At 9 min 03 s, shallow breathing could be heard, at close to tidal volume breaths.Ĭhart depicting the timeline for oxygen saturation (%) and heart rate (beats per minute) during the apnoea training. Coughing and apnoea restarted several times to 8 min 30 s. Thereafter, snoring and choking sounds were evident (resembling possible upper airway obstruction or upper airway muscle discoordination). At 4 min, the video tilted with only audio remaining the audio track suggests that breathing was resumed at 4 min 23 s. At 3 min 43 s there was bilateral upper extremity decerebrate posture in extension, along with sustained head extension, and the gaze continued to be right sided only. This caused the pulse oximeter to fall out of sight.
An evident change in mental status was seen at 3 min 30 s, with clinical presentation of a right-sided conjugate gaze to the horizon, a subtle loss of motor control of the arms, bilateral upper extremity extension, and right-hand thumb opposition. Thereafter, saturation dropped to 31% and the diver displayed swallowing movements and stronger contractions. Pulse oximetry measurements made from the finger may not represent central hypoxia, and equipment is rarely calibrated below 50%. The diver’s saturation declined steadily to 35%, at which point his first mild diaphragmatic contractions were observed, at 2 min 44 s. The course of events is described in Figure 2. In addition, a decrease of the intra-alveolar gas pressure down to -90 cm H 2O has been reported. This will decrease the gas diffusion gradient via reduction of PAO 2 by 1–2 kPa, but will also create a sub-atmospheric intrathoracic pressure that will increase fluid transfer, shifting blood stores centrally and possibly creating pulmonary oedema.Ī case is described which demonstrates these physiological phenomena and risk of this practice, hoping to raise awareness of the risks of unsupervised dry apnoea training at pulmonary RV. Some breath-hold divers can hold their breath for 2–3 minutes on empty lungs without loss of consciousness. In addition, some divers practice glossopharyngeal exsufflation to further reduce pulmonary lung volume to 200–300 ml below RV. This manoeuvre is used to practice flexibility of the ribcage and diaphragm, as well as to increase the rate of induction of hypoxaemia when pulmonary oxygen stores are limited. Residual volume (RV) apnoea is the performance of a breath-hold after a fully-controlled forced exhalation, creating inflexion of the diaphragm. When performing dry training, hyperventilation can be used to prolong apnoea time with the absence of diaphragmatic contractions, creating a state whereby hypoxia may be achieved without hypercapnia-induced dyspnoea. These apnoea exercises improve breath-hold ability their benefits are attributed to increased tolerance to hypercapnia, hypoxia, and onset and strength of the diving response. They also familiarise the diver to the uncomfortable sensation of dyspnoea/asphyxia. Describing the physiological phenomena observed in this case highlights the risks associated with unsupervised exhalatory breath-holding after hyperventilation as a training practice in competitive freediving.įreediving-related cerebral hypoxia is well documented. In-water activities bear a risk of cerebral hypoxia manifesting as loss of motor control, and loss of consciousness (LOC). Dry apnoea exercises (performed on land), which are commonly performed by competitive freedivers, also carry this risk albeit without risk of drowning. Upon imaging at the hospital, severe intralobular pulmonary oedema was noted, with similarities to images presented in divers suffering from pulmonary barotrauma of descent (squeeze, immersion pulmonary oedema). He also held his breath on empty lungs thus, trying to inhale created an intrathoracic sub-atmospheric pressure. Consequently, he suffered an extended period of severe hypoxia, with poor ventilation and recovery.
Here, we report on a case where an unsupervised diver used a nose clip that is thought to have interfered with his resumption of breathing after LOC. Cerebral hypoxia with loss of consciousness (LOC) can easily result. When hyperventilating and exhaling to residual volume prior to starting a breath-hold, hypoxia is reached quickly and without too much discomfort from respiratory drive. Many competitive breath-hold divers use dry apnoea routines to improve their tolerance to hypoxia and hypercapnia, varying the amount of prior hyperventilation and lung volume.
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