Being an anesthesiologist doesn't mean one knows everything about this stuff. Depends upon what their training is like or what they have specialized in (cardiac is much more "aware" of this stuff than Ob-GYN specialists). Anyhow, learning can come from all sorts of areas and I'll bet that anesthesiologist who lost the bet will never forget that "trick". Question is, does he realize this variation occurs in the healthy also (or the sick who are spontaneously ventilating), except it is backwards. Right heart output is lowest when the ventilator is causing inspiration and highest when the diaphragm is causing inspiration. It is all about intrathoracic pressure (higher intrathoracic pressure reduces venous return) and pulmonary vascular resistance (which is increased with higher intrathoracic pressure). BTW, the only way to get a true CO in the ICU is to disconnect the ventilator and do the measurement (that was our routine), the next best way is to do the measurement just before the ventilator fires.

OK, all you guys here now know something your doctor doesn't. Don't get too smug.

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Frank,
An original Ironman and the Inventor of PowerCranks