Unevenness of ventilation assessed by the expired CO(2) gas volume versus V(T) curve in asthmatic patients

Recently, we have shown that the expired CO2 gas volume versus tidal volume (VCO2-VT) curve is a useful tool for assessing unevenness of ventilation because it allows the separation of tidal volume into three functional compartments: (a) the CO2-free expired air (V0), (b) the transitional volume (Vtr), (c) the alveolar volume (VA) and the measurement of alveolar FCO2 during resting breathing in normal subjects and patients with COPD. In this paper, we have investigated whether changes pertaining to unevenness of ventilation taking place immediately after the administration of methacholine can be assessed using the VCO2-VT curve in asthmatic patients. The VCO2-VT curve was obtained during tidal breathing from 16 stable asthmatic patients who underwent a methacholine challenge test. It has been found that the Vtr, and hence Bohr's dead space (VD,Bohr = V0 + Vtr), over tidal volume ratios were significantly increased immediately after the methacholine administration, whilst the V0 over tidal volume ratio was not affected. The change of the above ratios was not related to the percentage decrease of FEV1.0 following methacholine administration.     

High‐frequency ventilation with the Dräger Babylog 8000plus: measuring the delivered frequency

Background: Ventilator frequency is one of the determinants of tidal volume delivery during high‐frequency ventilation. Clinicians increasingly use data on ventilator displays to inform their decisions. Aim: To measure the frequencies delivered by the Dräger Babylog 8000plus ventilator when used in high‐frequency mode. Methods: Ventilator waveforms using a test lung were recorded at the full range of settings 5–20 Hz using Spectra software at 1000 Hz. The changes in frequency produced by a 1‐ Hz change in set frequency were calculated. Actual and displayed frequencies were compared. Results: For settings up to 12 Hz, median (range) difference between set and delivered frequencies was 0 (?0.4 to +0.1) Hz. Above 12 Hz, delivered frequency varied by ?0.3 (?1.9 to +0.3) Hz. For 1‐ Hz changes in frequency settings, in the range 5–12 Hz, 1‐ Hz changes produced a change in delivered frequency of 1.0 (0.6–1.4) Hz. Above 12 Hz, the corresponding changes were 0.7 (0–2.9) Hz. The ventilator displays the set frequency during operation rather than the delivered frequency. Conclusion: At 12 Hz and below, the differences between set and delivered frequencies were relatively small compared with those at 13 Hz and higher. Above 13 Hz, the difference between set and delivered frequencies was up to 2.9 Hz. Some frequency setting changes did not result in a change in delivered frequency.     

Utilization of the lower inflection point of the pressure-volume curve results in protective conventional ventilation comparable to high frequency oscillatory ventilation in an animal model of acute respiratory distress syndrome

INTRODUCTION: Studies comparing high frequency oscillatory and conventional ventilation in acute respiratory distress syndrome have used low values of positive end-expiratory pressure and identified a need for better recruitment and pulmonary stability with high frequency. OBJECTIVE: To compare conventional and high frequency ventilation using the lower inflection point of the pressure-volume curve as the determinant of positive end-expiratory pressure to obtain similar levels of recruitment and alveolar stability. METHODS: After lung lavage of adult rabbits and lower inflection point determination, two groups were randomized: conventional (positive end-expiratory pressure = lower inflection point; tidal volume=6 ml/kg) and high frequency ventilation (mean airway pressures= lower inflection point +4 cmH2O). Blood gas and hemodynamic data were recorded over 4 h. After sacrifice, protein analysis from lung lavage and histologic evaluation were performed. RESULTS: The oxygenation parameters, protein and histological data were similar, except for the fact that significantly more normal alveoli were observed upon protective ventilation. High frequency ventilation led to lower PaCO2 levels. DISCUSSION: Determination of the lower inflection point of the pressure-volume curve is important for setting the minimum end expiratory pressure needed to keep the airways opened. This is useful when comparing different strategies to treat severe respiratory insufficiency, optimizing conventional ventilation, improving oxygenation and reducing lung injury. CONCLUSIONS: Utilization of the lower inflection point of the pressure-volume curve in the ventilation strategies considered in this study resulted in comparable efficacy with regards to oxygenation and hemodynamics, a high PaCO2 level and a lower pH. In addition, a greater number of normal alveoli were found after protective conventional ventilation in an animal model of acute respiratory distress syndrome.     

Perceived exertion and blood lactate concentration during graded treadmill running

The purpose of this study was to investigate the influences of treadmill gradients on the rating of perceived exertion (RPE) at two fixed blood lactate concentrations ( [La^–]_b). Ten subjects performed three different incremental treadmill protocols by running either uphill (concentrically-biased), downhill (eccentrically-biased), or on the flat (non-biased). Individual data of each protocol were interpolated to reflect [La^–]_b corresponding to 2.0 and 4.0 mmol·l^–1. At 2.0 mmol·l^–1 [La^– _b, RPE and treadmill speed during downhill running were greater than during level running which was greater than during uphill running (p < 0.05) . Also, the downhill heart rate (HR) was greater than the uphill HR, and downhill minute ventilation ( ) was greater than the level . Treadmill speed was the only measure at 4.0 mmol·l^–1 [La^–]_b to differ between gradients. There was a moderate correlation of RPE with HR at both [La^–]_b (r = 0.73 at 2.0 mmol·l^–1;r = 0.48 at 4.0 mmol·l^–1) while treadmill speed was moderately correlated with RPE only at 2.0 mmol·l^–1 [La^–]_b (r = 0.70). The results of this study demonstrated that the degree of eccentric-bias during running exercise is an influence of perceived exertion at a moderate but not at a high exercise intensity.     

Bicycle helmet ventilation and comfort angle dependence

Five modern bicycle helmets were studied to elucidate some of the variations in ventilation performance, using both a heated manikin headform and human subjects (n=7). Wind speed and head angle were varied to test their influence on the measured steady-state heat exchange (cooling power) in the skull section of the headform. The cooling power transmitted by the helmets varied from about 60% to over 90% of that of the nude headform, illustrating the range of present manufacturer designs. Angling the head forward by 30° was found to provide better cooling power to the skull (up to 25%) for three of the helmets and almost equal cooling power in the remaining two cases. Comparisons of skull ventilation at these angles with human subjects strongly supported the headform results.     

Cardio-respiratory measures following isocapnic voluntary hyperventilation

In some individuals, breathing is greater than at rest following voluntary hyperventilation. Most previous investigations have employed short hyperventilation periods; here we examine the time course of cardio-respiratory measures before, during, and after a 5-min voluntary hyperventilation, maintaining isocapnia throughout. We examined the possible co-involvement of the cardiovascular system; hypothesising that post-hyperventilation hyperpnoea results from an increase in autonomic arousal. In four subjects (two males, two females) of 18 (nine males, nine females) we observed a post-hyperventilation hyperpnoea, characterised by a slow decline of ventilation toward resting levels with a time constant of 109.0 +/- 16.1s. By contrast, heart rate, and systolic and diastolic blood pressure were unchanged from rest during and after voluntary hyperventilation for all subjects. We concluded that males and females were equally likely to exhibit post-hyperventilation hyperpnoea, and suggest that they may be characterised by an increased resting heart rate and the choice of breathing frequency to increase ventilation during the voluntary hyperventilation. We further concluded that post-hyperventilation hyperpnoea is rare, but when present is a strong and lasting phenomenon, and that it is not the result of an increased autonomic arousal.     

The effect of ventilation on spectral analysis of heart rate and blood pressure variability during exercise

Heart rate variability (HRV) and systolic blood pressure variability (BPV) during incremental exercise at 50, 75, and 100% of previously determined ventilatory threshold (VT) were compared to that of resting controlled breathing (CB) in 12 healthy subjects. CB was matched with exercise-associated respiratory rate, tidal volume, and end-tidal CO(2) for all stages of exercise. Power in the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, >0.15-0.4 Hz) for HRV and BPV were calculated, using time-frequency domain analysis, from beat-to-beat ECG and non-invasive radial artery blood pressure, respectively. During CB absolute and normalized power in the LF and HF of HRV and BPV were not significantly changed from baseline to maximal breathing. Conversely, during exercise HRV, LF and HF power significantly decreased from baseline to 100% VT while BPV, LF and HF power significantly increased for the same period. These findings suggest that the increases in ventilation associated with incremental exercise do not significantly affect spectral analysis of cardiovascular autonomic modulation in healthy subjects.     

The quantitative effect of an accessory ostium on ventilation of the maxillary sinus

The airflow and gas exchange behaviors of the human maxillary sinus were quantified to better understand the effect of an accessory ostium (AO). An anatomically correct numerical domain was constructed using CT data from a male patient with mild nasal obstruction. For the purpose of comparison, a numerical model without an AO was also generated by artificially removing the AO from the original model using CAD software. A steady-flow field through the nasal cavity was simulated using ANSYS-FLUENT v13.0 with a target flow rate of 250 ml/s. The Volume of Fluid (VOF) method was used to investigate the concentration field of nitric oxide (NO) initially filled in the maxillary sinus. The simulation results showed that a transit flow through the maxillary sinus developed in the presence of an AO. As the flow entered the sinus through either a natural or accessory ostium from the middle meatus, the velocity was significantly reduced to a local maximum of approximately 0.034 m/s inside the sinus. This by-pass flow rate through the sinus of 2.186×10(-1) to 3.591×10(-1) ml/s was a small fraction of the total flow rate inhaled from the nostril, but it effectively changed the local flow topology and led to a larger reduction in NO concentration in the maxillary sinus. This more rapid reduction in NO concentration was due to enhanced ventilation activity afforded by convective transport of the transit stream through the flow path connecting the natural ostium and the AO. The inspiration and expiration phases were qualitatively similar in flow pattern except for the flow direction in the maxillary sinus, suggesting that the AO plays a similar physiological role during both inspiration and expiration in terms of ventilation.     

Altered ventilatory and thermoregulatory control in male and female adult Pet-1 null mice

The integrity of the serotonin (5-HT) system is essential to normal respiratory and thermoregulatory control. Male and female transgenic mice lacking central 5-HT neurons (Lmx1b(f/f/p) mice) show a 50% reduction in the hypercapnic ventilatory response and insufficient heat generation when cooled (Hodges and Richerson, 2008a; Hodges et al., 2008b). Lmx1b(f/f/p) mice also show reduced body temperatures (T(body)) and O(2) consumption [Formula: see text] , and breathe less at rest and during hypoxia and hypercapnia when measured below thermoneutrality (24 °C), suggesting a role for 5-HT neurons in integrating ventilatory, thermal and metabolic control. Here, the hypothesis that Pet-1 null mice, which retain 30% of central 5-HT neurons, will demonstrate similar deficits in temperature and ventilatory control was tested. Pet-1 null mice had fewer medullary tryptophan hydroxylase-immunoreactive (TPH(+)) neurons compared to wild type (WT) mice, particularly in the midline raphé. Female (but not male) Pet-1 null mice had lower baseline ventilation (V(E)), breathing frequency (f), [Formula: see text] and T(body) relative to female WT mice (P < 0.05). In addition, V(E) and [Formula: see text] were decreased in male and female Pet-1 null mice during hypoxia and hypercapnia (P < 0.05), but only male Pet-1 null mice showed a significant deficit in the hypercapnic ventilatory response when expressed as % of control (P < 0.05). Finally, male and female Pet-1 null mice showed significant decreases in T(body) when externally cooled to 4 °C. These data demonstrate that a moderate loss of 5-HT neurons leads to a modest attenuation of mechanisms defending body temperature, and that there are gender differences in the contributions of 5-HT neurons to ventilatory and thermoregulatory control.     

急救转运呼吸机的研究进展

随着近年来公共卫生事件的发生频次不断上升,急救转运呼吸机的市场需求量激增,新型急救转运呼吸机厂家和品牌不断涌现。根据急危症患者的临床情况选择合适的急救转运呼吸机,并对其通气模式和各项参数进行正确调节,成为急救人员关注的焦点。因此,该文就急救转运呼吸机的类型和气路基本原理进行了扼要的介绍,并对当前国内外市场上流行的急救转运呼吸机关键技术性能做了详细的对比,最后总结了急救转运呼吸机的几种高级通气模式,旨在为急救转运呼吸机的选购和临床使用提供有益的参考。