Vascular responses to simulated breath-hold diving involving multiple reflexes

Abstract

Breath-hold diving evokes a complex cardiovascular response. The degrees of hypertension induced by the diving reflex are substantial and accentuated by the underwater swimming. This condition provides a circulatory challenge to properly buffer and cushion cardiac pulsations. We determined hemodynamic changes during the diving maneuver and hypothesized that central artery compliance would be augmented during simulated breath-hold diving. A total of 20 healthy young adults were studied. Hemodynamics were measured during exercise on a cycle ergometer, apnea, face immersion in cold water (trigeminal stimulation), and simulated breath-hold diving. Arterial compliance was measured by recording the carotid artery diameter from images derived from an ultrasound machine at the cephalic portion of the common carotid artery 1–2 cm proximal to the carotid bulb, whereas arterial pressure waveforms were obtained using an arterial tonometry placed on the contralateral carotid artery and recorded on a data acquisition software. The change in diameter was divided by the change in blood pressure to calculate arterial compliance. Arterial compliance increased with simulated diving compared with rest ( P = 0.007) and was elevated compared with exercise and apnea alone ( P < 0.01). A significant increase in heart rate was observed with exercise, apnea, and facial immersion when compared with rest ( P < 0.001). However, simulated diving brought the heart rate down to resting levels. Cardiac output increased with all conditions ( P < 0.001), with an attenuated response during simulated diving compared with exercise and facial immersion ( P < 0.05). Mean blood pressure was elevated during all conditions ( P < 0.001), with a further elevation observed during simulated diving compared with exercise ( P < 0.001), apnea ( P = 0.016), and facial immersion ( P < 0.001). Total peripheral resistance was decreased during exercise and facial immersion compared with rest ( P < 0.001) but was increased during simulated diving compared with exercise ( P < 0.001), apnea ( P = 0.008), and facial immersion ( P = 0.003). We concluded that central artery compliance is augmented during simulated breath-hold diving to help buffer cardiac pulsations.