Diaphragm efficiency estimated as power output relative to activation in chronic obstructive pulmonary disease

Divergent expiratory braking activity of costal and crural diaphragm

BACKGROUND

There is increasing clinical interest in understanding the contribution of the diaphragm in early expiration, especially during mechanical ventilation. However, current experimental evidence is limited, so essential activity of the diaphragm during expiration and diaphragm segmental differences in expiratory activity, are unknown.

OBJECTIVES

To determine if: 1) the diaphragm is normally active into expiration during spontaneous breathing and hypercapnic ventilation, 2) expiratory diaphragmatic activity is distributed equally among the segments of the diaphragm, costal and crural.

METHODS

In 30 spontaneously breathing male and female canines, awake without confounding anesthetic, we measured directly both inspiratory and expiratory electrical activity (EMG), and corresponding mechanical shortening, of costal and crural diaphragm, during room air and hypercapnia.

RESULTS

During eupnea, costal and crural diaphragm are active into expiration, showing significant and distinct expiratory activity, with crural expiratory activity greater than costal, for both magnitude and duration. This diaphragm segmental difference diverged further during progressive hypercapnic ventilation: crural expiratory activity progressively increased, while costal expiratory activity disappeared.

CONCLUSION

The diaphragm is not passive during expiration. During spontaneous breathing, expiratory activity -"braking"- of the diaphragm is expressed routinely, but is not equally distributed. Crural muscle "braking" is greater than costal muscle in magnitude and duration. With increasing ventilation during hypercapnia, expiratory activity -"braking"- diverges notably. Crural expiratory activity greatly increases, while costal expiratory "braking" decreases in magnitude and duration, and disappears. Thus, diaphragm expiratory "braking" action represents an inherent, physiological function of the diaphragm, distinct for each segment, expressing differing neural activation.

Noninvasive Assessment of Neuromechanical Coupling and Mechanical Efficiency of Parasternal Intercostal Muscle during Inspiratory Threshold Loading

This study aims to investigate noninvasive indices of neuromechanical coupling (NMC) and mechanical efficiency (MEff) of parasternal intercostal muscles. Gold standard assessment of diaphragm NMC requires using invasive techniques, limiting the utility of this procedure. Noninvasive NMC indices of parasternal intercostal muscles can be calculated using surface mechanomyography (sMMG_para) and electromyography (sEMG_para). However, the use of sMMG_para as an inspiratory muscle mechanical output measure, and the relationships between sMMG_para, sEMG_para, and simultaneous invasive and noninvasive pressure measurements have not previously been evaluated. sEMG_para, sMMG_para, and both invasive and noninvasive measurements of pressures were recorded in twelve healthy subjects during an inspiratory loading protocol. The ratios of sMMG_para to sEMG_para, which provided muscle-specific noninvasive NMC indices of parasternal intercostal muscles, showed nonsignificant changes with increasing load, since the relationships between sMMG_para and sEMG_para were linear (R² = 0.85 (0.75-0.9)). The ratios of mouth pressure (P_mo) to sEMG_para and sMMG_para were also proposed as noninvasive indices of parasternal intercostal muscle NMC and MEff, respectively. These indices, similar to the analogous indices calculated using invasive transdiaphragmatic and esophageal pressures, showed nonsignificant changes during threshold loading, since the relationships between P_mo and both sEMG_para (R² = 0.84 (0.77-0.93)) and sMMG_para (R² = 0.89 (0.85-0.91)) were linear. The proposed noninvasive NMC and MEff indices of parasternal intercostal muscles may be of potential clinical value, particularly for the regular assessment of patients with disordered respiratory mechanics using noninvasive wearable and wireless devices.

Effect of Abdominal Binding on Diaphragmatic Neuromuscular Efficiency, Exertional Breathlessness, and Exercise Endurance in Chronic Obstructive Pulmonary Disease

We tested the hypothesis that abdominal binding (AB) would reduce breathlessness and improve exercise tolerance by enhancing neuromuscular efficiency of the diaphragm during exercise in adults with chronic obstructive pulmonary disease (COPD). In a randomized, controlled, crossover trial, 20 adults with COPD (mean ± SD FEV₁, 60 ± 16% predicted) completed a symptom-limited constant-load cycle endurance exercise test at 75% of their peak incremental power output with concomitant measures of the diaphragm electromyogram (EMGdi) and respiratory pressures without (CTRL) vs. with AB sufficient to increase end-expiratory gastric pressure (Pga,ee) by 6.7 ± 0.3 cmH₂O at rest. Compared to CTRL, AB enhanced diaphragmatic neuromuscular efficiency during exercise (p < 0.05), as evidenced by a 25% increase in the quotient of EMGdi to tidal transdiaphragmatic pressure swing. By contrast, AB had no demonstrable effect on exertional breathlessness and exercise tolerance; spirometry and plethysmography-derived pulmonary function test parameters at rest; and cardiac, metabolic, breathing pattern, inspiratory reserve volume and EMGdi responses during exercise (all p > 0.05 vs. CTRL). In conclusion, enhanced neuromuscular efficiency of the diaphragm during exercise with AB was not associated with relief of exertional breathlessness and improved exercise tolerance in adults with COPD. Clinical Trial Registration: ClinicalTrials.gov Identifier: NCT01852006.

Role of bronchodilation and pattern of breathing in increasing tidal expiratory flow with progressive induced hypercapnia in chronic obstructive pulmonary disease

Hypercapnia (HC) in vitro relaxes airway smooth muscle; in vivo, it increases respiratory effort, tidal expiratory flows (V̇_exp), and, by decreasing inspiratory duration (Ti), increases elastic recoil pressure (Pel) via lung viscoelasticity; however, its effect on airway resistance is uncertain. We examined the contributions of bronchodilation, Ti, and expiratory effort to increasing V̇_exp with progressive HC in 10 subjects with chronic obstructive pulmonary disease (COPD): mean forced expiratory volume in 1 s (FEV₁) 53% predicted. Lung volumes (Vl), V̇_exp, esophageal pressure (Pes), Ti, and end-tidal Pco₂ ([Formula: see text]) were measured during six tidal breaths followed by an inspiratory capacity (IC), breathing air, and at three levels of HC. V̇_exp and V̇ with submaximal forced vital capacities breathing air (V̇_sFVC) were compared. Pulmonary resistance ( Rl) was measured from the Pes-V̇ relationship. V̇_exp and Pes at end-expiratory lung volume (EELV) + 0.3 tidal volume [V̇_(0.3Vt) and Pes_(0.3Vt), respectively], Ti, and Rl correlated with [Formula: see text] ( P < 0.001 for all) and were independent of tiotropium. [Formula: see text], Ti, and Pes_(0.3Vt) predicted the increasing V̇_(0.3Vt)/V̇_sFVC(0.3Vt) [multiple regression analysis (MRA): P = 0.001, 0.004, and 0.025, respectively]. At [Formula: see text] ≥ 50 Torr, V̇_(0.3Vt)/V̇_sFVC(0.3Vt) exceeded unity in 30 of 36 measurements and was predicted by [Formula: see text] and Pes_(0.3Vt) (MRA: P = 0.02 and 0.025, respectively). Rl decreased at [Formula: see text] 45 Torr ( P < 0.05) and did not change with further HC. IC and Vl_(0.3Vt) did not change with HC. We conclude that in COPD HC increases V̇_exp due to bronchodilation, increased Pel secondary to decreasing Ti, and increased expiratory effort, all promoting lung emptying and a stable EELV. NEW & NOTEWORTHY The response of airways to intrapulmonary hypercapnia (HC) is uncertain. In chronic obstructive pulmonary disease (COPD), progressive HC increases tidal expiratory flows by inducing bronchodilation and via an increased rate of inspiration and lung viscoelasticity, a probable increase in lung elastic recoil pressure, both changes increasing expiratory flows, promoting lung emptying and a stable end-expiratory volume. Bronchodilation with HC occurred despite optimal standard bronchodilator therapy, suggesting that in COPD further bronchodilation is possible.

Instantaneous changes in respiratory function induced by passive pelvic suspension in the supine position in relation to increased diaphragm excursion

[Purpose] This study aimed to introduce an approach of pelvic suspension (PS) using sling cords and to obtain evidence for changes in respiratory function of healthy subjects. [Subjects and Methods] Subjects were 25 healthy men. In the supine position, with hip and knee joints flexed at 90°, the subjects’ pelvises were suspended with sling belts. Diaphragm excursion, respiratory function, and respiratory comfort in these postures were measured using ultrasonography, respirometry, and visual analog scale (VAS), respectively. [Results] When the pelvis was passively suspended with sling cords, the diaphragm moved 5 mm cranially and diaphragm excursion showed an instantaneous increase compared with the control. The tidal volume (V_T) showed an increase and the respiration rate (RR) showed a decrease. The extent of diaphragm excursion was correlated with changes in V_T under the control and PS conditions. Independent measurements of pulmonary function revealed that PS reduced the expiratory reserve volume, being correlated positively and negatively to increases in vital and inspiratory capacities, respectively. Furthermore, VAS values for respiratory ease were greater with PS than with the control. [Conclusion] These results suggest that PS effectively changed diaphragm excursion and respiratory function, leading to ease of breathing (i.e., deep and slow respiration).

Diaphragmatic motion studied by M-mode ultrasonography in combined pulmonary fibrosis and emphysema

BACKGROUND

The coexistence of emphysema and pulmonary fibrosis is known as combined pulmonary fibrosis and emphysema (CPFE). The aim of this study was to compare diaphragmatic motion measured by M-mode ultrasonography of patients with CPFE, idiopathic pulmonary fibrosis (IPF), and chronic obstructive pulmonary disease (COPD).

METHODS

Pulmonary function, high-resolution computed tomography (HRCT), and diaphragmatic motion were examined in patients with CPFE (n = 25), IPF (n = 18), and COPD (n = 60), and in healthy controls (n = 21). Diaphragmatic motions were measured on M-mode ultrasonographic images during quiet breathing and deep breathing.

RESULTS

There were no significant differences in right or left diaphragmatic motion during quiet breathing among the four groups, whereas differences were significant in right and left motion during deep breathing. Diaphragmatic motion in CPFE patients was the lowest among the four groups. COPD patients, especially those with severe COPD, showed significantly lower diaphragmatic motion than IPF patients or healthy controls. There were no differences in diaphragmatic motion between IPF patients and healthy controls. Right diaphragmatic motions during deep breathing were negatively correlated with emphysema scores (r = -0.606, p < 0.001), but were not correlated with fibrosis scores on HRCT.

CONCLUSIONS

Diaphragmatic weakness was found in CPFE patients. Emphysema but not fibrosis may be one cause of limited diaphragmatic motion in patients with CPFE. M-mode ultrasonographic evaluation of diaphragmatic motion during deep breathing may be a useful tool in diagnosing CPFE and in discriminating CPFE patients from IPF or COPD patients.