Central chemoreflex sensitivity and sympathetic neural outflow in elite breath-hold divers

Repeated hypoxemia in obstructive sleep apnea patients increases sympathetic activity, thereby promoting arterial hypertension. Elite breath-holding divers are exposed to similar apneic episodes and hypoxemia. We hypothesized that trained divers would have increased resting sympathetic activity and blood pressure, as well as an excessive sympathetic nervous system response to hypercapnia. We recruited 11 experienced divers and 9 control subjects. During the diving season preceding the study, divers participated in 7.3 +/- 1.2 diving fish-catching competitions and 76.4 +/- 14.6 apnea training sessions with the last apnea 3-5 days before testing. We monitored beat-by-beat blood pressure, heart rate, femoral artery blood flow, respiration, end-tidal CO(2), and muscle sympathetic nerve activity (MSNA). After a baseline period, subjects began to rebreathe a hyperoxic gas mixture to raise end-tidal CO(2) to 60 Torr. Baseline MSNA frequency was 31 +/- 11 bursts/min in divers and 33 +/- 13 bursts/min in control subjects. Total MSNA activity was 1.8 +/- 1.5 AU/min in divers and 1.8 +/- 1.3 AU/min in control subjects. Arterial oxygen saturation did not change during rebreathing, whereas end-tidal CO(2) increased continuously. The slope of the hypercapnic ventilatory and MSNA response was similar in both groups. We conclude that repeated bouts of hypoxemia in elite, healthy breath-holding divers do not lead to sustained sympathetic activation or arterial hypertension. Repeated episodes of hypoxemia may not be sufficient to drive an increase in resting sympathetic activity in the absence of additional comorbidities

Glossopharyngeal insufflation induces cardioinhibitory syncope in apnea divers

Apnea divers increase intrathoracic pressure voluntarily by taking a deep breath followed by glossopharyngeal insufflation. Because apnea divers sometimes experience hypotension and syncope during the maneuver, they may serve as a model to study the mechanisms of syncope. We recorded changes in hemodynamics and sympathetic vasomotor tone with microneurography during breath holding with glossopharyngeal insufflation. Five men became hypotensive and fainted during breath holding with glossopharyngeal insufflation within the first minute. In four divers, heart rate dropped suddenly to a minimum of 38 +/- 4 beats/min. Therefore, cardioinhibitory syncope was more common than low cardiac output syncope

Cardiovascular regulation during apnea in elite divers

Involuntary apnea during sleep elicits sustained arterial hypertension through sympathetic activation; however, little is known about voluntary apnea, particularly in elite athletes. Their physiological adjustments are largely unknown. We measured blood pressure, heart rate, hemoglobin oxygen saturation, muscle sympathetic nerve activity, and vascular resistance before and during maximal end-inspiratory breath holds in 20 elite divers and in 15 matched control subjects. At baseline, arterial pressure and heart rate were similar in both groups. Maximal apnea time was longer in divers (1.7+/-0.4 versus 3.9+/-1.1 minutes; P5-fold greater muscle sympathetic nerve activity increase (P<0.01) with a massively increased pressor response compared with control subjects (9+/-5 versus 32+/-15 mm Hg; P<0.001). Vascular resistance increased in both groups, but more so in divers (79+/-46% versus 140+/-82%; P<0.01). Heart rate did not change in either group. The rise in muscle sympathetic nerve activity correlated with oxygen desaturation (r(2)=0.26; P<0.01) and with the increase in mean arterial pressure (r(2)=0.40; P<0.0001). In elite divers, breath holds for several minutes result in an excessive chemoreflex activation of sympathetic vasoconstrictor activity. Extensive sympathetically mediated peripheral vasoconstriction may help to maintain adequate oxygen supply to vital organs under asphyxic conditions that untrained subjects are not able to tolerate voluntarily. Our results are relevant to conditions featuring periodic apnea

Formalisme, formalisation, intuition et compr\ue9hension en math\ue9matiques : de la pratique informelle aux syst\ue8mes formels et retour \ubb (\uab FFIUM \ubb)

"Ce projet cherche \ue0 comprendre l'interaction dynamique entre les th\ue9ories math\ue9matiques informelles et leur formalisation. Le terme ambigu\ueb \uab formalisation \ubb est au centre du projet." (dal progetto ufficiale