The effect of a hot dry climate on the haemorrheology of healthy males and patients with acute myocardial infarction.

We studied the influence of an extremely hot dry summer and temperate winter on the haemorrheology of 82 healthy males (controls) and 101 male patients with acute myocardial infarction (AMI). The haematocrit (Hct), blood viscosity (B1V) and Hct/B1V ratio were measured in these subjects working 'outdoors' and in an air-conditioned environment ('indoors'). The 'summer outdoor' controls had a higher B1V and a lower Hct/B1V when compared to the 'winter outdoor' controls (P less than 0.01), and the 'summer indoor' controls had a lower Hct and Hct/B1V when compared to the 'winter indoor' control group (P less than 0.02). The haemorrheology of 'winter indoor' AMI patients was not different from the controls, except for the Hct/B1V. The 'summer indoor' group had a higher Hct (P less than 0.05) and B1V (P less than 0.001) and a lower Hct/B1V (P less than 0.02) when compared to the controls. 'Summer outdoor' AMI patients had the most abnormal haemorrheology of all groups. AMI patients with Hct/B1V less than 7 had a significantly higher prevalence of hypotension and shock syndrome compared to those whose Hct/B1V was greater than or equal to 7 (P less than 0.05). We conclude that in healthy males, there was a seasonal difference in haemorrheology which was due to acclimatization to heat. During summer, AMI patients working outdoors had the most abnormal haemorrheology on admission and the occurrence of complications was also higher in them. We believe that these abnormalities resulted due to inadequate adjustments to heat.