title: A circannual rhythm in unstimulated salivary flow rate when the ambient temperature varies by only about 2 degrees C.
abstract: OBJECTIVE
  To determine whether a circannual rhythm in the flow rate of unstimulated whole saliva could be detected in persons living in a region of Sri Lanka where the average monthly temperature is virtually constant throughout the year.
  
  
  METHODS
  Forty-six medical students, 26 male and 20 female, in Peradeniya collected saliva on 12 occasions about once per month from September 19, 2003 to September 28, 2004. A least-squares sine wave of the form: F(t)=M+A x(2 pi t/tau+phi), in which F is the flow rate at time t (in days), M the mesor or rhythm-adjusted mean value, A the amplitude, tau the period (365 days) and phi the phase shift in radians, was fitted to the data.
  
  
  RESULTS
  A statistically significant (p<0.05) circannual rhythm in salivary flow rate was detected with the following mean values and 95% confidence intervals: M=0.528 mL/min (0.514-0.543), A=0.0472 mL/min (0.0269--0.0674), phi=1.141 radians (0.704--1.578). The acrophase (peak value of the rhythm) was on October 14 (September 19--November 8). During the study, the average monthly temperature varied between 24.0 and 26.3 degrees C, with the peak temperature in April and minimum in December.
  
  
  CONCLUSIONS
  Even though the monthly ambient temperature variation in Peradeniya was very small, the peak temperatures occurred at the times of the lowest salivary flow rates, suggesting that a small change in ambient temperature (about 2 degrees C) in a warm climate may be sufficient to influence the unstimulated salivary flow rate. In conclusion, for saliva studies, which extend over a prolonged period, it may be important to take into account the circannual rhythm in salivary flow rate.
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Peradeniya, Peradeniya 20400, Sri Lanka.
authors.forename: A P
authors.initials: AP
authors.lastname: Kariyawasam
authors.forename: C
authors.initials: C
authors.lastname: Dawes
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D010507:Periodicity; D012472:Salivation / Q000502:physiology*; D013188:Sri Lanka; D013696:Temperature