The fall in exhaled nitric oxide with ventilation at low lung volumes in rabbits: An index of small airway injury

Small airways in asthma: From inflammation and pathophysiology to treatment response

Small airways are characterized as those with an inner diameter less than 2 mm and constitute a major site of pathology and inflammation in asthma disease. It is estimated that small airways dysfunction may occur before the emergence of noticeable symptoms, spirometric abnormalities and imaging findings, thus characterizing them as "the quiet or silent zone" of the lungs. Despite their importance, measuring and quantifying small airways dysfunction presents a considerable challenge due to their inaccessibility in usual functional measurements, primarily due to their size and peripheral localization. Several pulmonary function tests have been proposed for the assessment of the small airways, including impulse oscillometry, nitrogen washout, body plethysmography, as well as imaging methods. Nevertheless, none of these methods has been established as the definitive "gold standard," thus, a combination of them should be used for an effective assessment of the small airways. Widely used asthma treatments seem to also affect several parameters of the small airways. Emerging biologic treatments show promising results in reducing small airways inflammation and remodelling, providing evidence for potential alterations in the disease's progression and outcomes. These novel therapies have implications not only in the clinical aspects of asthma but also in its inflammatory and functional aspects.

Cardiovascular Responses During Sepsis

Sepsis is the life-threatening organ dysfunction arising from a dysregulated host response to infection. Although the specific mechanisms leading to organ dysfunction are still debated, impaired tissue oxygenation appears to play a major role, and concomitant hemodynamic alterations are invariably present. The hemodynamic phenotype of affected individuals is highly variable for reasons that have been partially elucidated. Indeed, each patient's circulatory condition is shaped by the complex interplay between the medical history, the volemic status, the interval from disease onset, the pathogen, the site of infection, and the attempted resuscitation. Moreover, the same hemodynamic pattern can be generated by different combinations of various pathophysiological processes, so the presence of a given hemodynamic pattern cannot be directly related to a unique cluster of alterations. Research based on endotoxin administration to healthy volunteers and animal models compensate, to an extent, for the scarcity of clinical studies on the evolution of sepsis hemodynamics. Their results, however, cannot be directly extrapolated to the clinical setting, due to fundamental differences between the septic patient, the healthy volunteer, and the experimental model. Numerous microcirculatory derangements might exist in the septic host, even in the presence of a preserved macrocirculation. This dissociation between the macro- and the microcirculation might account for the limited success of therapeutic interventions targeting typical hemodynamic parameters, such as arterial and cardiac filling pressures, and cardiac output. Finally, physiological studies point to an early contribution of cardiac dysfunction to the septic phenotype, however, our defective diagnostic tools preclude its clinical recognition. © 2021 American Physiological Society. Compr Physiol 11:1605-1652, 2021.

Effect of pulmonary rehabilitation on tidal expiratory flow limitation at rest and during exercise in COPD patients

We hypothesized that severe COPD patients who present with the disadvantageous phenomenon of Expiratory Flow Limitation (EFL) may benefit as COPD patients without EFL do after implementation of a Pulmonary Rehabilitation (PR) program. Forty-two stable COPD patients were studied at rest and during exercise. EFL and dynamic hyperinflation (DH) were documented using the negative expiratory pressure (NEP) technique and inspiratory capacity (IC) maneuvers, respectively. Patient centered outcomes were evaluated by the Saint-George's Respiratory Questionnaire (SGRQ) and the mMRC dyspnea scale. Before PR, 16 patients presented with EFL at rest and/or during exercise. After PR, EFL was abolished in 15 out of those 16 EFL patients who exhibited a significant increase in IC values. These were mainly accomplished through a modification of the breathing pattern. In the 26 NFL patients no increase was noted in their IC or a modification of their breathing pattern. However, both NFL and EFL COPD patients improved exercise capacity and patients centered outcomes undergoing the same PR program.

Effects of different ventilation strategies on exhaled nitric oxide in geriatric abdominal surgery

Exhaled nitric oxide (eNO) has been suggested to be a marker of small airway injury. We investigated the effects of different ventilation strategies on eNO. Sixty-nine patients who received elective open abdominal surgery under general anesthesia with more than 2 h of surgery duration were randomly divided into three groups: high tidal volume of 10-12 ml kg(-1) predicted body weight (PBW) with zero end-expiratory pressure (ZEEP) (high VT + ZEEP group); low tidal volume of 6-8 ml kg(-1) PBW with 8 cm H2O positive end-expiratory pressure (PEEP) (low VT + PEEP group); and low tidal volume of 6-8 ml kg(-1) PBW with 8 cm H2O PEEP and recruitment maneuvers (low VT + PEEP + RMs group). eNO, respiratory system compliance (Crs), oxygenation index, inflammatory mediators tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), IL-8, prostaglandin E2 (PGE2) and PGF2a as well as pulmonary function were measured during the perioperative period. The postoperative eNO decreased in 78.3% of patients in the high VT + ZEEP group and low VT + PEEP group, and increased in 56.5% of patients in the low VT + PEEP + RMs group (P = 0.016). The Crs level in the high VT + ZEEP group significantly decreased with time but significantly increased in the low VT + PEEP + RMs group (P < 0.05). The oxygenation index, inflammatory mediators and pulmonary function did not statistically differ among the three groups. Compared with the low VT + PEEP + RMs group, the decreasing rate of postoperative eNO in the high VT + ZEEP and low VT + PEEP groups was higher, which may imply small airway injury during geriatric abdominal surgery.

Methods for Assessing Expiratory Flow Limitation during Tidal Breathing in COPD Patients

Patients with severe COPD often exhale along the same flow-volume curve during quite breathing as during forced expiratory vital capacity manoeuvre, and this has been taken as indicating expiratory flow limitation at rest (EFL_T). Therefore, EFL_T, namely, attainment of maximal expiratory flow during tidal expiration, occurs when an increase in transpulmonary pressure causes no increase in expiratory flow. EFL_T leads to small airway injury and promotes dynamic pulmonary hyperinflation with concurrent dyspnoea and exercise limitation. In fact, EFL_T occurs commonly in COPD patients (mainly in GOLD III and IV stage) in whom the latter symptoms are common. The existing up-to-date physiological methods for assessing expiratory flow limitation (EFL_T) are reviewed in the present work. Among the currently available techniques, the negative expiratory pressure (NEP) has been validated in a wide variety of settings and disorders. Consequently, it should be regarded as a simple, non invasive, most practical, and accurate new technique.

Tidal lung recruitment and exhaled nitric oxide during coronary artery bypass grafting in patients with and without chronic obstructive pulmonary disease

BACKGROUND

We studied the occurrence of intraoperative tidal alveolar recruitment/derecruitment, exhaled nitric oxide (eNO), and lung dysfunction in patients with and without chronic obstructive pulmonary disease (COPD) undergoing coronary artery bypass grafting (CABG).

METHODS

We performed a prospective observational physiological study at a university hospital. Respiratory mechanics, shunt, and eNO were assessed in moderate COPD patients undergoing on-pump (n = 12) and off-pump (n = 8) CABG and on-pump controls (n = 8) before sternotomy (baseline), after sternotomy and before cardiopulmonary bypass (CPB), and following CPB before and after chest closure. Respiratory system resistance (R (rs)), elastance (E (rs)), and stress index (to quantify tidal recruitment) were estimated using regression analysis. eNO was measured with chemiluminescence.

RESULTS

Mechanical evidence of tidal recruitment/derecruitment (stress index <1.0) was observed in all patients, with stress index <0.8 in 29% of measurements. Rrs in on-pump COPD was larger than in controls (p < 0.05). Ers increased in controls from baseline to end of surgery (19.4 ± 5.5 to 27.0 ± 8.5 ml cm H(2)O(-1), p < 0.01), associated with increased shunt (p < 0.05). Neither Ers nor shunt increased significantly in the COPD on-pump group. eNO was comparable in the control (11.7 ± 7.0 ppb) and COPD on-pump (9.9 ± 6.8 ppb) groups at baseline, and decreased similarly by 29% at end of surgery(p < 0.05). Changes in eNO were not correlated to changes in lung function.

CONCLUSIONS

Tidal recruitment/derecruitment occurs frequently during CABG and represents a risk for ventilator-associated lung injury. eNO changes are consistent with small airway injury, including that from tidal recruitment injury. However, those changes are not correlated with respiratory dysfunction. Controls have higher susceptibility to develop complete lung derecruitment.

Partitioning of exhaled NO in ventilated patients undergoing cardiac surgery

The change in exhaled NO after cardio-pulmonary bypass remains controversial. The aims were to determine whether exhaled NO sources (alveolar or bronchial) are modified after bypass, and whether mechanical ventilation (MV) settings during bypass modify exhaled NO changes. Thirty-two patients were divided into three groups: without MV during bypass and positive end-expiratory pressure (PEEP) (n=12), dead space MV without PEEP (n=10) and dead space MV with PEEP (n=10). Alveolar NO concentration and bronchial NO flux were calculated before and 1h after surgery using a two-compartment model of NO exchange developed in spontaneous breathing patients. Whereas a significant decrease in bronchial NO was found after bypass in the two groups without PEEP during bypass, this decrease was not observed in patients with dead space ventilation with PEEP. Alveolar NO was not significantly modified whatever the ventilation settings. In conclusion, the impairment of bronchial NO seemed related to airway closure since dead space mechanical ventilation with PEEP prevented its decrease.