| Summary: | 博士 === 國立陽明大學 === 生理學研究所 === 92 === The breathing pattern in normal subjects displays a certain variability, which is maintained by a central neural mechanism, feedback loops of arterial chemoreceptors and lung vagal sensory receptors, and cortical influences. Deviations in breathing pattern variability from the normal level have been found in individuals in pathological conditions. Quantitative methods, including calculations of coefficients of variation, the Poincaré plot, and the spectral analysis have been applied to analyze the breathing pattern variability to serve as indicators of pathophysiological conditions in patients with respiratory diseases or weaning outcome in patients with respiratory failure. In order to investigate their clinical applicability to respiratory care, we took two groups of patients for study: the one was composed of the postoperative patients recovering from systemic inflammatory response syndrome (SIRS) / sepsis and the other was the group of patients in persistent vegetative state (PVS). The former group of patients was at the recovering stage of acute condition, whereas the latter was in the chronic condition of unusual breathing control. SIRS patients usually present rapid breathing pattern leading to hyperventilation that requires mechanical ventilation in acute phase, but can recover to normal. It is therefore worth to investigate whether that variability can serve as a potential predictor of their weaning outcome. The PVS patients have spontaneous breathing but show deficit in cerebral blood flow, O2 delivery to brain tissue, cortical influences, and feedback loops of visceral and somatic afferent. Their spontaneous breathing patterns have not been well characterized.
To investigate whether breathing pattern variability can serve as a potential weaning predictor for postoperative patients recovering from SIRS, 78 mechanically ventilated SIRS patients who had undergone abdominal surgery were included when they were ready for weaning. They were divided into success (n = 57) and failure (n = 21) groups based upon their weaning outcome. Another 19 successfully weaned patients who had undergone abdominal surgery without SIRS were included as control group. Before weaning, tidal volume, total breath duration, inspiratory time, expiratory time, and peak inspiratory flow were continuously monitored for 30 minutes, when the patients received 5 cmH2O pressure support ventilation. After the trial was successfully completed, the patients were extubated. Successful weaning was defined as the free from the ventilator over 48 hours, whereas failure referred to as reintubation of mechanical ventilation within 48 hours of extubation. The coefficient of variation and two values of standard deviation (SD1 and SD2；indicators of the dispersion of data points in the plot) obtained from the Poincaré plot of 5 respiratory parameters were lower in the failure group than in the success and control groups; there were no differences between the latter 2 groups. The areas under the receiver operating characteristic curve of these variability indices were within the range of 0.73-0.80, indicating their predicative accuracy. These results show that small breathing pattern variability is associated with a high incidence of weaning failure in postoperative patients recovering from SIRS and this variability may potentially serve as a weaning predictor.
We investigated the breathing patterns of 27 patients with persistent vegetative state (PVS) and 15 normal volunteers (the control). Tidal volume (VT), total breath duration (TTOT), minute ventilation (VE), oxygen saturation (SpO2), and end-tidal CO2 tension (PetCO2) were monitored for three 30-min periods breathing air, 100% O2, and air again. During breathing air, 15 PVS patients (the PVS-IB) exhibited irregular breathing (IB), whereas the other 12 (the PVS-OB) displayed oscillatory breathing (OB). Either the PVS-IB or PVS-OB maintained average values of VT, TTOT, VE, and SpO2 similar to those of the control. The PVS-OB, but not PVS-IB, displayed a significantly lower PetCO2 than that of the control suggesting hyperventilation. The VT, TTOT, VE, and PetCO2, but not SpO2, of the PVS-OB showed cyclic changes. The coefficients of variation (indices of respiratory variability) of VT, TTOT, and VI were: PVS-OB > PVS-IB > control. Spectral analysis of VT revealed that the PVS-OB had a central peak of power with a cycle duration of 45 ± 13 s. Chemical denervation of peripheral chemoreceptors by inhalation of 100% O2 did not affect the respiratory variability of the PVS-IB, but it significantly reduced the respiratory variability and prevented OB of the PVS-OB. The OB reappeared within 5-460 min after termination of O2 inhalation. We concluded that 1) PVS patients display respiratory instability in the form of either IB or OB and 2) brain damage, hyperventilation, hypocapnia, and / or dysfunction of peripheral chemoreceptors may contribute to the pathogenesis of OB, whereas the former presumably could be the cause of IB.
In conclusion, the analysis of variability provides an alternative method to describe the difference between two breathing patterns, especially when the patient presents significant change in breathing pattern but without changing the mean values of breathing pattern parameters. From the study of the variability of breathing pattern, we can further understand the mechanisms of breathing control to make it as a tool for clinical assessment and an index of therapeutic effect for patients with respiratory disorders.
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