Real-time monitoring of heart rate variability in critically ill patients.
OBJECTIVE
Heart rate variability (HRV) is widely used to evaluate autonomic nervous function; however, real-time monitoring of HRV has rarely been attempted in the intensive care unit (ICU). We report our experience in performing real-time monitoring of HRV in our ICU.


METHODS
We investigated 10 critically ill patients on total ventilatory support. Heart rate variability analysis was performed using the MemCalc system, which is a noninvasive, real-time analysis system. The low-frequency (LF) component of HRV reflects sympathetic and parasympathetic modulation, whereas the high-frequency (HF) component mainly reflects parasympathetic modulation. The LF/HF ratio represents a measure of sympathetic/parasympathetic balance.


RESULTS
The HRV parameters for patients breathing spontaneously after extubation were significantly higher than those for patients on total ventilatory support. These findings suggest that mechanical ventilation under sedation may reduce autonomic nervous function in critically ill patients. In a representative case with septic shock, systolic blood pressure and LF/HF ratio showed a significant increase after intravenous infusion of epinephrine and then the HF component showed a significant increase due to vagal reflex.


CONCLUSIONS
The MemCalc system is practicable for real-time monitoring of HRV in the ICU. Heart rate variability parameters may offer useful information in the management of critically ill patients.
Kasaoka
Shunji
S
Advanced Medical Emergency and Critical Care Center, Yamaguchi University Hospital, Ube, Yamaguchi 755-8505, Japan. skasa@yamaguchi-u.ac.jp
Nakahara
Takashi
T
Kawamura
Yoshikatsu
Y
Tsuruta
Ryosuke
R
Maekawa
Tsuyoshi
T
D001341:Autonomic Nervous System / Q000502:physiology*; D003422:Critical Care / Q000379:methods*; D016638:Critical Illness; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006612:High-Frequency Ventilation; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods*; D012121:Respiration, Artificial; D018746:Systemic Inflammatory Response Syndrome / Q000503:physiopathology* / Q000628:therapy