Presenting Author Formerly Loyola University Chicago Stritch School of Medicine, Maywood, Illinois
The liver is well known as a large blood reservoir that can shift both stressed and unstressed volumes passively and actively in response to changes in portal venous and hepatic arterial blood flow, inflow and outflow blood pressures, autonomic nervous stimulation, and various humoral and pathophysiological factors. Not described is the characteristic of the liver to intrinsically modulate its own vascular pressure and volume independent of extrinsic factors.
Methods: Male Holtzman rats (n=5) were anesthetized (30 mg/kg sodium pentobarbital, i.p.) and heparinized (500 IU/kg, i.v.), the portal vein and inferior vena cava were isolated and cannulated, the liver was flushed with room temperature normal saline, and the liver quickly removed. Each liver was mounted on a scale in a 37°C chamber (95% O2-5% CO2) and pump-perfused (Masterflex) with donor rat blood at a baseline 1 ml/min/g of tissue. The hepatic venous pressure (Phv) was regulated by raising and lowering the blood reservoir. At each Time (see table), portal venous oscillations were counted over 3 to 12 min and the portal venous wavelet pulse pressures (Ppv) were measured over at least 40 wavelets.
Results: The portal venous pressures of 3 of the 5 livers oscillated spontaneously. One lasted only 26 min while the others went on for over 200 min. The characteristics of these oscillations varied widely from animal to animal, but there usually was an irregular cycle length and uneven wavelet magnitude that tended to degrade to a diminished size with higher frequency over time (see Figure 1).
Rat
Time (Min)
Maneuver
Mean Portal Venous Pulse Pressure (mmHg)
Frequency (Wavelets/Min)
Frequency (Hz)
Cycle Length (Sec)
1
0
Baseline
2.1 ± 0.9 (SD)
8.08
0.135
7.42
95
Baseline
1.5 ± 0.8
16.10
0.268
3.73
107
Change Phv
(0 to 10 mmHg)
2.5 ± 1.3
(Plt;0.001 vs. 95 Min Baseline)
17.00
0.283
3.53
180
Baseline
1.3 ± 0.5
18.67
0.311
3.21
2
0
Baseline
0.8 ± 0.4
14.42
0.240
4.16
60
Baseline
0.4 ± 0.3
20.00
0.333
3.00
130
Baseline
0.4 ± 0.2
23.78
0.396
2.52
3
0
Baseline
0.6 ± 0.3
8.67
0.144
6.92
Conclusions: This is a very limited data set, providing more questions than answers, but it opens a curiosity to much more investigation to understand the function of these intrinsic hepatic vascular oscillations under normal, reflex, and pathophysiological conditions.
Support or Funding Information
Supported by the late James P. Filkins, Ph. D., Professor of Physiology.
