Diurnal Variance in Stroke Onset
To the Editor:
We were interested to read the article by Stergiou et al and response by Dr Burszstyn.1–3 The diurnal variation in stroke onset is of both practical and physiological interest. The hypothesis that siesta may be associated with stroke suggests real changes in physiology. In Calgary, Canada, siesta is not practiced. We collected time of stroke onset, defined by the last-seen-well principle, for all strokes (n=538) admitted to Foothills Medical Center in Calgary over the calendar year 2000. Stroke onset times were grouped by hour. The Figure shows the raw data and a fitted polynomial regression curve for the number of strokes admitted to hospital by hour of onset. The curve showed a reasonable fit to the data using linear regression corrected for autocorrelation of residuals (P=0.035).
The 1700-h peak in stroke occurrence, seen in Athens, does not occur in Calgary, providing some observational evidence that siesta may be an important risk factor for stroke occurrence. Alternately and perhaps more likely, ethnocultural differences in stroke risk factors and behaviors, stroke type, primary preventive treatments, and other factors may influence the local diurnal variation in stroke onset.
Stergiou GS, Vemos KN, Pliarchopoulou KM, Synetos AG, Roussias LG, Mountokalakis TD. Parallel morning and evening surge in stroke onset, blood pressure and physical activity. Stroke. 2002; 33: 1480–1486.
Bursztyn M. Parallel morning and evening surge in stroke onset, blood pressure and physical activity. Stroke. 2002; 33: 2346. Letter
Stergiou GS, Vemmos KN, Mountokalakis TD. Parallel morning and evening surge in stroke onset, blood pressure and physical activity. Stroke. 2002; 33: 2347. Letter
The letter by Hill and Newcommon raises important points: It strengthens the observations that practice of the siesta may be associated with stroke1 by showing that where there is no siesta the afternoon onset of stroke is not seen. However, the authors say that “in Calgary, Canada, siesta is not practiced.” In Jerusalem, Israel, we were also surprised to find that about 30% to 35% of those referred for ambulatory blood pressure monitoring practiced the siesta.2,3 We learned, however, that detection is easier when subjects are implicitly questioned about the siesta. In older people,4 we found the prevalence of the practice among 70-year-olds is even more common, almost 61%. Stergiou et al1 report that among their ambulatory blood pressure data set, the prevalence of the siesta may be as high as 75% to about 90% in those over 70 years of age!
As the siesta emerges as an important risk factor, it should be looked for. Of course there are cultural and ethnic differences:
“Mad dogs and Englishmen go out in the mid-day sun The Japanese don’t care to, the Chinese don’t dare to Hindus and Argentines sleep firmly from twelve to one
But Englishmen detest a siesta” —
— Noel Coward (1899–1973)
However, prejudice will not help identify those who sleep in the afternoon—only direct questioning will.
Stergiou GS, Vemmos KN, Pliarchopoulou KM, Synetos AG, Roussias LG, Mountokalakis TD. Parallel morning and evening surge in stroke onset, blood pressure, and physical activity. Stroke. 2002; 33: 1480–1486.
Bursztyn M, Mekler J, Wachtel N, Ben-Ishay D. Siesta and blood pressure monitoring: comparability of the afternoon nap and night sleep. Am J Hypertens. 1994; 7: 217–221.