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
Dr. Buteyko's finding was that the typical breathing rate at rest for people with 2-3 min CP (stress free breath-holding time test done after usual exhalation) was about 3-5 breaths per minute with a minute volume of about 1.5-2.5 l/min.