Toward a hyperventilation detection system in freediving: a proof of concept using force sensor technology

Figures

• 

  FIGURE 1. Custom-made buckle equipped with four strain gauges aligned on the sensor to measure the strain created by the applied force along with the data logger (A). Frontal (B) and lateral (C) view of the buckle in its operational position attached to the chest strap. Details of the data logger in operational position on the back of the participant (D).

• 

  FIGURE 2. Apnea test protocol, involving apneas of 1, 2, and 3 min duration (A1–A3). Icons represent the time of vital capacity and exhaled CO2 measurements. Baseline (3-min). Between apnea breathing intervals (2-min). Recovery (5-min).

• 

  FIGURE 3. Representative respiratory signal from one participant 60 s before the breath-hold. The inverted triangles show the detected peaks of the signal, corresponding to the end of inhalation, and are used to calculate the respiratory rate. The vertical lines show the amplitude of every wave (prominence) used as a surrogate of tidal volume. The horizontal lines show the duration measured at the midpoint of the prominence (width). N, newton; s, seconds.

• 

  FIGURE 4. Comparison of measured end-tidal CO2 (P ETCO2) with the estimated minute ventilation (eMV) before A1 (A), A2 (B), and A3 (C). The orange line represents the regression line, and the corresponding formula is expressed on each graph. mmHg, millimeters of mercury; n = 20 (A) and 21 (B, C).

• 

  FIGURE 5. Bland–Altman plots of the difference between P ETCO2 and predP ETCO2 before A1 (A), A2 (B), and A3 (C). The dotted lines represent the upper limit of agreement (mean + 1.96 SD) and lower limit of agreement (mean – 1.96 SD); mmHg, millimeters of mercury; n = 20 (A) and 21 (B, C).

• 

  FIGURE 6. Respiratory signal from two participants before competition performance in static apnea (A) and dynamic apnea without fins (B), depicting the differences in the breathing pattern as the diver in (A) shows shallower breaths but at an increased breathing frequency compared to diver (B). The two vertical lines show the period of lung packing, and the gray rectangle shows the beginning of the apneic performance. N, newton; s, seconds.