Abstract
AimsIt is known that blood pressure regulation differs seasonally. It is unknown, however, how the cardiovascular system in patients with a stroke reacts to postural changes in different seasons. The aim was therefore to investigate how different temperatures in cold and warm seasons influence the reactions of haemodynamic mechanisms as well as heart rate variability during a sit-to-stand test in patients with stroke and a control group.MethodsHemodynamic responses were assessed in both groups during a sit-to-stand test (5 min sitting followed by 5 min standing) beat to beat within two different seasons. Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP), heart rate (HR), stroke index (SI), cardiac index (CI) and heart rate variability (HRV) were continuously monitored.ResultsDuring the sitting baseline period delta values of DBP (+15.1 [Standard error (SE) 3.75] mmHg, p < 0.05) and MBP (+14.35 [SE 4.18] mmHg, p < 0.05) were significantly higher in colder months compared to warmer months whereas SI (−3.86 [SE 1.43] ml/beat/m2, p < 0.05) and CI (−0.4 [SE 0.11] l/min/m2, p < 0.05) were lower in colder months compared to warmer months in non-stroke participants. In patients with stroke during sitting, baseline period delta values of DBP (+19.92 [SE 8.03] mmHg, p < 0.05) and MBP (+19.29 [SE 8.6] mmHg, p < 0.05) were significantly higher in colder months compared to warmer months but SI (−5.43 [SE 1.96] ml/beat/m2, p < 0.05) was significantly lower in colder months compared to warmer months. After standing, there was a significant decrease in SBP in warmer months (−16.84 [SE 4.38] mmHg, p < 0.05) and a decrease in DBP in warmer months (−7.8 [SE 2.3] mmHg, p < 0.05) and colder months (−6.73 [SE 1.5] mmHg, p < 0.05) in non-stroke participants and a decrease in MBP in warmer months (−12.5 [SE 2.8] mmHg, p < 0.05) and colder months (−8.93 [SE 1.8] mmHg, p < 0.05) in non-stroke participants and in warmer months (−14.54 [SE 4.1] mmHg, p < 0.05) in patients with stroke.ConclusionElderly with and without stroke respond to orthostatic stress with a greater drop in blood pressure in the warmer seasons.
Highlights
It is well known that blood pressure is elevated in winter compared to summer [1, 9]
During the sitting baseline period delta values of diastolic blood pressure (DBP) (+15.1 [Standard error (SE) 3.75] mmHg, p < 0.05) and mean blood pressure (MBP) (+14.35 [SE 4.18] mmHg, p < 0.05) were significantly higher in colder months compared to warmer months whereas stroke index (SI) (–3.86 [SE 1.43] ml/beat/m2, p < 0.05) and cardiac index (CI) (–0.4 [SE 0.11] l/min/m2, p < 0.05) were lower in colder months compared to warmer months in non-stroke participants
In patients with stroke during sitting, baseline period delta values of DBP (+19.92 [SE 8.03] mmHg, p < 0.05) and MBP (+19.29 [SE 8.6] mmHg, p < 0.05) were significantly higher in colder months compared to warmer months but SI (–5.43 [SE 1.96] ml/beat/m2, p < 0.05) was significantly lower in colder months compared to warmer months
Summary
It is well known that blood pressure is elevated in winter compared to summer [1, 9]. Systolic blood pressure decreases with increasing temperature and the exposure temperature has been reported to influence the autonomic nervous system [25]. The reduction in blood pressure during standing is more pronounced in warmer seasons as a result of the effects of higher ambient temperature, hypovolemia (increased sweating, salt and fluid loss), and peripheral vasodilatation [38]. The sympathetic nervous system reacts by increasing heart rate and cardiac contractility preventing a collapse of the systemic blood pressure and cerebral perfusion [32]. Stroke is a common pathological condition among older people characterized by elevated blood pressure, autonomic dys-
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