Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Ponsen, C.
Hemodynamic Responses in Older People with a History of Stroke.
[ Diplomarbeit/Master Thesis (UNI) ] Universiteit van Amsterdam; 2016. pp.61.
- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Goswami Nandu
- Altmetrics:
- Abstract:
- Introduction Postural changes, e.g. sit-to-stand, have an important effect on the cardiovascular system. Due to gravity blood shifts to the abdomen and legs causing a decrease in cardiac output (CO) and blood pressure (BP). These changes are detected by the baroreceptors which causes activation of the autonomic nervous system (ANS), specifically the sympathetic nervous system (SNS). When this response is inadequate it may cause orthostatic intolerance (OI). OI is clinically important because among older people there is a risk of falls, which can have major consequences. Evidence shows that orthostatic hypotension (OH) is even more prevalent in stroke patients. In this pilot study we look for differences in hemodynamics, including autonomic function, during postural changes between stroke patients and age matched (control) subjects. Methodology We conducted a sit-to-stand test among stroke patients (> 1 year after onset, NIHSS <4)† and control subjects. 5 minutes of sitting (baseline) followed by 5 minutes of standing and 5 minutes of recovery. Task Force Monitor (TFM; CN Systems, Graz, Austria) was used to obtain the following continuous (beat-to-beat) data: heart rate (HR), RR-interval (RRi), heart rate variability (HRV), systolic BP (sBP), diastolic BP (dBP), mean arterial BP (MAP), blood pressure variability (BPV), total peripheral resistance index (TPRI), stroke index (SI) and cardiac index (CI). HRV and BPV were used to examine the autonomic function. HRV is expressed in high frequency RRi (HF-RRi) and HF-RRi expressed in normalized units (HFnu-RRi). BPV is expressed in low frequency and normalized units of sBP (sBP-LFnu) and dBP (dBP-LFnu). Means of all the variables were calculated during different intervals (epochs) of the sit-to-stand test including last 60 seconds of sitting (baseline) and first 30 seconds of standing. An independent-samples T test or a Mann-Whitney U test was performed to determine significant differences between the groups. Results 21 stroke patients (age 66,4±6,6; 16 males) and 23 control subjects (age 62,6±7,0; 9 males) participated. During the entire sit-to-stand test there was no significant difference in HR, HRV, BPV, SI, CI and TPRI between the groups. There was a tendency of a higher HF-RRi in the control group during the standing period, for example first 10 seconds of standing up (113,5±170,1 vs. 784,4±2542,3; P=0,236)‡. sBP, dBP and MAP were significantly higher in stroke group during the first 10 seconds (P=0,025 resp. P=0,026 resp. 0,032) and 30 seconds (P=0,047 resp. P=0,026 resp. P=0,038) after standing up. Discussion No difference in autonomic function (using normalized values of HRV and BPV) between the two groups was found, despite previous studies that have concluded that there is a predominance of SNS activity among stroke patients (using absolute values of HRV and BPV). Even though OH is more prevalent among stroke patients it cannot be explained by a lower BP (or larger decrease in BP) compared to controls. Other factors, including cerebral blood flow (CBF), are likely to play a more important role for the difference in prevalence. The insight of this pilot study can be used to set up new studies to evaluate the autonomic dysfunction in stroke patients and to investigate other factors such as CBF.