I ippie ippie 10+ Year Member Jun 12, 2006 162 0 NY Status (Visible) Pre-Dental Jul 31, 2006 #1 Negative pressure breathing in human lungs results from I. contraction of the diaphragm. II. relaxation of the diaphragm. III. incompressibility of intra-pleural fluid The answer is I and III. Anybody can explain III?