Stroke volume variability--cardiovascular response to orthostatic maneuver in patients with coronary artery diseases

Time- and Frequency-Domain Analysis of Stroke Volume Variability Using Indoor Cycling to Evaluate Physical Load of Body

A potential myocardial injury can be induced by intensive sporting activities, which may be due to ventricular tachycardia or fibrillation when individuals continue to exercise during the maximum physical loading period (the aerobic capability plateau, ACP). Herein, we conducted an incremental exercise test with the RR-interval and SV-series measurements as the input and output of the circulatory system. Through time and frequency analyses, we aimed to identify the indicators for distinguishing the normal stage (S1), last stage before ACP (S2), and ACP stage (S3) during different incremental physical loads. The cross-correlation results of the RR interval and SV series showed that the maximum coefficient of S2 was significantly greater (p < 0.05) than that of S1 (median 0.91 to 0.87), and also significantly lower (p < 0.05) than that of S3 (median 0.87 to 0.60). The corresponding spectrum shows that the decreasing correlation coefficient of SVV and Heart rate variability can be used to assess whether the body has reached the ACP. These findings can be used as a guide for exercise healthcare. Pausing or reducing the exercise load before entering the ACP could effectively reduce the risk of myocardial injury.

Hemodynamic findings in patients with brain stroke

INTRODUCTION

Standard procedures carried out at a stroke department in patients after a cerebral event may prove insufficient for monitoring hemodynamic indices. Impedance cardiography enables hemodynamic changes to be monitored non-invasively. The aim of the work was to describe hemodynamic parameters in patients with acute phase of ischemic and hemorrhagic stroke and to analyse the correlation between the type of hemodynamic response and long-term prognosis.

MATERIAL AND METHODS

The 45 consecutive subjects with ischemic stroke and 16 with a hemorrhagic stroke were examined additionally with impedance cardiography during the first day of hospitalization. The heart contractility, pump performance, afterload and preload indices were recorded and calculated automatically and the data analyzed in terms of 6-month mortality.

RESULTS

We found a significant association between the systemic vascular resistance index, Heather index, stroke index, heart rate, systolic and diastolic and mean arterial blood pressure and mortality in patients with ischemic stroke (p = 0.002, p = 0.008, p = 0.012, p = 0.005, p = 0.007, p = 0.009, p = 0.002 respectively). Logistic regression analysis identified the thoracic fluid content as the most significant variable correlating with the non-survival of the patients with ischemic stroke and in the whole group (ischemic and hemorrhagic stroke). The significant parameters were also mean arterial pressure and stroke index in ischemic stroke (the correct answer ratio was 86.67%) and heart rate in the whole group (the correct answer ratio was 80.33%). There were no significant associations in hemorrhagic stroke.

CONCLUSIONS

The hemodynamic parameters correlate with long term prognosis in patients with ischemic brain stroke.

The Contribution of Blood-Flow-Induced Conductivity Changes to Measured Impedance

The paper considers the contribution of conductivity changes undergone in an anisotropical medium to measured resistance. This was achieved by extending the relationship proposed by Geselowitz to anisotropical materials described, therefore, by a conductivity tensor. It was found that each element of a conductivity change tensor contributed to the measured resistance only if a corresponding component of the electrical field was nonzero. Numerical calculations were performed for blood-flow-associated conductivity changes. A special experiment stand was developed which allowed experiments to be performed proving the theoretical results. It was found that the absolute value of resistance change measured in the direction perpendicular to the vessel axis was much smaller than that measured along the vessel axis. The results obtained may explain the fact that the actual change of measured resistance created by changes of conductivity induced by aortic blood flow is lower than expected from simplified models.