Characterization of submicron systems via optical methods.

As a means of addressing the issues of drug delivery, submicron colloidal systems have become increasingly used as pharmaceutical formulations. Accurately characterizing physical properties of the constituent particulates present in these systems is an indispensable activity. However, measuring descriptors such as particle size distribution and surface potential presents an experimental challenge. This paper describes the physical basis for a number of optically based techniques that are useful in this task. In addition, the caveats and benefits of these methods are discussed and reference is made to their use in the examination of various multiphase systems such as liposomes, nanoparticles, and emulsions.

Site-directed mutagenesis to probe protein folding: evidence that the formation and aggregation of a bovine growth hormone folding intermediate are dissociable processes.

Bovine growth hormone (bGH) forms a stable folding intermediate that aggregates at elevated concentrations (greater than 10 microM). Thermodynamic and kinetic studies have shown that the formation of this bGH folding intermediate and its aggregation are separate processes, implying that selective modifications of bGH can lead to their independent modulation. In addition, a bGH region that includes amino acid residues 109-133 appears to be directly involved in this aggregation process. Human growth hormone (hGH), which is unable to aggregate via this mechanism, differs from the bovine primary sequence at eight positions within this protein region. We have characterized the folding of a bGH analogue that contains the hGH sequence between amino acid residues 109-133 (8H-bGH) at low and high concentrations. The equilibrium folding characteristics of bGH and 8H-bGH are similar when monitored at low protein concentrations (less than or equal to 2 microM). The wild-type and analogue proteins have equivalent denaturation midpoints when equilibrium unfolding is monitored by the use of far-UV circular dichroism, second-derivative UV, or fluorescence. In addition, the enhanced fluorescence that is associated with the formation of the bGH monomeric folding intermediate (Havel, H. A., et al. (1988) Biochim. Biophys. Acta 955, 154-163) is observed for 8H-bGH under similar conditions. In contrast, partial denaturation of 8H-bGH at higher concentrations (greater than 2 microM) leads to significantly less aggregation than is observed for bGH. This result is obtained from near-UV CD spectroscopy, kinetic folding, size-exclusion chromatography, and dynamic light-scattering data.(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of esophageal pill electrode atrial pacing with quantitative two-dimensional echocardiography for diagnosing coronary artery disease.

Noninvasive diagnosis of coronary artery disease (CAD) is difficult in patients who are unable to exercise. In this study esophageal pill electrode atrial pacing was used as a myocardial stress not requiring exercise, and changes in ejection fraction and pressure volume ratio during pacing with 2-dimensional echocardiography were quantitatively analyzed. All patients had completed a Bruce protocol treadmill exercise test and had undergone coronary arteriography. Of 26 patients, 22 were successfully paced (85%). Comparable rate-pressure products were obtained for treadmill exercise (23,500 +/- 5,900 mm Hg/min) and pacing (24,100 +/- 4,400 mm Hg/min; difference not significant). Of the 22 patients completing the study 8 had normal coronary arteries (group I) and 14 had CAD (group II). The change in ejection fraction with pacing in group I patients was not significant (3 +/- 8%). In group II ejection fraction decreased with pacing (-8 +/- 13%; p = 0.025). The pressure/volume ratio increased in group I with pacing (3.8 +/- 1.8 mm Hg/min/m2; p = 0.05) and was unchanged in group II (0.3 +/- 1.8 mm Hg/min/m2; difference not significant). Using an ejection fraction decrease with pacing or a failure to increase pressure/volume ratio with pacing as criterion for the presence of CAD, similar predictive accuracies were obtained when compared to treadmill exercise testing. Esophageal pill electrode atrial pacing with quantitative 2-dimensional echocardiography may be a useful noninvasive, nonexercise method to detect CAD.

Investigations of protein structure with optical spectroscopy: bovine growth hormone.

Optical spectroscopy provides a wealth of information about protein structure that is difficult to obtain from other methods. Investigations of changes in primary, secondary, tertiary, and quaternary structure are particularly well-suited for optical techniques such as UV absorption, circular dichroism, fluorescence, Raman and infrared spectroscopy, as well as light scattering methods. Each method has unique areas of applicability and contributes to structure determination in a different manner. The application of these methods is demonstrated with examples of studies performed on bovine growth hormone. Some of these include: determination of solution-state structure, monitoring differences between solution- and solid-state structure, determination of molecular size distribution, and investigations of protein folding mechanisms. It is demonstrated that by judicious choice of methods, a reasonably complete description of protein structure can be obtained.

Physiological importance of different atrioventricular intervals to improved exercise performance in patients with dual chamber pacemakers.

To determine the importance of different atrioventricular intervals during exercise in patients with dual chamber pacemakers, seven patients with complete heart block and sinus rhythm were exercised in different pacing modes and atrioventricular intervals: (a) ventricular inhibited (VVI) pacing with no synchronous atrial augmentation or rate responsiveness; (b) atrial synchronous ventricular or DDD pacing with a short mean (SD) atrioventricular interval of 66 (4) ms; and (c) DDD pacing with a long atrioventricular interval of 168 (12) ms. Pacing with a short or long atrioventricular interval gave similar maximum heart rates, oxygen uptake at the anaerobic threshold, end tidal pressure of carbon dioxide or oxygen pulse (a measure of stroke volume). Pacing with either a short or long atrioventricular interval produced a significantly higher oxygen consumption and anaerobic threshold and less lactate production than VVI pacing. During exercise a short atrioventricular interval does not provide a better cardiopulmonary performance than a long atrioventricular interval.

Physiological benefits of a pacemaker with dual chamber pacing at low heart rates and single chamber rate responsive pacing during exercise.

Dual chamber rate responsive pacing may be an ideal mode but may result in high current drain and premature battery depletion. To minimize battery drain during exercise, this study compared a combination pacing mode of DDD and ventricular rate responsive pacing (VVIR). Nine patients were studied who had complete heart block, sinus rhythm, DDD pacemakers, and a reduced mean left ventricular ejection fraction of 44%. Patients were exercised in DDD, VVIR, and a combination of DDD at low heart rates and VVIR at mean heart rates over 89 bpm. Blood pressure, heart rate, exercise duration, work rate, oxygen uptake, anaerobic threshold, and oxygen pulse were measured. There was no difference in symptoms or in mean cardiopulmonary function indices including exercise duration 10.7, 10.3, 10.3 minutes; heart rate 127, 133, 136 bpm; oxygen uptake 1.4, 1.5, 1.5 L/minute; or anaerobic threshold 5.6, 5.5, 5.7 minutes (p greater than 0.05) in any mode. A pacemaker that provides atrioventricular synchrony at low heart rates with ventricular rate responsiveness at high heart rates may be an alternative mode for some patients.

Accuracy of left atrial and pulmonary artery wedge pressure in pure mitral regurgitation in predicting left ventricular end-diastolic pressure.

In most clinical conditions pulmonary artery (PA) wedge pressure accurately reflects left ventricular (LV) end-diastolic pressure. In the presence of mitral regurgitation (MR), large V waves can distort PA wedge pressure and result in incorrect estimation of LV end-diastolic pressure. In 52 patients with MR simultaneous measurement of PA wedge pressure or left atrial pressure and LV end-diastolic pressure was recorded. Twenty-one (40%) patients had large V waves (V wave greater than A wave by greater than 10 mm Hg, group 1), and 31 (60%) patients had small V waves (group 2). Group 1 had significantly higher V waves than group 2 (46 +/- 3 vs 21 +/- 2 mm Hg, p less than 0.001). The LV end-diastolic pressure was similar in both groups (21 +/- 2 vs 19 +/- 2 mm Hg, difference not significant). The mean PA wedge or left atrial pressure in group 1 (26 +/- 2 mm Hg) overestimated LV end-diastolic pressure (21 +/- 2 mm Hg) by 30% (p less than 0.01), but the trough of the X descent (20 +/- 2 mm Hg) was similar to the LV end-diastolic pressure. In group 2 patients with small V waves the mean PA wedge pressure was not significantly different from the LV end-diastolic pressure (16 +/- 2 vs 19 +/- 2 mm Hg, p = 0.06), but the trough of the X descent (13 +/- 2 mm Hg) underestimated LV end-diastolic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Early experience with esophageal pill electrode atrial pacing in the diagnosis of coronary artery disease--a trend toward improved specificity compared to treadmill exercise.

Esophageal pill electrode pacing, treadmill exercise and coronary angiography were performed in 23 patients with chest pain. Atrial pacing produced fewer false positive studies resulting in higher specificity compared to treadmill exercise. Some possible explanations of the improved specificity are the better quality tracings obtained with atrial pacing and the increased control of the heart rate and blood pressure response during atrial pacing as opposed to treadmill exercise. This preliminary study suggests that esophageal pill electrode atrial pacing tachycardia studies may be a reasonable alternative to treadmill exercise testing in the noninvasive diagnosis of coronary artery disease.

Electrocardiographic diagnosis of left ventricular hypertrophy in the presence of left bundle branch block.

The electrocardiographic diagnosis of LVH in the presence of LBBB has previously been difficult. Thirty-seven patients with complete LBBB were identified and had echocardiography performed. Using an accepted echocardiographic formula, left ventricular mass was calculated. Twenty of the 37 patients (54%) were classified as having severe LVH. Multiple conventional ECG criteria for LVH were then evaluated. No QRS voltage criteria showed any difference between patients with and without LVH (P = NS). There was also no correlation between either QRS axis or left atrial enlargement and left ventricular mass (P = NS). However, the QRS duration was significantly longer in the patients with LVH (160 +/- 12 msec) than in the normal patients (148 +/- 11 msec) (P less than 0.001). The sensitivity, specificity, positive predictive value, and accuracy of several voltage criteria and QRS duration were examined. The best voltage criteria had a sensitivity of only 50% and a predictive value of 63%. However, a QRS duration greater than 155 msec had a sensitivity of 60% and a predictive value of 82%. This study demonstrates that the conventional QRS voltage criteria for LVH are not accurate in LBBB. A relationship exists between increasing QRS duration in LBBB and LVH; therefore, the relative probability adjectives: "consider," "possible," and "probable" should be used. QRS duration greater than 155 msec is predictive of LVH despite the presence of LBBB.

Esophageal electrocardiography in acute cardiac care. Efficacy and diagnostic value of a new technique.

Esophageal electrocardiography can detect atrial electrical activity during tachyarrhythmias when P waves are not evident by surface electrocardiography. However, patient discomfort, the difficulty of accurately interpreting cardiac signals against a background of electrical noise, and the complexity of use have limited widespread application. In this study, esophageal electrocardiography was used in 48 acutely ill patients with a new "pill electrode" system, consisting of a bipolar electrode pair (3 by 20 mm) attached to 0.5 mm diameter Teflon wires contained in a standard gelatin capsule. The capsule with enclosed electrodes was voluntarily swallowed, and the recording electrodes were positioned posterior to the left atrium. A preamplifier system with a low-frequency filter and a standard three-channel electrocardiographic recorder were used. Esophageal "pill" electrocardiographic recordings were made in 48 of 50 eligible study patients (96 percent) with tachyarrhythmias and absent or equivocal atrial activity on surface electrocardiography. In these patients, a high-quality esophageal electrocardiographic recording was obtained within one to 10 minutes with minimal patient discomfort. In 25 of 48 study patients (52 percent), the original diagnosis, based on the surface electrocardiographic recording, was incorrect after review of the esophageal recording. Results of esophageal recording altered management in 19 of 48 (40 percent) patients. This new and simple technique facilitates diagnosis and management of perplexing tachyarrhythmias in acutely ill patients by physicians with minimal training in the technique.

Left ventricular derived cardiac output.

Measurement of cardiac output (CO) requires right-sided cardiac catheterization. However, to save time and reduce costs, only left-sided cardiac catheterization is usually performed in most patients with suspected coronary artery disease. Thus, CO is not measured. To determine if CO can be measured from the left side of the heart, 24 patients undergoing cardiac catheterization had near-simultaneous determination of CO after indocyanine green dye was injected into the pulmonary artery and left ventricular (LV) cavity. There was close agreement between pulmonary artery and LV derived cardiac outputs (Pulmonary artery = 0.93 LV + 0.12). The pulmonary artery derived CO was 5.7 +/- 2.0 liters/min and the LV derived CO was 6.1 +/- 2.2 liter/min. Also, there was a close relation between pulmonary artery derived stroke volume (82 +/- 33 ml) and LV derived stroke volume (86 +/- 36 ml). Thus, CO can be accurately measured after injection of indocyanine green dye into the LV cavity.

Optimum AV interval in dual chamber pacemakers.

Approximately 50-70% of permanent implanted pacemakers are dual chamber pacemakers. However, little is known concerning adjustment of the atrioventricular (AV) interval to maximize cardiac output. Ten consecutive patients with complete heart block and dual chamber pacemakers were paced at heart rates of 80, 100, and 118 beats/minute and at five AV intervals with simultaneous measurements of cardiac output using pulsed Doppler. Maximum cardiac output occurred at AV intervals of 150 and 200 ms at rates of 80 and 100 beats/minute, and at 150 ms at a rate of 118 beats/minute (p less than .05). An increase in the AV interval to 250 ms resulted in a decrease in cardiac output at all heart rates (p less than .01). We recommend the noninvasive measurement of cardiac output, if available, for determining the optimum AV interval in an individual patient; otherwise, an AV interval of 150 or 200 ms will provide the highest cardiac output in most patients.

Cardiac tamponade as the initial presentation of malignancy.

Although neoplastic involvement of the pericardium frequently is present postmortem, cardiac manifestations before death are uncommon, and cardiac tamponade as the initial presentation of cancer is rare. In this study, a malignancy was first recognized in eight of 23 patients (35 percent) who presented with cardiac tamponade. Seven of these eight patients had lung and one patient thyroid carcinoma. The prognosis of these eight patients was poor with seven of eight patients dead within a mean of seven weeks (range 2.5 to 16). Overall, pericardial fluid cytology demonstrated a specific diagnosis of malignancy in 14 of 19 patients (74 percent). Earlier recognition of the possibility of malignancy may allow initiation of appropriate local or systemic treatment to lessen the probability of cardiac tamponade and improve survival. We recommend that all patients who present with tamponade have cytology performed on the pericardial fluid, even if malignancy is not suspected initially.

A cost-benefit analysis of California's mandatory premarital screening program for syphilis.

As do most states, California requires premarital serologic tests for syphilis. The Venereal Disease Research Laboratory (VDRL) test and a fluorescent treponemal antibody-absorbed (FTA-ABS) are often used in series for this purpose. In 1979 in California, there were approximately 300,000 persons tested premaritally, but only 35 were found to have asymptomatic infectious syphilis (incidence=0.012%). Including all the direct costs of this screening program, the yearly costs of premarital screening is $8.5 million or almost $240,000 per case found. If one takes into account the sensitivities and specificities of the tests, one still has 6 false-negative and 90 false-positive tests using the 1979 figures. The benefits of the program are the number of cases of congenital syphilis that are prevented. Using a worse-case method, no more than 1.5% of the cases of syphilis detected would result in a case of congenital syphilis. The estimated benefits would result in a savings of approximately $161,000. The economic costs of the premarital screening program far outweigh the benefits.

Duration of hypoglycemia and need for intravenous glucose following intentional overdoses of insulin.

To assess the treatment of intentional insulin overdoses with intravenous (IV) glucose, we reviewed the records of 17 attempts in 15 patients seen during a ten-year period. The mean age of our patients was 29 +/- 9 years, and the mean overdose of insulin was 386 +/- 276 units. Eight patients were insulin-dependent diabetics and seven patients had no history of diabetes. We found that the nondiabetics were more likely to present with hypoglycemia (serum glucose less than 50 mg/dL) and develop recurrent hypoglycemia, despite oral intake and IV glucose infusion, than were diabetic patients (P less than .05, Fisher's exact test). We also found a significant relation (P less than .01) between the amount of insulin taken as a single overdose and either the total amount of IV glucose administered or the total time of IV glucose treatment until the hypoglycemic effects of excess insulin had resolved (glucose [g] = 52 + (.699) (dose U), R = .929 and time [h] = 10.5 + (.028) (dose U), R = .817). No patient sustained permanent complications from hypoglycemia. We conclude that prolonged, aggressive IV glucose infusion and serial monitoring of serum glucose levels is required in insulin overdoses. These patients may become hypoglycemic much later than predicted from the conventional duration of action of the various insulin preparations.

A double-blind, randomized clinical trial of methylprednisolone in status asthmaticus.

Twenty-five consecutive patients admitted with status asthmaticus were blindly randomized to receive intravenous (IV) methylprednisolone every six hours for three days at one of the following dosages: (1) low, 15 mg; (2) medium, 40 mg; or (3) high, 125 mg. All other therapy, including IV and inhaled bronchodilators, was kept constant. We measured forced expiratory volume in 1 s (FEV1) to quantitate response. The high-dose group improved significantly by the end of the first day, the medium-dose group improved by the middle of the second day, but the low-dose group did not improve significantly in three days. Together, the high- and medium-dose groups were significantly improved (FEV1 greater than 50% of predicted) compared with the low-dose group. No serious steroid side effects were encountered. We conclude that the greater benefit of higher doses of steroids, such as 125 mg of methylprednisolone every six hours, justifies their use in severe asthma.

Auditory duration discrimination in the parakeet (Melopsittacus undulatus).

Two parakeets were trained by a method of avoidance conditioning to respond to duration differences in successively occurring tone bursts. Difference limens for duration were obtained at six durations (20-160 ms) of a 2.86-kHz tone presented at a sensation level of 60 dB. Calculations of the Weber fractions at each duration showed threshold values which compare favorably to similar measures for man ranging between 0.10 and 0.20.