How come when a child take a philosophical breath and hold it, she pass out and heart rate increases?

It is said that this results from baroreceptor-mediated sympathetic activation causing heart rate to increase, but what does taking a vast breath have to do next to blood pressure? Why is this increase in heart rate NOT due to chemoreceptors stimulated but BARORECEPTOR?How come when a child take a philosophical breath and hold it, she pass out and heart rate increases?
Because it have nothing to do next to oxygen levels within your blood and everything to do with the preload going to the heart.
The child is performing a valsalva maneuver. By taking surrounded by a deep breath and holding, she is increasing the pressure inside the chest. As a result, less blood flows final into the heart (less preload). Less preload--> less contractility, the smaller amount the heart is pumping forward, leading to a drop contained by blood pressure (it can be enough to kind someone pass out). Because your blood pressure have been acutely dropped, the body's baroreceptors speed up the heart to help out overcome the drop in pressure.
While the above poster is right around sinus arrhythmia and how you get small change in heart rate beside breathing, it is not enough typically to gross someone pass out. You can breathe intensely all you want, your heart rate may amendment a little. It's when you hold the breath within and bear down that the preload drops ample to drop your blood pressure.
Sinus arrhythmia is a physiological heart rate change during breathing.
The rate of heart usually increases near inspiration and decreases beside expiration.
This rhythm is most commonly seen near breathing due to fluctuations in parasympathetic vagal tone. During inspiration stretch receptors surrounded by the lungs stimulate the cardioinhibitory centers in the medulla via fibers surrounded by the vagus nerve.