title: Seasonal blood pressure and body weight variation in patients on chronic hemodialysis.
abstract: OBJECTIVE
  The relation of ambient temperature (AMT) and relative humidity to systolic blood pressure (SBP), diastolic blood pressure (DBP), body weight (BW), and body weight gain between dialysis sessions (DeltaBW) was examined in hemodialysis patients by Fourier analysis.
  
  
  RESULTS
  The authors recruited 144 dialysis patients from a hemodialysis center in Okinawa, Japan where there is distinct seasonal variation in monthly AMT but a constant intradiurnal temperature change throughout the year. All patients had been undergoing chronic and regular hemodialysis three times per week. SBP, DBP, and BW before dialysis sessions and DeltaBW were recorded in 1994. Mean monthly Okinawa AMT in 1994 was highest in August and lowest in February and March, and the mean monthly relative humidity in 1994 was highest in June and lowest in January. Mean SBP and DBP were lowest in August and June respectively, and greatest in December. BW was lowest in July and September, and greatest in February and March; DeltaBW was lowest in July and greatest in January. These seasonal patterns were well reproduced by the first Fourier component. The cross-correlation coefficient showed that monthly mean AMT and SBP, DBP, BW, and DeltaBW were correlated with a lag time of 5 or 6 months. The cross correlation coefficient showed that relative humidity and SBP, DBP and DeltaBW were also correlated with a 6-month lag time. In analyzing subgroups of patients according to the presence or absence of antihypertensive medications, a seasonal change was observed in the SBP and DBP of patients not being treated with antihypertensives, and in the DBP of patients taking antihypertensive medications, but not in the SBP of patients taking antihypertensive medications.
  
  
  CONCLUSIONS
  Seasonal variations in SBP, DBP, BW and DeltaBW were evident. AMT and the relative humidity correlated strongly with SBP, DBP, BW and DeltaBW. The clinical implications of these findings in hemodialysis patients warrant further investigation.
authors.affiliation: Third Department of Internal Medicine, University of The Ryukyus, Okinawa, Japan. tozawa@med.u-ryuku.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Tozawa
authors.forename: K
authors.initials: K
authors.lastname: Iseki
authors.forename: C
authors.initials: C
authors.lastname: Iseki
authors.forename: O
authors.initials: O
authors.lastname: Morita
authors.forename: S
authors.initials: S
authors.lastname: Yoshi
authors.forename: K
authors.initials: K
authors.lastname: Fukiyama
mesh_terms: D001794:Blood Pressure / Q000502:physiology*; D001835:Body Weight / Q000502:physiology*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D006813:Humidity; D007676:Kidney Failure, Chronic / Q000503:physiopathology* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis; D012621:Seasons; D013696:Temperature