Upper UTIs are infections of the kidneys. These are potentially life threatening, if bacteria move from the infected kidney into the blood. This condition is called sepsis. Sepsis can cause dangerously low blood pressures, shock, and death.
So whe you hold your breath, you stop getting oxygen in your lungs that go to your heart. The oxygen level in the blood drops, so your muscles need more oxygen, so the heart pumps faster. This is like running, your muscles need more oxygen so heart pumps faster
When you hold your breath the ongoing accumulation of carbon dioxide in your cells, in your blood and lungs will eventually irritate and trigger impulses from the respiratory center part of your brain. Rising levels of carbon dioxide signal the body to breathe and ensure our unconscious and autonomous respiration.