Filling and arterial pressures as determinants of left ventricular stroke volume in fetal lambs

Left ventricular (LV) function was investigated in 16 fetal lambs (125-140 days gestation), each instrumented with an electromagnetic flow sensor on the ascending aorta and vascular catheters. Control arterial blood values were pH 7.38 +/- 0.02 (SD), PCO2 46.3 +/- 3.2 Torr, PO2 19.4 +/- 1.3 Torr, and hematocrit 34.8 +/- 4.3%. Control values for LV output (228 +/- 108 ml X min-1 X kg-1) and arterial pressure (AP, 47.4 +/- 6.5 Torr) were unchanged by administration of atropine and propranolol. LV function curves relating stroke volume (SV) to mean left atrial pressure (LAP) were generated by rapid withdrawal and reinfusion of fetal blood with or without concomitant infusion of nitroprusside (NP) or phenylephrine hydrochloride (PE) to lower or raise mean arterial pressure (AP). The control LV function curve was composed of a steep ascending limb of 0.39 +/- 0.34 ml X kg-1 X Torr-1 and a plateau of 0.04 +/- 0.04 ml X kg-1 X Torr-1. The breakpoint joining the limbs of the control curve was LAP 3.1 +/- 1.2 Torr and LVSV 1.3 +/- 0.5 ml/kg, and these values were not different from control LAP and SV. Function curve slopes were not affected by PE or NP treatment. Multiple linear regression of SV, LAP, and AP showed a small but significant coefficient for AP [-0.002 +/- 0.001 (SE) ml X kg-1 X Torr-1] and LAP [+0.053 +/- 0.004 (SE) ml X kg-1 X Torr-1] at LAP greater than breakpoint.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamics of miniature swine during +Gz stress with and without anti-G support

Nine unanesthetized, chronically instrumented, female miniature swine (MS) (avg wt, 39.7 kg) were exposed to head-to-tail inertial load (+Gz) levels of +3, +5, and +7 Gz for 60 s, with and without anti-G-suit inflation. Venous flow (VF) was measured by an electromagnetic flow sensor around the inferior thoracic vena cava at the diaphragm. Central venous pressure (CVP), abdominal venous pressure (AVP), eye-level blood pressure (ELBP), and esophageal pressure (EP) were also measured before, during, and after +Gz. There was a progressive significant decrease from control of both ELBP (P less than 0.001) and VF (P less than 0.05) during the three +Gz exposures, both with and without G-suit inflation. Without G-suit inflation, most of the MS were unable to tolerate +5 and +7 Gz. Although VF was significantly (P less than 0.02) improved by G-suit inflation during +Gz there was no significant difference in VF between the three +Gz levels, with or without G-suit inflation. The MS does a spontaneous straining maneuver (cyclic Valsalva) during +Gz with G-suit support. Using EP as a trigger, the data were grouped as strain or no strain (relaxation). A continuous AVP-to-CVP gradient existed during G-suit inflation, which increased dramatically during no strain with increasing +Gz, and was associated with an increase in VF. Thus, the majority of VF occurred during relaxation between strains, even though relaxation time was shortened as +Gz increased. Although ELBP is obviously dependent on cardiac output and venous return, the progressive reduction in ELBP with increased +Gz loads was not significantly related to changes in VF at the diaphragm which was maintained, although at a reduced rate, by the AVP-to-CVP gradient during G-suit inflation.

Effect of feed intake on digesta flow and myoelectric activity in the gastrointestinal tract of the preruminant calf

SUMMARYThe effect of feed intake on abomasal digesta outflow and gastrointestinal motility of preruminant calves given whole milk was studied. Digesta collections were made from calves fitted with re-entrant duodenal cannulas. In other calves myoelectric activity was recorded from electrodes implanted on the abomasum and proximal small intestine, sometimes concurrently with recordings from an electromagnetic flow sensor on the duodenum. After a feed of 2–8 kg milk recurring patterns of intestinal myoelectric activity associated with fasting were temporarily interrupted by a period of continuous irregular spike activity; the duration of the post feeding activity increased with intake of milk. Patterns of abomasal digesta flow were characterized by alternating periods of rapid and slower flow with a frequency that corresponded to cyclic change in myoelectric activity of the small intestine. Hourly rates of abomasal emptying of digesta during a 6-h collection period were significantly greater (P < 0·05) after giving feeds of 6–8 kg milk compared with measurements of flow rate when 2 kg feeds were given. It is concluded that myoelectric activity of the proximal small intestine exercises control over abomasal emptying of digesta by a mechanism which adjusts the mixing and propulsive functions of gut motility in accordance with the amount of milk consumed.