tailieunhanh - Physics, Pharmacology and Physiology for Anaesthetists - 8

Mối quan hệ kháng lực mạch máu phổi là rất phi tuyến tính do tác động của việc tuyển dụng và căng của các mạch trong giường mạch máu phổi trong phản ứng để tăng dòng chảy máu phổi. PVR thường là khoảng 10 lần thấp hơn so với kháng lực mạch máu hệ thống, ở 50-150 . | 168 Section 7 Cardiovascular physiology Pulmonary vascular resistance The resistance to flow in the pulmonary vasculature against which the right ventricle must contract 5 MPAP - LAP _ PVR - -7 --------- X 80 CO where PVR is pulmonary vascular resistance MPAP is mean pulmonary artery pressure and LAP is left atrial pressure. The relationship for pulmonary vascular resistance is very non-linear owing to the effect of recruitment and distension of vessels in the pulmonary vascular bed in response to increased pulmonary blood flow. The PVR is usually around 10 times lower than the systemic vascular resistance at 50-150 . The Valsalva manoeuvre The patient is asked to forcibly exhale against a closed glottis for a period of 10 s. Blood pressure and heart rate are measured. Four phases occur during the manoeuvre. Phase 1 begins at the onset and is of short duration. Phase 2 continues until the end of the manoeuvre. Phase 3 begins as soon as the manoeuvre has finished and is of short duration. Phase 4 continues until restoration of normal parameters. Time s Draw and label all three axes. The uppermost trace shows the sustained rise in intrathoracic pressure during the 10 s of the manoeuvre. Mark the four phases on as vertical lines covering all three plot areas so that your diagram can be drawn accurately. Curves Draw normal heart rate and BP lines on the remaining two axes. Note that the BP line is thick so as to represent SBP at its upper border and DBP at its lower border. Phase 1 During phase 1 the increased thoracoabdominal pressure transiently increases venous return thereby raising BP and reflexly lowering heart rate. Phase 2 During phase 2 the sustained rise in intrathoracic pressure reduces venous return VR and so BP falls until a compensatory tachycardia restores it. Phase 3 The release of pressure in phase 3 creates a large empty venous reservoir causing BP to fall. Show that the heart rate remains elevated. Phase 4 The last phase shows how