what does the respiratory system has to do with partial pressure

Please make your question clear. Are you talking about the partial
pressures of inspired gases?

yes i am talking about the partial pressure of inspired gases

At sea level the usual partial pressure of oxygen is 0.21 bar. This
drops to about 0.2 bar in the lungs due to water vapor and carbon
dioxide that will be exhaled with the next out-going breath.  At an
altitude of about 18,000 feet, the oxygen partial pressure is about
0.1 bar and the air pressure is about 0.5 bar. Most people become ill
at 18,000 feet due to lack of oxygen. Unless the air is enriched with
oxygen, bringing the partial pressure into the 0.15 to 0.2 range
unconsciousness, sometimes death folows in less than one hour formost
people.   Neil