| PFR | parotid flow rate; peak flow rate |
|---|---|
| PRR | proton relaxation rate; pulse repetition rate |
| RRR | regular rhythm and rate; renin release rate (or ratio) |
| SER | sebum excretion rate; sensitizer enhancement ratio; sensory evoked response; service; smooth endopla... |
| UFR | ultrafiltration rate; urine filtration rate |