Fig 1.
Setup for each of the 3 conditions.
Ultrasound transducer is positioned submentally. (a) Voluntary hyperpnoea experiment. Subject lay supine and directly viewed the oscilloscope screen which displayed a signal of volume and a “target tracking” waveform based on the subject’s average tidal volume and respiratory frequency. The subject followed this waveform in real time. (b) Inspiratory resistive loading experiment. The subject wore a modified nose mask and were requested to breathe exclusively through the nose. The breathing apparatus was connected to a low resistive 2-way valve so that inspiration occurred through a pneumotachometer and pressure transducer whilst expiration took place at the valve to minimise rebreathing. The pressure, flow and respiratory inductance band signals were recorded in real time. An inspiratory resistive load was added by restriction of airflow distal to the pneumotachometer. (c) Imposed changes in end-expiratory level. The subject was supine in a head-out rigid-shell ventilation chamber. The chamber rested across the upper anterior chest just caudal to the suprasternal notch, with memory foam used to prevent pressure leak between chamber and torso. A vacuum/blower attachment was attached to the caudal part of the shell to allow changes in extra-thoracic pressure within the chamber.
Fig 2.
Schematic representation of ultrasound image, grid position and numbering system.
(a) Ultrasound image of the placement of grid with red line outlining the genioglossus and 15 black dots denoting the tracking points. GG–genioglossus, M–mucosa, S–tongue surface, GH–geniohyoid, MH–myohyoid (b) 15 grid points and columns represented. Points 1–5 are defined as the “anterior” column, 6–10 as the “middle” column and 11–15 as the “posterior” column. Points 11, 12 are defined as the “infero-posterior” points.
Table 1.
Characteristics of the total pool of 38 subjects.
Table 2.
Image grid characteristics across experiments.
Table 3.
Respiratory variables for the voluntary hyperpnoea experiment.
Table 4.
Average displacement of infero-posterior region of genioglossus (voluntary hyperpnoea).
Fig 3.
Mean peak inspiratory movement of grid during voluntary hyperpnoea experiment.
Mean for the 15 grid points at the start of the respiratory cycle are denoted as solid circles. Fig 3A and 3C Spontaneous and targeted tidal breathing. Fig 3B and 3D During voluntary study with two volumes. Fig 3A and 3B Mean for 20 subjects. Fig 3C and 3D Result for one of the study subject.
Table 5.
Respiratory variables for the inspiratory resistive load experiment.
Fig 4.
Mean peak inspiratory movement of grid for 20 subjects during resistive inspiratory load experiment and lung volume alteration experiment.
Mean for the 15 grid points at the start of the respiratory cycle are denoted as solid circles. (a) During inspiratory resistive loading experiment. Load A, B and C added an inspiratory resistance of 11.6 cmH2O/L/s, 22.3 cmH2O/L/s, and 75.2 cmH2O/L/s respectively. (b) During passive change in EELV experiment.
Table 6.
Average displacement of infero-posterior region of genioglossus (inspiratory resistive load).
Table 7.
Average displacement of genioglossus (lung volume alteration).
Fig 5.
Mean peak inspiratory movement of grid for 6 subjects inside or outside chamber during lung volume alteration experiment.
Mean for the 15 grid points at the start of the respiratory cycle are denoted as solid circles.
Table 8.
Summary of genioglossus activity during different respiratory states.