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Biomedical subjects

R M Lang

Publications and source records attributed to R M Lang.

At least 91 records · Page 5Linked to original sources
PubMed1995

Physiological relevance of T-tube model parameters with emphasis on arterial compliances.

The T-tube model of systemic arterial circulation was examined with respect to the physiological relevance of model parameters. root aortic pressure [Pao(t)] and flow [Qao(t)] and descending aortic flow [Qb(t)] were measured in anesthetized, open-chest dogs under control conditions, during inflation of a balloon positioned in the left external iliac artery (n = 5), and during infusion of vasoactive drugs nitroprusside (NTP, n = 4) and phenylephrine (PHL, n = 5). With Pao(t) as the input, the model accurately predicted both Qao(t) and Qb(t) under all conditions (r2 > 0.96). The balloon inflation data established the ability of the model to discriminate between proximal and distal arterial mechanical properties. Furthermore, proximal properties (i.e., tube characteristic impedances and transit times) were independent of distal properties such as terminal compliances and resistances (or equivalently, wave reflections). The effects of NTP and PHL were pharmacologically consistent and served to further validate this model. NTP primarily affected distal (load) properties, whereas PHL altered both load and tube parameters. Physiological interpretation of model parameters, particularly compliance, is also discussed. The ability of the model to correctly discriminate between proximal and distal arterial properties is relevant because these properties may affect cardiovascular function differently.

Animals↗
PubMed1995

Alterations in systemic arterial mechanical properties during septic shock: role of fluid resuscitation.

The effects of septic shock (endotoxin; EDTX) on arterial mechanical properties were studied in anesthetized rabbits, both in the absence (EDTX alone) and presence (EDTX + fluids) of fluid resuscitation. Aortic pressure-flow (n = 20) and pressure-diameter (n = 10) measurements were used to calculate systemic arterial and regional aortic mechanical properties. At 3 h of EDTX shock, EDTX-alone rabbits had elevated total peripheral resistance (TPR, + 30%, P < 0.05), reduced cardiac output (CO, -40%, P < 0.05), and increased aortic characteristic impedance (Zc, +78%, P < 0.05). In contrast, the EDTX + fluids group responded with decreased TPR (-30%, P < 0.05), a tendency to increase CO (+23%), and elevated Zc (+46%, P < 0.05). A reduction in aortic diameter (-20%, P < 0.05) and an increase in elastic modulus (+50%, P < 0.05) and water content (+23%, P < 0.02) of the aortic wall were observed following endotoxemia. Thus following EDTX 1) "hyperdynamic" septic shock profile (i.e., low TPR, high CO) was observed only when concomitant fluid replacement was provided, 2) aortic wall stiffening was present due to both increased smooth muscle tone and vessel wall edema, and 3) fluid resuscitation resulted in discordant changes in TPR and Zc, suggesting differential flow-induced vasodilation between arteriolar and aortic smooth muscle.

Animals↗
PubMed1994

First-dose effects of enalapril 2.5 mg and captopril 6.25 mg in patients with heart failure: a double-blind, randomized, multicenter study. The Enalapril-Captopril Investigators.

Significant decreases in blood pressure (BP) may occur when administration of angiotensin-converting enzyme (ACE) inhibitors is initiated for the treatment of heart failure. The purpose of this study was to compare the safety and tolerability of recommended initial doses of the longer-acting ACE inhibitor enalapril (ENAL) with those of the shorter-acting captopril (CAP) in patients with heart failure who were treated concomitantly with digitalis and diuretic agents. We evaluated BP, serum ACE activity, and clinical status when a low, first dose of ENAL (2.5 mg, n = 59) or CAP (6.25 mg, n = 58) was administered in a double-blind, randomized, and parallel fashion to 117 patients with mild to moderate heart failure. BP and serum ACE activity were measured at 30 min and hourly for 8 hours after drug administration. BP decreases were similar for both groups (mean supine BP -6.2/-4.8 mm Hg for ENAL vs -8.3/-6.4 mm Hg for CAP; mean standing BP -9.2/-5.6 mm Hg for ENAL vs -10.0/-4.7 mm Hg for CAP). Although the maximum mean decrease in BP occurred at hours 4 and 5 in the ENAL group and hours 1 and 2 in the CAP group, considerable between-group overlap was observed for individual patients. Decreases in mean serum ACE activity occurred earlier and were of shorter duration in the CAP group. ENAL significantly inhibited serum ACE activity to a greater extent than did CAP at all time points except the 1st hour. Administration of a first dose of ENAL, 2.5 mg or CAP, 6.25 mg to patients with heart failure was well tolerated.

Adult↗
PubMed1994

Effects of left ventricular pressure on sonicated albumin microbubbles: evaluation using an isolated rabbit heart model.

OBJECTIVES: We used an isolated, crystalloid-perfused rabbit heart model to test the hypothesis that the phasic changes in left ventricular contrast are due to bubble compression and decompression during systole and diastole, respectively. BACKGROUND: Contrast enhancement of the left ventricular cavity has been shown to decrease during ventricular systole. This phenomenon has been attributed to pressure-induced microbubble destruction. Such destruction, if confirmed, would severely confound the quantitative interpretation of contrast echocardiographic data. METHODS: A fixed volume of contrast solution (5% human albumin and Albunex, approximately 400:1 ratio) was introduced into a latex balloon placed within the left ventricular cavity of an isolated paced rabbit heart preparation (n = 12). Instantaneous left ventricular pressure was measured using a high fidelity microtip catheter and digitized on-line. The beating heart was placed in a water tank, and ultrasound images were obtained using a 7.5-MHz transducer and were recorded and digitized off-line at 12 frames/s. Simultaneously, the pacing signal was used for gated on-line acquisition of end-diastolic frames. A simple theoretic model based on surface tension physical principles was used to predict changes in bubble size and, consequently, the reflection intensity in response to the measured changes in left ventricular pressure. RESULTS: We found that under peak left ventricular systolic pressures ranging from 89 to 155 mm Hg, 1) end-diastolic videointensity decreased by 8 +/- 6% (mean +/- SD) over 25 consecutive heart beats; and 2) intracyclic variations in measured videointensity were in close agreement with the theoretic calculations: 80.1 +/- 2.9% versus 80.2 +/- 4.6% of diastolic videointensity at systole. CONCLUSIONS: The major cause of systolic decrease in contrast enhancement is periodic bubble compression (as opposed to bubble destruction) induced by high systolic pressures. The minor progressive decrease in end-diastolic videointensity reflects the degree of instability of Albunex microbubbles under left ventricular pressures. However, the clinical impact of these destructive effects is likely to be only minor because of the rapid transit of microbubbles through the left heart chambers and myocardial microcirculation.

Albumins↗
PubMed1994

Measurement of regional elastic properties of the human aorta. A new application of transesophageal echocardiography with automated border detection and calibrated subclavian pulse tracings.

BACKGROUND: Evaluation of regional aortic elastic properties in humans has been hampered by the need for invasive techniques to access instantaneous aortic pressure, wall thickness, and cross-sectional area or diameter. In this study, a new noninvasive method is presented for quantification of regional aortic elastic properties. METHODS AND RESULTS: Twenty-five patients were studied during transesophageal echocardiographic procedures. Measurements of instantaneous aortic cross-sectional area were obtained with an automated border detection algorithm applied to short-axis transesophageal two-dimensional echocardiographic images of the proximal descending thoracic aorta. Instantaneous aortic wall thickness was derived from combined two-dimensional targeted M-mode end-diastolic wall thickness and instantaneous aortic area measurements. Instantaneous aortic pressures were estimated from calibrated subclavian pulse tracings recorded simultaneously. Data were digitized to generate aortic area-pressure loops. Regional aortic mechanical properties were quantified in terms of compliance per unit length (C is the slope of the area-pressure regression), aortic midwall radius (Rm), and incremental elastic modulus of the aortic wall (Einc). To assess the independent effect of age, Rm and Einc values were compared at a common level of aortic midwall stress (0.666 x 10(6) dynes/cm2). Mean values (+/- SD) for C, Rm, and Einc were 0.01 +/- 0.004 cm2/mm Hg, 1.14 +/- 0.17 cm, and 7.059 +/- 4.091 x 10(6) dynes/cm2, respectively. An inverse linear correlation was found between aortic compliance per unit length and age (r = -.68, P < .0007). Incremental elastic modulus was related to age (r = +.80, P < .00003) in a nonlinear fashion such that it increased sharply after the age of 60 years. Finally, midwall radius was less tightly correlated with age (r = +.45, P < .05). Values for C, Rm, and Einc as well as the age dependency of these properties are similar to those reported previously when invasive techniques were used. CONCLUSIONS: This methodology constitutes a new tool to improve the clinical evaluation of regional aortic elastic properties in multiple disease states.

Adult↗
PubMed1994

Paradoxic improvement in regional wall motion during high-dose dobutamine stress echocardiography. A marker for hibernating myocardium?

Dobutamine stress echocardiography detects myocardial ischemia by inducing regional left ventricular systolic dysfunction. Augmentation of wall motion in hypokinetic segments has also been noted with low-dose dobutamine, suggesting myocardial viability. We report a case of regional ventricular improvement during high-dose dobutamine therapy, which may represent relief from myocardial hibernation or changes in regional loading conditions.

Aged↗
PubMed1993

Noninvasive assessment of the direct action of oral nifedipine and nicardipine on left ventricular contractile state in patients with systemic hypertension: importance of reflex sympathetic responses.

OBJECTIVES: This study was designed to noninvasively assess the direct action of calcium channel blockers on left ventricular contractility in humans and to establish a framework for determining the importance of reflex sympathetic responses to any pharmacologic intervention. BACKGROUND: Assessment of left ventricular contractility in patients taking calcium channel blockers by using traditional indexes of systolic performance is difficult because of the after-load-reducing and reflex sympathetic effects of the drugs. METHODS: Fifteen hypertensive patients (mean blood pressure 127 +/- 15 mm Hg) were studied with Doppler echocardiography and calibrated subclavian pulse tracings while receiving placebo and 1 week after randomization to treatment with oral nifedipine (20 mg three times daily; n = 7) or nicardipine (30 mg three times daily; n = 8). Left ventricular circumferential end-systolic wall stress versus rate-corrected velocity of shortening (Vcfc) relations were generated over a range of loads using nitroprusside. Data were acquired before and during esmolol infusion, thereby allowing assessment of hemodynamic responses with the sympathetic nervous system functionally intact as well as ablated. The adequacy of sympathetic blockade was confirmed with isoproterenol challenges. In each case, left ventricular contractile state was measured relative to placebo and esmolol data as delta Vcfc at a common end-systolic wall stress. Increased and decreased contractility were defined as delta Vcfc > 0 and delta Vcfc < 0, respectively. RESULTS: Nifedipine and nicardipine equally decreased blood pressure and end-systolic wall stress and increased left ventricular percent fractional shortening and stroke volume. Neither drug alone consistently altered ventricular contractility compared with placebo. Ablation of reflex sympathetic tone with esmolol unmasked a negative inotropic effect for nifedipine (p = 0.03 vs. esmolol alone) but not nicardipine (p = 0.68 vs. esmolol alone). The difference between the contractility effects of nifedipine plus esmolol versus those of nicardipine plus esmolol approached statistical significance (p = 0.07). CONCLUSIONS: Totally noninvasive techniques showed a differential effect on left ventricular contractility between nifedipine and nicardipine when alterations in afterload and reflex sympathetic responses were eliminated as confounding variables. This diagnostic approach, based on the use of pharmacologic probes, should have wide applicability for assessing the direct inotropic effect of any agent, even in the presence of complex primary and secondary physiologic modes of action.

Adrenergic beta-Antagonists↗
PubMed1993

Peripartum heart failure associated with prolonged tocolytic therapy.

beta-Adrenergic receptor agonist tocolysis has been reported to cause noncardiogenic pulmonary edema. We report an association between chronic terbutaline therapy and cardiomyopathy in peripartum women. Among 15 gravidas who had peripartum heart failure, 4 had received prolonged terbutaline tocolysis. Although those four patients had completely normalized ventricular function, only 7 of the 11 others recovered. We suggest that gravidas receiving long-term beta-sympathomimetic tocolysis undergo close evaluation of cardiac function.

Cardiomyopathies↗
PubMed1993

Ultrasonic backscatter system for automated on-line endocardial boundary detection: evaluation by ultrafast computed tomography.

OBJECTIVES: The purpose of this study was to evaluate the accuracy of the recently developed echocardiographic on-line endocardial border detection system using ultrafast computed tomography, an independent and proved tomographic imaging modality. BACKGROUND: The automated system for on-line endocardial border detection identifies the blood-tissue interface by acoustic quantification of the ultrasonic backscatter signal. METHODS: Eighteen subjects were screened by conventional echocardiography and acoustic quantification. Ten of these, with high quality echocardiographic images, were also examined by ultrafast computed tomography. Comparable image planes at the midpapillary level were analyzed. Measurements of left ventricular cavity area were compared at end-diastole and end-systole and time course analyses of cavity area during the cardiac cycle were performed. RESULTS: There was good correlation between values for left ventricular end-diastolic area (r = 0.99), end-systolic area (r = 0.93) and fractional area change (r = 0.91) using the two methods. The on-line backscatter system underestimated end-diastolic area (p < 0.001), but the negative bias was small (-1.6 cm2) and the 95% confidence intervals were narrow (-3.6 cm2 to +0.4 cm2). In contrast, the backscatter system overestimated end-systolic area (p < 0.02); the positive bias for this variable was also small (+2.6 cm2) but the confidence intervals were relatively wide (+7.9 to -2.8 cm2). The negative bias of backscatter values for cavity area was fairly constant during diastole and early systole (range -5% to -10%), but during the second half of systole, backscatter values increased progressively relative to computed tomographic values. Real time values for fractional area change measured by the backscatter system were 13% smaller than those determined by ultrafast computed tomography (p < 0.001), with wide confidence intervals (+3% to -30%). Absolute peak rates of area change during systole and diastole were lower by 39% (p < 0.001) and 41% (p < 0.01), respectively, using the on-line ultrasonic backscatter system. Time course analyses revealed the errors to be consistent with cardiac cycle-dependent alterations in gain sensitivity of the ultrasonic backscatter system. CONCLUSIONS: The ultrasonic backscatter system is associated with cyclic cavity area measurement errors that need to be addressed if its early promise for on-line assessment of ventricular function is to be fulfilled. Incorporation of an electrocardiographically triggered time-varying gain control may improve accuracy for on-line analysis of ventricular performance.

Echocardiography↗
PubMed1993

Cardiovascular consequences of correction of the anemia of renal failure with erythropoietin.

The purpose of this study was to define the physiologic responses of the heart and peripheral circulation to chronic anemia using noninvasive measurements while eliminating confounding biochemical, pharmacologic and physiologic variables. Stable chronic hemodialysis patients were studied at the University Hospital based chronic dialysis unit and echocardiography laboratory before and after therapy with human recombinant erythropoietin (rHuEPO). Subjects included maintenance hemodialysis patients free of left ventricular regional wall motion abnormalities discernible by echocardiography, rhythm disturbance, significant valvular or ischemic heart disease. Two-dimensional echocardiograms and simultaneous targeted M-mode echocardiograms, phonocardiograms and externally acquired subclavian artery pulse tracings were used to measure whole blood viscosity, arterial blood gases and ionized calcium, complete blood count, electrolytes, creatinine, blood urea nitrogen (BUN), and inorganic phosphate. All measurements were made immediately post-dialysis before and after therapy with rHuEPO. The interval between pre- and post-rHuEPO studies was 8.3 +/- 2.3 months. We found that post-dialysis hematocrit rose from 24.7 +/- 0.9 to 36.4 +/- 0.9%, hemoglobin from 83 +/- 3 to 121 +/- 3 g/liter and whole blood viscosity from 2.87 +/- 0.11 to 3.71 +/- 0.18 centipoise (all, P < 0.001 after therapy with rHuEPO). The remaining biochemical measurements did not change. Heart rate fell from 83 +/- 3 to 77 +/- 3 beats/min (P = 0.013). Left ventricular preload and afterload were not statistically different before and after rHuEPO. Total vascular resistance rose from 1313 +/- 84 to 1568 +/- 129 dynes.sec.cm-5, P = 0.029. Cardiac output and cardiac index fell by 12 and 15% (P = 0.024 and 0.030), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Non-invasive assessment of cardiovascular mechanics using a new, user-friendly software application.

Currently, in most non-invasive imaging laboratories, echocardiographic tracings are interpreted by "eyeballing" M-mode and 2-dimensional echocardiographic recordings. This subjective method of data analysis severely hampers the possibility of serial assessment of physiological interventions on cardiovascular disease states. Moreover, acquisition of important cardiovascular physiological data usually requires recordings of instantaneous aortic pressure and flow data that, until recently, could only be acquired invasively in the cardiac catheterization laboratory. Recently, our laboratory has developed and validated new "non-invasive" methods for the acquisition of aortic pressure and flow using calibrated subclavian pulse tracings and continuous wave aortic Doppler, respectively. With these limitations and new developments in mind, we developed new software that enables simultaneous non-invasive acquisition of left ventricular (LV) chamber geometry and aortic pressure and flow data. This new, user-friendly software in conjunction with other non-invasive tools allows non-invasive quantification of multiple cardiovascular physiological parameters. More importantly, the new software enables objective and serial assessment of multiple pharmacological interventions on various patients' disease states.

Aged↗
PubMed1992

Effects of simultaneous alterations in preload and afterload on measurements of left ventricular contractility in patients with dilated cardiomyopathy: comparisons of ejection phase, isovolumetric and end-systolic force-velocity indexes.

OBJECTIVES: The study was designed to critically evaluate the clinical utility of ejection phase and nonejection phase indexes of contractile state in patients with severe left ventricular dysfunction. BACKGROUND: Ejection phase indexes of left ventricular systolic performance are unable to differentiate contractility changes from alterations in loading conditions. Isovolumetric and end-systolic force-velocity indexes have been proposed as alternative measurements of contractile state that are load independent. METHODS: Seventeen patients with nonischemic dilated cardiomyopathy were studied during cardiac catheterization. High fidelity central aortic and left ventricular pressure measurements were made with simultaneous echocardiographic recordings of chamber minor- and long-axis dimensions and wall thickness. Data were acquired under control conditions, during nitroprusside infusion and with dopamine (6 micrograms/kg per min). RESULTS: Patients were classified into those without (group 1, n = 10) and those with (group 2, n = 7) a decrease in end-diastolic circumferential wall stress in response to dopamine. There were no baseline differences between the groups in functional class, left ventricular chamber geometry or cardiovascular hemodynamics. Ejection phase indexes were variably altered by changes in preload, afterload and heart rate, thereby complicating physiologic interpretation of data. Dopamine increased the commonly used isovolumetric index, maximal rate of rise in left ventricular pressure (dP/dtmax), by 64% for group 1 but by only 16% for group 2 (p less than 0.001), resulting in an underestimation of contractile state change in 41% of patients. In contrast, the left ventricular end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation, which incorporates afterload, ventricular wall mass and heart rate in its analysis, was a sensitive contractility measurement that was preload independent and equally augmented by dopamine for both groups. CONCLUSIONS: Of the left ventricular contractility indexes evaluated, the end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation was the most physiologically appropriate for assessing pharmacologically induced changes in inotropic state that were accompanied by complex alterations in loading conditions in patients with dilated cardiomyopathy.

Cardiac Catheterization↗
PubMed1992

Diurnal blood pressure variation and cardiac mass in American blacks and whites and South African blacks.

American blacks exhibit higher nocturnal blood pressure than American whites with similar daytime pressure. To determine whether this represents a true racial difference, as opposed to a consequence of different environmental factors, we measured ambulatory blood pressure, cardiac left ventricular mass, and urinary electrolyte excretion in 22 South African blacks (15 women, aged 36 +/- 12 years) and age, sex, and daytime mean pressure-matched American blacks and whites. While all three groups exhibited similar daytime blood pressure, American blacks displayed significantly higher nighttime mean blood pressure. Both African blacks and American whites experienced the same fall in nighttime blood pressure. Left ventricular mass index was highest in American blacks and lowest in South African blacks. Urine sodium excretion was similar in all groups, but both black populations excreted significantly less potassium than American whites. The data suggest that the differences in diurnal blood pressure rhythm between American blacks and whites do not represent a true racial difference, but more likely are environmental in origin. Furthermore, since both black populations had similar cation excretion rates, yet differed in blood pressure pattern and cardiac mass, divergence in dietary sodium or potassium intake cannot explain the ethnic group differences in the United States.

Adult↗
PubMed1992

A time-course study of the effects of pentobarbital, fentanyl, and morphine chloralose on myocardial mechanics.

Cardiovascular physiological studies in anesthetized animals may be confounded by the hemodynamic actions of the anesthetic agents themselves. To identify an anesthetic regimen that does not significantly influence cardiovascular physiology, the hemodynamic responses of 28 dogs were studied. Animals were equally divided among groups with 1) no anesthesia (i.e., trained conscious preparation), 2) pentobarbital sodium, 3) fentanyl citrate, and 4) a combination of morphine sulfate and alpha-chloralose. Anesthesia was maintained for 3 h. Data were acquired with the use of ultrasound imaging of the heart in conjunction with invasive pressure measurements. Left ventricular ejection phase indexes and end-systolic force-velocity relations were used to evaluate the effects of each anesthetic agent on overall systolic performance and myocardial contractility. Compared with the conscious animals, pentobarbital profoundly depressed systolic performance (P less than 0.05 vs. control) because of a reduction in myocardial contractility (P less than 0.01) and an increase in left ventricular afterload (end-systolic wall stress, P less than 0.05). Fentanyl increased myocardial contractility (P less than 0.05) but also tended to increase afterload with the net result that overall systolic performance remained unchanged. Morphine-chloralose did not affect overall ventricular systolic performance or its individual determinants. Pentobarbital and fentanyl also caused progressive time-dependent deteriorations in all parameters of systolic function during prolonged anesthesia. In contrast, cardiac function was stable for greater than or equal to 3 h after induction of morphine-chloralose anesthesia. The hemodynamic profile of dogs anesthetized with morphine-chloralose most closely resembled that of the conscious animals. Morphine-chloralose is recommended when prolonged anesthesia is required for studies of cardiovascular physiology.

Anesthetics↗
PubMed1992

Sex-associated differences in left ventricular function in aortic stenosis of the elderly.

BACKGROUND: In aortic stenosis, the response of the left ventricle to pressure overload varies from compensated hypertrophy to overt heart failure. The determinants of left ventricular adaptation are poorly understood. METHODS AND RESULTS: Left ventricular function was compared to assess the role of sex in 34 women and 29 men 60 years or older with both hemodynamic and echocardiographic data characteristic of severe aortic stenosis and no important coronary artery disease. Despite a similar degree of left ventricular outflow obstruction in women versus men (aortic valve area 0.54 +/- 0.20 versus 0.59 +/- 0.19 cm2, NS), the left ventricle of women had a greater fractional shortening (37 +/- 12 versus 25 +/- 12%, p = 0.001), achieved a smaller end-systolic chamber size (1.82 +/- 0.64 versus 2.17 +/- 0.65 cm/m2, p = 0.04), and generated more pressure (210 +/- 35 versus 182 +/- 29 mm Hg, p = 0.001) with a greater maximum positive dP/dt (2.153 +/- 794 versus 1,595 +/- 384 mm Hg/sec, p = 0.02). The men had a lower cardiac index (2.12 +/- 0.59 versus 2.49 +/- 0.63 l/min/m2, p = 0.02), higher mean pulmonary artery pressure (35 +/- 13 versus 27 +/- 10 mm Hg, p = 0.01), and shorter ejection period (340 +/- 40 versus 370 +/- 40 msec, p = 0.02). Women and men were equally symptomatic. Supernormal left ventricular ejection performance was present in 41% of the women and only 14% of the men (p = 0.002). This subgroup of women had a small, thick-walled chamber (end-diastolic radius to thickness ratio, 1.58 +/- 0.52 versus 2.45 +/- 0.51 in control women, p = 0.01) with low end-systolic wall stress. Subnormal ejection performance was present in 64% of the men and only 18% of the women (p = 0.002). This subgroup of men had an increased chamber size and high end-systolic wall stress compared with control men. Greater left ventricular mass was present in men compared with women (211 +/- 55 versus 179 +/- 55 g/m2, p = 0.03). CONCLUSIONS: Sex is a factor in left ventricular adaptation to valvular aortic stenosis in adults 60 years or older.

Aged↗