Pick the correct answer, and explain why it is correct.
If the pressure in the thoracic cavity increases and the pressure in the ventricles due to venous return remains the same,
A. Stroke volume will decrease
B. heart rate will decrease
C. Cardiac output will increase
D. Stroke volume will increase
E. blood pressure will increase
The correct answer is A. Stroke volume will decrease.
When the pressure in the thoracic (chest) cavity increases, it ultimately affects the pressure in the ventricles of the heart. This increased pressure in the thoracic cavity can occur due to factors such as increased intrathoracic pressure during activities like weightlifting or during forced expiration.
During normal heart function, the pressure in the ventricles needs to be higher than the pressure in the thoracic cavity for blood to flow effectively. However, if the pressure in the thoracic cavity increases, it can impede the normal filling of the ventricles during diastole (relaxation phase).
If the pressure in the ventricles due to venous return remains the same, it means that the volume of blood returning to the heart remains unchanged. Since the normal filling of the ventricles during diastole is hindered by the increased thoracic pressure, less blood can enter the ventricles during each cardiac cycle. This leads to a decrease in stroke volume, which refers to the amount of blood pumped out of the ventricles with each heartbeat.
Therefore, the correct answer is A. Stroke volume will decrease, as the obstruction of normal ventricular filling decreases the volume of blood ejected from the heart with each beat.