Posterior lymph heart function in two species of anurans: analysis based on both in vivo pressure-volume relationships by conductance manometry and ultrasound

Abstract

Rhinella marina and Lithobates catesbeianus have known differences in the capacity to mobilize lymph to stabilize blood volume following dehydration and hemorrhage. The purpose of these experiments was to assess whether there are interspecific differences in basic lymph heart functions. The end diastolic volumes of posterior lymph hearts averaged 10.8 μl kg⁻¹ in R. marina and 7.9-10.8 μl kg⁻¹ in L. catesbeianus by conductance manometry, and 9-32 μl kg⁻¹ in R. marina by ultrasound techniques, which correlated with body mass. Stroke volumes were approximately 20% of end diastolic volumes in both species. Peak systolic pressures and stroke work were correlated with the index of contractility (dP/dt(max)) in both species. Stroke volume was correlated to stroke work but not peak systolic pressure, end diastolic volume or end diastolic pressure indicating the preload variables do not seem to determine stroke volume as would be predicted from Starling considerations of the blood heart. Renal portal elastance (end systolic pressure/stroke volume) an afterload index did not differ interspecifically, and was equivalent to values for systemic flow indices from mice of equivalent ventricular volume. These data, taken together with predictions derived from mammalian models on the effect of high resistance indicate afterload (renal portal pressure), may be important determinants of posterior lymph heart stroke volume. The shape of the pressure-volume loop is different from an idealized version previously reported, and is influenced by end diastolic volume. Our data indicate that increasing end diastolic pressure and volume can influence the loop shape but not the stroke volume. This indicates that lymph hearts do not behave in a Starling Law manner with increased preload volume.

Fig. 1.

Calibration curve for Millar conductance catheter placed in tubing of differing diameters filled to a depth of 6 mm with 0.8% saline. Conductance in expressed as arbitrary units.

Fig. 2.

Captured ultrasound images of a single posterior lymph heart in one R. marina at end diastole (A) and end systole (B). Dashed lines outline the interior margins of the lymph heart. Scale bar, 1 mm.

Fig. 3.

Representative conductance pressure (kPa)–volume (μl) loops for four L. catesbeianus and five R. marina.

Fig. 4.

A series of pressure (kPa)–volume (μl) loops as 0.8% saline is infused into the lymphatic sac surrounding a posterior lymph heart in one R. marina. This illustrates that the end diastolic pressure increases the end systolic pressure of the heart, but stroke volume is independent of end diastolic volume and pressure.

Fig. 5.

The relationship between maximum contractility (kPa s^–1) and peak systolic pressure (kPa) of the posterior lymph hearts for R. marina (circles) and L. catesbeianus (crosses). The lines (solid for R. marina and dashed for L. catesbeianus) show a linear regression fitted to the data.

Fig. 6.

The relationship between maximal contractility (kPa s^–1) and stroke work (mJ) of posterior lymph hearts for R. marina (circles) and L. catesbeianus (crosses). The lines (solid for R. marina and dotted for L. catesbeianus) show linear regression fits to the data.

Fig. 7.

The relationship between variation in stroke volume (μl kg^–1) and stroke work (mJ) of posterior lymph hearts for R. marina (circles) and L. catesbeianus (crosses). The lines (solid for R. marina and dotted for L. catesbeianus) show linear regression fits to the data.

Fig. 8.

A representative pressure (kPa)–volume (μl kg^–1) loop (A) taken from R. marina (this study) compared with the only previously published pressure–volume loop for a lymph heart (B) (Jones et al., 1997).