Effects of thyroid state on venous compliance and left ventricular performance in rats

Abstract

The cardiovascular system of hypothyroid, normal, and hyperthyroid rats was studied by evaluation of the peripheral venous circulation and left ventricular (LV) systolic and diastolic performance in rats. Cardiac index (CI) and CI during a volume load were measured in open-chest rats. When compared with control, hypothyroid rats showed a decrease in heart rate, aortic pressure, LV systolic pressure, first derivative for LV pressure (LV dP/dt), CI, and CI during a volume load. LV pressure-volume relation was shifted to the right, muscle stiffness was unchanged, and LV relaxation was prolonged. There was a decrease in mean circulatory filling pressure (MCFP) to 6.3 +/- 0.2 from 7.6 +/- 0.2 mmHg in control rats. This was associated with an 11% decrease in unstressed vascular volume and 12% decrease in total blood volume but no change in venous compliance. In hyperthyroid rats there was an increase in heart rate, LV systolic pressure, LV dP/dt, CI, and CI during a volume load. LV chamber stiffness was increased, but muscle stiffness and LV relaxation were unchanged. There was an increase in MCFP to 9.5 +/- 0.3 mmHg and a decrease in venous compliance to 2.65 +/- 0.12 compared with 3.20 +/- 0.09 ml.mmHg-1.kg-1 in control rats. Unstressed vascular volume and total blood volume were unchanged. In conclusion, hyperthyroid rats have augmented LV systolic function and altered diastolic function which, combined with changes in the venous circulation, result in increased venous return and thus cardiac output. In hypothyroid rats both LV systolic and diastolic function are altered. When combined with changes of the venous circulation the changes result in a decrease in cardiac output.

Abnormal cardiac function in the streptozotocin-diabetic rat. Changes in active and passive properties of the left ventricle.

“…Rats were allowed to recover for 4 h. Left ventricular dP/dt was obtained from a differentiating circuit in the physiologic recorder (model 2400, Gould, Inc., Cleveland, OH) with the high-frequency filter cutoff set at 100 Hz. In conscious rats 100-150 consecutive beats of LV pressure were recorded directly onto a computer (model AT, IBM Corp., White Plains, NY) and digitized at 1,000 Hz (6,7). An example of an LV pressure recording in a conscious rat is shown in Fig.…”

“…From the recordings ofLV pressures and dP/dt, LV relaxation was determined in untreated diabetic, treated diabetic, and control rats using previously established methods (6,7). Briefly, the decay of LV pressure with time can be closely approximated by the exponential relation: P= PBe + PA, (1) where PB + PA is LV pressure at maximum negative LV dP/dt, PA is LV asymptote pressure, and a is the constant of the exponential relation.…”

“…dP/dt (mm Hg/s) Isolated LV pressure-volume relationship. Pressure-volume data were recorded using methods previously described (6,7). After the measurement of peak developed pressure, potassium chloride (2 meq/ ml) was injected through the femoral vein catheter to arrest the heart.…”

“…Myocardial stiffness. The incremental modulus (ENc) and the myocardial stiffness constant (K.) were calculated assuming a spherical geometry (inner and outer radii = a and b, respectively) for the left ventricle, according to previously described methods (7,9). Briefly, midwall radial stress (a) at each pressure point was calculated from the measured values for LV cavity volume and wall volume (mass/ 1.05) using the expression: where…”

Hemodynamic and tissue oxygenation responses to exercise and beta‐adrenergic blockade in patients with hyperthyroidism

“…Together, these effects result in a hyperdynamic circulatory state, 12 the overall effect of which is to alter loading conditions on the heart; the increase in total blood volume increases preload while the decrease in systemic vascular resistance reduces afterload. 12 Gay et al 20 demonstrated in experimental studies that ventricular filling pressures are increased in hyperthyroidism and associated with a decrease in venous compliance.…”