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Biomedical subjects

R D Latham

Publications and source records attributed to R D Latham.

At least 19 recordsLinked to original sources
PubMed1991

Cardiac dysfunction in patients seropositive for the human immunodeficiency virus.

To confirm the presence of cardiac dysfunction in a group of patients seropositive for the human immunodeficiency virus with either dyspnea on exertion or a reduced anaerobic threshold, 9 patients with no history of opportunistic infection underwent exercise right-sided heart catheterization. When compared with 13 control patients previously exercised in the same manner, the patients showed elevated exercise pulmonary capillary wedge pressure (14.6 +/- 3.3 mm of mercury versus 9.9 +/- 3.3 mm of mercury; P less than .005) and right atrial pressure (10.1 +/- 2.1 mm of mercury versus 4.7 +/- 3.2 mm of mercury; P less than .001) at a similar exercise oxygen consumption and cardiac index. Of the 9 patients, 8 had at least 1 catheterization value outside the 95% confidence limits for the control group and 4 patients had multiple abnormalities. Values for blood CD4 lymphocytes were 0.2 x 10(9) per liter or more for 7 of the 9. One patient underwent endomyocardial biopsy with findings consistent with a cardiomyopathy. We conclude that cardiac disease may occur at any immunologic stage of human immunodeficiency virus infection. These observations suggest an effect of this disease on the heart.

Adult↗
PubMed1990

Isolated aorta setup for hemodynamic studies.

A setup consisting of a high-performance hydraulic pump connected to the ascending part of an isolated aorta, including all major distal branches, each loaded with calibrated artificial resistors, was developed. The system was used to study total aortic compliance of the baboon as a function of mean aortic pressure (n = 5). The aorta loaded with the resistors was mounted in a custom-designed sink table, such that it was submersed in physiological saline maintained at 37 degrees C. Mean distending pressure in the entire aorta could be varied. The three-element Windkessel model was used to estimate total aortic compliance from pressure and flow waves generated by the pump. Total aortic compliance as a function of mean pressure was fitted with a logarithmic function: Ln(Compliance) = A + B * P. The value of A (+/- SE) was: 1.565 +/- 0.319 and B: -0.020 +/- 0.003 (P less than 0.001). The results were compared with previously published results (also using the same three-element Windkessel fit) obtained in three of the same animals in vivo. The in vivo data were A: 1.095 +/- 0.235 and B: B: -0.019 +/- 0.003. In vitro data had a significantly higher value of A than in vivo (P = 0.017), implying a significantly higher aortic compliance in vitro than in vivo. Occlusion of the proximal descending aorta was performed at a low distending pressure (55 mm Hg) to determine the proximal compliance. It was found (n = 4) that 46 +/- 11% (SD) of the total arterial compliance is to be attributed to the ascending and proximal descending aorta.

Animals↗
PubMed1990

Pulmonary arterial compliance at rest and exercise in normal humans.

We evaluated the feasibility of determining pulmonary arterial compliance (Cp) by a parameter estimation procedure based on the three-element windkessel model. Eight normal patients studied with multisensor micromanometry technology had simultaneous rest and exercise pulmonary artery pressures (PAP) and flows recorded. These were submitted to the model and independent methods to determine Cp, pulmonary characteristic impedance (Zc), and pulmonary vascular resistance (PVR). Significant changes in heart rate, PAP, and stroke volume (P less than 0.05) occurred with exercise. In comparing rest and exercise Zc and PVR values determined by the model and independent methods, and in comparing each method for these values, there was no significant difference. Model-derived and independently derived estimates of Cp were significantly different at rest (P less than 0.04) and exercise (P less than 0.001). There was no significant difference between rest and exercise values of Cp by either method. The model estimates of PVR at rest (64 +/- 11 dyn.s.cm-5) and exercise (41 +/- 7 dyn.s.cm-5) (P = 0.06) and the model Zc value at rest (22 +/- 3 dyn.s.cm5) were appropriate. The model Cp values at rest (0.22 +/- 0.05 ml.mmHg-1.kg-1) correlated with previously reported normalized values in other species. This study reports the successful use of a parameter estimation procedure based on the three-element windkessel model to describe pulmonary artery compliance in normal humans.

Adult↗
PubMed1989

Recently diagnosed idiopathic dilated cardiomyopathy: incidence of myocarditis and efficacy of prednisone therapy.

Fifty-two patients with recently diagnosed idiopathic dilated cardiomyopathy were studied to determine the incidence of myocarditis; patients were randomly assigned to receive either conventional therapy alone or conventional therapy plus prednisone to assess possible therapeutic efficacy with regard to survival. Inflammatory criteria were present in 23% of the population studied with 13% having overt myocarditis according to the Dallas criteria. The addition of prednisone to conventional therapy did not improve survival in a homogeneous population with new-onset dilated cardiomyopathy. Furthermore, the diagnosis of myocarditis by endomyocardial biopsy did not influence 2-year survival once dilated cardiomyopathy had developed. Biopsy-documented myocarditis resolved in all patients, according to results of 3-month follow-up endomyocardial biopsies, regardless of treatment group. There was a trend for patients with a left ventricular ejection fraction less than 20% to show reduced survival at 2 years compared to the group with a higher ejection fraction (p = 0.07). Right ventricular dysfunction determined at catheterization was present in 20 of 52 patients and was the most significant predictor of survival. Patients with preserved right ventricular function had a 95% 24-month survival rate compared to 47% for patients with right ventricular diastolic dysfunction (right ventricular end-diastolic pressure greater than or equal to 11 mm Hg) (p = 0.005).

Adult↗
PubMed1988

Aortic input impedance during Mueller maneuver: an evaluation of "effective length".

Aortic input impedance was calculated in seven subjects in the control state (normal reflection) and during the Mueller maneuver (increased reflection) to evaluate "effective arterial length" under altered physiological conditions. Regional foot-to-foot pulse wave velocities and pressure waveforms along the aorta were used to define an "apparent anatomic length" or distance to a dominant discrete site of reflection "seen" by the ejecting ventricle. Time of wave travel was taken to be one-half the interval from the foot of the incident wave to the midsystolic inflection point. Knowing the time of travel from the returning reflection and velocity, distances calculated to the "apparent anatomic length" were 35 +/- 2 and 34 +/- 2 during control and Mueller maneuver, respectively (P = NS). The frequency of the first minimum of the modulus (fmin) and the first zero crossing of the phase angle (f phi) were determined from the input impedance spectra. During baseline conditions, fmin (3.9 +/- 0.2 Hz) approximately equaled f phi (4.2 +/- 0.2 Hz), and the resulting "effective lengths" calculated using the quarter-wavelength formula were similar to the apparent anatomic length. These data suggested that the aortic region incorporating the renal arterial branches as a site of discrete reflection and that terminal load was not significantly frequency dependent. During Mueller maneuver, however, f min (3.3 +/- 0.2 Hz) and f phi (5.1 +/- 0.2 Hz) were significantly discordant, the terminal load became strongly frequency dependent, and effective length calculated from f min was dissimilar (P less than 0.05) from the unchanged apparent anatomic length.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Ventricular/vascular coupling and regional arterial dynamics in the chronically hypertensive baboon: correlation with cardiovascular structural adaptation.

Ventricular/vascular coupling dynamics and regional hemodynamics of five hypertensive baboons with concentric left ventricular (LV) hypertrophy (mean arterial pressure +/- SD, 148 +/- 16 mm Hg; LV mass/body weight ratio 3.42 +/- 0.8) were compared with five normotensive controls (mean arterial pressure 89 +/- 3 mm Hg; LV mass/body wt ratio 2.73 +/- 0.5) at different mean arterial pressures. Ventricular/vascular dynamics were assessed by aortic input impedance, pulsatile/total power ratio, effective arterial elastance and compliance from a three-element Windkessel "lumped" model of the circulation. Regional arterial dynamics were assessed by pulse-wave velocities and local reflection coefficients. Systemic arterial compliance was similarly decreased with elevated pressure in both groups but was significantly more reduced for the hypertensive group compared with control animals at control (0.49 +/- 0.16 vs. 0.96 +/- 0.09 ml/mm Hg; p less than 0.05) and acutely lowered arterial pressure (0.62 +/- 0.26 vs. 1.41 +/- 0.24 ml/mm Hg, respectively). Changes in compliance were paralleled by differences in effective arterial elastance derived from cineventriculographic pressure-volume ratios. Regional foot-foot and apparent phase pulse-wave velocities were significantly increased for distal aortic segments of the hypertensive animals during elevated pressures compared with controls (cff, 17.5 +/- 7.5 vs. 8.7 +/- 3.0 m/sec; p less than 0.05). Histology of the aorta revealed significant increases in collagen content (microgram/mg dry wt) from proximal to distal aortic segments (27 +/- 2 vs. 38 +/- 6; p less than 0.005) in hypertensive animals but not in controls (27 +/- 2 vs. 32 +/- 6; NS). With pharmacological normalization of systemic arterial pressures, hypertensive baboons developed aortic wave speeds similar to controls but manifested significantly reduced compliance compared with controls. In contrast, with acute elevations of pressure, systemic arterial aortic compliances were similar for both groups, but distal pulse-wave velocities were significantly increased for hypertensive animals compared with controls. We conclude that measures of ventricular/vascular coupling and arterial dynamics are determined by both the level of arterial pressure and the physical characteristics of the cardiovascular system in chronic systemic hypertension and pressure overload ventricular hypertrophy.

Adaptation, Physiological↗
PubMed1987

Cardiovascular reserve in idiopathic dilated cardiomyopathy as determined by exercise response during cardiac catheterization.

Simultaneous right- and left-sided cardiac high-fidelity hemodynamic measurements were obtained at rest and supine exercise during cardiac catheterization in 27 patients (mean age 32 +/- 10 years) with idiopathic dilated cardiomyopathy to investigate the hemodynamic exercise response and possible mechanisms for the wide variation in exercise tolerance observed clinically. There were no significant differences in other rest hemodynamic variables between group 1, patients with a normal exercise factor (more than 600, n = 10), and group 2, patients with an abnormal exercise factor (less than 600, n = 17). A greater increase in stoke volume index (12 +/- 6 vs 2 +/- 8 ml/beats/m2, mean +/- standard deviation) and a greater decrease in systemic vascular resistance with exercise occurred in group 1 than in group 2 (-614 +/- 304 vs -406 +/- 291 dynes cm-5). Elevation of right ventricular end-diastolic pressure with exercise was significantly greater in group 2 than in group 1 (7 +/- 5 vs 1 +/- 4 mm Hg, respectively, p less than 0.05). A maintained cardiac reserve in patients with idiopathic dilated cardiomyopathy appears to be largely dependent on 2 primary factors: preservation of normal right ventricular function during exercise; and preservation of systemic vasodilator capability sufficient to produce a significant degree of afterload reduction during exercise.

Adolescent↗