Use of a two-way non-rebreathing valve to simplify the measurement of twitch mouth pressure using an inspiratory pressure trigger and the establishment of an optimal trigger threshold for healthy subjects and COPD patients

Inspiratory Muscle Dysfunction Mediates and Predicts a Disease Continuum of Hypercapnic Failure in Chronic Obstructive Pulmonary Disease

INTRODUCTION

Advanced chronic obstructive pulmonary disease (COPD) is associated with chronic hypercapnic failure. The present work aimed to comprehensively investigate inspiratory muscle function as a potential key determinant of hypercapnic respiratory failure in patients with COPD.

METHODS

Prospective patient recruitment encompassed 61 stable subjects with COPD across different stages of respiratory failure, ranging from normocapnia to isolated nighttime hypercapnia and daytime hypercapnia. Arterialized blood gas analyses and overnight transcutaneous capnometry were used for patient stratification. Assessment of respiratory muscle function encompassed body plethysmography, maximum inspiratory pressure (MIP), diaphragm ultrasound, and transdiaphragmatic pressure recordings following cervical magnetic stimulation of the phrenic nerves (twPdi) and a maximum sniff manoeuvre (Sniff Pdi).

RESULTS

Twenty patients showed no hypercapnia, 10 had isolated nocturnal hypercapnia, and 31 had daytime hypercapnia. Body plethysmography clearly distinguished patients with and without hypercapnia but did not discriminate patients with isolated nocturnal hypercapnia from those with daytime hypercapnia. In contrast to ultrasound parameters and transdiaphragmatic pressures, only MIP reflected the extent of hypercapnia across all three stages. MIP values below -48 cmH2O predicted nocturnal hypercapnia (area under the curve = 0.733, p = 0.052).

CONCLUSION

In COPD, inspiratory muscle dysfunction contributes to progressive hypercapnic failure. In contrast to invasive tests of diaphragm strength only MIP fully reflects the pathophysiological continuum of hypercapnic failure and predicts isolated nocturnal hypercapnia.

Noninvasive Prediction of Twitch Transdiaphragmatic Pressure: Insights from Spirometry, Diaphragm Ultrasound, and Phrenic Nerve Stimulation Studies

BACKGROUND

Twitch transdiaphragmatic pressure (twPdi) following magnetic stimulation (MS) of the phrenic nerves is the gold standard for non-volitional assessment of diaphragm strength. Expiratory muscle function can be investigated using MS of the abdominal muscles and measurement of twitch gastric pressure (twPgas).

OBJECTIVES

To investigate whether twitch pressures following MS of the phrenic and lower thoracic nerve roots can be predicted noninvasively by diaphragm ultrasound parameters and volitional tests of respiratory muscle strength.

METHODS

Sixty-three healthy subjects underwent standard spirometry, measurement of maximum inspiratory (PImax) and expiratory pressure (PEmax), and diaphragm ultrasound. TwPdi following cervical MS of the phrenic nerve roots and twPgas after lower thoracic MS (twPgas-Thor) were measured using esophageal and gastric balloon catheters inserted transnasally. Using surface electrodes, compound muscle action potentials (CMAP) were simultaneously recorded from the diaphragm or obliquus abdominis muscles, respectively.

RESULTS

Forced expiratory flow (FEF25-75) was significantly correlated with twPdi (r = 0.37; p = 0.003) and its components (twPgas and twitch esophageal pressure, twPes). Diaphragm excursion velocity during tidal breathing was correlated to twPes (r = 0.44; p = 0.02). No prediction of twitch pressures was possible from CMAP amplitude, forced vital capacity (FVC), or PImax. TwPgas-Thor was correlated with FEF25-75 (r = 0.46; p = 0.05) and diaphragm thickness at total lung capacity (r = 0.38; p = 0.04) but could not be predicted from CMAP amplitude, FVC, or PEmax.

CONCLUSIONS

TwPdi and twPgas-Thor cannot be predicted from volitional measures of respiratory muscle strength, diaphragm and abdominal CMAP, or diaphragm ultrasound. Invasive recording of esophageal and gastric pressures following MS remains indispensable for objective assessment of respiratory muscle strength.

Using twitch tracheal airway pressure, negative inhale forced pressure, and Medical Research Council score to guide weaning from mechanical ventilation

Background

Weaning from mechanical ventilation (MV) is an important and universal issue in critically ill patients, with no consensus that predicts weaning success. Twitch tracheal airway pressure (TwPtr) may be a more objective indicator of diaphragm function. The present study evaluated TwPtr relative to negative inspiratory force (NIF) or Medical Research Council (MRC) score, for predicting success of weaning from MV.

Methods

From December 2015 to March 2017, 62 patients were included who received invasive MV >48 hours and then underwent a test for spontaneous breathing. The NIF and MRC score were sequentially determined. The TwPtr measurement was performed via magnetic stimulation of the neck phrenic nerve.

Results

Weaning success was achieved by 54 patients (87.1%), including 30, 12, and 12 patients who experienced simple, difficult, and prolonged weaning, respectively. The areas under receiver operating characteristic curves (AUCs) for NIF, MRC score, and TwPtr were 0.778, 0.560, and 0.792. When TwPtr was combined with NIF, the sensitivity and specificity of weaning success were 96.3% and 75.0%, and AUC was 0.807. In the weaning success group, after correction for age, the AUC of TwPtr was 0.878, which differentiated the simple weaning from non-simple group.

Conclusions

TwPtr was superior to either NIF or MRC score for differentiating patients in the simple weaning group from those patients who experienced difficult, prolonged, or failed weaning. TwPtr combined with NIF may be used to predict weaning success better than the MRC score alone.