The systolic blood pressure and pulse volume decreases during the inspiratory phase of respiration.
- During inspiration there is increased venous return (due to negative intrathoracic pressure)
- right ventricles expands more
- interventricular septum is pushed to the left side (Reverse Bernheim effect)
- This decreases the left ventricular volume
- Also the pooling of blood in the pulmonary circulation occurs, decreasing amount of blood reaching left ventricle
This causes decrease in stroke volume of left ventricle, thus decreasing the systolic blood pressure. The maximum decrease in blood pressure that is considered normal is 10 mm Hg. If the decrease is more than 10 mm Hg, it is called pulsus paradoxus.