Abstract
Blood in the splanchnic vasculature can be transferred to the extremities. We quantified such blood shifts in normal subjects by measuring trunk volume by optoelectronic plethysmography, simultaneously with changes in body volume by whole body plethysmography during contractions of the diaphragm and abdominal muscles. Trunk volume changes with blood shifts, but body volume does not so that the blood volume shifted between trunk and extremities (Vbs) is the difference between changes in trunk and body volume. This is so because both trunk and body volume change identically with breathing and gas expansion or compression. During tidal breathing Vbs was 50–75 ml with an ejection fraction of 4–6% and an output of 750–1500 ml/min. Step increases in abdominal pressure resulted in rapid emptying presumably from the liver with a time constant of 0.61±0.1SE sec. followed by slower flow from non-hepatic viscera. The filling time constant was 0.57±0.09SE sec. Splanchnic emptying shifted up to 650 ml blood. With emptying, the increased hepatic vein flow increases the blood pressure at its entry into the inferior vena cava (IVC) and abolishes the pressure gradient producing flow between the femoral vein and the IVC inducing blood pooling in the legs. The findings are important for exercise because the larger the Vbs the greater the perfusion of locomotor muscles. During asystolic cardiac arrest we calculate that appropriate timing of abdominal compression could produce an output of 6 L/min. so that the abdominal circulatory pump might act as an auxiliary heart.
Highlights
We have previously reported that in normal subjects exercising with experimentally induced expiratory flow-limitation there were blood shifts from the trunk to the extremities [1]
The blood shifts were calculated by integrating flow at the mouth to obtain expired and inspired volumes simultaneously with the volume change of the trunk during breathing measured by optoelectronic plethysmography [OEP, 2]
In the present communication we report the difference between DVb as measured by whole body plethysmography (WBP) and DVb and changes in trunk volume (DVtr) as measured by OEP during expulsive maneuvers of various sorts and during quiet breathing using different patterns of breathing
Summary
We have previously reported that in normal subjects exercising with experimentally induced expiratory flow-limitation there were blood shifts from the trunk to the extremities [1]. These amounted to about 300 ml, or ,70 ml per kPa alveolar pressure. During expiration when expiratory flow was limited, the volume change of the trunk led the volume exhaled at the mouth in time and was of greater amplitude We thought this was due to gas compression in the lung. To our surprise this accounted for less than half of the greater volume displacement of the trunk
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