Evaluation of near-infrared spectroscopy under apnea-dependent hypoxia in humans

Abstract

In this study we investigated the responsiveness of near-infrared spectroscopy (NIRS) recordings measuring regional cerebral tissue oxygenation (rSO2) during hypoxia in apneic divers. The goal was to mimic dynamic hypoxia as present during cardiopulmonary resuscitation, laryngospasm, airway obstruction, or the "cannot ventilate cannot intubate" situation. Ten experienced apneic divers performed maximal breath hold maneuvers under dry conditions. SpO2 was measured by Masimo™ pulse oximetry on the forefinger of the left hand. NIRS was measured by NONIN Medical's EQUANOX™ on the forehead or above the musculus quadriceps femoris. Following apnea median cerebral rSO2 and SpO2 values decreased significantly from 71 to 54 and from 100 to 65%, respectively. As soon as cerebral rSO2 and SpO2 values decreased monotonically the correlation between normalized cerebral rSO2 and SpO2 values was highly significant (Pearson correlation coefficient = 0.893). Prior to correlation analyses, the values were normalized by dividing them by the individual means of stable pre-apneic measurements. Cerebral rSO2 measured re-saturation after termination of apnea significantly earlier (10 s, SD = 3.6 s) compared to SpO2 monitoring (21 s, SD = 4.4 s) [t(9) = 7.703, p < 0.001, r(2) = 0.868]. Our data demonstrate that NIRS monitoring reliably measures dynamic changes in cerebral tissue oxygen saturation, and identifies successful re-saturation faster than SpO2. Measuring cerebral rSO2 may prove beneficial in case of respiratory emergencies and during pulseless situations where SpO2 monitoring is impossible.

Sustained apnea induces endothelial activation

“…The mean SpO 2 levels of the study subjects dropped to 79% at the end of apnea and to even lower levels within the first seconds after onset of respiration. This delay in desaturation is a result of the physiological diving response and has previously been described for apneic divers . Peripheral chemoreflex regulation, sympathetic nerve activity, and a norepinephrine increase leads to peripheral vasoconstriction and hypertension .…”

“…Peripheral chemoreflex regulation, sympathetic nerve activity, and a norepinephrine increase leads to peripheral vasoconstriction and hypertension . The increase in partial pressure of carbon dioxide (pCO 2 ) leads to an elevated cerebral blood flow, which ensures adequate oxygen supply to the brain, compared to the periphery . These vascular redistribution mechanisms help protect the brain during hypoxic events.…”

“…This delay in desaturation is a result of the physiological diving response and has previously been described for apneic divers. 5,7 Peripheral chemoreflex regulation, sympathetic nerve activity, 1 and a norepinephrine increase 7 leads to peripheral vasoconstriction and hypertension. 1,4 The increase in partial pressure of carbon dioxide (pCO 2 ) leads to an elevated cerebral blood flow, which ensures adequate oxygen supply to the brain, compared to the periphery.…”

“…Prolonged apnea leads to the so‐called diving response, which includes vasoconstriction, elevated mean arterial blood pressure, bradycardia, and increased cerebral blood flow . In the case of apnea, these compensatory mechanisms secure an adequate oxygen supply of the brain due to blood redistribution …”

“…4 In the case of apnea, these compensatory mechanisms secure an adequate oxygen supply of the brain due to blood redistribution. 5 Breath-holding burdens the cardiovascular system due to extreme peripheral vasoconstriction 6 and catecholamine release. 7 But apart from scientific interest in and public fascination with the sport, cardiac arrhythmias are commonly seen in people performing apnea.…”