Toru Komatsu

Differential effects of ketamine and midazolam on heart rate variability

Alterations in autonomic activity caused by anaesthesia can be assessed by spectral analysis of heart rate variability (HRV). This study examined the effects of ketamine and midazolam on HRV. Thirty patients of ASA PS 1 were studied. Fifteen were given ketamine (2 mg · kg−1) and 15 received midazolam (0.3 mg · kg−1), m The RR intervals of ECG were measured before and after induction of anaesthesia for ten minutes during spontaneous respiration. Power spectral density of the data was computed using fast Fourier transform. The spectral peaks within each measurement were calculated: low frequency area (LF, 0.04–0.15 Hz), high frequency area (HF, 0.15–0.5 Hz), and total power (TP, 0.04–0.5 Hz). Normalized unit power was derived as follows: low frequency area (nuLF): LF/ TP × 100%, high frequency area (nuHF): HF/TP × 100%. Both ketamine and midazolam caused reductions in all measurements of HRV power (P < 0.05). However, ketamine increased nuLF from 64 ± 14% to 75 ± 13% (P < 0.05) and decreased nuHF from 36 ± 14% to 25 ± 13% (P < 0.05), while midazolam decreased nuLF from 66 ± 15% to 54 ± 14% (P < 0.05) and increased nuHF from 34 ± 15% to 46 ± 14% (P < 0.05). These results documented that both ketamine and midazolam reduced the total power and all frequency components of power in spite of their opposing effects on autonomic nervous activity. However, normalized unit power showed the expected sympathetic activation with ketamine and sympathetic depression with midazolam since ketamine increased nuLFand midazolam decreased nuLF.RésuméIl est possible de mesurer l’activité autonome initiée par l’anesthésie au moyen de l’analyse spectrale des fluctuations de la fréquence cardiaque (FFC). Cette étude recherche les effets de la kétamine et du midazolam sur les FFC. Trente patients ASA PS I font partie de l’étude. Quinze ont reçu de la kétamine (2 mg · kg−1) et quinze du midazolam (0,3 mg · kg−1) iv. Les intervalles RR ont été mesurés à l’ECG avant et après l’induction de l’anesthésie pendant dix minutes de respiration spontanée. La densité de la puissance spectrale des données a été calculée après transformation rapide sur une échelle de Fourier. Les pointes spectrales de chaque mesure ont été calculées: zone de basse fréquence (LF, 0.04–0,15 Hz), zone de haute fréquence (HF, 0,15–0.5 Hz) et puissance totale (TP, 0,04–0,5 Hz). L’unité de puissance normalisée a été dérivee comme suit: zone de basse fréquence (nuLF): LF/TP × 100%, zone de haute fréquence (nuHF): HF/TP × 100% La kétamine et le midazolam provoquent des réductions de toutes les mesures de puissance des FFC (P < 0,05). Cependant la kétamine a augmenté nuLF de 64 ± 14% à 75 ± 13% (P < 0,05) et a diminue nuHF de 36 ± 14% à 25 ± 13% (P < 0,05), alors que le midazolam a diminué nuLF de 66 ± 14% à 54 ± 14% (P < 0,05) et a augmenté nuHF de 34 ± 15% à 46 ± 14% (P < 0,05). Ces résultats montrent que la kétamine et le diazépam réduisent tous deux la puissance totale et toutes les composantes fréquentielles de la puissance malgré leurs effets opposés sur l’activité nerveuse autonome. Cependant, l’unité de puissance normalisée a montré, comme on s’y attendait, l’activation sympathique par la kétamine et la dépression sympathique par le midazolam étant donné que la kétamine augmentait nuLF et que le midazolam diminuait nuLF.

Recovery of heart rate variability profile in patients after coronary artery surgery

We examined the different characteristics of heart rate variability (HRV) to define the time course of HRV profile after coronary artery surgery (CAS).Spectral analysis of HRV was performed on a 512-s segment of R-R intervals of the electrocardiogram on the preoperative day and on Postoperative Days 1, 2, 3, 4, 5, 6, 7, 14, 21, and 28. Power spectral area was divided into low (0.04-0.15 Hz; LF)-and high (0.15-0.5 Hz; HF)-frequency components. Fractal slope and sympathovagal slope of 1/f characteristics of HRV were determined in two different frequency ranges (from 0.01 to 0.15 Hz and from 0.01 to 0.5 Hz, respectively). Three recovery profiles of HRV were identified. Early HRV recovery profiles (Postoperative Days 1-6) included reduction in LF, HF, and sympathovagal slope, as well as an increase in fractal slope. Subsequent HRV recovery profiles (Postoperative Days 7-21) revealed reductions in LF, HF, and sympathovagal slope. Fractal slope became normal. Later HRV recovery profiles (Postoperative Day 28) demonstrated that all spectral components of HRV remained reduced, but sympathovagal and fractal slopes became normal. These changes in the HRV profile after CAS suggest significant postoperative alterations in cardiovascular homeostasis with significant but incomplete recovery during the first 28 postoperative days. Implications: Heart rate variability reflects normal neural regulation of cardiac function. This variability remains depressed as long as 28 days after coronary artery bypass surgery, but can recover as early as 1 wk postoperatively. Despite implied loss of normal neural regulation of cardiac function, a specific correlation between depressed heart rate variability and outcomes was not performed. (Anesth Analg 1997;85:713-8)

Alterations in Spectral Characteristics of Heart Rate Variability as a Correlate of Cardiac Autonomic Dysfunction after Esophagectomy or Pulmonary Resection

Background Both esophagectomy and pulmonary resection are associated with postoperative cardiac complications, partly because of autonomic perturbations involving the heart. This study was undertaken to determine whether heart rate variability (HRV), employed as an index of cardiac autonomic function, changes in patients undergoing esophagectomy or pulmonary resection. Methods Electrocardiographic RR intervals were measured in 20 esophagectomized patients, 10 undergoing right and 10 undergoing left pulmonary resection on the preoperative day as baseline data and on postoperative days 1, 3, 5, 7, 14, and 30. Instantaneous heart rate was calculated every 250 ms from 416-s data of RR intervals. Power spectra of HRV for 128 s were computed using a fast Fourier transform and normalized by squared mean heart rate. The averaged ten sets of normalized HRV power were obtained by integrating the following power spectral bands: the low-, (0.06-0.10 Hz), high- (0.15-0.40 Hz), and total-frequency regions (0.01-0.40 Hz). Results In the esophagectomy group, mean low-, high-, and total-frequency HRV power decreased after surgery to 17%, 6%, and 15% of their preoperative values, respectively, and these indexes remained suppressed for up to 30 days. After right pulmonary resection, low- and total-frequency HRV power decreased through 30 and 7 postoperative days, respectively. In the left pulmonary resection group, HRV remained unchanged. In the esophagectomy group, mean (+/-SEM) heart rate increased from 78 (+/-3) bpm to more than 90 bpm throughout the study, and body temperature from 36.5 (+/-0.1) degrees C to more than 37.0 degrees C through 14 postoperative days. Heart rate and body temperature remained increased for 3 days after pulmonary surgery. Mean arterial pressure remained unchanged in the three surgical groups. Conclusions Reductions in HRV after esophagectomy or right pulmonary resection indicate a substantial and prolonged surgical injury to the autonomic nervous control of pulse rate.

Evaluation of a new reflectance pulse oximeter for clinical applications.

The design of a noninvasive reflectance pulse oximeter that uses the same principle of transmittance pulse oximeter and analyses the oxygen saturation of arterial blood was described. Four sets of red and infra-red LEDs were used as light sources. The respective reflectance photoelectric outputs were used to make an internal calibration curve of the instrument relative to the arterial oxygen saturation values measured with a Co-Oximeter (OSM-3) in five healthy nonsmoking subjects during steady-state hypoxaemia. The accuracy of the present instrument was studied in six patients with respiratory failure. From 22 samples, a good correlation coefficient (0.98) with a standard deviation of 1.42 was obtained in the range between 73 and 100 per cent between the arterial oxygen saturation measured with the present instrument and that with the Co-Oximeter. The result strongly suggests the usefulness of this oximeter in monitoring patients with hypoxaemia.

No changes in cerebrospinal fluid levels of nitrite, nitrate and cyclic GMP with aging

SummaryNitric oxide (NO) is a free radical gas that plays a role in various signal transduction processes. NO has been proposed to have a function in the mechanism of synaptic plasticity, including long-term potentiation and memory formation in vivo. Because a failure in synaptic plasticity is considered to be involved in aging-associated brain dysfunction, NO production in the brain may be altered by aging. In the present study, we measured the levels of NO metabolites, nitrite and nitrate, and cyclic GMP in the cerebrospinal fluid (CSF) of human subjects without neurological or psychiatric disorders. There were no age-related changes in the CSF levels of either nitrite, nitrate or cyclic GMP. These results suggest that NO production in the brain may be maintained during the aging process.

Continuous, On-Line, Real-Time Spectral Analysis of Heart Rate Variations during Anesthesia

The autonomic nervous system (ANS) is of vital importance in regulating cardiovascular homeostasis. Most anesthetics, muscle relaxants, and surgical stimulus modulate ANS. Therefore, evaluation of the impact of anesthetics on ANS is important to determine subsequent compensatory responses of the cardiovascular system. Among the tests to assess ANS function are the measurement of heart rate variations during Valsalva maneuver, heart rate responses to postural changes, deep breathing, and pharmacological intervention, and blood pressure responses to postural changes or to sustained handgrip. These measurement cannot be clinically practical during anesthesia and surgery to monitor ANS activity.