Modulations of human autonomic function induced by positive pressure-assisted breathing

Effects of nasal high flow on sympathovagal balance, sleep, and sleep-related breathing in patients with precapillary pulmonary hypertension

BACKGROUND

In precapillary pulmonary hypertension (PH), nasal high flow therapy (NHF) may favorably alter sympathovagal balance (SVB) and sleep-related breathing through washout of anatomical dead space and alleviation of obstructive sleep apnea (OSA) due to generation of positive airway pressure.

OBJECTIVES

To investigate the effects of NHF on SVB, sleep, and OSA in patients with PH, and compare them with those of positive airway pressure therapy (PAP).

METHODS

Twelve patients with PH (Nice class I or IV) and confirmed OSA underwent full polysomnography, and noninvasive monitoring of SVB parameters (spectral analysis of heart rate, diastolic blood pressure variability). Study nights were randomly split into four 2-h segments with no treatment, PAP, NHF 20 L/min, or NHF 50 L/min. In-depth SVB analysis was conducted on 10-min epochs during daytime and stable N2 sleep at nighttime.

RESULTS

At daytime and compared with no treatment, NHF20 and NHF50 were associated with a flow-dependent increase in peripheral oxygen saturation but a shift in SVB towards increased sympathetic drive. At nighttime, NHF20 was associated with increased parasympathetic drive and improvements in sleep efficiency, but did not alter OSA severity. NHF50 was poorly tolerated. PAP therapy improved OSA but had heterogenous effects on SVB and neutral effects on sleep outcomes. Hemodynamic effects were neutral for all interventions.

CONCLUSIONS

In sleeping PH patients with OSA NHF20 but not NHF50 leads to decreased sympathetic drive likely due to washout of anatomical dead space. NHF was not effective in lowering the apnea-hypopnoea index and NHF50 was poorly tolerated.

Short-term usage of three non-invasive ventilation interfaces causes progressive discomfort in healthy adults

Purpose

To evaluate the effect of three different non-invasive ventilation (NIV) interfaces on the subjective discomfort of healthy individuals, and on a set of physiological parameters hypothesized to change in correspondence to discomfort.

Methods

Continuous pressure NIV was applied to 20 subjects using Total Face, Nasal, and Face masks for 10 min each. Tidal volume (VT) and respiratory period (RP) were estimated from respiratory inductance plethysmography. Electrodermal activity was estimated from conductance signals. Heart rate variability was measured using the time-domain indices SDNN and RMSSD, and the respiratory sinus arrhythmia amplitude (RSAp). Parameters were referenced to 5-min rest periods at beginning and end of protocol. A Likert-like scale of subjective discomfort with the masks and the ventilation was applied after 1, 5, and 9 min using each mask.

Results

RP and VT increased with the three mask models. Whereas the mean heart rate and RSAp did not change, both SDNN and RMSSD increased during NIV with Nasal and Face masks. Spontaneous electrodermal activity fluctuations were less frequent during NIV than at rest, with significant differences for Total Face and Nasal masks. Discomfort with all masks increased from minutes 1 to 9, markedly in the Total Face mask, considered most uncomfortable by 11 subjects.

Conclusion

In healthy subjects, the three masks resulted in similar respiratory responses to NIV. Correspondence between changes in physiological parameters and discomfort with NIV interface could not be detected, whereas self-report with the Likert-like scale identified progressive discomfort and the Total Face mask as the most uncomfortable interface.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42600-020-00114-3.

Effects of Pneumoperitoneum and the Steep Trendelenburg Position on Heart Rate Variability and Cerebral Oxygenation during Robotic Sacrocolpopexy

STUDY OBJECTIVE

The aim of this study was to investigate how steep Trendelenburg positioning with pneumoperitoneum modifies brain oxygenation and autonomic nervous system modulation of heart rate variability during robotic sacrocolpopexy.

DESIGN

Prospective study (Canadian Task Force classification III).

SETTING

Rambam Health Care Campus.

PATIENTS

Eighteen women who underwent robotic sacrocolpopexy for treatment of uterovaginal or vaginal apical prolapse.

INTERVENTIONS

Robotic sacrocolpopexy.

MEASUREMENTS AND MAIN RESULTS

A 5-minute computerized electrocardiogram, cerebral O₂ saturation (cSO₂), systemic O₂ saturation, heart rate (HR), diastolic blood pressure (BP), systolic BP, and end-tidal CO₂ tension were recorded immediately after anesthesia induction (baseline phase) and after alterations in positioning and in intra-abdominal pressure. HR variability was assessed in time and frequency domains. Cerebral oxygenation was measured by the technology of near-infrared spectrometry. cSO₂ at baseline was 73% ± 9%, with minor and insignificant elevation during the operation. Mean HR decreased significantly when the steep Trendelenburg position was implemented (66 ± 10 vs 55 ± 9 bpm, p < .05) and returned gradually to baseline with advancement of the operation and the decrease in intra-abdominal pressure. Concomitant with this decrease, the power of both arms of the autonomic nervous system increased significantly (2.8 ± .8 vs 3.3 ± .9 ms²/Hz and 2.5 ± 1.2 vs 3.2 ± .9 ms²/Hz, respectively, p < .05). All these effects occurred without any significant shifts in systolic or diastolic BP or in systemic or cerebral oxygenation.

CONCLUSION

This study supports the safety of robotic sacrocolpopexy performed with steep Trendelenburg positioning with pneumoperitoneum. Only minor alterations were observed in cerebral oxygenation and autonomic perturbations, which did not cause clinically significant alterations in HR rate and HR variability.

Analysis of heart rate variability in individuals subjected to different positive end expiratory pressure levels using expiratory positive airway pressure

INTRODUCTION

The increase in the number of studies has led to greater security in the application of this method and the determination of its effectiveness in adults.. The purpose of the present study was to evaluate heart rate variability in healthy individuals submitted to different levels of positive expiratory pressure using an expiratory positive airway pressure (EPAP) device.

MATERIAL AND METHODS

The study involved 27 healthy male individuals ranging in age from 20 to 35 years. Patient histories were taken and the subjects were submitted to a physical examination. The volunteers were monitored using the Polar 810s(®) and submitted to the EPAP experiment. Analyses were performed on variables of the frequency domain. Sympathetic and parasympathetic bands and their relationship with sympathovagal response were also analyzed.

RESULTS

The mean value of this variable was 526.89 (55.50) ms(2) in the first period, 2811.0 (721.10) ms(2) in the fourth period and 726.52 (123.41) ms(2) in the fifth period. Regarding the parasympathetic area, significant differences were detected when Periods 1 and 5 (no load) were compared with periods in which the individuals were subjected to the use of the therapy. Sympathetic and parasympathetic areas together, a significant difference was detected regarding the sympathetic/parasympathetic ratio in the comparison between Periods 1 and 4 (p < 0.01) as well as Periods 2 and 4 (p < 0.05).

CONCLUSIONS

The findings of the present study suggest that the therapeutic use of EPAP significantly alters the parameters of heart rate variability in the frequency domain, highlighting the importance of monitoring and care during the practice of EPAP.

Acute effects of different levels of continuous positive airway pressure on cardiac autonomic modulation in chronic heart failure and chronic obstructive pulmonary disease

INTRODUCTION

Non-invasive ventilation may improve autonomic modulation and ventilatory parameters in severely disabled patients. The aim of the present study was to evaluate the physiological influence of acute treatment with different levels of continuous positive airway pressure (CPAP) on the autonomic balance of heart and respiratory responses in patients with stable chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF).

MATERIALS AND METHODS

A COPD group (n = 10), CHF group (n = 8) and healthy subjects (n = 10) were evaluated. The participants were randomized to receive three different levels of CPAP on the same day: sham ventilation (Sham), 5 cmH(2)0 (CPAP5) and 10 cmH(2)0 (CPAP10) for 10 min. Respiratory rate, end tidal carbon dioxide (E(T)CO(2)), peripheral oxygen saturation (SpO(2)), heart rate (HR), blood pressure and heart rate variability in the time and frequency domains were measured during spontaneous breathing and under the sham, CPAP5 and CPAP10 conditions.

RESULTS

All groups experienced a reduction in E(T)CO(2) values during treatment with CPAP (p < 0.05). CPAP increased SpO(2) and HR in the COPD group (p < 0.05). The COPD group also had lower RMSSD values during treatment with different levels of CPAP when compared to the control group (p < 0.05). In the CHF group, CPAP5 and CPAP10 increased the SDNN value (p < 0.05). CPAP10 reduced the SDNN value in the COPD group (p < 0.05).

CONCLUSION

The findings suggest that CPAP may cause improvements in the neural control of heart rate in patients with stable COPD and CHF. For each patient, the "best CPAP level" should be defined as the best respiratory response and autonomic balance.

Positive end-expiratory pressure may alter breathing cardiovascular variability and baroreflex gain in mechanically ventilated patients

Background

Baroreflex allows to reduce sudden rises or falls of arterial pressure through parallel RR interval fluctuations induced by autonomic nervous system. During spontaneous breathing, the application of positive end-expiratory pressure (PEEP) may affect the autonomic nervous system, as suggested by changes in baroreflex efficiency and RR variability. During mechanical ventilation, some patients have stable cardiorespiratory phase difference and high-frequency amplitude of RR variability (HF-RR amplitude) over time and others do not. Our first hypothesis was that a steady pattern could be associated with reduced baroreflex sensitivity and HF-RR amplitude, reflecting a blunted autonomic nervous function. Our second hypothesis was that PEEP, widely used in critical care patients, could affect their autonomic function, promoting both steady pattern and reduced baroreflex sensitivity.

Methods

We tested the effect of increasing PEEP from 5 to 10 cm H2O on the breathing variability of arterial pressure and RR intervals, and on the baroreflex. Invasive arterial pressure, ECG and ventilatory flow were recorded in 23 mechanically ventilated patients during 15 minutes for both PEEP levels. HF amplitude of RR and systolic blood pressure (SBP) time series and HF phase differences between RR, SBP and ventilatory signals were continuously computed by complex demodulation. Cross-spectral analysis was used to assess the coherence and gain functions between RR and SBP, yielding baroreflex-sensitivity indices.

Results

At PEEP 10, the 12 patients with a stable pattern had lower baroreflex gain and HF-RR amplitude of variability than the 11 other patients. Increasing PEEP was generally associated with a decreased baroreflex gain and a greater stability of HF-RR amplitude and cardiorespiratory phase difference. Four patients who exhibited a variable pattern at PEEP 5 became stable at PEEP 10. At PEEP 10, a stable pattern was associated with higher organ failure score and catecholamine dosage.

Conclusions

During mechanical ventilation, stable HF-RR amplitude and cardiorespiratory phase difference over time reflect a blunted autonomic nervous function which might worsen as PEEP increases.

Autonomic tone in medical intensive care patients receiving mechanical ventilation and during a CPAP weaning trial

Mechanical ventilator support and the resumption of spontaneous ventilation or weaning create significant alterations in alveolar and intrathoracic pressure that influence thoracic blood volume and flow. Compensatory autonomic tone alterations occur to ensure adequate tissue oxygen delivery, but autonomic responses may produce cardiovascular dysfunction with subsequent weaning failure. The authors describe autonomic responses of critically ill patients (n = 43) during a 24-hr period of mechanical ventilatory support and during the 24 hr that included their initial spontaneous breathing trial using continuous positive airway pressure. Nearly two thirds of these patients demonstrated abnormal autonomic function and this dysfunction was more severe in those patients who were unable to sustain spontaneous ventilation (n = 15). With further systematic study, autonomic responses may be useful in the identification of patients who are likely to develop cardiac dysfunction with the resumption of spontaneous breathing.

Estimation of spontaneous baroreflex sensitivity using transfer function analysis: effects of positive pressure ventilation

To determine the short-term effects of non-invasive positive pressure ventilation (PPV) on spontaneous baroreflex sensitivity, we acquired time series of RR interval and beat-to-beat blood pressure in 55 healthy volunteers (mean age 46.5+/-10.5 years), who performed breathing tests on four occasions at frequencies of 12 and 15/min, with application of PPV of 5 mbar, and without positive pressure (control). Using spectral and transfer function analysis, we estimated RR interval variability (HRV) and systolic blood pressure variability (SBPV), as well as the gain (alpha-index) and phase shift (Phi) of the baroreceptor reflex for low- (LF) and high-frequency (HF) bands. Compared to control breathing, PPV at 12 and 15/min led to an increase in mean RR (p<0.001) and blood pressure (p<0.05). The alpha-index in the HF band increased significantly due to PPV for both respiratory frequencies (p<0.05). Phase shifts did not show significant changes in response to pressure ventilation. These results indicate that short-term administration of PPV in normal subjects elicits significant enhancement in the HF index of baroreflex gain. These findings may contribute to understanding the mechanisms, indications, and effectiveness of positive pressure breathing strategies in treating cardiorespiratory and other disease conditions.