Mean pulmonary aery pressure is: September 2007

Ans. B:15 mm HgPulmonary aerial pressure is generated by the right ventricle ejecting blood into the pulmonary circulation, which acts as a resistance to the output from the right ventricle. With each ejection of blood during ventricular systole, the pulmonary aery blood volume increases, which stretches the wall of the aery. As the hea relaxes (ventricular diastole), blood continues to flow from the pulmonary aery into the pulmonary circulation. The smaller aeries and aerioles serve as the chief resistance vessels, and through changes in their diameter, regulate pulmonary vascular resistance. In hemodynamic terms, the mean pulmonary aerial pressure (PAP) can be described byPAP = (CO x PVR) + PVPWhere CO = cardiac output, PVR = pulmonary vascular resistance, and PVP = pulmonary venous pressure.The PVP is essentially the same as left atrial pressure. Therefore, increases in CO, PVR or PVP will lead to increases in PAP. Normally, mean pulmonary aery pressure is about 15 mmHg, and the pulmonary aery systolic and diastolic pressures about 25 and 10 mmHg, respectively. Pulmonary venous pressure is about 8 mmHg. Therefore, the pressure gradient driving flow through the pulmonary circulation is rather small at about 7 mmHg (mean pulmonary aerial minus venous pressures).