On 2015 Dec 12, Donald Forsdyke commented:

LESS BP MEDICATION NEEDED IN HOT WEATHER This paper recommends “More aggressive blood pressure lowering treatment in the cold months … in high risk individuals” (1), which implies less aggressive blood pressure (BP) lowering treatment in hot months. Indeed, a well-documented “J-curve” observation is that, below a certain value, BP lowering is harmful – e.g. acute kidney injury (2). Quite rightly, the cartoon in the accompanying editorial has question marks at both the high and low ends of the temperature scale (3). However, the paper’s focus is on more treatment in winter, not on less treatment in summer, and it only scores the deaths attributed to cardiovascular disease (CVD), a number that declines in hot weather (1). Cases where mortality can be attributed to other causes are excluded.

Regarding CVD it is reported that “The excess risk was similar between people treated with blood pressure lowering agents and those without” (1). But given the widely different mechanisms of action of different BP lowering agents, surely this statement needs backing with more information on agents and their dosages? Large summertime systolic BP declines that mandate treatment adjustment are not uncommon (4). Differential responses in hot weather can depend on type and dosage of antihypertensive medication. Indeed, extrapolation from the supplementary plot (Fig 1) of Yang et al. (2015), the BP would be normal at 40°C and medication could be dispensed with (1). Taking medication at that temperature could be lethal (5). Indeed, a Canadian case study with an angiotensin receptor blocker found that medication could be dispensed with when summer temperatures reached 33°C (6).

It is obvious from Fig. 3 that the statement that “the seasonal variation in blood pressure … was abolished by the use of home central heating” (1), is incorrect. In Harbin province, where winter temperatures are similar to those in Canada, there is less BP increase in cold weather than in other provinces, and this is attributed to central heating. But the seasonal BP increase is clearly not abolished. Despite central heating, in the Canadian case study the BP decline for a 10°C increase in temperature was of the order of 20 mm Hg (6) – a far higher value than the 6 mm Hg reported here (1).

1 Yang L, Li L, Lewington S. Guo Y, Sherliker P, Bian Z, Collins R, et al (2015) Outdoor temperature, blood pressure, and cardiovascular disease mortality among 23000 individuals with diagnosed cardiovascular diseases from China. Eur Heart J 36:1178-1185. Yang L, 2015

2 Tomlinson LA, Abel GA, Chaudhry AN, Tomson CR, Wilkinson IB, Roland MO et al (2013) ACE inhibitor and angiotensin-II receptor antagonist prescribing and hospital admissions with acute kidney injury: a longitudinal ecological study. PLoS One 8:e78465.Tomlinson LA, 2013

3 Bruno RM, Taddei S (2015) ‘Tis bitter cold and I am sick at heart’: establishing the relationship between outdoor temperature, blood pressure, and cardiovascular mortality. Eur Heart J 36:1152-1154.Bruno RM, 2015

4 Stergiou GS, Myrsilidi A, Kollias A, Destounis A, Roussias L, Kalogeropoulos P (2015) Seasonal variation in meteorological parameters and office, ambulatory and home blood pressure: predicting factors and clinical implications. Hypertension Research 38(12):869-875. Stergiou GS, 2015

5 Editorial (2015) Health professionals: be prepared for heatwaves. Lancet 386:219. Anonymous, 2015

6 Forsdyke DR (2015) Summertime dosage-dependent hypersensitivity to an angiotensin II receptor blocker. BMC Res Notes 8:227. Forsdyke DR, 2015

On 2015 Dec 12, Donald Forsdyke commented:

LESS BP MEDICATION NEEDED IN HOT WEATHER This paper recommends “More aggressive blood pressure lowering treatment in the cold months … in high risk individuals” (1), which implies less aggressive blood pressure (BP) lowering treatment in hot months. Indeed, a well-documented “J-curve” observation is that, below a certain value, BP lowering is harmful – e.g. acute kidney injury (2). Quite rightly, the cartoon in the accompanying editorial has question marks at both the high and low ends of the temperature scale (3). However, the paper’s focus is on more treatment in winter, not on less treatment in summer, and it only scores the deaths attributed to cardiovascular disease (CVD), a number that declines in hot weather (1). Cases where mortality can be attributed to other causes are excluded.

Regarding CVD it is reported that “The excess risk was similar between people treated with blood pressure lowering agents and those without” (1). But given the widely different mechanisms of action of different BP lowering agents, surely this statement needs backing with more information on agents and their dosages? Large summertime systolic BP declines that mandate treatment adjustment are not uncommon (4). Differential responses in hot weather can depend on type and dosage of antihypertensive medication. Indeed, extrapolation from the supplementary plot (Fig 1) of Yang et al. (2015), the BP would be normal at 40°C and medication could be dispensed with (1). Taking medication at that temperature could be lethal (5). Indeed, a Canadian case study with an angiotensin receptor blocker found that medication could be dispensed with when summer temperatures reached 33°C (6).

It is obvious from Fig. 3 that the statement that “the seasonal variation in blood pressure … was abolished by the use of home central heating” (1), is incorrect. In Harbin province, where winter temperatures are similar to those in Canada, there is less BP increase in cold weather than in other provinces, and this is attributed to central heating. But the seasonal BP increase is clearly not abolished. Despite central heating, in the Canadian case study the BP decline for a 10°C increase in temperature was of the order of 20 mm Hg (6) – a far higher value than the 6 mm Hg reported here (1).

1 Yang L, Li L, Lewington S. Guo Y, Sherliker P, Bian Z, Collins R, et al (2015) Outdoor temperature, blood pressure, and cardiovascular disease mortality among 23000 individuals with diagnosed cardiovascular diseases from China. Eur Heart J 36:1178-1185. Yang L, 2015

2 Tomlinson LA, Abel GA, Chaudhry AN, Tomson CR, Wilkinson IB, Roland MO et al (2013) ACE inhibitor and angiotensin-II receptor antagonist prescribing and hospital admissions with acute kidney injury: a longitudinal ecological study. PLoS One 8:e78465.Tomlinson LA, 2013

3 Bruno RM, Taddei S (2015) ‘Tis bitter cold and I am sick at heart’: establishing the relationship between outdoor temperature, blood pressure, and cardiovascular mortality. Eur Heart J 36:1152-1154.Bruno RM, 2015

4 Stergiou GS, Myrsilidi A, Kollias A, Destounis A, Roussias L, Kalogeropoulos P (2015) Seasonal variation in meteorological parameters and office, ambulatory and home blood pressure: predicting factors and clinical implications. Hypertension Research 38(12):869-875. Stergiou GS, 2015

5 Editorial (2015) Health professionals: be prepared for heatwaves. Lancet 386:219. Anonymous, 2015

6 Forsdyke DR (2015) Summertime dosage-dependent hypersensitivity to an angiotensin II receptor blocker. BMC Res Notes 8:227. Forsdyke DR, 2015