Kari J. Antila

Interaction of Heart Rate and Respiration in Newborn Babies

ABSTRACT: Variability of heart rate (HRV) and transthoracic electric impedance respirogram (TEZ) were examined by spectral analysis in three groups of neonates: healthy term babies (22), healthy preterm babies (21), and preterm babies with respiratory distress syndrome (RDS) (11). Heart rate, TEZ, Ptco2, and Ptcco2 were monitored during quiet sleep on the 1st, 3rd, and 5th day of postnatal life. Autospectra for trend-corrected segments of heart rate and TEZ as well as their cross-spectra and coherence spectra were computed. The peak of HRV spectral density was in < 0.2 Hz [low frequency (LF)] area (< 12 cycles/min) in all the neonates. Intergroup comparisons of average band-integrated spectra revealed that the LF spectral density of HRV was greater in the term babies than in the preterm babies on day 3. In the babies with RDS, both LF and high-frequency (HF, > 0.2 Hz) were abnormally low throughout the study. In the term infants, the TEZ amplitude spectrum was flat on day 1. On later days, a peak corresponding to the average respiratory rate emerged. In the healthy preterm babies, there was a LF peak in TEZ autospectrum on all days. In the babies with RDS, the peak of ventilator frequency was initially present; finally, the respiratory activity accumulated in the LF area. In the cross-spectra of term babies, there was a LF peak on all days. On day 5, an additional HF peak appeared, representing respiratory sinus arrhythmia. In the healthy preterm babies, only a LF peak was present. In babies with RDS, there were three peaks in the cross-spectra: one in the LF area, another corresponding to the ventilator frequency, and a third one representing the first harmonic of the ventilator frequency. With increasing age, the ventilator-induced peaks disappeared and only LF activity remained. No correlation was found between the spectral patterns of HRV and cross-spectra and the values of PtcO2 and Ptcco2. The spectral patterns of HRV and TEZ indicate that in newborn infants most of the activity is generated by LF mechanisms. Respiratory sinus arrhythmia is detected in term infants when regular breathing becomes organized. In RDS, respiratory sinus arrhythmia HRV is induced by ventilator. In both groups of preterm babies, the LF regulation of HRV seems to be more firmly connected with regulation and mechanics of respiration.

Vincristine treatment of acute lymphoblastic leukemia induces transient autonomic cardioneuropathy

Reduced respiratory sinus arrhythmia, measured as heart rate variability, is a reliable indicator of autonomic nervous dysfunction, reflecting a damage in vagal cardiac control. The authors studied the heart rate variability (HRV) of nine children treated for acute lymphoblastic leukemia during the different phases of cytostatic treatment utilizing heart rate processing techniques with a computer. The indices of HRV as well as the spectral components of heart rate were examined with special relation to vincristine administration. The heart rate variability was significantly reduced during the vincristine induction phases as compared to the consolidation and maintenance phases without vincristine administration. In particular, the respiratory components of the HRV during deep breathing tests were significantly reduced during vincristine treatment. The authors conclude that the measurement of the HRV is a suitable method for monitoring transient autonomic neuropathy, which these results show to be a frequent complication of vincristine treatment.

Autonomic neuropathy and vibration exposure in forestry workers.

The variation in heart rate (HRV) at rest and during deep breathing (6 cycles a minute) of 88 professional lumber jacks was studied using a computer technique. The traditional indexes of HRV (CV, CVS, MEAN) were calculated and the spectral components of the HRV were also computed. There was a significant difference (p less than 0.001) between the HRV indexes during the deep breathing test in those with the shortest (CV = 10.1 +/- 1.1) and those with the longest (CV V 6.2 +/- 0.4) exposures to vibration. The values of the HRV indexes decreased with age, but multiple regression analysis showed that the total exposure time to vibration had an independent negative association with the HRV. There were significant differences in all the frequency bands (frequency related power, FRP) of the heart rate between those with the longest and those with the shortest exposures. The HRV during a deep breathing test is associated with the activity of the parasympathetic nervous system and is decreased in autonomic neuropathies. Our results suggest that prolonged exposure to the vibration caused by a chain saw has a negative effect on the parasympathetic activity and thus causes autonomic dysfunction.

Autonomic cardiovascular reflexes in pregnancy. A longitudinal study

Cardiovascular reflexes were studied in 22 healthy women before they were pregnant, once during each pregnancy trimester and after delivery to evaluate the effect of pregnancy on autonomic control of haemodynamics. The Valsalva manoeuvre, the deep breathing test, the orthostatic test and the isometric handgrip test were used to assess changes in autonomic nervous function. We found that pregnancy altered the heart rate response in the Valsalva manoeuvre, the deep breathing test and the orthostatic tests. The deep breathing difference (p = 0.03) and max/min ratio (p = 0.03) decreased in pregnancy, whereas standing heart rate increased (p < 0.0001). Both the systolic and diastolic blood pressure increased after standing up during pregnancy. The circulatory responses to isometric exercise were not affected by pregnancy. The results show that parasympathetic respon-siveness is decreased in pregnancy and that it returns to normal after delivery.

Regulation of heart rate variation by the autonomic nervous system in neonatal lambs

ABSTRACT: We studied the role of the autonomic nervous system in the regulation of heart rate variation (HRV) in 12 chronically instrumented neonatal lambs. HRV was quantified from ECG tracings by computing periodic HRV distributions at frequencies of 0.02-1.00 Hz, using power spectral analysis of heart rate, and also by HRV indices. Heart rate declined more during the 1st than the 2nd mo after birth. Multiple regression analysis showed that the heart rate responses to vagal and to β-adrenergic blockade had an independent negative association both with age and with the initial mean heart rate, whereas the overall HRV response had a positive association with age. Vagal blockade led to a 70-80% decrease in the beat-to-beat HRV in all lambs (p < 0.001). The overall HRV indices decreased by 40-65% in lambs (< 30 d old (p < 0.001) and about 30% in those >30 d old (p < 0.05). In the power spectrum the greatest decrease was seen in the high-frequency components of HRV. β-Blockade led to a decrease of about 50% in all HRV (p < 0.001) in the younger lambs, without frequency selection. In the older lambs, it had no effect on the beat-to-beat HRV, but the overall HRV (coefficient of variance) decreased maximally by 40% (p < 0.01), with a significant reduction in the low-frequency components of HRV. These results suggest that in the regulation of HRV after birth dual control via the autonomic nervous system is most important. In the older lambs, developmental changes result in precise regulation of the fast heart rate fluctuations mainly by the vagal division, whereas the slow fluctuations are partially regulated by the vagal and β- adrenergic divisions.

Impairment of heart rate variability during paclitaxel therapy

Paclitaxel, which has been reported to be effective in treating metastatic breast carcinoma and advanced ovarian carcinoma, has been associated with cardiac side effects. Therefore, the effect of paclitaxel on cardiovascular autonomic regulation was studied.

Effects of haemodialysis on heart rate variability in chronic renal failure.

The influence of haemodialysis (HD) on the heart rate variability (HRV) was investigated in nine non-diabetic patients on maintenance haemodialysis. The R-R intervals were measured in recordings during spontaneous quiet breathing and during controlled deep breathing before and after a single HD session. The HRV was expressed as the standard deviation of the mean R-R interval in 3 min ECG recordings. Heart rate variability is the irregularity in the heart rate mainly caused by autonomic control mechanisms. The long-term HRV during quiet breathing was statistically significantly (p less than 0.05) higher after the HD than before. The HRV in the intermediate frequency range of 0.075-0.125 Hz was also significantly increased by the HD. This suggests that some metabolic agents interfering with the heart rate regulation are removed by the haemodialysis, and as a result a better function of the autonomic cardiac control is achieved in uraemic patients.

Autonomic Hemodynamic Control in Pregnancy-Induced Hypertension

Objective: To elucidate the role of the parasympathetic and sympathetic control of circulation in pregnancy-induced hypertension (PIH) and to investigate whether the short-term regulation of blood pressure is disturbed in PIH.Methods: The Valsalva maneuver, the deep breathing test, the active orthostatic test, and the isometric handgrip test were used to study the autonomic circulatory control in 14 patients with PIH and 14 healthy pregnant controls. The Finapres® method was used to assess blood pressure continuously and noninvasively during the tests.Main Outcome Measures: The heart rate and blood pressure responses to standard cardiovascular reflex tests.Results: The Valsalva maneuver reduced the systolic blood pressure significantly more in PIH than in healthy pregnant controls (-19% vs. -10%, P = 0.02). In the orthostatic test the rise in diastolic blood pressure (20% vs. 29%, P = 0.03) and in the heart rate (19 bpm vs. 24 bpm, P = 0.05), and the max/min ratio (1.31 vs. 1.48, P = 0.04) were smaller in...

Increased amplitude modulation of continuous respiration precedes sudden infant death syndrome: –Detection by spectral estimation of respirogram

The immaturity of the control of the autonomic nervous system has been suggested as one of the key factors in the pathophysiology of sudden infant death syndrome (SIDS). Therefore, the attenuated control of respiration may also cause more slow oscillatory breathing among infants at risk of SIDS. In this study, patterns of respiratory activity (RAV) and heart rate variability (HRV) were examined in Medilog-records prospectively obtained from 22 tape recordings made on 16 babies subsequently suffering from SIDS and from 22 matched control babies. A total of 248 signal segments, 120 s in duration, representing the state of regular breathing were visually selected for further analysis. The digitised signal sets were detrended, Fast-Fourier-transformed and autospectra as well as cross-spectra for the HRV and HRV were computed. The RAV and HRV were examined at two spectral bands: (1) a low frequency (LF) band 0.03-0.17 Hz (1.8-10 cycles/min) and (2) a high frequency (HF) band 0.3-1.3 Hz (18-90 cycles/min). Different parameters of each band were tested in the spectral analysis of cardiorespiratory control. The LF/HF-ratio of the spectral peak area of the respiratory activity and the LF/HF-ratio of the spectral band area of the respiratory activity were greater in the SIDS group when compared to the controls. No significant intergroup differences were found in the parameters of HRV, or the cross-spectral parameters. Interestingly, the technique appeared helpful in displaying that the victims of SIDS had a significantly greater amount of slow oscillation in the continuous respiratory signal (1.05+/-1.89 vs. 0.41+/-0.57, P=0.02). In the victims of SIDS the respiratory control system seems to be less stable and cause more slow oscillatory breathing and this can be detected using spectral analysis of respiratory activity even during breathing that visually seems to be regular.

Paclitaxel changes sympathetic control of blood pressure

Paclitaxel has become part of standard therapy in the treatment of ovarian and breast cancer. Concern has been raised about the effects of paclitaxel on cardiovascular function. Therefore, this study of the effects of paclitaxel on autonomic cardiovascular control was initiated. Eighteen women treated for ovarian or breast cancer were examined with autonomic cardiovascular function tests, once before the treatment and once after the second course of paclitaxel. Heart rate and blood pressure variability and changes in heart rate and blood pressure responses to the tests were measured. Baroreflex sensitivity was calculated from the Valsalva manoeuvre non-invasively. Paclitaxel did not change heart rate variability at rest compared with the pretreatment level. However, medium frequency variability of blood pressure was smaller after treatment with paclitaxel. Paclitaxel treatment did not impair the heart rate and blood pressure responses to the autonomic function tests. The results do imply that paclitaxel alters sympathetic control of blood pressure. Nevertheless, paclitaxel does not appear to precipitate autonomic cardiac neuropathy.