Effect of Valsalva Maneuver on Cardiovascular Reflexes

الملخص

Valsalva maneuver (VM) is one of the most important tests used to investigate the integrity of the autonomic nervous system (ANS), it can be used to assess the baroreflex activity since the baroreceptors innervated by both sympathetic and parasympathetic nervous systems.
Therefore (VM) used to investigate the changes in the hemodynamic variables in order to assess the integrity of cardiovascular system. The procedure of (VM) involves four phases through these phases the following measurements take place:
1.Measurement of stroke volume (SV) which is the volume of bloodpumped from the heart by each beat using echocardiographic technique.
2.Heart rate (HR) is recorded by ECG in order to count the number of heart beats per each minutes.
3.Cardiac output (CO) which is the volume of blood pumped from the heart per each minute can be calculated by the equation CO = HR × SV from the above points (1,2).
4.Blood pressure measurement during (VM) by using mercury sphygmomanometer by which measurement of SBP, DBP and MBP.
5.Peripheral vascular resistance (PVR) can be calculated from the equation PVR = BP/CO. This study was carried out on seventy normal healthy subjects, their age range (20-40 years) with mean ± SD is (27.31 ± 5.28years). In this study a totally non-invasive techniques were used during all phases of VM. Concerning the responses in different phases of VM we found that there is sudden increase of BP with reflex bradycardia at the onset of straining(phase1). During phase2 (straining phase) there is significant reduction of SV and decreasing of BP to the low point lead to sympathetic stimulation and reflex tachycardia and increment in BP(systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean blood pressure (MBP), so phase 2 can be divided in to phase 2E and phase 2L. At release of strain of VM, there is transient reduction of SV and BP (phase3), phase 2E and phase 3 were not included in this study as BP changes need to be measured by invasive technique. few seconds after release of strain, the SV return to premaneuver level with BP “over shoot†(increased SBP, DBP and MBP) and peripheral vascular resistance (PVR) also increased as it is calculated from this equation (PVR = MBP/CO), and there is reflex bradycardia so cardiac output(CO) is decreased (phase4).