Increased frequency dependence of specific airway resistance in patients with laryngeal hemiplegia

Airway Resistance and Airflow Dynamics after Fat Injection into Vocal Folds

Objectives:

The aim of this prospective study was to verify whether vocal fold fat augmentation (VFFA) modifies upper airway patency. To the best of our knowledge, this is the first study analyzing the impact of VFFA on laryngeal resistance to airflow.

Methods:

Twenty-one consecutive patients 16 to 74 years of age underwent 24 VFFA operations because of glottic incompetence due to laryngeal hemiplegia (13 patients) or vocal fold tissue defects (8 patients). Flow-volume loop spirometry and body plethysmography were performed before and 1 to 6 months after surgery.

Results:

There were no significant differences between preoperative and postoperative pulmonary volumes (FVC and FEV1), expiratory flows (PEF, FEF50), or inspiratory flows (PIF, FIF50), although a slight increase in inspiratory flows meant that FEF50/FIF50 slightly decreased. Specific airway resistance (sRaw) increased after VFFA, but not in a statistically significant manner (p = .078). None of the patients experienced postoperative stridor. One obese woman with laryngeal hemiplegia had postoperative effort dyspnea; her respiratory studies showed a reduction in inspiratory flows and an increase in sRaw, and demonstrated progressive improvement.

Conclusions:

Flow-volume loop spirometry showed that VFFA does not significantly modify respiratory airflows, although a slight increase of inspiratory airflows suggested an improvement in variable extrathoracic obstruction. Body plethysmography proved to be a sensitive procedure that highlighted the subtle increase in upper airway resistance. Hence, VFFA can be considered a relatively safe procedure for achieving vocal fold medialization, and spirometry and plethysmography can be useful for preoperative assessment and postoperative follow-up.

Spirometric and Plethysmographic Assessment of Upper Airway Obstruction in Laryngeal Hemiplegia

Laryngeal hemiplegia (LH) is the most common disorder of laryngeal motility. It is deemed not to cause obstruction of the upper airway; in fact, the main symptoms are dysphonia and breathiness, and respiratory impairment is not commonly reported. The aim of this study was to objectively assess upper airway patency in 41 patients affected by LH (mean age, 54.4 +/- 15.2 years; 27 female) and 30 controls (mean age, 50.0 +/- 16.1 years; 19 female) by means of flow-volume loop spirometry and body plethysmography to measure specific airway resistance (sRaw) at increasing respiratory frequencies. The causes of LH were cervical surgery (28), tumor infiltration (5), and unexplained (8). None of the patients or controls was affected by lower airway disease. Spirometry showed that the patients had inspiratory flows (PIF, FIF50) significantly lower than those of the controls (p < .0001), whereas the expiratory flows (FEV1, FEF50) were normal, with the exception of peak expiratory flow (PEF), which was reduced, especially in female patients. The mean FEF50/FIF50 ratio (about unity in the normal subjects) was >1, as is typical of variable extrathoracic obstruction. Plethysmography showed that the values of sRaw of the LH group were not statistically different from those of the controls at 30 +/- 5 breaths per minute, but they progressively and significantly increased at 60 +/- 5 (p < .01) and 90 +/- 5 breaths per minute (p < .002), whereas no significant sRaw change was observed in the controls. These results show that LH causes obstruction of the upper airway that can be assessed and quantified by means of spirometry and body plethysmography. A dynamic narrowing due to inspiratory medialization of the paralytic vocal fold and flow turbulence during hyperventilation seem to be the causes of patency impairment. The flow-volume loop is an excellent, inexpensive, and easily available means of functionally evaluating upper airway obstruction, but some patients have difficulty in performing an inspiratory test that requires maximal effort, and the flow reduction during forced ventilation may be partially due to the effort dependency of the tests themselves. Plethysmographic assessment of airway resistance may be a valid alternative or complement, as it reveals an increase in sRaw at increasing respiratory frequencies.

Variability of Specific Airway Resistance in Patients with Laryngeal Hemiplegia

Objectives:

This study was designed to analyze whether respiratory flows and specific airway resistance (sRaw) depend on the degree of breathiness and on the position of the paralyzed vocal fold in laryngeal hemiplegia.

Methods:

We performed a prospective study involving 55 patients affected by laryngeal hemiplegia.

Results:

The paralyzed fold was in an intermediate position in 18 cases and in a paramedian position in 37. Breathiness was estimated with the GRBAS scale, and the patients were divided into four groups: B0 (12 patients), B1 (14), B2 (16), and B3 (13). Spirometry was used to measure the flow-volume loop, and body plethysmography was used to measure the sRaw at increasing respiratory frequencies (30 ± 5, 60 ± 5, and 90 ± 5 breaths per minute). The mean inspiratory flows (PIF, FIF50) were lower than predicted (<80%) in all four groups; there was no significant intergroup difference. In all four groups, the mean FEF50/FIF50 ratio was >1, as is typical of variable extrathoracic obstruction. The mean sRaw values increased with respiratory frequency, and the increase was higher in group B3, although the values varied widely. The frequency-dependent increase in the sRaw value was not significantly related to the degree of breathiness, nor to the position of the paralyzed fold. Furthermore, Spearman's coefficient did not reveal any correlation between the sRaw values and inspiratory flows, showing that plethysmography and spirometry explore different aspects of airway function.

Conclusions:

Respiratory flows and sRaw are not significantly influenced by either the degree of breathiness or the position of the paralyzed vocal fold.

Detecting upper airway obstruction in patients with tracheal stenosis

We propose a forced oscillation test modality for detecting upper airway obstruction (UAO) as an alternative to spirometric UAO indices in patients with tracheal stenosis. From oscillometry performed at different breathing flow rates, airway resistance at 5 Hz was determined at 0.5 l/s ( R), and flow dependence of resistance was computed as the regression slope of resistance vs. flow up to 1 l/s (Δ R/Δ V̇). It was first verified by measurement in 10 normal subjects and 10 patients with chronic obstructive pulmonary disease that Δ R/Δ V̇ was unaffected by the presence of peripheral airway obstruction and that external orifices (with lumen area down to 28 mm2) induced marked increases in R and Δ R/Δ V̇. Ten patients eligible for tracheal dilatation underwent spirometry and impulse oscillometry before and after intervention. Considering the lumen area of tracheal stenosis in the patients (42 ± 28 mm2, represented as the mean ± SD), the R and Δ R/Δ V̇ increases were of similar magnitude to those predicted by the external orifices. In addition, R ( r = −0.68; P = 0.001) and Δ R/Δ V̇ ( r = −0.65; P = 0.001) showed better correlations with minimal tracheal lumen than any spirometric UAO index. Δ R/Δ V̇, but not R, showed a consistent return to normal after intervention in the stenosis patients. We conclude that the forced oscillation test at different breathing flow rates up to 1 l/s provides a measure of UAO, namely flow dependence of resistance Δ R/Δ V̇, which can signal a critical level of tracheal stenosis and is not confounded by the presence of concomitant peripheral airway obstruction.

Tracheal stenosis: a flow dynamics study

Patients referred for treatment of tracheal stenosis typically are asymptomatic until critical narrowing of the airway occurs, which then requires immediate intervention. To understand how tracheal stenosis affects local pressure drops and explore how a dramatic increase in pressure drop could possibly be detected at an early stage, a computational fluid dynamics (CFD) study was undertaken. We assessed flow patterns and pressure drops over tracheal stenoses artificially inserted into a realistic three-dimensional upper airway model derived from multislice computed tomography images obtained in healthy men. Solving the Navier-Stokes equations (with a Yang-shih k-ε turbulence model) for different degrees of tracheal constriction located approximately one tracheal diameter below the glottis, the simulated pressure drop over the stenosis (ΔP) was seen to dramatically increase only when well over 70% of the tracheal lumen was obliterated. At 30 l/min, ΔP increased from 7 Pa for a 50% stenosis to, respectively, 46 and 235 Pa for 80% and 90% stenosis. The pressure-flow relationship in the entire upper airway model (between mouth and end of trachea) in the flow range 0–60 l/min showed a power law relationship with best-fit flow exponent of 1.77 in the absence of stenosis. The exponent became 1.92 and 2.00 in the case of 60% and 85% constriction, respectively. The present simulations confirm that the overall pressure drop at rest is only affected in case of severe constriction, and the simulated flow dependence of pressure drop suggests a means of detecting stenosis at a precritical stage.

Canine awake head-out plethysmography (HOP): Characterization of external resistive loading and spontaneous laryngeal paralysis

We applied a novel head-out plethysmographic (HOP) method to study awake canine responses to external resistive loading and natural laryngeal paralysis. Measurements of inspiratory and expiratory specific airway resistance (sRaw(insp), sRaw(exp)) were obtained before and after uni- and bidirectional loading (R(add) = 5 cmH(2)O/L/s) in large-breed dogs (n = 9). Mean sRaw(insp) after inspiratory, and sRaw(exp) after expiratory loading were 31.4 and 33.3 cmH(2)Os, respectively. Bidirectional loads induced a significantly greater rise in both sRaw(insp) and sRaw(exp) (55.1 and 61.3 cmH(2)Os) compared to unidirectional loading (P < 0.001). Yet, type of loading did not affect flow-volume indices. The mean R(aw) of dogs was 4.81 cmH(2)O/L/s. Expiratory loading resulted in a significant 8.8% increase in functional-residual-capacity (FRC), compared to FRC(baseline) (76.7 ml/kg). Dogs (n = 5) with laryngeal paralysis demonstrated a significant increase in sR(aw) and R(aw) compared to controls without changes in FRC. In conclusion, HOP precisely characterized sR(aw) in response to external resistive loading. Hence, we could accurately quantify airway obstruction in awake dogs with laryngeal paralysis.