrected for linear and nonlinear distortion. Digitization input was accurate to less than 0.3 mm and area computation demonstrated errors of less than 1.5%. A normal group (NG) without coronary artery (CA) disease (N = 31) defined a set of Gaussian distributed referent values for mean WM (magnitude of motion vectors) for all segments. WM amplitudes for the CA disease group (N = 125) demonstrated significant diviation in the areas supplied by occluded or stenosed coronary arteries. Qualitative and quantitative evaluation of the adequacy of coronary circulation and/or collateral vessel development could be made by inspection of WM amplitude computer plots. Proper WM was found to be highly specific for numbers and distribution of coronary arteries diseased.

Left ventricular function after cigarette smoking by chronic smokers: comparison of normal subjects and patients with coronary artery disease.

Twenty normal subjects and 25 patients with coronary artery disease underwent systolic time interval analysis before and after rapidly smoking two cigarettes. A slight increase in heart rate and arterial pressure was seen in both groups. In patients with coronary artery disease, preejection period/left ventricular ejection time ratio increased; in normal subjects it decreased. Left ventricular performance is diminished after cigarette smoking among subjects who have preexisting significant coronary artery disease.