Wyatt F. Voyles

Clinically Silent Atrial Septal Defects with Evidence for Cerebral Embolization

The cause of stroke in young patients frequently cannot be established. Eleven consecutive patients, age 50 and younger, had clinical evidence of cerebral embolization. Results of physical, radiographic, electrocardiographic, and two-dimensional echocardiographic examinations were normal in all patients. During normal respiration, eight of the patients had right-to-left shunts at the atrial level shown by microcavitation contrast two-dimensional echocardiography. Six of the eight patients with positive contrast studies had cardiac catheterization. Five of six patients had an atrial septal defect, normal right and left heart pressures, and small right-to-left shunts during a Valsalva strain. Four patients had surgical closure of the defect, which ranged in size from 5 to 10 mm. The remaining patients received anticoagulants. Interatrial communications appear to be common in young patients with stroke, suggesting paradoxical embolization as a possible mechanism. Contrast two-dimensional echocardiography should be done in such patients because it is the only noninvasive technique that reliably finds these defects.

Transdermal Nitroglycerin Patches in Angina Pectoris: Dose Titration, Duration of Effect, and Rapid Tolerance

The duration of effect of transdermal nitroglycerin patches was studied in 14 patients with angina pectoris. By titrating the dose to achieve specific circulatory effects, we chose a patch size that produced a consistent fall in systolic blood pressure of 10 mm Hg or greater for each patient (10 cm2 in 7 patients, 20 cm2 in 5, and 40 cm2 in 2; releasing 5, 10, and 20 mg of nitroglycerin per 24 hours, respectively). The effects of these individualized patches were compared with those of placebo patches. Compared with placebo, nitroglycerin patches increased exercise duration to the onset of angina (257 +/- 72 compared with 383 +/- 130 seconds, p less than 0.0001) and total exercise time (338 +/- 89 compared with 456 +/- 119 seconds, p less than 0.0001) and decreased ST segment depression (1.0 +/- 0.5 compared with 0.6 +/- 0.4 mm, p less than 0.05) at 4 hours but not at 24 and 48 hours. We conclude that nitroglycerin patches do not show objective evidence of antianginal or antiischemic effects for 24 hours. Tolerance to the circulatory and antianginal effects probably develops within 24 hours of patch application.

Doppler predictions of pulmonary artery pressure, flow, and resistance in adults.

We examined the accuracy of noninvasive predictions of pulmonary artery pressure (P), flow (Q), and resistance (R) by means of main pulmonary artery blood velocities and diameters measured with Doppler echocardiography (DE). The ratio of noninvasive acceleration time to ejection time (An) was correlated to invasively determined mean pulmonary artery pressure (Pl) and resistance (Rl). Noninvasive flows were correlated to thermodilution flows (Ql). Simultaneous invasive and noninvasive measurements were made in nine adult patients (ages = 22 to 73 years). The results were: Pl = 87 - 152An, r = 0.90, SEE = 7 mm Hg, p less than 0.05; Rl = 899 - 1722An, r = 0.79, SEE = 121 dynes X sec X cm-5, p less than 0.05; and Ql = -0.3 + 1.21Qn, r = 0.95, SEE = 0.81 L X min-1, p less than 0.05. We then used these equations prospectively to predict Pl, Rl, and Ql in 21 of 25 (83% technically adequate) consecutive patients. Pl, Rl, and Ql ranged from 10 to 35 mm Hg, 39 to 456 dynes X sec X cm-5, and 3.51 to 8.39 L X min-1, respectively. Results were: Pl = 0.80P + 3, r = 0.72, SEE = 6 mm Hg, p less than 0.05; Rl = 0.75R - 12, r = 0.64, SEE = 77 dynes X sec X cm-5, p less than 0.005; and Ql = 0.87Q + 0.38, r = 0.83, SEE = 0.86 L X min-1, p less than 0.05. These results suggest that DE predictions of pulmonary artery pressure, flow, and resistance correlate significantly with values subsequently obtained at catheterization.

Intracardiac shunting across a patent foramen ovale may exacerbate hypoxemia in high-altitude pulmonary edema.

Rapid ascent to altitude in susceptible persons may result in severe hypoxemia, pulmonary hypertension, and even pulmonary edema. This life-threatening syndrome affects approximately 1% of climbers...

A comparison of echo-Doppler and electromagnetic renal blood flow measurements.

The linearity and accuracy of noninvasive ultrasonic method of measuring beat‐to‐beat renal blood flow was evaluated by correlation with standard electromagnetic flowmetry. Using a combined real‐time ultrasonic imager and pulsed Doppler velocimeter known as a duplex scanner (DS), lumen diameter (D) and average blood velocity (V) within the imaged renal artery were recorded. Renal blood flow ( QDS ) was calculated offline using a microprocessor from the equation QDS = (pi x D2 x V)/4. This noninvasive method had previously been validated in vitro using a controlled hydraulic system which modeled steady‐state flow (QT) where QDS = 0.98 QT + 7.75, SEE = +/‐ 13.2, r = +0.98, P less than 0.001. In three anesthetized dogs, simultaneous QDS and electromagnetic flow ( QEMF ) measurements (range 44‐484 ml x min‐1) were made in the proximal left renal artery. Linear regression analysis gave QDS = 0.43 QEMF + 40.5, r = 0.78, SEE = 33.8 ml x min‐1, P less than 0.01; QDS = 1.2 QEMF + 2.9, r = 0.86, SEE = 20.8 ml x min‐1, P less than 0.01; QDS = 0.86 QEMF + 0.2, r = 0.93, SEE = 53.4 ml x min‐1, P less than 0.01. These results suggest that noninvasive QDS measurements of renal blood flow are linear and reasonably accurate compared with invasive QEMF in dogs. The method may have utility in the noninvasive measurement of beat‐to‐beat blood flow in human renal arteries.

A comparison of digital and analog methods of doppler spectral analysis for quantifying flow

Ultrasonic methods can be used for calculating flow when the mean Doppler frequency is representative of spatial average velocity. We have examined the capabilities of two commercially available methods of Doppler spectral analysis for providing measurements of spatial average velocity and flow. In a steady state flow model, Doppler audio spectra were recorded using a 5-MHz duplex scanner. Fast Fourier transform (FFT) spectral analysis was used to determine mean (M), mode (MO), and maximum (MAX) frequencies. An analog method (offset zero crossing detector = ZC) was used to determine root mean square (RMS) frequencies. The results of comparing Doppler flow estimates (QM, QMO, QMAX and QRMS) with direct flow measurements (n = 10; range = 128-1098 ml/min) were (1) QM = 0.67Q + 23 ml/min (SEE = 36 ml/min); (2) QMO = 0.96Q + 152 ml/min (SEE = 32 ml/min); (3) QMAX = 1.19Q + 171 ml/min (SEE = 23 ml/min); and (4) QRMS = 0.93Q + 76ml/min (SEE = 92 ml/min). Estimates of flow using M and RMS frequencies were adversely affected by experimental conditions likely to result in turbulence. We conclude that application of commercially available FFT determined M frequencies could result in significant errors in calculations of spatial average velocity and flow. Alternatively, FFT determined MO frequencies and ZC determined RMS frequencies resulted in accurate estimates of flow in this model. This study demonstrates the importance of evaluating the capabilities of commercially available methods of Doppler spectral analysis when using ultrasound for determining velocity and flow.

Long-term bepridil monotherapy for angina pectoris

The long-term efficacy of bepridil as once-a-day monotherapy was studied in 19 men with stable angina pectoris. After 2 weeks of single-blind placebo therapy and a 12-week parallel placebo-controlled, dose-response study, each patient received open-label bepridil. After a dose-titration period of 3 months, patients received bepridil (100 to 400 mg once a day, mean 290 mg) for 24 months. The response to treatment was assessed by patient diaries and serial treadmill exercise testing 24 hours after dose administration, every 3 months. Only 2 patients were released from the study due to therapeutic failure. Compared with placebo, 3 months of bepridil therapy resulted in a significant reduction in the weekly frequency of angina from 10.3 +/- 9.1 to 1.8 +/- 3.5 (p less than 0.002) and nitroglycerin consumption from 5.0 +/- 5.4 to 1.4 +/- 2.3 (p less than 0.01). In addition, there was a simultaneous significant increase in the walking time to angina from 5.2 +/- 2.3 to 7.9 +/- 2.6 minutes (p less than 0.001) and total exercise time from 7.1 +/- 2.2 to 8.8 +/- 1.9 minutes (p less than 0.001). These favorable effects were sustained throughout the 24 months of the study. Although resting QTc interval was prolonged by 36 to 42 ms (p less than 0.001) during bepridil therapy, ventricular dysrhythmias were not observed immediately before or during exercise testing and were not manifested by symptoms. Neurologic and gastrointestinal side effects of mild to moderate severity were observed, but none required discontinuation of therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler echocardiographic profiles in obstructive right and left atrial myxomas

Previous reports have suggested that atrioventricular (AV) flow disturbances accompanying atrial myxomas mimic mitral stenosis. Two patients complaining of orthostatic syncope and positional intolerance had a large right and left atrial myxoma, respectively. Doppler flow records showed abrupt early diastolic flow cessation and normal velocity half-times, unlike AV valve stenosis. Large, obstructing atrial myxomas may behave as ball valves.

Quantitative Evaluation of Atherosclerosis Using Doppler Ultrasound

During the last two decades, various Doppler methods have been successfully used to screen patients with significant cerebral and peripheral vascular disease. In general terms, the principal advantages of Doppler ultrasound techniques in the evaluation of atherosclerotic lesions are that they: 1) are noninvasive, 2) are nontraumatic, 3) are relatively inexpensive, 4) provide anatomical and physiological data, and 5) provide direct and dynamic measurements. Nevertheless, the general limitations of the techniques are of equal importance: 1) the techniques are difficult in some subjects due to obesity and anatomical variations; 2) the technique cannot examine tissues surrounded by air or bone; 3) the techniques require operator skill and a thorough knowledge of human anatomy and cardiovascular dynamics; 4) the techniques have finite spatial resolutions which may compromise the important measurement of vessel diameter, ulceration, and percent stenosis; and 5) the techniques have finite velocity measuring capabilities which may compromise some measurements of highly disturbed blood velocities outside the range of 2-200 cm/sec. As clinical demands for the early diagnosis and quantification of vascular lesions increased, improvements in Doppler ultrasonics and spectra analysis significantly increased the technical and clinical capabilities of existing simple, inexpensive instruments. Presently, both anatomical and physiological images along with quantitative Doppler spectra from superficial and deep-lying vessels can be obtained. Consequently, the ability of new expensive imaging equipment to quantitate atherosclerotic lesions using spectral analysis techniques compares favorably with the interpretational precision of standard invasive or intravenous digital angiography.

Noninvasive Doppler flowmetry for measuring regional blood flow.

Ultrasonic Doppler flowmetry should assume an increasingly important role in the serial evaluation of human cardiovascular physiology. The principal advantages of this method are that it (1) is noninvasive, (2) is nontraumatic, (3) provides anatomic and physiologic data, and (4) provides dynamic measurements. Nevertheless, the equally important limitations of the technique are that it (1) is difficult to apply in some subjects (ie, those who are obese or have anatomic variations), (2) requires operator skill and a thorough knowledge of human anatomy and cardiovascular dynamics, (3) has a finite spatial resolution that may compromise the measurement of small (1 mm) vessel diameters, and (4) has a finite velocity-measuring capability that will affect measurements of blood velocities outside the range of approximately 2 to 200 cm/sec. Full appreciation of the capabilities and limitations of noninvasive ultrasonic Doppler flowmetry makes possible a better understanding of the dynamic interplay of anatomy, pressure, flow, and resistance in the normal and abnormal intact human cardiovascular system.